AVR-Chat

At 10:49 AM 2/19/05 -0500, Robert Adsett wrote:
>Um, how are you getting the 10V to drive the gates then?  I don't believe
>either of these devices are logic level devices and while they will sort of
>work at 5V it is asking for trouble.  More importantly the high sides need
>to run at 10V ABOVE the input voltage to turn on,  If they are only running
>at 5V you will definitely have problems.  The gate drive issue, especially
>the high sides, is what worries me the most about what I've heard of this
>setup so far.  Is their a possibility the original circuit called for P
>type FETs on the high side?  That might explain the odd drive
>circuitry.  Even in that case though driving a high side gate off of more
>than 5 or 6 Volts is asking for trouble.  Truthfully I'm rather surprised
>the high sides turn on for any appreciable amount of time.

That should be driving the power section off of more than 5 or 6 Volts is 
asking for trouble.  You want the gate drive voltage to be 10-15V above 
it's reference.

>One more question (for now), do you have a large capacitor across B+ close
>to the H-bridge (physically close with short trace lengths)?

That's the B+ for the power section, not the logic section BTW

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