Switching power supply common fault

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Switching power supply common fault

(1) Fuse blown

In general, a blown fuse indicates a problem with the internal wiring of the power supply. Due to the high voltage and high current of the power supply, the fluctuations and surges of the power grid voltage will cause the current in the power supply to increase instantaneously and the fuse will be blown. The key points should be to check the rectifier diode of the power input terminal, high-voltage filter electrolytic capacitor, inverter power switch tube, etc., check whether the component has breakdown, open circuit, damage, etc. If the fuse is really blown, you should first check the components on the board to see if the appearance of these components is burnt and there is no electrolyte overflow. If the above is not found, use a multimeter to measure whether the switch has a breakdown short circuit. . It is necessary to pay special attention to: Do not directly detect the damage of a component when it is damaged. It is very likely that the other high-voltage components will still be damaged and the replacement components will be damaged. It is necessary to comprehensively apply all the high-voltage components of the above circuit. After the measurement is checked, the fuse blowout can be completely eliminated.

(2) No DC voltage output or unstable voltage output

If the fuse is intact, there is no output of DC voltage at all levels under load. This situation is mainly caused by the following reasons: open circuit, short circuit phenomenon in the power supply, overvoltage, overcurrent protection circuit failure, auxiliary power failure, oscillating circuit not working, power supply overload, rectifier diode in high frequency rectification and filtering circuit It is broken down, the filter capacitor is leaking, and so on. After measuring the secondary component with a multimeter and eliminating the breakdown of the high-frequency rectifier diode and the short-circuit of the load, if the output is zero at this time, it is sure that the control circuit of the power supply has failed. If some of the voltage output indicates that the pre-stage circuit is working properly, the fault is in the high-frequency rectification and filtering circuit. The high-frequency filter circuit mainly consists of a rectifier diode and a low-voltage filter capacitor to form a DC voltage output. The breakdown of the rectifier diode causes the circuit to have no voltage output, and the leakage of the filter capacitor causes the output voltage to be unstable. Statically measure the corresponding component with a multimeter to check the damaged component.

(3) Poor power supply capacity

Poor power load capacity is a common fault. It is usually found in old-fashioned or long-running power supplies. The main reason is that the components are aging, the switching tube is unstable, and there is no heat dissipation in time. It is important to check whether the Zener diode is hot or leaky, the rectifier diode is damaged, and the high voltage filter capacitor is damaged.