#230 MinimalLCOscillator

Test an LC oscillator of just 5 components

Notes

I borrowed this idea and circuit design from stoneslice’s 1MHz Oscillator video.

I’m not sure how the circuit fits into the taxonomy of oscillator circuits, but it is similar to a Colpitts oscillator circuit - but one capacitor is replaced with a resistor.

I tried a range of component values on a breadboard. To sustain the oscillation, I found I had to increase the value of the resistor - 4.7kΩ proved good for all cases.

The effect of the resistor seems to alter the resonant frequency of the “impure” tank circuit. For example, I’d expect with 150µH/47pF the frequency to be 1.89MHz when in fact I measure 2.819MHz.

Nevertheless, an interesting self-oscillating circuit.

Soldered on a PCB with 150µH/47pF and a J201 n-FET, there are no issues sustaining an oscillation, however the frequency is not particularly stable and there’s a distinct second harmonic.

Construction

Credits and References

• 1MHz Oscillator - stoneslice
• Colpitts oscillator - wikipedia
• J201 datasheet
• ..as mentioned on my blog