Power Amplifier TDA2040

Description:
This circuit uses the TDA2040 IC as the main part of a class AB audio amplifier that can produce up to 25 watts of power when connected to a 4-ohm speaker. The TDA2040 is famous for being efficient, having low distortion, and staying cool during use. It works well for small music systems, active speakers, or homemade audio projects that need clear and strong sound.

Introduction

In the field of audio electronics, sound quality and efficiency are always key considerations. One widely used component in power amplifier design is the TDA2040 IC. Created by STMicroelectronics, this IC is a monolithic class AB amplifier that includes built-in protection features such as thermal overload and short circuit protection.

The TDA2040 has a straightforward and efficient design that needs just a few extra parts, such as resistors and capacitors, to work best. It can produce about 25 watts of power when connected to a 4-ohm load, making it a great choice for home audio setups, small guitar amplifiers, or portable speaker builds.

This article explains in detail the working principle, circuit design, and component list of the 25W power amplifier using TDA2040, along with assembly tips and testing methods for best results.

Circuit Diagram

Figure: 25W Power Amplifier using TDA2040

TDA2040 25W Amplifier Circuit Diagram

Circuit Explanation

This circuit is configured as a non-inverting amplifier, where the input signal is fed to pin 1 (non-inverting input) of the TDA2040. The amplified output is taken from pin 4, while pin 3 is connected to ground. The positive supply voltage is connected to pin 5.

1. Input Stage

The input signal passes through a 2.2µF coupling capacitor that blocks DC and allows only the AC (audio) signal to pass. The 22kΩ resistor connected to ground serves as a bias resistor to stabilize the input voltage.

A combination of 22µF capacitor and 680Ω resistor in the feedback path forms a frequency compensation network to maintain low-frequency stability and prevent oscillation.

2. Feedback Network

The feedback path runs from pin 4 (output) to pin 2 (inverting input) through a 22kΩ resistor and a 680Ω resistor. This determines the amplifier gain, calculated by:

Gain = 1 + (Rf / Ri)
Gain = 1 + (22000 / 680) ≈ 33.4

This means the input signal is amplified about 33 times, making it suitable for sources like mobile phones, DACs, or preamps.

3. Power Supply Filter

The amplifier operates with a single supply voltage +Vs (typically between +18V to +22V DC). The 220µF and 100nF capacitors act as filters to remove supply noise and stabilize voltage during signal peaks.

4. Output Stage

The output from pin 4 passes through a large 2200µF capacitor before reaching the speaker. This capacitor blocks DC from reaching the speaker. A 2.2Ω resistor and 100nF capacitor in parallel form a Zobel network to maintain stability with inductive loads like speakers.

5. Additional Components

The 22µF capacitor on the inverting input enhances low-frequency response (bass). The TDA2040 also includes built-in protection such as:

Thermal shutdown (overheating protection)
Short-circuit protection
Safe Operating Area (SOA) protection

Component List

Component	Value	Function
IC	TDA2040	Main power amplifier
R1	22kΩ	Feedback resistor
R2	680Ω	Gain resistor
R3	22kΩ	Input bias resistor
R4	2.2Ω	Zobel resistor
C1	2.2µF	Input coupling capacitor
C2	22µF	Low frequency compensation
C3	22µF	Feedback capacitor
C4	100nF	Supply filter (HF)
C5	220µF	Supply filter (LF)
C6	2200µF	Output coupling capacitor
C7	100nF	Zobel capacitor
Speaker	4–8Ω	Load
Power Supply	+18V to +22V DC	DC source

Working Principle

The input audio passes through C1 and enters pin 1 of the IC.
TDA2040 amplifies the signal about 33 times.
The amplified signal is available at pin 4 and passes through C6 to the speaker.
The RC network at output ensures load stability.
Filter capacitors maintain supply voltage stability.

Assembly and PCB Tips

Mount a large heatsink on the TDA2040 to prevent overheating.
Keep input and output traces separate to avoid parasitic feedback.
Place the 100nF and 220µF capacitors close to the IC supply pins.
Use thick wires for the speaker output to reduce power loss.
Double-check capacitor polarity before powering the circuit.

Testing Procedure

Check all connections carefully before applying power.
Use a regulated +18V DC supply (or transformer 18V-0V-18V with rectifier).
Connect an audio source (phone, MP3 player) and slowly raise volume.
If there is no hum or distortion, the amplifier works correctly.
Measure output with a multimeter or oscilloscope — you should get around 25W RMS on a 4Ω load.

Advantages and Disadvantages

Advantages:

Simple and easy to build
Clean sound with low distortion (THD < 0.1%)
High output power up to 25W RMS
Built-in thermal and short-circuit protection
Low cost and widely available components

Disadvantages:

Requires a large heatsink
Not suitable for high-power (>50W) systems
No built-in tone control (bass/treble)

Additional Tips

Add a preamp tone control for better sound clarity.
Use shielded cables for the input to avoid hum and noise.
Build two identical circuits for a stereo amplifier.
Use a toroidal transformer (18V 3A) and filter capacitors above 4700µF for best results.

Conclusion

The 25W Power Amplifier using TDA2040 is an excellent project for audio enthusiasts who want high-quality sound with simple construction and low cost. Its balance of output power, efficiency, and protection features makes it a popular choice for DIY audio builders.

With only a few components, you can enjoy clear and powerful audio for home, workshop, or portable use. Hopefully, this guide helps you understand how the TDA2040 works and inspires your next audio project.