Simple Phase Shift Oscillator Circuit using a Single Transistor

Oscillators are similar to unique electrical circuits.

Like waves in the water it produces electrical ups and downs.

These waves can be rough or smooth and curved.

Frequency ups and downs are controlled by the circuit.

Circuits for oscillators come in many different kinds of forms.

To produce smooth curved waves on its output one kind of oscillator known as an RC oscillator requires a special component called an RC network.

By sending a signal to itself this RC network helps the circuit by maintaining the waves.

Circuit Working:

Parts List:

The circuits design uses a resistor and capacitor to form a network that uses feedback signals to supply the required phase shift.

The RC oscillator is used in a wide range of applications and has excellent frequency stability.

Oscillations within the necessary frequency range are produced by the RC or phase shift oscillator using an NPN transistor 2N2222 and other passive components.

With the help of a thorough circuit diagram this article explains the basic functioning and uses of RC oscillators.

An NPN transistor 2N2222 serves as a common emitter amplifier in this simple circuit receiving feedback from the RC network.

The transistors collector terminal which is connected to a capacitor is where the output comes from.

When a 9V DC power supply is used oscillations happen because of changes in the power sources voltage level and variations in the base current brought on by noise variations in the transistor.

The transistor then enhances these changes.

Each of the three stages that make up the RC network offers a 60° phase shift.

As a result the feedback element produces a 180° phase shift overall.

Also a 180° phase shift is introduced by the transistor amplifier producing a 360° overall phase shift and positive feedback.

A smooth curved waveform which is continuous provides the output.

Formulas:

The formula below describes the properties of a resistor capacitor circuit (RC circuit) and the two ways that frequency is expressed: regular frequency (f) and angular frequency (ω):

ω = 2 * π * ƒ = 1.732 / RC

where,

• When a periodic waveforms frequency is represented in terms of its angular rotation it is called its angular frequency (ω).
• The number of cycles (repetitions) of a periodic waveform per second are expressed in hertz Hz is known as the regular frequency (f).
• A constant of 2π (pi) provides the relationship between ω and f: ω = 2π * f.
• A resistor R connected in series with a capacitor C forms the basic electrical circuit known as RC.
• The formulas section 1.732 shows how the frequency response and the RC circuits time constant (τ) are related.

The formula connects everything in this way:

Using the formula ω = 2π * f one can multiply by 2π to get the connection between angular frequency (ω) and regular frequency (f).

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

How to Build:

To build a simple Simple Phase Shift Oscillator Circuit using a Single Transistor following are the steps required for connections

Configuring a Transistor:

• On the PCB place the NPN transistor 2N2222.
• Find which pins are the emitter, base and collector.

Positioning of Capacitors and Resistors:

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

Connection of Power:

• Connect the power supplies +9V to the transistors collector.
• Connect the transistors emitter to the ground.

R1 is the base resistor:

• Connect resistor R1 between junction point and base of C1 and R2s

Network of Feedback R2, C2, R3, C3:

• R2 and C2 must be connected in series between the base point where C1 and R2 meet.
• Between the base and the junction of R2 and C2 connect R3 and C3 in series.

Connection for Output:

• Connect the output from the R3 and C3 junction.

Testing:

• The circuit is powered by a 9V DC battery.
• Use an oscilloscope to view the output waveform if it is available.
• Adjust the resistor and capacitor values to get the desired frequency.

Troubleshooting:

• Ensure that the polarity and connections are right.
• Verify that the resistor and capacitor settings match to the necessary frequency range.
• Check how the RC circuits time constant (τ) and frequency response are connected.

Conclusion:

When working with electronic components keep in mind to use proper care and refer to component datasheets for full details.

Depending on the oscillation frequency one require to change the resistor and capacitor values.

One can also experiment to see how it affects the waveform.

Reference:

Phase-shift oscillator