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Sharing of isolated powersupply in a full bridge

Martin Belohorka47
Prodigy 60 points
Other Parts Discussed in Thread: UCC21540-Q1, SN6505B

Hi

Lets assume that i am building a fullbridge/H-bridge and that i am for instance using LMG341xR070 or UCC21540-Q1 to do so.

To power the high side of the H-bridge i want to power from an isolated module such as the murata PWR70C.

Can I power both left and high side from the same isolated supply or do i need one for each?

I am slightly baffled over having to ask such a simple question, but i have unfortunately not seen it answered anywhere. As far as I can see, it should be possible, but I would like a second opinion.

Regards

Martin

  • 0
    TI__Guru**** 189401 points

    Hi, Martin,

    Thanks for your question. Unfortunately, due to the switching of the H-bridge, you need a separate power supply for each high-side switch as they are normally out of phase from each other. In other words, when one is high, the other is low. We solve this problem in most applications by using a bootstrap technique. In this case, if your isolated supply is referenced to ground, you can share it amongst the high-side drivers using the bootstrap technique.  

    However, if you need to run 100% duty cycle, then you need an isolated supply for each high-side switch, and an additional one for the ground-referenced drivers.

    TI sells the SN6505B which we use in many of our evms that require an isolated supply instead of a bootstrap.

    Here is an example of an implementation of the SN6505B with one of our gate drivers:

    Is this clear? If so, please press the green button, if not, please let us know and we can provide further clarification.