source:power supply Popular:adapter release time:2021-10-09 10:46:39 Article author:sznbone
How to repair a switching power supply failure?
The switching power supply is a supporting equipment of various household electrical appliances. Once a failure occurs, it will affect the use of household electrical appliances. How to repair a switching power supply failure? Let's take a look today!
1. Starting circuit
The starting circuit of the switching power supply is mainly composed of RC series components. The common fault is the open circuit of the starting resistor or the starting capacitor, which prevents the switching tube from oscillating. Therefore, when this problem occurs, the rectified and filtered 300V voltage is normal, but + B has no output. The problem is naturally the "three noes". The checking method is very simple. Use the DC gear of the universal meter to measure the B pole of the switch tube. If the switch tube B pole voltage jumps at the moment of power-on, it indicates that the starting circuit is normal. If the test pen does not swing when the switch is pressed, it indicates that the starting circuit is open. NS.
2, switch vibration circuit
The circuit is mainly composed of a switch tube and its positive feedback circuit. Some circuits use the switch thick film method, and the components of the positive feedback circuit are relatively small, usually some RC series circuits or series circuits composed of diodes and resistors. Regarding the switch tube or the switch thick film, the common fault is the switch tube breakdown or malfunction. Once the switch tube is broken down, the whole machine will not work normally and will be in a "three-no" condition; as for the positive feedback loop, open-circuit faults are also more common, which will result in the positive feedback voltage not being normally applied to the open circuit. The tube B pole forces the switching tube to stop vibrating. When overhauling, as long as the resistance-capacitance component in the positive feedback loop is measured or the substitution method is used, the source of the problem can be found.
3, Sampling comparison circuit
This is mainly to sample the +B output voltage, compare an error voltage, and then use the pulse adjustment circuit to control the conduction degree of the switch tube. Common faults in the sampling comparison circuit are the breakdown or malfunction of the sampling comparison tube, the open circuit of the input circuit of the sampling circuit, and the open circuit of the sampling winding. If it is a parallel switching power supply, the leakage of the filter capacitor of the sampling voltage is a common fault. Because the sampling comparison voltage is the decisive factor that controls the switching tube's turn-on time, when the sampling and comparison circuit is faulty, the switching tube's turn-on time will be out of control, resulting in a high output voltage, which will cause the overvoltage maintenance circuit to operate and force the switching tube to stop. vibration. This is mainly about the parallel switching power supply. In the series switching power supply, the output terminal of +B is usually over-voltage to maintain the voltage regulator tube breakdown, but the switching power supply is still vibrating at this moment, just because the line output stage cannot be operated because there is no power supply, so there is no reverse process. Pulse output makes the switching power supply in a free vibration condition. The fault phenomenon is also "three noes", but the fuse will not be burned. After the rectification and filtering, 300V voltage is also applied, but there is no +B voltage output, and the overvoltage maintenance circuit is activated. Regarding the series switching power supply, the switching transformer will also announce the "creak" sound. The main point of the overhaul of this circuit is to put the sampling comparison tube, the optocoupler, and the sampling potentiometer on the components, which can be judged by the measurement method or the substitution method.
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