Glossary Of Terms
A - B - C - D - E - F - G - H - I - L - M - N - O - P - Q - R - S - T - U - V - WAmbient temperature:
Usually defined as ?room temperature.? Ambient temperature refers to the temperature of the air surrounding a power supply. Ambient Temperature refers to the temperature of the air in a designated area, which is directly surrounding a power supply. The ideal ambient temperature of the immediate environment that a power supply is operating in would be what is referred to as the “average room temperature” which is generally 68°F to 77°F (68°C to 77°C). However, well-designed power supplies can operate in much higher and much lower ambient temperatures. Elpac Power Supplies are designed to and will operate reliably at ambient temperatures from 0°C to +40°C with absolutely no detrimental effect on performance or reliability.
Bandwidth:
When used in reference to a power supply, bandwidth means the difference between the lowest and highest frequency and is measured in hertz. Bandwidth is the spectrum of frequencies that are of interest for a particular test or specification and is measured in Hertz. In reference to Power Supply testing and specifications bandwidth frequencies may be specified for the Electromagnetic Interference (see EMI) specification. Another area where bandwidth may be specified is in the Ripple/noise specification where the bandwidth used for testing is usually 20MHz.
Bleeder resistor:
This type of resistor functions by reducing the charge of a capacitor. This is referred to as a small current drain. A type of resistor that is specifically designed into a power supply’s filter circuitry to act as both a load to improve the output voltage stability and as a safety feature to ensure that the charge of the capacitors are reduced. The bleeder resistor provides a path for the current to drain to ground from the large filter capacitors so that the capacitors are kept at a safe condition when the unit is turned off.
Bridge:
A type of circuit, also called a rectifier that will use either four diodes or two diodes. A four diode circuit is referred to as a full bridge, while a two diode circuit is referred to as a half bridge. Also called a bridge rectifier. This is a type of circuit that is used to rectify or convert an AC (alternating current) sine wave into a DC (direct current) pulsating wave. The DC pulsating wave can then be further filtered and regulated to produce a clean pure DC voltage. The bridge rectifier may consist of four discreet diodes or may be in an integrated package. The bridge rectifier is a much more efficient design than other types of half or full wave rectifiers.
Brownout:
A brownout occurs when a utility company reduces their nominal line voltage by 10 to 15% in response to an overload of demand for electricity. Brownouts occur when the voltage supplied to operate electrical equipment sags below the level that is required for proper operation. A brownout may be localized to a specific building and be caused by overloaded circuits (trying to use too many appliances or other equipment simultaneously) in that building. A brownout can also be caused by a widespread utility overload due to excessive demand for electricity at peak times (such as on a hot summer afternoon) that may affect all of the utility company’s customers is a given area. The utility company may respond to this high demand for electricity by lowering the nominal line voltage by 10% to 15%. This lowered voltage, if occurring repeatedly, may adversely effect electrical equipment by forcing it work harder and possibly eventually may cause the equipment to fail. Using well a designed power supplies that compensate for brownouts or using other brownout protection will greatly help to prevent the detrimental effects of brownouts.
Brownout Protection:
A power supply that will enable equipment to continue functioning in the midst of a brownout, without any discernable loss of functionality. Brownout protection may involve the use of devices such uninterruptible power supplies (UPS), auxiliary generators and line conditioners. These devices will keep the voltage supplied to electrical equipment at the correct level so that the adverse affects of repeated brownouts may be eliminated. It is also advisable to use power supplies, such as those manufactured by Elpac, that are designed with a broad input range to help protect against the problems that can caused by brownouts and other voltage fluctuations issues.
Brute-Force Supply:
This is the most rudimentary form of a power supply. A brute-force supply does not regulate DC output voltage. A Brute-Force power supply is the most rudimentary and basic form of a power supply consisting only of a transformer, rectifier and a low pass filter. The simple output filtering may allow the Brute-Force power supply to typically exhibit a lot of ripple voltage and other AC noise that is superimposed on the DC output. Also, since the Brute-Force power supply is not regulated the DC output voltage will vary proportionally to changes in the AC input and also to changes in the load. The advantages of the Brute- Force power supply is that it is economical, simple and efficient and will work well for simple, uncomplicated power applications. Elpac’s Brute-Force power supplies are available in the BFS Series of 15W, 30W, 60W, 100W, 200W and 500W and with output voltages that include 12V, 20V, 24V and 48V, depending on the series.
Burn-in:
Burn-in refers to continuously operating a circuit at an increased temperature and voltage. This technique is often used to identify sub-standard power supplies immediately after manufacturing. Burn-In refers to continuously operating a Power Supply at an increased temperature and increased voltage to demonstrate reliability. This technique is often used to identify any sub-standard power supplies immediately after manufacturing and before shipping to customers. Burn-in is used by Elpac for life testing to demonstrate Mean Time Between Failures (see MTBF). Elpac’s life testing burn-in consists of running actual production units at higher than normal temperatures (for example 40C instead of room temperature) while stressing the units with severe on/off cycling at the rated full load. Many Elpac Power Supplies series are life tested to 100,000 hours or more without any failures. In addition to the life testing burn-in Elpac further ensures reliability to our customers by performing a two hour final test burn-in at full load on 100% of all Power Supplies sold.
