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Original question:

TIDA-00779: Current Limit Resistor Bypass Circuit Equation for 0.2s calculation and other Queries

TIDA-00779: TIDA-00779 Inrush Protection Circuit Reference Design Circuit for PFC 3.3kW.

Meet Pandya
Prodigy 60 points
Part Number: TIDA-00779


Dear TI Expert,

Please let me know the purpose of the D9 Diode in Series. Also, if we provide the PFC ON the initial, then this Inrush-Limiting circuit won't generate a delay, right?
Also, 1K (R39), 47.5k (R31), and D10 are used. Why? The diode might be for protection, but what about the 1k and 47.5k resistor roles? Please Explain.

Thanks & Regards,
Meet Devendra Pandya

  • 0
    TI__Intellectual 2320 points

    Hi,

    If the input line voltage is 265Vrms, the peak voltage of R27 will reach to 89V, which is much higher than the maximum Vgs of Q5 and Q3. So we need D9 and D10 to protect MOSFET.

    It is not recommended that providing the PFC ON the initial 12V, because the PFC ON port also controls the relay. We need to wait the output capacitor reach to a high voltage and then turn on the relay to limit inrush current.

    I see in the latest version schematic, R39 is 20kΩ, and 1kΩ is also OK. R39 and R31 are used to control the Vgs of Q5. A higher Vgs can reduce the on-resistance of the MOSFET.

    BR

    Jim

  • 0 in reply to Jim Chen (SEM)
    Prodigy 60 points

    Hi Jim,

    Thanks. You suggested that a PFC ON switch is required and should be ON afterward once DC is built without boost switching, right?

    Also, can you please share the latest schematic link or pdf so that we can know the 20k ohm and 1k ohm for R39 and R31 instead of 47.5k ohm and 1k ohm? as per our reply?

    Thanks & Regards,
    Meet Devendra Pandya

  • 0 in reply to Meet Pandya
    TI__Intellectual 2320 points

    Hi,

    Meet Pandya said:
    You suggested that a PFC ON switch is required and should be ON afterward once DC is built without boost switching, right?

    Yes, you would better turn on the AC power source, wait for stable DC bus voltage, and then turn on the PFC ON.

    Meet Pandya said:
    Also, can you please share the latest schematic link or pdf so that we can know the 20k ohm and 1k ohm for R39 and R31 instead of 47.5k ohm and 1k ohm? as per our reply?

    You can find the latest schematic in https://www.ti.com/lit/df/tidrka5/tidrka5.pdf?ts=1707188800776

    R39 is 20kohm and R31 is 47.5kohm.

    BR

    Jim