Resonant Converter Design Calculator

Calculator Inputs

The page stays in a single-column layout. The calculator area uses three columns on large screens, two on medium screens, and one on mobile screens.

Topology

Bridge Type

Minimum Input Voltage (V)

Nominal Input Voltage (V)

Maximum Input Voltage (V)

Output Voltage (V)

Rated Output Power (W)

Efficiency Estimate (%)

Resonant Frequency (kHz)

Target Loaded Q

Lm/Lr Ratio

Used mainly for LLC estimation.

Rectifier Drop Allowance (V)

Design Margin (%)

Sweep Points

Example Data Table

This sample illustrates a common isolated power stage sizing case.

Parameter	Example Value	Unit
Topology	LLC Resonant	—
Bridge Type	Full Bridge	—
Input Voltage Range	340 / 380 / 420	V
Output Voltage	48	V
Output Power	500	W
Efficiency	93	%
Resonant Frequency	120	kHz
Loaded Q	0.45	—
Lm/Lr Ratio	6	—
Rectifier Drop	0.6	V
Design Margin	10	%

Formula Used

1. Design Power:

P_design = P_out × (1 + margin/100)

2. Effective Secondary Voltage:

V_sec,eff = V_out + V_{rectifier drop}

3. Turns Ratio:

n = (V_in,nom × bridge factor) / (V_sec,eff × M_nom)

4. Load Resistance:

R_load = V_out² / P_design

5. Reflected AC Load:

R_ac = (8 × n² × R_load) / π²

6. Characteristic Impedance:

Z_r = Q × R_ac

7. Tank Components:

L_r = Z_r / ω₀

C_r = 1 / (ω₀ × Z_r)

ω₀ = 2πf₀

8. LLC Magnetizing Inductance:

L_m = (L_m/L_r ratio) × L_r

The gain equations in this tool are approximate screening models for LLC, SRC, and PRC behavior. They are useful for first-pass sizing, comparison, and sweep visualization, but final designs should still be validated through magnetics design, time-domain simulation, stress checks, and thermal analysis.

How to Use This Calculator

Choose the resonant topology and bridge type.
Enter minimum, nominal, and maximum input voltage values.
Enter the required output voltage and rated output power.
Provide expected efficiency, resonant frequency, and target loaded Q.
For LLC designs, set the Lm/Lr ratio for magnetizing behavior.
Add rectifier drop and design margin to reflect practical implementation.
Click Calculate Design to see results above the form.
Review tank values, operating frequencies, sweep graph, and export files.

Frequently Asked Questions

1. What does this calculator design?

It provides first-pass resonant tank sizing, transformer turns ratio, reflected load, estimated gain window, and suggested operating frequencies for LLC, SRC, or PRC power stages.

2. Is this enough for production hardware?

No. It is a sizing and comparison tool. Final hardware still needs magnetics design, semiconductor stress checks, thermal review, control loop analysis, and simulation before release.

3. Why does LLC need an Lm/Lr ratio?

LLC converters use a magnetizing branch that changes gain shape, current circulation, and soft-switching behavior. The Lm/Lr ratio helps create a more realistic preliminary estimate.

4. What is the loaded Q used for?

Loaded Q links reflected resistance to tank impedance. It influences gain sharpness, current stress, and how quickly the converter response changes around resonance.

5. Why include rectifier drop?

Secondary rectifiers, synchronous stages, or wiring losses reduce available output voltage. Adding this allowance makes the turns ratio and gain requirement more practical.

6. What does the graph show?

It shows approximate gain and estimated output voltage across switching frequency sweep points. This helps identify whether low-line and high-line requirements are reachable.

7. How should I choose the resonant frequency?

Start from switching device limits, magnetics size goals, efficiency targets, and control range. Then verify losses and stress with simulation and hardware measurements.

8. What do the CSV and PDF downloads contain?

The CSV exports design summary values and the sweep dataset. The PDF exports the main calculated parameters and operating frequency targets for reporting.

Engineering Notes

Resonant converters trade switching stress for frequency-dependent gain control. In practice, component tolerances, leakage inductance, stray capacitance, rectifier behavior, dead time, winding layout, and thermal drift can shift the real operating point. Use this tool as a structured front-end design helper, then confirm performance through simulation and prototype testing.