Bus:
A system of conductors that deliver power to the power supply load. Bus can also refer to the communications field, when a bus is used to control a sub-system, for example an IEEE-488 bus. A Bus (sometimes spelled buss) is system of conductors that are designed for the distribution of electrical power. A bus may consist of a series of usually heavy traces that are on a printed circuit board (PCB) and are used to distribute power to all the components on the PCB. A bus may also consist of an array of wires for the purpose of carrying voltage and current from a power supply to the load. Bus can also refer to the communications field, when a bus is used to control a sub-system, for example an IEEE-488 bus.
Centering:
Design limitations or differences in manufacturing can result in centering, or a disparity in voltage output.
Class 2:
This is a UL definition for an output which is below 60Vdc (42.4Vpk) and 8A. Virtually all Elpac power supplies are designed to be class 2. Class 2 is a UL1310 classification that calls out the requirements for indoor or outdoor, low voltage power supplies and battery chargers. Output power levels called out for Class 2 power supplies are in accordance with the National Electrical Code and require that the maximum output voltage does not exceed 60Vdc for continuous direct current and 42.4Vpeak for alternating current and that the output power does not exceed 100VA. Class 2 power supplies are designed primarily to provide low voltage power to electrically operated devices such as computer and other similar equipment.
Class II
This is a European definition for a 2 pin input WITHOUT Ground present. To comply, a power supply design would include reinforced insulation as it could not rely on Ground for safety. Examples of Elpac power supplies that are Class II compliant are the WM1005 and W4012. A classification for power supplies and other electrical equipment that requires an additional layer of reinforced insulation in addition to the basic layer as for Class I. Another requirement of Class II is that power supplies do not rely on earth ground for protection against shock hazards, as Class I does, but only on the insulation itself. As a result a Class II power supply will have only a 2 pin plug on the input power cord since the ground connection pin is not required. Class II power supplies are also often referred to as “double insulated” products. Examples of Elpac power supplies that are compliant with Class II requirements include the WM1005 and W4012.
Class I
This is a 3 pin input type - tied to earth ground. Output may or may not be tied to earth ground. A classification for power supplies and other electrical equipment that calls for the use of a basic insulation system combined with grounding to earth for protection against shock hazard. Class I power supplies will have a 3 pin input plug on the power cord that includes the pin for the ground connection. Output of the Class I power supply may or may not be tied to ground.
Common-Mode Noise:
When you have an electrically fixed point, such as chassis ground, there is a commonality in noise between the output and return lines. This is referred to as common-mode noise. Also called asymmetric mode noise or CM. Common-Mode Noise is electrical interference that occurs between a fixed point, such as the chassis of a power supply or earth ground, and all output lines (hot and common) in a power supply. The electrical interference occurs simultaneously in the output lines in respect to the fixed point.
Constant Current:
A power supply that can control current, despite different conditions, resulting in a consistent level of current. A Constant Current Power Supply will regulate the output current to a specified value in spite changes that might occur to the line input voltage, the load resistance, ambient temperature or over time. A Constant Current Power Supply should be used whenever there is the need to deliver a steady and consistent level of current to a load even though there might be fluctuations in the load resistance.
Constant Current Limiting Circuit:
If an overload occurs, a constant current limiting circuit will provide protection by restraining that current to a certain value. A type of overload protection for power supplies. If an overload occurs a constant current limiting circuit will provide protection by restraining that current to a safe value. A constant current limiting circuit uses a type of diode called a constant current diode (also called a current-regulating diode) that is designed to allow current to pass through it until a designated maximum level is reached. When the maximum level is reached the diode will then react by cutting off the current flow until the current level drops below the maximum.
Constant Voltage:
A type of power supply that functions by maintaining voltage, despite variations in load resistance. A Constant Voltage Power Supply functions while regulating the output voltage to a specified value in spite of changes that might occur to the line input voltage, the load resistance, ambient temperature or over time. A Constant Voltage Power Supply should be used whenever there is a requirement that a steady and consistent voltage level be delivered to a load even though there might be fluctuations in the load resistance.
Convection:
When unequal temperatures affect a current, thermal energy is transferred. This commonly refers to convection in a gas or liquid.
Converter:
(1) A type of device that produces DC power when energized by another DC source. (2) Can also refer to a part of a switching power supply that converts power and produces final rectification.
Cooling:
When a power supply is heated through regulation, rectification or transformation, it is necessary to cool the device. Common cooling agents include liquids, convection or forced air.
Core:
A core, in the field of electronics, is a device used in the construction of an inductor that can enhance its amount of inductance that will be produced.
Cross regulation:
When a power supply has more than one output, changes in the load for one output cause changes in voltage for the other outputs. To determine cross regulation, you divide the voltage change by its nominal value.
Crowbar:
In order to provide overvoltage protection, a Silicone Controlled Rectifier (SCR) is placed over the output terminals in a power supply. This type of protection is referred to as a "crowbar." A crowbar is a circuit that is designed into a power supply to provide a means of over-voltage protection to equipment that might be connected to the power supply. The crowbar circuit usually consists of a Silicone Controller Rectifier (SCR) and a zener diode as well as other components and is designed into in the power supply’s circuitry between the voltage output terminals and ground. The crowbar will be automatically triggered in the case of a power supply malfunction that causes the output voltage to exceed the rated value to where there may be a risk of damage to equipment that is connected to the power supply. When triggered the crowbar prevents this damage by shorting the output voltage to ground thus protecting the user’s equipment.
