voltage regulation using TL494

[anshuii]

I am using the given schematic for voltage regulation using TL494. When feedback is not given, that is point A and B are not connected, then I am getting a pulse of 35% duty cycle of 0-12V. But when the feedback is given ( A and B gets connected), then in the output I am getting a 12V DC rather than a pulse even though the positive and negative terminal of error amplifiers have some difference of voltage and there's a sudden large amount of current flow at point C and D that is the primary side of the transformer. I am not understanding why the pulse is getting vanished with 12V dc and sudden large  increase in current( i. e from 0.8 A to 1.6 A) in the primary side of the transformer circuit . Is there any blunder in the schematic.

[T3sl4co1l]

Use emitter output instead.

Tim

[anshuii]

still the issue remains same

[Alex-lab]

It looks like too high gain for error amplifier (x56). As desired output of 20V corresponds to 2V ref, the 1/10 divider is enough, and further amplification is not necessary.
Try to put 1k resistor instead of 56k (pin3).