IC LM 386: The Complete Guide

Introduction to the LM386 Amplifier

The LM386 is a low-voltage audio power amplifier designed for use in battery-operated devices. This versatile integrated circuit (IC) is known for its ease of use, low cost, and reliable performance. In this comprehensive guide, we will explore the features, applications, and circuit configurations of the LM386 amplifier.

Key Features of the LM386

• Low supply voltage range: 4V to 12V
• Low quiescent current drain: 4mA
• Voltage gains from 20 to 200
• Wide supply voltage range
• Minimum external parts required
• Low distortion: 0.2% (at 1kHz, 6W, 9V)
• Available in 8-pin PDIP, SOIC, and MSOP packages

Understanding the LM386 Pinout and Functions

The LM386 comes in an 8-pin package, with each pin serving a specific function. Here’s a breakdown of the pinout:

Pin	Function
1	Gain 1
2	Input –
3	Input +
4	Ground
5	Output
6	VS+
7	Bypass
8	Gain 2

Pin Functions in Detail

1. Gain 1: This pin is used to set the voltage gain of the amplifier. By connecting a capacitor between pins 1 and 8, you can increase the gain from 20 (default) up to 200.

2. Input –: The inverting input of the amplifier. This pin is typically connected to ground through a resistor to set the DC bias point.

3. Input +: The non-inverting input of the amplifier. The audio signal is usually applied to this pin through a coupling capacitor.

4. Ground: The ground reference for the amplifier. All voltages are measured with respect to this pin.

5. Output: The amplified audio signal is available at this pin. A coupling capacitor is used to block DC and pass the AC audio signal to the load (e.g., a speaker).

6. VS+: The positive supply voltage pin. The LM386 can operate with supply voltages ranging from 4V to 12V.

7. Bypass: This pin is used for frequency compensation and supply voltage decoupling. Connect a 10μF capacitor between this pin and ground to ensure stable operation and reduce noise.

8. Gain 2: Connected to pin 1 to set the voltage gain of the amplifier.

Basic LM386 Amplifier Circuit

A basic LM386 amplifier circuit can be built with just a few external components. Here’s a step-by-step guide to creating a simple audio amplifier:

Components Required

• LM386 IC
• 10μF electrolytic capacitor (C1)
• 0.1μF ceramic capacitor (C2)
• 100μF electrolytic capacitor (C3)
• 10Ω resistor (R1)
• Audio input source (e.g., microphone, phone, or MP3 player)
• Speaker (4Ω to 8Ω)

Circuit Diagram

                   +-----+
           C1     |     |
 Input >---||-----| 3   |
                  |     |
                 +-| 2   |
                 | |     |     +-----+
                 | | 8 7 |-----| C3  |
                 | |     |     |     |
                 +-| 1   |     +-----+
                   |     |       |
                   | 6   |       |
                   |     |       |
                  +| 4   |-------+
                  -| 5   |
                   |     |
                   +-----+
                     |
                    C2
                     |
                    ===
                    GND
                     |
                    R1
                     |
                    ///
                 Speaker
                    ///

Step-by-Step Instructions

1. Connect the positive terminal of the input capacitor (C1) to the audio input source and the negative terminal to pin 3 (Input +) of the LM386.

2. Connect pin 2 (Input -) to ground.

3. Connect a 10μF capacitor (C3) between pin 7 (Bypass) and ground.

4. Connect pin 6 (VS+) to the positive supply voltage (4V to 12V).

5. Connect pin 4 (Ground) to the ground of the power supply.

6. Connect a 0.1μF capacitor (C2) between pin 5 (Output) and ground.

7. Connect a 10Ω resistor (R1) between pin 5 (Output) and one terminal of the speaker. Connect the other terminal of the speaker to ground.

8. Apply an audio signal to the input and adjust the volume as needed.

This basic circuit provides a voltage gain of 20. To increase the gain up to 200, connect a capacitor between pins 1 and 8. The capacitor value determines the gain:

Capacitor Value	Voltage Gain
10μF	200
2.2μF	50
1μF	26

Advanced LM386 Circuit Configurations

While the basic LM386 amplifier circuit is suitable for many applications, there are several advanced configurations that offer improved performance or additional features.

Bass Boost Circuit

To enhance the bass response of the amplifier, you can add a low-pass filter to the feedback loop. This is achieved by connecting a series RC network between pins 1 and 5.

        +-----+
        |     |
     +--| 1   |
     |  |     |
    === |     |
    C4  | 5   |
     |  |     |
     +--+-----+
        |
        R2
        |
       ///

Typical values for C4 and R2 are 0.033μF and 10kΩ, respectively. Adjust these values to fine-tune the bass response.

Bridged Output Configuration

For higher output power, two LM386 ICs can be connected in a bridged configuration. This allows the amplifier to drive a load with twice the voltage swing, effectively quadrupling the output power.

