i am new to PID theory and circuit design, and I threw this together over a few days.
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the goal is to create a voltage controlled current driver for an LED, where the current is directly proportional to the voltage, i.e. 100mV = 100mA, and the driver is useful up to at least 50khz, including square waves.
what mystifies me is how well adding the 1nF cap worked. without it there was about 15% overshoot (instead of rising to 100mV, it rose to about 113mV).
i tried everything i could think of to make a derivative section, but none of it worked as well as that cap.
so, is this circuit close to being good? what have I done wrong?
Asa