This is our general purpose glossary of electronic terms that we hope you will find useful.
A single-wire communications protocol. Data and addressing can be sent by different timings of the pulses on the wire. Return path is via a common ground connection.
A two-wire communication protocol, e.g. 4-20mA Loop. Analog measurements are sent by modulating the current in an isolated 2-wire loop. A reading of 100% is 20mA and 0% is 4mA, leaving up to 4mA available to power the sensor. The digital I²C protocol also uses 2-wire communication, but is arranged as clock (SCL) and serial data (SDA) with a common ground.
In a three-phase power supply system, three live conductors each carry an alternating current of the same frequency and voltage but each with a phase difference of one third of the period (120°). A return (neutral) conductor is not necessary as return currents cancel if the load is equally shared among the phases. Earth is a common reference but no current flows in it.
A three-wire communication and power protocol, e.g. IO-Link where device power is supplied by one wire and bidirectional data is sent over another wire with a common ground return for both data and power.
A four-wire communication protocol, e.g. RS485 Modbus. Differential transmit and receive data are sent on separate twisted pairs.
EN 50155 is the European standard for Railways (rolling stock), commonly accepted worldwide.
Six-wire communication is commonly used for telecommunications (two twisted pairs + voice). Eight-wire (four twisted pairs) is used for the Ethernet communication protocol.
The main safety standard for Safety of Household Equipment (often also required by building automation applications). UL, IEC and EN versions of this standard exist.
The main safety standard for medical-grade power supplies. The international (IEC 60601-1), North American (ANSI/AAMI 60601-1) and the European versions (EN 60601-1) are all very similar, but require separate certificates. The current version is the third edition (3rd Ed.).
The main EMC standard for medical-grade power supplies. The current version is the fourth edition (4th Ed.).
The main safety standard, originally intended for office equipment, that has been used for power converters in general. The international version (IEC 60950-1) and the US/Canada versions (UL 60950-1, CSA C22.2 No. 60950) remain valid for legacy products, but the European version (EN 60950-1) has a date-of-withdrawal of the end of 2020, after which it can no longer be used for presumption of CE conformity and other standards must be applied such as EN 62368-1.
The main safety standard for measurement, control and laboratory equipment. UL, CSA, IEC and EN versions of this standard exist.
The safety standard for the particular requirements of control equipment. UL 61010-2-201 replaces the popular UL 508 standard.
61347-1 61347-2-13
The main international safety and EMC standard for LED lighting power supplies. The international (IEC 61347-1) and the European versions (EN 61347-1) are very different from UL8750. IEC/EN 61347-2-13 covers EMC and harmonics interference.
61558-1 61558-2-16
Power supply safety and switch-mode power supply safety standards. Often used in conjunction with 60355-1.
The replacement for the 60950-1 standard for audio/visual (AV) and Information and Communication Technologies (ICT) equipment . The new standard is Hazard-Based (HB) which means that in addition to the electrical, fire and other safety tests, an extra risk assessment must be made to identify any serious consequences of faults and abuse.
UL 8750 is an American safety standard for LED lighting power supplies.
A/D Converter
Analog to Digital converter: A circuit that converts analog signals into digital data (not to be confused with an AC/DC converter).
Alternating current. Single phase mains (115V in USA, 230V in Europe) alternates its polarity 60 times a second (USA and other countries) or 50 times a second (EU and other countries).

Safety certification defines various levels of accessibility. Anything that is easily accessible must be safer than something that has restricted access (behind a locked door, at an unreachable height or requiring tools to gain entry, for example).

The definitions include:

  • Operator Accessible – access can be gained without the use of a tool
  • Restricted Access – access is through use of a tool or lock and key and the service person has been instructed about the necessary precautions
  • Service Access – same as restricted access, but where it may be necessary for the equipment to be kept powered while adjusting or calibrating the system
An automotive-grade qualification test sequence developed by the AIAG automotive organization. AEC-Q100 covers active components (such as ICs), AEC-Q200 covers passive components and AEC-Q104 covers modules.
Air Discharge
A method for testing ESD-protection in which an ESD generator creates a spark which arcs over to the device under test (DUT).
Ambient Temperature
Temperature of the air surrounding equipment such as a power supply. The operating temperature given in datasheets of RECOM parts is always the ambient temperature. The maximum case temperature may also be specified (temperature of the case or baseplate). Ambient temperature is measured close to, but not directly above the converter.
The unit of electrical current. Current is defined as the amount of charge that flows per unit of time. The symbol ‘I’ is used for current in equations and ‘A’ or ‘amp’ is the abbreviation for ampere.
Commonly used to define battery capacity. One ampere-hour (1Ah) is a current of one ampere flowing for one hour. The amount of charge transferred in that hour is 3,600 coulombs (ampere-seconds).
Amplifier Class
Amplifier circuit types are divided into ‘classes’ which describe whether the amplifier operates in a linear, quasi-linear or switching mode, and any techniques used to restore linearity of output. Most common classes are: Class A (analog high quality audio amplifiers), Class AB (analog quasi-linear with better efficiency than Class A) and Class D (digital switching amplifier).
American National Standards Institute
Application-Specific Integrated Circuit. Typically, a full custom or a semi-custom IC made up from pre-defined functional blocks.
Automated Test Equipment. Commonly used in a production line to check the correct functionality of each product manufactured (100% test).
A transformer that uses a common primary and secondary winding (no isolation). An autotransformer is often used to convert from 115V to 230V or vice-versa.
American Wire Gauge: A measure of wire thickness (which also dictates cross-sectional area, and for a given material, ampacity). For example: 24 AWG wire has a nominal diameter of 0.02in or 0.511mm. Enamel insulation on the wire adds to the diameter.
Bandwidth (BW) is a range of frequencies, or information data rate, that a circuit can operate with, or the range of frequencies that a signal contains or occupies. When measuring low-frequency ripple and noise, high frequency interference can give false readings, so the input of an oscilloscope is restricted to a bandwidth of 20MHz using a special filter: ‘20 MHz B/W Restricted’.
Baseplate cooling
A method of cooling a power converter through an integrated metallic baseplate which is thermally connected to external heatsinking.
Basic Insulation
The minimum insulation in a power supply to provide ‘basic’ protection against electric shock. Safety agencies require that an extra level of protection must also be included to achieve ‘double’ or ‘reinforced’ isolation between live and accessible parts that are not earthed.
Ball Grid Array: A packaging technology where IC connections are made by a grid of solder balls underneath the chip.
Relating to a device that accommodates signals traveling in either direction though a single channel. A bidirectional DC/DC converter can transfer power in either direction.
Bipolar Junction Transistor (BJT)
A solid-state device in which the current flow between two terminals (the collector and the emitter) is controlled by the amount of current that flows through a third terminal (the base). BJTs come in two versions: NPN (symbol arrow faces outwards) and PNP (symbol arrow faces inwards). NPN transistors are commonly used to switch a signal to ground. PNP transistors are commonly used to switch a signal to +V.
BluetoothTM/ Bluetooth LETM
A technology that allows voice and data connections between a wide range of mobile and stationary devices through short-range digital two-way radio. A Bluetooth LETM (Low Energy) module is an essential part of most IoT products. It requires either unregulated 4-6Vdc or a regulated 3.3V supply. The consumption varies from <1µA in sleep mode up to >100mA when active.
Battery Monitoring System. A system that monitors and controls charge and discharge of a battery. It may also monitor the voltage on the individual cells of a battery to ensure that they are equally charged and discharged or ‘balanced’. In which case, an isolated DC/DC converter is often required to power monitoring and charge control circuitry offset from ground potential.
Boost Converter
A switch-mode voltage regulator that steps an input voltage up (boosts it) to a higher, regulated voltage. The input voltage must always be lower than the output voltage. The term normally refers to a non-isolated converter.
A condition where the voltage supplied to the system momentarily falls below the specified operating range, but not to 0V.
Buck Converter
A 'buck' or 'step-down' switch-mode voltage regulator is one in which the output voltage is always lower than its input voltage.The term normally refers to a non-isolated converter.
A switch-mode voltage regulator in which output voltage can be above or below the input voltage but with inverted polarity.
Burst Mode
If an AC/DC converter is operated without a load, it may have a burst mode function where the main oscillator is switched on only for a short burst and then switched off. This reduces the no-load power consumption considerably.
Data or power path that connects to a number of devices.
Computer-Aided Design/ Computer-Aided Manufacture
CAN bus
Controller Area Network bus. The CAN protocol is an international data communications standard defined by ISO 11898.
A capacitor is a passive electronic component that consists of two conductive plates or foils separated by an insulating dielectric. A voltage applied to the plates develops an electric field across the dielectric and causes the plates to accumulate a charge. When the voltage source is removed, the field and the charge remain until discharged, storing energy. Capacitance is measured in farads, but typical values are microfarads (µF), or nanofarads (nF).
Category 5: Refers to Ethernet cabling that satisfies the criteria for the EIA/TIA-568 standard's Category 5, which allows data transfers up to 100Mbps. The next generation is CAT7 cable which allows up to 1Gbps.
