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Components of SWITCH MODE POWER SUPPLY (SMPS)

Components of SWITCH MODE POWER SUPPLY (SMPS) Most of the components used in SWITCH MODE POWER SUPPLY (SMPS) can be easily identified. However, some components are difficult to identify. Some components are designed especially for a particular model. The different components of SWITCH MODE POWER SUPPLY (SMPS) are:

Components of SWITCH MODE POWER SUPPLY (SMPS)

Most of the components used in SWITCH MODE POWER SUPPLY (SMPS) can be easily identified. However, some components are difficult to identify. Some components are designed especially for a particular model. The different components of SWITCH MODE POWER SUPPLY (SMPS) are:

Switch Mode (chopper) Transistors and other Semiconductors

A transistor is small and fast semiconductor used for amplification and voltage stabilization.

Bipolar Power Transistors (often BU or 2SC/2SD numbers)- High voltage power transistor, which is used as the main switch Mode transistor.

Diodes and Rectifiers - AC line rectifier uses a combination of 2 or 4 diodes. High efficiency diodes are used to rectify output voltages. These diodes look like normal axial lead diodes. They can be combined in pairs inside TO220 type packages. To troubleshoot SWITCH MODE POWER SUPPLY (SMPS) problems, test for shorted and open junctions.

Capacitors (filter and bypass) in an SWITCH MODE POWER SUPPLY (SMPS)

Filter Capacitors - Used to filter the rectified AC line input voltage and various outputs of the power supply.

Bypass Capacitors - These are green colored, high quality plastic dipped or rectangular molded capacitors part of RFI filter. They are placed at output section and seldom fail.

ors (normal and flameproof), NTC thermistors

Resistors - Test for proper value with the help of multimeter. While measuring the resistor in-circuit, if the value is higher than normal value, then resistor is bad.

Startup Resistors - They are high value (100K) medium wattage resistors. Test for open circuit results in dead supply without blown fuses or fusable resistors.

Flameproof or Fusable Resistors - They are rectangular ceramic blocks which are blue or gray in color. They function as fuses; hence they cannot be replaced with higher wattage types. Test for open circuits.

WTC Resistors (thermistors) - Negative Temperature Coefficient resistors act as inrush surge limiters. There may be one or two of these in series with the AC input. These often look like fat black disk capacitors.

Transformers and Inductors required in a SWITCH MODE POWER SUPPLY (SMPS)

High Frequency Transformers - They consist of the switch Mode power transformer and feedback transformer. They provide line isolation and generate multiple output voltage. They rarely cause problems and can be tested for open circuit. Some supplies use small Transformers for feedback instead of optoisolators. Optoisolator is used to isolate the input line with the rest of the section.

Inductors - Output inductors rarely fail and they can be tested for open circuit. Replace the faulty inductor if found.

Coupled Inductors - They are used as a part of Pi type RFI filter which is placed in the AC input circuit. The windings of inductor are in series with AC line. They look like small transformer. They are very reliable and help to reduce noise and spikes. They can be tested for open circuit.

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Comments (1)
Amarendhar

ur total information is superb...Thanks.....

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