What are the vulnerable components and faults of switching power supply?

Nowadays, many failures in electronic circuits are caused by the failure of switching power supply, and most of the common failures of switching power supply are caused by the damage of some spare parts.

For example, the switching tube in the switching power supply, habitual damage, but the switching transformer, damage probability is very small! Basically be able to ignore.

Therefore, switching power supply manufacturers share a summary of some easily damaged components in switching power supply, and what failure conditions occur after damage, and share with everyone.

1. Fuse tube

Burn commercial insurance is mostly caused by the large current flow of the power supply circuit, in other words, the power circuit behind the short circuit fault, such as the switch tube, current limiting resistance, bridge pile burn short circuit fault, integrated ic damage, large filter capacitor damage these are caused by burn commercial insurance, the fault condition is no reflection of the power supply. (Warm reminder: if you change the fuse tube, do not need to connect the power supply detection, must find the fault or adopt certain countermeasures before connecting the power supply)

2, filter capacitor damage (300V capacitor)

When the filter capacitor is powered off or the volume is reduced, it will lead to stuck or no response when starting. The damage of the filter capacitor is generally visible from the appearance of the capacitor pack. (Of course, you can't afford it.)

3. Output filter capacitor: The fault condition is similar to the bad filter capacitor.

4. Switch tube

The first point said, after the switch is damaged, it will generally burn commercial insurance, current limiting resistance will also follow the damage, and in some cases even PWM integrated ic will also follow the burn (but this is rarely the case).

Even though the fuse tube is burned, the fault situation is no doubt connected to the power supply.

5, voltage regulator diode.

In the diode bearing the opposite direction of the voltage exceeds its tolerance of the regulator value, the regulator will reverse direction of thermal breakdown, but this kind of thermal breakdown can be repaired, that is, after the voltage value is reduced, the regulator will get rid of the thermal breakdown situation, equal to the lead. If it is a short circuit fault, then the regulator has already been damaged, and the current flow exceeds the voltage regulator to bear the current flow, which is a breakdown and cannot be repaired.

6. Lotus root and TL431

The damage of these two components will generally lead to unstable output voltage or no voltage output. How to check it has been introduced in professional detail in my previous article (the damage of sampling resistance will also lead to similar problems).

7. Starting resistor:

The starting resistor is connected to the 300V switching power supply and the base of the switching tube. The damage of the starting resistor will lead to 300V, but there is no voltage output, and the whole equipment has no reaction.

8. Current limiting resistance:

To put it bluntly, the resistor damage overcurrent protection circuit work, and starting resistor 300V no output voltage.

9, PWM control integrated ic:

PWM damage will lead to 300V, but no output voltage will also repeatedly burn switch tube and commercial insurance, inspection can be hit to distinguish the merits of the ground resistance value, all normal ground resistance value apart from its foot, the other foot is often several hundred ohm.