I have previously posted this circuit, asking about RFI, but I have a fundamental problem somewhere.
The resistor in parallel with the zenner is actually 6k8
Testing this with a PSU on the left, and a load on the right seems to work.
Configured as drawn its ok until the power go's up when I see an unstable oscillation when the FET is supposed to be off.
I am reasonably sure the cause could be identified If I could measure it but as the FET's immediately get very hot leaving insufficient time to investigate.
I suspect that the slew rate of the transistor base node is too slow and as the FET turns off the PV voltage climes faster than the base node thus increasing VGS and turning the FET back on again. I am assuming VPV is recovering slowly in partial sun and quickly in full sun.
Does my scenario sound plausible? I am asking because testing it will be hard.
Given that I am aiming for VGS <1v and VGS > VPV-12V is there a batter way to shift the 5V control signal?
I have dropped the PWM frequency to 40Hz for testing and the oscillation is evident for the whole of period.
Basically I am trying to make a solid state relay circuit that can operate with a PWM frequency above 20kHz
I would appreciate comments, good or bad, and should be able to perform any suggested tests in the morning but only if there is enough sun.
I did remove the 223 caps but all that seemed to do was make the switching spikes higher.
The resistor in parallel with the zenner is actually 6k8
Testing this with a PSU on the left, and a load on the right seems to work.
Configured as drawn its ok until the power go's up when I see an unstable oscillation when the FET is supposed to be off.
I am reasonably sure the cause could be identified If I could measure it but as the FET's immediately get very hot leaving insufficient time to investigate.
I suspect that the slew rate of the transistor base node is too slow and as the FET turns off the PV voltage climes faster than the base node thus increasing VGS and turning the FET back on again. I am assuming VPV is recovering slowly in partial sun and quickly in full sun.
Does my scenario sound plausible? I am asking because testing it will be hard.
Given that I am aiming for VGS <1v and VGS > VPV-12V is there a batter way to shift the 5V control signal?
I have dropped the PWM frequency to 40Hz for testing and the oscillation is evident for the whole of period.
Basically I am trying to make a solid state relay circuit that can operate with a PWM frequency above 20kHz
I would appreciate comments, good or bad, and should be able to perform any suggested tests in the morning but only if there is enough sun.
I did remove the 223 caps but all that seemed to do was make the switching spikes higher.