Snubber RC Calculator
Dimension a resistor-capacitor snubber for a switching node: choose Rs and Cs from switching voltage, current, parasitic capacitance and frequency.
About This Calculator
Switching nodes ringing from parasitic capacitance and loop inductance cause EMI and extra loss. An RC snubber across the switch damps the ringing: the resistor is chosen near the characteristic impedance of the ringing path (approximated as V/I), and the capacitor a few times the parasitic capacitance. The loss is the charge/discharge of the snubber cap once per cycle: P = ½·C·V²·f.
How to Use
- Enter the switch-node voltage, load current and the measured/estimated parasitic capacitance at the node.
- Enter the switching frequency to compute snubber power dissipation.
- Start with Rs = V/I and Cs = 4× C(parasitic), then tune experimentally.
- If snubber loss is too high, raise Rs or reduce Cs (accepting more ringing).
Formulas
| Snubber resistance | Rs ≈ V(switch) / I(load) |
| Snubber capacitance | Cs ≈ 3-5 × C(parasitic) |
| Snubber loss | P = ½·Cs·V²·f(sw) |
Design Notes
Measure ring frequency with a scope to refine: Rs ≈ 2π·f(ring)·L(parasitic) and Cs sized so 1/Cs dominates.
Use a low-inductance (0603/0402) resistor for the snubber to avoid adding inductance.