Published November 6, 2026

An Isolated 12V Flyback Power Supply Using Infineon ICE3BS02

This project demonstrates how to design an isolated 12V AC-DC flyback power supply using the Infineon ICE3BS02 offline PWM controller.

IntermediateWork in progress13

An Isolated 12V Flyback Power Supply Using Infineon ICE3BS02

Things used in this project

Hardware components

Infineon ICE3BS02

Main offline flyback PWM controller

External Power MOSFET

Primary-side switching device

Flyback Transformer

Provides energy transfer and galvanic isolation

Fast Recovery Rectifier

Secondary-side output rectification

TL431

Adjustable output voltage reference and feedback control

Optocoupler

Transfers isolated feedback signals to the primary side

Current Sense Resistor

Monitors primary switch current

Electrolytic Capacitors

Film Capacitors

Gate Resistors

Arduino Uno

Voltage Divider Resistors

LCD Display

Fuse and Surge Protection Components

Software apps and online services

Arduino IDE

KiCad

LTspice

Serial Plotter

Hand tools and fabrication machines

Digital Multimeter

Oscilloscope

Electronic DC Load

Soldering Station

PCB Prototyping Equipment

Wire Strippers and Cutters

Insulated Hand Tools

Isolation Transformer

Story

1. Introduction

Switching power supplies are widely used in embedded systems, industrial electronics, communication equipment, and consumer devices. Many of these applications require a stable low-voltage DC supply from an AC mains input.

An isolated flyback converter is a practical solution for low-power AC-DC conversion because it provides galvanic isolation while keeping the circuit relatively compact.

For this project, I selected the Infineon ICE3BS02, a member of the CoolSET F3 family. It is an offline current-mode PWM controller designed for flyback power supply applications.

One interesting feature of this IC is its integrated 500V startup cell. This simplifies the startup circuit by allowing the controller to obtain its initial supply from the rectified high-voltage input. After startup, the auxiliary transformer winding supplies the controller's VCC voltage.

The ICE3BS02 also operates at a fixed switching frequency of approximately 67 kHz and supports a maximum duty cycle of 72%.

2. Project Objectives

The main objective is to develop a practical isolated flyback power supply design and understand how its major circuit sections work together.

The project focuses on:

Understanding the operating principles of an offline flyback converter.
Implementing primary-side switching using an external MOSFET.
Using the ICE3BS02 for current-mode PWM control.
Designing an isolated secondary-side voltage feedback loop.
Understanding startup behavior and protection mechanisms.
Monitoring output voltage during startup and load variations.

The target output for the proposed prototype is 12V DC. The output current and power rating must be established through transformer design, MOSFET selection, thermal calculations, and verification of the complete power stage. No unverified power rating is assumed here.

3. Understanding the ICE3BS02

The ICE3BS02 integrates several functions that are useful in offline power supply applications.

Integrated High-Voltage Startup Cell

The integrated 500V startup cell helps charge the VCC capacitor during initial startup. Once the converter is operating, the auxiliary winding takes over the controller supply.

Current-Mode PWM Control

The controller monitors the voltage across an external current-sense resistor connected to the MOSFET source. This information is used for cycle-by-cycle current limiting and PWM regulation.

Active Burst Mode

At light loads, the controller can enter Active Burst Mode to reduce standby power consumption while maintaining a fast response to load changes.

Soft Start

An external capacitor connected to the SoftS pin controls the startup ramp and helps reduce excessive current during startup.

Protection Functions

The controller includes protection mechanisms associated with overload, open-loop conditions, VCC undervoltage, VCC overvoltage, and overtemperature detection.

These features make the ICE3BS02 a useful device for studying practical offline flyback converter design.

4. How the Power Supply Works

The power conversion process consists of several stages.

First, the AC input passes through the input protection and EMI filtering circuits. A bridge rectifier then converts the AC voltage into a high-voltage DC bus.

The ICE3BS02 controls an external MOSFET connected to the primary winding of the flyback transformer. When the MOSFET turns on, energy is stored in the transformer magnetizing inductance. When the MOSFET turns off, the stored energy is transferred to the secondary winding.

A fast rectifier and output capacitor convert the secondary-side pulses into a DC output.

For voltage regulation, a TL431-based feedback circuit monitors the output voltage. An optocoupler transfers the feedback information across the isolation barrier to the ICE3BS02 FB pin.

The controller adjusts its PWM operation according to the feedback signal to maintain the desired output voltage.

5. Arduino-Based Output Monitoring

To make the project more useful for embedded developers, I added a separate Arduino-based output monitoring module.

The Arduino does not control the ICE3BS02 or participate in the primary-side switching loop. Its purpose is simply to monitor the isolated 12V output.