Cloud-Based Manufacturing (CBM) is a networked manufacturing model that forms temporary, reconfigurable production lines according to demand – both within and across different manufacturing sites - an example of Industry 4.0.
Constant Current/Constant Voltage: Typical selectable operating modes of a laboratory power supply.
Charge Coupled Device: One of the two main types of image sensors used in digital cameras. When a picture is taken, the CCD is struck by light coming through the camera's lens. Each of the thousands or millions of tiny pixels that make up the CCD convert this light into electrons. The accumulated charge at each pixel is measured, then converted to a digital value.
Cold Cathode Fluorescent Lighting: Often used as a backlight for LCD displays.
Continuous-Conduction Mode; an operating mode of power converters where current in the inductive energy storage element does not fall to zero during each switching cycle.
Closed Circuit TeleVision: often used in building security systems.
Charge Pump
A circuit using switched capacitors to typically increase a DC voltage. A low cost, low power DC/DC boost converter.
Class A EMC
FCC, EN Class A EMC limits for power converters define the maximum interference generated by equipment (conducted and radiated emissions) and immunity of equipment to interference (conducted and radiated susceptibility) for industrial applications.
Class B EMC
FCC, EN Class B EMC limits for power converters define the maximum interference generated by equipment (conducted and radiated emissions) and immunity of equipment to interference (conducted and radiated susceptibility) for domestic and commercial applications. Class B limits are harsher than Class A EMC limits.
The minimum distance through air between two conductive parts. Specified by safety standards for electrical isolation.
Clock Jitter
When a wanted phenomenon: Fluctuating or jittering the frequency of a clock of a power converter to reduce EMI by spreading the main clock frequency over a wider range which reduces the EMI power in a standard measuring receiver bandwidth, indicating lower EMI levels. (also called spread spectrum). When an unwanted phenomenon: the inaccuracy of a timing clock pulse.
Cloud Computing
The Cloud is an on-demand system of interconnected computers that can share resources without direct active management by the user, relying on the Cloud Service Provider (CSP) to manage data traffic and secure the system.
Complementary Metal-Oxide Semiconductor) technology in which P- and N-channel field effect transistors (FETs) are used in tandem.
Common Mode Rejection Ratio: A measure of the ability of an amplifier to reject common mode input voltages and not pass them on to its output.
Common Mode
Refers to voltages which are common to two signal or power lines with respect to ground.
Common Mode Choke
An electrical inductive filter that blocks high frequency noise common to two or more data or power lines while allowing the desired DC or differential signal to pass.
Common Mode Interface
Identical unwanted signal components on both the positive and negative inputs or outputs of a power converter with respect to ground. It is attenuated by capacitors to ground and/or a series common-mode choke.
Contact Bounce
When a mechanical switch or relay closes, the switch elements will often bounce before making final contact. This is of consequence if the contact passes power to downstream power converters which are sensitive to the switching transients. For relay contacts connecting signals, a contact de-bouncing circuit (also called a snubber) is often used to reduce the effect.
Contact Discharge
An ESD test method where the ESD generator makes direct contact with the device under test (DUT).
The minimum distance across an insulating surface between two conductive parts. Specified by safety standards for electrical isolation.
Cross Regulation
For dual or bipolar converters only, the amount by which one output voltage changes when another output is subject to specified load changes.
A phenomenon where a signal on one conductor is inductively or capacitively coupled to an adjacent conductor. In transformers, leakage capacitance between the windings allows interference generated on the primary to appear on the secondary and vice versa. A low isolation capacitance reduces this effect.
A power supply protection circuit that rapidly short-circuits (‘crowbars’) a power line if the voltage exceeds a defined limit. In practice, the resulting short blows a fuse or triggers other protection, effectively shutting down the supply. It is usually implemented by an SCR (a latching device that can only be reset by powering off).
A control function, mainly for DC/DC converters which can be a positive or negative voltage, to enable or disable the output.
Current Limiting/Current Limitation
A feature of a power converter that limits input or output current to provide protection against overload.
Current Sense Amplifier
An amplifier that measures current by sensing the voltage drop typically across a shunt resistor. The current sense amplifier outputs either a voltage or a current that is proportional to the current through the shunt.
Current Share 'Ishare'
A function that can be used to force output current sharing of two or more power converters. Typically implemented by interconnecting ‘ishare’ pins of the converters.
Current-Mode Controller
A power converter control method that samples output voltage and switch current on a cycle-by-cycle basis to output a regulated voltage, despite variations in load-current and input-voltage. A higher performance alternative to voltage mode control.
D/A Converter
Digital-to-Analog Converter (DAC): A data converter that receives digital data and outputs a voltage or current proportional to the binary value of the data.
Direct Current: Current that is unidirectional e.g. from a battery or voltage regulator.
Discontinuous Conduction Mode: A power converter mode of operation where current in the inductive energy storage element falls to zero in each switching cycle.
A specified reduction in rated output power of a power converter at higher and sometimes low temperature and at high altitude, necessary to limit converter thermal stress.
Design Failure Mode and Effects Analysis: A method for evaluating a design for robustness against potential failures.
DIN EN 50128 2012/03
Railway applications - Communication, signalling and processing systems - Software for railway control and protection systems; EU version EN 50128:2011
DIN EN 50129 2019/06
Railway applications - Communication, signalling and processing systems - Safety related electronic systems for signalling; EU version EN 50129:2018 + AC:2019
A metal rail of a standard type meeting standard IEC/EN 60715, widely used for mounting circuit breakers and industrial control equipment and power converters inside equipment racks.
A device that passes current in one direction only.
24-pin Dual Inline Package: A package design with two rows of 12 pin positions. Other common packages are DIP14 or DIP16 (2x7 or 2x8 pins).
Distributed Power Architecture
An arrangement of power converters such that end voltages are generated by multiple converters powered from a higher common bus voltage.
Double Insulation
Electrical isolation between primary and secondary side of a power converter. Double Insulation is the general term for ‘basic’ insulation and necessary additional insulation for agency safety compliance. Each element provides ‘basic’ protection against electric shock.
Double-Pole/Double-Throw: A mechanical switch with two sets of contacts which can be switched together between two terminals with a center common connection.
Double-Pole/Single-Throw: A mechanical switch with two sets of contacts which can be opened or closed together.
One of the three terminals that comprise a Field Effect Transistor (FET). A voltage on the gate controls the current flow in the drain-source channel.
Dropout Voltage
The minimum input-output differential voltage which is required for a non-isolated DC/DC converter to operate correctly.
A method for packing SMD parts in a moisture-free environment. The device is baked and immediately sealed in a vacuum-sealed bag. This process is reserved for package types which have a specified Moisture Sensitivity Level (MSL) and are especially susceptible to moisture intrusion.
Dual Output
A power converter with an additional output available. This can be isolated from the main output or use a common ground.
Dual Phase Converter
A power converter with two power switches operated 180° out of phase to reduce input and output noise and boost output current capability.
Duty Cycle
The ratio of on-time to cycle time in power converter switches
Dynamic Regulation
Also ‘transient load response’, the response of a power converter output voltage to rapid load changes.
The ratio of power converter output power to input power, the standard symbol is the Greek letter ƞ. With no load, the efficiency is always zero (the input side is active, but the load draws no power).
Electronic Industries Alliance: Among other things, the EIA sponsors electrical and electronic standards.
Electronic Industries Alliance/Joint Electron Device Engineering Council.
A standardized converter case size: 2.3 x 0.9 x 0.5 inches (58 x 23 x 12.7mm), normally baseplate-cooled.
Embedded System
A system in which a computer (generally a microcontroller or microprocessor) is included as an integral part of the system.
ElectroMagnetic Compatibility: The ability of electronic equipment to be a 'good electromagnetic neighbour'and neither cause, nor be susceptible to, electromagnetic interference (within the limits of applicable standards).
ElectroMagnetic Emission
ElectroMagnetic Interference
ElectroMagnetic Susceptibility
EN 45545-1 2016/02
Railway applications - Fire protection on railway vehicles - Part 1: General; EU version EN 45545-1:2013
EN 50121-3-2 2017/11
Railway applications - Electromagnetic compatibility - Part 3-2: Rolling stock - Apparatus; EU version EN 50121-3-2:2016
EN 50121-4 2017/11
Railway applications - Electromagnetic compatibility - Part 4: Emission and immunity of the signalling and telecommunications apparatus; EU version EN 50121-4:2016
EN 50124-1 2017/12
Railway applications - Insulation coordination - Part 1: Basic requirements - Clearances and creepage distances for all electrical and electronic equipment; EU version EN 50124-1:2017
EN 50163 2005/07
Railway applications - Supply voltages of traction systems; EU version EN 50163:2004
EN 61373 2011/04
Railway applications - Rolling stock equipment - Shock and vibration tests (IEC 61373:2010); EU version EN 61373:2010
Energy Harvesting
(Also known as power harvesting or energy scavenging), the process by which energy is captured from a system's environment and converted into usable electrical power. Energy harvesting allows electronics to operate where there is no conventional power source, eliminating the need to run wires or to replace batteries. An energy harvesting system generally includes circuitry to charge a storage capacitor or battery. Energy source examples include light (captured by photovoltaic cells), vibration or pressure (captured by a piezoelectric element or an oscillating mass with a pick-up coil), temperature differentials (captured by a thermo-electric generator or TEG) or radio energy (captured by an antenna).
