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The power module is an indispensable part of various electronic equipment, and its performance is directly related to the technical indicators of the electronic equipment and whether it can work safely and reliably. Because the key components of the power module work in the high-frequency switching state, the power consumption is small, the conversion rate is high, the volume and weight are only 20% and 30% of the linear power supply, and it has become the mainstream product of the regulated power supply. The maintenance of electrical faults of electronic equipment follows the principle of easy to difficult. Basically, it starts with the power supply, and maintains other components after determining the normal power supply. Power failures account for the vast majority of electrical faults in electronic equipment. Therefore, understanding the basic working principle of the initial power supply, familiar with its maintenance skills and common failures, will help shorten the maintenance time of electronic equipment and improve the maintenance skills of personal equipment.

1. No output, normal insurance pipeline

This phenomenon indicates that the power module is not working or entering the protection state. First of all, it is necessary to measure whether the startup pin of the power control chip has a startup voltage. If there is no starting voltage or the starting voltage is too low, you must check whether the external components of the starting resistor and the starting pin leak. At this time, if the power control chip is normal, the fault can be quickly detected through the above inspection. If there is a startup voltage, then whether the output of the control chip has high or low level jumps at the time of startup. If there is no jump, it means that the control chip is not good, and there is a problem with the peripheral circuit oscillation component or the protection circuit. The control chip can be replaced, and then Check the peripheral components; if there is a jump, the switch tube is generally broken or damaged.

2. Burn or fry in insurance

Mainly check the large filter capacitors of 300 V, rectifier bridge diodes and switch tubes. The anti-interference circuit problems will also cause safe burning and blackening. It should be noted that due to the failure of the switch tube, the current detection resistor and the power control chip will be burned. Negative temperature coefficient thermistors are also easy to be burned by insurance.

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

This kind of trouble usually comes from stable voltage sampling and voltage stabilization control circuit. When the DC output, sampling resistor, error sampling amplifier (such as TL 431), optical coupling circuit, power control chip and other circuits form a closed loop control loop, any problem will cause an increase in output voltage.

4. In addition to the stable voltage control circuit, the output voltage is too low, which will cause the output voltage to be low. The following reasons will also cause the output voltage to be low:

a. The load of the power module has a short circuit fault (especially a short circuit or poor performance of the DC/DC converter, etc.). At this time, all loads of the power module circuit should be disconnected to distinguish the power module circuit from the load circuit. If the voltage output of the load circuit is normal, the load is too heavy, or the power module circuit is faulty, it is still abnormal.

b. The output voltage terminal rectifier diode, filter capacitor failure, etc., can be judged by alternative methods.

The performance degradation of the switching tube will inevitably lead to the normal conduction of the switching tube, the increase of the internal resistance of the power supply and the decrease of the load capacity.