At present, there are many faults in electronic circuits caused by the failure of switching power supply, and most of the common faults of switching power supply are caused by the damage of some wearing parts.

For example, the switch tube in the switching power supply is often damaged, but the switching transformer, the probability of damage is very small! Almost negligible.

So below, I summarize some of the components that are easy to be damaged in the switching power supply, and what fault phenomena will occur after damage, and share them with you.

1. Fuse tube

Most of the burning fuses are caused by the large current of the post-circuit circuit, that is to say, there is a short circuit in the back circuit, such as the switch tube, current limiting resistor, bridge pile burned out short circuit, chip damage, large filter capacitor damage, etc. (Tips: If you change the fuse, don't rush to power on the test, be sure to find out the fault or take certain measures before powering on)

2. Filter capacitor is damaged (300V large capacitor)

Leakage or capacity reduction of the filter capacitor will cause a crash or no response when booted, and the damage of the filter capacitor can generally be seen from the appearance of the capacitor bulging. (Of course, there are also non-bulging ones)

3. Output filter capacitor: The fault phenomenon is similar to that of the filter capacitor.

4. Switch tube

As mentioned in the first point, after the switch is damaged, the fuse will generally be burned, the current limiting resistor will be damaged, and sometimes even the PWM chip will be burned out (but this phenomenon is not much).

Since the fuses are burned, the fault phenomenon must be that there is no response when the power is on.

5. Voltage regulator diode.

In the case that the reverse voltage of the diode is greater than its nominal voltage regulation value, the voltage regulator tube will reverse breakdown, but this breakdown can be recovered, that is, after the voltage value is reduced, the voltage regulator tube will get out of the breakdown state, which is equivalent to an open circuit. If it is a short circuit, then the regulator tube has been damaged, and the current exceeds the current borne by the regulator tube, which is a thermal breakdown and cannot be recovered.

6. Light lotus with TL431

Damage to these two components will generally cause unstable output voltage or no voltage output, how to detect, in my previous article specifically introduced (damage to the sampling resistor will also cause similar problems).

7. Starting Resistance:

The starting resistance is connected between the 300V power supply and the base of the switch, and the damage of the starting resistance will cause 300V, but there is no voltage output, and the whole machine does not respond.

8. Current Limiting Resistor:

As the name suggests, this resistor damages the overcurrent protection circuitry and has no output voltage of 300V like the start-up resistor.

9, PWM control chip:

PWM damage will cause 300V, but no output voltage will repeatedly burn the switch and fuse, you can hit the ground resistance value to judge its quality when testing, the normal ground resistance value in addition to its ground pin, other pins have hundreds of ohms.