Why Are There Notches Instead of Square Wave Voltage in My Flyback Transformer?

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shom_show
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Hi friends,

I am trying to design a Flyback converter(Vin=15 volts, Vout=15 volts, fsw=140kHz) in general purpose PCB. The Mosfet(IRF510) is being driven from TL494. I have checked that the mosfet is being successfully driven by TL494. But after connecting the transformer(E 16/7/6) in sec side, I observed some notches for usec duration instead of a square wave voltage. I have checked the xformer separately after winding it by giving signal from a SIGNAL GENERATOR, where the output is coming correctly.
Can anyone suggest me any tests that can be done to sort out the cause of the xformer malfunctioning, which will be of great help to me.
Thanks in advance.

Sumanta
 
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shom_show said:
Hi friends,

... But after connecting the transformer(E 16/7/6) in sec side, I observed some notches for usec duration instead of a square wave voltage...

I'm sure you know what you mean , but those words do not paint a picture in my mind.

"notches" ? TL494 does have "dead time" per datasheet.

At 140 kHz a whole cycle is only ~7 microseconds and each half of a square wave is just 3and a half microseconds.
How wide are these usec "notches" ?
 
It would help greatly if you could show a detailed schematic of your setup and, if possible, include a dump of your waveforms. A datasheet (if available) for your transformer would also be appreciated.