Signal defined in the VMEbus specification indicating an input voltage error

ACFAIL is asserted when the input voltage (AC line voltage) fails or drops below the minimum level and thus indicates that the output voltage Vo is about to fail.
The signal is implemented as an open collector output of an NPN transistor which is switched through to 0VF or -Vo (only for a limited period while Vo drops or after it has dropped) on „fail“ (undervoltage at the power supply input).
The ACFAIL signal always occurs in combination with the SYSRESET signal.

See also buffer time

Range of output voltages within which it is permitted to adjust Vo without compromising safety

The adjustment range is specified either relative to the nominal output voltage (factory setting) or as an absolute value.
The user can set Vo by means of a potentiometer fitted in the unit.

(Cf. parallel connection)

Certificate indicating compliance with standards (electrical safety) issued by an independent approval body

For example: GS mark (German approval mark) for EN60950, UL mark for UL1950

See also Standards


Period for which Vo is guaranteed at 95% of the nominal value after the ACFAIL signal or the PF signal has been asserted (as a result of insufficient input voltage)

The buffer time is specified for the nominal output current (nominal load) and increases for lower output loads.

See also ACFAIL signal, PF (signal)


The dissipation of lost power (heat) from the power supply unit

Standard units are designed to be cooled by free convection or using internal fans.
Free convection cooling requires that the unit is operated in an upright position and that cool air can enter the unit and warm air can escape from the unit unhindered.
Ideally, there should be an unobstructed flow of air from bottom to top. There should be a minimum gap of 20 mm above and below the unit.

The orientation of units equipped with a fan is not critical. It must, however, be ensured that the fan can draw in fresh air and that the (warm) exhaust air is able to escape through the apertures provided.

Components of the housing are often used as cooling surfaces. A gap (5 mm) between neighboring modules considerably improves cooling of the power supply unit, particularly in the case of convection cooling. The more efficient the cooling, the greater the life of a power supply unit.

See also Temperature range

Limitation of the maximum output current by circuitry within the power supply unit

The specification is a range or a typical value for the trigger point for current limitation with reference to the nominal output current Inominal. If the output current reaches the current limitation value (overload), the power supply unit reduces the output voltage.

The behavior of the power supply units under overload conditions varies from model to model. The following variants are common:
• The unit continues to operate in accordance with the current limitation characteristic, even in the event of a complete short circuit. The output voltage rises again immediately when the overload condition is no longer present (e.g. the P110 model).

• The power supply unit shuts down on overload. After a brief pause (0.5 – 2 s), the power supply attempts a restart. If the overload condition persists, the units shuts down again („hiccup mode“, e.g. the P90 model)

• The power supply unit only shuts down under severe overload conditions. „Hiccup“ mode only occurs if the overload is so severe that Vo is considerably (e.g. 40%) below the nominal value (e.g. the PH120 model).

Curve describing the behavior of the output voltage and the output current under overload conditions (I>Inominal)

The most common variant is the „straight characteristic“ where the output current remains virtually constant under overload or short-circuit conditions (e.g. the P110 model).

See also Current limitation


See Power good

Reduction in the maximum output power which may be drawn from a unit as the ambient temperature rises

The application must ensure that the derating specifications are adhered to. Current limitation is not implemented in such a way that it takes account of temperature.

2%/K as of +60°C means that as of an ambient temperature Ta of 65°C, the maximum output power must be reduced by 2%/K x (65°C–60°C) = 10%. The output power must thus not exceed 90% of the nominal output power.

35mm mounting rail compliant with DIN EN50022 (material thickness 1 through 2.3 mm)

The unit is mounted by clipping it onto the mounting rail (PH series).


Ratio of the output power to the input power (effective power)

The specification is the typical value at the rated input voltage and the nominal output current (nominal power). For series of units (with different output voltages), the efficiency is expressed as a range. In this case, the larger values relate to the units with higher output voltages.

Electromagnetic compatibility

The term EMC covers immunity and emission including flicker and harmonic currents.

See also PFC

Generic term for electromagnetic interference caused by a power supply unit. Interference propagates either along the conductors or by radiation and can depend on the precise conditions under which the unit is installed (cable lengths, PE connection etc.). MGV power supply units are tested under typical application conditions (power cable and load cable approx. 1 m in length) with a resistive load. See also Standards.


