Amplifier, Differential:   An amplifier with two signal ports whose output voltage amplitude and polarity are proportional to the voltage difference and polarity between the voltages applied to the inverting and non-inverting input ports.

Auxiliary Ouputs:   All outputs of a multiple supply other than the main output. Auxiliary outputs usually have a lower rating and limited performance.

Bandwidth:   A system's frequency response, normally the difference in frequency between the upper and lower "half power" or 3-dB-down frequencies. When applied to power supplies, this normally refers to the frequency band over which output ripple and noise components are to be measured or specified.

Brownout - GM:   A drop in supply voltage to a value below the minimum specified by the supply authority, but above zero.

Choke:   An inductor specifically designed to carry a large DC current component. (To prevent saturation, chokes will often have gapped cores or cores of especially low permeability material.)

Chokes, RFI:   Chokes which are specifically designed to have a high self-resonant frequency, to provide maximum impedance at RF frequecies. Various space winding or wave winding techniques are used to minimize interwinding capacitance.

Chokes, Swinging:   A choke whose inductance is designed to increase significantly as the DC current is reduced toward zero. The swinging choke has a more linear characteristic than the "nonlinear choke", the change in permeability being a function of the properties of the bulk core material.

Common-mode Ripple and Noise:   The components of ripple and noise voltages or currents, which exist between input or output lines and defined ground plane.

Constant-Current Supply:   Any high-impedance current souce whose current is essentially constant regardless of the load resistance. Desicribes a type of power supply in which the major controlled parameter is the output current. Such supplies will maintain the output current constant for a range of load resistance, normally from zero to some maximum value defined by the compliance voltage.

Constant-Voltage Supply:   A power source in which the main controlled parameter is the output voltage.

Control ICs:   Dedicated integrated circuits used for the control of power supplies, both switchmode and linear.

Converter:   A general term for any siwtchmode power supply which converts a DC voltage at the input to a DC voltage at the output while providing galvanic (often transformer) isolation. Where regulation is not provided, the term "DC transformer" is more correctly used. Where input-to-output isolation is not provided, the term "switchmode regulator" is normally used.

Cross Regulation:   The regulation effect measure on one output as a result of changes on other outputs. (Very often, in multiple-output supplies, the main output is fully regulated, and cross regulation would refer to the output voltage variation son the auzilairy outputs as a result of load changes on the main output.)

Current-Mode Control:   A switchmode power supply control technique in which a fast-acting control loop defines the maximum current in the switching element on a pulse-by-pulse basis. In constant-voltage supplies, the fast current control loop is then adjusted by a slower form voltage control loop to provide a constant ouput voltage. The two control loops thus form a voltage-controlled current source. This method of control effectively eliminates the output filter inductor from the small-signal model, automatically improving the stability margin and small-signal dynamic performance. It also has the advantage of providing fast current limiting.

DC Current Transformer:   A type of current transformer in which a DC primary current controls the pulsating output current. (Very useful for isolated low-loss current limiting in high-current push-pull topologies.)

Differential-Mode Ripple and noise:   That part of the input or output ripple and noise voltage which exists between two supply or output lines with respect to each other. In multiple-output units, the ripple and noise voltage between output lines and a common return line.

Direct-Off-Line Swithcher:   A switchmode power supply that provides isolated DC outputs from AC line inputs without using line frequency transformers.

Duty Cycle:   The ratio of operating time to total elapsed time for a device that operates intermittently. Usually expressed as a percentage.

Dynamic Load:   A load that is varying, an active load. An electronic load that can be rapidly changed to test transient response. May also refer to an adjustable constant-current electronic load used for test purposes.

Efficiency:   Ratio of output power to input power as a percentage. (Note: True power must be used, with due allowance for power factor. With capacitive input filters, often iused for "off-line" SMPS).

EMI (Electromagnetic Interference):   Also referred to as RFI (radio-frequency interference). EMI levels, both radiated and conducted, are controlled by national and international standards.

Faraday (electrostatic) Shield:   An electrostatic shield, usually copper, place between a source of high-voltage noise and a low-noise area. Typical examples would be electrostatic screens in transformers and the screens between switching elements and heat sinks.

FCC (Federal Communications Commission):   A US federal regulatory body that, among other things, defines maximum permitted EMI conduction and radiation levels in the United States.

Filter:   Normally refers to power level low-pass filters, intended to give nearly continuous DC output currents. Power filters differ from signal filters in that input and output impedances are not matched and are often variable. Because of the need for energy storage, power filters are large.

