News

on video Howto repair switch mode power supplies

electrical-1


 In the second video in the series of repairing switch mode power supplies (SMPSs) we look at the importance and the functionality of the so called Stand-by circuit. Namely, the low power Stand-by circuit is responsible for generating the Stand-by voltage, which should be always generated by the power s

upply unit (PSU) as soon as your device is plugged into the power grid. This is because the stand-by

voltage is feeding those circuits (most of the time microcontrollers) which are checking the state of

 your device and they are waiting for a turn-ON signal. After a microcontroller receives the turn-ON

signal, again the stand-by power is used to send the wake-up signal to the high power portion of the

Switch Mode Power Supply.

Therefore, whenever you try to repair a switch mode PSU, firs you have to make sure, that the Stand-by power section of the PSU is working properly, and it is providing the right voltages to the stand-by circuit. This is because if there is no stand-by power, the device will never able to turn on.

The Stand-by circuit it mostly formed by a small transformer, a medium-power FET transistor and an in

tegrated circuit, which is controlling the gate electrode of the FET. 

Thus, if you are able to spot a small transformer on the printed circuit board of your switch mode PSU you are trying to repair, you can be almost sure that it is the stand-by transformer.


No comments