I've using an LM324 to drive the gate of a MOSFET in a current controlled source.
I'm feeding a 1MSec 2.5V pulse into the + terminal of one of the LM324 op amps. I've got a 0.1 ohm sampling resistor downstream of the MOSFET. It connects to the - terminal of the LM324 op amp. I've used this circuit many times and its always worked well.
Right now though it doesn't work. When the current hits 25 amps the feedback voltage will be 2.5V and the op amp should lower its output. But for some reason it doesn't. If I put a scope on the current feedback I am seeing 5 volts or more ! 50 amps ! And the + input is 2.5V just like it should be. If I put a scope on the output of the op amp, its trailed to the positive supply voltage, 13V in this case. It never moves down from that, even when the feedback current voltage is way above the positive input voltage.
I've swapped in several LM324s with no change in behavior.
What is going on with my circuit ?
Thanks
I'm feeding a 1MSec 2.5V pulse into the + terminal of one of the LM324 op amps. I've got a 0.1 ohm sampling resistor downstream of the MOSFET. It connects to the - terminal of the LM324 op amp. I've used this circuit many times and its always worked well.
Right now though it doesn't work. When the current hits 25 amps the feedback voltage will be 2.5V and the op amp should lower its output. But for some reason it doesn't. If I put a scope on the current feedback I am seeing 5 volts or more ! 50 amps ! And the + input is 2.5V just like it should be. If I put a scope on the output of the op amp, its trailed to the positive supply voltage, 13V in this case. It never moves down from that, even when the feedback current voltage is way above the positive input voltage.
I've swapped in several LM324s with no change in behavior.
What is going on with my circuit ?
Thanks