Glossary


TERMS AND ACRONYMS CONTINUED..
See below for the special

Off-line power supply is a PSU that takes its power directly from AC line without using line frequency transformer. Such supply can still be isolating if it uses high frequency transformer in one of its power conversion stages. A typical off-line SMPS rectifies input AC line voltage, converts it into high-frequency AC voltage by using semiconductor power switches, steps that voltage up or down by using inductors and/or transformers, then rectifies it again and filters for DC output. An example of isolating off-line PSU is a computer switching power supply.

Open-frame construction: A construction technique common to OEM power supplies where the supply is not provided with an enclosure. It can be either a simple printed circuit board or circuit board mounted on a metal chassis without a cover.

Operating temperature: The range of temperatures within which a power supply will perform within specified limits.

Opto-isolator: Device that provides electrical isolation and a signal path by making an electrical to optical to electrical signal transformation from its input to output terminals. This is accomplished with a light-emiting diode in close proximity to a phototransistor. Opto-isolators are used in the feedback loop to maintain electrical isolation between the input and output of the power supply. Ageing may provoke degraded feedback response.

Output impedance: The value of a fictional resistor in series with an ideal voltage source that would give the same magnitude of AC voltage across the supply terminals as observed for a particular magnitude and frequency of alternating current.

Output voltage: The voltage measured at the output terminals of a power supply; A feature or device that senses and responds to current or power overload conditions;

Overcurrent protection: See: Current limiting circuit.

Overshoot: The amount by which an output exceeds its final value in response to a rapid change in load or input voltage, measured as a percentage of the nominal. It is an important value at turn-on and following a step change in load or line voltage.

OVP (overvoltage protection): A protection mechanism for the load circuitry that does not allow the output voltage to exceed a preset level. In most cases, the output voltage is reduced to a low value, and the input power must be recycled to restore the power supply output

Parallel operation: The ability of power supplies to be connected so that the current from corresponding outputs can be combined into a single load.

PARD: Acronym for “Periodic And Random Deviation” and used as the specification term for ripple and noise. Ripple is the unwanted portion of the output harmonically (periodically) related in frequency to the input line and to any internally generated switching frequency. Noise is the unwanted, a periodic output deviation.

Pass element: The active circuit element, typically a transistor, that forms the output power stage of a linear power supply.

Peak charging: A rise in voltage across a capacitor caused by the charging of the capacitor to the peak rather than rms value of the input voltage. This generally occurs when a capacitor has a high discharge resistance across it and large ripple and noise or spikes on its input line. In a switcher, this parameter may affect minimum load conditions (discharge resistance) on each output required to maintain regulation.

Peak transient output current: The maximum peak current that can be delivered to a load during transient loading conditions, such as electric motor starts.

Phase controlled modulation: A circuit used in switching regulators where the operating frequency is held constant (typically 50 or 60 Hz line frequency) and the phase angle at which the control elements are turned on its varied, controlling both line and load changes with minimal dissipation.

Pin fins: Type of heatsink that uses pins in place of conventional extruded fins.

Planar Magnetics: Use of high volume manufacturing processes and technologies to replace conventional wire windings in magnetic components with patterned conductors formed on a single or multi-layer substrates. Planar magnetic offer advantages in terms of cost, reliability, manufacturability and predictable electrical parameters.

Post regulator: Usually a linear regulator used on the output of a switching or ferro power supply to improve overall (load) regulation.

Power factor: The ratio of actual power used in a circuit to the apparent power. Power factor is the measure of the fraction of current in phase with the voltage and contributing to average power.

Power fail detect: A circuit that senses the DC voltage across the input capacitors of a switching power supply. Should the AC input line fail, it senses an abnormally low DC level across the capacitors and provides an isolated TTL output signal warning of imminent loss of output power.

Power supply or Power Supply Unit (PSU) is a device that transfers electric energy from the source to the load using electronic circuits. A common application of power supplies is to convert raw input power into a regulated voltage and/or current required for an electronic equipment.

Pre-regulator: A regulator circuit that provides a line-regulated output, which is then processed by a second regulator, the post-regulator, which provides load regulation.

Programming: The capability of controlling the voltage of each output.

Push-pull converter: Used in switching power supplies where the main switching circuit uses two transistors operating in push-pull. The main advantage is simplicity of design.

PWM (Pulse width modulation): A circuit used in switching regulated power supplies where the switching frequency is held constant and the width of the power pulse is varied, controlling both line and load changes with minimal dissipation.

Rated output current: The maximum continuous load current a power supply is designed to provide under specified operating conditions.

Recovery time: The time required by a transient over or under shoot in a stabilised output quantity to decay within specified limits

Redundancy: The ability to connect power supplies in parallel so that if one fails the other will provide continuous power to the load. This mode is used in systems when power supply failure cannot be tolerated.

Reference: A known stable voltage to which the output voltage is compared for the purpose of stabilizing the output voltage.

Regulated power supply is a PSU that maintains a given output parameter (usually output voltage) to within specified limits under varying operating conditions, such as input line, output load, ambient temperature. PSU can be linear or switched-mode (switching) depending on the method of regulation and mode of operation of power handling components.

Regulator: The part of a power supply that controls the output voltage. In most cases, the regulator acts to stabilize the output voltage at a preset value.

Remote on-off: See: Inhibit.

Remote sensing: A method of moving the point of regulation from the output terminals to the load. Compensates voltage drops in the power distribution bus, but negative impact on dynamic load behaviour must be tolerated.

Response time: The time required (usually ms) for the output of a power supply or circuit to reach a specified fraction of its new value after a step change or disturbance.

Return: An arbitrary name for the common terminal for all the outputs. It carries the return current of all the outputs.

Reverse voltage protection: The ability of a power supply to withstand reverse voltage at the input terminals when hooked up in the reverse polarity.

RFI (radio frequency interference): See: EMI.

Ripple: The periodic AC component at the power source output harmonically related to source or switching frequencies.

Ripple voltage: The periodic AC component of the DC output of a power supply.