End of Life: After a product has reached End of Life status, it will be removed from the standard product range and is no longer for sale. The datasheet is still available on the RECOM website. In a period before this, the product will be designated as ‘No longer Recommended for New Designs (NRND)’.
Erasable Programmable Read-Only Memory. Electrically Erasable Programmable Read-Only Memory.
Energy-related Products: A term used in the EU Eco-design directive. Previously EuP, Energy-using Products.
Energy Recovery System. Typically refers to methods of recovering electrical energy from kinetic energy such as from a car braking system.
Electro-Static Discharge: Release of stored static electricity. ESD is generated when two surfaces rub together to build up charges of thousands of volts which then suddenly arc over.
ESD Protection
Devices added to input and output pins of an IC or other component/system to protect the internal circuitry from the damaging effect of electrostatic discharge.
Equivalent Series Inductance (typically of a capacitor).
Effective Series Resistance (or Equivalent Series Resistance): The series resistive component of an inductor or capacitor's equivalent circuit. A capacitor can be modelled as an ideal capacitor in series with a resistor and an inductor. The resistor's value is the ESR.
A system for connecting a number of computer systems to form a local area network, with protocols to control the passing of information and to avoid simultaneous transmission by two or more systems.
Electric Vehicle. A plug-in EV (PEV) is a pure EV. A hybrid EV (HEV) has both an internal combustion engine and an electric motor. If the internal battery can also be recharged from the mains, it is a plug-in HEV (PHEV). In Asia, EVs are commonly called New Energy Vehicles (NEV).
Evaluation Kit
(EV Kit, Development Kit): A printed circuit board with an integrated circuit or power converter and support components to produce a working circuit for evaluation and development.
Evaluation Module
Exposed Pad
Offered in some IC packages to improve thermal dissipation or lower the impedance of the ground connection. Normally not electrically isolated, the pad typically needs to be connected to a ground or power plane, depending on the device.
A design that does not generate a hazardous condition under fault conditions. Fail-safe elements include fuses, over-voltage clamps or over-temperature trips.
The unit of capacitance.
Ferrite Bead or Feed-Back.
Feedback compensation
A circuit that shapes the frequency-dependent gain and phase response of a feedback loop so that it remains stable under all operating conditions.
Feedback Loop
A control loop where negative feedback compares an output with a reference and generates an error signal to correct the output if it drifts. Such feedback loops are the heart of any regulated power converter. Positive feedback is generally avoided in power converters, although it has some uses in oscillator circuits and hysteretic control power converters.
Field-Effect Transistor: A transistor in which the voltage on one terminal (the gate) creates a field that allows or blocks conduction between the other two terminals (the source and drain). The most common FET is the MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) which comes in two versions: N-type (most common) and P-type.
The Fast Fourier Transform (FFT) is a common algorithm for translating a signal from the time domain, (signal strength as a function of time) to the frequency domain, (signal strength as a function of frequency). It shows the signal's spectral content, divided into discrete frequency bands.
An industrial network system for real-time distributed control. It is a way to connect instruments in a manufacturing plant. Fieldbus works on a network structure which typically allows daisy-chain, star, ring, branch, and tree network topologies.
A filter blocks a certain range of frequencies. It can be low-pass (only low frequency signals get through, e.g. a bass filter), high-pass (only high frequency signals get through, e.g. a treble filter) or band-pass (only a certain frequency range of signals gets through, e.g, an equalisation filter). Low-pass filters are commonly used to block EMI and as output networks in power converters.
Filter Inductor
Normally a series choke in a power line to filter noise, together with parallel capacitors.
Failures In Time (number of failures per billion (109) hours). FIT = 109/MTBF (Mean Time Between Failures).
An output is said to be ‘floating’ if it is not electrically connected to any input voltage supply, ground, or ground-referenced signal source.
Flyback Converter
An isolated power converter switching topology that transfers energy to the transformer secondary and output, only when the switching transistor is off.
Foldback is a current limiting feature of power converters and power amplifiers. When the load tries to draw overcurrent from the supply, foldback reduces both the output voltage and the output current below normal operating limits. Usually the converter must be disconnected to reset to the original current limit.
Forward Converter
An isolated power converter switching topology that transfers energy to the transformer secondary and output, only when the switching transistor is on.
Field Programmable Gate Array: A family of general-purpose logic devices that can be configured by the end-user to perform many different, complex, logic functions.
A standardized converter case size: 4.6 x 2.4 x 0.5 inches (116.8 x 61.0 x 12.7mm) usually baseplate-cooled.
A power converter or drive topology where one end of an inductor or transformer winding is alternately switched from V- to V+, while the other end is simultaneously switched from V+ to V-
Functional Insulation
Electrical isolation which is required for the function of equipment but which does not provide any protection against electric shock if the isolation fails. DC/DC converters may have functional isolation between input and output.
Gallium Arsenide: A semiconductor material used for optoelectronic products such as LEDs, and for high-speed electronic devices.
The amount of amplification accomplished by a circuit or transistor. For example, a current gain of 200 would mean output current is scaled to 200x the amplitude of the input current.
Galvanic Isolation
Galvanically isolated circuits such as in a power converter have no common electrical connection between input and output.
The controlling terminal of a FET. A voltage on the gate controls the current flow between the drain and source or: A basic logic element (e.g. AND, OR, NOT, NAND, NOR, XOR).
General Purpose Interface Bus: A standard bus for controlling electronic instruments with a computer. Also called IEEE-488 bus because it is defined by ANSI/IEEE Standards 488-1978, and 488.2-1987. Also called HP-IB, a trademarked term of Hewlett-Packard, who invented the protocol.
General Purpose I/O: A flexible parallel interface that allows a variety of test equipment (bench power supplies, meters, etc.) to be controlled by a central computer.
Global Positioning System: A satellite-based navigation system in which two or more signals, received from satellites, are used to determine a receiver's position on the globe.
Graphical User Interface.
Henry: The unit of inductance. Most EMI filters require inductors or 'chokes' in the range of µH (microhenries) up to a few mH (millihenries). Also ‘magnetising force’ in inductors.
A standardized converter case size: 2.3 x 2.4 x 0.5 inches (58 x 61 x 12.7mm) usually baseplate-cooled.
A power converter or drive topology where one end of an inductor or transformer winding is alternately switched from V- to V+, while the other end is fixed at half of the supply voltage.
Data transmission over a circuit capable of transmitting in either direction, but not simultaneously.
Highly Accelerated Lifetime Testing/ Highly Accelerated Stress Screening. A way to demonstrate and calculate by extrapolation the expected lifetime and reliability of a product by combining several stress factors such as high temperature, high humidity and shock/vibration. Used to set the warranty period for new products, for example.
Use of vibration and other mechanical feedback in a Human Machine Interface (HMI) as opposed to visual or audio cues.
Harmonic Distortion
The presence of frequencies in the output of a device or circuit that are not present in the input and are multiples of components of the input signal. Clipping is a common cause but other nonlinearities can also introduce harmonics. In AC/DC power supplies, harmonic distortion normally relates to the unwanted harmonic currents induced in the AC supply by the power supply input circuitry.
Highway Addressable Remote Transducer communication is a commonly used mode of transmission for digital signals that are superimposed on the analog signal of a 4–20mA current loop. This allows both instantaneous analog readings with supplementary digital data on the same wiring system.
High-Brightness Light Emitting Diode.
High-Definition Television: An all-digital system for transmitting a TV signal with far greater resolution than the analog standards (PAL, NTSC, etc.).
Heat Sink
A metal block thermally connected to a heat-producing component, designed to conduct heat away from the device. Most heat sinks are aluminum with fins to increase surface area and encourage the transfer of heat to the surroundings.
High Electron Mobility Transistor (GaN transistors are HEMT cells).
HF (High Frequency) is typically between 2MHz to 30MHz. VHF (Very High Frequency) is in the range 30 to 300MHz and UHF (Ultra High Frequency) is 300MHz to 3GHz.
Hi-Pot test
Abbreviation for High Potential test: The standard test for insulation breakdown voltage. A high voltage is applied across an isolation barrier for 1 second or 1 minute and no arc-over should occur. All RECOM products are 100% Hi-Pot tested in production.
Hi-Z (or High-Z or high impedance) of a data line refers to an output signal state in which the signal is not being actively driven. The signal is left open, so that another output pin (e.g. elsewhere on a bus) can drive the signal or the signal level can be determined by a passive device (typically, a pull-up resistor).
