Glossary


TERMS AND ACRONYMS CONTINUED..
See below for the special

Schottky diode: A device that exhibits a low forward voltage drop (e.g.0.4 V) and a fast recovery time. This type of diode is especially useful at high current, low voltage (typically 5VDC), where low losses and high switching speed are important.

Semi-regulated output: A secondary output on a multiple-output power supply that receives line regulation only.

Sense line: S+ and S- lines, complementary to the Vo+ and Vo- lines, allowing the compensation of voltages drops due to line resistance.

Sequencing: Controlling the time delay and order of output voltage appearance and drop-out upon power supply turn on and turn off.

Series regulator: A linear regulator in which the active control element (transistor) is in series connection with the load.

Short-circuit protection: See: Current limiting circuit.

Shunt regulator: A linear power supply in which the active control element (transistor) is in parallel with the load.

Slave: The unit in a master-slave paralleling scheme that is controlled by the master unit. See: Master/Slave operation.

Snubber: A network containing a resistor, capacitor, and diode used in the switching power supplies to trap high-energy transients and to protect sensitive components.

Soft start: Input surge-current limiting in a switching power supply where the switching drive is slowly ramped on.

Stability: The change in output voltage of a power supply over a specific period of time, following a warm up period, with all other operating parameters such as line, load and ambient temperature held constant.

Standby current: The input current drawn by any power supply under minimum load conditions.

Static load: A load that remains constant over a given time period. It is usually specified as a percentage of full load.

Step change: An abrupt and sustained change in one of the influence or control quantities (e.g. load current).

Stress-ageing: The process of subjecting a completed power supply to a variety of stresses to force the occurrence of all burn-in-failures.

Surface Mount Technology (SMT): A space saving technique whereby special leadless components are soldered onto the surface of a PCB rather than into holes in a PCB. The parts are smaller than their leaded versions and PCB area is thus saved.

SMPS or Switched-mode power supply is a PSU that incorporates power handling electronic components that are continuosly switching on and off with high frequency in order to provide the transfer of electric energy. By varying duty cycle, frequency or a phase of these transitions an output parameter is controlled. Typical frequency range of SMPS is from 20 kHz to several MHz. The actual choice of operating frequency is usually the trade off between size and efficiency.

Switching frequency: The rate at which the source voltage is switched in a DC to DC converter.

Switching regulator: A high-efficiency non-isolated DC to DC converter consisting of inductors and capacitors to store energy and switching elements (typically transistors or SCRs), which open and close as necessary to regulate voltage across a load. The switching duty cycle is generally controlled by a feed-back loop to stabilize the output voltage.

Synchronous Rectification: A circuit arrangement where the output rectifier diodes of a power supply are replaced with active switches such as MOSFETs. The switches are turned on and off under control and act as rectifiers. This results in considerably lower losses in the output stage and subsequently much higher efficiency. They are particularly useful with low voltage outputs.

Temperature coefficient: The average percentage of change in output voltage per degree change in temperature with load and input voltage held constant.

Thermal protection: A protective feature that shuts down a power supply if its internal temperature exceeds a predetermined limit.

Thermal regulation: See: Temperature coefficient.

Thermistor: A device with relatively high electrical resistance when cold and almost no resistance when at operating temperature. Thermistors are sometimes used to limit inrush current in off-line switchers.

Topology: Topology is the fundamental circuit design of a clearly identifiable and characteristic type. DC-DC converters can be designed along several different topologies (using different fundamental design principles). A patent for a particular topology can be very powerful in that it can encompass any circuit solution regardless of power output, falling within the design principles of the topology in question.

Transformer: A magnetic device that converts AC voltages to AC voltages at any level. An ideal transformer is a lossless device in which no energy is lost and that requires no magnetising current.

Transient: A temporary and brief change in a given parameter. Typically associated with input voltage or output loading parameters.

Transient response time: The amount of time taken for an output to settle within some tolerance band, normally following a step change in load.

UL (Underwriters’ Laboratories): An independent, non-profit organization testing for public safety in the United States.

Undershoot: The amount by which an output falls below its final value in response to a rapid load change.

UPS or Uninterruptible power supply is a PSU that continues to supply electric power to the load for specified periods of time during a loss of input power or when the input line varies outside normal limits. UPS is implemented with a backup battery and an additional DC-AC inverter.