vIPER22a MULTI OUTPUT

[SATENDER]

i am using viper 22A. having three outputs. one output is regulated and other two are non regulated.

I am having below problems

1. i keep fan load of 120mA, output is regulated but as soon as i connect other load , all voltages dips including regulated ones.

2. if i add more load on regulated winding, my voltage drops on regulated ones.

3. if i increase grid voltage beyond 210v, ic enters into some kind of protection. it turns on and off.

 

i have attached the transformer  and circuit diagram.

It will be very helpful if anybody could help

[Peter BENSCH]

Welcome @SATENDER, to the community!

From the symptoms it looks as if the supply is simply leaving its regulation range and the VIPer22A is going into protection / restart.

Key things to check:

1. Transformer design: If the primary inductance or peak current are wrong, the converter will saturate or hit current limit when you add load or raise the mains

2. Cross‑regulation of the three outputs: Only one secondary is in the TL431 feedback loop. When you load the other two windings, the energy is redistributed and the regulated output will also drop. For three independently loaded outputs you normally need post‑regulators or a different topology

3. VDD / auxiliary winding Check VDD at high mains with an oscilloscope. If it goes above the OVP clamp or below UVLO, the VIPer will start and stop periodically (what you see above 210V)

Practically, the easiest way forward is to take an ST reference design for VIPer22A, copy the transformer and feedback network exactly, verify it works, and only then add your extra outputs with very tightly coupled windings.

Hope that helps?

Regards
/Peter

[SATENDER]

Hello peter ! thanks for your prompt reply.

There was mistake from transformer winding side. I changed the winding
polarity, it worked and everything is working fine now.



Why we are not implementing type II compensation network. Please support
with some reference design.

[Peter BENSCH]

At the output power you specified for the flyback, it operates in DCM at 230V and on the boundary between DCM and CCM at 115V, so a type-II network should indeed improve stability. You can start with 22k+10nF (fz~3.4kHz) in parallel to the 10k between Vo and Vref; if necessary, 4.7k+10nF (fz~725Hz) might also be sufficient.

Regards
/Peter