current limiting circuit

Thread Starter

Matthias98

Joined Mar 14, 2020
12
Hi
I am trying to design a current limiting circuit to power an RGB LED array.
Can somebody tell me if this circuit will work and if it doesn't how to improve it.
I planed to control the colors with an Arduino and three mosfets.
Thank you for helping me.
Matthias

Current limiter.JPG
 

AlbertHall

Joined Jun 4, 2014
9,670
You need to swap the values of R3 and R4 and swap the connections to pins 1 and 3 of the opamp (as drawn you have positive feedback) but apart from that it looks good to me.
 

crutschow

Joined Mar 14, 2008
24,756
If you want to control the current with a ground based signal from an Arduino, then I suggest moving R2 between the MOSFET source and ground, and connect the (-) op amp input to the junction of the two.
The current will then equal the input voltage to the (+) op amp input divided by the value of R2.

That connection also minimizes any instability/oscillations due to the added open-loop gain the MOSFET adds in the original circuit.
 

danadak

Joined Mar 10, 2018
4,057
Between OpAmp output and input to MOSFET gate should have something like
100 ohms to kill the Cload on OpAmp. Or make sure the OpAmp is speced
as stable with a Cload = MOSFET gate C.

Note the phase margin of that OpAmp is speced at 100 pF, all the more reason
to use a R in series with gate to decouple all the gate C. Otherwise you will have
a great oscillator.


Regards, Dana.
 
Top