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Original question:

UCC24630: UCC24630 dead time

UCC24630: UCC24630 dead time

Rock Shao
Expert 2895 points
Part Number: UCC24630

Hi,

My customer used UCC24630 for ACF flyback and on the secondary side high side.

They found the dead time will form 2us~0.5us in High/Low AC input voltage, As a result, the current passes through the body diode of the MOSFET for too long, causing the mos to become hot.

We had to change the Rtblk from 22k  to 47k but it doesn’t work. Is there any other reason for this phenomenon?

The following table was the customer calculations, and I checked with the TI tool also as below

UCC24630_skynet.XLSX

And also found the Vgs not fully turned on after 12% output load.

Red: SR GATE, Blue: SR VDS

  • 0
    TI__Mastermind 31740 points

    Hello Rock, 

    The UCC24630 Excel calculator tool (TI #SLUC582A) is specifically for the "Low-Side SR" configuration, and does not account for the 7/13 Bias:Sec turns-ratio effect on the VPC and VSC voltages, along with some other details.  

    Please refer to this Configuration Guide https://www.ti.com/lit/pdf/slua861 page 4 on modifications to the VPC and VSC resistor value calculations for "High-Side SR with Bias Winding".

    Regards,
    Ulrich