• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 38 subscribers
  • Views 362 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TIDA-01464: UCC28740

Hamid Kiabi
Prodigy 10 points
Part Number: TIDA-01464
Other Parts Discussed in Thread: UCC28740, TL431,

QR_FLYBACK_VCFB w SW.pdf

Hi, please see attached pdf document of the power supply based on the reference design TIDA-01-01464. The  values for the Lm and turns ratios as shown for 85-256Vac input

The power supply do not operate correctly, the Vdd shows the ramp error voltage and restarts continuously. There is no three pulses as mentioned in the notes, instead there is a single pulse from the DRV output of the UCC28740. The waveforms on the AUX, and the Secondary are correct.  Since there is not enough time for the secondary voltage to rise and provide feedback, the device keep restarting. even with lowering the capacitor value on the Vdd pin from 10uf to 1uf do not provide much benefit. The feedback tested by itself and works correctly by back signal injection to the output.

The Resistor RS1, and RS2 are set fo 77K, and 20K. The value of the current sense resistor has been lowered without improvement.

Another step taken as to examine another similar reference design  TIDUAN0B which is for 100W 24V. An identical transformer from Wurth was used, with exact components including using the TL431 feedback as was used in the reference design. Except our project utilizes two switch. Basically the design is identical to the 100Watt, except we uses two switch flyback, Nothing else is different. The problem remains.

Many people are working on this project, and it is affecting the staff in very negative way, please after review contact us immediately. If need additional data please contact.  Thanks

  • 0
    TI__Intellectual 1380 points

    Hi Hamid,

    Can you clarify the test you conducted for the feedback loop? I reviewed your schematic and the only difference seems to be the feedback portion.

    Is it possible for you to modify the board to have the op-amp output connected to the opto-coupler cathode? So have U6-2 connected to U4A-1, then have U6-1 pulled up through a resistor to P12V. Then remove U4B, R59 and D19.

    It may be that the logic is inverted for the feedback loop which is causing the fualt detection at start-up.

    Thanks,

    John

  • 0 in reply to John Dorosa
    Prodigy 10 points

    Thank you for the response, appreciate it.

    The feedback test is independent test, a test voltage of 28-31V is injected from output across the C27., as the voltage increase from 28V upward, the input to U6 (opto-coupler) and the  output of the U6 is monitored. when the voltage reaches the threshold  which is 30V,the output of the opto-coupler changes state from high to low.

    Next things I asked our colleague to do, is just remove all the feedback, and instead revert back to using TL431 with the opto-coupler only. The Rtop for TlL431 is 47.5K, Rbottom is around 4.2K, to set the threshold around 30V Output. The  output of the  opto-coupler  (pin-4) is connected to  U5 VDD (12V-PRI), and the Emitter of the Opto-coupler connected to U5  (UCC28740) pin 5, and  it is shunted with a 10K to ground. (Pin 3 is connected to ground with a 10K Resistor).

    The same method was applied to verify the new simple feedback, and it works correctly. The problem remain. That is the U5 VDD ramps, and the UCC28740 pin-6 Drive output, repeats the three sequence pulses, Attached are few waveforms,  The power supply never reaches steady state, the Auxiliary should reach 20V, while the Secondary should be 30Vdc.

    Attached are few pictures, hope that will help. Also two different transformer was used (one made by my friend at Minntronix, and another one from Wurth (catalog part). The wave forms attached are from using the Wurth Transformer 250uH, 27, 6A.

    the s. 750316326 27V 6A.pdf21151 Rev 3Minntronix 140uh Designed by HK.pdf

  • 0 in reply to Hamid Kiabi
    Prodigy 10 points

    Thank you for the response, appreciate it.

    The feedback test is independent test, a test voltage of 28-31V is injected from output across the C27., as the voltage increase from 28V upward, the input to U6 (opto-coupler) and the  output of the U6 is monitored. when the voltage reaches the threshold  which is 30V,the output of the opto-coupler changes state from high to low.

    Next things I asked our colleague to do, is just remove all the feedback, and instead revert back to using TL431 with the opto-coupler only. The Rtop for TlL431 is 47.5K, Rbottom is around 4.2K, to set the threshold around 30V Output. The  output of the  opto-coupler  (pin-4) is connected to  U5 VDD (12V-PRI), and the Emitter of the Opto-coupler connected to U5  (UCC28740) pin 5, and  it is shunted with a 10K to ground. (Pin 3 is connected to ground with a 10K Resistor).

    The same method was applied to verify the new simple feedback, and it works correctly. The problem remain. That is the U5 VDD ramps, and the UCC28740 pin-6 Drive output, repeats the three sequence pulses, Attached are few waveforms,  The power supply never reaches steady state, the Auxiliary should reach 20V, while the Secondary should be 30Vdc.

    Attached are few pictures, hope that will help. Also two different transformer was used (one made by my friend at Minntronix, and another one from Wurth (catalog part). The wave forms attached are from using the Wurth Transformer 250uH, 27, 6A.

    the s. 750316326 27V 6A.pdf21151 Rev 3Minntronix 140uh Designed by HK.pdf

  • 0 in reply to Hamid Kiabi
    Prodigy 10 points

    I think I pressed reply button too many times, oops. Please review and follow up, thank you.

  • 0 in reply to Hamid Kiabi
    TI__Intellectual 1380 points

    Not a problem, thanks for the reply. It sounds like the logic is flipped, can you have the opto circuit configured to be like TIDA-01464? For the diode pin 1 should be pulled up to a DC voltage through a resistor, then have the output of the op-amp connected to the cathode (pin 2).

    The three pulses indicate that a fault is being detected. Section 7.3.4 of the UCC28740 datasheet has the possible fault conditions that could be detected. An incorrect feedback network may tell the controller that there is an output overvoltage event.