Low frequency interference of the line voltage by consumers

With luminaires or monitors, flicker manifests itself in the form of fluctuations in brightness. Flicker is caused by the inrush current while the capacitors fitted in the power supply unit are charging
(see also inrush current limitation) or pulsed loading of the power supply unit.
Threshold values in accordance with EN61000-3-3 (the „flicker standard“) are defined for both one-off and periodic events. Compliance with the threshold values laid down in EN61000-3-3 is ensured for when the power supply unit is turned on, but not when the output voltage is placed under extreme pulse loads.

Specification in the data sheets referring to the internal fuse of a power supply unit

The fuse rating is designed for the maximum effective input current (lower threshold of the input voltage range , nominal output current).
Any specifications on external fuses (PH models) refer to automatic circuit breakers. The minimum value for the external fuse is determined by the maximum inrush current (see also inrush current limitation). A maximum value for the external fuse is required as a result of the maximum current carrying capacity of the input contacts and for approval reasons.

Where a DC input voltage range is specified for an AC voltage unit, an external fuse rated for the maximum DC input voltage is required for DC operation.


Also mains feedback, Feedback from a power supply unit with an AC input into the mains supply Peak charging of the input capacitor in the power supply unit (devices without active PFC) causes the input current of a power supply unit to be pulse-shaped (small current conduction angle). This causes harmonic distortion on the powerline. See also PFC


Capability of a power supply unit to resist interference which influences the unit either along the conductors or as a result of electromagnetic radiation (from external sources)

If the unit is subjected to interference of the relevant severity, it does not suffer damage and correct operation is not affected beyond what is permitted. Depending on the type of influence (e.g. failure of the line power supply), it may be permissible for the power unit to shut down.

See also Standards.

Range of input voltage values within which the unit will start up and retain data correctly

See also Line voltage range ,Rated voltage range

Limitation of the maximum input current at the moment the unit is switched on

The limitation circuitry is often implemented in the form of a thermistor (NTC) in the input circuit. This is why the values for a cold start (NTC at room temperature) and for a warm start (restart after the input voltage has been switched off for 1 minute) are specified separately.
Typical values at the rated input voltage are specified. A spike at the start of the inrush current with a duration of only a few milliseconds is ignored. This is caused by the radio interference suppression capacitors being charged.

Generally used abbreviation for output current

An IT power supply system is one which is not directly earthed. A power supply unit suitable for use with an IT system (intended and designed to operate with such a supply system) is subject to stringent requirements regarding effective isolation of the primary and secondary circuits. The conducting parts of the housing must be connected to the protective earth (PE).


Static fluctuation of the output voltage as a result of variations in the input voltage (line voltage) while other conditions (output load, temperature) remain constant

Line regulation is specified as a relative deviation of the output voltage over the input voltage range.

As input voltage range, but specifically for units with AC voltage input.

Static fluctuation of the output voltage as a result of variations in the output load (output current) while other conditions (line voltage, temperature, loads from any other Vo) remain constant

Load regulation is specified as the relative deviation in voltage between the no-load (or base load) condition of the output and the nominal output voltage.
On units fitted with an output diode (for redundant operation), the relationship between the output voltage and the output current is shown graphically.

See also Parallel connection


AC voltage component of the output voltage as the sum of ripple and voltage spikes in the MHz range

The specification is a peak-to-peak value. Pulse spikes are caused by switching processes of transistors and diodes in the power supply unit which typically have a duration of around 50ns and excite damped oscillations on the output lines (periodic with the switching frequency).
In real applications, the input capacitance of the consumer and the inductivity even of short connection cables (a few centimeters) drastically reduce these pulse spikes. The measured values can differ greatly depending on the way in which the measuring apparatus is set up.

The specifications in the data sheets apply for measurements made at the output with an oscillograph with a 20 MHz bandwidth, a 1:1 probe and a ground connection with no loop. For units compliant with the Compact PCI specification, a 100nF ceramic capacitor and a 20µF electrolytic capacitor should be fitted at the measuring point.


See Temperature range

Current at the output terminals of a power supply unit (indicated by Io)

In the order data (data sheet), the value shown under Io is the permitted range between the base load and the nominal output current (Inominal), for example 0 – 70A).
As a general rule, no base load is necessary (stability at no load, Io=0A). There are a few exceptions, particularly for multiple voltage units, where a certain base load is required (Io>0A).

