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UCC2805: ucc2805

Sammi Shang
Expert 4450 points
Part Number: UCC2805

Dear team,

Customer has several question about ucc2805:

1. As the start-up current is very small, R491 should be tens of K Ohm, but I found that only Vin 12V, R491=2k that the system could power on normally. But if R491 is small, the auxiliary winding could not supply power to VCC.

2. Currently in the schematic, there are independent auxiliary winding to power supply for VCC. Could customer use 10V connect to VCC through diode to decrease a winding?

3. What about the recommend voltage for auxiliary winding?

Thanks.

Best regards,

Sammi

  • 0
    TI__Guru 72955 points

    Hi,

    Can you remove R481 and R482? These two resistors are most likely the cause to ask a small resistance of R491. You need to design the aux voltage correctly, but if you wan to be sure, you can add a zener say 9V at location of R482 so to make sure VDD < 11V by specs.

    Yes, you can use a 10V to bias the IC.

    If you want to have an aux, its voltage should be about 7 V to 9V.