RE: SSTC bridge driver

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mccauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com> 





Which coilers?  Driving SSTC bridges (gates) with steep pulses offers
the advantage that you are switching the FET
on very quickly, thereby reducing the time which the FET operates in its
linear region.  Depending on how slow your
rise and fall times are on the gate pulse can add significant heat,
especially during hard switching.  Ringing can
be easily controlled and really isn't much of a problem.

The reason gate transformers are used is to isolate the power section of
h-bridge driver from the control section.
Not sure where you are getting this ringing thing from.  Are you
referring to ringing on the gate pulse itself?
This is normal, and is easily controlled.  In fact, any ringing well
above the turn-on point of the FET doesn't
affect performance at all (unless the ringing peaks are above the max.
ratings of the device, or below a point where
the FET will start turning off.

High side driving is a bit more complex than using isolated gate
transformers.  You have to remember the top FETs of
the h-bridge are floating with respect to the incoming power voltage.
The gate must also be referenced to this
top source as well.

If your top rail was 300VDC, your gate would have to be biased at
accordingly and the Gate-Source voltage differential
would have to be enough to turn on the device.

Dan



List,

Driving SSTC bridges with very steep pulses offers many advantages, but
SSTC coilers claim, that this "rings the heck out of everything".

Most driver circuits I have seen, employ pulse transformers to control
the powerMOSFETs and these create a lot of ringing.

Why are no high-side-drivers used in this place? To small drive current
/ to slow / to expensive / ..... ??

Could somebody please enlighten me?

Cheers,

Herwig

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