Abnormal Failure: An artificially induced failure of a component, usually as a result of "abnormal" testing for regulatory agency safety compliance.

AC - Alternating Current: Used to indicate that voltage or current in a circuit that is alternating in polarity at a set frequency, most often 50 or 60 Hz.

Agency Approval: UL, CSA, and TUV are safety agencies that test specifications such as component spacing, HI-pot insulation, leakage currents, circuit board flammability, and temperature rating.

Ambient Temperature: The still air temperature in the immediate vicinity of a power supply, measured a minimum of 4 inches from the supply.

AMP - Ampere: An AMPERE or an AMP is a unit of measurement for electrical current or rate of flow of electrons (coulombs per second) through a wire. If a group of electrons whose total charge is 1 coulomb passes a point in a conductor in 1 second, the electric current is 1 ampere. Its mathematical symbol is "I". In an AC power system, current (AMPS) is delivered to a load through a wire called the "hot" wire and returns through a wire called the "neutral" wire.

ANSI - American National Standards Institute: An industry body that publishes standards, such as standards developed by the IEEE.

Applied Patient Current: Any diagnostic or therapeutic current intended to be administered to a patient. This includes currents applied for measurement purposes.

Bandwidth: A range of frequencies over which a certain phenomenon is to be considered.

Basic Insulation: The insulation applied to live parts to provide basic protection against electric shock. Does not necessarily include insulation used exclusively for functional purposes.

Battery Backup: A power supply system where if the ac line fails, a battery will provide input energy to keep the dc outputs from failing.

Blackout: A total loss of electrical power.

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

Brown out: A planned voltage reduction by a utility company to counter excessive demand on their generation and distribution system.

Burn-in: 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.

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

CE: The CE-marking is a European Union regulatory community sign. It symbolizes the compliance of the product with all essential requirements relating to safety, public health, consumer protection.

CISPR 22: This is a European Community standard specifying the limits of radio frequency emissions which appliances and other electrical equipment are allowed.

Common Mode Noise: The component of noise which is common to both the DC output and return lines with reference to input neutral.

Constant Current Power Supply: A power supply that regulates its output current for changes in line, load, ambient temperature, and time.

Constant Voltage Power Supply: A power supply that regulates its output voltage for changes in line, load, ambient temperature, and time.

Control Section: In a closed-loop system, the circuitry which maintains the control loop is referred to as the control section by incorporating an error amplifier in the feedback of the system.

Converter: 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: In an AC circuit, Crest Factor is the mathematical ratio of the peak to RMS values of a waveform. Crest factor is sometimes used for describing the current stress in AC mains supply wires, since for a given amount of power transferred, the RMS value, and hence the losses, become greater with increasing peak values. Crest Factor gives essentially the same information as Power Factor, and is being replaced by Power Factor in power supply technology.

Cross Regulation: The effect of a load change to one output upon the other outputs in a system.

Crowbar: A method of overvoltage protection which shorts the output to ground in the event an excessive voltage is detected.

CSA - Canadian Standards Organization: This is a Canadian government organization that evaluates the safety of electrical equipment.

Current Limiting: The limiting of the output current to prevent damage to the power supply and the system in which it is used.

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

Current: The flow of electricity expressed in amperes. Current refers to the quantity or intensity of electricity flow, whereas voltage refers to the pressure or force causing the electrical flow.

DC - Direct Current: Electrical current which flows in one direction.

Derating: The specified reduction in an operating parameter to improve reliability. Generally for power supplies, it is the reduction in output power at elevated 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.

Dip: A short term voltage decrease.

DOC - Declaration of Conformity: The objective of D.O.C. from FCC: The FCC seeks to determine the standards, test procedures, and equipment authorization requirements that should be applied to computers as well as to CPU boards, power supplies, and enclosures used in personal computers in order: 1) to reduce regulatory burdens on computer manufacturers; 2) to remove impediments to flexible system design and construction techniques for computers; and, 3) to reduce the potential for interference to radio services by improving FCC’s ability to ensure that personal computers comply with FCC’s standards. CPU boards, power supplies, and enclosures designed for uses in computers are proposed to be included under FCC’s standards and equipment authorization requirements. These components, which were not previously subject to FCC’s rules, will be included under an equipment authorization procedure similar to FCC’s verification procedure with the addition of a Declaration of Conformity that would be included with each product marketed. In addition, FCC proposed to permit any party to assemble computers from authorized CPU boards, power supplies, and enclosures without further testing provided the instructions accompanying the components are followed during assembly. Computers assembled in this fashion would also be accompanied by a Declaration of Conformity. Alternatively, the computer may be assembled using unauthorized components provided the resulting system is tested and accompanied by a Declaration of Conformity. While the measurement data, where required, must be retained by the responsible party, there is no requirement to file an application with, and obtain authorization from, the Commission prior to marketing or importation. The rules permit manufacturers and suppliers of personal computers and personal computer peripherals to put a product on the market after testing it to ensure compliance and including a "Declaration of Conformity" ("DOC") in the literature furnished with the equipment without having to submit an application for equipment authorization and await FCC approval. Ref.: FCC 95-46 [10 FCC Rcd 8345 (1995) (ET Docket No. 95-19)

