I am in need of a high voltage supply, capable of 15mA at around 200V for a valve/tube preamp. This supply has to be low noise and any switching noise kept out of the audio band.
The incoming voltage is 24V.
After a little time, I decided to try a boost converter circuit, the switching done with a 80kHz PWM signal from an Arduino, trying at low voltages for testing.
My first attempt at controlling the voltage via feedback was to simply switch on the PWM signal if the voltage fell below the threshold, and off if was above. This resulted in unacceptable ripple and audible noise on the output.
The second attempt was to vary the duty cycle. This was much better, but I wondered if I could do better with a more simple and more 'analog' way of implementing feedback.
This is what I came up with:
This seemed to work quite well and noise was kept to a minimum. Best of all, it's super simple!
The only thing I don't like is it only takes 600mv(ish) to start attenuating the signal, meaning a large voltage divider.
I know I could get lots of different ICs to do this for me, but I prefer a challenge and designing my own gives better control and flexibility.
Is this a good approach? If so, why do we not see this more often?