TOP246 failing

Posted by: ratheesh92 on 08/04/2013

Hi ,

I have designed a TOP246 based 36W(12V,3A) supply. Randomly in some boards the TOP246 is failing.

We have a valley-fill circuit infront to improve the pf. Please find the attached sch. Kindly help us to resolve this issue.

Regards,

Ratheesh

Files

V101-sch.pdf (18.05 KB)

Comments

I do not see any wrong in your schematic. Could you please attach the transformer documentation and a picture of the PBC layout?

Do you know the conditions when the device fails? Is it at low line voltage? High line? Start up? Full load?

PI-Worf

HI,

thank you for your reply, Please find the pcb layout and transformer details attached. Failures are random some baords have failed at startup and some boards have failed during load.

Regards,

Ratheesh.K

HI,

thank you for your reply, Please find the pcb layout and transformer details attached. Failures are random some baords have failed at startup and some boards have failed during load.

Regards,

Ratheesh.K

I notice your schematic is showing a TOP244Y and you said your design is a TOP246Y. Is your transformer designed for TOP244Y or TOP246Y?

Please clarify.

PI-Worf

Hi,

Thank you for your reply.

The actual design was for TOP244Y but due to non availability in local market we used TOP246Y , Assuming that 246 is higher rated device. Do we have to redesign the transformer for TOP246Y?

Regards

Ratheesh.K

Rathesh:

You do not need to redesign the transformer but you need to externally lower the Maximum DRAIN current (IDMAX) of the TOP246 to match the IDMAX of the TOP244.

You need to connect a resistor between the pin X of the TOP246H and primary return. This resistor reduces IDMAX and prevents the transformer to go into saturation.

Open your original PI expert file that uses TOP244H as the controller. Notice the values on rows 20 and 21.

Now enter TOP246H in row 17.

Use KI (row19) to adjust row 20 and 21 to values as with TOP244.

Use the TOPswitch data sheet to find the value of the resistor corresponding to your KI vale.

Connect this resistor from X pin to primary return.

When adding this new resistor pay attention to your PCB layout. The node connecting X pin and the new resistor should be very short. The negative node of the new resistor should not be connected far from the SOURCE pin of the TOPswitch. Avoid having a long trace between the resistor and the SOURCE pin.

See the TOPswitch data sheet PCB layout recommendations.

Hi,

Thank you for the great support. I will check this out and get back to you.

With regards,

Ratheesh.K

I think this is the problem, good luck