Hi all,

I'm new to the forums and wanted to post my current project for feedback / advice.

I am using an ATmega644p to control the output of an MCP4902 2 channel 8 bit DAC via spi, which I am using each output channel to drive one half of a centre tapped transformer, see attached schematic.



So far everything is progressing, I have a slightly distorted output waveform from my transformer though so that is what I am currently investigating, see attached scope screenshot, the half wave if the - input to one of the op amps and the full wave is the transformer output.



Thanks for looking
Graham

 

I think you would have a hard time finding a piece of equipment that would not be happy with that waveform. It's not perfect but it's pretty good.

Have you looked at the waveform under load?

 

Aren't you using Pulse-Width-Modulation? Your input signal to the opamp is not PWM because it has amplitude modulation.
An opamp is not fast enough for PWM anyway.

Maybe you are trying to feed a halfwave low frequency analog signal to the opamp? Then the amplifier will waste a lot of power making heat.

Here is a PWM waveform. The output devices switch completely on and completely off so they are never linear and do not waste power making heat:

 

Thank Audioguru, using PWM like that is something I had never thought about.

I shall look more into it as heat is becoming an issue already.

 

Hello,

The technique that @Audioguru mentioned is called SPWM.
The following page of the EDUCYPEDIA has some links with infoemation on SPWM:
http://educypedia.karadimov.info/electronics/powercontrolspwm.htm

Bertus