Power-Plus

Power Supply Terminology

Glossary of Electronic Power Supply Terminology

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Absolute Maximum Ratings - Specifications that, if exceeded, could cause permanent damage to the power supply. These are not continuous ratings, and proper operation is not implied.

A. C. Power Fail Signal - This is an active TTL high signal and can source or sink 5mA current. It is located on the main position 1 module. Power fail signal indicates the condition of the AC line and offers a warning time of a minimum of 5mS between P.F. signal going low and output losing regulation.

Ambient Temperature - Temperature of still air immediately surrounding a power supply. The temperature measurement should be made about 0.5 inches from the body of the power supply. See also Operating Temperature.

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B

Base Plate - Substrate to which circuit components are mounted or, a metal plate to which the power supply is attached. Normally used to draw heat away from critical circuit components. See also Heat Sink.

Base Plate Temperature - See Case Temperature.

Breakdown Voltage - Maximum AC or DC voltage that can be applied from the input to output (or chassis) of a power supply without causing damage.

Burn-In - Operation of newly manufactured power supplies for some period of time prior to shipment. The intent is to stabilize the power supply and eliminate infant mortality by aging the device. The time period and conditions (input power cycling, load switching, temperature, etc.) varies from vendor to vendor. However, the less stringent the conditions, the less likely it is that potential problems will be caught by the vendor.

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C

CFM - Cubic feet per minute, which is a measure of the volume of air flowing in system.

Canadian Standards Association (CSA) - Independent organization that establishes and tests safety standards for electronic components and systems for the Canadian marketplace.

Case - See Enclosure.

Case Temperature - Temperature of the case when the power supply and surrounding system are operating normally. Often used as a specification for DC-DC converters with extended temperature ranges. Case temperature is at times referred to as Base Plate Temperature.

Common - Conductive path used as a return for two or more circuits. Common is often used interchangeably with ground, which is not technically correct unless it is connected to earth. See also Ground.

Common Mode Noise - Noise component that is common to both the power supply output and return lines with respect to the input common.

Conduction Cooled - Cooling a power supply via a solid material. Cools a power supply by adding a heat sink or attaching the module to the system chassis.

Convection Cooled - Cooling of a power supply via the movement of air over the surface of it's heat dissipating components. "Free-air convection" means that the natural movement of air (unassisted by a fan blower) is sufficient to maintain a power supply within specified operating limits.

Converter (DC/DC) - Device that accepts a DC input voltage. Typically the output produced is at a different voltage level than the input. However, converters sometimes have the same input/output and are used to provide noise isolation, power bus regulation, etc.

Cross Regulation - For a multiple output power supply, the change in voltage on one output (expressed as a percent) caused by a load change on another output.

Current Foldback - See Foldback Current Limiting.

Current Limiting - Feature that protects the power supply (or load) from damage under overload conditions. The maximum output current is automatically limited to a predetermined safe value. If the power supply is specified for auto restart, normal operation is automatically restored when overload condition is removed.

Current Limit Knee - On a plot of output voltage vs. current, the point at which current begins to limit. Fold forward Current Limit is when the short circuit current is greater than the Current Limit knee value. See also Current Limiting, Foldback Current Limiting.

Current Mode Control - Control method used with switching power supply topologies. A dual loop control circuit adjusts the PWM operation in response to a measured output current.

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D

DC/DC Converter - See Converter (DC/DC).

Density - See Power Density.

Derating - For an AC-DC power supply, the specified reduction in output power required for operation at elevated temperatures. The most common operating temperature range specified for commercial grade power supply is 0ºC to +50ºC without derating. See also Convection Cooled.

Differential Mode Noise - Noise component measured between two points with respect to a common point (minus common mode noise).

Distributed Power - System level architecture in which power supplies operating from a central power bus provide localized power (and various voltage levels) to individual subassemblies/components. The type of power distribution system used is highly dependent upon the needs of a particular application.

Drift - Change in the output voltage of a power supply over a specified period of time. All other operating parameters (load, line, etc.) are assumed to be held constant. Often specified as starting after a warm-up period.

Dynamic Load - Output load that changes rapidly. Normally specified as both a load change value and a rate of change.

Dynamic Response - Output overshoot that occurs when the power supply output load is turned on/off or abruptly changed. This overshoot gives the high frequency output impedance of the power supply. See also Output Impedance.

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E

Efficiency - Ratio of total output power to input power expressed as a percentage. Efficiency is derived by the equation:

  (OutputPower / InputPower) * 100

Efficiency is normally measured at full rated output power and nominal input line conditions.

