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UCC24612: Recommendation on Depletion Mode MOSFET

Part Number: UCC24612

Hello,

Could you please provide any guidance on selection of the depletion MOSFET shown in Figure 34  circuit?  

Thank you, Keith

 

 

 

  • Hello Keith,

    I am not sure how this circuit is supposed to work.  You will start at Vgs = 0V which will charge VDD but as VDD charges and Vgs becomes more negative it will pinch off.

    There is an application note that explains how to extend the voltage range of the SR drivers.  You can find it at the following link.

    Regards,

    Mike

  • Here are calculations for a depletion mode MOSFET:

    Vds needs be rated for Vout +Vinmax*Ns/Np

    The VDD pin will regulate at roughly 9.4 V (Vreg) with this circuit.

    The current when Vg is shorted to the source of the depletion mode FET needs to be.

    Ids > 2*(IVDDrun  + Qg*fsw), estimation on 50% D,

    Example of a 100 kHz design driving a 10 nC of gate charge.

    Ids > 2*(1.5mA + 10n*100kHz) = 5 mA.

    The power dissipation of the UCC24612 =  Ids*Vreg = 23.5 mW.

    The power dissipated by the JFET.

    PJFET = Ids*(Vout +Vin*Ns/Np – Vreg)*(Duty Cycle)