SMPS flickering prblem

Posted by: sankalp.gitaje on 01/28/2014

Hi,

We have designed 50W smps using TOP271JX. In some smps we observed problem that smps output gets on & off continously(once in second). Most of the time this problem observed @ hige side voltage i.e. above 230Vac.

Our observation is smps which are going in thermal shutdown that have flickering problem. i.e TOP switch IC derating. when we replaces TOP switch and fitted it with clip on heat sink the same smps works fine.

Comments

Hi,

Basically what are you saying is that you will need the heatsink for the power supply design. What is the question then?

Hi...

Thanks for reply.

I want to confirm that flickering problems occure when IC not properly mounted with heatsink? and TOP Switch IC derating beacase of same??

Hi,

I will not say this is a problem, the IC is actually doing the right thing, it is protecting the power supply when the heatsink is not correctly mounted.

We have monitored waveforms at control pin of flickering smps we observed IC going in auto restart mode.

After replacing the IC same smps works fine. What will be reason for Top switch IC going in auto restart mode??

Hi,

Here is the information from the datasheet:

Auto-restart limits power delivery to <3% during overload faults

Output short-circuit protection (SCP)
Output overcurrent protection (OCP)
Output overload protection (OPP)

Accurate thermal shutdown with large hysteresis (OTP)

Thanks for reply.

As mentioned in datasheet we have checked flickering smps for SCP,OCP and OPP and we not found any problem related to this.

Hi,

Sorry for my misunderstanding, I thought you want to know what will cause the IC to auto restart mode.

So to make it clear, this is the situation: You put one IC on the board, with correct heatsink mounted, the power supply went to auto-restart mode. After you replace it with another IC, the power supply is normally funtional. Is this right?

If it is right, would you put the first IC on another working board, make sure the heatsink is well mounted, see if the power supply is working correctly.

Thanks