Electromagnetec Interference (EMI) - Noise generated by a power supply (typically by the switching action of the more popular power supply topologies). Usually specified as meeting agency limits for conducted EMI (noise reflected back onto the power bus) or radiated EMI (noise emitted into the area surrounding a power supply).

Electrostatic Discharge - Current produced by two objects having a static charge when they are brought close enough to produce an arc or discharge.

EMI Filter - Filter that is placed at the input to an off-line power supply that minimizes the effect of EMI on the power supply and the associated system.

Enclosure - Case or container used to package a power supply. Typically, power supplies are packaged in metal cases that protect the internal components from the outside environment and also improve thermal and noise performance.

Error Amplifier - Operational or differential amplifier used in the control feedback loop of a power supply. The amplifier produces an error voltage when the output (tapped off a voltage divider network) differs from a reference voltage. This error voltage is used to adjust the operation of the PWM so as to correct the sensed output voltage. Sometimes called a Reference Amplifier.

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F

Failure Mode - Reason for which a power supply either does not meet or stops meeting its specified parameters.

Fan Cooled - See Forced Air Cooling.

Fault Mode Current - Input current drawn by a power supply when the output is shorted.

Federal Communications Commission (FCC) - US government agency that sets standards for, and governs the testing of conducted and radiated emissions. These are system level standards, but they are typically used in specifying power supplies. See also Electromagnetic Interference.

Floating Output - Power supply output that is ungrounded and not referenced to another output. Typically, floating outputs are fully isolated and maybe referenced positive or negative by the user. Outputs that are not floating share a common return and as such, are referenced to one another.

Filter -See Input Line Filter.

Foldback Current Limiting - Protection technique. The circuit is protected under overload conditions by reducing the output current as the load approaches short circuit. This minimizes internal power dissipation under short circuit conditions.

Forced Air Cooling - Use of a fan (or other air moving equipment) within a (sub) system to move air across heat producing components in order to reduce the ambient temperature. Also called forced convection.

Free Convection - Operating environment where the natural movement of air (unassisted by fans or blowers) maintains the power module within its operating limits. Also called natural convection.

Frequency of Operation -See Switching Frequency.

Full Load -Maximum value of output load specified for a power supply under continuous operating conditions.

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G

Ground - Electrical connection that is made to earth (or to some power supply that is connected to earth). A power supply common is not actually ground unless somehow connected to earth. See also common.

Ground Loop - Condition caused when two or more system components share a common electrical ground line. A feedback loop is unintentionally induced, causing unwanted voltage levels.

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H

Heat Sink - Metal plate, extrusion, case, etc. used to transfer heat away from sensitive components and/or circuits. See also Base Plate.

High Line - Maximum value of input line voltage specified for normal power supply operation. See also Low Line and Input Voltage Range.

High Potential Test - Test used to determine whether a power supply passes its minimum breakdown voltage specification. See also Breakdown Voltage.

Hold-Up Time - Period of time that a power supply output remains operating within specification following the loss of input power. This is a more common specification for AC/DC supplies.

Hot Plug - Also referred to as Hot Swap, a common requirement in distributed power systems wherein the power board must be capable of being connected/disconnected from the power bus without damage. Power board components must be protected against the resultant high currents.

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I

Input Current - Current drawn form the input power but by a power supply when operating under nominal conditions.

Input Line Filter - Low-pass or band-reject filter on the power supply input (internal or external) that attenuates noise introduced onto the power supply form the power bus.

Input Surge Current - See Inrush Current.

Input Transient - Spike or step change in the input to a power supply. Input transient protection circuits are used to shield sensitive components (such as the semiconductor switch) from possible damage due to transients.

Input Voltage Range - Minimum and maximum input voltage limits within which a power supply operates to specifications. Often given as a ratio of high line to low line (i.e. a range of 9 VDC to 18 VDC is 2:1).

Inrush Current - Maximum, instantaneous input current drawn by a power supply at turn on. Also called Input Surge Current.

Inrush Current Limiting - Protection circuit that limits the current a power supply draws at turn on.

Insulation - Non-conductive material used to protect and separate electronic components or circuits.

Insulation Resistance - Resistance offered by an insulating material to current flow.

Internal Power Dissipation - Power dissipated (as heat) within the power supply during normal operation. Primarily a function of the power handling capability and efficiency of the power supply. Internal power dissipation is normally given as a maximum specification that cannot be exceeded without risking damage to the power supply.

