Draw and explain the circuit of wein bridge oscillator, Electrical Engineering

Q. Draw and explain the circuit of Wein bridge oscillator. Obtain the expressions for the

(i) frequency of oscillation and (ii) condition for oscillation. Will oscillations take place if the bridge is balanced?

Wien bridge oscillator is one of the most popular type of oscillators used in audio and sub. audio frequency ranges (20 - 20 kHz). This type of oscillator is simple in design, compact in size, + Vcc and remarkably stable in its frequency output. Furthermore, its output is relatively free from distortion and its frequency OUTPUT can be varied easily. However, the maximum frequency output of a typical Wien bridge oscillator is only about 1 MHz. It employs two transistors, each producing a phase shift of 180, and thus producing a total phase-shift of 360 or 0degree.

289_Draw and explain the circuit of Wein bridge oscillator1.png

The circuit diagram of Wien bridge oscillator is shown in figure. It is essentially a two- stage amplifier with an R-C bridge circuit. R-C bridge circuit {Wien bridge) is a lead- lag network. The phase-shift across the network lags with increasing frequency and leads with decreasing frequency. By adding Wien-bridge feedback network, the oscillator becomes sensitive to a signal of only one particular frequency. This particular frequency is that at which Wien bridge is balanced and for which the phase shift is 0degree. If the Wien-bridge feedback network is not employed and output of transistor Q2 is fedback to transistor Ql for providing regeneration required for producing oscillations, the transistor Ql will amplify signals over a wide range of frequencies and thus direct coupling would result in poor frequency stability. Thus by employing Wien-bridge feedback network frequency stability is increased. In the bridge circuit Rl in series with Cl, R3' R4 and R2 in parallel with C2 form the four arms.

2172_Draw and explain the circuit of Wein bridge oscillator.png

Thus we see that in a bridge circuit the output will be in phase with the input only when the bridge is balanced i.e., at resonant frequency given by expression (20.39). At all other frequencies the bridge is off-balance i.e. the voltage fedback and output voltage do not have the correct phase relationship for sustained oscillations.

So this bridge circuit can be used as feedback network for an oscillator, provided that the phase shift through the amplifier is zero. This requisite condition is achieved by using a two stage amplifier, as illustrated in fig.  In this arrangement the output of the second stage is supplied back to the feedback network and the voltage across the parallel combination C2 R2 is fed to the input of the first stage. Transistor Ql serves as an oscillator and amplifier whereas the transistor Q2 as an inverter to cause a phase shift of 180°. The circuit uses positive and negative feedbacks. The positive feedback is through Rl' C1, R2' C2 to transistor Ql and negative feedback is through the voltage divider to the input of transistor Ql. Resistors Ra and R4 are used to stabilize the amplitude of the output.

Posted Date: 6/12/2013 3:24:56 AM | Location : United States







Related Discussions:- Draw and explain the circuit of wein bridge oscillator, Assignment Help, Ask Question on Draw and explain the circuit of wein bridge oscillator, Get Answer, Expert's Help, Draw and explain the circuit of wein bridge oscillator Discussions

Write discussion on Draw and explain the circuit of wein bridge oscillator
Your posts are moderated
Related Questions
Explain LOOP instructions in 8086 family with example and their effect on flag. LOOP: (Jump to given label until CX = 0) it is used to repeat a sequence of instructions for

Q What is Dual Tone Multi Frequency? Dual Tone Multi Frequency (DTMF) was first introduced in 1963 with 10 buttons in Western Electric 1500 -type telephones. DTMF was originall

Calculate Voltage and Current Phasors on a Phasor Diagram A synchronous motor is operated at rated load and unity power factor. The field current is increased by 20%. Show the

Can I have formulas for calculation of 50TN seting on 33KV overhead line

1.   Calculate the combined resistance of three resistors connected in series with resistance of 20 ohm, 30 ohm and 40 ohm? (to achieve a pass grade, solve problems with resisto

What do you mean by Circuit Analysis Techniques?   One simplifying technique often used in complex circuit problems is that of breaking the circuit into pieces of manageable

1) Draw the state diagram for the state machine described by Table 7.5 in the text. Note, the table shows the transition to the next state S* from the current state S for the next


Define the term real time clock. A real-time clock maintains the time in real time, which is, in hours and minutes. For the real-time clock the software contains an interrupt

1. For the following network: a. Find the differential equation assuming that v ( t ) is the input and the charge on the capacitor q ( t ) is the output. Hints: i R1= ( i R2