Hi !
can anyone please tell me what could be the output waveform of these cheap chinese 12V dc to 220V ac inverters which use H bridge and a ferrite core transformer in the circuit
will it be all right to run ceiling fans for an hour from it?
thanks !

 

I don't see any output inductor/transformer, so actually at the output you should have the pwm voltage unfiltered. This is how inverters are built that you use to drive motors (the sine wave current is created because of the inductive load).

I don't think there will be a problem driving fans... The input transformer is there just to convert the input voltage from 12VDC to 155VDC.

 

This is from a 300W inverter simmilar to your circuit & i have used it to drive a fan & it worked ok. Was a little noisier than when on a sinewave.

 

@debe
thanks for the picture of the waveform, looks all right to me

 

debe: Your probe needs adjustment <grin>

(I hate when people tell that to me)

 

The TL494 drives the output bridge, and with Ct being ~150nF and Rt being around 56k to 86k, looks like the output will be in the 100Hz range - so a square wave or modified square wave output.