                   +-----+           +-----+
           C1     |     |           |     |     C5
 Input >---||-----| 3   |           | 3   |-----||---+
                  |     |           |     |          |
                 +-| 2   |         +-| 2   |          |
                 | |     |         | |     |          |
                 | | 8 7 |------+  | | 8 7 |--+       |
                 | |     |      |  | |     |  |       |
                 +-| 1   |      |  +-| 1   |  |       |
                   |     |     C6   |     |  C7      |
                   | 6   |------+   | 6   |--+       |
                   |     |           |     |          |
                  +| 4   |-----------| 4   |+         |
                  -| 5   |         +-| 5   |-         |
                   |     |         | |     |          |
                   +-----+         | +-----+          |
                     |             |   |              |
                    C2             R3  R4            ///
                     |             |   |         Speaker
                    ===            |   |            ///
                    GND            +---+

In this configuration, the output of the first LM386 (pin 5) drives the non-inverting input (pin 3) of the second LM386. The output of the second LM386 (pin 5) is connected to the other terminal of the speaker. A resistor divider (R3 and R4) is used to set the DC bias point at the input of the second LM386.

Typical values for the components are:
– C1, C5: 10μF
– C2, C6, C7: 0.1μF
– R3, R4: 10kΩ

Stereo Amplifier Configuration

To create a stereo amplifier, simply use two LM386 ICs, one for each channel (left and right). Follow the basic amplifier circuit for each IC, using separate input sources and speakers.

PCB Layout Considerations

When designing a PCB for an LM386 amplifier, consider the following guidelines to ensure optimal performance and minimize noise:

1. Keep the input and output traces separated to avoid crosstalk and feedback.
2. Use a ground plane to provide a low-impedance return path for the currents.
3. Place the bypass capacitor (C3) as close to pin 7 as possible to minimize the effect of stray inductance.
4. Use short and wide traces for the power supply connections to minimize voltage drops and improve current handling.
5. If using a bridged output configuration, ensure that the traces connecting the two ICs are short and well-matched to maintain signal integrity.

Troubleshooting Common Issues

Distortion

If you experience distortion in the audio output, consider the following:

1. Check that the input signal level is not too high, causing the amplifier to clip. Reduce the input signal level or increase the supply voltage if necessary.
2. Ensure that the speaker impedance matches the amplifier’s output. Using a speaker with too low impedance can cause distortion and damage the IC.
3. Verify that the bypass capacitor (C3) is connected correctly and has the appropriate value (10μF).

Noise

To minimize noise in the amplifier output:

1. Use a regulated power supply to avoid supply voltage fluctuations.
2. Keep the input traces away from noisy digital circuits or power supply lines.
3. Use shielded cables for the input signals to reduce electromagnetic interference (EMI).
4. Ensure that the ground connections are properly made and that there are no ground loops in the circuit.

Low Output Volume

If the output volume is lower than expected:

1. Check that the input signal level is sufficient. Increase the input signal level if necessary.
2. Verify that the gain setting is correct. Add a capacitor between pins 1 and 8 to increase the gain if needed.
3. Ensure that the speaker is connected correctly and that there are no shorts or open circuits in the wiring.

Applications of the LM386 Amplifier

The LM386 is a versatile amplifier IC that finds use in a wide range of applications, including:

1. Portable audio devices (e.g., radios, MP3 players, and headphone amplifiers)
2. Intercom systems
3. Guitar and instrument amplifiers
4. Alarm systems
5. Multimedia projects
6. Automotive audio systems
7. Telephone amplifiers
8. Hearing aids

Frequently Asked Questions (FAQ)

1. Can I use the LM386 with a single-ended power supply?

Yes, the LM386 can operate with a single-ended power supply ranging from 4V to 12V. Connect the positive supply to pin 6 (VS+) and ground to pin 4 (Ground).

2. What is the maximum output power of the LM386?

The maximum output power depends on the supply voltage and the speaker impedance. With a 9V supply and an 8Ω speaker, the LM386 can deliver approximately 0.5W of output power. Increasing the supply voltage or using a lower impedance speaker will increase the output power.

3. How do I adjust the gain of the LM386?

The default voltage gain of the LM386 is 20. To increase the gain, connect a capacitor between pins 1 and 8. The capacitor value determines the gain, with 10μF providing a gain of 200, 2.2μF providing a gain of 50, and 1μF providing a gain of 26.

4. Can I use the LM386 for stereo applications?

Yes, you can use two LM386 ICs to create a stereo amplifier. Simply build two separate amplifier circuits, one for each channel (left and right).

5. Is the LM386 suitable for driving headphones?

The LM386 can drive headphones, but it is important to ensure that the output power is limited to avoid damaging the headphones or the user’s hearing. Use a resistor in series with the output to limit the current and power delivered to the headphones.

Conclusion

The LM386 is a popular choice for low-voltage audio amplification due to its simplicity, low cost, and good performance. By understanding the pinout, basic circuit configuration, and advanced techniques, you can quickly design and build LM386-based amplifiers for a variety of applications. Remember to consider PCB layout guidelines and troubleshoot common issues to ensure optimal performance. With its versatility and ease of use, the LM386 is an excellent choice for both beginners and experienced electronics enthusiasts.