Low Power Audio Amplifier using 555 Timer

For spaces such as an auditorium or any other hall, traditional audio amplifier methods use high-power circuits to drive a loudspeaker. However, we can meet the requirements for applications involving the use of small loudspeakers with modest range requirements by building a low power amplifier with a low output current, such as 200 mA.

The theory, design, and operation of a low-power audio amplifier using a 555 Timer are described in this article. To produce a modulated signal, the 555 Timer generates a carrier signal that is modulated by the amplified audio source. A small loudspeaker is driven by this signal.

Outline

• Low Power Audio Amplifier Circuit Principle:
• 555 Timer as an Amplifier Circuit Diagram:
• Circuit Design of Low Power Audio Amplifier:
• Low Power Audio Amplifier using 555 Timer Circuit Simulation:
• How 555 Timer as an Amplifier Circuit Works?
• 555 Timer as an Amplifier Circuit Applications:
• Limitations of Audio Amplifier Circuit:

Low Power Audio Amplifier Circuit Principle:

This design is based on the principles of audio amplification and pulse width modulation utilising a 555 Timer. The audio signal is boosted using the TL071 low noise high input operational amplifier before being sent to the 555 Timer’s control pin. The 555 Timer is used to generate an oscillating signal as an astable multivibrator. The audio signal modulates this signal, generating pulse width modulation, in which the width of the output pulse varies with regard to the voltage at the control pin (the audio signal).

555 Timer as an Amplifier Circuit Diagram:

Circuit Design of Low Power Audio Amplifier:

The circuit design method is straightforward, with only two steps: creating the preamplifier portion and designing the astable multivibrator section.

We’re using the TL071 low noise JFET input operational amplifier, which has a low input bias current and a fast slew rate of roughly 13V/s. A voltage divider network with two 47K resistors is designed to apply a voltage of 6V to the non inverting terminal of the OPAMP. Assuming we need a gain of roughly 22(V/V) or 27.2dB and the value of one of the feedback resistors to be around 1K, we calculate the value of another resistor to be around 22K. Since output impedance is low for this amplifier, we use a resistor of about 1K at the output to connect it to the control pin of the 555 Timer.

The 555 timer astable circuit is the next phase in the design process. We employ two resistors for both charging and discharging the capacitor in a standard 555 Timer as an astable multivibrator circuit. However, instead of the resistor, we use a diode 1N4007 to create a quicker discharge rate. We may compute the value of the threshold resistor to be about 1K if the necessary output frequency is around 145 KHz and the capacitor value is around 10nF. (Forward resistance of 1N4007 is around 1Ohms).

Low Power Audio Amplifier using 555 Timer Circuit Simulation:

Once the circuit is designed, the next step involves timer circuit simulation. Here we follow a series of steps to simulate the circuit using Multisim software.

1. Under the Simulate option, select the microphone simulation model from the LabView instruments.
2. The required parameters are specified in this manner (The time of recording and sampling rate).
3. The software is used to build the circuit, and the microphone is attached as an input to the circuit.
4. Under the Simulate menu, a loudspeaker model is selected from the LabView instruments and linked as an output to the circuit.
5. The interactive simulation is activated by setting the end time to be equal to or greater than the recording time.
6. The loudspeaker’s “Play” button is greyed out while the circuit simulation is running, and it is enabled once the simulation is over.

How 555 Timer as an Amplifier Circuit Works?

The pre-amplifying (electric signal amplification) operation and the pulse width modulation operation are the two parts of the circuit operation. The low noise operational amplifier TL071 performs the amplifying action. The microphone detects the incoming audio signal, which is then transformed to a low-voltage electric signal. This low-voltage AC signal is sent to the OPAMP’s non-inverting terminal through a 1uF electrolyte capacitor, which blocks the audio signal’s DC current.

The operational amplifier amplifies the signal, with the gain determined by the values of the feedback resistors. Using the feedback network, the OPAMP works in linear mode to make the voltage at the non inverting terminal equal to the output voltage. Through the capacitor (to eliminate the DC component) and the resistor, this amplified signal is supplied to the control pin of the 555 Timer. The 555 Timer is in astable mode here, with the output signal frequency dictated by the combination of resistors R1 and C1.

However, because the control voltage is applied here, the width of the output pulse fluctuates depending on the control voltage. The audio voltage modulates the 555 Timer’s carrier output signal, and the resulting modulated signal is used to drive the loudspeaker. The loudspeaker responds to the DC value of the modulated signal rather than the high frequency signal, and hence the audio signal looks amplified.

555 Timer as an Amplifier Circuit Applications:

1. This application can be used to develop low power music systems used in vehicles.
2. It can be used in classrooms with limited areas.

Limitations of Audio Amplifier Circuit:

1. This circuit is suitable only for low power loudspeakers.
2. 555 Timer doesn’t produce 50% duty cycle signal.
3. This circuit is theoretical and may require changes in hardware implementation.