Hi I have this power supply unit which is 85W . 5V , 17Amp output

I have one resister heating up very much ( R13). It is currently 100 Ohm and 2W.

Can anyone tell me the what is the use of that resister R13 ? can i replace with high wattage resister and would that solve the issue?

 

Looks to me like R13 and C17 are a snubber circuit to protect Q1 from high reverse EMF when Q1 cuts off.

Are you certain that C17 is not leaking? i.e. shorted?

 

Check all electroletics with a good in circuit ESR meter when troubleshooting switching power supplies. This is often overlooked by many when repairs air made. If the tops of any of the electroletics look rounded compared to others, replace them. If the temperature rating is 85 c make sure to replace with 105 c and save your additional repairs in the future.
Good luck !!!!!

 

Looks to me like R13 and C17 are a snubber circuit to protect Q1 from high reverse EMF when Q1 cuts off.

Are you certain that C17 is not leaking? i.e. shorted?

Hi thanks for replying. no its not leaking I have 150 units of these power supply and i have tested 10 of them and they are having same behaviour. looks to me it as a design issue..how to calculate the appropriate value for snubber circuits ?

 

See this link:
"DESIGN OF SNUBBERS FOR POWER CIRCUITS"
http://www.cde.com/tech/design.pdf

 

Here are a couple of pdf snubber articles and a link.

http://www.cde.com/tech/design.pdf

John

 

Same problem with the link this morning, but not last night.

Here is a pdf of the article mentioned by SgtWookie plus another.

John

View attachment 5066

Edit: Previous post was approved by moderator, so removed duplicate pdf attachment. Sorry of the virtually duplicate posts. It seemed those with links in them were being subjected to some glitch.

 

Hi Thanks guys,

I shall handle this issue now... this forum was helpful solving my issue. I would like to thank all of the contributors and creator of this website.