Checking Supply Voltage Rise When a Motor Stops or Reverses

A motor drive can operate correctly at steady speed and overvoltage its supply during stopping, reversal, or external motion. Energy stored in the winding and mechanical system must go somewhere. Review the selected bridge state and the source’s ability to absorb energy before relying on its normal output voltage rating.

Map the stopping method

Identify the commanded brake, coast, or controlled deceleration behavior and the resulting current paths. The TI report on motor drive system considerations discusses energy returned by the motor and the role of bulk capacitance or an appropriate dissipation path in controlling supply rise.

Do not infer the current path solely from a software function named stop. Read the driver’s truth table and determine which switches remain on, which are off, and how current commutates during the transition.

Review the input source

Determine whether the supply can sink current, only source it, or disconnect under reverse current. Include blocking devices between the source and drive. A battery, a bench supply, and an adapter can respond differently even at the same nominal voltage.

Measure the local motor rail near the bridge because cable inductance and protection elements can separate it from the source terminal voltage. A source display may not capture the brief peak seen by the driver.

Estimate the available energy capacity

For a capacitor, the energy absorbed between two voltages is one half of capacitance times the difference of their squared voltages. Use that relationship to estimate the scale of rail rise from a bounded returned energy event.

Include capacitor tolerance, initial voltage, losses, and the highest permitted rail voltage. Do not assume that adding capacitance alone can absorb repeated or sustained mechanical input indefinitely. A required dissipation or regeneration path must be rated for the actual duty cycle.

Verify controlled transitions

Test stopping and reversal at representative speed, load, and source conditions using a setup appropriate to the motor’s energy. Capture local supply voltage, current direction, bridge command, and motor response. Include externally driven motion if it is a realistic operating case.

Save the energy path, source behavior, protective components, waveforms, and repetition pattern. Recheck the result after changing motor inertia, firmware deceleration, cable length, or supply type. A valid stop command must produce acceptable mechanical behavior and electrical stress. Demonstrating that the shaft stops quickly is not enough if the returned energy pushes the board beyond its reviewed voltage envelope. Document the maximum repetition rate used in this verification.