problem with sine wave circuit

Thread Starter


Joined Nov 9, 2011
Hello everyone I have a great problem I have been trying to get this sine wave inverter circuit to work for days but cannot i saw it on the internet . It is supposed to produce a near enough sinewave output. Please help me look through the circuit and see where something is wrong please. I await the help of everyone here. Thank u I have upload the circuit here



Joined Jul 9, 2011
What exactly is it (not) doing? Can you provide more details? What's the input voltage supposed to be? What's the transformer ratio?

You have an oscilloscope I assume?


Joined Jul 17, 2007
You found it over on

It doesn't work there, either.

I fooled around with it in LTSpice for a bit, but it wasn't really worth pursuing. It's basically a very parts-intensive way of trying to avoid using a proper PWM switching regulator IC, or a microcontroller. It has no way of regulating the output voltage.


Joined Aug 8, 2005
I am not saying this is a quality circuit, however:

One problem is that both Vcc and Vss on U4 are connected to +8V. C11 should go to the Vcc pin, but Vss should be connected directly to GND.

Theoretically, voltage regulation comes from the R20 xfmr feedback. As more load current is required the output voltage will sag, and the voltage at U3A (-) will drop; this will create a wider pulse width that generates a higher output voltage.

Also, I'd replace the snubber R18/C12 with reverse diodes across each primary (cathodes to V+), and add a pair of snubbers across Q3/Q4. Note that values are not given for C12/C13.