Hi all,
I have designed a circuit to digitally and proportionally cpntrol a heater. The circuit works fine however the problem i am having is with the frequency of the PWM signal. The circuit opperates as follows;
the pic takes a variable voltage input of 0-5V and converts that to a propotional PWM output. This output is put thrugh a FET that triggers an optoisolator which in turn fires a thyristor to control the AC mains supply to the load. My problem is that i cannot get the PWM signal at a low enough frequency for full control (it sits at arround 250Hz). This is a problem because as we know AC mains is at arround 50 HZ so any control signal with a frequency above this is will work, but only randomly so the control is pants. I have been using the mikroC compiler as it has a very user friendly PWM library. I understand that the PIC12F683 has selectable clock frequencies that go as low as 31.25Khz. With a clock this speed i have calculated that i should be able to get a PWM signal as low as 3 HZ however i do not know how to select the different frequency ranges...
I have looked through all forums and have found it is possible to create a lower PWM frequency using timer interupts. however i have limited programing experiance so any guidence on how to do this would be greatly appreciated.
Thank you for any help in advance
I have designed a circuit to digitally and proportionally cpntrol a heater. The circuit works fine however the problem i am having is with the frequency of the PWM signal. The circuit opperates as follows;
the pic takes a variable voltage input of 0-5V and converts that to a propotional PWM output. This output is put thrugh a FET that triggers an optoisolator which in turn fires a thyristor to control the AC mains supply to the load. My problem is that i cannot get the PWM signal at a low enough frequency for full control (it sits at arround 250Hz). This is a problem because as we know AC mains is at arround 50 HZ so any control signal with a frequency above this is will work, but only randomly so the control is pants. I have been using the mikroC compiler as it has a very user friendly PWM library. I understand that the PIC12F683 has selectable clock frequencies that go as low as 31.25Khz. With a clock this speed i have calculated that i should be able to get a PWM signal as low as 3 HZ however i do not know how to select the different frequency ranges...
I have looked through all forums and have found it is possible to create a lower PWM frequency using timer interupts. however i have limited programing experiance so any guidence on how to do this would be greatly appreciated.
Thank you for any help in advance