Breadboard and meter a circuit.

[Lightium]

Does somebody want to breadboard my circuit and measure the output with oscilloscope?

 

[Nigel Goodwin]

Well it looks completely non-functional, what's with Q2 base/emitter?.

 

[Lightium]

Oh no, it oscillates at a variety of frequencies.

 

[Lightium]

Q2? The power supply is so small there is no need for biasing.

 

[Nigel Goodwin]

Q2? The power supply is so small there is no need for biasing.

Q2 base emitter junction connects the supply directly to the top of R2, so the emitter of Q1 is only 0.7V below it's collector, with 2.3V just wasted across R2. I'm doubtful if it will work on only 0.7V, but in any case why use a 3V supply and throw 2.3V of it away?

 

[Lightium]

mmm, I'll keep going and look at what you say and fix it.

 

[AnalogKid]

Your question is lacking some important information, such as What is the circuit supposed to do? What are the inputs and where are they connected? What is the output and where is it connected?

ak

 

[Lightium]

It's just an oscillator I am playing with. L1 determines frequency. R1 is the load.

 

[NightMoth]

Hello

I breadboarded this circuit. My Vcc is 3.3V, L1 = 1uH||10uH||10uH||22uH = 803nH.
Here is what I got:

here is breadboard:

 

[Lightium]

NightMoth, thank you so much. 16.7MHz, wow!

 

[rjenkinsgb]

That could be the voltage regulator IC oscillating as it does not appear to have any decoupling??

The LT1086 must have a capacitor on its output, with fairly critical characteristics.

See "Stability" on page 8 of the datasheet:

https://www.digikey.co.uk/en/htmldatasheets/production/79267/0/0/1/lt1086cm-3-6-tr

 

[Lightium]

The application info mentions a 150uF cap, but in my sim I get similar values.

 

[NightMoth]

Hello

I have added 10uF input and 100uF output cap to LT1086 voltage regulator.
Oscillations still here, but its frequency drops to 15.86MHz.

Also I have checked values of inductors and capacitors from LC tank with RLC meter, and it confirms why oscillations is about 16MHz but not 26MHz:
Ideal: L1 = 1uH||10uH||10uH||22uH = 803nH, C1 = 47pf ==> Fres = 25.907 MHz
Real: L1 = 3uH||10.2uH||10.2uH||21uH = 1733nH, C1 = 56pf ==> Fres = 16.156 MHz
(My 1uH inductor acually is 3uH...and 47pf cap is actually 56pF...)

Also without C1 capacitor, only breadboard parasitic capacitance left, frequency is 20.77MHz.
According to tank frequency formula it means that parasitic capacitance between three rows on my breadboard is 34pF, but I think it is too high capacitance, maybe 20.77MHz is a limit of frequency 2N2222 can support?

 

[Lightium]

Wow, you got right into it. Thank you NightMoth. Yes, I've notices I can remove C1 and the circuit oscillates differently.

 

[Lightium]

With C1=34pF and L1=800nH I simulate 23.011MHz.