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# UCC24636: UCC24636

Part Number: UCC24636

Hi Sir：

I use the ucc24636 as auxiliary power controller, Vout =12V.. And  I use the excel UCC24636-Calc to set the external resistance. I have a resistor Q1 in parallel  and Q1 is 1200V MOSFET.  it Out of work,The Vout  i can get 12V. and when i make the DRV float. This pin no single out.

• Hello Lei,

Thank you for using the UCC24636 synchronous rectifier controller. I’ll try to help you solve your problem using it.

You say that Q1 is a 1200-V MOSFET. That is a very high rating for a 12-V output. The on-resistance will be very high and efficiency will be low. Is that a typographical error (do you mean 120-V MOSFET)?

If I understand correctly, your circuit produces Vout = 12V but the DRV output of the UCC24636 has no signal. Is that correct?

I have entered into the design calculator the same numbers that you posted.
The results are:
R15 = 853.64K (use 845K or 866K)
R16 = 10.0K
R17 = 894.14K (use 887K or 901K)
R18 = 49.9K
R19 = 17.22K (use 17.4K)

Are these the resistor values that you are using in your circuit?
Are these resistors connected properly according to the schematic diagram?

Can you please provide oscilloscope waveforms of these signals (2 or 3 cycles):
a. Drain voltage of Q1
b. Gate voltage of Q1
c. The VPC signal at pin-1 of the UCC24636
d. Vout
All signals with respect to output GND.

If there are any differences in your schematic compared to the posted schematic, please let me know.

Regards,
Ulrich
• Hello Lei,

It has been about a week since I've replied to your posting. Has my response helped you to resolve your issues?

Regards,
Ulrich
• Hello Lei,