modifying a square wave into sine wave


Joined Jul 17, 2007
I bought a 400 Watt sine wave inverter for around $40 US dollars a few years ago.
It would be very difficult to build one for that little amount of money.

Why do you want to try to build one, when you can buy one ready-made better than you can build, and for less money?

The design you used is not good.
The 4017's outputs are overloaded.
The D313's won't supply enough current to the TIP35's bases.
The TIP35's are sharing one base resistor per primary winding; this is not how one parallels transistors.
There are no snubbers, so the transistors will quickly fail due to having their Vce exceeded every time they turn off due to the transformer primary's inductance.
There is no voltage regulation.
There is no current limiting.
It's really quite bad.
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Joined Sep 9, 2010
How can i modify it to get a sine wave?
Or to put it bluntly, you can't.

It's not simple to generate a true sine wave from DC. There are intermediate solutions such as stair-step square waves, RC decay curve waves and such, but a true sine is tough. Especially when you can go buy one purpose-built. Is there a reason you want to build one instead? Are you trying to do a grid tie-in? That's even MORE complex.