Active Current Limit

A Nifty Circuit !

This circuit offers active current limiting, without the associated complicity expected. Tried and tested, it works like a dream. The transistor begins to switch on when it's 0.55V threshold is exceeded, trimming the gate voltage down to where the voltage over the sensing resistor limits it.

Applications could range from LED current limiting to active current control for dc or stepper motors.
A higher supply voltage for stepper motors would gain extra speed without the risk of overcurrent.
Note that the drive signal does not have to be PWM, it could be just a 0 ro 1 to the gate also.

Remember if you switch the FET with DC, the FET will be in linear mode when current limiting occurs,
so watch the wattage in the FET ! It is less of a problem in switched (PWM) applications.




The original circuit was submitted by David from Auckland, New Zealand.