Voltage at the output terminals of a power supply unit (indicated by Vo)

The nominal output voltage (factory set) forms the basis for the order data (data sheet).
The output voltage is measured directly at the output terminals or at the sense lines if the outputs use sensing technology. At MGV, all output voltages are (<60V) SELV as standard. [/av_toggle] [av_toggle title='Overtemperature protection' tags='' av_uid='av-4esugc'] Protection of the power supply unit against thermal overload If the temperature sensor in the power supply unit overheats, the unit shuts down (and restarts when it has cooled down) or the output voltage and power are reduced, depending on the model. The following are possible causes of overheating: • insufficient cooling /ventilation • operation outside the • operation outside the a href=” index.php?content=glossar&glossar_id=13”> input voltage range or with excessive output current or power (multiple voltage units with overall power limitation)

Also OVP,
Protection of the output voltage against overvoltage as a result of an error in the power supply unit

If regulation of Vo fails, the output voltage is limited (by a „secondary control circuit“) in order to prevent consequential errors in the power supply unit, damage in the load circuit or „hazardous voltages“ (>60VDC). The specification is a value relative to the nominal output voltage or a range of absolute values. In the standard power supply units, the unit does not shut down after the secondary OVP has triggered.
br> Models in the DG series and increasingly models of the P and PH series also feature a shut-down function in the event of the input voltage being too great (primary overvoltage protection) in order to avoid damage to the power supply unit as a result of overvoltage (within certain limits).


Parallel connection of the output voltages of several units to increase power or to achieve redundancy Permission to connect outputs in parallel must be expressly included in the manufacturer´s data sheet, otherwise damage may be caused to the units (circuits with synchronous rectifiers). In such cases, parallel connection of no more three units of the same kind is allowed without consulting the manufacturer. Distributing the overall current across the outputs of the individual units is advantageous for thermal considerations and is achieved using a load share controller (with a control line between all the units) or by varying the output voltage in dependence on the load. Load regulation is approx. 4% when distribution of the current is achieved by varying the output voltage in dependence on the load. Effective current distribution can only be achieved if the output voltage of each of the individual units is set virtually identically (at nominal load). Current distribution is performed with a deviation of up to 20% of the nominal output Io. The total power consumption of all the components which are connected in parallel must be 10% below the sum of the power consumption of the individual units in order to ensure that individual units are not overloaded.

Power Fail signal
, Signal indicating errors in the input voltage and/or output voltage

It indicates that the input (line) voltage has fallen below the minimum threshold or has failed or that the output voltage Vo has dropped to typically 95% of the nominal value for Vo.
On undervoltage at the input of the power supply unit or if Vo drops too low, an NPN transistor is switched to 0VF/-Vo (only for a limited period while Vo drops or after it has dropped). If the PF signal is asserted as a result of insufficient line voltage, Vo is maintained for the duration of the buffer time.
The PF signal is active (switched to 0VF/-Vo) for 200ms – 600ms after Vo has risen (the power supply unit is switched on). In normal circumstances (rated input voltage/no overloading of Vo) the PF signal level is typically 5V.

Power Factor Correction
, Correction (reduction) of the input current by increasing the current conduction angle

PFC is necessary on high-power units using AC input voltage in order to remain within the limits for harmonic current laid down in EN61000-3-2 and at the same time increases the power factor. PFC is implemented by an additional transducer stage (active) or a choke (passive).
The passive solution does not ensure that the limits are adhered to if several units are used on the supply network at the same time.

See also Harmonic current emissions.

Increased output power as a result of increased output current available for a limited period

In MGV units with power boost, the maximum increased output current is at least 130% (up to 150% depending on the model) of the nominal output current Io and is available for approx. 0.4s (up to 3s depending on the model).
Depending on the model, the power boost is only available during and immediately after startup (application of the input voltage). In newly developed units with power boost, the increased output power is also available during operation (details available on request).

Ratio of the apparent input power to the effective input power (AC input voltage units)

Typically 0.6 for units without PFC. Typically 0.95 for units with active PFC.

See PFC.

See PF signal.

Also DC-OK
, signal indicating the presence of output voltage (on units for use on mounting rails – PH series)

An output voltage above approx. 80% of Vo is taken as „good“ (e.g. > approx. 19V for Vo=24V). Depending on the model, signaling is implemented either by transistor (switched through to +Vo on DC-OK) or via a relay output (all contacts floating).
In newly-developed models, the unit also evaluates whether the overvoltage protection has triggered, in which case DC-OK is not asserted.

