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UC1825 and UC1825A duty cycle operations

gG
Intellectual 915 points
Other Parts Discussed in Thread: UC1825A, UC1825, UC1825A-SP

Hi,

UC1825 and UC1825A has below functions.

UC1825: Dual Totem Pole Outputs (Alternating) - Duty Cycle Range (%80max) - Dead-Time Control by Ct pin.

UC1825A: Dual Totem Pole Outputs (Alternating) - Duty Cycle Range (%50max) - Maximum-duty cycle control upto (%100max) (!but used for VMC!)

My questions are as below,

1) For UC1825 - If I set internal oscillator frequency to 100kHz and get the UC1825 worked as a 100V input 80V output buck converter,which means %80 duty. How will be the OUTPUTA and OUTPUTB waveforms? Is it will be as figure below?

Figure-1

OR 

Figure-2

OR

Figure-3

1) For UC1825A - If I set internal oscillator frequency to 100kHz and get the UC1825A worked as a 100V input 80V output buck converter,which means %80 duty. How will be the OUTPUTA and OUTPUTB waveforms? Is it will be as figure below?

Figure-4

OR

Figure-5

Thanks

  • 0
    TI__Expert 7445 points

    gG,

       Typical application using UC1825A will be to drive a push-pull converter as highlighted in the applications  section on pg. 16 of UC1825A-SP. 

    Since you want to operate a synchronous buck coveter  and the two outputs are referenced to ground.   Also the input voltage is 100V for your application.

    Output A and B are totem pole and alternating, thus their on-time/ duty cycle of two outputs will be the same.

    a. you take the two outputs and go thru a pulse-xfmr and generate full wave output to drive the high side MOSFET.  Now you have an isolated full-wave rectified signal that can drive the high side NMOS MOSFET.

    b. You can take the tow outputs and invert them and add the signals to drive the synch mosfet.

    Let me know if this is clear or you want me to draw the waveforms for more clarity.