viper25

sam_niraj · ‎2011-11-08

Posted on November 08, 2011 at 11:01

In my design iam using Viper25DTH.

My o/p power is upto 6W i.e. 4.1V@1.5A.

But whenevr i am ging 1W load, the voltage on VDD pin starts to oscillate between 4.5V to 15V and feedback voltage is upto 3.4v, it seems that OLP protection is on at this stage.

I have selected Rlimt=18K

Rovp=100K

Rff=1000K

I have done many iterations to achieve o/p but invain.

Please suggest

#urgent

mallik.ranajay · ‎2011-11-14

Posted on November 14, 2011 at 14:28

Hi Niraj,

Can you tell me :

1) What is the switching frequency at no load?

2) What is the core that you are using and how many primary turns and value of primary inductance?

This information may help throw some light.

Best regards,

Ranajay

sam_niraj · ‎2012-01-03

Posted on January 03, 2012 at 11:34

Sorry for the very late reply.

I have solved the problem.

I have coming up with a new problem.

1. Earlier my design was for isolated smps, but i need to make it to non-isolated smps.

For this i replaced the opto from circuit and directly connected the output of TL431 to FB pin of viper 25.

With doing this my line regulation becomes very poor.

I am not able to trouble shoot the problem.

Primary inductance :1mH

E20 core

Switching frequency at no load under above mentioned condition is 28Khz.

Please help