CSA (Canadian Standards Association)
The CSA is an independent organization which performs public safety testing. This organization is similar in nature to the Underwriters? Laboratories in the United States.
Current Limiting Circuit:
There are three types of current limiting circuits: constant, foldback and cycle-by-cycle. These circuits prevent a constant-voltage power supply from overloading. There are essentially three types of current limiting circuits that are used in power supplies to control output current and protect against overload conditions. The three types are: constant, foldback and cycle-by-cycle. These circuits prevent a constant-voltage type of power supply from overloading due to excessive current demand. See Constant Current Limiting Circuits, Cycle-by-Cycle Current Limiting Circuits and Foldback Current Limiting Circuits.
Cycle-by-Cycle Current Limiting Circuit:
This type of current limiting circuit functions by reducing the current output to a set minimum level to avoid an overload. A type of over-current protection for power supplies. A cycle by cycle current limiting circuit consists of special current sensing components that, when an overload condition is detected, will force the output switch low thereby reducing current to a safe level.
Derating:
When an operating parameter is reduced in order to compensate for changes in other parameters, the process is referred to as derating. In the case of a power supply, derating may be achieved by reducing the power level when temperatures become elevated.
Differential-mode Noise:
Separate from common-mode noise, this type of noise is calculated in output return. Differential mode currents flow in opposite directions and are out of phase with each other. Also called symmetric-mode noise, normal-mode noise or DM. Differential–mode noise is an electrical interference that occurs between the conductor paths in one output line in respect to the other output line. Differential-mode currents flow in opposite directions from each other and are out of phase with each other.
Dynamic Load:
This is a type of load that can quickly change levels. In order to state this type of load, you must calculate the total change and the rate of change.
Efficiency:
Efficiency can be measured in several different conditions, such as full-load or nominal line. If you are using a multiple output switching power supply, you would calculate efficiency based on the total power output and the division of the separate outputs.
EMI (electromagnetic interference):
When switching transistors operate, they can produce a high-frequency energy referred to as EMI. Other causes of EMI include output rectifiers and zener diodes. This can also be called RFI or radio-frequency interference. EMI has the ability to be conducted both in input and output lines, as well as being radiated through space. Electromagnetic Interference (also called RFI (Radio Frequency Interference)) is an unwanted electromagnetic energy that usually occurs in the frequency range that are used for communications, 10 KHz to 2 GHz. EMI can actually be produced by power supplies because when components such as switching transistors, output rectifiers or zener diodes operate they can produce the high frequency energy that can then be emitted from power supplies either by conduction or by radiation. EMI is undesireable because it can disrupt the operation of communication, electrical and electronic equipment. So for this reason the FCC and other regulatory agencies strictly control the amount of EMI that can be emitted by electronic and electrical equipment. Elpac’s power supplies are designed to comply with and have been approved to meet either FCC Class B, CISPR 22 Class B or CISPR 11 Class B as required.
ESR (equivalent series resistor):
ESR refers to the amount of resistance in series with an ideal capacitor. If the ESR level is low, the capacitor will operate more effectively. ESR is used to determine the cause of a ripple in switching power supplies. ESR or Equivalent Series Resistance is one of the more important parameters when specifying capacitors. The ESR measurement gives an indication of how a capacitor will perform in its application as well as an indication of life and reliability. ESR is actually a measure of the power loss in a capacitor and is expressed in ohms at a given frequency. This measure includes all of the series and parallel losses so that the capacitor equivalent circuit will appear as a simple RC circuit with a capacitor and a resistor in series. ESR is usually specified at 100KHz, however for circuit analysis it is always better to perform measurements at the actual operating frequency that will be used whenever practical. All else being equal, a capacitor with a lower ESR measurement is usually preferable and will most likely operate more efficiently in the circuit and have a longer life. A low ESR is a prime consideration in selecting filter capacitors for use in switching power supplies to provide for the optimum suppression of noise and ripple.
External Power Supply:
A device that is designed to supply the DC power that is needed to operate
electrical equipment and is located outside of the equipment which it
powers. An external power supply is typically housed in a fully enclosed
plastic case. It has an input power plug that connects to the AC wall
socket (providing for example 110-120Vac) and an output cable that plugs
into the electrical equipment to deliver the DC power. The location outside
of the unit being powered differentiates an external power supply from an
open frame power supply (which is designed to be actually hard-wired to and
used inside of the electrical equipment it powers).
Faraday Shield:
In order to reduce common or differential noise in a power supply?s output, a faraday shield is applied to reduce intertwining capacitance.
Federal Communications Commission (FCC):
A government agency in the United States. The FCC?s recent limitations on EMI have greatly affected digital electronic systems and power supplies in design and production.
