Current limiting circuit


Joined Sep 17, 2013
At low load current (<150mA) Q1 is off and R4 pulls the gate of M1 low, so M1 is on.
When load current exceeds 150mA, the voltage developed across R3 exceeds 0.6V, so Q1 turns on, pulling the gate of M1 high and so turning M1 off.


Joined Jun 4, 2014
Once that current limit is reached if the load resistance is reduced further the current will stay roughly constant and the voltage across the load will reduce and the voltage across M1 will increase. With a short circuit load the full supply voltage and limit current will be applied to M1 so check the rated dissipation of M1.

Also when the current is below the limit the gate source voltage will equal the supply voltage so you must check the maximum gate voltage rating for M1.


Joined Jul 11, 2016
the type of scheme is pretty much impractical with significant currents
because the mosfet develops a high power dissipation in it's linear region /!\ which pretty much in all cases destroys it /!\
. . .
with PWM/PPM(PFM) you just about might "fit in" (to the SOA of the MOS-Fet) . . . requires a bit more complex schematic . . .