

AC Noise


Ampere (Amp)

Electric current measurement unit.

Ampere hours (AH)

Number of amperes used/produced in a given hour.

Back-up time

Time during which the UPS can supply the rated load with nominal-quality power while utility power is down. This time depends on the battery and the efficiency of the UPS. Typical backup ranges from five minutes to several hours.

Battery on shelves

Battery cell installation system whereby the cells are placed on several vertically stacked shelves or racks made of insulating material.

Battery (recombination)

Battery with a gas recombination rate at least equal to 95%, i.e. no water need be added over battery life. So, usually called “maintenance free.”

Battery (tier-mounted)

Battery cell installation system whereby the cells are placed on tiers made of insulating material.

Battery (vented)

The battery cells are equipped with a filling port for distilled, demineralised water used to top up the free electrolyte.

Battery cells

The interconnected battery elements that supply electrical power created by electrolytic reaction.

Battery bank

A group of batteries wired in a fashion that allows power storage in a solar power system.


A resistor or group of resistors, used permanently to drain current from charged capacitors. It establishes the predetermined initial load level for a power supply or signal source, and it serves a safety device in high voltage power supplies.


A total loss of electrical power.

Breakdown voltage

The voltage at which the insulation of an insulator fails and current flows through or across the surface as a discharge.

Bridge Converter

A DC to DC converter topology (configuration) employing four active switching components in a bridge configuration across a power transformer.


A reduction of the AC mains’ distribution voltage, usually caused deliberately by the utility company to reduce power consumption when demand exceeds generation or distribution capacity.


Operating a newly manufactured power supply, usually at rated load, for a period of time in order to force component infant mortality failures or other latent defects before the unit is delivered to a customer.


The act of taking the UPS offline and feeding the critical bus from utility power. This can be done either manually, for service, or automatically in the event of failure or overload.

Capacitive Coupling

Coupling of a signal between tow circuits, due to discrete or parasitic capacitance between the circuits.


Device associated with the rectifier and used to supply the battery with the electrical power (DC current) required to recharge and/or float charge the battery

Circuit breaker (battery)

DC circuit breaker that protects the battery of a UPS


A regulator of electric current drawn from the solar charger into the battery bank.


An electrical circuit which accepts a DC input and generates a DC output of a different voltage, usually achieved by high frequency switching action employing inductive and capacitive filter elements.

Crest factor (Fc)

Ratio between the peak current value to the rms current value.


The rate of flow of electric charges and is measured in units of amp.

Current (inrush)

Temporary current observed in a network when electrical devices are energized, generally due to the magnetic circuits of the devices. The effect is measured by the currentís maximum peak value and the rms current value it generates.

Current Limited

A circuit in which, if a maximum current value reached (or approaches a short circuit), the source voltage will drop as power demand increases.

Current Monitor

An analog power supply signal which is linearly proportional to output current flow. Usually only feasible for single output power supplies.


Direct Current. Electric energy of constant value and flowing in one direction.


A reduction in an operating specification to improve reliability. For power supplies it is usually a specified reduction in output power to facilitate operation at higher temperatures.

Design Life

The expected lifetime of a power supply during which it will operate to its published specifications.

Differential Mode Noise

Noise that is measured between two lines with respect to a common reference point excluding common-mode noise. The resultant measurement is the difference of the noise components of the two lines. The noise between the DC output and DC return is usually measured in power supplies.


A short term voltage decrease.


The change in an output voltage, after a warm-up period, as a function of time when all other variables such a line, load, and operating temperature are held constant.



Duty factor

The ratio of the pulse duration to the pulse period. Also, the ratio of the average pulse power to the peak pulse power.

Earth Leakage

Leakage from an active circuit to ground.


The ratio expressed as a percentage of the output power to the input power.

Electromagnetic Interference (EMI)

It is the noise generated from the switching action of a given power supply. There are two types of Emi, Conducted EMI and radiated EMI. As the name implies, Conducted EMI effects the power line which can be addressed via a line filter. Radiated EMI is broadcast into free space and is addressed by encasing the power supply circuitry in a metal case (note, this is one reason not to purchase a power supply utilizing clear plastic casing).

Electronic Load

An electronic device designed to provide a load to the outputs of a power supply, usually capable of dynamic loading, and frequently programmable or computer controlled.

Equivalent Series Resistance (ESR)

The value of resistance in series with an ideal capacitor which duplicates the performance characteristics of a real capacitor.

Fault Mode Input Current

The input current to a power supply with a short circuit on the output.

Ferro Resonant Power Supply

Power supply used at higher power levels in fixed applications, since they are very heavy. Can only be used effectively when the line frequency is very stable as they are sensitive to variations of input AC frequencies.


