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LM386: Circuit of Oscillator

Author: Irene
Date: 24 Feb 2022
 12009
Simplest Oscillator

Introduction

LM386 is a low voltage audio power amplifier. LM386 adopts 8-pin double in-line plastic package with a working voltage of 4V-15V. When the power supply voltage is 12V, 300mW output power can be obtained on an 8Ω load. Various oscillators can be easily produced with LM386.

Catalog

Introducton

Catalog

I Simplest Oscillator

II Blocking Oscillator

III Electronic Piano

IV Square-wave Oscillator

V Sinusoidal Oscillator

FAQ

Ordering & Quantity

I Simplest Oscillator

Figure 1. Circuit of Simplest Oscillator

In Figure 1, the output end and in-phase input end of LM386 are connected by piezoelectric ceramic chip HTD. The amplifier forms positive feedback and generates oscillation. Here HTD is both a feedback capacitor and a sound-generating device.

Component parameters in the figure: D1~D4 are 1N4001, C1=220pF, HTD is a piezoelectric ceramic sheet with an auxiliary acoustic cavity.

II Blocking Oscillator

Figure 2. Circuit of Blocking Oscillator

As shown in Figure 2, a simple oscillator consists of LM386, C3, C4, and loudspeakers. RP and C2 make this oscillator produce blocking- oscillation,  After connecting the power supply, LM386 does not work because the initial terminal voltage of C2 is zero, and the power supply charges C2 through RP. When the C2 charging voltage is higher than a certain value, the LM386 oscillator starts to vibrate. As the amplitude continues to increase, the current consumption of the oscillator also increases. This current flows through RP, and its voltage drop on RP also increases, causing the LM386 power supply terminal 6 pin voltage to continue to drop. Eventually, the LM386 cannot work and the oscillator stops. The power supply recharges C2 via RP again, causing the voltage at C2 to rise. When the voltage at C2 rises to a certain value, the LM386 oscillator starts again. In this way, the oscillator will produce blocking-oscillation, and the speaker emits a “beep, beep, beep” sound.

Component parameters in the figure: D1~D4 are 1N4001.  C1=C3=220μF,C2=47μF.C4=0.01μF,RP=4.7K.

III Electronic Piano

Figure 3. Circuit of Electronic Piano

Figure 3 is a simple electronic piano circuit. On pin 3 of LM386, the integrated circuit has a 10KΩ resistor to ground. This built-in resistor and ten scale resistors RP1~RP10 constitute the timing resistor of the oscillator. C2 is the timing capacitor. By adjusting the values of RP1~RP10, the speakers can sequentially emit musical sounds from low octave "do, re , mi" to high octave "do, re, mi". KI~K10 are key switches.

Component parameters in the figure: Cl=C3=220μF.C2=2200μF

IV Square-wave Oscillator

Figure 4. Circuit of Square-wave Oscillator

Figure 4 shows a square-wave oscillator composed of LM386. R1 is the timing resistor. C2 is the timing capacitor. R2 and R3 provide voltage bias for LM386 in-phase input. Because the voltage at the C2 terminal cannot change abruptly, the inverting input terminal pin  2 of the LM386 is low level, and pin 5 is the midpoint of the internal OTL output stage of the amplifier. It is 1/2Voc in a static state, and it is supplied to the third-phase input pin 3 after dividing pressure via R2 and R3. Obviously, the potential of this pin is higher than the second pin. Therefore, pin 5 outputs a high level. This high-level charges C2 via R1. When the voltage of the C2 terminal is higher than the potential of pin 3, pin 5 outputs a low level. C2 discharges to pin 5 via R1. When C2 is discharged, the potential of pin 2 drops and is lower than the potential of pin 3. Pin 5 outputs high level again. In this way, the circuit forms oscillation.  and the oscillation signal drives the loudspeaker to sound through C3.

Component parameters in the figure: C1=C3=220μF,C2=0.33μF.R1=22K,R2=1K.R3=9.4K

V Sinusoidal Oscillator

Figure 5. Circuit of Sinusoidal Oscillator

Figure 5 is a sinusoidal oscillator made of LM386. The circuit adopts Wien bridge oscillation mode, and the output signal distortion coefficient of the circuit is very low. The flashlamp H and the resistor R3 form a negative feedback circuit, which keeps the amplitude of the oscillator output signal stable and has low distortion. When the values of capacitors C1 and C2 are the same, the oscillation frequency of the circuit can be obtained by the formula f=1/2C1 R1R2. In actual production, H can use 3V, 15mA flashlamp.


FAQ

  • What type of package does LM386 adopt?

8-pin double in-line plastic package

  • What is the power supply voltage of LM386?

12V

  • What can be easily produced with LM386?

Various oscillators

  • 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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