Flyback:   The property of an inductor that enables it to reverse its terminal voltage when the conducted current is interrupted. The term is often applied to transformers and diodes which utilize this flyback voltage property.

Flyback Converter:   The most popular low power (<100W) converter. A member of the buck, boost, buck-boost family of converters. Typically referred to as a flyback transformer but technically it is an energy storage device or inductor. The primary stores the energy and the secondary removes the energy.

Full-Wave Recifier:   A circuit that rectifies both half cycles of an AC input.

Ground Loop:   Normally refers to noise-generating current loops set up as a result of grounding the common output of the power supply at more than one place. (In switched power supplies, ground loops are normally minimized by grounding the common output of the supply at the output terminals. If the system demands other ground points, loop currents can be minimized by a common-mode inductor in the output leads.)

Heat Sink:   A term generally used to describe a thermal shunt, normally metal, used to aid in the transfer of heat from a hot spot (often a semiconductor) to an "infinite heat sink" (often free air).

Inrush Current:   The peak uncut current that flows into the power supply when it is first switched on.

Inverter:   A device that provides and AC output from a DC supply.

Line Regulation:   The change in the controlled output parameter as a result of an input line voltage change. Normally expressed as a percentage of change of the output for a full-range input voltage change.

Linear Regulator:   A dissipate series or shunt regulator technique which gives continuous control of the regulated parameter. More commonly, these will be series transistor voltage regulators.

Load Regulation:   The change in the controlled output parameter as a result of a defined load change on the measured output. Usually given as a percentage change in output for the defined load change.

Main Output:   In multiple-output supplies, the principal output, often the highest-current or highest-power output. The control loop is normally closed to the "main output" and therefore it will have the best overall performance.

Master:   The controlling power supply in a parallel "master slave" configuration.

Master Slave Operation:   A method of interconnecting two or more units in such a way that a defined "master" unit controls the behavior of the remaining "slave" units. Normally power supplies must be specially designed for this mode of operation, if required.

Modulator:   An electronic control device which varies one parameter in response to the changes of another, used as part of the control loop to vary the ouput of a power supply. A typical example would be a pulse-width modulator or current-mode control modulator in a switchmode supply.

Output Impedance:   The magnitude of the complex resistive and reactive components seen by looking into the power supply output terminals at frequencies other than DC. Normally measured by dividing the RMS output voltage change by the force RMS load current change over the required range of frequency.

Overshoot:   A transient excursion of the controlled parameter outside the regulation limits, as a result of initial turn-on or turn-off, or a a sudden load variation.

Post-Regulator:   A regulator positioned in the output side of a DC/DC converter. Post regulators are often applied to multiple-output supplies to provide additional regulation on auxiliary outputs. Post-regulators may be linear or switching and , in high-power applications, magnetic amplifier or saturable reactor techniques are commonly used.

Power Factor - GM:   The ratio of real power to apparent power in AC supply applications. In direct-off-line power supplies with capacitive input filters, current flows only at the peak of the applied sine wave. The products of RMS input voltage and RMS current gives the input VA (apparent power, not true power). The power factor of a capacitive input is approximately VA x 0.63 or VA x 0.9. (To measure true input power accurately, a watt meter is required. This may be a dynamometer or digital type, but it should have a bandwidth exceeding 1 kHz for reasonably accurate results.)

Power Suppy:  A power source. Normally applied to the prime source, e.g. line supply, battery or generator. More often, a unit that conditions a source of unregulated power to provide a regulated output. Not necessarily a prime source of power.

Resolution:   The smallest increment of change that can be made in the controlled parameter.

Response Time:   The time taken for the controlled output parameter to change from 10 to 90 percent of its programmed change in response to a step change in the programming signal.

Series Regulator:   A regulator in which the active element is in series with the supply output. A term often applied to linear regulators.

Shunt Regulator:   A method of control in which the power controller is in parallel with the output terminals. Shunt regulators have the advantage of absorbing minimum power when the output is fully loaded. A shunt-regulated output can source or sink current and is useful for servomotor control during overrun conditions.

Snubber:   (1) A network used to reduce the stress on a switching component. (2) A network used to reduce the rate of change of voltage on diodes or switching devices to minimize RF components and dv/dt stress.

Soft Start:   A mehtod of controlling the initial rate of increase in duty ratio in a switchmode power supply during the turn-on transient. (Used to reduce the stress on internal components and to prevent transformer saturation.)

Switching Regulators:   A switchmode DC/DC regulator in which input and output share a common line.