The IC LM386 is a 8-pin tiny power amplifier chip, specially made for operating under relatively low voltage parameters, yet provide considerable amplification.
IC LM386 amplifier circuit becomes suitable for applying in small low power audio gadgets like in FM radios, door bells, telephones etc.
Let's begin the IC LM386 amplifier explanation by studying its absolute maximum ratings first, meaning the parameters which should not be exceeded while using this IC in any circuit:
Technical Specifications of IC LM386
- Supply Voltage: 4V to Max. 15V (Typical)
- Input Voltage: +/- 0.4 volts
- Storage Temperature: -65 degrees to +150degrees Celsius
- Operating Temperature: 0 to 70 degrees Celsius
- Power Output: 1.25 watts
- IC manufactured by: National Semiconductor
How to Control Gain for the IC LM386
In order to make the IC better with its response, its pin#1 and 8 have been attributed with a gain control facility which may be set externally.
Gain simply means the capacity or the amplifying level of the device up to which it is able to amplify the applied input low signal audio input.
When the above pin outs are kept unconnected to anything, the internal 1.35K resistor sets the gain of the IC to 20.
If a capacitor is joined across the above pin outs, the gain is suddenly lifted to 200.
The gain may be simply made adjustable by connecting a pot in series with the above explained capacitor across the pin 1 and 8.
Practical Application Amplifier Circuits Using the IC LM386
The following figure shows a typical IC LM386 amplifier circuit having the bare minimum number of components required to make the IC operate at its internally set level of gain 20.
The speaker used is a 2 watt, 8 Ohms type.
The input at Vin may be fed from any audio source such as a cell phone headphone socket, a CD/DVD player RCA L or R socket or any other similar source.
The pin Vs should be connected to +12V DC supply from an AC DC adapter or a home made transformer/bridge power supply unit.
Pin #4 should be connected to ground or the negative of the power supply.
The earth wire or the negative wire from the input audio source should also be connected to the above negative of the power supply.
The input pin#2 goes to a 10K pot which becomes the volume control, one of its end terminals is picked for receiving the input signal while the other end is connected to ground, the center one goes to the hot end of the IC.
The speaker is connected to in #8 via a high value blocking capacitor, the resistor/capacitor arrangement connected across pin #5 and ground has been included for frequency compensation and to provide greater stability to the circuit.
The next circuit shows a similar design as above, except that its pins 1 and 8 have been connected to a capacitor of 10uF, which as explained above helps to pull the gain of the amplifier to 200
MIC amplifier circuit using LM386 IC
The following image shows how the above explained LM386 may be applied for achieving a simple yet powerful microphone amplifier circuit as shown below