An electronic device that allows only certain frequencies to pass.


A protective device which heats and melts so interupting a circuit when the current exceeds a certain value.


Distortion of a pulse waveform in the form of a short-distortion distribution.


An electrical connection to earth or some other conductor that is connected to earth. Sometimes the term “ground” is used in place of “common,” but such usage is not correct unless the connection is also connected to earth.

Ground Loop


H – Henry

The unit of self-inductance or mutual inductance.

Hz – Hertz

The frequency of electrical current is described in cycles per seconds. Appliances in the US use 60 Hz, elsewhere it is 50 Hz.


Used in conjunction with series pass regulators, and is the difference between the input and output voltages.


A waveform that is sinusoidal in nature, but consists of a portion of a sine wave superimpose
d on another waveform. The input current waveform to a typical off-line power supply has the form of a haversine.


Abbreviation for High Potential, and generally refers to the high voltages used to test dielectric withstand capability for regulatory agency electrical safety requirements.

Hold-Up Time

The measure of time after loss of input power that a power supply output will remain within specified limits.


An unwanted low-frequency noise originating from mains driven equipment and comprising harmonics of the mans frequency.

Induced Noise

Noise generated in a circuit by a varying magnetic field produced by another circuit.

Input Line Filter

An internally or externally mounted low-pass or band-reject filter at the power supply input which reduces the noise fed into the power supply.

Input Surge Withstand

The amount of momentary surge voltage, above the normal input range, that can be applied to the input without causing an interruption in operation.

Input Voltage Range

The nominal input power range that will allow a power supply to deliver its rated output.

Insertion gain (loss)

The gain (loss) resulating from the inseration of a network between a generator and its load.


Generation of unwanted and sustained oscillations.

Interference (high-frequency)

High-frequency parasitic current that is either conducted (electrostatic origin) or radiated (electromagnetic origin) by a device.


A device that is used to convert DC power (eg. from a battery) into AC current to power household appliances. When comparing inverters check the continuous wattage rating, surge power, and efficiency for each.


Two circuits that are completely electrically separated with respect to DC potentials, and almost always also AC potentials. In power supplies, it is defined as the electrical separation of the input and output via the transformer.

Isolation Voltage

The maximum AC or DC voltage which maybe continuously applied from input to output and/or chassis of a power supply.

Johnson noise

It is also called as thermal noise, which arises from the thermal agitation of electrons in a conductor.

Joule effects

The heating effect generated by an electric current in a conductor by virture of its resistance.


A hot-cathode high vacuum diode used for high voltage low current rectification in industrial applications such as X-ray equipment.

Leakage Current

term relating to current flowing between the AC supply wires and earth ground. The term does not necessarily denote a fault condition. In power supplies, leakage current usually refers to the 60 Hertz current which flows through the EMI filter capacitors which are connected between the AC lines and ground (Y caps).

Line Frequency

It is the number of times the AC flows in one direction during one second. Frequency is measured in Hertz (Hz) or cycles per second. The standard power frequency may differ. For example the AC frequency in India is 50Hz. (i.e. the current changes its direction 50 times per second) while in the U.S.A. it is 60 Hz.

Line loss

A voltage drop over the length of electric line wire.

Line Regulation



The amount of lighting and number of electric appliances need be supported by your local power supply system.

Load Regulation


Magnetic Amplifier

Sometimes abbreviated “Mag Amp,” a saturating inductor which is placed in series with a power supply output for regulation purposes.


Adjusting a power supply output voltage up or down from its minimal setting in order to verify system performance margin with respect to supply voltage. This is usually done electrically by a system-generated control signal.

Minimum Load

The minimum load current/power that must be drawn from the power supply in order for the supply to meet its performance specifications. Less frequently, a minimum load is required to prevent the power from failing.

MTBF (Mean Time Between Failure)

A measure of the reliability of an equipment, ie. the time to the first failure.

MTTF (Mean Time To Failure)

Mathematical calculation of the duration of normal operation of a non-reparable device, i.e. for which a MTBF is not possible. The product, expressed in hours, is an indication on the reliability of the device.

MTTR (Mean Time To Repair)

Mathematical calculation (or statistical average if available) of the time required to repair a device.

No-Load Consumption

The amount of input power consumed by a power supply under a no-output load condition.

Nuclear energy

The generation of energy by nuclear fission of fissionable nuclei.


A power supply which receives its input power from the AC line, without using a 50/60 Hz power transformer prior to rectification and filtering, hence the term “off line” power supply.

Offset voltage

For a differential amplifier the output voltage arising from inherent DC unbalance of the amplifier.

Operating Relative Humidity

The range of humidity that a power supply can tolerate and continue to meet its rated specifications.