International Electrotechnical Commission - Organization based in Switzerland that sets standards for electronic products and components. IEC does not conduct any testing. However, their standards have been adopted by many of the national safety standards agencies.

Isolated Output - See Floating Output.

Isolation - Electrical separation between the input and output of a power supply. Normally determined by transformer characteristics and components spacing.

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J

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K

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L

LFM - Linear feet per minute, which is a measure of air velocity used to cool a power supply.

Leakage Current - Current flowing from input to output or input to case of an isolated power supply at a specified voltage level.

Life Test - Reliability test in which a power supply is operated (typically under accelerated conditions) over some period of time in order to approximate its life expectancy.

Line - Bus used to deliver power to the input terminals of a power supply. See also High Line and Low Line.

Line Regulation - Percentage change in output voltage caused by varying the input voltage over a specified range (with output load, temperature, etc. remaining constant).

Line Transient -See Input Transient.

Load - Electronic components/circuits connected to the output of a power supply. The characteristics (resistance, reactance, etc.) of the load determine the amount of power drawn from the converter.

Load Regulation - Percentage change in output voltage caused by varying the output load over a specified range (with input line, temperature, etc. remaining constant).

Local Sensing - Using the output terminals of the power supply to provide feedback to voltage regulation circuits. See also Remote Sensing.

Logic Inhibit/Enable - Signal (typically TTL/CMOS compatible) used to turn a power supply output on/off. Also called Remote On/Off.

Long-Term Stability - Change in output voltage of a power supply over time with all other factors (line, load, temp. etc.) remaining constant. Expressed as a percent, the output change is primarily due to component aging.

Low Line - Minimum value of input line voltage specified for normal operation. See also High Line and Input voltage Range.

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M

Maximum Load - Highest amount of output load allowable under the continuous operating specifications of a power supply.

Mean Time Between Failure - Unit of measure, expressed in hours, that gives the relative reliability of a power supply. MTBF data is based upon actual operating data (demonstrated) or derived per the conditions of MILHDBK-217F (calculated) or Bellcore.

Minimum Load - Minimum amount of output load required on a power supply in order to maintain normal continuous operating specifications. Usually associated with PWM (Pulse width Modulation) controlled power supplies.

Minimum Operating Temperature - Minimum ambient temperature at which a power supply will start and operate within specifications.

Module - DC/DC converter.

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N

N+1 Redundancy - A paralleled power system configuration used in distributed power systems. Requires that at least one more current sharing power supply than is necessary be used to power a load.

No Load Voltage - Voltage level present at the output of a power supply when 0% load is applied.

Noise - Unwanted variations in the power supply output that are unrelated to the switching frequency. Normally called "Ripple and Noise" and given as a peak value with a specified bandwidth. Measured with 0.1 m F cap across output as shown in diagram

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O

Offline Power Supply - Power supply (linear or switching) that operates directly off the AC line. The input voltage is rectified and filtered prior to any isolation transformer.

Open-Circuit Voltage - See No Load Voltage.

Operating Temperature Range - Range of temperatures over which a power supply can be operated safely within specified limits. Normally specified as ambient, however, at times case or base plate temperature is also used.

Output Current Limiting - See Current Limiting and Foldback Current Limiting.

Output Impedance - Ratio of change in output voltage to a change in output load current. Sometimes referred to as Dynamic Response.

Output Ripple And Noise - See Noise and Periodic and Random Distribution.

Output Voltage - Value of DC voltage measured at the output terminal of a power supply.

Output Voltage Accuracy - Maximum allowable deviation of the DC output of a power supply from its ideal or nominal value. Expresses as a percentage of output voltage. Often called output voltage tolerance.

Output Voltage Range - Minimum and maximum output voltage limits within which a power supply meets its operating specifications.

Overload Protection - See Current Limiting and Foldback Current Limiting.

Overshoot - Transient change in output voltage that exceeds specified accuracy limits. Typically occur on power supply turn on/off or with a step change in output load or input line.

Overcurrent Protection - Output monitoring circuit activated if the power supply exceeds a preset current level.

Overvoltage Protection (OVP) - Output monitoring circuit activated if a preset voltage level is exceeded. Depending on the type of circuit used, the OVP shuts the power supply down, "crowbars" the faulty output or switches the power supply to a different operating mode.

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P

Parallel Operation - Operating mode in which two or more power supplies are connected in parallel. The output currents are summed together into a single load, providing a higher level of output power than that available from a single supply. Parallel operation requires power supplies specifically designed to share loads.

