Designing a 20W Audio Amplifier Circuit using IC LM1875

The IC LM1875 is a really cool audio power amplifier that works super efficiently.

It can produce 20 watts of power while using very few extra parts.

It sounds great and has low distortion making it a fantastic choice for different audio needs.

This design is perfect for small home audio systems, powered speakers or even amplifying musical instruments.

In this post, we will explore Designing a 20W Audio Amplifier Circuit using IC LM1875 and how the audio amplifier works.

We will provide detailed calculations for the circuit components and outline the steps you need to follow to build the circuit successfully.

Circuit Working:

Parts List:

The diagram above shows how a 20W audio amplifier works using the IC LM1875 chip.

To start the audio signal comes in through resistor R5 and capacitor C4 to the non inverting input, which is pin 1 on the LM1875.

Resistor R4 is important because it creates a DC bias for the non inverting input.

The feedback loop is made up of resistors R1 and R2 .

You can find the amplifiers gain using a specific formula mentioned below.

When you plug in the right numbers:

The amplifier gets a voltage gain of 19.

Capacitors C2 and C3 help to decouple the negative power supply, while capacitors C6 and C5 do the same for the positive power supply.

This setup is really important for keeping things stable and cutting down on noise from the power supply.

The amplified output goes to a 4 ohm speaker through pin 4 of the IC LM1875.

Also, resistor R6 and capacitor C7 work together as a Zobel network, which helps stabilize the amplifier and reduce high frequency noise.

Fuses F1 and F2 are included to protect the power supply from too much current.

To keep the LM1875 from getting too hot when it is working hard a heat sink is attached to it.

Formulas with Calculations:

The formulas with calculations for Designing a 20W Audio Amplifier Circuit using IC LM1875 is mentioned below:

Voltage Gain:

Gain = 1 + (R1 / R2)

where,

• R1 is 180k in this article and
• R2 is 10k

Substituting the values:

Gain = 1 + (180k / 10k) = 19

Input Impedance:

The input impedance is determined by R5 and R4.

Since R4 is much larger than R5:

Zin = R5 = 1k

Output Power:

Pout = Vrms² / Rload

Assuming a maximum RMS output voltage of 12.65V for a dual ±25V supply:

Pout = (12.65²) / 4 = 20W

Coupling Capacitor (C4):

To pass audio frequencies without attenuation:
Xc = 1 / (2πfC)

Assuming f = 20Hz low frequency limit:
C = 1 / (2πfR) = 1 / (2π × 20 × 1k) = 1μF

How to Build:

For Designing a 20W Audio Amplifier Circuit using IC LM1875 follow the below steps for connections and assembling:

• Assemble all the components mentioned in the above circuit diagram
• Connect pin 1 of IC1 LM1875 to positive of capacitor C4 and negative of capacitor connect to one end of resistor R5 and other end of resistor R5 to audio input.
• Connect resistor R3 between pin 1 and positive of capacitor C4 and GND, and connect resistor R4 between negative of capacitor C4 and resistor R5.
• Connect pin 2 of IC1 LM1875 to one end of resistor R2 and positive of capacitor C1 and negative of capacitor to GND.
• Connect pin 3 of IC1 LM1875 to one end of fuse2 and other end of fuse2 to -25V DC, connect from pin 3 capacitor C2 and GND.
• Connect the positive end of capacitor C3 to pin 3 and negative of capacitor to GND.
• Connect pin 4 of IC1 LM1875 to one end of resistor R1 and other end to pin 2 of IC1 LM1875
• Connect pin 4 of IC1 LM1875 to one end of 4Ω speaker and other end of speaker to GND.
• Connect resistor R6 and capacitor C7 from pin 4 of IC1 LM1875 and GND.
• Connect pin 5 of IC1 LM1875 to one end of fuse1 and other end of fuse1 to +25V DC, connect capacitor C6 from pin 5 and GND.
• Connect positive of capacitor C5 to pin 5 of IC1 LM1875 and negative of capacitor to GND.

Conclusion:

Designing a 20W Audio Amplifier Circuit using IC LM1875 is a dependable and effective choice for boosting sound.

It is easy to design, excellent sound quality and minimal distortion make it great for different audio uses.

If you stick to the calculations and building steps given you can create a strong amplifier that produces clear sound.

This project also shows how crucial it is to choose the right parts and arrange the circuit properly in audio electronics.

References:

LM1875 20W Audio Power Amplifier