Why exactly is a charging capacitor/intermediate circuit capacitor required?
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When braking or stopping a stepper motor acts like a generator and gives energy to the power supply so that the power supply voltage increases. Due to the maximum admissible voltage of the transistors used and elements in the power drive, the braking energy or the voltage increase can damage the components in the power drive. A generously dimensioned capacitor with corresponding electric strength can, by contrast, accommodate this braking energy for a certain time and thus limit the voltage.
In addition to the charging capacitor, an active ballast circuit is also used in part that converts the surplus energy into heat and, hence, also limits the increase in voltage. The capacitor is already integrated in the PDx-I motors.
The active ballast circuit acts considerably more effectively than the charging capacitors against fast voltage spikes as it also reacts quickly and, above all, works independently of the directly available storage capacity of the capacitors. Charging capacitors are necessary, however, in any case as they can take up and deliver the energy almost free of loss whereas the active ballast circuit presents an additional fast overvoltage protection.
