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Common faults and troubleshooting knowledge of switching power supply

The common electrical and electronic circuit faults in life cannot work normally. Most of them are caused by the failure of the switching power supply. The switching power supply is composed of a variety of components. The switching power supply failure is generally caused by the damage of individual components. The switching power supply cannot be used normally.

If you want to repair the fault of the switching power supply, you must recognize the overall structure of the switching power supply components and the switching power supply components that are prone to failure and not easy to be damaged, so that the efficiency can be greatly improved when the fault of the switching power supply is eliminated, and a more correct repair Damaged switching power supply components, Mega Power R&D engineers have summarized a variety of components that are prone to failure in switching power supplies, and give beginners a little help

1. Fuse/Wire


The general switching power supply includes the power adapter, the monitoring power adapter, etc. If the fault occurs, the first faulty component to be eliminated is the fuse/wire. In most electronic products, the fuse/wire plays the first safety guarantee for the circuit. The circuit behind the wire is short-circuited, etc., causing the circuit current to be too large, thereby burning the fuse.

Switch tube, current limiting resistor, bridge stack burnt short circuit, chip damage, large filter capacitor damage, etc. These switching power supply components will cause the fuse to burn out, and the fault phenomenon is that there is no response to power-on. After replacing the fuse, the fault of other components must be eliminated before powering on! ! !

2, the filter capacitor is damaged (300V large capacitor)


Failures such as crashing and no response when starting up are caused by leakage or capacity reduction of the filter capacitor. The damage to the filter capacitor can be seen on the surface, and there are also some that are not easy to see.

3. Output filter capacitor: The fault phenomenon is basically the same as that of the filter capacitor.

4. Switch tube

As mentioned in the damage to the fuse/wire, the damage of the switch tube will generally burn the fuse/wire, the current limiting resistor and the PWM chip will also be damaged, but the PWM chip is generally less damaged. Since the fuses are all burned, it is a natural failure. The phenomenon is also no response to power on.

5. Zener diode


When the reverse voltage is greater than the nominal voltage regulation value of the Zener diode, the Zener tube will cause reverse breakdown. After the voltage is reduced, the Zener tube will leave the breakdown state and become an open circuit. If the current exceeds the Zener tube The current value that can be endured will cause damage to the Zener tube. This is called thermal breakdown, or short circuit, which is irreversible.

6. Optical coupling and TL431: Optical coupling and TL431 cause unstable output voltage or no voltage output






PWM损坏会造成有300V,但是无输出电压 还会重复烧开关管和保险,检测时可以打对地阻值来判断其好坏,正常对地阻值除了其对地脚外,其他引脚都有几百欧姆。

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