Tuned Collector Oscillator Circuit Working And Application

An oscillator is one kind of an electronic circuit that generates an oscillating, periodic electronic signal such as a sine wave (or) a square wave. The main function of an oscillator is to convert DC (direct current) from a power supply to an AC (alternating current) signal. These are widely used in several electronic devices. General examples of signals produced by oscillators comprise signals broadcast by the transmitters of a TV and a radio transmitter, CLK signals that control the quartz clocks and computers. The sounds generated by video games and electronic beepers. The oscillator is often characterized by the output signal’s frequency. Oscillators are mainly designed to generate an output of high-power AC from a direct current supply that is frequently called inverters.

The different types of oscillators have the same functions, that they generate continuous undamped o/p. But, the main difference between the oscillators lies in the method by the energy which is supplied to the tank circuit to meet up the losses. The common types of transistor oscillators mainly include tuned collector oscillator, Colpitt’s oscillator, Hartley, phase shift, Wein bridge and a crystal oscillator

What is a Tuned Collector Oscillator ?

The tuned collector oscillator is one kind of transistor LC oscillator where the tank circuit comprises of a capacitor and a transformer, that is connected to the collector terminal of the transistor. The tuned collector oscillator circuit is the simplest & the basic kind of LC oscillators. The tank circuit connected in the collector circuit performs like a simple resistive load at resonance and decides the oscillator frequency. The general applications of this circuit include signal generators,RF oscillator circuits, frequency demodulators, mixers, etc. The circuit diagram and working of a tuned collector oscillator are discussed and shown in the following below.

Tuned Collector Oscillator Circuit

The circuit diagram of the tuned collector oscillator is shown below. For the transistor, the resistors R1, R2 form a voltage divider bias. The emitter resistor ‘Re’ is which is intended for thermal stability. It also stops the transistor’s collector current and the emitter bypass capacitor ‘Ce’. The main role of ‘Ce’ is to avoid improved oscillations. If the emitter bypass capacitor is not there, the amplified AC oscillations will fall across emitter resistor ‘Re’ and will add on to the ‘Vbe‘ base-emitter voltage of the transistor. And after this, this will change the conditions of DC biasing. In the circuit below, primary of the transformer L1 and capacitor C1 shapes the tank circuit.

Tuned Collector Oscillator Circuit
Tuned Collector Oscillator Circuit

Tuned Collector Oscillator Circuit Working

When the power supply is turned ON, the transistor gets the current and starts conducting. The ‘C1’ capacitor starts charging. When the C1 capacitor gets the charge, then the charge starts discharging through the primary coil L1 of the transformer.

When the capacitor C1 is fully discharged, the energy in the capacitor as the electrostatic field will be stirred to the inductor as the electromagnetic field. Now there will be no more voltage across the capacitor to maintain the current through the primary coil in the transformer starts to collapse. In order to resist this, the L1 coil generates a back emf which may charge the capacitor again. Then capacitor ‘C1’ discharges through the L1 coil and the series is constant. This charging & discharging sets up a sequence of oscillations in the tank circuit.

The oscillations generated in the tank circuit is fed back to the base terminal of the Q1 transistor by the minor coil by inductive coupling. The quantity of feedback can be regulated by changing the ratio twists of the transformer.

The direction of the secondary winding coil ‘L2’ is in such a way that the voltage across it will be 180° phase opposite to that of the voltage across the primary (L1). Therefore the feedback circuit generates 180° of phase shift and the Q1 transistor produces 180° of phase shift of another.As a result the total phase shift is acquired between input & output. It is an extremely required condition for positive feedback and continued oscillations.

The collector current (CC) of the transistor balances the lost energy in the tank circuit. This can be done by adopting a little amount of voltage from the tank circuit, strengthening it and applying it back to the circuit. The Capacitor ‘C1’ can be made variable in the applications of variable frequency.

In the tank circuit, the frequency of oscillations can be expressed using the following equation.

F = 1/ 2π√[(L1C1)]

In the above equation, ‘F’-denotes the frequency of oscillation and L1-is the inductance of the transformer’s primary coil and C1-is the capacitance.

Application of Tuned Collector Oscillator Circuit

The applications of tuned collector oscillator involves in the local oscillator of a radio. All transformers introduce 180º of a phase shift between primary & secondary.

Electronics receiver principles make use of an LC tuned circuit with the following

C1 = 300 pF and L1 = 58.6 μH

Frequency of oscillations can be calculated by the following procedure

C1 = 300 pF

= 300 × 10−12 F

L1 = 58.6 μH

= 58.6 × 10−6 H

Frequency of oscillations, f = 1/ 2π√L1C1

f = 1/ 2π √58.6 × 10−6 x300 × 10−12 Hz

1199 × 103 Hz

= 1199 kHz

Thus, this is all about Tuned collector oscillator circuit working and applications. We hope that you have got a better understanding of this concept. Furthermore, any doubts regarding this concept or to implement the electrical and electronics projects, please give your valuable suggestions by commenting in the comment section below.Here is a question for you, what is the main function of an oscillator?

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