On 4/22/06, Wouter van Ooijen <wouter@voti.nl> wrote:
> more questions...
>
> Should I have a decoupling cap on the power lines near the H bridge?

Absolutely.

If
> so, I think I can work out a calculation of the value. But should it be
> a special type?

It must have as low ESR as possible and cut all noise frequency
generated by the motor switching (including heavy mechanical load
balancing which have very low frequency -if any).
Choose one tantalum capacitor 47uF-150uF (usually highest voltage have
lowest ESR, so the package is large) with quite large voltage compared
with the supply. (ie for a 24V supply, minimum 50V capacitor- 63V to
100V better). Chose one X7R 1uF capacitor for medium frequencies and
another 0.1uF for highest frequencies. For those 1206 could be enough.
Connect them in parallel.
If your choose was right, those capacitors must remain cold at the
ambient temperature. If you have *very large* switching spikes, these
capacitors would be slighty warm (the first one heated is the
tantalum).

Vasile




>
> Wouter van Ooijen
>
> -- -------------------------------------------
> Van Ooijen Technische Informatica: www.voti.nl
> consultancy, development, PICmicro products
> docent Hogeschool van Utrecht: www.voti.nl/hvu
>
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist