A failure of a switching power supply
01 Switching AC power supply
I. Introduction
I have a power adapter that I received on the side of the road when I was eating at noon. According to the information on the front nameplate, it should be a power frequency switching power supply. It should have been damaged if it was thrown away. After opening the case, as expected, there is a switching power supply board inside. Let's see where it is damaged.
▲ 图1.1.1 工频电源内部电路板
2. Internal circuit board
The cause of the internal damage is quite obvious. There was a small fuse blown at the entrance. Cut the outer leads and replace this fuse next. Then retest to see if it still works. Solder off the fuse and replace it with a wire. It can be seen that the fuse has indeed blown inside.
Directly jump the external power line over the fuse and cross the boundary to the input terminal of the rectifier bridge. Use 120V DC to power the power board. It can be seen that the output current is limited. This shows that there is indeed a device short circuit in the input stage, which makes the fuse blown. It can be seen from the power board that the power input circuit is relatively clear. After the input AC power is rectified by the bridge, it is filtered by a capacitor and supplied to the inverter chip to work. Let's rule out the problem of the rectifier bridge first, and cut it off the circuit board. Then the direct current is directly introduced into the subsequent stage circuit.
Then pass through 120V DC for testing. But this time, I felt the sound of chip bursting below, and observed smoke in the circuit board. Observing closely, it can be seen that the inverter chip on the circuit board has burst, leaving an unknown liquid inside. This is also the reason for the smoke. Well, according to the observed situation now, it can be judged that the short circuit inside the chip should cause the power supply to be damaged. At this point, it is impossible to continue to check down.
3. Another circuit board
There is another switch circuit board that I also picked up on hand, and observe that its input fuse is intact. On the face of it, there is nothing wrong with it. Next, apply 120V direct current to him. See the power output indicator is on. Seems to indicate that the board is fine.
The measured output voltage is 12.785V, in line with its nominal output voltage. This basically means that the board is still functional.
※ Summary ※
This article tests a switching power supply and gives a preliminary look at its basic functions.
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