RCDZ clamp for flyback

Posted by: treez on 12/15/2011

Hello,

I am doing a high power flyback with TopSWITCH-jx.

I wish to use the TVS, LCE28A as part of the RCDZ clamp.....

http://www.vishay.com/docs/88357/88357.pdf

....The datasheet says it can dissipate 6.5W continuously when attached to infinite heatsink.

However, we have virtually no appreciable pcb copper area to solder it to.

So in our case, what is the CONTINUOUS maximum power dissipation of LCE28A?

Comments

Hi,

You can use PIExpert design software to design your power supply. PIExpert gives the BOM and suggested PCB layout as well. You can download the PIExpert design software at following location

http://www.powerint.com/en/design-support/pi-expert-design-software

If at all you want to use some other device for the clamp circuit for a specific reason, you need to calculate leakage energy stored in the transformer. That gives the maximum power that have to be dissipated in the clamp circuit. For more information please go through the TOPSwitch-JX application note

http://www.powerint.com/sites/default/files/product-docs/an47.pdf

In order find out the power handling capability of the LCE28A device, please measure the temperature of the device by passing some current through the device for the given copper area and then look at the power derating curve given in device data sheet.

Regards,

PI-NANO

the problem is that the power derating curve that you speak of concerns the temperature of the leads when the leads are connected to an infinite heatsink.........i wont be able to make a trst set-up like that.....what we need is a graph showing the case temperature and corresponding deratings.

Hi,

You can always find out the power dissipation in the diode by measuring current flowing through the diode and voltage across the diode. Based on the maximum temperature allowed you can find out the maximum power that can be dissipated with out connecting it to a infinite heat sink. If you need the graph, then please contact device manufacturer. They should be able to provide the graph.

Regards,

PI-NANO