Today, the editor saw a problem that we may encounter in actual applications: When PMOS is used as a high-side switch, damage failure will occur when high current is turned off.

 The input side of this circuit is a 15KW rectifier module, and the output side is connected to an 8 Ω fixed load resistor. The rectifier module can adjust the output voltage and current.

The test found that when the rectifier module output was 40V/5A, 48V/6A, 56V/7A, and the no-load was 100V/0A, 48V/0A, and 56V/0A, the PMOS switch was normal. However, when it was set to 64V/8A (no-load 64V/0A), the PMOS could be turned on, but short-circuited when turned off. After replacing the PMOS, it was set to 80V/10A, and it was still short-circuited when turned off.

Why does this malfunction occur?

This short circuit failure may be caused by overcurrent or overvoltage of PMOS. Under high load, PMOS needs to withstand large current and voltage, and it is easy to fail if the rated value is exceeded. As a high-side switch, if the current cannot be quickly cut off when the PMOS is turned off, it may turn on again and cause a short circuit. At the same time, if the driving circuit cannot provide enough current and voltage to drive the PMOS, it will also cause its switching to be abnormal.

So how to solve this problem? You can use a PMOS with higher power and current ratings to enhance its load bearing capacity. You can also add overcurrent and overvoltage protection circuits to the control circuit to add a layer of "protection cover" to the PMOS. In addition, you must ensure that the parameters of the drive circuit and PMOS are matched, so that the PMOS can work properly.