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I need to drive H bridge mosfets in hard-switching type. I got signal generator that can make pulses at the output with specific frequency and duty cycle.

My task

I need to divide this signal frequency by 2 and keep duty cycle information from each pulse. Such as one pulse and according duty cycle goes to one leg of the H bridge (a) and the second pulse go to another leg of the H bridge (b). Just like in standard PWM controller. This duty cycle defines Ton time of MOSFETs. Dead time is not considering here. I have created logic schematic using 74hc components and it looks fine in simulator, but I am not professional in the digital design. Can anyone confirm that my solution is any good, or it has some disadvantages. P.S. Logic will drive MOSFET driveres. That driver should have builе-in programmable dead time. How do I design a circuit with that feature?

Schematic Waweform

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  • \$\begingroup\$ Excuse me. I don't understand your question. (1) Let me twist your schematic a little bit, to make me easier to explain why I don't understand your question. (2) Let us relabel your four inputs to your H-bridge from A, B, B, A, to A, B, C, D. (3) Usually the input signals are PWM, by definition is a "periodic" signal with a fixed frequency. (4) The top part of your picture show a aperiodic signal. (4) I don't understand the meaning of "FSW", is it "fixed period"? \$\endgroup\$
    – tlfong01
    Aug 28, 2021 at 12:52
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    \$\begingroup\$ (2) Yeah, it is fine, let's call them A for Q1 B for Q2 C for Q3 and D for Q4. The thing is signals A and D are the same and B and C are the same too. So I simply called A and B. But it doesn't matter. (3) Picture above shows 3 different cases for D=0.25; 0.5; 0.9. The frequency is the same in all cases. (4) Fsw=switching frequency (5) I can link you to the soft switching type of H bridge so hard switching is a basically classic H bridge. vishay.com/docs/90936/an847.pdf \$\endgroup\$
    – Vasiliy
    Aug 28, 2021 at 14:21

1 Answer 1

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Your circuitry is well thought. Meantime, what you describe is a single phase AC. And the circuitry can be improved.

  1. Divide by 2 happens while alternating A and B.
  2. DFF (a MUX select) has to switch while the PWM is inactive. Thus, the clock has to come from the falling-edge of the input PWM signal.

Below logic is a modification of your circuitry. On DigiKey or Mouser, search for "High side driver" & "Low side driver".

enter image description here

enter image description here

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    \$\begingroup\$ Thank you. A2 and A3 is the MUXs? I didn't find it in 74hc series. Could you please tell part number? \$\endgroup\$
    – Vasiliy
    Aug 28, 2021 at 17:31
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    \$\begingroup\$ @Vasiliy , A2 and A3 are just a NAND, those work as a MUX (q=0 selects A3, Q=1 selects A2), you may use 74HC00. My LTSpice did not have 2-input-NAND. \$\endgroup\$
    – jay
    Aug 28, 2021 at 20:47

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