Ferrite:
A ferrite is a specific type of inductor that uses a core that is made of a certain type of ferromagnetic compound. A ferrite is a specific type of inductor that uses a core that is made of a certain type of ferromagnetic compound. The ferromagnetic compound is a non-metallic and ceramic like material that is typically comprised of ferric oxide along with other oxides. One principal advantage of a Ferrite core inductor is that it has extremely high electrical resistance. This low conductivity characteristic allows the ferrite inductor it to have low losses especially at the higher frequencies up into the radio range.
Ferroresonance:
This term refers to a principle that is used in open-loop (non-feedback) power supplies that are intended to stabilize voltage.
Filter:
A filter is a frequency sensitive network that functions by removing unwanted noise and/or ripple components in rectified outputs.
Floating Ground:
A circuit whose electrical common point in not tied to earth ground. The common point potential can be different than that of earth ground.
Flyback Converter:
When you have a power supply that uses a single transistor as well as a flyback diode, this is referred to as a flyback converter. One of the more basic switching power supply configurations. It may consist of a switch comprised of one or two switching transistors, a Flyback diode and a magnetic element (transformer). The transformer is usually constructed so that it combines the function of the transformer and the choke making it very efficient and economical. The operation of the Flyback Converter is as follows. During the first half of the switching cylce when the switching transistor is on, energy is stored in the primary of the transformer. Then, during the second half of the switching cycle when the switching transistor is off, the energy is transferred to the secondary of the transformer and to the load in what is called the Flyback period. The Flyback converter is generally used for low power (under 200 Watt) AC to DC switching power supplies.
Foldback Current Limiting Circuit:
A current limiting circuit that functions by reducing output currents during overload conditions. This type of circuit will continue to operate under a direct short circuit until a set minimum current level is attained. A type of over current protection for power supplies. A Foldback Current Limiting Circuit functions by reducing output currents during overload conditions. This type of circuit will continue to operate under a direct short circuit until a set minimum current level is attained. The Foldback Current Limiting Circuit controls the current by decreasing both the output current and the output voltage at the same time. This results is much lower power dissipation for the internal components of the power supply.
Forward Converter:
A type of power supply that is configured using a single transistor.
Frequency Changer:
This is a type of equipment that can convert AC electrical power to different frequencies without changing any other characteristics.
Full-Bridge Converter:
This type of power supply uses four transistors to control high power levels.
Full-Wave Rectifier:
A diode network that transforms an AC source into a full-wave DC source.
Ground Loop:
Some power supplies have difficulties with feedback, usually as a result of two or more circuits on a common electrical line, which is also a common ground line. In order to rectify this situation, single-point grounding is recommended.
Grounding:
Establishing a zero voltage connection between electrical equipment and the earth. Usually accomplished with a grounding rod or by connecting the device to a conductive water pipe.
Grounding Pin:
An all-metal rod that is utilized in a ground loop.
Half-Bridge Converters:
This type of power supply uses two transistors. Commonly used for medium-power equipment or applications.
Half-Wave Rectifier:
This is a single diode rectifier circuit that will only rectify half of an AC wave?s input.
Head Room:
Head room is calculated by figuring the difference between a secondary voltage, which is normally supplied by a power transformer or nominal input voltage and the voltage of a regulated output. In order to have proper regulation in both full-load and low output voltage operations, it is essential to have head room.
Heat Sink:
A device that conducts and disperses heat commonly produced by electronic equipment and components.
Hi-Pot (High Potential Voltage):
A specification that is necessary for safety. Hi-Pot is the ability of a power supply to effectively handle high voltage potential that comes from either input terminals to ground, output terminals to ground or between the interaction of input and output terminals. This specification can vary on the individual power supply. Hi-Pot Testing, also called Dielectric Withstand Voltage Testing, is a safety test designed to check a power supply’s insulation system and verify it’s ability to protect against electrical shock even when tested with a much higher than normal voltage. The nature of the Hi-Pot testing being performed depends on the Standards of the particular Safety Agency doing the testing and will generally include a Primary to Ground Test, a Primary to Secondary Test and a Secondary to Ground Test. The High-Pot Test voltages that are used depend also on the Standards of the Safety Agency and additionally on the specific power supply’s rated AC input voltage, the insulation system being used and the general layout construction used. The actual testing voltages used are generally 1000Vac-1500Vac for the Primary to Ground Test, 3000Vac to 4000Vac for the Primary to Secondary Test and 500Vdc for the Secondary to Chassis Test.
Holdup Time:
Holdup time is the total amount of time that output will remain at a regulation band following an input voltage line being turned off. This is measured both at full load and under nominal line conditions.
Hybrid Supplies:
This type of power supply combines several regulation techniques, including linear, ferroresistant or liner and switching.
Hybrid Thermal Design:
This type of power supply uses two methods of cooling, such as convection and forced air.
Inductor:
An inductor is a passive electrical component that is designed to have a specific value of inductance. An inductor is a passive electrical component that is designed to have a specific value of inductance. Inductance is an electrical characteristic that opposes changes in current flow so that any change in the flow of current passing through an inductor will produce a counter force that blocks or slows the flow of current through it. This principle also causes inductors to created or “induce’’ an electro-magnetic field. Inductors in electrical circuits use this principal to store energy or block or impede the current flow. Inductors physically consist of a certain number of turns of wire in a coil that are proportional to the amount of inductance that is desired. Other factors that determine the value of inductance are the size of the coil and the type of material, called the core, that the coil is wound on. Inductors are important in the design of electronic equipment such as power supplies for functions such as voltage transformation, filtering and energy storage. Among the types of electrical components that use the property of inductance are chokes, coils, toroids, relays, transformers and motors.
