LM386 is an audio amplifier that utilizes very low power. This IC takes an input voltage from devices (like microphone, radio or guitar, etc.) and amplifies them to a tens or hundreds times magnitude of input signal for driving loudspeakers. It can drive loads from 4Ω to 32Ω. It provides a feature of gain control and a bass boost with only two external components. The gain is set to 20 but it can be enhanced to 200 by adding external components.
LM386 Pinout Diagram
This picture shows the pinout diagram of the LM386 low voltage audio power amplifier. By default, it offers a bandwidth of 20 but we can increase it by adding external resistors and capacitors with pin1 and pin8.
Pin layout Description
It consists of eight pins. All these pins are described below:
Pin#01, 08: GAIN
These two pins are used to control the gain of IC. The internal gain is 20 but by adding a capacitor and resistor between these two pins, Gain can be increased up to 200.
Pin#02: -INPUT
It is the negative terminal of the operational amplifier.
Pin#03: +INPUT
It is the positive terminal of an operational amplifier.
Pin#04: GND
It should be connected to the ground.
Pin#05: Vout
This pin gives the amplified output signal.
Pin#06: Vs
It is the pin for voltage supply.
Pin# 07: BYPASS
Bypass terminal is left unconnected when a gain of 20 is required. A decoupling capacitor is connected at this pin for increasing gain.
Alternative Audio Amplifiers
LM386 Low Voltage Audio Power Amplifier Features
The main features of LM386 includes:
- The voltage gain range of this amplifier is from 20 to 200.
- The range of voltage supply depends on the model used. It is from 4volts to 12volts or 5volts to 18 volts depending on the model.
- The inputs are referenced by the ground.
- It has a self-centering output voltage which automatically biases to one-half the supply voltage.
- It has a low static current of 4mA.
- The harmonic distortion is less than 0.2%.
Where to Use Low Voltage Audio Amplifier?
This LM386 is available in three different models in the market which include LM386N-1, LM386N-3 and LM386N-4. The first two voltage models have a voltage range of 4V to 12V while LM386N-4 has a voltage range of 5V to 18V. LM386 IC is ideal for 6V battery operation applications.
It can be used in FM radio amplification, intercoms, line and servo drivers, TV sound systems, power converters etc. It is basically designed for low voltage applications.
How to use LM386?
It is relatively simple to operate. The signals to be amplified are applied at pins 2 and 3. Here pin 2 is grounded and pin 3 is connected to a potentiometer of 10kΩ. The potentiometer acts as a knob for controlling volume. A 250µF coupling capacitor is connected to the output pin. It removes DC offset from the output if any and allows only AC signal to pass through it. A network of 0.05µF filter capacitor and 10k resistor is used at the pin 5. This network also called the “Zobel network” and it is used to remove the oscillations or noise due to sudden high frequencies. The gain of this amplifier is 20.
Example Circuit with Gain 20
Pins1 and Pin8 are internally connected with each other through a 1.35kΩ resistor.
LM386 Amplifier with 50 and 100 Gain Example Circuits
This circuit shows an LM386 Amplifier with gain 50.
LM386 Amplifier with gain 100 Example
How to increase Gain?
To increase the gain, a 10µF capacitor is connected between the terminals 1 and 8. The gain will become 200. If a resistor is connected in series with this capacitor, the gain can be set from 20 to 200 by choosing the appropriate value of a resistor.
Main Advantage
One of the main advantages of the LM386 is its adjustable bass boost functionality. It is just like a low pass filter. You need only two extra components. Add a decoupling capacitor of 0.033μF and a 10kΩ resistor in series between pins 1 and 5.
Square Wave Oscillator Circuit
This circuit generates a square wave output. Output depends on the resistive and capacitive network circuit. The square wave oscillator on time depends on the charging and discharging time of capacitor.
Applications
Few applications are enlisted below:
- Low Power Audio amplifiers
- Ultrasonic, line and small servo drivers
- AM and FM Radio amplifiers
- Portable music players and TV sound systems
- Wien bridge oscillator
- Intercoms
- Power converters
- Audio boosters