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Cute little oscillator, but theory of operation?

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eti:
Found this nice little oscillator (boost conv?) online, and it works a treat; I’ve got it running TWO white 2.5v LEDs in series from one “AA” battery… but I’m at a loss as to the complete theory of operation. Clearly the field collapse across L is causing the voltage boost, but I can’t work out why it remains in oscillation.

If anyone could de-muddy the waters, I’d be indebted to them. Many thanks.

eti:
Oddly (or NOT so oddly), it doesn't oscillate in LTSpice OR in "Every Circuit"; surprise surprise...

KE5FX:

--- Quote from: eti on December 24, 2021, 07:55:05 pm ---Oddly (or NOT so oddly), it doesn't oscillate in LTSpice OR in "Every Circuit"; surprise surprise...

--- End quote ---

You may not have let it run long enough.  Try adding a .startup directive. 

Bud:
Don't assume simulators always work. They do not. Years ago i was simulating a _simple_ RF mixer. Out of 4 simulators only one produced proper result. I recall it was Agilent ADS.

amyk:
It's a simple blocking oscillator. When power is first turned on, the two transistors start conducting and the current through the coil increases, while this is happening the top is positive and through the feedback capacitor keeps the transistors on. Once it saturates, the potential difference across it is no longer enough to keep them on, and that results in the transistors turning off, causing the field in the inductor to collapse and pull current through the LED (it is now in series with the inductor and the power source, so you get a boost in voltage). Since its top is now negative, it keeps the transistors off. The transistors start turning on again once the energy has dissipated, and the cycle repeats.

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