PFC Boost Inductor

L = Vin² × (Vout − Vin) / (Vout × ΔI × f × Pout)

Quick answer

This calculator solves L = Vin² × (Vout − Vin) / (Vout × ΔI × f_sw × Pout) for L. With Input Voltage (RMS) 12 V, Output Voltage 26.4 V, Max Ripple Current 2 A, Switching Frequency 100 kHz, Output Power 10 W, the result is 39.27.

Calculator

Result
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Formula

L = Vin² × (Vout − Vin) / (Vout × ΔI × f_sw × Pout)

Description

Active power factor correction uses a boost converter operated in continuous conduction mode to shape the input current waveform to follow the input voltage, achieving near-unity power factor. The PFC inductor is the critical component determining the ripple current magnitude. The worst-case ripple occurs at the peak of the input voltage (or at specific duty cycles depending on the topology). This formula gives the inductance needed to limit the maximum current ripple to ΔI. PFC is mandatory for power supplies above 75 W per IEC 61000-3-2.

Variables

  • V_in — RMS input voltage (V)
  • V_out — PFC output voltage, typically 380-400 V (V)
  • ΔI — Maximum allowable ripple current (A)
  • f — Switching frequency (Hz)
  • P_out — Output power (W)

Practical Notes

Typical values: 230 V input, 400 V output, 65 kHz switching, 20% ripple gives L ≈ 200-600 µH for 100-1000 W supplies. The inductor must handle the peak current (√2 × Iin_rms + ΔI/2) without saturating. Powdered iron or gapped ferrite cores are typically used. Core loss is significant due to the 100/120 Hz current envelope and must be carefully evaluated.

Symbols and units

Symbol Meaning Default unit Accepted units
Vin Input Voltage (RMS) V pV, nV, µV, mV, V, kV
Vout Output Voltage V pV, nV, µV, mV, V, kV
dI Max Ripple Current A pA, nA, µA, mA, A, kA
f Switching Frequency kHz Hz, kHz, MHz, GHz
Pout Output Power W µW, mW, W, kW

Step by step

  1. 1. What you know: Input Voltage (RMS) 12 V, Output Voltage 26.4 V, Max Ripple Current 2 A, Switching Frequency 100 kHz, Output Power 10 W
  2. 2. The relation: L = Vin² × (Vout − Vin) / (Vout × ΔI × f_sw × Pout)
  3. 3. Substitute: Vin = 12 V, Vout = 26.4 V, dI = 2 A, f = 100 kHz, Pout = 10 W
  4. 4. Result: L = 39.27

Related quantities from the same inputs

  • P = V × I = 24 W

Worked examples

Minimum range

Given: Input Voltage (RMS) 0.33 V, Output Voltage 0.726 V, Max Ripple Current 2 mA, Switching Frequency 100 Hz, Output Power 10 mW

Result: L = 2.97 × 10⁷

Low range

Given: Input Voltage (RMS) 3.3 V, Output Voltage 7.26 V, Max Ripple Current 20 mA, Switching Frequency 1 kHz, Output Power 100 mW

Result: L = 2.97 × 10⁶

Typical

Given: Input Voltage (RMS) 12 V, Output Voltage 26.4 V, Max Ripple Current 2 A, Switching Frequency 100 kHz, Output Power 10 W

Result: L = 39.27

High range

Given: Input Voltage (RMS) 0.23 kV, Output Voltage 0.506 kV, Max Ripple Current 100 A, Switching Frequency 0.5 MHz, Output Power 1 kW

Result: L = 0.5771

Maximum range

Given: Input Voltage (RMS) 2.3 kV, Output Voltage 5.06 kV, Max Ripple Current 1 kA, Switching Frequency 5 MHz, Output Power 10 kW

Result: L = 0.05771

How L changes with Input Voltage (RMS)

Input Voltage (RMS) (input) L (result)
1.2 V 0.6873
3 V 3.989
6 V 13.91
9 V 26.69
12 V 39.27
18 V 51.55
24 V 26.18
48 V -942.5
84 V -7697
120 V -25530

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Frequently asked questions

How do you calculate PFC Boost Inductor?

Use L = Vin² × (Vout − Vin) / (Vout × ΔI × f_sw × Pout). With Input Voltage (RMS) 12 V, Output Voltage 26.4 V, Max Ripple Current 2 A, Switching Frequency 100 kHz, Output Power 10 W, L works out to 39.27.

What is the formula for PFC Boost Inductor?

The formula is L = Vin² × (Vout − Vin) / (Vout × ΔI × f_sw × Pout). Active power factor correction uses a boost converter operated in continuous conduction mode to shape the input current waveform to follow the input voltage, achieving near-unity power factor.

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