Double Insulation: Independent insulation applied to basic insulation in order to reduce the risk of electric shock in the event of a failure of the basic insulation.

Drift: 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.

Dropout: The lower limit of the AC input voltage where the power supply just begins to experience insufficient input to maintain regulation. The dropout voltage for linears is quite load dependent. For most switchers it is largely design dependent, and to a smaller degree load dependent.

Ease of Use PC: Ease of Use PC: this is an initiative proposed by the computer industry to produce personal computers that allow for the following: faster out-of-box setup, simpler operation for first time users, simpler upgradeability and increased reliability. These computers are meant to attract more first-time users with little or no computer experience.

Efficiency: The ratio of total output power to input power, expressed in percent. This is normally specified at full load and nominal input voltage.

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.

EMC - Electromagnetic Compatibility: The requirement for electromagnetic emissions and susceptibility dictated by the physical environment and regulatory governing bodies in whose jurisdiction a piece of equipment is operated.

EMI - Electromagnetic Interference: EMI usually refers to unwanted electrical noise present on a power line. This noise may "leak" from the power lines and affect equipment that isn't even connected to the power line. Such "leakage" is called a magnetic field. Magnetic fields are formed when unwanted noise voltages give rise to noise currents. Such noise signals may adversely affect electronic equipment and cause intermittent data problems. EMI protection is provided by placing noise filters on the AC power line. The filter reduces the noise voltage on the protected line, and by doing so also eliminates the magnetic fields of noise generated by the protected line. Noise signals that act over a significant distance are called RFI (Radio Frequency Interference). Equipment power cords and building wiring often act as antennas to receive RFI and convert it to EMI.

Electromagnetic interference (EMI) is the noise generated by the switching action of the power supply. Conducted EMI, that portion reflected back into the power line, is normally controlled with a line filter. Radiated EMI, that portion which is radiated into free space, is suppressed by enclosing the circuitry in a metal case. The FCC governs conducted and radiated emission levels.

ESR - Equivalent Series Resistance: The value of resistance in series with an ideal capacitor which duplicates the performance characteristics of a real capacitor.

Fan Rating: Airflow in cubic feet per minute. A 100% increase in airflow will reduce system operating temperatures by 50% relative to ambient. For each 10°C (18°F) reduction, the life of the system is doubled. (Arrhenius equation)

Fault Mode Input Circuit: The input current to a power supply with a short circuit on the output.

FCC - Federal Communications Commission: The US Federal Communications Commission specifies the maximum amounts of conducted noise signals (EMI) and radio frequency interference (RFI) that computer equipment is permitted to generate in Part 15 of the FCC Rules and Regulations. These limits are set in order to prevent computer equipment from interfering with the operation of radio and television receivers. Two different limits have been set, depending on the typical application and marketing of the computer equipment. The class "A" FCC limits are for equipment intended for use in commercial and industrial environments. The more stringent class "B" limits are for residential environments where TV and radio interference is more of a problem. Most personal computers are required to meet the class "B" limits since they are often sold for home use. Sale of such equipment requires that the manufacturer receive a FCC CERTIFICATION letter and registration number. Larger mini-computers and networking equipment are only required to meet class "A" because they are sold for commercial use. Compliance with the FCC class "A" limit need only is verified by the equipment manufacturer.

FCC Certified: A statement of compliance with US FCC class "B" limits for radio frequency emission, which is issued by the FCC and accompanied by a FCC "registration" or "ID" number. Certified equipment must be marked with the ID number. Personal computer equipment marketed to the residential user must be FCC certified.

FCC Verified: Equipment, which has been tested by either the manufacturer or an independent laboratory, found to be in compliance with the FCC class "A" limit for emission. Computer equipment that isn't required to be FCC CERTIFIED is required to be verified to the less stringent class "A" limit. Equipment, which may be verified, includes mini-computers, network file servers, and other network equipment.

