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UC3846: Use UC3846 as an H-bridge PWM controller, what is the max duty?

hello111
Prodigy 100 points
Part Number: UC3846

As the title suggests, using UC3846 as an H-bridge hard switch, PWM signal drives 4 MOS with a power of 20kw.

The problem is as follows:

1. Is the A and B PWM output of UC3846 complementary to pin11 and pin14? If complementary, is the maximum duty cycle not exceeding 50%?

2. If it doesn't exceed 50%, why do many people ask UC3846 about slope compensation?

3. If it is an application of H-bridge inverter, does slope compensation need to be done

4. I made a model of UC3846, is the internal logic correct?

5. UC3846 is a chip that was released a long time ago. It is a relatively new chip that meets the requirements of H-bridge hard switching, high power, current control, and complementary PWM output. What are the recommended new models?

  • 0
    TI__Mastermind 27595 points

    Hi,

    1. Is the A and B PWM output of UC3846 complementary to pin11 and pin14? If complementary, is the maximum duty cycle not exceeding 50%?

    • Yes

    2. If it doesn't exceed 50%, why do many people ask UC3846 about slope compensation?

    • sub harmonic instability can happen using peak current mode control as the D approached 50%. It's a good practice to include slope comp if the power stage will be approaching 50% D.

    3. If it is an application of H-bridge inverter, does slope compensation need to be done

    • Depending on your VIN range and anticipated max D, you may get away without using slope comp. Otherwise see above answer to 2.

    4. I made a model of UC3846, is the internal logic correct?

    • Not sure, run the model to see if the behavior is as you expect?

    Regards,

    Steve

  • 0 in reply to Steven Mappus1
    Prodigy 100 points

    If I use MCU to sample the output voltage and current, perform PI calculation to control the output voltage, and provide the PI result to E/A+, can I not use slope compensation?
    Is this control method feasible?

  • 0 in reply to hello111
    TI__Mastermind 27595 points

    Whether you sense/sample the current through analog or digital, I believe the same rules around subharmonic stability will apply. If the transformer current waveform is such that, ton>0.5*T^2, you should consider to add some artificial ramp mixed with the sensed/sampled current as a way to assure stability. Plan for it is what I recommend.

    Steve