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  1. #1
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    transistor current limiter

    I'm driving a load with a pnp transistor. The current is 1A max, the voltage is 24V. I want to turn off the output above this current but i don't want to use a power resistor and do not want to use a complex circuit. Can you suggest me simple yet effective current limiting scheme for this task without using a power resistor? Thanks.

    •   Alt28th May 2009, 08:31

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  2. #2
    FvM
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    pnp current limiter

    A current sense resistor is obviously needed, unless you can rely on a only roughly known transistor current gain.

    A simple circuit uses Vbe of an auxilary transistor as threshold, it has to accept e.g. 0.5 V voltage drop in normal operation. More complex circuits are sensing the current by a lower valued resistor and an OP or a current mirror.

    You should also consider, if simple current limiting is appropriate, cause the output transistor must be able of handling high dissipated power permanently. Bistable electronic fuses are sensitive to inrush currents and also need a reset signal.



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