Inhibit:
This refers to the ability to turn off the output of a power supply from another location.
Input Voltage Range:
The specification for power supplies under different ranges of line voltage.
Inrush Current:
A surge of current which occurs during the turn on phase of a power supply as the bulk capacitors are charged.
Interaction:
When line and load changes occur at the same time, interaction refers to the total static regulation in a power supply.
International Commission on Rules for the Approval of Electrical Equipment (CEE):
A European safety agency that is mainly regional. The United States participates in the CEE in the observer capacity only.
International Electrotechnical Commission (IEC):
A safety agency located in Geneva, Switzerland.
Inverter:
(1) A section referred to as a ?chopper section? in a switching power supply. (2) A kind of device that will deliver AC power when provided with DC power. Types of inverters include frequency, amplitude or pulse-width. These inverters are modulated in order to vary voltage output.
Isolation:
To maximize a power supply?s effectiveness, proper input-to-output isolation is essential. This is calculated by discerning the degree of the electrical separation between two points, either by voltage (breakdown) and current (galvanic) or by resistance and/or capacitance.
Leakage Current:
Leakage current occurs when there are flaws in certain electrical components,
or in the design of the components themselves. The result is current that
flows between the current ground and output buses. It is essential to
control leakage current to maintain compliance with UL and VDE safety
regulations. Leakage current (or Touch Current) may be present in electrical equipment as result of unintentional current flow from capacitors to ground, inadequate spacings between circuit board traces or improperly designed or applied insulation among other reasons. If a person were to touch electrical equipment that has an unsafe amount of leakage current while also touching earth ground a hazardous potential for a dangerous electrical shock would exist. This is especially important for electrical equipment that is being used in a hospital environment around patients where even the mildest shock may cause dangerous complications to a patient already in a weakened state. To prevent these hazards leakage current must be controlled and held to the absolute minimum as prescribed in the EN60601-1and UL2601-1 Safety Standards for Medical Equipment and in the EN60905 Safety Standards for Commercial Equipment. Elpac Power Supplies are designed and safety tested to the appropriate Safety Agency Standards to eliminate any hazard from Leakage Current.
Line-Frequency Regulation:
When a change in line input frequency occurs, but all other factors remain the same, a change in output voltage is referred to as a line-frequency regulation. For users of linear or switching power supplies, this type of problem is infrequent, but should be of concern for users of ferroresistant power supplies.
Line Regulation:
Line regulation occurs as the result of output voltage variance caused by input voltage variance. This is defined by the maximum amount of percentage change in output voltage as input voltage varies in a specified range.
Line Regulator:
A type of power-conversion equipment that manipulates filters, noise, the degree of regulation or voltage changes that result from incoming AC power.
Linear Regulator:
This is a technique used to stabilize voltage. Usually accomplished with a transistor that is placed either in series or parallel to the power source in order to regulate voltage across a load. Since the voltage drop in the device is not constant, this type of technique is referred to as ?linear.?
Load:
Defined as the output current in voltage regulated power supplies.
Load Regulation:
A change of output voltage that occurs as the result of a change in an output?s load (usually from no-load to a full load). This is expressed by a percentage of nominal DC output voltage.
Logic Enable:
Logic enable refers to the ability to use a Transistor-Transistor Logic (TTL) signal to turn a power supply off or on. Low logic will turn a supply on, while high logic turns a power supply off. Refer also to Logic Inhibit.
Logic High:
Can be referred to as Logic 1. Logic High is voltage that is more than 2.3 V, but no higher than 5.5 V.
Logic Inhibit:
When a TTL signal can be used to turn a power supply either off or on. See also Logic Enable.
Logic Low:
Voltage that is less than 0.8 V. Also referred to as Logic 0.
Magnetics:
Magnetics is the branch of science that studies magnets and their attraction for iron as well as electromagnetism and its association with magnetic fields. In general, magnetics is the branch of science that studies magnets and their attraction for iron as well as electromagnetism and its association with magnetic fields. In the field of electronics and specifically in the area concerning power supply design and manufacture, magnetics refers to the components used in power supplies that perform their function using the property of inductance. The theory, design and manufacture of transformers used in AC to DC transformation, chokes and toroids used for filtering circuitry, and coils used for energy storage all fall under the category of magnetics. Typically there are three components used in power supplies which fall under the general category of magnetics – the input inductor, the transformer, and the output inductor.
Margining:
Usually used in system testing techniques. Margining is the ability to adjust output manually, commonly by a switch. In most cases, margining can adjust the output to within +/- 5% of nominal.
Master:
A unit that can control outputs of at least one slave unit. This allows proper load sharing with parallel power supplies.
Modular:
A power supply that consists of numerous subsections, for example, an input module, filter module or power module. This type of power supply generally results in a lowering of MTTR.
