12V to ±50V Dual Rail SMPS Using KA3525A | PCB Layout, Transformer Winding & Gerber Files

If you're building a high-power audio amplifier, one of the most important parts is a reliable power supply. This tutorial explains how to build a 12V to ±50V Dual Rail SMPS using the KA3525A PWM Controller IC.

This project is designed and tested for DIY audio amplifier enthusiasts who need a compact, high-efficiency switching power supply capable of delivering stable dual-rail output.

In this guide you'll learn:

Complete circuit overview
PCB Layout
Transformer winding details
Component list
Heat sink installation
Testing procedure
Troubleshooting guide
Gerber download

SMPS Specifications

Parameter	Specification
Input Voltage	12V DC
Output Voltage	+50V / 0V / -50V
PWM Controller	KA3525A
Switching Frequency	200–500kHz
Power MOSFET	P55NF06
Transformer Type	Ferrite Core EE55
Output Type	Dual Rail
Application	Audio Amplifier Power Supply

Project Features

High efficiency switching power supply
Compact PCB design
Stable ±50V dual rail output
Suitable for Class AB power amplifiers
Low transformer loss using ferrite core
Easy to modify output voltage
Gerber files included
Simple DIY construction

How This Circuit Works

The KA3525A is a PWM (Pulse Width Modulation) controller IC widely used in switched-mode power supplies. It generates two complementary PWM signals that drive six P55NF06 MOSFETs.

The MOSFETs rapidly switch the 12V DC input into a high-frequency AC waveform. This waveform is applied to a ferrite transformer where the voltage is stepped up.

The transformer output is then rectified using HER308 fast recovery diodes and filtered using electrolytic capacitors, producing a clean and stable dual output:

+50V
Ground (0V)
-50V

Because the circuit operates at high frequency (200–500kHz), the transformer remains much smaller and more efficient than traditional iron-core transformers.

Required Components

Component	Quantity
KA3525A PWM Controller	1
P55NF06 MOSFET	6
HER308 Fast Diode	8
6A4 Diode	1
1N4007 Diode	1
1000µF / 25V Capacitor	2
102pF Capacitor	1
103J Capacitor	1
15Ω Resistor	6
2.2KΩ Resistor	2
12KΩ Resistor	3
100Ω Resistor	1
Ferrite Core EE55	1

PCB Layout

The PCB has been designed with wide copper traces to handle high current efficiently. Special attention has been given to MOSFET placement, transformer location, and diode arrangement to minimize switching noise and improve thermal performance.

Circuit Diagram

The circuit uses the KA3525A PWM controller to drive six MOSFETs connected in a push-pull configuration. Fast recovery HER308 diodes rectify the transformer output, while large electrolytic capacitors smooth the DC voltage.

Insert Circuit Diagram Here

Ferrite Transformer Winding

The ferrite transformer is the heart of this SMPS. Proper winding is essential for stable output voltage, high efficiency, and reliable operation. Even a small mistake in the winding process can cause low output voltage, excessive MOSFET heating, or complete circuit failure.

Recommended Ferrite Core

Core Type: EE55 Ferrite Core
Material: High-frequency ferrite
Core Size: Approximately 50 × 20 × 10 mm
Wire: 20 AWG Enamel Copper Wire

Primary Winding

The primary winding is connected to the MOSFET switching stage and operates directly from the 12V DC input.

Wire Size: 20 AWG
Number of Wire Pairs: 4
Length of Each Pair: Approximately 18 inches
Keep all wires tightly twisted together.
Maintain proper insulation between winding layers.

Neat and tightly packed windings improve transformer efficiency and reduce switching noise.

Secondary Winding

The secondary winding determines the output voltage. For a ±50V output, use the following configuration.

Wire Size: 20 AWG
Number of Wire Pairs: 3
Length of Each Pair: Approximately 74 inches
Wind evenly across the bobbin.
Keep equal spacing to maintain balanced output voltage.

If a higher output voltage is required, increase the number of secondary turns while ensuring all output components are rated for the higher voltage.

