AC/DC Converter

Electrical network, powered by a AC voltage or current source and capable of supplying DC power to a load. An AC operated power supply performs two functions, to isolate the primary AC input from external loads and to provide output levels different than that of the primary AC input. Special case: nonisolated AC/DC-Converter. Other Terms: Switched mode power supply (SMPS), Off-Line switcher, primary and/or secondary switcher, Linear Power Supply.

Cooling

The process of removing heat, dissipated within the power converter during normal operation. This may be managed by natural convection, or by forced air.

DC/DC Converter

Electrical network, powered by a DC voltage or current source and capable of supplying DC power to a load. A DC operated power supply performs two primary functions, to isolate the primary DC input from external loads and to provide output levels different than that of the primary DC input. Special case: nonisolated DC/DC-Converter.

Dynamic Load Rep.Rate and Duty Cycle

The over-and undershoot measurement values are dependend on: current change, slope di/dt, frequency (repetition rate) and duty cycle of the load pulse trains. It is recommended to use an electronic load as a test equipment. Example: The duty cycle is the ratio between the individual times for two applied levels of loads, i.e. 100% load for a time t1, 10% load for a time t2. If t1 is equal to t2, the duty cycle results in 1:1.

Efficiency

The ratio of output power to input power, measured at full load and nominal line voltage. Efficiency=output power/(output power+losses). The Efficiency can also be measured as a function of the output power at different input voltages and depicted in a graph.

Electro Magnetic Compatibility EMC

Switched mode Power Supplies (SMPS) are well known and appreciated for their significant benefits in reductions of physical size and power loss. One major drawback is the generation of high frequency electrical noise associated with the fast switching waveforms in the power converter. EMI is generated by rapidly changing electric or magnetic fields. It is necessary that SMPS are designed to minimize EMI and that they can operate in close proximity with other electronic equipment, without interfering with its operation. They should also be resistant to interference from external or internal sources, meaning they should be Electromagnetically Compatible (EMC) with other systems. The EMC Directives refer to relevant standards.

Hold Up Time

The total time any output will remain within its regulation after the input line voltage has turned off at a specified level of input voltage and load (typically at full load).

Input Current Limiting

A high surge of input current drawn by a power supply at turn on. Such a surge is often caused by capacitor charge up and /or transformer startup events. Thermistor and Resistor / SCR or Bypass switch combinations solve this problem and keeps the inrush current within limits. A Fuse is used in most cases to prevent from catastrophic failures.

Input/Output Connections

Describes which connectors (plug-in , screw terminals etc.) and pin assignments are used to connect the power converter with the Line (Input) and Load (Output). The Pin assignment includes also other informations for terminals with electrical functions of relevance, such as sense leads, control functions, signals etc.

Input Variables

Variables to specify electrical parameters at the input side of the Power Converter.

Input Voltage Limiting

A method to suppress voltage transients across the input terminals of the power supply (Input Transient Protection). A second protection is to measure the window of the input voltage of the Power Converter and react with a shut down, if input voltages other than specified are applied.

Input Voltage Range

The range of the input voltages for which the power supply meets its specifications.

Leakage and creepage distance

Safety distance in a power supply between high-operating voltage and isolation voltage areas. Printed circuit board layout (PCB-layout) and transformer construction are of major importance to meet safety approvals.

Line and Load Regulation

Line Regulation is the percentage change in output voltage caused by the input voltage varying over the specified range. Load Regulation is the percentage change in output voltage caused by a specified load variation.

Line (Mains) Frequency

The frequency of the AC input voltage. Line frequency range defines the upper and lower limit for which the power supply meets its specifications. Line is used in USA, whereas Mains is a common term in UK.

Nominal Input Voltage

The nominal value of input voltage for which the power supply is specified to operate.

Nominal Output Current

The maximum load current which a power supply is designed to provide at the specified ambient temperature.

Nominal Output Voltage

The nominal value of output voltage. In power supplies with adjustable output voltage.

Operating Temperature Range

The range of ambient temperature in which a power supply may be safely operated and meets ist specifications.

Output Current Limiting

Electronic circuit as a part of a Converter, to protect the constant voltage power supply from overloads. The characteristic may have the form of: constant current, foldback, cycle by cycle and current cut-off. The trip level at which the protection circuits takes place, is specified as well.

Output Variables

Variables to specify electrical parameters at the output side of the Power Converter.

Over Voltage Protection (OVP)

A protection mechanism which prevents the load from rising its voltage over a preset level. The energy which may be absorbed by the mechanism is limited by the specification of the OVP-elements (crowbar or transient suppressor diode). In some case a separate regulation loop is used to shut off the converter completely.

Power Derating

The need to reduce the rated output power of a power supply as a function of elevated ambient temperatures. The rate of power reduction at the trip temperature point has to be defined in the specifications.

Power Factor

The ratio of true to apparent input power. In the special case, when both the input current and voltage are sinusoidal, the power factor is defined as: cos(phi). Special circuit designs,called Power Factor Correction(PFC) take care to keep harmonic line currents within limits, given by European standards.

Pulse Load Frequency

Frequency of a pulsed Load, applied to the output of a power supply.

Rate of Current Rise

Rate of Rise of a pulsed Load current di/dt. Voltage undershoots and transient response time beside others are dependend on this parameter.

Ripple + Spikes

An AC voltage superimposed on the DC output voltage. Ripple is the unwanted portion of the output harmonically and periodically related in frequency to the input line (AC supplies) and to any internal generated switching frequency. Noise is the unwanted, aperiodic output variation. Common mode noise is common to each output terminal. It flows to the input via the external ground. Spikes are coming from fast switching speeds within the converter, seen on the output terminals. The measurement results are rather dependend on the measurement bandwidth of the scope and the length of the measurement cables. Terminated Coax connectors are recommend to measure Spikes.

Safety Isolation

Input to Output Isolation. The degree of electrical isolation between the input and output terminals of an electronic power supply.

Storage Temperature Range

The range of environmental temperature in which a power supply can be safely stored.

Temperature Coefficient

The average percentage of change in output voltage (or current in a current regulator) per degree change in temperature. Other variables, such as input voltage and load are kept constant.

Temperature Limiting Tue

Overtemperature protection feature. A circuit that shuts down the power supply in the event of excessive internal temperatures. It is recommended to place the temperature sensors in areas of critical temperature spots.

Transient Response Time

The maximum time for the output voltage (or current in a current regulator) to return within regulation limits following a specific load step change. A sudden change in input voltage can cause an output voltage transient as well.

Voltage Overshoot

A decrease in load current results in a positive voltage transient, called overshoot.

Voltage Undershoot

A increase in load current causes the output capacitor to discharge resulting in a negative voltage transient, called undershoot.