protectionstepper motorzener
I have a stepper motor driven by an Allegro A4983 stepper driver chip and in some cases the motor can be back driven even while being powered up. This leads to blown motor driver chips.
Would I be able to use a pair of zener diodes placed in opposite directions between the A+ and A-, B+ and B- coils to to clip high voltages when the motors are back driven to protect my motor driver from being fried or is there another solution to this?
The voltage coming out of your motor probably is AC, but that is being rectified by the kickback catch diodes in the driver circuit. Assuming this circuit was designed and wired up correctly, only the correct polarity voltage will be fed back onto the DC power input net. As long at this voltage doesn't exceed what the circuit is rated to operate at, there should be no problem with this.
I like using the closed-loop Hall effect LEM current transducers for this sort of application. They're a lot cheaper than a genuine current probe for a scope (only about $20 or $25), have excellent accuracy and bandwidth from DC up to a couple hundred kHz.
The particular one I've linked has a +/-6A range, but you can put a couple loops through to get +/-3A full scale. Just feed it a reasonably clean +5V and Robert's your uncle.
If you want to make more of a project of it, you can offset the output with differential output between the LEM and a 2.5V reference, or actually subtract it with an op-amp and bipolar supplies, but for most purposes, just adjusting the scope zero will do the trick.
Best Answer
Yes. Back to back series zeners will work OK. Ensure voltage rating of any one zener is at least slightly greater than maximum voltage that will occur across windings. Note that if you have a centre tapped winding (or motor coil) and the CT is connected to V+ and you ground one end, the other end will rise to +2V+ - so using clamp diodes direct to 1 x V+ will badly affect motor operation.
Another solution is diode from each motor terminal to a voltage sink that is slightly higher than the allowed maximum voltage in normal use. The sink may be a formal power supply with enough load to absorb the spikes or a common zener or clamp regulator which is diode connected from each winding.
You may have to implement a below ground clamp as well depending on circuitry.