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PMP21366: PFC and LLC Resonant Converter Reference Design Help

Mustafa Yuce
Prodigy 125 points
Part Number: PMP21366
Other Parts Discussed in Thread: UCC256302, PMP21683
Hi All,

I am working on a design which is based on a TI Power Reference Designs and I was wondering if you can help me out with the some issues that I am facing.

I am using PMP21366 - 700W PFC reference design, alongside with PMP21683
- 550W resonant converter reference design. I have prototyped the PFC
design and resonant converter design and connect them together. At first
glance the operation looked pretty straight forward under no-load
conditions! During testing and validation, I have attached and external
load resistor to resonant converter design to consume constant current
of 7Amps, after 30 seconds, system tripped the RCD.

Everything on the PFC board seems undamaged and I have replaced the MOSFETS and Diodes on the PFC design but I am still having issues, such as 10 Ohm Resistor is getting damaged when I apply power to the system.
I have checked the component parameters as well, to make sure that I am not operating the PFC in a single stage. I have used the RVCC provided by UCC256302 for PFC VCC as well.
 
Regards
Mustafa
  • 0
    TI__Expert 4740 points

    Hi Mustafa,

    What is RCD stands for?

    The 10ohm resistor (R808 on PMP21366) is used to handle the surge power before relay is turned on.

    If relay is never turned and there is heavy load at the output of PFC, then the 10ohm resistor will be burned open.

    So the first thing you might want to check why the relay isn't turned on? Maybe you have too heavy load on RVCC?

    To reduce the surge stress, we generally set the power on sequence to be 

    1. Start PFC first.

    2. When PFC output voltage >380V, we let LLC start to switching.

    So please make sure you have BLK resistor divider of UCC256302 set to turn on LLC at around 380V.

    Let me know if you have any additional information to share regarding the issue you have.

    Regards,

    Sheng-Yang Yu

  • 0 in reply to Sheng-yang Yu1
    Prodigy 125 points

    Hi Sheng-yang,

    Thanks for your response, RCD is the residual current protection , in terms of high earth leakage cuts the power off.

    In regards to sequencing, I am not using RVCC from the UCC256302 to power the PFC, currently I am using an isolated High Voltage DC-DC converter to generate the 12V to power the PFC.

    Currently LLC programmed to start switching 362V, based on the PMP21683 reference design values.

    What would be the ideal way to do sequencing, Is it a better option to run the PFC straight from the RVCC of the UCC256302? or Run the PFC and LLC stage from external DC-DC converter?

    I can forward the design files that I have put together for you to have a look as well.

    Hope to hear from you soon

    Cheers

    Mustafa

  • 0 in reply to Mustafa Yuce
    TI__Expert 4740 points

    Hi Mustafa,

    It is better to startup PFC then DC-DC. Doing so, you are allowing a lower startup current stress. UCC25630x or UCC25640x RVCC is designed for this purpose. Once AC input is provided and VCC reaches 26V level, RVCC voltage is generated to power up PFC controller for PFC to boost. Once PFC boost to a level above UCC25630x BLK setting, LLC DC-DC start to operate.

    If you are using external VCC, you should still keep the same sequence: PFC first then DC-DC.

    Please note that PCB layout for both UCC2806x and UCC25630x are critical. If the circuit isn't worked as calculated, please double check if your layout is optimized.

    Regards,

    Sheng-Yang Yu