Periodic and Random Deviation (PARD) - Noise and ripple voltage superimposed on a power supply DC output. Typically specified at full load, it is expressed in peak-to-peak or RMS volts over a given bandwidth.

Polarity - Ability of a power supply to produce an output that is positive or negative referenced to ground. See also Floating Output.

Power Density - Ratio of power supply output power supply to power supply volume.

Power Factor Correction (PFC) - Design technique usually applied to the input of off-line power supplies that improves the power supply's power factor and minimizes harmonics generated by the power supply onto the AC power line.

Power Good - Signal (typically a visible LED) that indicates the DC output of the primary channel of a power supply is still present.

Power Rating - Specified power available at the power supply output.

Primary Circuit - Input side of an isolated AC-DC power supply.

Pulse Width Modulation - Circuit used in power supplies to regulate output voltage. Regulation is achieved by varying the conduction time of the transistor switches.

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Q

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R

Rated Output Current - Maximum output current that can be continuously drawn from a power supply under specified conditions.

Redundant Operation - Parallel configuration of power supply used in distributed power system to increase system reliability. Power supply may be used in a "N+1" architecture.

Regulation -Ability of a power supply to maintain an output voltage to within specified limits under varying conditions of input line and output load. See also Line Regulation.

Remote Sensing - Using sense leads connected at the output load provides feedback to voltage regulation circuits of a power supply. This arrangement is used to compensate for voltage losses from long loads to a load. See also Local Sensing.

R Remote Shutdown - See Logic Inhibit/Enable.

Ripple And Noise - See Periodic and Random Deviation (PARD).

Reverse Current - See Leakage Current.

Reverse Voltage Protection - Power supply feature that prevents damage to internal components if a reverse voltage is inadvertently applied to the input or output terminals.

Ripple Voltage - Periodic AC component imposes on the output voltage of a power supply. Normally expressed as part of ripple and noise and given as a peak-to-peak value over a specified bandwidth. See also Periodic and Random Deviation (PARD).

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S

Sense Line - Output line used on a remote sensing connection to route athe output voltage (at the load) back to the control feedback loop. See also Remote Sensing.

Series Operation - Master-slave configuration in which two or more isolated power supplies are connected to obtain a higher output voltage level (power supply inputs connected in parallel) or wider input voltage range (power supply inputs connected in series) than that obtainable from one.

Short Circuit Protection - See Current Limiting and Foldback Current Limiting.

Soft Start - Power supply input circuit that limits the inrush current at turn on.

Stability - See Long-Term Stability.

Standby Current - Current drawn by a power supply when it had no load and has been shut down by a logic inhibit signal.

Step Change - Sudden change in a power supply parameter. Typically used in referring to changes in output load or input line during power supply testing.

Storage Temperature Range - Range of ambient temperature over which a power supply can be safely stored.

Switching Frequency - Rate at which the input voltage is switched or chopped in a power supply. Sometimes referred to as frequency of operation.

Switching Regulator - Circuit (typically a pulse width modulator) that uses a closed loop design to regulate the output voltage.

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T

Technischer Uberwachungs-Verein (TUV) - Organization approved for testing products to VDE standards. US-based companies often use TUV in place of VDE because they have established facilities in the US.

Temperature Coefficient -Average change in output voltage per degree centigrade. Expressed as a percentage over a specified temperature range.

Temperature Range - See Operating Temperature Range and Storage Temperature Range.

Thermal Protection - Feature that shuts the power supply down if the internal temperature exceeds preset limits. Also called thermal shutdown.

Thermal Resistance - Measure of a given material's opposition to the flow of heat. Units are oC/W.

Transient - Spike or step change in a power supply parameter. Commonly used in describing input line and output load characteristics. Transient Recovery Time - Time required for a power supply output to return to with specified limits following a step change in output load current. Expressed as percentage of rated value.

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U

Underwriters Laboratories (UL) - Independent organization that conducts safety testing of products to established standards.

Undershoot - Transient change in a power supply output voltage that does not meet the lower limit of the voltage accuracy specification. Typically occurs at power supply turn on/off or with some step change in output load or input line.

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V

Verband Duetsher Elekttrochniker (VDE) - German organization that sets standards for products safety and noise emissions and tests and certifies products by those standards.

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W

Warm-up Draft - See Drift.

Warm-up Time - Time required for an Ac-DC power supply to operate within specifications after turn0on. This time normally precedes a long-term drift specification.

Withstand Voltage - Maximum voltage level that can be applied between circuits of components without causing a break down. See also Breakdown Voltage.

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X

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Z

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