Simple Phase Shift Oscillator Circuit using a Single Transistor

An oscillator is like a special electronic circuit.

It makes electrical ups and downs, like waves on an ocean.

These waves can be smooth and curvy or choppy.

The circuit can control how fast frequency ups and downs happen.

There are many kinds of oscillator circuits.

One type called an RC oscillator uses a special part RC network to make the circuit create smooth, curvy waves on its output.

This RC network helps the circuit by sending a signal back to itself that keeps the waves going.

Circuit Working:

Parts List:

The design of the circuit involves the utilization of a capacitor and resistor to create a network that imparts the necessary phase shift through feedback signals.

The RC oscillator demonstrates notable frequency stability and finds applicability across a broad spectrum of uses.

Utilizing an NPN transistor 2N2222 and other passive components the RC or phase shift oscillator generates oscillations within the desired frequency range.

This article elucidates the comprehensive working principles and applications of RC oscillators, accompanied by a detailed circuit diagram.

In this uncomplicated circuit, an NPN transistor 2N2222 functions as a common emitter amplifier, obtaining feedback from the RC network.

The output is acquired at the transistors collector terminal, which is coupled with a capacitor.

Upon applying a 9V DC power supply oscillations arise due to voltage level variations in the power source and fluctuations in the base current caused by noise variations in the transistor.

These variations are then amplified by the transistor.

The RC network is divided into three stages with each stage providing a 60° phase shift.

Consequently, a total of 180° phase shift is achieved from the feedback element.

Additionally, the transistor amplifier introduces a 180° phase shift resulting in a total phase shift of 360° and positive feedback.

The output yields a continuous smooth curvy waveform.

Formulas:

The below mentioned formula refers to the characteristics of an RC circuit (Resistor Capacitor circuit) and the two ways that frequency is represented: angular frequency (ω) and regular frequency (f):

ω = 2 * π * ƒ = 1.732 / RC

where,

• Angular frequency (ω): This is the frequency of a periodic waveform expressed in terms of its angular rotation.
• It is measured in radians per second (rad/s).
• Similar to rotational speed, but using radians rather than cycles per second as the unit of measurement.
• Regular Frequency (f): This is the number of cycles (repetitions) of a periodic waveform per second, measured in hertz Hz.
• This is the way we usually talk about frequency.
• The connection between ω and f is given by a constant of 2π (pi): ω = 2π * f
• RC: This is a simple electrical circuit made up of a capacitor C and a resistor R coupled in series.
• The resistor prevents current flow whereas the capacitor has the capacity to store electrical charge.
• The circuits response to AC (alternating current) signals is influenced by the RC combination.
• 1.732: This section of the formula represents the connection between the frequency response and the RC circuits time constant (τ).
• Another characteristic of an RC circuit is the time constant (τ), which may be expressed as τ = RC (the product of capacitance and resistance).
• It shows how long it takes for the voltage across the capacitor to charge or discharge to around 63.2% of its ultimate value.

This is how everything is connected by the formula:

We may determine the relationship between angular frequency (ω) and regular frequency (f) by multiplying by 2π using the equation ω = 2π * f.

The reciprocal of the time constant (τ) of the RC circuit (1/τ) is roughly equal to the equation 1.732 / RC.

How to Build:

Building an phase shift oscillator circuit involves assembling a circuit follow the below mentioned steps:

Transistor Setup:

• Place the NPN transistor 2N2222 on the PCB.
• Identify the collector, base and emitter pins.

Capacitor and Resistor Placement:

• Connect capacitors C1, C2 and C3 between the collector and base of the transistor.
• Connect resistors R1, R2 and R3 between the bases of the transistor and the junction points between capacitors.

Power Connection:

• Connect the +9V from the power supply to the collector of the transistor.
• Connect the ground to the emitter of the transistor.

Base Resistor R1:

• Connect resistor R1 between the base and the junction point of C1 and R2.

Feedback Network R2, C2, R3, C3:

• Connect R2 and C2 in series between the base and the junction of C1 and R2.
• Connect R3 and C3 in series between the junction of R2 and C2 and the base.

Output Connection:

• Connect the output from the junction of R3 and C3.

Testing:

• Power the circuit with a 9V DC battery.
• Observe the waveform at the output using an oscilloscope if available.
• Adjust the values of resistors and capacitors for desired frequency.

Troubleshooting:

• Ensure proper connections and polarity.
• Check the values of resistors and capacitors to match the desired frequency range.

Conclusion:

Remember, to take necessary precautions when working with electronic components and consult component datasheets for specific details.

Adjust resistor and capacitor values based on your desired oscillation frequency and feel free to experiment to understand the impact on the waveform.

Reference:

Phase-shift oscillator