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Full-Bridge resonant converter circuit:

enter image description here

Each transistor (Mosfet) has its own driver (ISO5852S).

I assumed that a full bridge could be controlled with two PWMs.

PWM1A, PWM1B, PWM2A, PWM2B.

Each PWM, at its own time step, drives two transistors.

The driver has both inverted and non-inverted inputs, so we can protect the system from through-current in the event of a PWM failure.

I have also seen circuits where 4 separate PWMs are used to control the FULL-Bridge. (PWM1, PWM2, PWM3, PWM4), with A, B outputs for each.

It turns out that in the case of 2 PWMs, only two groups of transistors can be controlled separately. And in the case of 4 PWMs - each transistor separately.

Question:

  1. Why are 4 PWMs used instead of 2 to control Full-Bridge?
  2. What does the separate control of each transistor give?
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    \$\begingroup\$ Dead band, phase shift ability, flexibility? \$\endgroup\$
    – winny
    Dec 28 '20 at 11:17
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Why are 4 PWMs used instead of 2 to control Full-Bridge?

Phase Shifted PWM (PS-PWM) control,Space Vector Modulation (three phase)..., other kinds of switching sequence to those you have in mind.

What does the separate control of each transistor give?

HiZ control, adjustable dead time on driving side,...

Your app. can be a quasi resonant LLC converter, driven with PS-PWM.

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  • \$\begingroup\$ Thank you for your answer! \$\endgroup\$
    – Delta
    Dec 23 '20 at 1:48

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