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UCC28950: Imitation of the PMP-6712 circuit problem

Taiwan
Prodigy 70 points
Part Number: UCC28950
Other Parts Discussed in Thread: PMP6712, UCC27714

Dear Sir about the previous circuit, PMP-6712, after the actual board test, found a problem, that is, the output voltage of 330V can not be stabilized, its output voltage will rise to OVP (set 350V), I suspect the circuit There is something wrong with the resistance, please ask your help to solve the problem.
The difference between our application and the PMP-6712 circuit:
1 The output is high voltage, so you are recommended to use a diode instead of a synchronous rectified FET. Therefore, UCC-28950 out-E out-F is connected to a resistor 13K to ground.
2 Because the output is high voltage, you are also recommended to use a 12V power supply in the transformer to provide Photocupler and TL-431 VCC applications. After testing, the Photocupler has normal operation, and the resistance of pin 3.4 is 4K12 when it is turned on.
3 UCC-28950 OPTO-E=4.88V, EA-=2.5V EA+=2.496V, is this condition in line with the specifications?
4 Photocupler and TL-431 The power supply is only provided by another group of 12V transformers, and there is no additional LM-5017 isolated power supply. Is this OK?
5 The board layout adopts 4 layers. If Top-layout has Polygon, can it be connected directly to Input Ground? Can the same inner layer (2.3 Midlayout) Polygon be directly connected to Input Ground?
6 In addition to this circuit, is there any place we should pay attention to?
   Thank You
   Dick Liu 11/8/2018

  • 0
    TI__Mastermind 31580 points
    Hi Dick

    Our application engineer who supports the UCC28950 is travelling at the moment so his response may be delayed.

    As the output voltage increases and if it exceeds the regulation setpoint the then OPTO-E node should be driven high towards REF1 voltage and this should reduce the duty cycle on the bridge primary is the circuit functioning in this way.

    Can you also check the resistive divider network and value of the reference that is used in the design to ensure that they are correct for the 330Vdc output voltage setpoint.

    We will need to review the PCB layout before we can recommend any changes.

    Thanks

    Peter
  • 0 in reply to Peter Meaney
    Prodigy 70 points
    Hello Peter
    How do we offer P C Board Layout Fire ?
    Is the problem found related to the layout?
    Thank you
    Dick
  • 0 in reply to Taiwan
    Prodigy 70 points
    Dear Sir
    I found that Leonardo suggested that: "The UCC27714 EVM may be of interest - it uses the UCC28950 as a secondary side controller - an ISO7240 isolator and a UCC27714 high/lo side driver. Neither the isolator nor the driver were available when the PMP6712 was designed . Is this the main reason why our current circuit is out of control? (Our current practice is the same as PMP-6712 UCC28950 and FET Driver.)
    Please tell us, if the ground wire of UCC28950 is determined to be at the same potential as the secondary side, can we refer to SLUUB02A (UCC-27714 EVM)? Is the UCC28950 output isolated by ISO-7240, and then the UCC-27714 to push the FET? UCC28950 Peripheral part values, should we refer to that circuit? Can I refer to the UPC28950 part value and architecture of PMP6712?
    Thanks you
    Dick Liu
  • 0 in reply to Taiwan
    TI__Mastermind 31580 points

    Hi Dick

    Can you send me your schematic in pdf format and the PCB Gerber files to my email address and I can review them.

    petermeaney@ti.com

    Thanks

    Peter