Raspberry-piHow-ToBeginner · 3 min read

How to Calculate Inductor Value for Buck Converter

To calculate the inductor value (L) for a buck converter, use the formula L = (V_in - V_out) × V_out / (ΔI_L × f × V_in), where V_in is input voltage, V_out is output voltage, ΔI_L is the desired inductor current ripple, and f is the switching frequency. This ensures the inductor smooths current properly for efficient voltage conversion.

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Syntax

The formula to calculate the inductor value L in a buck converter is:

L = (V_in - V_out) × V_out / (ΔI_L × f × V_in)

V_in: Input voltage to the converter
V_out: Desired output voltage
ΔI_L: Allowed ripple current in the inductor (peak-to-peak)
f: Switching frequency of the converter

This formula balances voltage, current ripple, and switching speed to pick the right inductor size.

none

L = (Vin - Vout) * Vout / (Delta_IL * f * Vin)

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Example

This example calculates the inductor value for a buck converter with 12 V input, 5 V output, 30% ripple current of 3 A load current, and 100 kHz switching frequency.

python

Vin = 12.0  # Input voltage in volts
Vout = 5.0   # Output voltage in volts
Iout = 3.0   # Output current in amperes
f = 100000  # Switching frequency in Hz
ripple_percent = 0.3  # 30% ripple of output current

Delta_IL = ripple_percent * Iout  # Inductor ripple current

L = (Vin - Vout) * Vout / (Delta_IL * f)  # Inductor value in henries

print(f"Inductor value L = {L*1e6:.2f} µH")

Output

Inductor value L = 58.33 µH

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Common Pitfalls

Choosing too small an inductor: Causes high ripple current, increasing losses and noise.
Choosing too large an inductor: Slows response time and increases size and cost.
Ignoring switching frequency: Higher frequency allows smaller inductors; forgetting this leads to wrong sizing.
Not accounting for ripple current: Ripple current affects efficiency and component stress; it should be 20-40% of load current.

Always verify calculations with datasheets and consider inductor saturation current ratings.

none

## Wrong approach: Ignoring ripple current
L_wrong = (Vin - Vout) * Vout / (f)  # Missing Delta_IL term

## Correct approach:
L_correct = (Vin - Vout) * Vout / (Delta_IL * f)

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Quick Reference

Parameter	Description	Typical Values/Notes
V_in	Input voltage	Depends on power source, e.g., 12 V
V_out	Output voltage	Desired voltage, e.g., 5 V
ΔI_L	Inductor ripple current	20-40% of output current recommended
f	Switching frequency	Typically 50 kHz to 500 kHz
L	Inductor value	Calculated in henries (H), usually microhenries (µH)

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Key Takeaways

Use the formula L = (Vin - Vout) × Vout / (ΔIL × f × Vin) to calculate inductor value.

Choose ripple current (ΔIL) as 20-40% of the output current for balance between size and performance.

Higher switching frequency allows smaller inductors but may increase switching losses.

Verify inductor current rating to avoid saturation and ensure reliable operation.

Avoid skipping ripple current in calculations to prevent inefficient or unstable designs.