Electronics > Power/Renewable Energy/EV's

Flyback converter voltage stability issue

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Ravi Kumar S:
I have designed flyback convertor using pi expert, the output is 5v and 12v both are isolated output. 5v has control circuit using TL741 shunt regulator. The problem is i can only get 12v when 5v consumption is 300mA. If 5v rail is 1A or above 12v rail will be above 18v. Please anyone help me to understand the mistake and fix the issue. It’s my first try. I have attached schematic image for reference

Someone:
No mistake, only cross-regulation

nctnico:
What happens if you load the 12V rail with a couple of hunderd mA? Goes it back into regulation? What you see on the output might be caused by the transformer pushing a little bit power into the 12V output due to the leakage inductance. If there is no load on the 12V, the output will rise.

mtwieg:
These sort of multi-output flybacks typically don't regulate well with very light loads. Light load cross regulation is mainly a function of coupling between the output windings, IIRC.

Poor cross regulation with high loads is more likely because of transformer secondary resistances (and possibly poor transformer coupling as well).

Can you share details on your transformer construction?

Ravi Kumar S:
Thank you for support. That is the problem it was designed to provide upto 4A. But it not stable. If i drive 5V at 200mA 12v output with 1A. 5v is table and 12v become 11v with 1A.

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