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?

  • 1
    \$\begingroup\$ If you want answers to the extended question you should edit them into the question. Comments tend to get deleted with time and people reading the question need to be able to see what the question is and not to have to look through all the comments to see what else is said. Not so bad here but often enough the distributed q&a in the comments exceeds the question content. \$\endgroup\$
    – Russell McMahon
    Commented Jun 20, 2016 at 10:46
  • \$\begingroup\$ A bit more clairification and detail on the circuit and situation would be useful. A circuit diagram is a very good idea. If the application is too simple to justify a circuit diagram then the existing simple answers will probably suffice :-). eg knowing where the stepper is bipolar / monopolar / ... . What do YOU mean by back driven? That may be mechanical reverse drive or electrical drive against current rotation or ...? |Both existing answers mention use of diodes as well as zeners. My answer mentions a voltage sink for the diode(s) or a clamp regulator or ... . ... \$\endgroup\$
    – Russell McMahon
    Commented Jun 20, 2016 at 10:54
  • \$\begingroup\$ ... This could be a large enough capacitor and a shunt resistor fed by a diode - dissipating excess energy. Or ... . | More input please. \$\endgroup\$
    – Russell McMahon
    Commented Jun 20, 2016 at 10:54
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    \$\begingroup\$ @Jodes: If you want to offer a bounty on the question as asked by the OP, that's fine. But it sounds like you have a different question in your bounty comment, which you should ask as a separate question. \$\endgroup\$
    – Dave Tweed
    Commented Jun 20, 2016 at 12:20

2 Answers 2


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.

  • \$\begingroup\$ @RusselMcMahon please could you provide more info, as requested in the bounty? \$\endgroup\$
    – Jodes
    Commented Jun 19, 2016 at 17:09

The A4983 stepper driver has internal diodes which will shunt any excess power back into the supply rails (the internal mosfet body diodes), which means that if the motors are back driven and there is no dynamic braking/load dump then the supply rails will climb until something blows up. The most common ways to deal with this is to both add lots of bulk capacitance (many millifarads) to absorb shorter bursts and a single zener across the supply rails that will burn off any excess power that would otherwise cause the supply rails to go beyond 35V.


simulate this circuit – Schematic created using CircuitLab

You mentioned that you wanted clamping diodes but unless you have something to keep the supply rails fixed, the drivers will continue to blow, it is for very similar reasons why most linear audio amplifiers have really big supply capacitors as the speakers can sometimes generate enough back emf to blow the main transistors, the energy has nowhere to go so it causes the voltage to keep rising until a new path is created (usually through a fried transistor)


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