PMP9656: DC_DC Converter isolated issue at output side flickring

Hi Ashish,

Are you using the same MOSFETs from the original PMP9656 design, or did you use a substitute?

thanks,
Brian

Hi Brian

Thanks for your response.

Due to shortage issue UCC27511DBV this part no i have not used for Mosfet driving, i used alternate for the switching as per below part no 1EDN8511BXUSA1.

All are same i have used part no.

Hi Ashish,

It looks like the substitute driver should be OK.  Did you use the same layout as PMP9656?  Which parts are getting hot?

Just to be clear: all other parts (except the driver) are the same as used in PMP9656?

thanks,

Brian

Hi Brian

I have used same layout as PMP9656.& Except the driver all parts we have same used in layout.. I am facing issue of heat  in MOSFET & Transformer  & temperature rise above 100 degree.

After 2 hour MOSFET goes to short due to heating .

Thanks & Regards

Ashish

HI Brian

PMP9656 input voltage is Upto 60VDV , but we are checking operation at 82V .

heating issue is coming after 65VDC.

May i go uptp  82VDC in PMP9656 because showing was there upto 60VDC.

Hi Ashish,

PMP9656 was not designed for 82V input.  I am concerned that the SR FETs might be avalanching.  Can you capture a scope picture of the Vds voltage on Q1/Q2 and Q4/Q7?

thanks,
Brian

Hi Brian,

I was seeing the transformer input voltage in PMP9656 upto 60V .  if I change the transformer upto 84VDC Max. so design PMP9656 will execute or not

.what are your suggestion if i change the transformer i put the max upto 84VDC .

Thanks & Regards

Ashish

Hi Ashish,

You should be able to use the same transformer for up to 84VDC input, but you might need to change some of the FETs.  Can you check the voltage stress on each FET with 84V input?  Make sure the scope probes are not bandwidth limited when you make the measurement.  You might need to increase the voltage rating of Q4/Q7 to 80V or 100V.  Q3/Q5/Q6 voltage rating might need to increase to 200V.

thanks,
Brian

Hi Brian 

Our team is testing as you suggested voltage rating should be increase. will get back to you.

please suggest in PMP9656 how overcurrent resistance set in this design .

Thanks & Regards

Ashish

Hi Ashish,

If the CS pin voltage reaches the 0.48V (typical) level or 0.43V (min), it will initiate pulse-by-pulse current limit.  The voltage on this pin is equal to the output current multiplied by the turns ratio of the power transformer (T1), the turns ratio of the current sense transformer (T2) and the current sense resistance R5.  Also, the output inductor ripple current, the magnetizing current and slope compensation will add to the CS pin voltage. 

Typically, we pick the current sense resistance set the peak CS voltage to be around 20% below the 0.43V min level at maximum load.

regards,

Brian