Relaxation Oscillator
Category: Oscillators
Designer: RANA MUHAMMAD ADNAN KHALIL
Notes
This circuit is designed and simulated in Proteus 7.10. In this circuit you will learn how to make oscillator using npn and pnp transistor. The working of this circuit is given below: 1. This circuit is one of the electronic oscillator circuits. This circuit can be called as relaxation oscillator. 2. The relaxation oscillator is a nonlinear electronic oscillator and it produces non-sinusoidal repetitive output signal. 3. Lets consider initial state, the npn transistor Q2 is turned ON through resistor R2. 4. The collector of npn transistor is connected with the base of pnp transistor Q1, emitter of pnp transistor is connected with the positive terminal of battery and emitter of npn transistor is connected with ground (-ve terminal of battery). 5. The collector of pnp transistor is connected with the speaker and posistive terminal of capacitor C1 (resistance of speaker is less than 10 ohm), and other end of speaker is connected with the ground (-ve terminal of battery). 6. When Q2 is ON, it will turn ON Q1 by connected its base with ground, and capacitor C1 charges through Q1 transistor. 7. The the charge of C1 equals battery voltage, then Q2 become off and capacitor C1 discharges, again when C1 is discharged, the npn transistor Q2 will again turned ON through resistor R2, and this phenomenon continuous and provides oscillation in audible range, which can be listen through speaker. 8. The frequency of oscillation can be changed by changing resistor R2 or capacitor C1, that is changing R2*C1 time constant (product of R2 and C1). Application: 1. This circuit can be used to test the speaker. 2. This circuit can be used to generate non-linear oscillations. Download these files to perform more experiments.