How should switching power supply failure be repaired?

Switching power supply as a variety of household appliances supporting equipment, once the failure will affect the use of household appliances. How should switching power supply failure be repaired? Today let's learn about it!

1. Start the circuit

The starting circuit of the switching power supply is mainly composed of RC series components. The common problem is that the starting resistance or starting capacitor is open, so that the switching tube can not vibrate. Therefore, when this problem occurs, the 300V voltage after rectification and filtering is normal, but there is no output of +B. The fault phenomenon is naturally "three nots". Viewing method is very simple, with the DC range of the multimeter measuring switch tube B pole, at the start of the moment such as switch tube B pole voltage jump is to clarify the starting circuit is normal, if the switch is not sway when the pen is explained to open the starting circuit.

2, switch vibration circuit

The circuit is mainly composed of the switching tube and its positive feedback circuit, some circuits are selected switch thick film mode, and the positive feedback circuit components are relatively small, usually some RC series circuit or series circuit composed of diodes and resistors. On the switch tube or switch thick film, the common fault is the breakdown or poor function of the switch tube. Once the switch tube breakdown, the whole machine can not work normally, in the "three" situation; And about the positive feedback loop, open circuit fault is also more common, so that the positive feedback voltage is not normally added to open in the tube B pole and force the switch tube stop vibration. Maintenance, as long as the positive feedback loop in the resistance component measurement or through the replacement method can find the source of the fault.

3. Sampling and comparison circuit

This is mainly to sample the output voltage of +B, compare an error voltage, and then control the conduction degree of the switch tube through the pulse adjustment circuit. The common faults in the sampling comparison circuit are breakdown or poor function of the sampling comparison tube, open sampling circuit input loop, open sampling winding and so on. If it is a shunt type switching power supply, the filter capacitor leakage of sampling voltage is a common problem. Because the sampling comparison voltage is the determining factor to control the switching tube turn-on time, when the sampling comparison circuit is faulty, it will make the switching tube turn-on time out of control, forming a high output voltage, so that the overvoltage maintenance circuit action, forcing the switching tube to stop vibration. This is mainly about the parallel switching power supply. And in the series type switching power supply, usually the output end of the +B overvoltage maintenance regulator breakdown, but at the moment the switching power supply is still vibrating, just because the line output stage can not work due to no power supply, so there is no reverse pulse output, so that the switching power supply is in free vibration. The fault phenomenon is also "three", but it will not burn the fuse. After rectification and filtering, there is also 300V voltage added to it, but there is no +B voltage output, overvoltage maintenance circuit action. For series type switching power supply, the switching transformer will also announce a "squeak" sound. The maintenance of the circuit, the main point is to put the sampling comparison tube, optical coupling and sampling potentiometer and other components, can be measured or replaced to determine the fault point.

4, pulse adjustment circuit

It is mainly composed of triode and resistive and capacitive components to control the conduction degree of the switching tube circuit. The common fault is the breakdown of the transistor, poor function. If the circuit is faulty, the switching tube will not work normally. There are generally three kinds of problems: first, the output voltage of the switching power supply is too high, forming overvoltage maintenance circuit action; Second, switching power supply vibration stop, output voltage is 0V; Three is the output voltage of the switching power supply is too low, this kind of fault is small, usually because of the poor function of the voltage regulator part of the component, or the load current is too large and the formation of the switching power supply can not keep up. The main point of the overhaul is the pulse-width-modulated triode, as well as some regulated diodes, to see if they are broken down.

For the switching power supply failure should be how to repair here, I hope everyone can use the correct switching power supply!