Test an LC oscillator of just 5 components
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.
| L | C | frequency |
|---|---|---|
| 470µH | 47pF | 1.6MHz |
| 150µH | 47pF | 2.9MHz |
| 470µH | 68pF | 1.5MHz |
| 150µH | 68pF | 2.7MHz |
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.
- 1MHz Oscillator - stoneslice
- Colpitts oscillator - wikipedia
- J201 datasheet
- ..as mentioned on my blog