LM3875 IC : PinOut, Features, Specifications, Vs LM3886 Circuit, Working & Its Applications

LM3875 IC is a 56-watt amplifier designed by Texas Instruments so this amplifier chip was very famous in DIY audio devices for its low parts count & its high-performance audio abilities. It was the significant chip in several gain clone amplifiers which depend on the Gaincard amplifier. The Gaincard from 47 Labs is a solid-state audio amplifier launched in 1999. Thus, has a simple design with fewer parts and capacitance than other amplifiers. This article elaborates on the LM3875 IC, pinout, features, specifications, and applications.

What is LM3875 IC?

The LM3875 is a high-performance-based audio power amplifier that delivers 56W continuous 8Ω average power into an 8Ω load through 0.1% THD+N from 100W instant peak output power with 20Hz to 20kHz. So this IC is protected totally with a SPiKe protection circuit at the output. So it provides dynamically protected SOA (Safe Operating Area), an inherently from under voltage from overvoltage, overloads with thermal runaway, sudden temperature spikes & supply shorts. Thus, this IC maintains an outstanding signal-to-noise ratio > 95dB with a typical 2.0μV low noise floor.

LM3875 IC Working

The LM3875 audio power amplifier IC works by letting electrical signals supply between components on the surface of the chip enabling the chip to achieve its function. So the surface of this chip includes a pathways network that connects different components. The LM3875 IC generates audio signals. Automated test equipment or IC tester is used to test the IC if it functions as designed. Thus, this tester transmits electrical signals to the chip and evaluates the output signals to the estimated values.

LM3875 IC Pin Configuration:

The pin configuration of LM3875 IC is shown below so this IC includes 11 pins which are discussed below.

                LM3875 IC Pin Configuration

• Pins 1 & 7 (V+): It is a positive voltage supply pin of IC which provides supply to operate properly.
• Pins 2, 5, 6, 9, 10 & 11 (NC): These are not connected pins of IC.
• Pin-3 (Output): It is an output pin of IC.
• Pin-4 (V-): It is a negative voltage supply pin of IC.
• Pin-8 (Vin-): It is a negative input voltage pin.

Features & Specifications:

The features and specifications of LM3875 IC include the following.

• LM3875 is a 56W high-performance-based audio power amplifier IC.
• This IC has 11 pins.
• It is available in the TO-220-11 package.
• The mounting type is Through a Hole.
• Its quiescent current is 30mA
• The bandwidth is 20 kHz.
• Max o/p power is 56W.
• The gain is 8 dB.
• Operating temperature ranges from -20°C~85°C TA
• The input bias current is 1μA.
• Minimum voltage supply is 20V.
• The output current is 6A.
• The maximum voltage supply is 84V.
• Its continuous average 6Watts output power is used to drive an 8 Ω load.
• This IC has 100 watts instantaneous peak o/p power.
• Its minimum signal-to-noise ratio is >95 dB.
• This IC has output protection from a short to GND or toward the supplies through internal current limiting circuitry.
• It has output over-voltage protection.

Equivalents & Alternatives:

Equivalents of LM3875 ICs include; LM4780, LM3886, LM1875, LM3876, etc. So alternative audio power amplifier ICs are; LM386, TDA2005, LM380, LM383, LM2002, D2030A, TDA1521, TDA7293, TDA7294, LM1875, etc.

80Watts LM3875 Audio Power Amplifier Circuit

The 80Watts LM3875 audio power amplifier circuit is shown below. So it is a very simple and high-efficiency-based 80Watts audio power amplifier circuit that is designed with the LM3875 IC. This high-performance-based audio power amplifier IC is capable of delivering continuous 56 watts of average power to an 8ohms load from 20 Hz to 20 kHz with 0.1% THD+N.

The required components to make this circuit mainly include; two LM3875 ICs, an 8ohms speaker, resistors 1K, 20K, and 24K, and capacitors like; 10uF, 1000uF, and 0.1 uF. So, connect this circuit as per the diagram shown below.

       80Watts LM3875 Audio Power Amplifier Circuit

Working

This circuit uses two LM39875 audio ICs, connected within a bridge mode. So this amplifier IC delivers 80 watts of o/p power to drive an 8-ohms load. The LM3875 IC must be correctly heat-sinked because it generates heat. Thus, this 80Watts audio power amplifier allows from 20 up to 84 volts a wide range of input voltage, however is recommended to use a dual +/-25 V DC power supply.