Hiccup Mode
’Hiccup’ behavior of a power converter describes a special form of overload protection. In the event of an output overload or a short circuit, the power supply switches off and attempts to restart cyclically (approximately in the range of seconds) to query the elimination of the overload.
An element connected between the supply and the load. High-side current sensing measures current by looking at the voltage drop across a resistor placed between the supply and the load. High-side switches connect to an input supply without reference to 0V.
Human-Machine Interface. How people interact with machines, for example, keyboards, touchscreens or haptic interfaces.
Hold Up Time
The length of time a power supply can operate in regulation after failure of the AC input.
An industry-standard method for transmitting data via domestic power lines. It can transmit audio, video, control signals, etc. HomePlug is a trademark of the HomePlug Powerline Alliance; Powerline Communications is the generic term for the method. 
Hot Plug
The ability to connect a device, typically a power converter, to an already powered system without any disruption to the system.
A power supply arrangement consisting of two or more units wired in parallel, any one of which can be removed and replaced while the system remains powered up, without interruption to the output supply to the load.
Human Body Model
An ESD test method where the ESD generator consists of a charged 100pF capacitor and a 1.5k ohm series resistor which matches the typical real-life values of a charged human being.
Heating, Ventilation, and Air Conditioning: An Industry term for the systems and technology responsible for the heating, ventilation, and air conditioning in buildings.
The phenomenon in which the value of a physical property lags behind changes in the effect causing it, as for instance when magnetic induction lags behind the magnetizing force.
Hysteretic Converter
A power converter topology characterised by positive feedback, used for simple regulated DC/DC converters.
Hertz: A measure of frequency. An older term is cycles per second, or cps.
Quiescent current. IQ(Q should be subscripted but is sometimes printed as 'IQ' without subscripting) is the no-load input current drawn by a power converter.
A protocol for intra-board digital communication which may be used for diagnostics and control of power converters. I²C (pronounced 'I-squared-C' and typeset as I²C but often typed as I2C) is short for 'inter-IC bus.' I²C is a two-wire, low-speed, serial data connection bus used to interconnect integrated circuits, generally on the same board.
Integrated circuit: A semiconductor device that combines multiple transistors and other components and interconnects on a single piece of semiconductor material (die).
The International Electrotechnical Commission prepares and publishes international standards for all electrical, electronic and related technologies. IEC standards are accepted in 34 countries (including those in Europe as well as Australia, Canada, USA, India, Israel, Korea and USSR).
The Institute of Electrical and Electronics Engineers, IEEE (Eye-triple-E) is a non-profit, professional association of more than 360,000 individual members in approximately 175 countries. The IEEE also sponsors many electrical and electronic standards.
Impedance, represented by the symbol Z, is a measure of the opposition to electrical current flow. It is measured in ohms. For DC systems, impedance and resistance are the same (Z=R=V/I). In AC systems, 'reactance' enters the equation due to the frequency-dependent contributions of capacitance and inductance. Impedance in an AC system is the vector sum of reactance and resistance and is still measured in ohms and represented by the equation Z = V/I, but V and I are frequency-dependent.
Inductive Kickback
The very rapid change in voltage across an inductor when current flow is interrupted. Snubber diodes are often used to clamp this energy in relay coils, and other inductive loads. Kickback can be a problem (causing EMI and component failure) or it can be used in ‘boost’ or ‘flyback’ power supply circuits to develop higher or opposite-polarity voltages from a single supply.
Industry 4.0
After iron & steam, electricity and computing, the 4th industrial revolution will be networked industry which can automatically predict and repair faults, adapt to changes or new conditions and rearrange production and logistics for maximum efficiency, quality and safety, e.g. Cloud-Based Manufacturing
Ingress Protection
An Ingress Protection (IP) rating indicates how well an enclosure is protected from penetration by foreign objects (first number) and by contaminants such as dust or fluids (second number). Common IP ratings are:
  • IP20 = Protected against fingers touching live parts, but not against moisture.
  • IP44 = Protected against 1mm particle ingress and splashing water.
  • IP67 = Dust tight and protected against water ingress up to 1m immersion.

Inrush Current Control
An ‘intelligent’ circuit which can reduce inrush currents during start up of power converters.
Inrush Current/Soft-start
A momentary input current surge, measured during the initial turn-on of a power converter, usually dominated by charging current of input capacitors. This current reduces to a lower steady-state value once the converter is running. The inrush current can be very high (typically 10x steady-state input current) but usually lasts only a few milliseconds. If a converter has a soft-start circuit, the inrush current peak can be substantially reduced at the expense of turn-on delay.
A non-conductive barrier between two conducting materials, for example, the plastic bobbin that insulates the primary and secondary windings in a transformer from each other and also the core.
Insulation grade
Safety standards specify three classes or grades of insulation: Functional, where there is no separate physical barrier between conductors except the insulation coating on wires or a minimal separation, Basic, where there is a physical barrier in addition to the wire coating or a prescribed physical separation, and Reinforced, where there are two independent physical barriers in addition to the coating on the wires, or a larger prescribed physical separation, or a minimum solid thickness of insulation. Supplementary insulation is a barrier in addition to Basic insulation that is equivalent to Reinforced isolation.
Intellectual Property
Intellectual Property, IP, is creation of the intellect such as trade knowledge, technical information, and literary or artistic work, including patents, copyrights, and trademarks. The 'Know-how' in a business.
A technique where two power converter stages or PFC stages are switched in anti-phase to double the effective current but with reduced input and output ripple voltage. Can be extended to three or more interleaved stages to increase the power delivery and decrease ripple further.
Internet Protocol (IP)
The standard method for data transfer used on the Internet. Also known as IP or TCP/IP.
A logic circuit which inverts a signal or a power converter that produces AC output, either line voltage and frequency or variable voltage and frequency for motor drives, for example.
Inverting Switching Regulator
A switch-mode voltage regulator in which output voltage is negative with respect to its input voltage. An example is the ‘buck-boost’ regulator.
Internet of Everything. A superset of IoT that includes people, processes, data and IoT devices in one intelligent, networked fabric. IoE connects people in more relevant ways, delivers the right information to the right person or device at the right time and interprets data to allow useful decision making.
Internet of Things. A network of ‘smart’ devices, each with a unique IP address to allow internet connectivity. IoT allows embedded technology to communicate and interact with the environment, people and other machines.
IoT Device
An IoT device consists of three distinct elements: a sensor or actuator, a controller to make it 'smart' and an internet connection.
Internet Protocol Version 6: Internet Communications protocol with a 128 bit address-space, multi-casting and auto-configuration. It has the ability to uniquely address up to 3.4x1038 individual devices and is essential for the IoT concept.
Infrared: Light that has a frequency just below the visible light spectrum, used for remote controls and night vision applications, for example.
Industrial, Scientific and Medical: Radio frequency bands made available for use by communication equipment without license, within certain maximum emitted power limits. Equipment which uses the ISM band must tolerate interference from other such equipment. Common uses include WiFi (802.11a, b, and g) and cordless phones.
International Standards Organization. ISO9001 for example, is the main quality control standard for companies and organisations.
Quality management system based on ISO 9001 for the automotive industry supply chain and production.
See Galvanic Isolation
Isolation coupling capacitance
Between any two separated conductors, an isolation resistance exists that can pass DC current and a coupling capacitance that can pass AC current. In DC/DC converters, the isolation resistance is 100M Ohms or higher, so can usually be ignored. The isolation coupling capacitance can range from 200pF to as low as 4pF depending on the transformer construction. Low coupling capacitance is desirable in fast switching circuits where the DC/DC converter ‘sees’ external high voltage, signals with high slew rate, on its output.
Isolation Voltage
The maximum voltage which can be applied for a defined time between the primary and secondary side of a transformer or power converter without breakdown.
Joint Electron Device Engineering Council. JEDEC J-STD-020D is the main standard for SMD soldering.
A Junction Field-Effect transistor, or JUGFET, is an FET in which the gate is created by a reverse-biased junction (as opposed to the MOSFET which controls drain-source current by a field generated by a gate, separated from the drain-source channel by a thin insulator).
Abbreviated J: A measure of energy or work. One joule is one watt of power, applied for one second (a watt-second). The energy absorption capability of transient protection components (diodes, varistors, etc.) is measured in joules.
Joint Photographic Experts Group; more commonly, files that are compressed using the JPEG standard.
K, k
Kelvin: Temperature scale. Zero K is defined as absolute zero. +273.15K is 0°C. The K symbol is uppercase and used without a degree symbol. Kilo: Metric unit representing 1000. E.g. 1kHz is 1 kilohertz (1000 Hertz). Note that the k is always lowercase.
Keep-Out Zone
The area under a power converter on a circuit board that the layout design cannot use, due to the danger of short circuiting to the case or to high voltage pins.
Kelvin connection
A Kelvin connection is a separate connection for measuring the voltage at a node independently of the current flowing through that node. Kelvin connections are commonly used in power transistors and in shunt resistors.