Ferroresonant 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.

Filter: An electronic device that allows only certain frequencies to pass.

Firmware: A software program that is stored in semiconductor memory, such as read only memory (ROM) integrated circuits. Such programs are often embedded in hardware systems for control applications.

FlexATX: FlexATX: a new addendum to the microATX form factor. This new mainboard (7.5" x 9") form factor uses all of the same high performance of microATX, but allows for use in a much smaller space. It has no slots, no connectors and a highly integrated design. 'Flex' refers to flexible and this new form factor has the following goals in mind: leverage benefits of legacy removal, higher feature integration, more reliable and allows for more consumer look and feel consideration in smaller PC enclosure designs. This reduced chassis size improves the aesthetic value for the end-user and is intended to promote higher satisfaction with system ownership. For more info check out Intel's http://www.teleport.com/~ffsupprt/.

Foldback Current Limiting: A power supply output protection circuit whereby the output current and voltage decrease with increasing overload, reaching a minimum at short circuit.

Ground Loop: An unintentionally induced feedback loop caused by two or more circuits sharing a common electrical ground.

Ground: Electrical ground in an AC power system is a wire that is connected to the earth, hence the name "ground". The reason for such connection stems from the need to protect users of electrical equipment from shock hazards. Power is delivered to the utilization site using a pole mounted or other type of transformer. The output of such a transformer consists essentially of two lead wires, with the utilization voltage available between the leads. For a variety of complicated reasons involving safety, one of these transformer lead wires is connected to the earth using a copper bar driven into the ground. From this ground connection, two wires are taken to the power utilization point. One of these wires is called the "safety ground" or "green" wire and the other is called the "neutral" wire. The ungrounded lead from the transformer is also taken to the utilization point and is called the "hot" wire. These three wires together (hot, neutral, and safety ground) make up the connections found on a typical office power receptacle. The safety ground wire appears to be redundant since the neutral wire is derived from the same point. In fact the safety ground wire isn't needed as evidenced by the large number of electrical appliances which only use only two (hot and neutral) prongs. In electrical equipment which has a safety ground connection (as evidenced by a three prong plug), the safety ground is always connected to any exposed metal parts of the equipment. The purpose of this connection is to prevent any exposed part of the equipment to become energized with a hazardous voltage in case of a wiring fault inside the equipment. In computer equipment, computing circuits and mainboards are electrically connected to the chassis and therefore to the safety grounding wire.

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

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

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

Holdup Time: The time during which a power supply's output voltage remains within specification following the loss of input power. (Typically 16-20ms)

IEC - International Electro-Technical Commission: It’s an international organization that writes standards for safety for electrical and other equipment. Many IEC standards were adopted from the German VDE, which was the main historical standards-writing body in Europe. One goal of the IEC is to harmonize differing standards between European countries to facilitate free trade. The US Underwriters Laboratories (UL) and the Canadian CSA are members of the IEC.

IEC 601 (EN60601): The safety standard specified by the International Electro-Technical Commission, which cover electrical medical and dental equipment that is intended for professional use. Although this specification's primary focus is on safety, there are some requirements regarding reliable operation.

IEEE - Institute of Electrical & Electronic Engineers: A professional society and standards writing body for the US Electronics industry

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.

Inrush Current: The peak instantaneous input current drawn by a power supply at turn-on.

Inverter: A power supply which produces an AC output, usually from a DC input.

Isolation Transformer: A transformer in which one or more output windings is electrically separated from the input winding and all other output windings by an insulation at least equivalent to double insulation or reinforced insulation.

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

Isolation: 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.

Leakage Current: The AC or DC current flowing from input to output and/or chassis of an isolated power supply at a specified voltage.

Legacy Free: Legacy-Free: According to Intel, "legacy is defined as technology for which a feasible replacement exists." The specs of the ideal legacy-free PC's of the near future will have any combination of the following "pruned away" features to allow for room for better technological solutions: floppy drive, PS/2, ISA slots, PCI slots, Parallel and Serial Ports, standard height power supplies, etc.

Line Regulation: The change in output voltage due to variation of the input voltage with all other factors held constant. It is expressed as a percent of the nominal output voltage. A power supply with tight line regulation delivers optimum voltages throughout the operating range.

Load Regulation: The percent change in output voltage as the load is changed from minimum to maximum, at constant line and constant temperature.

Magnetic Amplifier: Sometimes abbreviated "Mag Amp," a saturating inductor which is placed in series with a power supply output for regulation purposes.