MTBF (mean time between failures):
A type of standard used to calculate reliability, using the procedures set down by MIL-HDBK 217. The MTBF standard is used to provide our customers with an indication of the reliability and long life that they can expect from Elpac Power Supplies. MTBF testing is conducted per procedures set down by Military Specification MIL-HDBK 217. There are some power supply manufacturers that may use a “calculated” MTBF standard that is based on calculations and assumptions which may result in an MTBF that does not accurately show the true reliability of their product. Elpac, however, is different. Elpac uses actual production Power Supplies to “demonstrate” the MTBF. These actual production Power Supplies are subjected to high temperatures (e.g. 40C) and severe on/off cycle stressing thus clearly demonstrating the true reliability you can expect from an Elpac Power Supply. Many Elpac Power Supply series have demonstrated an MTBF of 100,000 hours or more without a single failure.
MTTR (mean time to repair):
The amount of time that is required to repair a power supply. This time can be influenced by numerous factors, such as electrical problems or actual design of the supply.
Multiple Output Supply:
When a power supply has two or more different output voltages, it is referred
to as a multiple output supply.
Noise:
A component, normally random, of deviations in output voltage. Noise is undesirable, and normally will be specified in conjunction with ripples. See also PARD and Ripple. Electrical noise, also called electrical interference, periodic and random deviation (PARD) or ripple is a normally random component of deviations in the output voltage of a power supply. It is an unwanted electrical or electromagnetic energy that can interfere with and in some cases cause damage to communication and other electrical and electronic equipment. Noise may be generated by natural events such as lightening or it can be produced, as in the case of switching power supplies, when components such as switching transistors are operating. In the case of Elpac Power Supplies, noise is suppressed through effective filtering and shielding to a level mandated by the FCC and other regulatory agencies so that the adverse effects of noise are eliminated. Noise is usually shown as Ripple/noise (Vp-p) on specification sheets and is specified as a percentage of the output voltage and measured at a 20MHz bandwidth.
Nominal Output Voltage:
The model voltage of an output.
Off-Line Switcher:
This type of configuration of circuits is usually found in PWM (Pulse-Width
Modualtion) switches. In this type of circuit, the input rectifier and
filter sections will sit directly across an AC input line.
Open Frame Power Supply (Open-Frame Construction):
A power supply that does not have an enclosure. Commonly seen with OEM power supply manufacturing techniques. An open-frame construction may consist of a circuit board that is mounted on a chassis that does not have a cover or a stand-alone printed circuit board.
Operating Temperature:
A specified limit wherein a power supply can perform at optimal levels.
Opto-Isolator:
An opto-isolator consists of a light emitting diode that is located next to or close by a phototransistor. Commonly used within a feedback loop in order for a power supply to achieve electrical isolation between input and output. An opto-isolator functions by using a signal path from an electrical to optical to electrical signal transformation.
Output Impedance:
The value of an ideal voltage source in conjunction with a fictional resistor that would supply the same amount of AC voltage across a power supply?s terminal that the magnitude and frequency of alternating current would supply.
Overshoot:
This is the amount that an output exceeds its final value as the result of a sudden change in input voltage or load. This amount is usually measured as a percent of nominal and is essential during turn-on or after a step change occurs in line or load voltage.
OVP (overvoltage protection):
A type of mechanism that protects load circuitry by preventing output voltage from exceeding its current, preset level. Whenever output voltage is lessened, input power is recycled to maintain the output of a power supply.
Parallel Operation:
When two or more power supplies are connected, it is referred to as parallel operation. This allows supplies to combine current into a single load.
PARD:
PARD stands for ?periodic and random deviation.? Used as a term for noise and ripples. Noise is unwanted output deviation and a ripple is an undesired portion of an output that is harmonically related in frequency to internal frequencies of switching or the frequency of an input line.
Pass Element:
Commonly refers to a transistor that comprises an active circuit element which forms an output power stage of a linear power supply.
Peak Changing:
When a capacitor charges to a peak instead of the Root-Mean-Squared (RMS) value of input voltage, voltage across the capacitor rises, resulting in peak changing. This can affect minimum load in switchers on each output that is necessary to continue regulation. This will normally take place if a capacitor has a high discharge resistance across, and noise or spike on an input line.
Peak Transient Output Current:
During transient loading conditions, peak transient output current refers to the utmost amount of peak current that can be delivered to a load.
Phase-Controlled Modulation:
A type of circuit that is commonly employed in switching regulators. It
is used when an operating frequency is kept at a constant level, usually
60-Hz. It can control line and load changes simultaneously without causing
much dissipation.
Pin Fins:
A heat sink that has pins instead of the widely used extruded fins.
Postregulator:
A type of linear regulator that is employed on an output for a switching or ferro power supply. A post regulator can be used to improve load regulation.
Power Conversion:
A type of processing for medium-quality electrical power that is delivered by utilities. This conversion makes this power acceptable for electronic circuits that are sensitive.
