LM1875 20W HiFi Audio Amplifier Circuit

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Introduction

The LM1875 audio amplifier is a high-performance, low-distortion integrated circuit designed for high-quality audio applications. It is capable of delivering up to 30 watts of continuous power to an 8Ω speaker load, making it ideal for home audio systems, musical instruments, and compact amplifiers. This circuit uses a dual power supply configuration (+Vcc and -Vee), ensuring efficient operation and minimal distortion across the audio spectrum. The input stage includes capacitors to block DC signals and resistors to set the input impedance, ensuring stable operation and compatibility with various audio sources.

The gain of the amplifier is determined by a feedback network, which stabilizes the system and reduces noise. Additional capacitors and resistors are used for power supply decoupling, output coupling, and oscillation control, contributing to the amplifier's reliable performance. The LM1875 amplifier circuit is highly regarded for its simplicity, ease of implementation, and ability to deliver crisp, clear audio output in small form factors.

Key Features of the LM1875

  • Up to 30 Watts Output Power
  • Avo Typically : 90 dB
  • Low Distortion: 0.015%, 1 kHz, 20 W
  • Wide Power Bandwidth: 70 kHz
  • Protection for AC and DC Short Circuits to Ground
  • Thermal Protection with Parole Circuit
  • High Current Capability: 4A
  • Wide Supply Range: 16V-60V
  • Internal Output Protection Diodes
  • 94 dB Ripple Rejection
  • Plastic Power Package TO-220

Components Requried

  1. Audio IC LM1875
  2. Resistor 1MΩ, 22KΩ, 1KΩ, 1Ω, 20KΩ
  3. Capacitor 100uf, 0.1uf, 2.2uf, 0.22uf, 22uf
  4. Speaker 8Ω
  5. Audio Input
  6. Dual Power Supply 24vDC

Pinout Diagram for the LM1875 IC


The image shows the pinout diagram for the LM1875 audio amplifier IC. Here’s a brief explanation of the pins:

  1. +IN (Pin 1): The non-inverting input terminal where the input audio signal is connected.
  2. -IN (Pin 2): The inverting input terminal. It is used in conjunction with the feedback network to set the gain of the amplifier.
  3. VEE (Pin 3): The negative power supply pin, connected to the negative voltage rail.
  4. OUTPUT (Pin 4): The output terminal where the amplified audio signal is delivered to the connected load (e.g., speaker).
  5. VCC (Pin 5): The positive power supply pin, connected to the positive voltage rail.

Circuit Diagram with Dual Power Supply

specifications for the LM1875 audio amplifier:

  1. Output Power: Delivers up to 30 watts per channel.
  2. Load Resistance: Operates with a load resistance of 4 to 8 ohms.
  3. Input Bias Current: Maximum of 2 µA at ±25V.
  4. Voltage Gain: Typical gain of 90 dB (Avo).
  5. Harmonic Distortion: Low distortion of 0.015% at 1 kHz, 8-ohm load, and 20 watts output.
  6. Input Offset Voltage: Maximum of 15 mV at ±25V.
  7. Power Bandwidth: Wide range of 70 kHz.
  8. Current Capability: Handles a maximum current of 4A.
  9. Temperature: Maximum operating temperature is 150°C.
  10. Supply Current: Maximum of 100 mA at ±25V.
  11. Supply Voltage:
    • Single Supply: 16V (min), 18V/24V/28V (typical), 60V (max).
    • Dual Supply: ±8V (min), ±9V/±12V/±15V/±18V/±24V/±28V (typical), ±30V (max).
  12. Ripple Rejection: 94 dB, ensuring minimal noise interference.
  13. Gain Bandwidth Product: Typical value of 5.5 MHz.
  14. Supply Current: Typically 70 mA at ±25V.
  15. Protection Features: Includes thermal protection, short-circuit protection for AC and DC to ground, and internal output protection diodes.
  16. Package: Available in a TO-220 plastic power package.

Working Explaination

The LM1875 audio amplifier circuit is a high-performance design capable of delivering up to 20W of power to a connected speaker. It operates using a dual power supply (+Vcc and -Vee), which ensures efficient and low-distortion output. The input audio signal is coupled through a capacitor (C1) to prevent DC offset, and resistors (R1 and R2) set the input impedance. The amplifier's gain is determined by the feedback network, consisting of R3, R4, and C2, which stabilizes the circuit and minimizes distortion. Decoupling capacitors (C3 and C4) ensure smooth power delivery by filtering noise from the power supply.

Additional capacitors (C5 and C6) provide further filtering and stability. The load is connected at the output through a coupling capacitor (C5) to block DC from reaching the speaker, and resistor R5 helps control oscillations and improve performance. This circuit is ideal for use in high-quality audio systems, offering low distortion and high fidelity.

Applications

  • Hi-Fi audio systems
  • Home theater systems
  • High Performance Audio Systems
  • Instrument amplifiers
  • DIY audio projects
  • Bridge Amplifiers

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