Re: H bridge progress

Chris,
Have you added a deglitching across each IC? A value of
.01uf to .1uf from ground to +5 or +12. Most diagrams leave these
caps out. They prevent spikes from and to an IC.

Bob Watters

--- In CAD_CAM_EDM_DRO@y..., Chris Stratton <stratton@m...> wrote:
> First, I want to thank everyone who has offered advice on the H
bridge
> circuit. What I have at the moment is the FET's and 2104's on a
> little milled PCB, with the L297 on a breadboard. Next revision is
> going to put it all on the PCB, but I want to be more sure of the
> design first.
>
> The gate resistors in question are shown in the IR2104 example
circuit
> between the 2104 and the gates.
>
> > > 1. The gate resistor is there to prevent oscillations.
Keeping the
> > > driving circuit VERY close to the FET helps to reduce this, as
do
> > > ferrite beads on the gate line placed very close the FET.
>
> It sounds like maybe I should go for a 10 ohm or so resistor,
possibly
> with a ferrite bead on one of its leads? Another idea, from the
ARRL
> handbook, would be to use a larger value resistor as a physical
> carrier over which to wind a small coil of wire (shunting the
> resistance). The main issue I need to decide now though is if I
plan
> for a component like this on the PCB, which does increase the
distance
> between the 2104 and FET's, but also provides a convenient way to
> cross over a power trace (at right angles, so coupling should be
> minimal).
>
> > > 3. The L297 turns both sides of the bridge high when turning
off a
> > > winding as this is the fastest way to get the energy out of the
winding.
> >
> > No, that actually allows current to recirculate (through the
reverse diode
> > on one of the transistors) indefinitely, reduced mostly by the IR
drop of
> > the coil itself.
>
> Fortunately, switching modes on the 297 is a matter of chaning one
> jumper, so I can try both ways.
>
> Chris
>
> --
> Christopher C. Stratton, stratton@m...
> Instrument Maker, Horn Player & Engineer
> 22 Adrian Street, Somerville, MA 02143
> http://www.mdc.net/~stratton
> NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT