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  • Contents

I Description

This blog uses LM386 integrated block as the core device to make a simple sound amplifier. Its production cost is relatively low. This blog is suitable for beginners to learn about power tubes, integrated operational amplifiers, speakers, language chips and other components. So we can master the principles, characteristics and usage of the basic amplifier circuit and power amplifier circuit.

lm386

Figure 1. LM386

Catalog

I Description

II Introduction to LM386

2.1 Features

2.2 Internal Structure

III Working Principle of LM386 Sound Amplifier

IV LM386 Sound Amplifier Debugging

V Conclusion

FAQ

Ordering & Quantity

II Introduction to LM386

2.1 Features

LM386 is a kind of audio integrated amplifier. It has the advantages of low power consumption, adjustable internal chain gain adjustment, large power supply voltage range, few external components and low total harmonic distortion. Therefore, LM386 is widely used in recorders and radios, mainly in low-voltage consumer products. LM386 features are:

  1.  Battery Operation
  2.  Minimum External Parts
  3.  Wide Supply Voltage Range: 4 V–12 V or
  4.  5 V–18 V
  5.  Low Quiescent Current Drain: 4 mA
  6.  Voltage Gains from 20 to 200
  7.  Ground-Referenced Input
  8.  Self-Centering Output Quiescent Voltage
  9.  Low Distortion: 0.2% (AV = 20, VS = 6 V, RL = 8 Ω,
  10.  PO = 125 mW, f = 1 kHz)
  11.  Available in 8-Pin MSOP Package

Based on the characteristics shown above, lm386 components are widely used in communication equipment, small radios, and walkie-talkie circuits. It is also called "universal power amplifier circuit" by the majority of electronic enthusiasts.

2.2 Internal Structure

 LM386 adopts 8-pin dual in-line package. See Figure 2 for the pin arrangement diagram.

lm386 pinFigure 2. LM386 Pin Arrangement

  •  Pin 6 is connected to the positive pole of the power supply;
  •  Pin 4 are grounded;
  •  Pin 2 inverting input terminal;
  •  Pin 3 non-inverting input terminal;
  •  Pin 5 is the output terminal;
  •  Pins 1, 7, and 8 are used to improve the performance of the circuit. The external component ends, and the internal circuit is a three-stage amplifier circuit:
    • The 1st stage consists of VT1~VT6 to form a differential amplifier circuit,
    • The 2nd stage is composed of VT7 voltage amplifier circuit,
    • The 3rd stage is composed of VT8~VT10 to form a complementary symmetrical OTL output circuit that can eliminate crossover distortion.
  • R5, R6, and R7 form a negative feedback network.

III Working Principle of LM386 Sound Amplifier

The core of the LM386 sound amplifier is the LM386 power amplifier integrated circuit. As shown in Figure 3.

The electret microphone B1 converts sound signals into electrical signals. This signal is very weak, how to amplify it? We can add the coupling capacitor C1 to the base of VT1, and VT1 forms a common emitter amplifier circuit to amplify the signal. Also, the signal is output from the collector of VT1, and added to the inverting input terminal of LM386 via coupling capacitor C2 to pin 2 and pin 3 is grounded. After the signal is amplified by the internal three stages of LM386, the signal is output from pin 5, and then passes through the coupling capacitor. C3 is sent to the speakers. After going through these processes, it can make a sound.

  lm386

Figure 3. LM386 Sound Amplifier

lm386 circuit

Figure 4. LM386 Audio Amplifier Circuit

Then how to adjust the signal magnification of LM386? Here, we can connect an adjustable resistor R5 and capacitor C6 to pin 1 and pin 8 to form a series RC network. When R5=0, the voltage magnification is 200.

Pin 7 is connected to capacitor C5 to prevent LM386 from generating self-excitation. In addition, pin 5 is grounded through R4 and C4 to make the speaker sound softer.

IV LM386 Sound Amplifier Debugging

After the circuit is assembled, we should carefully check for errors or false soldering. If there is no abnormality after the inspection, turn on the 6V power supply for debugging:

  • Step 1: Don't pick up the microphone first. When there is no input signal, test the quiescent current of the whole machine, which is about 7mA.
  • Step 2: Test the static voltage value of each pin of LM386, as shown in Figure 2.
  • Step 3: After the voltage and current are normal, place the RP volume regulator in the middle and touch the base of VT1 with a screwdriver. The speaker will emit a "click————click——" sound, indicating that the circuit is normal.
  • Step 4: Connect the microphone B1, and then fine-tune the RP. If nothing goes wrong, speak into the microphone, the speaker should have amplified sound. If there is no sound, check whether the microphone cable is connected incorrectly or the quality of the microphone is defective.
  • Step 5: When using a sound amplifier, do not place the microphone and speaker too close together. If they are unfortunately too close, the speakers will make a harsh sound. Therefore, it is best to use shielded wire for the microphone lead-out.

lm386

Figure 5. LM386

V Conclusion

Through the design of this blog, we have an essential understanding of the working principle of LM386. We have mastered the pin function, internal structure circuit and working principle of LM386. In addition, the sound amplifier made by LM386 has the characteristics of simple circuit, convenient debugging, and complete functions.

After reading this blog, have you better understand LM386?


FAQ

  • How does an LM386 work?

The Lm386 integrated chip is a low power audio frequency amplifier, which uses low level power supply like batteries in electronic circuits. It is designed as 8 pin mini DIP package. This provides voltage amplification of 20. By using external parts voltage gain can be raised up to 200.

  • Is lm386 an op amp?

The LM386 is a type of operational amplifier (Op-Amp). ... In an amplifier circuit, the LM386 takes an audio input signal and increases its potential anywhere from 20 to 200 times. That amplification is what's known as the voltage gain.

  • What is lm386 IC?

The LM386 is an integrated circuit containing a low voltage audio power amplifier. It is suitable for battery-powered devices such as radios, guitar amplifiers, and hobby electronics projects.

  • How do you calculate lm386 gain?

Voltage Gain Analysis:
Without any external components, it has a gain of Gv = 2x15K/(150+1350) = 20 (26 dB).
With a capacitor (or shortcutting) between pins 1 and 8 , it has a gain of Gv = 2x15K/150 =200 (46dB).

  • Which IC is used in audio amplifier?

The IC LM386 is a low-power audio amplifier, and it utilizes low power supply like batteries in electrical and electronic circuits. This IC is available in the package of mini 8-pin DIP.

  • What are some projects that use the LM386 audio amplifier circuit?

LM 386 is an integrated class AB amp and is good for beginners small audio amplifier applications…for example in a RF receiver,small Stereo system,cheap low voltage amplifier etc…drawbacks is that it cannot handle much power and hence creates distortion when you crank up the volume too much.. So other ICs are used in practical.

  • How to make an LM386 audio amplifier circuit?

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