William ChopsWestfield wrote:

>> That's what I figured. I'd need 4 of them (two full bridges);
> 
> Huh?  Why would you need four of them?  Don't you get by with one 12V
> power supply and four mosfet drivers (of the non-boosting variety)...

Depends on how you wire it:

1) Needs 4: Each one is referenced to each of the high-side MOSFETs
sources. The sources go up and down between 0V and power supply voltage,
and the DC/DC converters create just the right gate voltage referenced to
each source. (That's basically what the driver ICs do, just that they don't
use isolated DC/DC converters, but rather capacitor switchers.)

2) Needs 1: I reference the DC/DC converter's output to the power supply
voltage and get and auxiliary voltage that's 12V above the power supply
rail. But in this case there is not much point in an isolated DC/DC
converter; a simple boost switcher or so that provides this higher
auxiliary voltage does it just as well. In this case (isolated or not)
there are zeners necessary to limit the Vgs for each high-side MOSFET.

Gerhard

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