Switching power supply common fault – power adapter supplier

1) The fuse is blown

In general, a blown fuse indicates that the internal wiring of the power supply has failed. Since the power supply operates under high voltage and high current conditions, the fluctuation of the grid voltage will cause the current in the power supply to increase instantaneously and the fuse to be blown. The key points should be to check the rectifier diode of the power supply, high-voltage filter electrolytic capacitor, inverter power switch tube, etc., check whether the components have 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 the switch tube for short circuit.

It is necessary to pay special attention to: When it is found that a component is damaged, it cannot be directly turned on after the replacement. This is very likely to damage the component due to other components still malfunctioning. It is absolutely necessary to carry out a thorough inspection and measurement of all the high-voltage components of the above circuit in order to completely eliminate the fault.

2) No DC voltage output or unstable voltage output

If the fuse is intact, there is no output of DC voltage 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, excessive power load, rectifier diode breakdown in high frequency rectification and filtering circuit, filtering Capacitor leakage 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 may cause an unstable output voltage. Statically measure the corresponding component with a multimeter to check the damaged component.

(3) Poor power supply capacity

The poor load capacity of the power supply is a common fault. It usually occurs in a power supply that has been aging or has a long working time. The main reason is that the components are aging, the operation of the switch tube is unstable, and heat dissipation is not performed 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. (Related Article: Common quality problems with power adapters)