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Free RC Snubber Circuit Calculator Electronics & RF
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Free RC Snubber Circuit Calculator

Calculate snubber capacitance (C_snub), damping resistance (R_snub), ringing frequency, and resistor power dissipation for MOSFET, IGBT, and Triac protection.

⚡ Circuit Parasitics & Switching

DC bus or AC peak voltage
e.g. 100 kHz (or 0.06 kHz for AC line)
Trace & transformer leakage
Output capacitance Coss
Higher capacitance provides tighter clamping but increases power loss

⚡ Recommended Component Values

Snubber Capacitor (C) -- Film / C0G ceramic
Snubber Resistor (R) -- Non-inductive resistor
Resistor Power Dissipation --
Recommended Resistor Rating --
Undamped Ringing Frequency --
Characteristic Impedance (Z0) --
RC Time Constant (τ) --

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Why Inductive Ringing Destroys Power Semiconductors

In high-speed switching circuits (MOSFET, IGBT, GaN, Triac, and flyback converters), abrupt current interruption (( rac{di}{dt})) excites parasitic loop inductances ((L_p)) and device capacitances ((C_{ ext{oss}})). Without damping, this creates high-frequency voltage oscillations (ringing) that routinely overshoot the DC bus voltage by 150% to 250%, exceeding semiconductor avalanche breakdown thresholds and broadcasting massive electromagnetic interference (EMI).

The RC Snubber Damping Formula

An RC snubber dampens ringing by absorbing high-frequency transient energy in resistor (R_{ ext{snub}}) while capacitor (C_{ ext{snub}}) blocks low-frequency DC current to avoid short-circuiting the power rail:

f_ring = 1 / [2 × π × √(L_p × C_p)]
Characteristic Impedance: Z_0 = √(L_p / C_p)
Optimal Snubber Resistor: R_snub ≈ Z_0
Optimal Snubber Capacitor: C_snub = 2 to 3 × C_p

Resistor Power Dissipation and Selection

At every switching cycle, capacitor (C_{ ext{snub}}) is charged to (V_{ ext{bus}}) and discharged, dissipating energy as heat inside (R_{ ext{snub}}):

P_resistor = C_snub × V_bus² × f_switch

Crucial Rule: Always specify non-inductive resistors (such as metal film, carbon composition, or planar thick film). Wirewound resistors have intrinsic spiral inductance that prevents them from responding to nanosecond rise-time ringing pulses.

Frequently Asked Questions

How do I experimentally measure parasitic Lp and Cp on an oscilloscope?

First, measure the ringing period (T1) of the un-snubbed voltage overshoot. Then, solder a small known test capacitor across the switch until the ringing frequency drops to exactly half (T2 = 2 * T1). That test capacitor is equal to 3 * Cp, allowing you to calculate exact parasitic Lp and Cp.

Why must the snubber capacitor be a C0G/NP0 ceramic or polypropylene film?

Standard Class 2 ceramics (X7R, X5R) lose up to 70% of their effective capacitance under high DC bias voltage and have high dielectric dissipation factors that cause catastrophic internal self-heating at RF frequencies. C0G (NP0) and polypropylene film maintain rock-solid capacitance under full voltage and RF currents.

What is the difference between an RC snubber and an RCD snubber?

A simple RC snubber dissipates power during both turn-on and turn-off transitions. An RCD snubber adds a fast-recovery diode in parallel with the resistor so the capacitor charges through the diode with zero resistance during turn-off and discharges slowly through the resistor, cutting power loss in high-power flyback supplies.

Can a snubber be placed directly across a Triac or solid-state relay (SSR)?

Yes. Triacs controlling inductive motors or solenoids suffer from high dv/dt commutating stress when current crosses zero, which can falsely re-trigger the Triac. An RC snubber placed across MT1 and MT2 limits dv/dt below the manufacturer threshold (typically < 50V/µs).

How close should the RC snubber be placed to the MOSFET?

The snubber components must be placed immediately adjacent to the drain and source terminals with the shortest, widest PCB traces possible. Adding even 10 mm of thin trace introduces parasitic loop inductance that defeats the purpose of the snubber.