Wheelchairs use electric clutches (similar to Car Air Conditioning
clutches), unclutch then apply power to the motor (so you could use that
sort of thing.)  Really a fast way to stop the motor (locks the wheels!)
but not always scalable, and eats a bit of power.  Could use a solenoid
and a friction brake?  (2 coils, 1 for Go, 1 for Brakes On, just apply
friction from the piece moved by the solenoid's core, to the flywheel?)

  Or, put a resistor in series with a "relay" (optoisolated analog
switch?) across the motor, close relay to brake, using the motor as a
generator.  Smaller resistor, faster braking.  (Could PWM the switch, to
proportional brake.)

  Not my field of expertice (obviously) but a couple thoughts.  Need to
get back current on this for one project next year <G>

  Mark Willis, mwillis@nwlink.com

Shahid Sheikh wrote:
>
> Greeting everyone,
>
> Anyone has any idea on how to implement an electric brake for a small DC
> motor driven by a H bridge mosfet arrangement. The normal running current
> the motor consumes is about 300 ~ 400 mA at full speed and average load.
>
> The problem is that the motor has a small flywheel attached to it which
> keeps it going for a while after the supply has been shut off.
>
> This is for a model train decoder and I'm trying to figure out how I'm going
> to implement an emergency stop. The motor's speed and direction is
> controlled by a PIC using PWM. Right now I dont have any plans of using back
> EMF for speed control so I'm trying to find a braking solution that doesn't
> use back EMF.
>
> Thanks,
>
> Shahid