Last time buy
A product with the designation NRND (Not Recommended for New Designs) can also have a last time buy date found in the header of the datasheet. The product can be ordered up to this date but no later. The product has then reached EoL status.
Low Drop Out (regulator): A linear voltage regulator that will operate with a very small differential voltage between input and output.
Leakage Current
Undesirable AC or DC current flow, typically across power transformers or from power supply input connections to ground.
Leakage Inductance
A series inductive component that results from the imperfect magnetic linking of one transformer winding to another. In an ideal transformer, 100% of the energy is magnetically coupled from the primary to the secondary windings. Imperfect coupling reduces the signal induced in the secondary windings. The electrical equivalent is some self-inductance in series with primary windings that are 100% coupled to secondary windings. This non-coupled series inductance is the 'leakage inductance.'
Light-Emitting Diode. A diode which emits electroluminescence with a frequency (color) determined by the band-gap energy of the P-N junction. White light LEDs are made by either combining three red, green and blue LEDs in one package or by using a phosphor coating to convert UV to visible light.
Land Grid Array: An IC packaging technology where the device’s SMT connections are made by a grid of flat pads on the bottom of the package.
Line Derating
An indication of power rating reduction necessary in a power converter caused by changed input voltage. At lower input voltages the input current increases for the same output power and efficiency. Higher currents cause higher resistive losses, so line derating is often required.
Line Regulation
The ability of a stabilised power converter to maintain its output voltage despite variations in its input voltage, expressed as a percentage output voltage change across an specified input voltage range.
Linear Regulator
A voltage regulator that is placed between a supply and the load which provides a constant voltage by varying its effective resistance. Excess power is dissipated as heat, so typical linear regulators are only 60% efficient or less.
Lithium batteries
Lithium batteries (typically in coin-shaped cells), are used for low-power, high-reliability, long-life applications such as power for non-volatile memory and real time clocks. The cells can use a variety of lithium-based chemistries (as differentiated from lithium-ion).
Lithium-ion batteries
Lithium-ion (Li+, Li-Ion, Lion) cells are generally used as power sources for portable equipment. They are usually rechargeable. Lithium-ion and Nickel-Metal-Hydride (NiMH) have displaced Nickel-Cadmium (NiCd or nicad) as the dominant rechargeable chemistry for portable applications.
A resonant power converter topology using an additional inductor and capacitors connected in series/parallel with the transformer primary winding inductance to make a resonant ‘tank’ circuit so that the voltage across the transformer primary is sinusoidal or very close to it. A very efficient topology for higher power converters.
Load Regulation
The ability of a power converter to maintain its output voltage despite variations in the load current. Expressed as a percentage output voltage change for a specified load current change.
Low Line
The minimum allowable input voltage for a power converter. At full load, this is the highest input current condition.
Typically in bridge converter topologies, circuitry or devices that are referenced to 0V.
Machine-to-Machine communications, where smart nodes talk to each other via wireless technologies such as the cell phone network, WLAN, Bluetooth or Zigbee without human interaction. Applications include automatic meter reading, fleet management, vending, monitoring and control, security and alarms, and telemedicine.
Milliampere, or milliamp: 1/1000 of an ampere, the basic unit of electrical current. The ‘m’ is always lower case.
Manchester Data Encoding
Manchester encoding is a form of Binary Phase-Shift Keying (BPSK) used for low-cost radio-frequency (RF) transmission of digital data. Its main characteristic is that it encodes data in a way that ensures that there are never long strings of continuous zeros or ones. The presence of guaranteed transitions means that a clock can be recovered from the transmitted data, allowing the link to function with variable signal strengths from transmitters with imprecise, low-cost, data-rate clocks.
A test procedure that determines ’safety margin’. A parameter is varied to determine a device's sensitivity or ability to perform, given a range of inputs. A large number of parts can be characterized to determine a safe range for the specification, to guarantee performance and yield.
Micro-Electro-Mechanical Systems: Systems that combine mechanical and electrical components on the same die and are assembled using semiconductor fabrication techniques. Common examples are pressure and acceleration sensors which combine the sensor and associated amplification or conditioning circuitry.
Metal Oxide Varistor
(MOV, or surge-suppressor): A discrete electronic component that diverts current from excessive voltage to ground in DC systems or neutral lines in AC systems. It is commonly used on the inputs of AC/DC power supplies to suppress differential input voltage surges. A MOV can divert and dissipate high energy, but reacts slowly and its breakover point is not well defined, so it is often used in combination with a transient suppressor diode that reacts quickly and has an accurate breakover voltage, but has limited power absorption characteristics. MOVs degrade with use.
A Multiple Input, Multiple Output (MIMO) system has multiple antennas and multiple radios. MIMO is used in the implementation of the 802.11n wireless LAN standard.
Multi-Layer Ceramic Capacitors are generally the device of choice for applications where medium-value capacitances are needed, 1nF - 100uF. They are used as bypass capacitors, in op-amp circuits, filters, and more. They are increasingly used as the main filter capacitors in the outputs of power converters.
Means of Patient Protection/Means of Operator Protection:MOPP and MOOP are defined by medical electrical safety standard IEC 606001-1 and are formal descriptions of methods of ensuring protection against electric shock in the medical environment.
Metal-Oxide Semiconductor Field-Effect Transistor: In a MOSFET, the channel between the drain and source contacts is controlled by a metal gate separated from the channel by a very thin insulating layer of oxide. The gate voltage establishes a field that allows or blocks current flow in the channel.
Old term for a Micro-Processing Unit (Microprocessor).
Moisture Sensitivity Level is a measure of the sensitivity of an SMD part to air moisture, defined as the length of time of exposure allowed, from MSL1 (insensitive) to MSL5A (24 hours), with MSL6 reserved for components that must be baked in a drying oven before use. Above MSL2 requires dry-pack.
Mean Time Between Failures. A statistical measure of the reliability of an installed population of components, modules or systems during their operating lifetime. Numerically, the inverse of failure rate.
In radio transmission, multipath refers to the simultaneous reception of two copies of a signal that arrive via separate paths with different delays. A common example is when a signal bounces off a building or other object and is received along with the direct (unbounced) signal. In television reception, this causes 'ghosting', a faded echo is seen on the screen horizontally displaced from the main image. One of the main reasons why GPS does not work well in large cities is multipath signals bouncing off tall buildings.
Murphy's Law
If anything can go wrong, it will.
One milliwatt is 1/1000 of a watt.
One megawatt is 1 million watts. Always capital M when stated as ‘MW’, for example.
Nanoampere(s): Unit of current measurement. A billionth of an amp.
Not Connected. Used to denote a pin that is present only for mechanical stability. It is not normally electrically connected internally, but this is not a hard-and-fast rule. If a pin is labelled as ‘NC’, the pin should be soldered onto its own isolated pad and not connected to any other pin.
Without galvanic isolation that is, with no common electrical connection.
Non-Recurring Engineering cost: One-time engineering costs associated with a project (usually for the design effort or for tooling or certifications).
A product Not Recommended for New Designs will be withdrawn at some future date. The NRND status can be found on the RECOM website and on the datasheet of the relevant series and/or product. If an alternative product is available, a button will indicate this.
Negative Temperature Coefficient (thermistor): A component whose resistance decreases with increasing temperature. The nominal resistance value is always given at 25°C (room temperature).
Nyquist principle
In A/D conversion, the Nyquist principle (derived from the Nyquist-Shannon sampling theorem) states that the sampling rate must be at least twice the maximum bandwidth of the analog signal in order to allow the signal to be reproduced. The maximum bandwidth of the signal (half the sampling rate) is commonly called the Nyquist frequency.
Over-Current Protection. Electronic limitation of load current to protect a power converter. Typical techniques are to limit current to a set value, ‘foldback’ the current to a safe value with increasing load or ‘hiccup’ protection (the output is turned off and then back on again after a delay. If the overcurrent condition still exists, the cycle repeats).
Original Equipment Manufacturer: A manufacturer who controls sourcing of material and assembly of products for onward sale and distribution sometimes under different branding.
OF, Open Frame
A power converter design without a case or housing.
Organic Light-Emitting Diode: An LED made with organic materials. Useful for flat film displays, but still rather weak compared with standard LEDs.
Op amp
Operational amplifier: An amplifier which has inverting and non-inverting inputs allowing use of feedback to achieve a wide range of functions. Op amps can be configured to form amplifiers, comparators, logarithmic functions, filters, oscillators, data converters, level translators, voltage references and more. Analog mathematical functions such as addition, subtraction, multiplication, and integration can also be easily accomplished. A rail-to-rail op amp can work with input signals up to its own supply voltages.
An open-drain or open-collector output is driven by a single transistor, which pulls the output only down to ground. The output must be pulled up to +V by the load or by an external pull-up resistor.
Operating Temperature
The operating temperature (range) over which a device is warranted to perform to published specifications – refer also to power derating.
OR-ing Diode
OR-ing diodes are used in series with the outputs of separate power converters connected to a common load in a redundant configuration for high system availability. OR-ing diodes prevent failure of one converter from affecting others and facilitate ‘hot-swapping’.
