I'm working on a project one part of which involves driving a brushed DC motor from an Arduino. I happen to have a few TA6586 DC motor driver ICs which I have tested to work with my microcontroller using a potentiometer and PWM. Here is the schematic of this part of the design:
I have been told that to protect the various circuit components, I should have a flyback diode across an inductive load. The motor is an inductive load. However, placing a diode across the motor here does not make sense, because the motor can be driven in either direction. If I placed a diode from MOTOR- to MOTOR+, it would result in a short circuit when driving the motor in reverse.
The datasheet does not give any indication as to whether a diode is needed or included in the IC. Is there any way to find out besides experimenting and seeing if something blows up? If there were a flyback diode in this circuit, where would it be placed? GND to VBATT?
Diodes are built in. If they were not, you would need 4 diodes. Two on each motor lead... regard the motor as a AC power source. The diodes rectify the AC to feed into your power supply.
Ah, and those diodes would not connect the motor leads to each other, but rather to VBATT and GND, right? This would have the effect of clamping the voltage of the leads to between VBATT and GND by dissipating any excess current that comes from the inductor when its magnetic field collapses?
For my own edification, I made this in CircuitLab:
Without the clamping diodes, you see momentary voltages of -60kV at the switch after it switches from 6V to the floating side of the switch. With the clamping diodes in place, the maximum momentary voltage is reduced to about -1V. (I don't know how the simulated values correspond to a real circuit but the principle seems to be clamping diode = much lower max reverse voltage.)
