RC Snubber (Resistor-Capacitor Damper)
A damper made of a series-connected resistor and capacitor, placed in parallel with the switch or the motor terminals. The capacitor takes up the oscillation energy and the resistor turns that energy into heat, stopping the oscillation from continuing. Typical values in DC drivers are 5–20 Ω and 1–22 nF.
The working principle of an RC snubber is simple: add loss to the resonant circuit formed between the parasitic inductance and the parasitic capacitance. The capacitor passes only the high-frequency component and behaves as an open circuit at DC, so it does not affect normal operation. The resistor limits the current and absorbs the energy.
Choosing values relies on measurement. The capacitor is chosen typically 2–4 times the parasitic capacitance to be damped; the resistor is taken close to the characteristic impedance of the circuit. Enlarging the capacitor increases the damping but also increases the energy spent on every switching event: because the capacitor charges and discharges once per period, C × V² of energy is dissipated in the resistor per period; multiply by the frequency and you get the power.
As an example, at 24 V with 10 nF and 20 kHz the power in the resistor is about 0.12 W; a small figure. If you raise the capacitor to 100 nF in the same circuit it reaches 1.2 W and sizing the resistor starts to matter. That is why a snubber is always chosen as small as it needs to be.
Where this term is used: DC motor and driver fault diagnosis matrix