Bootstrap vs Isolated supplies for gate driver

[chinuhark]

I am surprised how little discussion I found on this topic online. The title says it all but my major questions are:
1) Which is more reliable?
2) Which is better in terms of driving switches requiring large gate currents?
3) Which method is is used in commercial VFDs and Inverters?

The third question is one I am very curious about.

 

[Yosmany325]

Hello chnuhark. Regarding to your questions there are too information around.

I have no information in reliability but I think is better to use Bootstrap solutions. Also the most designs you can find use this solution.

Among the factors are the costs, is cheaper to use an integrated bootstrap driving IC (I mainly know about IRF´s ones). Using an integrated solution saves PCB area which also simplifies design.

Regarding current sourcing/sinking capabilities also there are good integrated solutions. Maybe at this point you can consider using discrete components at some points, but also using bootstraped solutions (this is what I have seen).

I have not seen commercial implementations but I guess they should not be so far from manufacturer of semiconductor suggestions. You can see on Microchip´s web site, IRF website and others you may know, searching for motor control application notes.

I hope this can clarify some of your questions.

Best regards Yosmany325.

 

[chinuhark]

Yes there is large amount of information about how to implement either technique. What is missing is a comparison.

What I really want to know is what is done by commercial manufacturers.

 

[KlausST]

Hi,

Commercial manufacturers will keep on the driver chip manufacturers information.

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One main point between bootstrap and isolated supply (not a pulse transformer drven gate) is that a bootstrap circuit can't work to 100% duty cycle. It needs low phases to charge the bootstrap capacitor.

Klaus