PWM signal generation & questions

[salgulsen]

Hi,

I'm using a high voltage power supply which outputs high voltage that is proportional to the input voltage. I've tried to use the hardware PWM function of a PIC16F877A (which has a 20 Mhz crystal) with a SSR which I use to drive a 12 V supply (and which has an on/off time of 0.1 ms). I thought I have to generate a pwm signal which is lower than 5000 Hz just to control the SSR and I thought the minimum PWM freq of the pic is 1220 Hz and it was enough to control the high voltage supply. But high voltage is supplied with 12V and there was very little change with the pwm duty cycle. (in mV scale)

So I tried a 4 Mhz crystal to get a lower freq PWM signal (I could be able to go down to 245 Hz) just to make sure I can control the device. I could manage to get a voltage change between 7-12V that is to be supplied to the high voltage device. But I couldn't manage to scale the whole voltage range.

How can you determine a "required PWM signal frequency" of a device? I'm now trying to find a good PWM frequency that I can change the input voltage in experimental ways. I mean, I generated a PWM signal that is 1220 Hz at first, now I'm using 245 Hz which is not optimum and I don't know how to find an optimum PWM freq.

Any help is appreciated..Thank you!

*Edit : I've found some software PWM algorithms. Deleted the second question