Snubber Circuit
A small auxiliary circuit added to the power stage to absorb the voltage spikes and high-frequency oscillation that appear at the moment of switching. In DC motor drivers, typical RC snubber values are chosen in the 5–20 Ω and 1–22 nF range according to the motor inductance.
The source of the spike is parasitic inductance. The motor cable, the terminals and the printed circuit traces have a small but non-zero inductance; when the switch turns off, the energy stored in that inductance, together with the parasitic capacitances on the board, produces an undamped oscillation. Its peak can exceed twice the supply voltage.
A snubber adds a damping path to that oscillation. Its most common form is a series resistor–capacitor pair connected in parallel with the switch or the motor terminals; the capacitor passes high frequencies and the resistor turns the energy into heat. RCD (resistor–capacitor–diode) arrangements are used for higher-energy situations.
A snubber is not needed in every application. If the cables are short, the terminals tight and the bus capacitor close to the switches, the spikes are limited anyway. A long motor cable, a loose connection or a driver mounted far from the supply, on the other hand, makes the spike larger. In the field the first fix is always the cable layout: shortening the motor cable and running it twisted is often more effective than adding components.
Where this term is used: DC Motor Driver Selection Guide