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current limiter/breaker

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dima_a123

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Hi all,
I need help designing a special circuit.
The circuit is basically should monitor a current to the load and break the supply once the load consumes more than maximum current.
The circuit should retry to connect to the load after programmable time period.
I've manage to build only a partial circuit - it monitors the current, when overcurrent occures - it disconnects the load, but never restarts, so the circuit is basically latched and can be released only when I disconnect the supply voltage.
is there any other way to build such a circuit?
I found a popular "emiter follower current limiter design", but the MOSFET gets very hot and can't be use with high power loads.
I have to use only discrete components, no ICs (this is the basic demand)
 
I believe if you add an NPN transistor from the base of Q1 to ground, you can reset the limit circuit by momentarily turning the transistor on.

You will then need to build some type of one-shot timer circuit to momentarily pulse the transistor.
 
you could also use a foldback limiter similar to the pdf below. the limiter will begin dropping voltage (all the way to zero if need be) when the current limit is reached. once the fault is removed the voltage will return to normal. no need for a timer circuit. the MOSFET and regulator should be heat sinked.
 
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How much voltage drop can you tolerate at the point just before the circuit trips?
What is the desired current limit?
 
you could also use a foldback limiter similar to the pdf below. the limiter will begin dropping voltage (all the way to zero if need be) when the current limit is reached. once the fault is removed the voltage will return to normal. no need for a timer circuit. the MOSFET and regulator should be heat sinked.
The advantage of the hiccup circuit, of course, is that it dissipates little power and so likely doesn't need a heat sink. So the tradeoff is an added timer versus an added heatsink.
 
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