Also hold-up time Period for which the output voltage is still available (Vo = 95% of the nominal value) after failure of the input voltage (power failure) The power ride-through is specified as the typical value at the rated input voltage (prior to power failure) and nominal output current (nominal load) and increases in the case of lower output loads and higher input voltages.


Period during the startup phase of a power supply unit between the time that Vo begins to rise and the time at which Vo reaches 95% of the nominal output voltage

The value specified is a typical value at nominal output current without any capacitive load on the output voltage. The ramp-up time is largely independent of the input voltage.

(Cf. Turn-on delay)

Nominal value for an input voltage range

For example:
230VAC for a unit with a range 187 …264VAC
230VAC for a unit with a range 94 …264VAC
3x400VAC for a unit with a range 3 x 340 …550VAC
24VDC for a unit with a range 18 …40VDC
48VDC for a unit with a range 40 …80VDC

Specification of a range of input voltages on the rating plate

The EN60950 standard (Information technology equipment -Safety) specifies that an electrical device must remain functional within an input voltage tolerance or input voltage range (specification on the rating plate of the end device) of +6% through -10%.
For this reason, the actual input voltage range (as per the data sheet) is sometimes greater than the specification on the rating plate.

Period which elapses between the time the load changes and the time the output voltage returns to a value within the range ± 1% of Vo when there is a sudden change in load

The recovery time depends on the magnitude of the change in load (change in current).
For example: <0.5ms at 20 – 80% means that if the current changes by between 20 % and 80 % of the nominal current, Vo returns to within a tolerance of ± 1% after a maximum of 0.5ms. [/av_toggle] [av_toggle title='Redundancy' tags='' av_uid='av-751zg'] Parallel operation of power supply units to ensure that power supply is not interrupted if one unit fails See also Parallel connection. [/av_toggle] [av_toggle title='Ripple' tags='' av_uid='av-1t12oc'] AC voltage component of the output voltage with the switching frequency of the power supply unit (triangular or sine waveform, e.g. with 100kHz) Ripple is measured immediately at the output with a bandwidth of approx. 700kHz (MGV functional testing unit), since the output voltage can also be overlaid with higher frequency noise voltages. The specification is a peak-to-peak value. Ripple depends on the operating temperature of electrolytic capacitors in the unit. It falls as the ambient temperature rises or as the power supply unit warms up. Ripple is at its maximum immediately after the power supply unit is switched on at the lower threshold of the operating temperature range, and then falls as the unit warms up. The values in the data sheet are guaranteed as of an operating time of one minute. At room temperature or higher ambient temperatures, the value in the data sheet is achieved immediately after switching on. Cf. Noise voltage. [/av_toggle] [/av_toggle_container] [av_textblock size='' font_color='custom' color='#017655' av-medium-font-size='' av-small-font-size='' av-mini-font-size='' av_uid='av-jnegtikq' admin_preview_bg=''] S

Safety with respect to the risk of electric shock or dangerous bodily currents (electrical safety) Standard MGV units are designed to be compliant EN60950 („Safety of information technology equipment including electrical office machinery“) and for safety class I (with protective conductor connection). Design compliance with other standards is indicated as appropriate in the data sheet (e.g. UL60950). Units belonging to the P, PH, SPH and DG series are galvanically isolated, being fitted with double or reinforced insulation between the input and output circuits. All output voltages below 60VDC are safe to touch (SELV). Units belonging to the P, PH, SPH and DG series are designed for installation in 19-inch racks or switching cabinets. The apertures in the housing ensure optimal ventilation under typical operating conditions, but are larger than those allowed for „touchable surfaces“ according to EN60950. Protection against electrical hazards in the event of accidental contact with the power supply unit and against hazards in the event of fire must be provided by the outer container. Requirements for the safe operation of electrical equipment: – Connect to a protective conductor (PE) with an adequate cross section – Install in a container which provides protection against accidental contact and fire – Operate power supply unit at an input voltage within the rated input voltage range – Adhere to the maximum total output power (units with more than one Vo) – Operate within the temperature range, observing the derating if necessary – To be operated and maintained by trained personnel only – Disconnect from power supply during installation and dismantling See also Standards.


Generally used abbreviation for output voltage