Overvoltage Protection
It is the protection that disables the driver or clamps the excess energy when the supply voltage exceeds the permitted limit. In 12 V and 24 V systems the main sources of voltage rise are chargers, alternator behaviour and energy flowing back into the supply during braking.
In a nominally 24 V system, while the battery is charging the line voltage can rise into the 28–29 V band; going somewhat above that value during braking is normal. The driver's voltage window must cover these peak values.
The protection is usually in two layers:
- Clamping: the TVS diode at the input passes fast pulses on the order of nanoseconds through itself, turning them into heat and keeping the voltage at a safe level.
- Shutdown: if the measured voltage exceeds the threshold, the controller shuts the output down and waits until the voltage returns to normal.
In vehicles with an alternator there is one more event: the load dump pulse that appears when the battery connection is broken can last hundreds of milliseconds and carries energy a TVS diode cannot absorb on its own. In such installations, separately sized protection is needed on the input side.
If you are getting overvoltage faults in the field, first measure the supply voltage under load and at the moment of braking; a static measurement most often does not show the problem.
Context where this term is used: DC Motor Driver Selection Guide