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UCC28700-Q1: Multiple split rail supplies for 3 phase motor IGBT drivers

Element Green
Prodigy 220 points
Part Number: UCC28700-Q1
Other Parts Discussed in Thread: UCC21520, UCC28C41-Q1, UCC28C43, TIDA-00199

I'm working on an open source 3-phase AC motor controller and came across a rather elegant 4 output isolated supply for the IGBT drivers.  However the design is found in the LT3748 spec sheet, which appears to have limited availability.  I would rather use a TI part such as the UCC28700-Q1.  So my question is if this same circuit can be accomplished with this TI part or another TI Flyback controller.

The example circuit uses a 6 tap 1:1 VERSA-PAC VP4-0075-R transformer.  3 outputs for the 3 phase top IGBTs and 1 common output for all 3 bottom IGBTs.

I've attached a schematic of my current circuit design using the LT3748.  I changed the MOSFET to be a FDD770N15A.  I also made each of the secondary outputs split rail supplies using a 15V Zener diodes to create a 15V and -8V dual voltage supply.  These supplies are fed as inputs to three UCC21520 half bridge IGBT drivers.  The source voltage will be a 12V automotive supply and each of the top IGBT supplies should be at least 100mA and the bottom shared supply should be at least 300mA.  Depending on the IGBTs I may need even more power, since they may be switching up to 600A of current, depending on the application.

The 6 tap transformer has an extra tap in this case which can be used as the aux winding.  I would appreciate any and all feedback on the feasibility of using the UCC28700-Q1 for this application.

Best regards,

Element Green

EvaDrive-Motor1-Motor1 Driver.pdf

  • 0
    Prodigy 220 points
    After some more research I realized that the UCC28700-Q1 will not operate at 12V. So far I have not been able to find a TI flyback controller IC that operates down to this level with primary side regulation (PSR), which would be nice. I'm not opposed to an opto-coupled solution though. Just trying to figure out a way to simplify the design and reduce costs. Any pointers to an automotive grade flyback solution which could be used for this application (12V input to 4 split rail +15V and -8V outputs) would be greatly appreciated.

    Best regards,

    Element Green
  • 0 in reply to Element Green
    TI__Expert 4015 points
    Hi Element, TI does not have a low voltage PSR controller that I am aware of. You could do it with a UCC28C41-Q1 device or similar using opto coupled feedback from the secondary side outputs. It would probably be desirable to drive the feedback divider from all four secondary side outputs.
    Alternatively, you could regulate the primary side Aux rail as a proxy for the secondary side outputs which would possibly be simpler and save you from using an opto-coupler.
    Thanks
    Billy
  • 0 in reply to Billy Long
    Prodigy 220 points

    Hello Billy,

    Thank you for the reply and pointing out the UCC28C41-Q1 device.  I'm a bit of a novice at DC/DC circuits, so I'm still struggling to figure out if what I'm trying to do is feasible.  I've attached an updated schematic which is using the UCC28C43, which is still missing some values (Rstart to VCC resistance, current sense resistor value).

    The main question in all of this is, can a flyback circuit create a voltage which is higher than the turns ratio of the transformer?  Like a boost converter?  The transformer I was planning on using for this has equal turns on all windings.  If it is not possible to get ~24V from 12V on the primary with a 1:1:1:1:1:1 ratio transformer, than I'll probably just have to resort to 4 individual isolated supplies with 1:2 ratio transformers.

    If it is feasible to create a 12v to 24v flyback converter using a unity transformer, then some questions follow:

    - Would the 100% max duty parts be better than the 50% duty parts for this application?

    - R60 (the current sense resistor) should be chosen to yield a voltage of 1V at the maximum current correct?

    - Any idea what R53 (Rstart to VCC of UCC28C4x) should be?

    Thank you again for any tips on this.

    Best regards,

    Element Green

    0020.EvaDrive-Motor1-Motor1 Driver.pdf

  • 0 in reply to Element Green
    Prodigy 220 points

    After more research, I realize that what I really want is best described as a circuit like the TIDA-00199 reference design, but which can run on 12V.  The transformer appears to have a 1:2.33 ratio between the primary and all secondaries, which explains why the primary voltage (Vpri) is 10.5 volts.  I guess the reason why 20V is set as the minimum input voltage is that this would result in roughly 50% PWM duty cycle, which I understand is the highest recommended duty cycle for a DC-DC flyback converter.  Having a 1:4.66 single primary and 4 secondary winding transformer would be ideal.  As mentioned, I may just have to resort to 4 single isolated supplies.  If anyone has any ideas though for a good cost effective way for a multi-tap IGBT flyback solution which can operate down to 10V or so, that would be great.

    Best regards,

    Element Green