Ok. Thanks to all that answered.
First of all... Yes, the LED is white. And it does in fact only use 1 AA.
I took a better look at that "transistor" and it has the code SC6202C. And I found some datasheet of a Chinese led driver meant for 3V as SC6202, So it is most likely a low voltage version of that. And it is paired to an inductor in the example circuit. So, most likely that is what that "resistor" is. I didn't know those existed. I'm gonna have to look at how those work. Does the controller do some switching, like a switching power supply?
And about the circuit... I would have to take it apart to show more. But you wouldn't see more than what I showed. It is just those 3 components.
I've also managed to fix it. It had a spring that was supposed to rest on top of the 3 solder bulges at the edge of the PCB. Clearly a terrible Idea. And I have soldered the spring directly. Now shines bright as it should.
By the way, I leave the datasheet I've found here. Don't know if the site is safe. Visit it at your own risk.
https://html.alldatasheet.com/html-pdf/1146369/FUMAN/SC6202B/174/1/SC6202B.html
Hi,
The basic action of an inductor in a switching circuit is to act like a current source for a short time. Because it looks like a current source, if there is very high resistance across it the voltage will shoot up very high because it tries to keep the current constant, and a current across an open circuit (LED not conducting yet) means the voltage shoots up high until the LED starts to conduct, then the LED clamps the voltage at the nominal LED voltage (3v or so for white LEDs).
All this happens after the inductor is 'charged' and that is done with the voltage of the battery. The battery is connected across the inductor for a short time and during that time the inductor current increases. When the battery is removed via the switch, the inductor current tries to maintain that original charging current and so it shoots up to the LED voltage and the LED turns on.
This action is similar to how a car keeps rolling even when you take your foot off the gas pedal. It tries to keep rolling at the same speed as before you took your foot off the gas but eventually it does slow down due to friction. The inductor tries to keep the current flowing but Ohm's Law tells us that a current thought a very large resistor (open circuit) will generate a very high voltage, enough to turn the LED on.
For example say we charge the inductor such that it then has 1 amp flowing through it. Now we remove the charge source and connect a 100 Ohm resistor across the inductor (very very quickly). The voltage jumps up to:
V=i*R=1*100=100 volts
and it stays like that for a short time, just enough for the LED to light up (although it gets clamped to 3v or so with an LED).
And this could all be because we charged the inductor up with as little as 1.5 volts to begin with.
Once the designed time period has passed, the inductor has to be charged again. During that time the LED may be off, but even though it turns on and off you dont see the pulsing because it's too fast. Other circuits use a rectifier and capacitor to hold some of that voltage so the LED stays on during that time too. So those are two different kinds of circuits. The minimum component type will not have a capacitor so the LED turns on and off very rapidly. They usually overdrive the LED too so that during the 'on' time it is much brighter than usual, so during the 'off' time it averages to a lower level of light output. Your eyes act as a light intensity integrator so it averages out the high and low light to an average value that is the intended brightness of the flashlight. You may see it pulse though if you turn your head very fast or sweep the light across your field of vision because then the light output varies with time and distance and your eye may pick that up unless the frequency is very high then it will be hard to notice.
Just to be complete, inductors are also used in filter circuits and resonant circuits but that's not usually a principle that is used in switching circuits, at least not until of late where the idea of switching in step with the resonant frequency was found to waste less energy so the flashlight or other device would be more efficient. That's a more modern design though not sure if it appears in any low power circuits like a flashlight circuit yet it's mainly more of a concern with high power converters.