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UCC28810: Pmp4860

Mohitha Venkit
Prodigy 230 points
Part Number: UCC28810
Other Parts Discussed in Thread: TL431,

Hi sir,

Iam designing an led driver circuit with pmp4862.1 for 100v,  1.2 a.  I've taken output across r100 Without connecting u4 circuit of led driver A.  I haven't connected d11 to vdc. My circuit is not working.  Please help.

Regards

Mohitha

  • 0
    TI__Mastermind 26525 points
    Hi Mohitha,

    Please check the following:

    1. Verify VCC sees sufficient voltage.

    2. Check EAOUT pin voltage. Make sure the voltage is greater than 2.3V

    3. Verify VSENSE is 2.5V

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 230 points
    Hi,

    Sir, I took the readings vcc 17.9v, eaout 2.5v vsense 2.5v. Still nothing. Please help.
  • 0 in reply to Mohitha Venkit
    TI__Mastermind 26525 points
    Hi Mohitha,

    Do you see any gate drive pulses? What is the behavior of the converter?

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 230 points

    Hi sir,

    No gate pulses. Converter not working. Vdd pin is fluctuating between10- 15v when ic is connected. Otherwise 18V. Eaout is 4.9V. Vsense is not reaching 2.5V fluctuating between 1.0 to 1.3 above certain value it starts decreasing then increasing. Gdrv pin is  0.04V. What may be the issue?

    Ive used the same  circuit  in page1 of pdf

    Regards

    Mohitha

  • 0 in reply to Mohitha Venkit
    TI__Mastermind 26525 points
    Hi Mohitha,

    If VDD is oscillating between 10V and 15V it is likely hitting UVLO and turning off. As an experiment, you can try feeding VDD with an external voltage to see if you can get the device switching.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 230 points

    Hi sir,

    Thank you for replying. We had a connection issue at TL431. Now its working. But however the output is 65V at 230AC V. We need to reach 100v with current 1.2A. We are taking output across R100. What may be the reason? we have connected a 4.9Ohm resister between GDRV pin and Mosfet gate. IS that a reason? Please reply asap. Thank you in advance. 

  • 0 in reply to Mohitha Venkit
    TI__Mastermind 26525 points
    Hi Mohitha,

    I am glad the converter is switching now. I would suggest double checking the resistor values in the FB divider (R23, R28). Check the voltage across R21. If the feedback divider is correct then the TL431 should be sinking very little current through the opto-coupler. The gate drive resistor should not have an impact on the regulation set point.

    If the secondary side feedback circuit is behaving correctly then we can look at the voltage at COMP and CS.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 230 points

    Hi sir,  

    We considered changing r28 and r23.  But output didn't change much.  So we changed r100 to 1 M and at 230v ac output was 65 to 74v dc. So i have a doubt about zener diodes D101 and D 102 ie 62v zener. When Cross checked with other Ti circuit S with ucc28810 i under stood that zener there is slightly higher than the output we need.  For eg 59v output zener is 62v,  80v output zener is 82v. So i was thinking can i change these zener to 100v zener diode? Please reply.

    Subject to availability in Indian market, We are having some queries about equivalent components

    Can use 1n4007 instead of us1k

    And also 1n4148 instead of mmbt 914?

  • 0 in reply to Mohitha Venkit
    TI__Mastermind 26525 points
    Hi Mohitha,

    D101 and D102 form an OVP circuit. You can test with these diodes depopulated. I will look at the parts you asked about and get back to you.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 230 points
    Hi,

    Thank you for replying so fast.What if we change that to 62v zener or 85v zener?How to attain 90vdc output then? Your support means a lot for us.
  • 0 in reply to Mohitha Venkit
    Prodigy 230 points

    Hi Sir

        Greetings of the day.  Today we found out something strange in the output,  Our load is 100V 350mA LED lighting.  Without load the output is showing  around 98.9V whenever we connect the load to the output,  the output voltage decreases to 74.1 V but the load is consuming around 300mA. I would like to know what is the reason for this.  Kindly help,  Thanks in Advance

    *note : led is glowing in dim

  • 0 in reply to Mohitha Venkit
    TI__Mastermind 26525 points
    Hi Mohitha,

    The output voltage is likely being limited to the forward voltage of your LED string.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 230 points

    Hi sir,  

    Sorry for the late reply.  The leds are less brighter because the current is 350mA instead of 1.2 A.  The output voltage is 100v. Can you please help me to spot the current increasing element of the circuit.? eaout pin voltage is 4.9v

    Regards

    Mohitha

  • 0 in reply to Mohitha Venkit
    TI__Mastermind 26525 points
    Hi Mohitha,

    Do you have your LEDs connected to the flyback output? The flyback regulates output voltage. It does not regulate output current however. It is capable of supporting up to 1.2A output but the exact output current will depend on how much the load (in this case, the LED string) consumes. If you want the ability to force a set current through the LED string you would need a LED driver or to add a constant current loop to the flyback control loop. You could use a sense resistor in series with your LED string and regulate the voltage across the LED string.

    As an example, you can look at the feedback network in PMP20946 for implementing a constant current feedback loop (U202, U201A, R203, etc).

    Best Regards,
    Ben Lough