Analysis of transistor protection circuit!

CcKk

Analysis of transistor protection circuit! [Copy link]

Is there anyone who can help analyze the working principle of this part of the circuit when SW and ground are short-circuited?

qwqwqw2088

Where is the land in the picture you posted?

When pasting a picture, I have to erase part of it.

chunyang

When the current flowing through R14 is large enough, the base potential of Q7 will be low enough to turn on Q7, and then Q8 will turn on, so that the gate potential of Q5 will rise, and the conduction degree of Q5 will decrease until it is cut off and the power is cut off. After Q8 is turned on, it will continue to turn on Q7, forming a self-locking state. At this time, unless the power is turned off and restarted or Q6 is turned on to force the base potential of Q7 to rise and enter the cut-off state, the circuit will continue to cut off the power. However, there is a problem with this self-locking circuit. Once Q6 continues to saturate after entering the current limiting state, in that case, the current limiting circuit will not work, so the reliability of the circuit requires the control logic of Q6 and Q5.