Electronic – Operation of the current limiter circuit

current-limitingpower supply

I have been trying to understand the current limiter circuit design. I am having problem decoding them. Could anybody help me understanding this circuit?

Here I_VCC_AUX is 12 V and R247 comes from a monostable multivibrator circuit and the output goes to actuator.

schematic

Best Answer

Note the red arrows I've added: -

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Because there will be approximately one forward diode drop (0.6 to 0.8 volts) across R243, there has to be a current flowing through R243 that cannot exceed approximately 0.7 volts ÷ 0.5 Ω = 1.4 amps. Hence the circuit current limits at about 1.4 amps.

The signal into R247 is used to turn off the pass transistor i.e. it acts like an enable input.