LM386 Amplifier

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. When it operates from a 6 volt power supply, quiescent power will be 24 milliwatts, which makes LM386 for ideal battery operation.

LM386 Audio Amplifier Circuit Diagram and Working

An LM386 is a very popular and widely used audio amplifier chip that permits a user to amplify sound.  LM386 chip comprises of 8 pins where, pin 1 and 8 denotes the gain control of the amplifier, and you can adjust the gain by placing resistor or capacitor in between these two terminals

LM386 Pin Diagram

LM386 pin diagram consists of 8 pins where each pin has  some function, such as

LM386 Pin Diagram

• Pin 2 and 3 are the sound input pins and by using these pins you can place the sound and you can amplify
• pin4 is the GND terminal
• Pin5 is the output of the amplifier
• Pin6 is the terminal which receives the positive DC voltage, so that the op-amp amplifies the signals
• Pin7 is the bypass terminal, it can bypass 15kohm resistors. This pin is usually wired to ground or left open

LM386 Amplifier Circuit Diagram

Here, in the above diagram lm386 audio amplifier circuit using transistors,  R1 is a potentiometer, which is used as a volume control for the audio signal. To make the LM 386 more flexible, two pins (1and 8)  of the audio amplifier are provided for gain control and gain adjustments. When the pins 1 and 8 open, the 1.35 kW  internal  resistances set the gain at 20 (26 dB). If a capacitor is placed from pin 1 to 8, bypassing the 1.35 kW internal resistors, the gain will go up to 200 (46 dB)

To get desired gain,  you can select one of the above external parts and can connect between the parts mentioned below. By selecting circuit A, we can get amplification of 200, circuit B will give a gain of 50, circuit C will raise the bass  level about 5dB, and this C must be Connected in between 1 and 5 pins.

The circuit A, shows the basic format of wiring up the IC as an amplifier. Here, as discussed in the previous section, the gain of the circuit is restricted to 20 by keeping the pins 1 and 8 open. The internal connection of a 1.35K resistor across these pin-outs shunts the IC to the gain above. The output is connected to a loudspeaker via a filter capacitor, which is normally witnessed in all linear IC amplifier circuits. The pot VR1 at the input functions as the volume control for enabling the output to be adjusted to the desired level.

External Circuits of LM386

The second circuit B shows how the gain of the above fundamental design may be boosted to almost 200 by adding a capacitor across pin 1 and 8 of the IC. The value of the capacitor should not be increased above 10 µF though.

The gain can be made adjustable from 20 to 200 by including a variable resistor of 4K7 in series with the above capacitor. Excess offset conditions may be reduced by engaging the unused input to a resistor from the ground. However, all offset issues are cancelled-OFF if the active input is coupled through a capacitor. With the circuit set at a gain of 200, it becomes essential to bypass the unused pin #7 via a 0.1µ capacitor to ground for keeping the circuit stable and avoiding unnecessary oscillations or clipping. A simple but interesting bass boost arrangement can be inserted by introducing a resistor/capacitor network across pin 1 and 5.

PCB Layout for LM386

The output power may around 550MW for 16 ohm speaker impedance. When we use circuit A, replace Rx with jumper wire in PCB. When we use circuit C, solder additional resistor and capacitor into the PCB points labeled Ry and Cy.

It is an audio power amplifier IC that applies much like an operational amplifier. As such, it can be configured as a power oscillator in a siren. Adding switches or clever circuitry makes it multi-tone.

Gain Control of LM386

To make the LM386 a more versatile amplifier, two pins (1and 8) are provided for gain control. With pins 1 and 8 open the 1.35 kW resistors sets the gain of 20 (26 dB). If a capacitor is put from pin 1 to 8, bypassing the 1.35 kW resistors, the gain will go up to 200 (46 dB). If a resistor is placed in series with the capacitor, the gain can be set to any value from 20 to 200. Gain control can also be done by capacitive coupling a resistor (or FET) from pin 1 to ground. Additional external major components can be placed in parallel with the internal feedback resistors to tailor the gain and frequency response for individual applications.

For example, you can compensate poor speaker bass response by frequency shaping the feedback path. This is done with a series RC from pin 1 to 5 (paralleling the internal 15 kW resistor). For 6 dB effective bass booster 15 kW, the lowest value for good stable operation is R = 10 kW if pin 8 is open. If pins 1 and 8 are bypassed, then R as low as 2 kW can be used. This restriction is because the amplifier is only compensated for closed-loop gains greater than 9.

Input Biasing of LM386

The schematic shows that both inputs are biased to ground with a 50 kW resistor. The base current of the input transistors is about 250 nA, so the inputs are at about 12.5 mV when left open. If the DC source resistance driving the LM386 is higher than 250 kW it will contribute very little additional offset (about 2.5 mV at the input, 50 mV at the output). If the dc source resistance is less than 10 kW, then shorting the unused input to ground will keep the offset low (about 2.5 mV at the input, 50 mV at the output).

For DC source resistances between these values we can eliminate excess offset by putting a resistor from the unused input to ground, equal in Value to the DC source resistance. Of course, all offset problems are eliminated if the input is capacitive coupled. When using the LM386 with higher gains (bypassing the 1.35 kW resistors between pins 1 and 8) it is necessary to bypass the unused input, preventing degradation of gain and possible instabilities. This is done with a 0.1 μF capacitor or a short to ground depending on the DC source resistance on the driven input. Other than audio amplifiers many different small circuits can also be built using this versatile chip; the following datasheet will provide you with more added information.

Features of LM386

• Operated on battery
• Minimum external parts
• Wide voltage range: 5v-18v
• 4ma current drain which is very low
• 20 to 200 voltage gain
• Input refers to the ground
• Output is self centered quiescent voltage
• Distortion is very low
• Available in 8 dip pin package

Applications of LM386

• In radio amplifiers, especially in AM and FM
• Portable audio players
• In TV sound systems
• Line drivers
• Ultrasonic drivers
• Servo drivers
• Power converters

Therefore, this is all about LM386 audio amplifier IC which circuit working with applications and features.Furthermore, any queries regarding this article or labVIEW based electrical projects you can approach us by commenting in the comment section below.

photo Credits:

• LM386 Amplifier by rlocman
• LM386 Pin Diagram by ece.mtu
• LM386 PCB by vakits
• External Circuits of LM386 by electroschematics
• LM386 Circuit Diagram by wordpress