• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 402 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC28180: Bootstrapping start up?

Philip Thackray
Prodigy 80 points
Part Number: UCC28180
Other Parts Discussed in Thread: TIDA-01623, UCC28740, UCC256404

Any ideas on how to bootstrap startup on this part number?  I know that bootstrapping is not recommended on page 36 of datasheet due to limited hysteresis on Vcc.  The PFC is followed by a flyback controller that starts immediately after the 400Vdc is valid.  A winding of the flyback inductor would have a fixed voltage when the flyback transistor is on.  This would provide Vcc for the UCC28180.  I just need to get from line voltage applied to 400 Vdc good.  Any ideas?

  • 0
    TI__Mastermind 27135 points

    Hi Phillip,

    You could do a high voltage linear circuit similar to what was done in TIDA-01623 to power the PFC for startup. Take a look at the section in the schematic labeled "high voltage startup". While this reference design is not using UCC28180 you could do something similar here to bias the PFC controller until the flyback AUX winding takes over.

    Best Regards,

    Ben Lough

  • 0 in reply to Benjamin Lough
    Prodigy 80 points

    Ben,

    Thanks for the suggestion.  I checked out TIDA-01623 and see the start up circuit that you mentioned.

    Also, I found it odd that the UCC28180 data sheet basically stated that a bootstrap circuit would best not be used. How many systems that would use a low power PFC would already have an available 12 or 15 volt DC buss to use in this application?  I found that so odd that I wondered if there was some reason that a bootstrap circuit like the one suggested at TIDA-01623 would not work.  As I spent more time reading about the UCC28180 it seems that a bootstrap circuit will work.

    Thanks again Ben!

    Philip Thackray

  • 0 in reply to Philip Thackray
    TI__Mastermind 27135 points

    Hi Phillip,

    I believe what the UCC28180 refers to as "bootstrapping" is when you tie a resistor string from high voltage down to the VCC pin and VCC gets trickle charged through the resistor string. I believe the reason the datasheet is not recommending to do this is because the hysteresis between VCCon and VCCoff is not very big, only 2V. So the capacitance you would need to place the VCC pin would need to be very big to hold up VCC above VCCoff until an AUX winding takes over. The high voltage startup circuit in TIDA-01623 is a discrete linear regulator with higher current capability so I don't think it will present the issues that the UCC28180 datasheet is highlighting.

    Generally, there is a downstream DC/DC whenever a PFC pre-regulator is being used and for more modern controllers, they may contain integrated high voltage startup capability. UCC256404 and UCC28740 are a couple examples. The idea would be that in the overall AC/DC power supply, at least one of the controllers will have the ability to self-bias and then an AUX winding could take over and provide bias to any controllers on the primary or secondary side. 

    Best Regards,

    Ben Lough

  • 0 in reply to Benjamin Lough
    Prodigy 80 points

    Thanks Again Ben!

    Philip Thackray