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UCC24630: Can I check if this IC gives the drive outputs without running it in a flyback circuit?

Seçkin Zeybek
Prodigy 50 points
Part Number: UCC24630

How can I run the UCC24630 for testing without connecting it to a flyback circuit? I just want to see the square wave output.

  • +1
    TI__Mastermind 40350 points

    Hello Seckin,

    To run the UCC24630 SR controller in an open-loop test circuit, its inputs must be provided with signals that mimic those of an actual flyback converter. 
    The signal levels must correspond to levels that would be seen in an actual circuit. 

    Rather than recreating all that with signal generators, I suggest to use an actual flyback circuit with a diode rectifier and install the SR controller (with associated components) in parallel with it, but NOT connected to an SR-FET.  Use the design calculator tool ( https://www.ti.com/lit/zip/sluc582 ) to determine the appropriate values. This way the signals will be the actual signals, and you can compare the DRV output to the duration of the output rectifier conduction time.

    Regards,
    Ulrich 

  • 0 in reply to Ulrich Goerke
    Prodigy 50 points

    I did exactly what you said. I added the components according to the formula in Excel. But I still couldn't get drive output.I am attaching my schematics. Can you help me where am I going wrong?Bel1.pdf

  • 0 in reply to Seçkin Zeybek
    TI__Mastermind 40350 points

    Hello Seckin,

    In your schematic diagram, you have the output diode in the "high-side" configuration, while the SR controller is in the "low-side" configuration.

    The VPC and VSC signals from the high-side are not correct for the low-side SR configuration, so the controller will not work as expected.
    Please refer to this application note: https://www.ti.com/lit/pdf/slua861 for information on circuit changes and equation changes (for modified resistor values) needed to accommodate a high-side rectifier.  As an alternative, if it is possible, moving the diode to the low-side might be a simpler change to make.

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 50 points

    Thanks for your answer. Actually, I only connected the VPC and VSC pins to try the driver output. But if it is as you say, it may not have worked correctly. I think taking the diode to the bottom might break my circuit.

    Instead, if I set up a circuit like the attached schematic without try, will it work? Do you see an error in the schematic?

    All the parameters like output voltage etc. are the same.

    Best regards.

    Bel2.pdf

  • 0 in reply to Seçkin Zeybek
    TI__Mastermind 40350 points

    Hi Seckin,

    Placing the SR-FET in the bottom leg (low-side) of the transformer is exactly like moving the ordinary diode to that position.
    The diode "points" in the same direction as the body-diode of the MOSFET.

    Without connecting the gate drive, you are using the MOSFET body-diode as the output rectifier. On first order, this should work but be careful about temperature rise at high load, from conduction loss and reverse recovery loss. 
    Also, please note: The values in the R-C snubber across the SR MOSFET are inappropriate. 10K is too high for the resistance and will prevent the snubber from damping the voltage spikes.  It should be less than 100 ohms. 10nF is too high and will result in excessive snubber loss, once the R is reduced.  Search the web for articles on R-C snubber design to determine the optimal values for R and C.

    In the SR controller schematic, the VSC pin (pin2) should go to the junction of RVSC1 and RVSC2, like you had it in "Bel1.pdf".

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 50 points

    I totally copied the snubber values from TI UCC24630EVM application note. The input and output values are very similar to those in my circuit.

    https://www.ti.com/lit/ug/sluub81b/sluub81b.pdf?ts=1625561117575&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM5023

    I missed the VSC pin. Other than that, do you think this circuit will work when I fix the snubber? Do you think there is another mistake?sluub81b.pdf

  • 0 in reply to Seçkin Zeybek
    TI__Mastermind 40350 points

    Hello Seckin,

    I looked through the UCC24630EVM User Guide document and found no mention of the snubber R4-C6 across the SR-MOSFET, except in the schematic diagram and the Bill of Materials list.  I conclude that these are "placeholder" values used to establish a footprint on the pcb, reserving places for an R and C with values that would actually be effective, if such snubbing was deemed to be necessary.  As I mentioned above, the 10K value makes the snubber completely ineffective.

    But the SR control circuit can work whether the snubber is effective or not.  It is irrelevant to the SR control.  I mentioned it earlier because I thought you had designed it that way on purpose. I didn't know you had copied it from the EVM.

    Getting back to the SR control circuit: With the VSC connection fixed, I don't any mistakes in the control network. I presume that the component values chosen do not result in a violation of any of the design constraints listed in the UCC24630 Excel Calculator Tool.    
    I expect that you should see pulses on the DRV output when you run the power supply.

    Regards,
    Ulrich