OTP, Over-temperature Protection
Circuitry that shuts a power converter down when an internal preset temperature is exceeded.
Output Voltage Trimming
The facility in a power converter to adjust the output voltage within a limited range. Adjustment may be either by resistor value or external applied voltage to an adjustment pin.
OVP, Overvoltage Protection,
Over-Voltage Protection (OVP) in a power converter refers to a circuit that protects downstream circuitry from damage due to excessive output voltage, typically when output regulation circuitry fails. At its simplest, it is a Zener diode across the output which clamps the voltage and then typically fails short circuit, shutting down the converter. A more controlled technique is to add a separate opto-coupler which is triggered by an output overvoltage condition to shut-down the power supply on the input side.
A P-channel Metal-Oxide Semiconductor transistor is one in which P-type dopants are used in the gate region of the 'channel'. A negative voltage on the gate turns the device on.
Peak-to-peak. Often used as a measure of the output voltage ripple.
Parallel Interface
A multiline channel interface, with each line capable of transmitting several bits of data simultaneously.
Parallel Operation
Refer also to Ishare. Some power converters can be connected in parallel to increase the current available for a load, typically with an active or passive load share function. Parallel operation can also be used for redundancy where one or more ‘redundant’ power converters can be removed from the system leaving sufficient power available for the load.
Periodic And Random Deviation: A measure of the total voltage ripple and noise on a power converter output.
Partial Discharge (testing)
A non-destructive way of testing for isolation strength. A Hi-Pot test is very destructive because if an insulator fails, the arc-over destroys the part. PD testing measures the charge migration through the insulation layers and will stop the test before any permanent damage occurs.
Picocoulomb(s), a unit of electrical charge (10-12 coulombs). Used as a measure of partial discharge in insulation testing.
Printed Circuit Board: The most common PCB material is FR4: a glass fibre reinforced laminate which is flame resistant in compliance with UL94V-0
Pulse-Code Modulation: The conversion of an analog signal into binary (0 or 1) coded pulses. Not to be confused with PWM.
Abbreviation for pieces.
Peak Inverse Voltage
Peak Reverse Voltage (PRV:, The maximum voltage a diode or other device is rated to withstand when reverse-biased.
Power Factor Correction: A passive or active circuit that synchronises and shapes the AC mains input current to better match the mains input voltage. When current and voltage are perfectly aligned, the power factor (PF) is unity. Passive PFC circuits can typically improve the PF from around 0.4 to 0.7, active PFC circuits can achieve >0.99. PFC is required by the EMC standards for AC/DC power supplies of >75W, but for LED drivers, the limit is 25W.
Pulse-Frequency Modulation: A pulse modulation technique in which the frequency is varied with an input signal amplitude. The duty cycle of the modulated signal does not change. Commonly used to reduce the quiescent input current in a power converter by reducing the switching frequency at low loads.
Process Failure Mode and Effects Analysis (PFMEA): A methodology for assessing the weaknesses of production processes and the potential effects of process failures on the product being manufactured.
Power-good: A pin that is only active when the output voltage of a power converter is within specification.
A Programmable Logic Controller (PLC, or Programmable Controller) is a ruggedised, typically DIN-Rail mounted, microprocessor-based control system for plant automation by monitoring sensors and controlling actuators (relays/pneumatic /hydraulic valves) in real time. Commonly used with 24V DIN-Rail power supplies.
Plastic Leaded Chip Carrier: A square surface-mount IC package in plastic with leads (pins) on all four sides.
A Phase-Locked Loop: A control system that generates a signal that has a fixed relation to the phase of a 'reference' signal. A phase-locked loop circuit responds to both the frequency and the phase of the input signals, automatically raising or lowering the frequency of a controlled oscillator until it is matched in both frequency and phase.
Power Management Bus is a communications protocol targeted at digital management of power converters.The PMBus typically uses I2C hardware.
Power-over-Ethernet: A means for delivering power to a remote device using the same cable lines used to deliver Ethernet data. Can be used to power remote devices (cameras, LED-lighting, door entry systems) over a single combined power and bi-directional data cable. The nominal PoE voltage supply is 44-57VDC, so a DC/DC converter is typically required at the end device. This DC/DC must negotiate with the primary power supply to release enough current for its needs (available power is restricted between 4W and 100W depending on a complex sequence of signature resistances offered by the DC/DC negotiation IC). The relevant standard defining this interface is IEEE 802.3af /at/bt. Many think that PoE is the future for indoor LED lighting.
Point-of-load (POL) converters deliver high peak currents and low noise, as required by high-performance ASICs and microcontrollers, by placing individual non-isolated voltage regulators close to their point of use.
Power-OK: A signal indicating that a voltage rail is within specification.
Post Regulation
The technique of placing a separate voltage regulator on the output of a typically un-regulated power converter.
A variable resistor in which a ‘wiper’ sweeps from one end of a resistive element to the other, resulting in resistance that is proportional to the wiper's position. Commonly abbreviated to ‘pot’.
Power Converter
Generic term for a circuit that converts AC to DC, DC to DC, AC to AC or DC to AC with or without isolation.
Power Fail
A signal, often generated by an AC/DC power supply that provides early warning to a system of imminent power failure.
Power Good Signal
A signal which indicates the status of a power converter.
Power Module
Step-down non-isolated buck regulator typically in a SMD format with integrated passive and active components in a single package.
Power Supply
A term taken usually to mean an AC to DC power converter.
Production Part Approval Process: Used by the automotive industry for acceptance of new or modified products for release and use on automobiles.
A vendor-independent open Fieldbus standard used in manufacturing, building automation, and process control. Utilizes a non-powered two-wire (RS-485) network.
Phase-Shifted Full Bridge: A full bridge power conversion topology where the switching waveforms have a fixed 50% duty cycle but are phase shifted to control the power delivery and regulate output voltage. Particularly suitable for high power converters.
Positive Temperature Coefficient (thermistor): When the resistance of a component rises with temperature, it is said to have a positive temperature coefficient. Example: Hewlett-Packard's first commercial product, an audio oscillator, used a common light bulb as a PTC element in the feedback circuit to maintain constant output amplitude regardless of frequency. PTC Thermistors can be used in power supplies for overtemperature protection and temperature measurement.
A power converter topology that uses two switches to alternately drive the ends of a center-tapped transformer primary winding to ground. Commonly used in low-power DC/DC converters in a self oscillating arrangement (Royer converter).
Pulse Width Modulation. A technique to vary the duty cycle of a periodic waveform to increase or decrease its average value. In switch-mode power converters, the duty cycle of the oscillator driving the main power switch is varied to maintain the desired output voltage.
Q Factor
A measure of the quality of a resonant (tank) circuit. A ‘high-Q’ circuit has mostly reactive components (inductive and capacitive), with low resistance. It resonates strongly, with little damping, and will have low bandwidth relative to its center frequency (that is, it will have a narrow bandwidth vs frequency curve). Q = 2 π * (Energy stored / Energy dissipated per cycle).
Quad, Flat, No-lead package.
Reverse recovery charge: the charge that accumulates on a PN junction when it is forward biased. The current needed to overcome the Qrr when a transistor or diode is reverse biased causes significant losses.
A standardized converter case size: 2.3 x 1.45 x 0.5 inches (58 x 37 x 12.7mm), usually baseplate-cooled.
Quasi-Resonant (Q-R)
A Flyback power converter topology where the transformer primary winding is not switched on when the output current falls to zero, but kept off until the primary voltage starts to resonantly drop. The primary is switched on at one of the resonant minima (valley switching) where the voltage stress across the switching transistor is at a minimum. Q-R switching is thus highly efficient.
Quiescent current
The supply current consumed by a power converter with no-load, but still enabled.
The drain-to-source resistance of a switching FET or MOSFET when it is turned on. The lower the RDS(on) value, the lower the conduction losses in the device.
Redundant Array of Independent Disks: A redundant array of inexpensive disks. RAID is a performance-enhancing method of storing the same data in different places on multiple hard disks to achieve high speed and/or data redundancy.
Commonly used to describe Op-amps that can be operated from single power rails (no negative supply) and whose input and output voltages include the power rails.
Random Access Memory
Resistance-Capacitance: An RC network comprises resistors and capacitors typically in a series-parallel combination to filter or delay a signal.
Reflected Ripple Current
DC/DC converters contain power oscillators that draw current peaks every cycle. This is seen as a ripple current superimposed on the average DC input current. Measured as a peak-to-peak or rms value.
Reinforced Insulation
The minimum electrical isolation between primary and secondary side of a power converter to achieve agency-rated protection against electrical shock. Reinforced insulation is equivalent to Double Insulation and can be achieved with minimum creepage and clearance, solid insulation of a specified thickness or multiple layers of thin insulation, each rated for the full specified isolation test voltage.
Remote Sense/ Remote Sensing
Used to compensate for voltage drops in connections to a power converter load. Implemented with positive and negative ‘sense’ wires which connect to the point where most accurate regulation is required.
