Wiring And Schematic

The LM386, also known as JRC386 is one of the most used amplifiers integrated circuits, the reason is very simple, its versatility, low cost and consumption. An amplifier, as the name implies, amplifies, the signal increases in x times, depending on your configuration, in the case of the LM386 is an audio amplifier. It is very different from operational amplifiers as the LM741, these have different configuration requirements and use, since the LM386 audio amplifier is an innate, or whether it was designed to be an audio amplifier.

To get an idea of the grandeur of the LM386, the largest and best manufacturer of amplifiers, Marshall uses in their amplifiers miniature model MS-2 and MS-4 as output an integrated circuit manufactured by CCI NJM386.



Features of LM386

The LM386 is a power amplifier designed for use in low power and low voltage applications. Its configuration is a Class AB amplifier, it consists of an IC 8 pin dual in line, DIP-8, with 3 basic types that are LM386N-1, LM386N-3 LM386N-4 and the most common of these is the LM386N -1. The gain is internally set at 20 times for technical reasons, but the addition of an external resistor or capacitor between pins 1 and 8 will increase the output gain up to 200 times.

The quiescent current is very low, consuming less than 30 mW with 5 Volt supply, making it ideal for circuits powered by batteries or batteries. Called IC power amplifier low voltage, he was considered the jewel for amateur projects where you need a good audio amplifier with the advantage of having fewer components, low power consumption and low voltage.
 

Its input resistance is 50k OHMs and the output impedance is 8 ohms and the LM386N-1 LM386N-3 and 32 ohms versions in LM386N-4 version. The consumption quiescent current is 4mA and if its distortion is very low, 0.2% (AV = 20, VS = 6V, RL = 8 [Ohm], PO = 125mW, f = 1 kHz).



Pin out LM386

Pin 1: Gain
Pin 2: Input -
Pin 3: Input +
Pin 4: Earth
Pin 5: Vout (Output)
Pin 6: Vs (Power)
Pin 7: Bypass
Pin 8: Gain

Pins 1 and 8 are control gain. When not connected (NC), the amplifier gain is 20 times. Adding a 10uF capacitor between them passes to gain 200 times. Intermediate values ​​and a resistor will vary the gain as described in the datasheet, we will see below.

Pin 2 is the negative input ( GND ) will usually land or - .

Pin 3 is the positive input that is the input signal to be amplified . A 10K ohm pot before the pin that adjusts the level of the input signal, ie , a volume control .

Pin 4 ( GND - Ground) and Pin 6 ( VCC + Vs ) are the power inputs for amplification , an electrolytic capacitor of at least 100uF between them near the IC prevents unwanted oscillations .

The pin 5 is the output of the amplifier. The electrolytic capacitor 250uF filter the DC component and the remaining AC vam to the speaker . A 0.05uF capacitor and a resistor of 10 Ohm pin 5 to ground is used to prevent high frequency oscillations .

Pin 7 is called bypass ( bypass ) , but the data sheet does not provide any additional detail about him or their use . But technically serves to reduce the noise ( humming ) input and also decrease the distortion
inter- modulation. It isolates the input stage high-gain power supply noise . A 100nF capacitor of 10uF can be used to this pin.

Below is a table with the main characteristics of the types of LM386

Chip Name Min Max Voltage Power Voltage Minimum Output Power

LM386N-1 4 Volts 12 Volts 250 mW 325 mW
3 LM386N-4 Volts 12 Volts 500 mW 700 mW
LM386N-4 5 Volts 18 Volts 700 mW 1,000 mW

Typical circuit LM386 amplifier with gain of 20 times



Under an amplifier circuit using the LM386 with a gain of 20 times, requires a minimum of external components, this makes it compact and simple.

Typical circuit LM386 amplifier with gain of 50 times



This is the LM386 scheme for a gain of 50 times, addition of the capacitor between pin 1 and 8 is used 1K2 ohm resistor for limiting the gain. Another change is the placement of a capacitor to ground on pin 7 which is the ByPass to avoid instabilities in the circuit, it should be done whenever the gain is more than 20 times.

Typical LM386 amplifier circuit with a gain of 200 times



Varying the gain of the LM386

To make the LM386 amplifier is more versatile, both pins 1 and 8 are used for gain control. With pins 1 and 8 open, without any component and the gain of 20 times or 26 dB. But if a capacitor is placed between pin 1-8, the internal configuration is ignored, and the gain will go up to 200 times or 46 dB. If we place a resistor in series with the capacitor, the gain can be adjusted to any value of 20x and 200x.

We see that the LM386 is an integrated amplifier ideal for amateur and professional circuit assemblies. Here is an IC that should not miss on the bench, and along with the 555 makes a perfect pair of multipurpose components.