SMPS Transformer Calculator | High Frequency Design Tool
Power Electronics

SMPS Transformer Calculator

Design High-Frequency Isolated Transformers for Forward, Half-Bridge, Full-Bridge, and Push-Pull converters.

This tool includes a database of standard cores (EE, ETD, PQ), calculates primary/secondary turns, and provides Wire Gauge (AWG) suggestions based on skin depth and current density.

Design Specs

Configuration
Core Selection
mm²
mm²
Operating Points
V
kHz
V
0-1
Advanced
T
A/mm²
0-1
Secondaries

Design Analysis

Result
Primary Winding
—
—ΔB Used
—Ipri,rms
—Wire Area
Wire: —
Window & Losses
—%Window Fill
— WPcu (Total)
Skin Depth: —

Secondary Winding Details

How to Use This Calculator

1

Define Core & Topology

Select your topology (e.g., Half-Bridge) and choose a core from the preset list (e.g., ETD-39). The calculator will automatically fill in the core’s Magnetic Area ($A_e$) and Window Area ($A_w$).

2

Set Input Parameters

Enter the Min/Max Input Voltage and your switching Frequency. These determine the volt-seconds the primary winding must support to avoid saturation.

3

Add Secondary Windings

Click the + Output button to add voltage rails. For each rail, specify the target Voltage, Current, and the type of rectification (Sync, Diode, or Bridge).

4

Analyze & Tune

Check the Window Fill result. If it is >100%, the copper won’t fit in the bobbin. Try reducing the current density ($J$) or selecting a larger core.

Troubleshooting Results

Error: “Window Fill > 100%”

The required copper wire area is larger than the available window space in the core.
Fix: Increase Current Density ($J$) to 5-6 A/mm² (if cooling permits), or select a physically larger core (e.g., move from ETD-34 to ETD-39).

Error: “Flux Saturation Risk”

The operating flux density ($\Delta B$) exceeds the core’s limit ($B_{max}$).
Fix: Increase the number of primary turns, increase the core area ($A_e$), or increase the switching frequency ($f_{sw}$).

Wire Recommendation “Litz”

If the calculator suggests “Multi-strand” or Litz wire, it means the required wire diameter is thicker than twice the skin depth. Using a single solid wire would result in excessive overheating due to the skin effect.

Topology Selection Guide

TopologyPower RangeSwitch VstressTypical Use
Forward< 150 W2 × VinAdaptors, low power supplies
Push-Pull150W – 1kW2 × VinLow voltage DC inputs (12V/24V Inverters)
Half-Bridge150W – 500W1 × VinMains voltage inputs, ATX supplies
Full-Bridge> 500 W1 × VinHigh power, high efficiency industrial