AVR-Chat

At 07:05 PM 12/24/04 +0000, you wrote:
>----- Original Message -----
>From: "kc wong" <studioee03@yahoo.com>
> >From what I see, you are driving your upper MOSFETs with
>just 15 volts relative to GROUND.  They are working like
>voltage followers.
>
>To fully turn on the upper MOSFETs, thier gate voltage has
>to be a 6..12 volts higher than the voltage at thier source.
>
>So you will need an isolated high-side driver for the two
>upper MOSFETs.

Actually the 2110 does provide an isolated (500 or 600V as I remember) 
drive for the high side.  The diode from the 12-15V supply in concert with 
the capacitor across the high side supply acts as a charge pump.  However, 
that capacitor will drain over time into the leakage on the MOSFET gate and 
other stray leakage paths.  That's why I expressed a concern about the 
frequency of the drive PWM.  That can be worked around (an isolated high 
side supply for the hi side of each 1/2 H for example) but a reasonably 
high frequency PWM will eliminate the need as long as THE PWM doesn't go 
too close to DC.

The 2110 is an effective drive chip within it's limitations.  Eliminating 
the need for isolation is one of its nicer attributes.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III