Margining: 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 measurement of the relative reliability of a power supply based upon actual operating data or calculated according to MIL-HDBK-217.

NEMA - National Electrical Manufacturers Association: This is an organization that sets standards in the United States for electrical equipment including circuit breaker boxes, wiring, and electrical connectors.

Noise: Acoustical noise in dB(A) at 1 meter. Logarithmic scale. Each 3dB reduction represents 50% less noise. Issues include the pitch and speed of the fan blades, the hub size, the venturing depth, the bearing quality, and the layout of the power supply components.

Off-line: 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.

Operating Range: The minimum and maximum input voltage limits within which a power supply will operate to specifications. A power supply with a wide input range is recommended when the line voltage is subject to brownouts and surges.

Operating Temperature: The range of ambient temperatures within which a power supply can be safely operated.

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

Output Current: The maximum current which can be continuously drawn from the output of a power supply. PC motherboards and expansion cards draw 5 volt current. Drive motors draw 12 volt current.

Output Good: A TTL signal which indicates that the output voltage is within its specified regulation levels. If the output goes out of regulation, the state of this signal changes.

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.

Output Power: The specified level of power of which a power supply is capable. Typically, power supplies have a continuous rating and a peak rating. These are usually a function of the ambient temperature. See "Derating."

Overcurrent Protection: A circuit that protects the power supply and computer from excessive current, including short-circuit current.

Overvoltage Protection: A power supply feature which shuts down the supply, or clamps the output, when its voltage exceeds a preset level.

Patient Connected Circuits: All patient connections, such as pads, contacts, probes, sensors or cuffs applied to the patient, plus any associated leads, cables, components or wiring, either within or external to the appliance enclosure. As seen from the patient into the equipment, these circuits extend to the points where the required degree of isolation or protective impedance is reached.

Patient Connections: (a) Isolated: Direct or indirect patient contact that is deliberately separated from the supply circuit and ground by spacing, insulation, protective impedance or a combination of these methods. (b) Ordinary: Direct patient contact that does not have the spacing, insulation or protective impedance associated with an isolated patient connection.

Patient Vicinity: Area in which patients are normally cared for. The patient vicinity is the space with surfaces likely to be contacted by a patient or an attendant who can touch the patient; encloses a space within the room 6 feet (1.83m) beyond the perimeter of the bed (examination table, dental chair treatment booth, etc.) in its intended location, and extending vertically 7.5 feet (2.29m) above the floor.

Peak Current: The maximum amount of current which an output is capable of sourcing for brief periods of time.

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.

PFC - Power Factor Correction: Technique of increasing the power factor of a power supply. Switching power supplies without power factor correction draw current in short, high-magnitude pulses. These pulses can be smoothed out by using active or passive techniques. This reduces the input RMS current and apparent input power, thereby increasing the power factor.

Post Regulation: A linear regulator used on the output of a switching power supply to improve line and load regulation and reduce output ripple voltage.

Power Factor: The ratio of true power to apparent power in an AC circuit. In power conversion technology, power factor is used in conjunction with describing the AC input current to the power supply.

Power Fail: A TTL signal which indicates that the input power has failed. This signal gives the user a chance to store information or switch over to backup power before the system goes down.

Power Good Signal: A delay circuit used to initialize the computer and provide a logic signal upon low line voltage.

Power Limiting: The limiting of the total output power of a power supply.

Power Supply: A source for the power needed for active electronic circuitry. Can consist of one or more batteries, or an electronic circuit which converts AC line voltage to the type of power required by a particular device.

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

Pulse Width Modulation: A method of voltage regulation used in switching supplies whereby the output is controlled by varying the width, but not the height, of a train of pulses which drive a power switch.

RAID - Redundant Array of Independent / Inexpensive Disks: It is a technology through which several physical storage disks are grouped into an array that appears to an operating system as one or more physical devices. RAID technology, when applied to storage disks, allows the RAID array drives to be configured into a variety of data configurations, which provide varying levels of data integrity protection and storage capacity.

Rated Output Current: The maximum load current that a power supply can provide at a specified ambient temperature.

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.

Regulation: The ability of a power supply to maintain an output voltage within a specified tolerance as referenced to changing conditions of input voltage and/or load.

Reinforced Insulation: An improved basic insulation with such mechanical and electrical properties that, in itself, the insulation provides the same degree of protection against electrical shock as double insulation. It may consist of one or more layers of insulation material.