Transformer Assembly Tips

Apply insulating tape between winding layers.
Use varnish or insulating lacquer to reduce vibration.
Keep winding direction consistent.
Avoid overlapping wires unnecessarily.
Check continuity using a multimeter before installation.

Insert Transformer Winding Images Here

PCB Assembly Guide

Before soldering, inspect the PCB carefully for manufacturing defects. Clean the board surface and verify all component values.

Recommended Assembly Order

Resistors
Small Signal Diodes
Capacitors
KA3525A IC Socket
HER308 Diodes
MOSFETs
Transformer
Input & Output Terminals

Installing components in this order makes soldering easier and reduces the risk of damaging larger components.

MOSFET Installation

The six P55NF06 MOSFETs are responsible for switching high current through the transformer. Proper installation is important for efficiency and reliability.

Install Q1–Q3 on one heat sink.
Install Q4–Q6 on another heat sink.
Use thermal paste between MOSFETs and the heat sink.
Tighten mounting screws evenly.
Ensure the heat sinks are electrically isolated if required.

Leave approximately 3–5 mm spacing between the two heat sinks to avoid accidental short circuits.

Insert MOSFET Installation Image Here

PCB Layout Design Tips

High-current paths should always use wide copper traces to minimize voltage drop and heat generation. The transformer should be placed close to the MOSFET section to reduce switching losses.

Keep high-current traces as short as possible.
Separate power traces from feedback signals.
Maintain proper spacing between high-voltage pads.
Use thick copper traces for the output section.
Keep the feedback circuit away from switching noise.

Safety Precautions

Although the input voltage is only 12V DC, the output voltage can exceed ±50V. Incorrect assembly may damage electronic components or create a risk of electric shock.

Always verify component polarity before powering the circuit.
Double-check transformer winding connections.
Inspect all solder joints carefully.
Use a current-limited bench power supply for the first power-up.
Never touch the output terminals while the circuit is operating.

Visual Inspection Before Power-On

Before applying power, complete the following checklist.

✔ All resistor values verified
✔ Diode polarity checked
✔ MOSFET orientation confirmed
✔ Capacitor polarity correct
✔ Transformer connections verified
✔ No solder bridges
✔ Heat sinks securely installed

Taking a few minutes to inspect the PCB can prevent costly component damage during the first test.

First Power-On Test

Before connecting this SMPS to an audio amplifier or any other load, perform a safe first power-up test. This helps identify assembly mistakes and prevents damage to expensive components.

Required Test Equipment

Regulated 12V DC Power Supply (Current Limited)
Digital Multimeter
Oscilloscope (Optional but Recommended)
Dummy Load (Optional)

Step-by-Step Testing Procedure

Inspect the PCB for solder bridges and loose connections.
Verify the transformer winding connections.
Connect a regulated 12V DC power supply.
Set the current limit to approximately 1 Ampere.
Power ON the circuit.
Measure the positive output voltage.
Measure the negative output voltage.
Check MOSFET temperature after one minute.
Listen for unusual transformer noise.
If everything is normal, increase the available input current.

Expected Output Voltage

Test Point	Expected Voltage
Positive Rail	+50V DC
Ground	0V
Negative Rail	-50V DC
Input	12V DC

Small voltage variations are normal depending on the input voltage and transformer winding accuracy.

Performance Testing

After confirming the correct output voltage, perform a practical load test.

Connect a suitable dummy load or amplifier.
Monitor the output voltage while increasing the load.
Observe MOSFET temperature.
Check transformer temperature after 15–20 minutes.
Verify that the output voltage remains stable.

Common Problems and Solutions

1. No Output Voltage

Possible Causes

Incorrect transformer winding
Faulty KA3525A IC
MOSFET installed incorrectly
Broken PCB track
Poor solder joint

Solution

Check transformer continuity.
Measure PWM output from KA3525A.
Inspect MOSFET orientation.
Repair damaged solder joints.

2. Low Output Voltage

Possible Causes

Low input voltage
Incorrect secondary winding turns
Heavy output load
Poor transformer coupling

Solution

Verify the input supply voltage.
Recalculate transformer turns.
Inspect output rectifier diodes.

