Hi,

I design current source to 0-8A for 3ohm load 24V supply.
The circuit has two working mode:
1. Switching between two currents: 0A and 8A. (digital control input)
2. Variable current source 0A to 8A. (analog control input)



The load must be connected to ground and the opamp supply is 5V.
Due to above limitation I use M2 to drive M3.
(Ignore M4, it is option to get 0A/8A without current sense)

It is the first time I use the above configuration for current source, I will appreciate your advice.

Thanks,
Erez

 

Welcome to AAC!
Looks as though it should do the job, providing you have sufficient heatsinking/cooling of M3. Personally I would have chosen a heavier-duty P-FET.

 

I worry that this circuit will not be stable (will oscillate) due to the gain of M2 and M3. If it doesn’t it will probably be very slow to respond to step changes in load or supply voltage. Also interested to see the network R8 - C1. Seems strange values in this position. Basically R8 might as well be a wire link! The IC then becomes an integrator. How did you arrive at these values? Simulation?

 

I worry that this circuit will not be stable (will oscillate) due to the gain of M2 and M3. If it doesn’t it will probably be very slow to respond to step changes in load or supply voltage. Also interested to see the network R8 - C1. Seems strange values in this position. Basically R8 might as well be a wire link! The IC then becomes an integrator. How did you arrive at these values? Simulation?

Hi,

Thanks for your replay.
1. The load is constant 3ohm.
2. The raise time is 100msec (0A to 8A).
3. I use pspice simulation. (I want to have option in the PCB, R8 will probably be 0ohm)

An suggestion How to avoid oscillations?

Thanks,
Erez

 

Welcome to AAC!
Looks as though it should do the job, providing you have sufficient heatsinking/cooling of M3. Personally I would have chosen a heavier-duty P-FET.

Hi,

Thanks,
I will check it out