Remote Sensing: A technique of regulating the output voltage of a power supply at the load by means of sensing leads which go from the load back to the regulator. This compensates for voltage drops in the load leads.

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.

RFI - Radio Frequency Interference: This is electrical noise which is present in communications or computing equipment that results from some parts of the equipment or attached wiring acting as a radio antenna. Under certain conditions the amplitude of this noise may be large enough to disrupt communications or cause computing errors.

Ripple: The magnitude of AC voltage appearing superimposed on the DC output, specified in peak to peak volts or expressed as a percent of the nominal output voltage. A power supply with clean DC output is essential for computers with high-speed processors and memory chips.

RMS - Root Mean Square: It is the square root of the average value of the squares of all the instantaneous values of current or voltage during one-half cycle of an alternating current. For a sine wave, the RMS value is approximately equal to 0.707 times the peak value of the waveform. RMS is also called the effective value.

Safety Circuit: Any circuit (either the primary or the secondary) that is relied upon to reduce risks of electrical shock or fire (an interlock circuit, for example).

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.

Secondary Circuits: Secondary circuits are those circuits supplied from transformer output windings that are electrically separated from the input windings.

Secondary: 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.

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

Short Circuit Protection: In the event that the output is shorted, this circuit will protect the power supply by limiting the amount of current flowing through the short circuit.

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

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

Switching Frequency: The rate at which the DC voltage is switched in a DC/DC converter or switching power supply.

Temperature Coefficient: The average output voltage change expressed as a percent per degree centigrade of ambient temperature change. This is usually specified for a predetermined temperature range.

Temperature Derating: The reduction in output power due to an increase in ambient temperature.

Temperature Range: Operating: The specified ambient temperature over which it is safe to operate the power supply. Storage: The specified ambient temperature in which the power supply can be stored without risk of damage.

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

Tracking: 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 standby or off-line type UPS to sense a power interruption and switch from utility output to inverter output. Normally expressed in milliseconds.

Transient Recovery Time: The time required for the output voltage of a power supply to settle within specified output accuracy limits following a step change in output load current or a step change in input voltage.

Transient Response: The time required for the output voltage to return within the regulation envelope following a 50% load change. A power supply with quick transient response will reduce the risk of read/write errors during access.

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.

TÜV: TÜV is a safety-testing laboratory with headquarters in Germany. TÜV can test products for compliance with IEC or VDE requirements. Products that have the TÜV insignia have been tested by TÜV for compliance with applicable standards for sale in the European market.

UL - Underwriters' Laboratories: This private organization was originally founded as a result of the need for insurance companies to help consumers choose safe electrical and safety equipment. UL evaluates equipment submitted to them by the equipment manufacturer using standards, which UL has written for the equipment category. Equipment, which is evaluated and found to meet the safety requirements, is either UL Listed or UL recognized. Many insurance companies and local electrical codes in the US require that installed electrical equipment be UL Listed.

UL Approved: This is a widely used term that is technically not correct. The correct terms are UL LISTED or UL RECOGNIZED.

UL Listed: UL grants this form of approval to equipment that will be user installed or operated and that is found to meet the safety requirements of the applicable UL standards. If a product is UL Listed, then it must be marked with the UL symbol.

UL Recognized: This is a form of formal approval granted by UL to devices that are not used as free standing equipment on their own, but are to be installed into some other system by a manufacturer, electrician, or possibly by an end-user.

UL2601-1: The safety requirements specified by Underwriters Laboratories Inc. that cover electrical medical and dental equipment that is intended for professional use by personnel in hospitals, nursing homes, medical care centers, medical and dental offices and similar health care facilities. These requirements cover portable equipment rated at 300 V or less and permanently connected equipment rated at 600 V or less.

UPS - Uninterruptible Power Source: A power supply which continues to supply power during a loss of input power. Two types are the stand-alone UPS, which is located external to the equipment being powered, and the battery back-up power supply, which is embedded in the equipment being powered, such as a POWER-ONE SAM series high power product with a G5 battery back-up module.

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

Warm-up Drift: The initial change in output voltage of a power supply from turn-on until it reaches thermal equilibrium at nominal line, full load, ambient temperature.

Warm-up Time: The time required after initial turn on for a power supply to achieve compliance to its performance specifications.

Wattage: This is a form of power measurement. For AC power systems, the watts rating is the volts rating multiplied by the amps rating multiplied by the POWER FACTOR. Watts represent actual delivered energy. In a typical AC power system, some of the Amps delivered to the load do not deliver energy to the load.