Power Factor:
A ratio of actual power to apparent power in a circuit. Also defined as
the measure of a fraction of current that is in phase with voltage and
contributes to average power. Power Factor is defined as the ratio of actual power to apparent power in a circuit. Ideally, we want the input current waveforms and input voltage waveforms to match and be in phase. When this happens we get Power Factor of 1 (1:1 Ratio) which is the maximum in efficient power handling. Power Factor is important in switching power supply discussions because, unlike traditional electrical devices (those with resistive loads such as light bulbs, heaters etc.) which are driven by a smooth sine wave, switching power supplies draw input current in high peaked pulses that are out of phase with the input voltage waveform. This mismatch of waveforms will cause inefficient power handling resulting in higher operating costs and may also inflict harmful stress to the electrical wires and network.
Power Factor Correction (PFC)
A method of increasing the power factor of a power supply. Typically referring
to a European requirement. Needed when input power is above 70 watts -
normally 60 watts of output will pass without special circuitry. Elpac
power supplies with FWP or MWP in the series name have PFC circuitry included. Switching Power Supplies by their nature are susceptible to having low Power Factors (sometimes in the 0.5 to 0.6 range). Because this low Power Factor can cause inefficient and costly power handling a method may be desired that will increase the Power Factor of a switching power supply. This method is referred to as Power Factor Correction (PFC). PFC adds components to the input circuitry of a power supply which work to raise the Power Factor by bringing the input current closer into phase with the input voltage. As a result the Power Factor may be increased to as high as 0.99% which will remedy most of the negatives aspects of having a low Power Factor. At this time PFC is required for power supplies that are sold in Europe that have an input power that is greater than 70 Watts. (Normally 60 Watts of output will pass with out the PFC circuitry). Elpac FWP and MWP Power Supply Series have the PFC circuitry included.
Power-Fail Detect:
A type of circuit that can tell when DC voltage crosses input capacitors in a switching power supply. It can also tell when the AC input line does not provide power. A power-fail detect circuit sends an isolated TTL output signal warning that loss of output power is forthcoming.
Power Supply:
A term that refers to a device that is powered by an AC source, but produces DC output voltages.
Preregulator:
A type of regulator circuit that operates by providing a line-regulated output, which in turn is processed by another regulator, called the postregulator, which then provides load regulation.
Programming:
The ability to control voltage on each output of a power supply.
Pulse-Width Modulation (PWM):
A type of circuit that is used in switching regulated power supplies.
This type of circuit holds the frequency constant while the width of power
pulse is varied, and controls both line and load changes without major
dissipation.
Push-Pull Converter:
This type of converter is used in a switching power supply when the central switching circuit utilizes two transistors that operate in a push-pull. This type of converter is very simple in design.
Quasi-Regulated Power Supply:
A Quasi-Regulated Power Supply is sometimes also referred to as a Non-Regulated Power Supply. A Quasi-Regulated Power Supply is sometimes also referred to as a Non-Regulated Power Supply. However, the term Quasi-Regulated indicates that there is a form of regulation occurring. A true regulated power supply senses and compensates for variations in input voltage and load so that the output is very stable and constant. A Quasi-Regulated power supply offers a type of input voltage regulation by means of an input voltage option, typically 105/115/125 VAC. The input voltage option allows the user to connect the AC line voltage to the most appropriate input terminal on power supply when serves to reduce variations. The input voltage option allows the Quasi-Regulated Power Supply to deliver a fairly regulated voltage to the load since the actual value of input voltage is being is identified to the power supply. Quasi-Regulated Power Supplies, however, are not able to keep the output voltage as stable and constant as true regulated power supplies can when variations in output current demand occur. Elpac manufactures several Quasi-Regulated Power Supplies including the BSF Series. BSF Series Power Supplies are available in several configurations ranging from 15Watt to 500 Watt and in 12V, 20V, 24V or 48V.
Rated Pulse Power:
When a power supply operates on a pulse basis, this is the maximum amount of power that the power supply can deliver. This amount of rated pulse power is usually averaged out to the maximum continuous output power.
Recovery Time:
The amount of time that is necessary for a transient undershoot or overshoot in a stabilized output quantity to decay, usually within a precise limit.
Redundancy:
By connecting more than one power supply, or using parallel power supplies, a redundancy is created. This means that should one power supply fail, the others can continue to provide power to the load. Redundancy is commonly employed when power supply failure is not an option.
Reference:
A known amount of stable voltage that is used to compare output voltage in order to stabilize the amount of voltage in a power supply.
Regulator:
A component of a power supply that controls output voltage. Also acts as a stabilizer to maintain output voltage at a present level.
Remote Sensing:
This type of sensing can compensate for drops in IR in a power distribution bus. It is a way of moving the point of regulation between an output terminal to a load.
Response Time:
The reaction time for an output to react to a dynamic load change. Response time also includes the time that it takes for the load to settle within the tolerance band after a load change.
Return:
The often used term that refers to the common terminal for all of the
outputs on a power supply. It also carries the return current for all
of the outputs on the device.
Reverse Voltage Protection:
A power supply?s capacity to withstand reverse voltage in output terminals when it is hooked up in reverse polarity.
Ripple:
A power supply output voltage AC noise component that is periodic.
Second Breakdown:
When transistors are turned off, a coincidence of high voltage and current
levels occurs, causing failure in a switcher?s power transistors. Unfortunately,
this is irreversible, and can happen suddenly. It is always fatal to the
power supply. However, circuits that are properly designed can control
this type of breakdown.
