Flyback clamp Calculator

Stored coil energy	500 µJ
Estimated release time	580.76 µs

Stored coil energy

500 µJ

Estimated release time

580.76 µs

Voltage across clamp	12.7 V
Initial clamp power	1.27 W

Voltage across clamp

12.7 V

Initial clamp power

1.27 W

How flyback clamp works

L1 starts with the selected current and V2 opens the low-side switch S1 almost immediately; D1 and D2 return that current to the supply rail. Increasing the Zener voltage releases the coil faster but raises switch voltage. R1 represents winding resistance; C1 represents 100 pF of switch-node capacitance; it can ring with the coil after the clamp stops conducting.

E_L=\tfrac12 L_1I_0^2

Constant 0.7 V diode drop and nominal Zener voltage in the equations. The guest uses a nonlinear Zener; actual clamping varies with current. The short initial on-time is 0.01% of the estimated decay time, keeping the turn-off current close to the selected initial current.

Change the form inputs or click a component value on the schematic. Choose Try in CircuitSim to simulate the configured circuit.

Do the math

Selected input values
V1	12 V
L1 — Coil inductance	100 mH
L1 — Current at switch-off	100 mA
D2	12 V
R1	100 Ω

Stored energy: $E_L=\tfrac12 L_1I_0^2$
$\tfrac12\times100\,\mathrm{mH}\times(100\,\mathrm{mA})^2$
≈ 500 µJ
Switch voltage: $V_{pk}=V_1+V_Z+V_D$
$12\,\mathrm{V}+12\,\mathrm{V}+0.7\,\mathrm V$
≈ 24.7 V
Current decay time: $t=\frac{L_1}{R_1}\ln\!\left(1+\frac{R_1I_0}{V_Z+V_D}\right)$
$1\,\mathrm{ms}\ln(1+0.79)$
≈ 580.76 µs

Configure

Schematic

Results

How flyback clamp works

Flyback clamp calculator

Configure

Schematic

Results

How flyback clamp works

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