# Circuit Simulator - Colpitts Oscillator

Colpitts Oscillator
Circuit Description:
This is a Colpitts oscillator, an oscillator that uses an LC circuit combined with a transistor for feedback.

With the transistor removed, the inductor and two capacitors form a resonant circuit, like the LRC example. Current moves back and forth as the capacitors charge and discharge through the inductor. The transistor amplifies this oscillation and prevents it from dying out.

The transistor cannot conduct until C1 is charged to about 680mV. When the transistor is off, the output is around 4.5 V. Current from the 1k resistor and the inductor charges C2. The current through the inductor slows and then reverses, charging C1 again. When it is charged, the transistor conducts, bringing the output low. As the oscillation continues, the transistor turns off again. Current through the 1k resistor keeps the oscillation going.

Discussion:
9 comments Page 1 of 1.

Leftside said:   7 years ago
@Arthur, f=1/(2*3.1416* [square root of ( L * ( (C1*C2)/(C1+C2) ) ) ] ).
(7)

Hueby said:   7 years ago
Hi. Any simulation program I can use to simulate the above circuit. A program that can show the full output waveform and not just the charging part/first 2-3 periods.

(5)

Arthur said:   8 years ago
What is the formula for circuit oscillation frequency ?
I tried using f = 1 / ( 2Ψï¿½ ( LC ) ) to compare with a simulation, but the result was a little different.
(7)

Monika said:   8 years ago
What is the use of r.f.c. in this circuit diagram?
(7)

THOOYAVAN V said:   8 years ago
How to get the pure sine wave by using this colpitts oscillator? Please tell me.
(6)

Amar said:   9 years ago
Can we feed a signal to this colpitts oscillator to make a fm transmitter? If yes where to feed the input signal?
(3)

Abhishek said:   9 years ago
If we change the values of inductor and capacitor will it give different frequency with the formula f=1/(2-pi under root(lc)).
(5)