Motor Control Circuit Kludge Fix

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I have a situation with a device that has already been put into
production. It can drive 8 solenoids both push and pull using a scheme
that in testing appeared to work but in practice was mostly folly.
Basically there are 8 Half H bridge outputs to each individual solenoid
and one comon Half H for the other side of the solenoids. The Comon side
can be enabled high or low independantly (there is no inverter that
allows high or low output to be mutually exclusive) so it is basically
the "ON" part of this scheme.
Anyone in the art of inductance control can already see where the
problem lies. With Solenoids we are using the back emf isn't tremendous,
and not enough to generally effect other solenoids so they work OK,
however I wanted to use the same output scheme to drive motors.
The problem is when you drive one motor and then allow it to shut off,
it immediately creates a voltage strong enough to drive another motor
connected to the comon part of the bridge circuit.
I don't really want that to happen.
Some things I am thinking of.
1. I was thinking of a daughter board at each motor with an active sense
and dampening circuit (in both directions) that would detect motor off
back EMF and clamp it "before" the comon H bridge.
The fun part is the detection of motor EMF versus actual reverson ON
voltage. Need to actually diferentiate (probably with a very small
resistor between the drive output and the motor) the driver being on and
the motor supplying voltage.
Another this detection and shunting must be powered by the motor supply,
while it exists, that is probably a big deal there...unless a Capacitor
keeps it alive for the shunt time.
2. I didn't actually have the motors loaded, something tells me, as I
type this that maybe that would be significant. Without the strength of
the power supply behind it, perhaps the motors will just act like a
resistor instead of actually moving.

Anyways, if anyone is interested in entering their two cents, I will listen.
T.


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