Quote:
Originally Posted by Al Skierkiewicz
Chris,
The diodes only conduct when the EMF is higher than 2.5 volts above the battery voltage. This will only occur (theoretically) during the inductive spike. The EMF is lower than the applied voltage except if the motor is supplied mechanical speed at greater than the applied voltage would produce. You also want to consider that the current only flows when a circuit is closed. Once the diodes stop conducting, there is no where for the current to flow. Open circuit voltage rules apply, even though the difference is small. I think that actually works in your favor if you are considering high impedance voltage monitoring. I have no specifications on the inductance of the motors. However the L/R equations go out the window with no current flow don't they?
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Well, my assumption is that during the "off" phase the inductive spike keeps the voltage high enough to turn on the diodes. This condition remains until the current goes to zero at which time we have an open ckt condition with no current. If the current does not make it to zero before the next "on" pulse then a closed ckt was there for the whole off phase.
I am not fooling with the diode drops yet because I think they are secondary effects. I also think there is only one diode in the picture, since it looks like they keep the lowside FET in ON state and feed the pwm pulse to the High side FET on the other side of the motor.
I will probably wind up just doing a simple hbridge simulation and run it.