Semiregulated Output:
A multiple outlet power supply has secondary outputs that are referred to as semiregulated outputs. These outputs simply receive line regulation.
Sequencing:
Sequencing controls the order and time delay for output voltage appearance as well as dropout when power supplies are turned on and/or off.
Series Regulator:
A type of linear regulator where a transistor or active control element is in series with a load.
Schottky Diode:
This is a type of diode that features a fast recovery time and a low forward voltage drop (0.6V). If a diode is needed for a high current, low voltage supply (5v DC) and when low losses and high speed are important, a schottky diode can be used with great success.
Shunt Regulator:
A type of linear power supply where a transistor or active control element is used in parallel with a load.
Slave:
A secondary unit that is controlled by a master, typically used in master-slave paralleling configuration schemes.
Snubber:
A network comprised of a capacitor, resistor and diode that is used in switching power supplies. This network works by trapping high-energy transients as well as for the protection of sensitive components.
Soft Start:
A type of input surge-current limiting that is used in a switching power supply, where the supply drive is gradually ramped on.
Stability:
Refers to the ability of a power supply's control circuit to maintain control and produce a constant output voltage as load and environmental conditions fluctuate.
Standby Current:
The amount of input current that is drawn in by a power supply during minimum load conditions.
Static Load:
A type of load that does not change over a specified amount of time. This can also be referred to as a percentage of a full load.
Stefan-Boltzmann Law:
A thermodynamics law that illustrates emission rates of radian energy from the surface of a body.
Step Change:
A sudden change that is sustained, occurring in either the influence or control quantities.
Stess-Aging:
A process that forces burn-in failures by exposing a power supply to several different stressors.
Switching Frequency:
When source voltage is switched, either in a switching regulator of by chopping in a DC-to-DC convertor, switching frequency refers to the rate at which this occurs.
Switching Regulator:
A type of DC-to-DC converter that is comprised of inductors and capacitors that sort energy and switch elements, which then open or close, as needed to regulate the voltage across a load. This is normally controlled by a feedback loop in order to even out output voltage.
Temperature Coefficient:
The temperature coefficient is determined by the average percent of change in output voltage per temperature degree change while the input voltage and load levels remain the same.
Thermal Protection:
A type of device that provides protection through a thermally actuated switch that will stop the operation of a power supply once the temperature inside the supply reaches a specified level.
Thermistor:
A type of device that can be used to limit inrush current in certain types of power supplies, such as off-line switchers. They have a very high electrical resistance when they are cold, and practically no resistance when used at operating temperature.
Transformer:
A type of magnetic device that will convert AC voltages to AC voltages, no matter what the level is. An ideal transformer will require no magnetic current, and will be a lossless device where no energy is stored.
A Transformer is an electronic component that performs a function called transformation. Transformation is the changing of the value of the AC line voltage to a value that will allow a specified DC voltage to be produced. Transformation also provides a very important safety feature of isolating electronic equipment from the AC voltage coming in from the utility power pole. A transformer consists of two or more coils of wire that are wrapped around the same iron core. One of the coils of wire, which is connected to the AC input voltage is called the primary. The other coil of wire, which goes on to provide the output voltage is called the secondary. In some transformers there may be more than one secondary. The principle behind the transformers operation is a characteristic called induction. The property of induction causes the varying current of the AC input voltage that is being applied to the primary coil to produce a magnetic field. This magnetic field, also by the properties of induction, causes a current to be produced or “induced” in the coil of the secondary. The voltage produced in the secondary coil can be the same as that of the primary or it can be of a higher value (called stepping up) or a lower value (called stepping down) than the voltage in the primary. Whether the induced voltage in the secondary is stepped up or down depends on the ratio of the number of turns of wire in the primary as compared to the number in the secondary. Additionally, the very important safety feature of isolation is also being performed since the only connection between the primary and the secondary is by the magnetic fields. Since there is no actual connection that can transfer the high current from the utility power pole a dangerous shock hazard is reduced.
Transient:
A type of temporary change that occurs within a given parameter. This terms is commonly used in reference to output loading or input voltage parameters.
Transient Response Time:
After a stated change in load occurs, the amount of time that is required for an output to settle back to a tolerance band is referred to as transient response time.
UL (Underwriters? Laboratories):
A public safety testing company located in the United States that is an independent, not-for-profit agency. A UL recognition may be mandatory for equipment that is used in certain applications.
Undershoot:
Undershoot is the amount that an output falls under its final value after a sudden change in load.
UPS (Uninterruptible Power Supply):
A device that can operate either with a DC battery back-up or an AC input line. Commonly used to provide power for equipment during temporary or permanent loss of power.
VDE (Verband Deutscher Elektrotechniker):
A public safety testing company located in Germany. Similar in operation
to its United States counterpart, UL.
Warm-Up Drift:
Warm-up drift occurs during a normally 30 minute time period after a cold
power supply is turned on. This is calculated at constant load, ambient
temperature and AC line and occurs as a result of internal components
of a power supply reaching their thermal equilibrium.
Warm-Up Time:
The amount of time that the internal components of a power supply need to reach thermal equilibrium. This process normally takes 30 minutes.