/diy/ - Do It Yourself

>>1603530
No infinitum. An amplifier limits its output by clipping above a certain level. To get a clean sine you set the loop gain to just cover the losses, such that the clipping is soft and the sine shape has as little distortion as possible.

The image only shows the principle of the Colpitts oscillator, no power supply, no biasing. The circuit at the bottom is even more simplified. You see that the LC circuit acts as a π filter that can be used to match output to input by means of the C1 to C2 ratio, like a transformer. When you tap the inductor instead of the capacitor the circuit changes its name to 'Hartley' oscillator.

>>1538394
In my view the mystery circuit is a variant of the traditional Colpitts oscillator where one capacitor is 'parasitic'. C2 is the capacitor at the base and C1 is the effective output capacitance of the transistor.

Since C2 >> C1, the high output impedance is transformed down to the low input impedance of the transistor in common emitter configuration to uphold the loop gain. The phase difference between the two ends of a resonant LC circuit is always 180°.

This is probably the simplest possible garden light circuit not invented in CN.
Kudos to >>1537393 for the original content!