Last Updated on October 22, 2023 by Kevin Chen
Image source Freepik
The main working mechanism of the oscillator circuits entails creating oscillations. While doing so, they end up generating the sinusoidal waves. These waves are in continuous form and tend to have constant frequency and voltage.
In most applications, the oscillator circuits are used for converting power from AC to DC. There are two main types of oscillators, sinusoidal and non-sinusoidal. As the names suggest, the oscillations from the sinusoidal are in the sine wave. These have stable frequency and amplitude. On the other hand, the non-sinusoidal oscillators generate quite complex waveforms.
Many electronic devices tend to utilize these circuits for various reasons. You will find them in radios, audio devices, visual devices, and communication devices among many others.
In all the oscillator circuits, the output waveform is higher than the incoming signals. This is achieved without having to connect the circuit to an external power supply. This is where the power of transistors comes in.
Well, amplification is just one of the functions of transistors in oscillator circuits. There are many other functions and even benefits of transistors and this is the primary goal of this article. We are going to discuss key reasons why transistors have oscillator circuits. We will also look at the impact of having these electronic components in these circuits.
What is a transistor oscillator?
A transistor can be used as a switch, an amplifier, and an oscillator. When used as an oscillator, it is referred to as a transistor oscillator. This type of transistor has positive feedback, a feature that makes it an ideal component of the oscillator circuit.
This transistor ensures that the oscillator generates continuous oscillations when it is connected to a power source. The presence of the transistor in this circuit eliminates the need of upgrading the power source in case you need oscillations of higher frequency. This is possible because the transistors will serve as the amplifiers.
Illustration of the transistor in the oscillator circuit
The diagram below illustrates the use of transistors in an oscillator.
Image source Learn About Electronics
The above image of a transistor in oscillators is divided into different parts, which we are going to look at.
- Tank circuit: This is a part of the oscillator circuit where the actual oscillations are generated. The waves generated at this point of the circuit may have small waves and will need to be amplified by the transistor so that they can be useful in their respective application areas.
- Amplifier circuit: After the generation of the oscillations, the next part of the circuit focuses on amplifying them It is in this section that the role of the transistors is made clear. It raises the frequency and amplitude of the oscillations or sinusoidal waves.
- Feedback circuit: This is another special section of the oscillator circuit. It supplies the energy that is required to amplify the oscillations. The feedback section is among the main reasons why we say that transistor oscillator circuits are independent. The energy from the feedback section of the circuit is supplied through the mutual induction mechanism.
How transistors in oscillators work
When in oscillator circuits, transistors work in the common emitter circuits whereby the emitter is connected to both the collector and emitter terminals. A tank circuit that we have described in the previous section is connected between the base and the emitter terminals of the transistor. The oscillations in this circuit are generated by the inductor and capacitor. These two electronic components are connected parallel to each other.
The flow of electric current or signals at the base of the emitter keeps fluctuating due to the oscillations that are generated at the tank circuit. When you forward-bias the base current, the current at the collector region will also change.
The fact that the LC oscillations are sinusoidal means that the current at the collector will also keep changing in a sinusoidal manner. These changes will eventually affect the output current and voltage. The circuit will also have a sinusoidal output.
So, how is the oscillation circuit able to maintain continuous oscillations? As we have already mentioned, there is no external DC applied to maintain the oscillations. Inductors and capacitors have the solutions. They are connected to the base and collector of the circuits whereby the provide the energy, which will be amplified by the transistor. The circuit will be able to sustain the oscillations at a specific frequency for as long as it will be needed.
Advantages of transistors in oscillator circuits
Here are the top reasons why transistors are used in oscillator circuits:
- Amplification capacity: This is the primary benefit of transistors in the oscillator circuit. It amplifies the electric signals and frequency that generate the oscillations.
- Frequency stabilizer: Transistors in oscillator circuits are also used for stabilizing the frequency of oscillations. The power regulation property of the transistors ensures that the signals for running frequency remain within a defined range.
- Fast operation; We all know that transistors have fast-switching properties. This is an important aspect in ensuring that the circuit has a short reaction time.
Types of a transistor oscillator
There are different types of oscillators that utilize the power and effectiveness of the transistors. These circuits include:
Hartley oscillator circuits are tuned to determine the oscillation frequency in their respective application areas. A typical Hartley oscillator circuit comprises a capacitor and two inductors. The two inductors are connected in series while the capacitor is in parallel to the two inductors. Hartley oscillators are used in circuits that generate a frequency of more than 30MHz.
The working mechanism of Colpitt’s oscillator circuit is different from the Hartley oscillator. The extra benefit that of Colpitt is its oscillations are more stable than for Hartley. They also tend to generate oscillations of higher frequency than Hartley.
Wien Bridge Oscillator
Wien bridge is a common oscillator circuit that is mainly used in audio applications. It has a wide frequency range, a feature that makes it useful in most audio and communication devices.
With this guide, you will be able to appreciate the role of transistors in oscillator circuits. If you are building such a circuit, it will be prudent to get the right transistors for the job.
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