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Why does this simple oscillator circuit need a transistor?

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rata478

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Why does this simple oscillator circuit need a transistor?

ColpittsOscillator.png

I just don't seem to understand, any help would be appreciated.

Also, would this circuit work /efficiently/?
 
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Your circuit is too simple:
1) It is missing a power supply.
2) It is missing a DC path to 0V for the emitter of the transistor.
3) It is missing a bias current for the base of the transistor.
4) It is missing a coupling capacitor to block DC from the collector to the base of the transistor.

Here is a complete Colpitts oscillator: (Read about how it simply works on the internet)
 

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  • Colpitts oscillator.png
    Colpitts oscillator.png
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Your circuit is a theoretical circuit drawing, where only the active or directly relevant components are shown which are involved in the actual oscillation process. A real practical circuit would have many additions to it to get everything at the proper voltage/ current levels to make it actually work, as explained by Audioguru.
 

rata478 said:
Why does this simple oscillator circuit need a transistor?
Click to expand...

A theoretical model of an oscillator consists of an active element achieving a gain (much) greater than the unity - generally represented by a block called 'A' - and a passive resonant element which performs the feedback for the desired frequency - generally represented by a block called 'B', as bellow:

AB.PNG

A fundamental prerequisite to keep some transient signal ringing continuously around the structure is an overall gain above the unity, as the mathematical representation |A.B| > 1. This concept can be used to represent the working of an generic oscillator circuit similar to the one posted above:

OSC.PNG

Therefore, any resonant based circuit oscillator might contain these basic components.



+++
 

an oscillator is basically an amplifier whose output is connected back to its own input. transistor is a basic amplifying element thats why transistor is needed, you can also make oscillator circuit with op-amp ic. but keep in mind certain conditions.
1. The transistor must have enough gain to overcome the feedback losses.
2. Feedback must be in correct phase, it must be positive feedback.
 

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