Hello, I am new to the forum but have been in electronics for a number of years.
I am trying to design a voltage-controlled current sink or source. A sink seems more stable and capable of being implemented with least parts count / board space.
Basically, I need to provide "0" to 50mA @ 80VDC, with maximum practical resolution. The load pulses at 10-250uS, with 300-500nS rise and fall times.
What I have done: I have looked at number of both sources and sinks, using either BJT or MOSFET pass transistors driven by an op amp. Since the output voltage is 80, sources seem to me to require floating the op amp, which contributes to stability problems and adds to parts count.
But sources and sinks that I have tested in sim suffer from severe overshoot on the pulse rising edge, because the circuit starts at max current and needs time to respond to a limit. This appears to be confirmed by the fact that overshoot is not seen when the control voltage is set for max current. I have played with a comp cap between the op amp inverting input and output, noting that the width of the overshoot is inversely proportional to capacitance because of its effect on the op amp's output rise time (overshoot occurs during the 'ramp' in the op amp output).
It seems to me that I need a very fast op amp, but I suspect the overshoot will still be present as a spike. That could create problems for downstream current sensing, either making it less precise or more complex.
If someone can point me in the direction of a solution, that will be most appreciated.