Operating Temperature

This is the range of ambient temperatures that a given power supply can be operated within.


An electro-optical device which transmits a signal across a DC isolation boundary.


Conditions of a source of electrical power when more poer is drawn from it than the source can supply continously without overheating or damage.


Form of transient distortion of a step or pulse signal in which the respone temporarily exceeds the final value.

Over-Current Protection

This circuit protects a given power supply where present from excessive current as well as short-circuits.

Over-Voltage Protection

This circuit will shut down a given power supply where present, if the output voltage exceeds the given specified limits.

Output Current

This is simply the maximum power current which can be drawn from any given power connector for said power supply.

Output Impedance

The ratio of change in output voltage to change in load current.

Output Noise

The AC component that may be present on the DC output of a power supply. Switch-mode power supply output noise has two components: a lower frequency component at the switching frequency of the converter and a high frequency component due to fast edges of the converter switching transitions. Noise should always be measured directly at the output terminals with a scope probe having an extremely short grounding lead.

Parallel wiring

A method of connecting electric modules / batteries in order to increase current output (i.e., amperage).

Peak Power

The absolute maximum output power that a power supply can produce without immediate damage. Peak power capability is typically well beyond the continuous reliable output power capability and should only be used infrequently.

Photoelectric effect

The formation and liberation of electrons in materials when irradiated by light or other electromagnetic waves.


A process by which light power is converted directly into electric power and is often referred to as PV for short. Crystalline silicon or gallium arsenide or other semi-conductor materials are used in such as process.

Pilot lamp

A lamp used to indicate the condition of an associated circuit.

Power factor

In a AC circuit the ratio of the real power to the apparent power.

Power supply circuits

These are alternative options to batteries as af power source (regulated DC ) used nowadays in most electronic equipments.

Power Transistor

A heavy-duty transistor designed for power-amplifier
and power-control service.


A form of transient distortion of a step or pulse signal in which the reproduced step is preceeded by oscillations.


The input section of an isolated power supply which is connected to the AC mains and hence has dangerous voltage levels present.

Proximity effect

In a conductor caryying an alternating current a concentration of the curent towards the edges of the cross section caused by interaction between the conductor and the ElectroMagnetic field setup by neighbouring conductors carrying the same current.

PWM (Pulse Width Modulation)

Inverter high-frequency chopping technique using a means of regulation enabling rapid modification of pulse widths over a single period, thus making it possible to maintain the inverter output within tolerances even for non-linear loads.

Quiescent point

Quiescent point of an active device is the position of the operating point when no input signal is applied. It indicates the mean current and the mean voltage in the output circuit and so measures the dissipation within the active device in the absence of an input signal.

Rated Output Current

The maximum load current that a power supply can provide at a specified ambient temperature.


A process of converting electric AC current into DC current.



Regulation Band

The total error band allowable for an output voltage. This includes the effects of all of the types of regulation: line, load, and cross.


Probability that a device will accomplish a required function under given conditions over a given period of time. Rms value of AC current with harmonics The rms value Yrms of a non-sinusoidal alternating current may be determined on the basis of the individual harmonic currents: where Y is the rms value of the fundamental.

Return current (voltage)

In a transmission line the current (voltage) which is setup at any impedence discotinuity and travels back to the source.

Reverse Voltage Protection

A protection circuit that prevents the power supply from being damaged in the event that a reverse voltage is applied at the input or output terminals.


Ripple is simply AC voltage compositing on the DC output normally expressed as a percent of the nominal output voltage for a given power supply.

Rise time

A measure of the steepness of the loading edge of a pulse, ie. it is the time taken for the instantaneuous amplitude to change from 10% to 90% of the peak value.

Safety Ground

A conductive path to earth that is designed to protect persons from electrical shock by shunting away any dangerous currents that might occur due to malfunction or accident.


It is a form of distortion of a pulse signal in which the instantaneous amplitude falls during the period of the pulse.

Sawtooth signal

A periodic signal in which each cycle consists of a lnear change followed by a rapid return to the value at the begining of the linear change.


The output section of an isolated power supply which is isolated from the AC mains and specially designed for safety of personnel who might be working with power on the system.


Certain solar electric modules have an optional circuit that prevents the battery from overcharging. In this case, no regulator is required if such a circuit ensures battery storage capacity matching.


The technique of establishing a desired order of activating the outputs of a multiple output power supply.

Short Circuit Protection

Protection of a power supply not to be damaged if the output circuit is short circuited or connected to a very low impedance source.

Shot noise (Schotky noise)

Noise arising from random variations in the emission of electrons from a cathode.

Single-Crystal silicon

Pure silicon is grown into crystalline only to be cut into very thin slices in order to make efficient state-of-the-art solar solar cells.

