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Resonant LLC Converter Tank Parameters Calculator

Half-bridge LLC resonant converters are the premier topology for high-efficiency DC-DC telecom rectifiers, server power supplies, and EV chargers.

DC bus voltage supplied from PFC front end (typically 380 - 400 V DC).

Regulated DC output voltage (e.g. 12 V or 24 V).

Continuous maximum output power delivered by converter.

Target series resonant frequency fr = 1 / (2π √(Lr Cr)) (typically 70 - 200 kHz).

Ratio of transformer magnetizing inductance to series resonant inductance (typically 4 - 8).

Primary-to-secondary turns ratio n = Np / Ns = Vin_nom / (2 · Vo).

Calculated Result
356.68 µH

Resonant Inductor (L_r)

Resonant Capacitor (C_r)

7.1 nF

Magnetizing Inductance (L_m)

1783.4 µH

Reflected Load (R_ac)

498.01 Ω

Quality Factor (Q)

0.45

Max Attainable Gain

1.22

Calculation Breakdown

  1. FHA Reflected AC Resistance (R_ac)R_ac = (8 · n² / π²) · (Vₒ² / Pₒ) = 498.01 Ω
  2. Resonant Tank Sizing (L_r, C_r)C_r = 1 / (2π · 100 kHz · 0.45 · 498.01 Ω) = 7.1 nF; L_r = 356.68 µH
  3. Transformer Magnetizing Inductance (L_m)L_m = k · L_r = 5 · 356.68 µH = 1783.4 µH

LLC Tank Component Values

Interactive visualization based on your current inputs

Value
0.082164246328L_r (µH)C_r (nF x 10)L_m (µH / 10)R_ac (Ω / 10)ParameterValue

What Is the Resonant LLC Converter Tank Parameters Calculator?

Half-bridge LLC resonant converters are the premier topology for high-efficiency DC-DC telecom rectifiers, server power supplies, and EV chargers.

By exploiting resonant tank characteristics, LLC converters achieve Zero-Voltage Switching (ZVS) for primary switches and Zero-Current Switching (ZCS) for secondary rectifiers across entire load ranges.

This calculator utilizes First Harmonic Approximation (FHA) modeling to size series resonant inductance (Lr), resonant capacitance (Cr), and transformer magnetizing inductance (Lm).

How Does the Resonant LLC Converter Tank Parameters Calculator Work?

The calculation evaluates user-provided measurements using recognized domain equations, converts between measurement units, and adjusts for real-world efficiency factors.

Resonant LLC Converter Tank Parameters Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

R_{ac} = \frac{8 n^2}{\pi^2} \frac{V_o^2}{P_o}, \quad C_r = \frac{1}{2\pi f_r Q R_{ac}}, \quad L_r = \frac{1}{(2\pi f_r)^2 C_r}, \quad L_m = k L_r

Rac is AC reflected resistance, Cr is series capacitor, Lr is resonant inductor, and Lm is transformer magnetizing inductance.

How to Use the Resonant LLC Converter Tank Parameters Calculator

  1. Enter your primary measurements in the input fields above.
  2. Select your preferred units (e.g. metric or imperial) if applicable.
  3. Review or adjust operational assumptions such as field efficiency.
  4. Click Calculate to instantly generate the full results breakdown and visual chart.
  5. Use the Reset button at any time to clear the form and test a new scenario.

Step-by-Step Example Calculation

400V to 24V 240W Server Power Supply

Input Values:

inputVoltageNominalV:400
outputVoltageV:24
outputPowerWatts:240
resonantFrequencyKHz:100
inductanceRatioK:5.0
transformerTurnsRatioNpNs:16.0
Worked Steps: Determines Cr = 7.7 nF, Lr = 328 µH, and Lm = 1640 µH.

Understanding Your Result

Your calculated result represents the realistic operational capacity or baseline output under the specified conditions. Comparing theoretical and effective outputs reveals the direct impact of turns, overlap, and practical downtime.

Factors That Affect the Result

Field terrain, operator experience, equipment maintenance, overlap margin, and weather conditions can significantly influence real-world output.

When Should You Use This Calculator?

Use this calculator whenever you need quick, verified estimates for job planning, budgeting, equipment sizing, or project timelines.

Assumptions & Limitations

  • Uses First Harmonic Approximation (FHA) where Rac = (8 n² / π²) · RL.
  • A lower ratio k increases peak gain capability at the expense of higher circulating magnetizing current.
  • Resonant tank is optimized for near-unity gain operation at nominal input voltage.

Frequently Asked Questions

Calculation Accuracy & Reference Note

This calculator implements verified, deterministic mathematical equations based on published standards. Results should be treated as professional engineering estimates; always verify critical operations with local equipment manuals and site inspections.

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