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UCC28070: Questions about inductor selection in bridgeless configurations

Kaji@PAN
Mastermind 7280 points
Part Number: UCC28070
Other Parts Discussed in Thread: PMP9640, UCC28051, PMP40261

Hello,

I am considering a bridgeless circuit with UCC28070.
The materials I refer to are SLUA479B and SLUA517.
I would like to ask you about the inductor selection.

(Question 1)
K(DPLL) is no longer considered in the SLUA517 data when calculating ΔIL.
Is it because the inductor ripple current is not canceled because it operates one phase at a time if it is semi-bridgeless?

(Question 2)
If Question 1 is "YES", does the bridgeless configuration increase the inductor ripple current when comparing the normal configuration and the bridgeless configuration with the same L value and output power?

(Question 3)
Is there any reason for setting the inductor ripple content to "0.3"?

(Question 4)
In the calculation formula of the inductor current effective value, SLUA479B has "Pout / 2", but SLUA517 has "Pout".
Please tell me the reason for the above difference.
Is the reason why the bridgeless configuration cannot halve the current because it is a single-phase operation?

(Question 5)
Please tell me the calculation of the peak current of the inductor that is not described in SLUA517.
Considering from equation (17) of SLUA479B, it is estimated that Ipeak = (Pout x √2) / (Vin_min x η) + ΔIL / 2.
As mentioned above, will it be doubled if it is bridgeless?

Best regards,

  • 0
    TI__Genius 9790 points

    Hi, Kaji

    UCC28070 can support 2-phase interleaved PFC and semi-bridgeless PFC. But there is difference between 2-phase interleaved PFC and semi-bridgeless PFC, PFC inductor only handle half of power with 2-phase interleaved PFC, but PFC inductor need to handle full power with semi-bridgeless  PFC. So Q1 and Q2 and Q4 can be answered. 

    Q3: to keep CCM, inductor current ripple should<2，othervies it going to CRM or DCM. Becuase PFC is hardswitching topology, if current ripple is small, the turn off current of PFC MOSFET is small which can improve efficiency.

    Q5: Peak current of inductor is related to power and current ripple, so the formula of Ipeak = (Pout x √2) / (Vin_min x η) + ΔIL / 2. is correct for bridgeless PFC. Pout/2 should be used in 2-phase interleaved PFC.

    Yunsheng

  • 0 in reply to Yunsheng Qu
    Mastermind 7280 points

    Thank you for your reply.
    Regarding Q3, after all, if I make a semi-bridgeless configuration, do I have to increase the inductor constant to increase the size?
    If the inductor used in the normal configuration is used as it is, will the ripple current increase and noise increase?
    I am concerned about inductor size and noise in a semi-bridgeless configuration.
    I'm considering a semi-bridgeless configuration to improve efficiency, but I also want to understand the disadvantages.
    Please let us know what you think.

    I've also seen the PMP9640 with UCC28051, how much power is this configuration suitable for?
    This time, my specifications assume 700W.

    Best regards,

  • +1 in reply to Kaji@PAN
    TI__Genius 9140 points

    Hi Kaji,

    since each PFC inductor need to cover full load at one half main line cycle, so the peak current through each inductor is almost two times compare to interleaved PFC mode. For the peak current requirement, you need a bigger size for PFC inductor.

    your understanding is correct, with bridgeless PFC using UCC28070, the effeciency can increase for about 0.8% at low line input, but you need a bigger PFC inductor, and because of the common mode noise, usually you need clamped diode for EMI.

    PMP9640 is 310W with CRM bridgeless.

    for UCC28070 ccm bridgeless PFC, you can follow PMP40261 which is 800W design.

    Below is the link to the reference design.

    www.ti.com/.../PMP40261