The converter is an indispensable part of all kinds of electronic equipment, and its performance is directly related to the technical specifications 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, and the volume and weight are only 20% and 30% of the linear converter, which has become the mainstream product of the voltage regulator converter. The maintenance of electrical faults of electronic equipment follows the principle of easy to difficult. Basically, it starts from the power supply, and the maintenance of other components is determined after the normal power supply is determined. Power faults account for the vast majority of electrical faults of electronic equipment. Therefore, to understand the basic working principle of the initial converter, familiar with its repair skills and common faults, is conducive to shorten the fault repair time of electronic equipment and improve the maintenance skills of personal equipment.

1. No output, normal insurance pipeline

This phenomenon indicates that the converter does not work or enters the protection state. First of all, 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, you must check the starting resistor and the external parts of the starting pin for leakage. At this time, if the converter control chip is normal, the failure can be quickly detected through the above inspection. If there is a starting voltage, then whether the output of the control chip has high and low level transitions at the start time, if there is no transition, it means that the control chip is not good, there is a problem with the peripheral circuit oscillation components or protection circuit, you can replace the control chip, and then Check the peripheral components; if there is a jump, the switch is generally bad or damaged.

2. Burn or fry in insurance

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

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

Such failures usually come from stable voltage sampling and voltage regulation control circuits. When the DC output, sampling resistor, error sampling amplifier (such as TL 431), optocoupler circuit, power control chip and other circuits form a closed-loop control loop, any problem will cause the output voltage to increase.

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 converter has a short-circuit fault (especially short-circuit or poor DC / DC converter performance, etc.). At this time, all loads of the circuit should be disconnected to distinguish between the power module circuit and 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. Output voltage terminal rectifier diode, filter capacitor failure, etc., can be judged by alternative method.

The decrease of the performance of the switch tube will inevitably lead to the normal conduction of the switch tube, the increase of the internal resistance of the converter and the decrease of the load capacity.