rc snubber calculator - Aaron Graves, PhDude Replica

Quick RC Snubber Estimator

Use your measured ringing frequency and estimated parasitic capacitance to get a practical starting point for snubber R and C.

Measured ringing frequency (MHz)

Parasitic capacitance at switching node (pF)

Snubber capacitor multiplier, k × Cpar (typical 2 to 5)

Voltage swing across snubber (V)

Switching frequency (kHz)

Optional peak current during turn-off (A)

Enter your values and click Calculate Snubber.

This tool provides first-pass design values. Final tuning should always be done on real hardware with an oscilloscope and proper probing technique.

What this RC snubber calculator does

An RC snubber is a resistor and capacitor in series, typically placed across a switch (MOSFET, IGBT, relay contact, triac, etc.) to reduce voltage overshoot and ringing. This calculator estimates:

Parasitic inductance implied by your ringing measurement
A practical starting snubber capacitor value
A damping resistor value for useful ring suppression
Approximate snubber power dissipation for resistor sizing

How to use the calculator

1) Measure ringing frequency

Capture the switching waveform and identify the ring frequency after turn-on or turn-off. Use good probing technique (short ground spring, differential probe where needed).

2) Estimate parasitic capacitance

Use device output capacitance (such as MOSFET Coss at your operating voltage), plus layout and stray capacitance. If uncertain, estimate and tune experimentally.

3) Choose multiplier k

Start with k = 2 to 5. Larger values improve damping but increase losses.

4) Enter voltage and switching frequency

These values estimate dissipation in the snubber resistor. Use conservative thermal margins.

Equations used

The calculator uses common first-order snubber relationships:

L_parasitic = 1 / ( (2π f_ring)^2 · C_par )

C_snubber = k · C_par

R_snubber ≈ √(L_parasitic / C_snubber)

P_C ≈ 0.5 · C_snubber · V^2 · f_sw

If peak current is provided, the tool also shows:

E_L = 0.5 · L_parasitic · I_peak², P_L = E_L · f_sw

Practical tuning tips

Start with the calculated resistor and capacitor.
Increase C if overshoot remains high.
Adjust R upward if heating is excessive and damping is still acceptable.
Choose pulse-rated film or ceramic capacitors with adequate voltage margin.
Use non-inductive, pulse-capable resistors and check temperature rise.
Place snubber parts physically close to the switching loop.

Limitations and safety notes

This is a design aid, not a substitute for full EMI/thermal validation. Real circuits include nonlinear capacitance, layout-dependent inductance, and operating-point variation. Always verify:

Device Vds/Vce peak margin
Snubber resistor pulse stress and continuous dissipation
Capacitor ripple current and temperature rise
Efficiency impact at full load and high line

For mains and high-voltage systems, follow safety standards and isolation practices.