Mosfet heating Up in DC DC converter

[praveen]

Hello Mr. Tony,

Thanks for the reply.

Yes i did. 0.72 W include the total power losses.

Total conduction loss:0.27W
switching loss:
Upper FET: 0.45W
Lower FET: 0.03 W
Gate loss: 0.03 W(upper)+.0075 W(lower)
Switching frequency 250 kHz.
Average current =2A
rise time/fall time=30 nsec

Thanks and regards
Praveen

 

[Tony Williams]

In article <ff8a3afb.0412231746.4de65098@posting.google.com>,
praveen <praveenkumar1979@rediffmail.com> wrote:

Yes i did. 0.72 W include the total power losses.

Total conduction loss:0.27W
Average current =2A.

I think it should be RMS current for the
I-squared*R power dissipation calculation.

Any chance that your lack of heat sink puts the
device into the dRds(on)/dT thermal runaway ambush?

ie, The increase in Tj increases Rds(on), which
increases the power dissipation, and if the heatsink
is inadequate the resultant increase in Tj increases
Rds(on) further, increasing Pdiss..... and so on.

This phenomenon is nicely explained in International
Rectifier App Note No. 942.

--
Tony Williams.