What are the common switching power supply failures? How to repair?

1, no output, safe tube normal

This phenomenon indicates that the switching power supply is not working or entering a maintenance condition. First, it is necessary to measure whether the starting pin of the power control chip has a starting voltage. If there is no starting voltage or the starting voltage is too low, it is necessary to check whether the starting resistance and the components connected to the starting pin are leaking. At this time, if the power control chip is normal, the fault can be quickly detected by the above check.

If there is starting voltage, measure whether the output end of the control chip has high or low level jumps at the moment of starting up. If there is no jump, it indicates that the control chip is bad, the peripheral oscillating circuit element or the maintenance circuit is faulty. You can replace the control chip first, and then check the peripheral component. If there is a jump, generally bad or damaged switch tube.

2, safely burn or fry

Mainly check the large filter capacitor on 300V, rectifier bridge diode and switch tube and other parts, anti-interference circuit problems will also lead to safe burning, black. The need to note that: due to the breakdown of the switching tube caused by safe burning will generally burn the current detection resistor and power control chip. Negative temperature coefficient thermistors are also easily burned out with safety.

3. There is output voltage, but the output voltage is too high

This kind of fault generally comes from the stable voltage sampling and the stable voltage control circuit. In the DC output, sampling resistance, error sampling amplifier such as TL431, optical coupler, power control chip and other circuits together to form a closed control loop, any problem will lead to the output voltage rise.

4. The output voltage is too low

In addition to the voltage regulator control circuit will cause the output voltage low, there are the following reasons will also cause the output voltage low:

a, the switching power supply load has short circuit fault (especially DC/DC converter short circuit or poor function, etc.), at this time, should disconnect all the load of the switching power supply circuit, in order to distinguish the switching power supply circuit is still the load circuit fault. If the voltage output of the disconnected load circuit is normal, it indicates that the load is too heavy; Or still not normally clarify the switching power supply circuit is faulty.

b. Failure of rectifier diode and filter capacitor at output voltage end can be judged by substitution method.

c, the function of the switch tube decline, inevitably lead to the switch tube can not be normally switched on, so that the internal resistance of the power supply is added, can be reduced with load.

The above 4 small failures are relatively easy to occur, we will continue to share for you in the future, to help you save resources, better use of switching power!