A resistor divider scales the output voltage to a suitable range for the Arduino analog input.

The monitoring module can be used to:

Measure the DC output voltage.
Observe the startup voltage ramp.
Record voltage changes during load transitions.
Identify excessive output voltage variations.
Display measurements through the Arduino Serial Monitor.

This arrangement keeps the power regulation loop independent of the monitoring firmware.

6. Testing and Evaluation

The proposed prototype should be evaluated in several stages.

Startup Test

Apply the specified AC input through an appropriately protected laboratory setup and observe the controller startup sequence and output voltage ramp.

No-Load Test

Measure the output voltage and input power under no-load conditions. Check whether the converter enters Active Burst Mode as expected.

Load Variation Test

Use an electronic DC load to gradually increase the secondary-side load. Record the output voltage and observe its regulation behavior.

Protection Test

Evaluate the documented protection responses using controlled fault conditions and appropriate laboratory procedures. Do not deliberately create hazardous primary-side faults on an exposed prototype.

Thermal Test

Monitor the MOSFET, transformer, rectifier, and other power components during sustained operation.

The results should be compared against the actual design targets and the component ratings.

7. What Makes This Project Useful?

This project demonstrates more than simply connecting a PWM controller to a transformer.

It provides a practical learning path for understanding:

Offline AC-DC power conversion.
Flyback transformer operation.
Current-mode PWM control.
Isolated feedback regulation.
Startup and protection behavior.
Embedded voltage monitoring.

The combination of the ICE3BS02 and Arduino also illustrates how traditional analog power electronics can work alongside modern embedded monitoring systems.

8. Conclusion

The Infineon ICE3BS02 provides an integrated control solution for offline flyback power supplies. Its high-voltage startup cell, current-mode PWM control, Active Burst Mode, soft-start function, and protection mechanisms make it an interesting controller for studying isolated AC-DC conversion.

By combining the flyback converter with an independent Arduino voltage monitoring module, this project offers a practical way to investigate power supply behavior and understand the interaction between power electronics and embedded systems.

The same design approach can serve as a starting point for exploring auxiliary power supplies and other low-power isolated AC-DC applications.

Code

Code

/*
  Project: ICE3BS02 Flyback Power Supply Monitor
  Board: Arduino Uno

  Function:
  - Monitor isolated 12V DC output
  - Calculate output voltage using a resistor divider
  - Display voltage through Serial Monitor

  Hardware:
  - 100k resistor (upper divider)
  - 33k resistor (lower divider)
  - Arduino Uno
  - Analog input A0

  IMPORTANT:
  Connect this circuit only to the isolated
  secondary side of the flyback converter.
*/

const int voltagePin = A0;

const float referenceVoltage = 5.0;
const float upperResistor = 100000.0;
const float lowerResistor = 33000.0;

const float dividerRatio =
  (upperResistor + lowerResistor) / lowerResistor;

const int adcResolution = 1023;

void setup() {
  Serial.begin(9600);

  Serial.println("ICE3BS02 Power Supply Monitor");
  Serial.println("-----------------------------");
  Serial.println("Output Voltage Monitoring");
}

void loop() {

  int adcValue = analogRead(voltagePin);

  float measuredVoltage =
    (adcValue * referenceVoltage) / adcResolution;

  float outputVoltage =
    measuredVoltage * dividerRatio;

  Serial.print("ADC Value: ");
  Serial.print(adcValue);

  Serial.print(" | Output Voltage: ");
  Serial.print(outputVoltage, 2);

  Serial.println(" V");

  delay(500);
}

Credits

Robert Fletcher

20 projects • 1 follower

Senior semiconductor engineer at AVAQ Semiconductor. With extensive experience in electronic components, supply chain solutions & sourcing.

An Isolated 12V Flyback Power Supply Using Infineon ICE3BS02

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

1. Introduction

2. Project Objectives

3. Understanding the ICE3BS02

4. How the Power Supply Works

5. Arduino-Based Output Monitoring

6. Testing and Evaluation

7. What Makes This Project Useful?

8. Conclusion

Schematics

1. Main flyback converter architecture

2. Arduino output monitoring circuit

Code

Code

Credits

Robert Fletcher

Comments

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An Isolated 12V Flyback Power Supply Using Infineon ICE3BS02

An Isolated 12V Flyback Power Supply Using Infineon ICE3BS02

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

1. Introduction

2. Project Objectives

3. Understanding the ICE3BS02

4. How the Power Supply Works

5. Arduino-Based Output Monitoring

6. Testing and Evaluation

7. What Makes This Project Useful?

8. Conclusion

Schematics

1. Main flyback converter architecture

2. Arduino output monitoring circuit

Code

Code

Credits

Robert Fletcher

Comments

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