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TMS320F280049: Implementing a specialized synchronous rectification control (50%<D≦100%)

HSIN-CHE HSIEH
Prodigy 110 points
Part Number: TMS320F280049

Hi,

I would like to implement an unusual synchronous rectification control for a specialized resonant converter. When the positive to negative zero crossing of the drain-source voltage (Vds) or current (Ids) of the SR MOSFET is detected (will likely be detected by an external comparator), the SR MOSFET should be turned on for a given amount of time ignoring the negative to positive zero crossing of Vds or Ids. This on time will be generated inside the DSP based on an internal reference or feedback from output.

For my specialized converter to work, I need to allow some reverse current to flow. I want to control this by controlling the total on time of the SR MOSFET. The duty cycle of the SR MOSFET need to be able to reach 100% (resulting in a complete short) for at least a couple of (primary side) switching cycles. There is only one SR MOSFET to be controlled in my converter.

I have limited experience with DSP. Any suggestions on how this can be done reliably?

Thanks

  • 0
    TI__Genius 15705 points

    Hi HSIN-CHE,

    Could you also draw a brief pic to help understand how you would like to setup your SR?

    Regards,

    Chen

  • 0 in reply to Chen Jiang ti
    Prodigy 110 points

    Here are some simplified waveforms showing how I expect the SR MOSFET to be driven. Forward or reverse voltage drop of SR MOSFET is not included in my figure, which I understand may be necessary for sensing.

    On time of the SR MOSFET (t_on) needs to be programmable (t_on command would be generated inside the DSP). Duty cycle (t_on/T) need to be able to reach 100%.

  • 0 in reply to HSIN-CHE HSIEH
    Prodigy 110 points

    I think what I need here is actually just an edge triggered, software programmable monostable or one-shot pulse generator. Mentioning SR just over-complicate things. Is there anyway to make the a DSP behaves like a software programmable monostable multivibrator?

  • +1 in reply to HSIN-CHE HSIEH
    TI__Genius 15705 points

    Hi HSUN-CHE,

    Sorry for the late reply. I think that should be doable. I assume you would like to ZVS turn on the SR. You can use the CMPSS(no need to use external comparator) to detect the ZVS and send the signal to PWM module inside which you can use T1/T2 or trip zone action.  

    You can setup a EPWM counter to start counting at the rising edge of your SR pulse. Then use pre-calculate CMPA/CMPB to turn if off. And also use DCEVT(comes from CMPSS) to reset the counter to 0. 

    Regards,

    Chen

  • 0 in reply to Chen Jiang ti
    Prodigy 110 points

    My team come up with something similar but we use external comparator instead of CMPSS because we need isolation.

    Thank you

  • 0 in reply to HSIN-CHE HSIEH
    TI__Genius 15705 points

    Ok, thanks for letting us know.

    Regards,

    Chen