Resonant Circuit
A resonant, or tuned, circuit combines an inductor and capacitor to make a circuit that has an impedance peak or dip at a particular frequency. Depending on the configuration, the circuit can operate as a band pass or band stop filter, or as an oscillator with associated active components. It may be called an LC, LLC or LRC circuit because of the inductive (L), resistive (R), and capacitive (C) components used.
Reverse Recovery Time
When switching from the conducting to the blocking state, a diode junction has stored charge that must first be ‘recovered’. This discharge takes a finite amount of time known as the Reverse Recovery Time, during which the diode does not block the reverse current. When dealing with high frequency oscillators or very steeply rising signals, the reverse recovery time can lead to significant losses in a circuit, as high current and high reverse voltage can be present simultaneously.
Radio Frequency Interference: Redundant Array of Independent DisksRedundant Array of Independent Disks.
Radio Frequency IDentification: A method for remotely identifying an object using a tag or module that carries a unique ID code, which can be activated by an external RF field which powers the tag, enabling transmission of the code back to a ‘reader’.
Relative Humidity: Normal room humidity is between 40-60% rH.
Ripple and Noise
The voltage ripple and noise caused by the internal switching of a power converter which can be seen at the output terminals. Measured values are strongly dependent on test methods.
Rise Time
The rise time (or slew rate) of the output voltage of a power converter on power-up, typically measured from 10 - 90% of nominal output.
Root Mean Square value of a waveform is the equivalent DC value that would deliver the same power to a given load (the average value of a 50/60Hz sine wave is zero as positive and negative half-cycles cancel out, so RMS must be used instead). For example, 115VAC is the RMS value of the US mains supply. The peak voltage is actually ≈163V.
The term serial interface is often used for an RS-232 interface, consisting of Tx, Rx and ground wires, plus optional RTS and DSR handshaking lines. However, there are other serial interfaces in addition to RS-232 (e.g. RS-422)
RS-485 and RS-422 are serial interface standards in which data is sent in a differential pair (two wires, or twisted pair cable), which allows greater distances and higher data rates than RS-232.
Real-Time Clock: An Integrated circuit that contains a timer that supplies the time/date, usually powered by a long-life battery to allow it to keep track of time even when there is no system power applied.
S, s
Siemens, the standard unit for conductance (the inverse of resistance). Siemens is used for singular and plural. Lower case s is the standard abbreviation for seconds.
Surface Acoustic Wave: A sound wave that propagates along a hard surface. Used to make touchscreens by timing when and where a finger stops the wave.
Also known as Euro-connector, a 21-pin connector commonly used in Europe to interconnect satellite receivers, television sets, and other AV equipment. Sometimes needs a DC/DC converter to supply a 10-12V ‘Device present’ signal.
Schottky Diode
A 'Schottky-barrier junction' is a metal-semiconductor junction, rather than the P-N junction used in conventional semiconductor diodes. Schottky diodes are often chosen for their high switching speed and low forward voltage drop, (around 0.3V, compared to a standard diode’s typical 0.7V).
Silicon-Controlled Rectifier: A semiconductor switch that once activated by a gate voltage, stays on until the input voltage turns off or reverses and therefore can be used as a latch. Typical uses include fault protection (OVP, OTP) which forces the user to turn off the device to reset the SCR.
Secure Digital, a media format for non-volatile external memory cards. SD memories typically operate from 3.3V supplies and are best known as storage for digital cameras, smart phones, and other consumer electronic devices.
Sense or Shunt Resistor
A resistor placed in a current path to allow the current to be measured. The voltage across the sense resistor is proportional to the current that is being measured. Typical value is in milliohms. A Kelvin shunt has separate current and voltage connections to increase the measurement accuracy.
Single Ended Primary Inductor Converter: A non-inverting, non-isolated DC-DC converter topology that acts both as a boost and a buck converter, that is, the output voltage can be higher or lower than the input voltage.
A control pin typically used for sequencing of the turn-on or turn-off of a power converter with other converters.
Serial Interface
A digital interface in which data is sent in a single stream of bits, usually on a single wire-plus-ground, wire-pair, or single wireless channel (or two sets, one for each direction). Examples include USB, RS-232 and I2C
In one ‘leg’ of bridge power converter topologies, one transistor ‘pushes’ current to the output to drive it toward a positive voltage; a second device ‘pulls’ current down to 0V. The transistor drivers are designed so both devices should never be on at the same time, which would effectively short the power supply. However, unintentional timing delays can sometimes cause both to be on simultaneously and the transient, high current that occurs while both devices are on is called shoot-through current.
Signal-to-Noise Ratio
The ratio of the amplitude of a desired signal to the amplitude of superimposed noise signals. Usually expressed in decibels, dB. The larger the number, the better for data or signal quality
Subscriber Identity Module: A SIM card identifies your cellphone so the system knows which phone should ring when someone calls your number.
A topology where only one end of a transformer primary winding is switched, the other end being permanently connected to a DC bus voltage. Used in both DC/DC and AC/DC converters.
Smart Sensor
A sensor that processes the raw measurement data and only sends relevant updates to reduce the amount of data traffic. Important for the concept of IoT if billions of devices are to be networked.
System Management Bus: A 2-wire serial-interface standard similar to I²C, but with a faster clock speed.
Surface Mount Device: An electronic component that mounts on the surface of a printed circuit board (as opposed to 'through-hole' or THT components which have pins or leads that are inserted into holes).
Switch-Mode Power Supply. Much more efficient than ’linear’ power supplies, so almost exclusively used for power conversion above a few watts (with the exception of powering broadband RF amplifiers where the switching harmonics can cause interference).
Surface Mount Technology
A device which suppresses voltage transients and spikes. Usually a capacitor and resistor in series but can be more complex for lower losses.
Soft Start
A feature in some switching power converters that limits the startup inrush current and sometimes output slew rate, at initial switch-on.
Small Outline Integrated Circuit. If an SMD IC has 8 pins, it is often an SOIC-8
The connection to a MOSFET conduction channel, opposite the drain.
Serial Peripheral Interface. A 3-wire serial interface.
Simulation Program with IC Emphasis. Software which allows a circuit to be simulated to predict its real-life behavior.
Spread Spectrum
Techniques used to reduce electromagnetic interference by dithering a power converter clock frequency so emissions are no longer concentrated at one frequency.
Single-Pole/Single-Throw switch.
Static RAM: Random Access Memory that does not require a clock to retain its data.
Soft-start: Typically a pin on an IC to which a capacitor can be connected to set the start-up timing of a power converter to reduce the inrush current and/or output slew rate.
Shrink Small-Outline (IC) Package
Star Ground
A layout or wiring technique in which all components connect to ground at a single point.
Start-up time
The time from applying input voltage to a power converter until typically 90% of specified output voltage is achieved.
Set Top Box: Typically a cable or satellite TV receiver.
Step-Up DC-DC
A switch-mode voltage regulator in which output voltage is higher than its input voltage (boost converter).
Switch Mode
Power converter topology with a switching transistor and an inductive or sometimes capacitive energy storage element.
Switching Regulator
A voltage regulator that uses a switching element to transform the supply into an alternating current, which is then converted to a different voltage using capacitors, inductors, and other elements, then converted back to DC. The switching regulator term often refers to an non-isolated converter.
Synchronous Rectification
A technique used in switch-mode power supplies, in which the output rectifier diode is replaced with a MOSFET switch to reduce losses and thereby increase efficiency. The MOSFET is turned synchronously on and off with the main switch(es) to reproduce the effect of a diode.
System on a Chip
A System on a Chip (SoC) integrates most of a system's elements on a single integrated circuit (chip). It typically combines a microprocessor core along with interface elements and analog and mixed signal functions.
A tap is an additional connection to a transformer winding besides the ends. The most common arrangements are the centre-tap in the middle of the winding and asymmetric taps used to make a 50/60Hz transformer primary compatible with 100 V, 115 V, 120 or 230/240 VAC supplies by connecting to the appropriate tap.
Abbreviation for case temperature. The hottest case point and the maximum allowable operating temperature must be marked on all LED lighting AC/DC drivers.
Transmission Control Protocol/Internet Protocol: The protocols or conventions that computers use to communicate over the Internet.
A Thermo Electric Cooler is a small cooling device that relies on a semiconductor Peltier effect junction. Composed of two semiconductors made of different materials, a Peltier junction acts as a heat pump which can cool or warm when current is passed through it.
Temperature coefficient: The amount a value drifts with temperature in %/°C
Tesla (abbreviated T) is a measure of magnetic flux density (B-field), named for engineer and inventor Nikola Tesla. 1 tesla=10,000 gauss.
Thin-Film Transistor
Total Harmonic Distortion: A measure of signal distortion which assesses the energy in harmonics in a distorted signal compared with an original signal.
