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kubeek 12th February 2009 10:51 AM

Power supply current limit for testing
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I recently designed this circuit to help me when I repair high-power amplifiers, without variac or the classical bulb-protection. This allows to set predictable current limit, which will not be exceeded.

This circuit should be used in series with standard power rails, the power FET limits current to the load. The current is sensed on Rm, then through differential amplifier and another amplification stage it is compared to the preset current limit, which then turns off the FET.

The opamps need some power, so you can add some simple zener regulator to power them from the actual supply.
In simulation the circuit regulates current with PS from 5V (with separate PS for opamps), up to the voltage limit of the two transistors.

The resistors Ra and Rb set the range, PotA and PotB are the two halves of a 10k potentiometer, currently form 0 to cca 3.5A.

Of course you need to build a symetric half for the -rail voltage, because there often are shorts to ground, which the single rail limiter doesn´t necesarily block.

kubeek 12th February 2009 10:57 AM

2 Attachment(s)
And this is the circuit in MicroCap8 if you want to try it in computer :)
BTW, who knows if there is a potentiometer in microcap 8 instead of the two resistors I use?

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