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2kW PFC SMPS controller

Marius Marti
Prodigy 30 points
Other Parts Discussed in Thread: UCC28180

Dear all,

I need to design a converter with PFC and the following specifications. Vin 85V - 265VAC, Vout 230VDC, Output Power 2kW.

I am new to the design of SMPS and could need a little help choosing the right controller.

The most important factors for my applications are low cost and low space usage.

Could someone propose a topology and controller that works for that specifications? I already tried to build this using a PFC controller with SEPIC topology, but i can not reach my output specifications.

Thanks in advance for any help.

  • 0
    TI__Genius 14580 points

     Hello,

    If the requirement is Vin 85V - 265VAC, Vout 230VDC, this is not pure boost converter or buck converter. 

    I recommend you can look at UCC28180 CCM PFC controller, and output voltage is increased to 400V.

    Regards,
    Sean

  • 0 in reply to Sean Xu
    Prodigy 30 points

    Hello Sean

    Thank you for your reply. Output voltage of 400V would be much easier, but it must be 230V. Therefore I tried to implement a SEPIC converter but could not get it to run properly under load condition.

    What I could do is to implement 2 different topologies, one boost and one buck. The boost would not be the problem. Could you propose a PFC controller that works fine with buck topology? I am unsure which one would be the most suitable.

    Thank you for your help.

  • +1 in reply to Marius Marti
    TI__Expert 6515 points

    Hello Marius,

    We should divide your problem into 2 stages: PFC stage and DC/DC stage. Trying to do both in one stage in a SEPIC converter may result in poor performance and efficiency so it may be better to use more stages.

    PFC Stage

    The PFC stage's purpose is purely to improve your system's PF. The boost converter is the best solution to improve PF, as you can see through this E2E post.

    Since a boost converter is used, a 390VDC output minimum is required for a universal AC input. The boost converter requires boosting at least x√2. For example, in the UCC28180EVM the input is 85VAC to 265VAC. 265V  * √2 = ~375V so we choose 390VDC for headroom. 390VDC output is a common standard across PFC stages for universal AC input. The UCC28180EVM can achieve up to PF = 0.99.

    At 2kW, we can either choose a single-phase or interleaved CCM controller. A single-phase CCM, such as the UCC28180 that Sean recommended, would be best since it requires fewer components than an interleaved CCM while achieving your power requirements. See the below description on page 1 of the UCC28180 datasheet:

    The TIDA-00779 is a good reference design that applies to your system. 

    DC/DC Stage

    Now that we have a high PF, we need to focus on the DC/DC conversion. Our input will be 390VDC at 2kW. An output of 230VDC at 2kW (~8.7A) is quite high so this will be a challenge. A buck converter may work but typically isolation is used since we need protection at such a high power level.

    Most of our high power AC/DC converters use a PFC followed by a PSFB that leads to a low voltage output. For example, the PMP8740 uses a PSFB to convert the 390VDC to 32VDC at 2kW. Is your 230VDC output a hard requirement? If not then I would recommend a PSFB controller as your DC/DC stage, such as the UCC28951. 

    Regards,

    Jonathan Wong

  • 0 in reply to Jonathan Wong
    Prodigy 30 points

    Dear Jonathan

    Thank you for your elaborated answer. I will try to implement this the next time I need to design a SMPS with this power output. For the moment, I need to create two versions with a boost or buck topology. At this stage of development I am very restricted with the space i have and the costumer wants us to reduce costs.

    Boost will not be a problem, I am more concerned about the buck PFC, do you have any experience with that?

    Regards,

    Marius

  • 0 in reply to Marius Marti
    TI__Expert 6515 points

    Hello Marius,

    A Power Factor Correction (PFC) controller seeks to improve Power Factor (PF) because every circuit has inherent inductance/capacitance that causes:

    1. Voltage and current phase misalignment
    2. Harmonic distortion

    Low power applications (typically <75W) usually are not worth designing a PFC. However, higher power applications, such as yours, will waste too much power without a PFC. There are also standards, such as those set by IEEE or EU, that mandate a minimum PF at different power levels and applications.

    It just so happens that a boost converter is the best way to solve this problem. As a byproduct of using a boost converter, we MUST boost the output voltage, whether we want to or not. Since the world arbitrarily decided to have AC voltages from 110V to 220V, we have an industry standard of 85VAC - 265VAC as the "Universal AC Input". This allows our designs to work across countries. Thus, 390VDC is the typical output of a PFC. This application note is a great introduction to PFC basics and calculation. 

    So, your problem is not an AC/DC:

    • Vin: 85VAC - 265VAC
    • Vout: 230VDC at 2kW

    Your actual problem is a DC/DC:

    • Vin: 390VDC
    • Vout: 230VDC at 2kW. 

    There are other topologies such as a buck PFC or flyback PFC. However, I typically do not see these applications in such high power levels. Notice how in a buck converter or flyback converter the MOSFET is on the direct path from Vin to Vout. This makes them worse for high power PFC. 

    We have flyback PFC converters, such as the UCC28810. However, these applications are typically for much lower power. The UCC28810EVM, for example, is only 110W. 

    We also have some buck PFC converters, such as the UCC29910A. However, this will not work since a buck converter can only reduce voltage. Your output voltage is in the middle of your input voltage range, making it impossible to use a buck converter. Inputting your values into the UCC29910A design calculator shows an impossible duty cycle is required to achieve your design. Thus, your only real solution is to boost to a set high 390VDC and then reduce to your desired 230VDC. 

    Here is an application note on designing a buck PFC if you are interested. 

    Regards,

    Jonathan Wong