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Cute little oscillator, but theory of operation?
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eti:

--- Quote from: SiliconWizard on December 25, 2021, 02:55:23 am ---
--- Quote from: rfclown on December 25, 2021, 02:19:11 am ---A single AA battery is less than 3 diode drops so both transistors don't initially conduct. With a 1.5V supply the PNP is almost always conducting, but the NPN cycles on and off. Circuit doesn't work well with two cells.

--- End quote ---

The "duty cycle" depends a lot on the supply voltage. Beyond a certain voltage, it won't work properly indeed. And then below a certain voltage, it won't work either. It would probably not work right for the whole life of a typical AA alkaline battery, and would just hardly start with a NiCd battery, I think.

--- End quote ---

Strangely someone had it working at 0.2-0.3v!!!
ledtester:

Another well-known blocking oscillator design is the "Joule Thief".

This guy has been running one continuously for over five years:

Blinking Joule Thief: 5 Year Update -- Eman2000
https://youtu.be/AWDX3L07qyc
SiliconWizard:

--- Quote from: eti on December 25, 2021, 03:03:43 am ---
--- Quote from: SiliconWizard on December 25, 2021, 02:55:23 am ---
--- Quote from: rfclown on December 25, 2021, 02:19:11 am ---A single AA battery is less than 3 diode drops so both transistors don't initially conduct. With a 1.5V supply the PNP is almost always conducting, but the NPN cycles on and off. Circuit doesn't work well with two cells.

--- End quote ---

The "duty cycle" depends a lot on the supply voltage. Beyond a certain voltage, it won't work properly indeed. And then below a certain voltage, it won't work either. It would probably not work right for the whole life of a typical AA alkaline battery, and would just hardly start with a NiCd battery, I think.

--- End quote ---

Strangely someone had it working at 0.2-0.3v!!!

--- End quote ---

I'd be curious to see that, and even more curious to get an explanation. (Oh and if you haven't actually witnessed it yourself, don't believe everything people say...)
Unless maybe this was done with hand-selected germanium transistors.
David Hess:

--- Quote from: rfclown on December 25, 2021, 02:19:11 am ---A single AA battery is less than 3 diode drops so both transistors don't initially conduct. With a 1.5V supply the PNP is almost always conducting, but the NPN cycles on and off. Circuit doesn't work well with two cells.
--- End quote ---

With 1.5 volts from an AA cell divided three ways to place 0.5 volts across the emitters, they do conduct a little bit which is enough to start operation.
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