Solar cell

The device which generates electric power when exposed to sunlight through what is known as the photovoltaic process.

Solar constant

The strength of the solar radiation at the Earth atmosphere, at average distance from the sun, and is equivalent to 1.37 x 106 ergs/s cm2

Solar cooling

The utilization of solar energy as a heat source in a absorption cooling cycle (refrigeration).

Solar electric

The common term for the technical term photovoltaic.

Solar energy

The radiant energy produced in the sun as a result of nuclear (H and He) fusion reactions.

Standby Current

The input current drawn by a power supply when shut down by a control input (remote inhibit) or under no load.

Storage Temperature

The maximum range of temperature that the power supply can safely be kept in storage when no circuit power is applied.


An abnormally high voltage lasting for a short period of time.

Surge Suppressor

A semiconductor device used to absorb potentially destructive transients or over voltages on a utility power line.

Switching Frequency


Temperature Coefficient

The average output voltage change expressed as a percent per degree centigrade of ambient temperature change. This is usually specified for a pre-determined temperature range.

Thermal Protection

A power supply protection circuit which shuts the power supply down in the event of unacceptably high internal temperatures.

Thin-Film silicon

A tiny solar cell that charges found in many hand-held wrist watches and calculators.


Also called as Sag. It is a form of distortion of a pulse signal in which the instantaneous amplitude falls during the period of the pulse.

Time constant

Time constant of a quantity that vary exponentially with time, the time taken for a quantity to vary by 63% of the full extent of the charge.


A characteristic in a multiple output power supply where any changes in the output voltage of one output caused by line, load, and/or temperature are proportional to similar changes in accompanying outputs.

Transfer Time

The amount of time it takes a stand-by or off-line type UPS to sense a power interruption and switch from utility output to inverter output. Normally expressed in milliseconds.


The signal which persists for a brief period following a sudden disturbance to the steady state condition.

Transient response

The ability of a circuit or device to reproduce transients without distortion.


An electric device consisting of two coils that can be used to raise (step-up) or reduce (step-down) voltage through the use of induction between the coils. There are two types : Single-phase (residential) and three-phase (industrial) transformers.

True Power

In an AC circuit, true power is the actual power consumed. It is distinguished from apparent power by eliminating the reactive power component that may be present.


A form of transient distortion of a step or pulse signal in which the response makes a temporarily excursion before the main transtion and in the opposite direction.

Unilateral impedence

A mutual impedence through which power can be transmitted in one direction only.

Uninterrupted Power Supply (UPS)

A power supply which continues to supply power during a loss of input power. Two types are the stand-alone UPS, which the battery is located external to the equipment being powered, and the battery back-up power supply, which the battery is embedded in the equipment being powered.


The amount of electrical pressure that forces electricity to flow in power lines. 110 V in the USA and Japan, and 220 V in most other coun
tries. Three-phase voltage is 380 V.

Voltage amplifier

A circuit incorporating one or more active devices and designed to amplify voltage waveforms.

Voltage Balance

The difference in magnitudes, in percent, of two output voltages that have equal nominal voltage magnitudes but opposite polarities.

Voltage Breakdown

The voltage at which current suddenly passes in destructive amounts of dielectric.

Voltage feedback

A system in which the negative feedback signal is directly proportional to the voltage across the load.

Voltage Limited

The maximum amount of voltage available at the power supply output.

Voltage – Multipier rectifier

A combination of rectifiers and capacitors which produces an output voltage approximately equal to an exact multiple of the peak value of the AC input voltage.

Volt-Ampere (VA)

This is the simple product of voltage and current and is used to express the amount of power. VA gives the apparent power.

Warm-Up Time

The time required after initial turn on for a power supply to achieve compliance to its performance specifications.


A unit for measuring total electric power. A KiloWatt (kW) is 1000 Watts.


The quantity of electrical energy used/produced when on Watt of electric power is used/produced for one hour.


An instrument used to measure electrical power. The scale usually reads directly in watts, kilowatts, milliwatts, or microwatts.


A coil in an inductor or transformer such as the primary and secondary winding.


A machine that converts wind into useful energy (usually regulated electricity or water pumping, pressing oil from seeds and irrigations). There are two types : horizontal-axis and vertical-axis towers. Typical machines starts operating at about 20 km/h with optimum performance at about 50 km/h.

Zener breakdown

In a reverse-biased pn junction, a rapid increase in the current which occurs at a particular reverse voltage as a result of the Zener effect.

Zener effect

Zener effect is a condition through a reverse-biased pn junction caused by spntaneous generation of the hole-electron pairs within the inner electron shelss of atoms in the junction region.