This 80W audio power amplifier IC features mainly include; output protection from a short to GND (or) to the supplies through internal current limiting circuitry,o/p over-voltage protection against transients from under-voltage protection supply, inductive loads, etc. Thus, the power audio amplifier IC in the above circuit diagram requires a few external electronic components. This IC maintains an outstanding S/N ratio above 95dB with a 2.0μV low noise floor.

56Watts Gainclone Stereo Amplifier Circuit with LM3875 IC

The 56Watts gain clone stereo amplifier circuit using LM3875 IC is shown below. The Gaincard’s design is simpler and uses fewer components & less capacitance. This circuit uses a 56-watt chip like LM3875 IC from National Semiconductor for amplification. So the LM3875 IC with a 2.0 V low noise floor maintains a good S/N ratio > 95 dB. Thus, it has outstanding linearity & is very low.

The required components to make this circuit mainly include; LM3875 ICs-2, resistors like; 1K, 120K, 33K, 47K, 1 Ohm, and 0.1uF, capacitors like 10uF, 0.1uF, 220pF, 22uF and 0.22uF, 4 to 8-ohm speakers and 2A fuse. Thus, connect this 56Watts gain clone stereo amplifier as per the circuit shown below.

     56Watts Gainclone Stereo Amplifier Circuit with LM3875 IC

Working

This circuit uses two channels the right and the left channel. To understand these two channels, we see only one channel working i.e., the left channel. So in the above circuit, the R2 resistor works as a set and the C2 coupling capacitor makes the impedance 33K of the circuit. Here, C3 capacitor, R1 & R3 resistors together will make the ultrasonic filter circuit.

The RF signal needs to be reduced before it goes into pin-7 to defend it from radio noise & attenuate it thus, this has a 25 times high gain. Here (1 + R5 / R6) equation is utilized to calculate the gain that is sent from the i/p signal back toward the input with the help of R5 & R6 resistors.

To reduce frequency to -3dB at 10Hz frequency, the C5 capacitor is connected to resistor R6. So now the signal is amplified before the IC is excited at pin-3 of the IC. Thus, the connected speaker in the circuit must proceed near the Zobel network circuit before it departs and it has an R4 resistor and C4 capacitor which fixes the load capacity problem and maintains stability at higher frequencies

So, the voltage of AC power is reduced by the transformer supply. Here 5Amps of current is provided from 220VAC higher voltage to lower voltage. After that, this lower voltage is sent to the bridge rectifier, which improves the voltage by approximately + 31 V DC. So, C13 & C14 capacitors smoothen the voltage to serve as the supply voltage of the amplifier circuit.

Difference between LM3875 and LM3886

The differences between LM3875 and LM3886 ICs include the following.

Advantages & Disadvantages

The advantages of LM3875 IC include the following.

• The LM3875 is a high-performance audio power amplifier
• The LM3875 maintains an excellent signal-to-noise ratio greater than 95 dB(min) with a typical low noise floor of 2.0 µV.
• LM3875 is a good and stable IC for 4/8 Ohm.
• It has a less-parts count with high-performance audio abilities.
• This LM3875 is the simplest amplifier to build with only a few parts needed.

The disadvantages of LM3875 IC include the following.

• This IC is applicable for 8-ohm loads.
• These are noisy for extremely low listening levels.

Applications

The applications of LM3875 IC include the following.

• LM3875 is a popular IC used in the DIY audio community.
• It is an essential chip in various gainclone amplifiers which depends on the Gaincard amplifier.
• It is a high-performance audio power amplifier that generates continuous 56 W average power to an 8Ω load through 0.1% (THD + N).
• The LM1875 is used in audio applications due to less distortion & high-quality efficiency which ranges from home theaters to sound systems.

Please refer to this link for the LM3875 IC Datasheet.

Thus, this is an overview of LM3875 IC, pinout, features, specifications, circuit, working, and its applications. This is a 56-watt amplifier chip designed for DIY audio projects because of its higher performance & lower parts count. So this IC maintains an outstanding S/N Ratio above 95 dB with a typical 2.0 µV low noise floor. Thus, here is a question for you, what is LM3886 IC?