MOSFET Avalanche Energy
Eas = 0.5 × L × I² × Vbr/(Vbr − Vcc)
Quick answer
This calculator solves E_as = ½ × L × I² × V_br / (V_br − V_cc) for Eas. With Inductance 100 µH, Current at Turn-Off 2 A, Breakdown Voltage 12 V, Supply Voltage 26.4 V, the result is -1.67 × 10⁻⁴.
Calculator
Formula
Description
When a MOSFET turns off an inductive load without a freewheeling diode, the inductor current forces the drain voltage above the supply voltage until the MOSFET enters avalanche breakdown. The MOSFET must absorb the stored inductive energy (½LI²) multiplied by a factor Vbr/(Vbr − Vcc) that accounts for the supply voltage sourcing additional energy during the avalanche event. The MOSFET datasheet specifies a maximum single-pulse avalanche energy (EAS) rating. Exceeding this value causes permanent damage or destruction.
Variables
- L — Parasitic or load inductance (H)
- I — Current flowing when the switch opens (A)
- V_br — MOSFET avalanche breakdown voltage (V)
- V_cc — Supply voltage (V)
Practical Notes
The result is in joules. Always ensure the calculated energy is well below the MOSFET EAS rating, accounting for temperature derating. EAS ratings decrease significantly at elevated temperatures. For reliable operation, keep the avalanche energy below 25% of the rated EAS. Adding a snubber (RC or RCD) or a TVS diode across the MOSFET can clamp the voltage and prevent avalanche entirely.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| L | Inductance | µH | nH, µH, mH, H |
| I | Current at Turn-Off | A | pA, nA, µA, mA, A, kA |
| Vbr | Breakdown Voltage | V | pV, nV, µV, mV, V, kV |
| Vcc | Supply Voltage | V | pV, nV, µV, mV, V, kV |
Step by step
- 1. What you know: Inductance 100 µH, Current at Turn-Off 2 A, Breakdown Voltage 12 V, Supply Voltage 26.4 V
- 2. The relation: E_as = ½ × L × I² × V_br / (V_br − V_cc)
- 3. Substitute: L = 100 µH, I = 2 A, Vbr = 12 V, Vcc = 26.4 V
- 4. Result: Eas = -1.67 × 10⁻⁴
Related quantities from the same inputs
- P = V × I = 24 W
Worked examples
Minimum range
Given: Inductance 100 nH, Current at Turn-Off 2 mA, Breakdown Voltage 0.33 V, Supply Voltage 0.726 V
Result: Eas = -1.67 × 10⁻¹³
Low range
Given: Inductance 1 µH, Current at Turn-Off 20 mA, Breakdown Voltage 3.3 V, Supply Voltage 7.26 V
Result: Eas = -1.67 × 10⁻¹⁰
Typical
Given: Inductance 100 µH, Current at Turn-Off 2 A, Breakdown Voltage 12 V, Supply Voltage 26.4 V
Result: Eas = -1.67 × 10⁻⁴
High range
Given: Inductance 0.47 mH, Current at Turn-Off 100 A, Breakdown Voltage 0.23 kV, Supply Voltage 0.506 kV
Result: Eas = -1.958
Maximum range
Given: Inductance 4.7 mH, Current at Turn-Off 1 kA, Breakdown Voltage 2.3 kV, Supply Voltage 5.06 kV
Result: Eas = -1958
How Eas changes with Inductance
| Inductance (input) | Eas (result) |
|---|---|
| 10 µH | -1.67 × 10⁻⁵ |
| 25 µH | -4.17 × 10⁻⁵ |
| 50 µH | -8.33 × 10⁻⁵ |
| 75 µH | -1.25 × 10⁻⁴ |
| 100 µH | -1.67 × 10⁻⁴ |
| 150 µH | -2.5 × 10⁻⁴ |
| 0.2 mH | -3.33 × 10⁻⁴ |
| 0.4 mH | -6.67 × 10⁻⁴ |
| 0.7 mH | -0.001167 |
| 1 mH | -0.001667 |
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<p><a href="https://vbatpower.com/formulas/avalanche-energy/">MOSFET Avalanche Energy</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate MOSFET Avalanche Energy?
Use E_as = ½ × L × I² × V_br / (V_br − V_cc). With Inductance 100 µH, Current at Turn-Off 2 A, Breakdown Voltage 12 V, Supply Voltage 26.4 V, Eas works out to -1.67 × 10⁻⁴.
How do you calculate mosfet avalanche calculation?
Rearrange for E_as: with Inductance 1 µH, Current at Turn-Off 20 mA, Breakdown Voltage 3.3 V, Supply Voltage 7.26 V, E_as is -1.67 × 10⁻¹⁰.
What is the formula for MOSFET Avalanche Energy?
The formula is E_as = ½ × L × I² × V_br / (V_br − V_cc). When a MOSFET turns off an inductive load without a freewheeling diode, the inductor current forces the drain voltage above the supply voltage until the MOSFET enters avalanche breakdown.
Related Concepts
All Semiconductors formulas →Need more features?
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