Thermal Derating
An indication of power reduction required by changed ambient temperature. At higher ambient temperatures the headroom to the internal temperature limits in a power converter will decrease. Above a certain temperature, a load reduction is required to reduce internal losses and for internal heat dissipation to stay below acceptable limits. Some power converters also require power derating at low temperatures to ensure start-up.
Thermal Management
The use of various cooling methods, such as heatsinks, thermal interface materials (TIM) or fans to control temperature of power converters and their internal components.
Thermal Shutdown
Deactivation of a circuit when a measured temperature exceeds a predetermined value. Can be latch-off or auto-reset upon cooling down. The reset temperature is typically lower than the trip temperature, exhibiting hysteresis.
A resistor with a high temperature coefficient. As a negative temperature thermistor, it can be used as a series inrush current limiter (high resistance when cold, low resistance when hot).
A temperature sensor formed by the junction of two dissimilar metals. A thermocouple produces a voltage proportional to the difference in temperature between the hot junction and the lead wire (cold) junction.
Three-State or Tri-State
A three-state output has three electrical states: One, zero, and ‘Hi-Z’, or open’. ‘Tri-State’ is a registered trade mark.
A method for mounting components on a printed circuit board (PCB) in which pins or leads of the component are inserted into holes in the board and soldered in place.
Through-Hole Technology
Tin Whiskers
Tin whiskers (also called Sn whiskers or metal whiskers) are microscopic, conductive, hair-like crystals that emanate spontaneously from pure tin surfaces and can cause short circuits and malfunction. There are various whisker mitigation processes that can be applied to reduce this effect, such as matt finishes, under-plating or over-plating.
Totem Pole
A standard logic gate output structure, originally implemented with bipolar transistors, but now typically in CMOS, where a P-channel MOSFET is connected in series with an N-Channel MOSFET and the connection point between the two is the output. The P-FET sits on top of the N-FET like a ‘totem pole’. This creates a push-pull output using just two transistors.
Thin version of the QFN package (the JEDEC 'W' option) 0.8mm thick.
Thin Quad Flat Pack
Trans- conductance Amplifier
An amplifier that converts a voltage to a current. Also known by several other terms, such as OTA, or Operational Transconductance Amplifier. The term derives from ‘transfer conductance’ and is measured in siemens (S), where 1 siemens = 1 ampere per volt. It is represented by the symbol gm. The basic gain of vacuum tubes and FETs is expressed as transconductance. Siemens is used for singular and plural of the unit.
An inductive electrical device for changing the voltage of alternating current, consisting of two magnetically coupled coils. Alternating current in one (called the ‘primary’) creates a changing magnetic field which induces a current in the second coil (the ‘secondary’). Multiple secondary coils can be energised from a single primary winding. There is no such thing as a DC transformer, so an isolated DC/DC converter has to convert the DC input to an AC signal for the transformer primary and then rectify the resulting AC on the transformer secondary to a DC output.
AC/DC power supplies that are non-isolated and use switched capacitors, high voltage regulators or switching converters to generate a low voltage DC output which is directly referenced to the AC input. These may only be used where human access to the secondary connections is prevented.
Transient load response
See Dynamic Regulation.
A basic term for a solid-state control device which allows or disallows current flow between two terminals, based on the voltage or current delivered to a third terminal.
TS 16949
An ISO Technical Specification that aligns various automotive quality systems standards within the global automotive industry. Together with ISO 9001:2000, ISO/TS 16949:2002 specifies the quality system requirements for the design/development, production, installation and servicing of automotive related products. RECOM’s factories in Taiwan are ISO/TS 16949 certified.
Thin Small-Outline Package
Transistor-Transistor Logic: Logic gates implemented with bipolar transistor technology requiring a 5V±0.25V supply. Now almost universally superseded by CMOS logic.
Transient Voltage Suppressor: A semiconductor device designed to protect a circuit from voltage transients. Typically implemented as a large silicon diode operating in avalanche mode to absorb large energy pulses quickly when the avalanche voltage is exceeded.
A power converter topology that uses two transistors to switch each end of a transformer primary winding separately. Can be used with forward, flyback and tapped transformers.
Microampere, or microamp: A millionth of an ampere. Ampere is the basic unit of electrical current.Often written as uA, but the u is a plain-text substitute for the Greek letter mu.
Universal Asynchronous Receiver-Transmitter: An IC that converts parallel data to serial and converts received serial data to parallel data.
Uninterruptible Power Supply (UPS)
A device that maintains AC power in the event of a mains failure. A UPS commonly includes a battery that is kept charged. When power fails, the battery powers an AC inverter to maintain the mains voltage for a duration defined by the capacity of the battery. This allows an orderly power-down of the system or to bridge short power outages. An off-line UPS connects the inverter only when power fails and may exhibit a short power interruption on changeover when mains fails. An on-line UPS routes power through the inverter permanently and shows no interruption on mains failure at the expense of lower operating efficiency. An on-line UPS also inherently provides protection against mains spikes and surges.
Uniform Resource Locator: A web address.
Universal Serial Bus (USB): A standard port that enables the connection of external devices to computers. The USB standard supports both data and power transfer. The new USB ‘Type C’ connector standard allows for 5V @ 3A (15W) up to 20V @ 5A (100W), as well as faster data transfer rates.
Ultraviolet: The part of the electromagnetic spectrum just higher in frequency than visible light.
Under-Voltage Lockout: A mechanism in a power converter to prevent operation if the input voltage is below a specified threshold.
V p-p
Peak-to-peak voltage.
Volt-Ampere(s): If voltage and current are not in phase because a load has an inductive or capacitive element, then the power is measured in VA and not watts. This is because the product of the voltage and current values in a reactive circuit is higher than the power consumed. That is, real power consumed does not equal volts x amps.
Vcc, Vss
The supply voltage for a circuit is often given as V plus a double-letter suffix. The double letter is usually related to the lead of the transistors that are commonly connected to that supply, e.g. VCC is a positive-voltage supply and connects to the Collector terminal of bipolar transistors. VSS connects to the Source terminal of a FET, etc. V+ and V- are also used.
Voltage-Controlled Oscillator: An oscillator device in which output frequency is proportional to a control voltage.
Voice over Internet Protocol: A method for transmission of telephone calls over the Internet, e.g. Skype.
Unit of measure for electromotive force (EMF), the electrical potential between two points. An electrical potential of 1 volt will push 1 ampere of current through a 1 ohm resistive load.
Voltage Doubler
A capacitor charge pump circuit which produces an output voltage which is twice the input voltage. A low cost, low power, non-isolated DC/DC converter.
Voltage Regulator
A circuit which is connected between a power source and a load, which provides a constant voltage despite variations in input voltage or output load. Voltage regulator is a generic term but is normally taken to imply non-isolated.
Voltage-mode control
A method of regulating a power converter output by sensing output voltage alone. See current mode control.
Voltage Regulator Module. Another name for a switching regulator normally non-isolated DC/DC.
Watt (W) is the unit of power. One watt is one joule of energy transferred or dissipated in one second. Electrical power is calculated as: watts = volts x amps x Power Factor Power factor can be disregarded for DC circuits or for AC circuits with a resistive load (it is unity in those situations).
Semiconductor manufacturing begins with a thin disk of semiconductor material, called a ‘wafer’. A series of processes defines transistors and other structures, interconnected by conductors to build the desired circuit. The wafer is then sliced into 'die' which are mounted in packages, creating the semiconductor device.
Wide Area Network: Any Internet or network that covers an area larger than a single building.
Worldwide Interoperability for Microwave Access, a broadband, wireless access defined by the IEEE 802.16 standards. Wi-Fi (802.11) covers a small area with a radius of a few hundred meters, but WiMax (802.16) can cover up to 6 miles with only one base station.
Wireless power
Circuits that transfer power using radio or inductive or capacitive coupling. Protocols include Qi, commonly used in mobile phone charging pads.
Wireless Local Area Network
X Cap,

Y Cap

X-Capacitors are certified for use across AC mains inputs. Y-capacitors are certified for use between AC mains and ground or in limited situations, across an isolation barrier. They are designed to self-repair after an over-voltage condition (self-healing). Y-capacitors have extra insulation as they must have at minimum ‘basic’ insulation, so are more expensive and only available in low capacitance values. Y capacitors pass leakage current so must not exceed prescribed capacitance values.
Zero Current Switching: a mode of switch operation where it only operates when the current through the switch is zero, for minimum losses.
Zener Diode
A diode manufactured to have a specific reverse-breakdown voltage. Its most common use is as a voltage reference.
Zero Insertion Force (socket): A class of IC sockets which clamp the IC pins after insertion (via a small lever on the side of the socket), and require no downward force on the IC or its pins to insert it into the socket.
A standard for short-distance, low-data-rate, mesh (not point-to-point) communications. Created and maintained by the ZIGBEE Alliance Group.
Zero Voltage Switching: a mode of switch operation where it only operates when the applied voltage is zero, for minimum losses.
Prefix that is used with many inanimate things (homes, offices, phones, cities) to mean some sort of embedded intelligence and interconnectability.