3. MOSFET Heating

Possible Causes

Incorrect gate resistor value
Poor transformer winding
Insufficient heat sink
Switching frequency too low

Solution

Use quality thermal paste.
Improve airflow around heat sinks.
Check gate drive waveform.
Inspect transformer construction.

4. Transformer Noise

Possible Causes

Loose ferrite core
Poor winding tension
Core vibration

Solution

Apply insulating varnish.
Secure the ferrite core firmly.
Rewind the transformer if necessary.

Applications

This dual-rail SMPS can be used in a wide range of electronic projects, including:

Class AB Audio Amplifiers
Class H Power Amplifiers
Professional Sound Systems
Laboratory Power Supplies
DIY Electronics Projects
High-Power DC Converters

Gerber Files & Downloads

All PCB design files used in this project are available for download. The Gerber files can be sent directly to most PCB manufacturers without modification.

Download Files:

PCB Gerber Files
PCB Layout
Schematic Diagram
Component Placement
Bill of Materials (BOM)

👉 Download.

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Author's Notes

This SMPS was designed for educational and DIY purposes. Every transformer may produce slightly different output voltage depending on the ferrite core material, winding quality, and operating frequency.

Always verify component ratings before applying higher input power. Careful PCB assembly and transformer construction are essential for reliable long-term performance.

Frequently Asked Questions (FAQ)

1. Can I use a 24V DC input instead of 12V?

Yes, but the transformer winding, MOSFET voltage rating, and feedback circuit must be redesigned accordingly. Using a 24V input with the current transformer design may damage the circuit.

2. Can I increase the output voltage to ±60V or ±70V?

Yes. The output voltage mainly depends on the transformer secondary winding. Increase the secondary turns and ensure all capacitors, diodes, and MOSFETs are rated for the higher voltage.

3. Which ferrite core should I use?

An EE55 ferrite core is recommended for this project because it offers good efficiency at high switching frequencies. Similar high-frequency ferrite cores with equivalent specifications may also be used.

4. Why are my MOSFETs getting hot?

Excessive heating is usually caused by incorrect transformer winding, poor gate drive, insufficient heat sinking, or incorrect PCB assembly. Double-check the transformer, gate resistors, and MOSFET orientation before increasing the load.

5. Can this SMPS power a Class AB amplifier?

Yes. This power supply is specifically designed for DIY Class AB audio amplifiers requiring approximately ±50V DC rails.

6. Is the PCB tested?

Yes. The PCB layout was designed and tested before publication. However, verify all component values and connections before powering the circuit because construction quality can affect performance.

Important Safety Notice

Although this project uses a 12V DC input, the output voltage can exceed ±50V DC. High voltages can damage electronic components and may present a risk of electric shock if handled incorrectly.

Always use a regulated DC power supply during initial testing.
Never short the output terminals.
Disconnect power before modifying the circuit.
Use appropriate heat sinks and insulation.
Verify transformer wiring before applying power.

Conclusion

The KA3525A 12V to ±50V Dual Rail SMPS is an efficient switching power supply suitable for DIY audio amplifier projects. With correct transformer winding, careful PCB assembly, and proper testing, it can provide stable dual-rail output for Class AB amplifiers and other high-power electronic applications.

This guide covered the complete design process, including the component list, transformer construction, PCB layout, assembly, testing, and troubleshooting tips. Following these steps carefully will help improve the reliability and performance of your power supply.

If you build this project, feel free to share your experience, measurements, or suggestions in the comments. Your feedback helps improve future DIY electronics tutorials.

About the Author

Subas Bhusal is an electronics enthusiast and PCB designer who shares practical DIY electronics projects, amplifier circuits, SMPS designs, Arduino projects, and repair tutorials. Every project published on this website is intended to help students, hobbyists, and electronics engineers learn through hands-on experience.

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Have a question about the transformer winding, PCB layout, or testing procedure? Leave your question in the comments below, and I'll do my best to help.

Last Updated: August 2026

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