type
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Input Parameters Specification
Peak Current IpkMaximum switching current through the device or diode used for RC snubber sizing.
Rail Voltage VrailDC bus or switching rail voltage used to estimate capacitor stress and power loss.
Rise Time and FrequencyRise time method uses transition time and switching frequency to size snubber capacitor and resistor.
dV and InductanceInductance method uses parasitic inductance and allowed voltage rise to control switching spike energy.
Practical Operational Examples
MOSFET Switching Spike
Use the rise time method when peak current, rail voltage, switching frequency and transition rise time are known.
Parasitic Inductance Snubber
Use the inductance method when leakage inductance or wiring inductance creates voltage overshoot across the switch.
Flyback / SMPS Clamp
Estimate capacitor, resistor and dissipation when a fast switching node rings due to leakage inductance.
Relay Contact Protection
Use RC snubber values as a starting point to reduce arcing and ringing in inductive load switching.
Diagrams & Theory
An RC snubber is placed across a switching device, diode, relay contact or transformer winding to absorb leakage energy, reduce voltage spikes, and damp high-frequency ringing.
Formulas & Mathematical Logic
Rise Time Method: Convert rise time from µs to seconds and frequency from kHz to Hz.
Capacitance: C = Ipk × rt / Vrail, then C is displayed in nF.
Resistance: R = 1 / (F × C × 20).
Power: P = C × Vrail² × F / 2.
Inductance Method: Convert inductance from µH to H and frequency from kHz to Hz.
Capacitance: C = L × Ipk² / (dV × (dV + 2 × Vrail)), then C is displayed in nF.
Resistance: R = 10 / (F × C).
Power: P = (L × Ipk² / 2) × F.
Step-by-Step Example
Example 1 — Rise Time Method: Ipk = 5 A, Vrail = 48 V, frequency = 100 kHz, rise time = 0.2 µs.
Step 1: Convert rise time: 0.2 µs = 0.0000002 s.
Step 2: C = 5 × 0.0000002 / 48 = 20.83 nF.
Step 3: R = 1 / (100000 × C × 20).
Step 4: P = C × 48² × 100000 / 2.
Example 2 — Inductance Method: use parasitic inductance and allowed voltage rise when ringing energy is known from layout or transformer leakage.
How to Use This Calculator
Select Rise Time Method or Inductance and Voltage Spike Method.
Enter peak current, rail voltage and switching frequency.
For Rise Time Method, enter the switching rise time in microseconds.
For Inductance Method, enter allowed voltage rise and circuit inductance.
Click Calculate to get snubber capacitor, resistance and power dissipation.
Select real capacitor voltage rating and resistor wattage with safety margin.
About This Calculator
Design RC snubber values for switching spike and ringing control.
The CalcBoy Snubber Circuit Design Calculator estimates RC snubber capacitor, resistor and power values using either a rise-time method or a parasitic inductance voltage-spike method.
Switching circuits often produce voltage overshoot and high-frequency ringing because of leakage inductance, PCB trace inductance, transformer winding leakage, diode reverse recovery and fast MOSFET transitions. An RC snubber gives that unwanted energy a controlled path so the switching node settles faster and the device sees less peak voltage stress.
This calculator is useful for MOSFET switching circuits, SMPS designs, flyback transformers, buck and boost converters, diode snubbers, relay contact protection, motor drivers and pulse power circuits. The rise-time method is convenient when you know peak current, rail voltage, switching frequency and transition time. The inductance method is better when you know parasitic inductance and the allowed voltage overshoot.
Snubber design is always a trade-off. More capacitance can reduce spikes but increases dissipation and slows the switching edge. Too low a resistance may create high current pulses, while too high a resistance may not damp ringing well. Use the result as a starting point, then confirm with an oscilloscope, thermal check and real switching waveform.
Best UseRC snubber sizing for switching spikes and ringing.
Supported InputsPeak current, rail voltage, frequency, rise time, dV and inductance.
Helpful ForMOSFETs, diodes, flyback supplies, relay contacts and power switches.
Design ReminderSnubber resistor wattage can become significant at high frequency.
Tip: After calculating, always check snubber resistor temperature. A snubber that looks electrically correct can still fail if power dissipation is ignored.
Frequently Asked Questions
What is an RC snubber?
An RC snubber is a resistor-capacitor network used to reduce voltage spikes, ringing and switching stress.
Where is a snubber connected?
It is commonly connected across a MOSFET, diode, relay contact, transformer winding or noisy switching node.
Which method should I use?
Use the rise time method when transition time is known. Use the inductance method when parasitic inductance and allowed voltage rise are known.
Why is snubber power important?
The snubber resistor dissipates energy every switching cycle, so high frequency can create noticeable heat.
Can this replace oscilloscope tuning?
No. It gives starting values. Final snubber selection should be verified by measuring ringing and temperature on real hardware.
What voltage rating should the capacitor have?
Use a capacitor voltage rating comfortably above the rail voltage and expected spike voltage, with suitable pulse current capability.
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