Reverse-engineering camera flash charger

Question

I am trying to understand how exactly the voltage from a 1.5 V battery gets connected to a 1000+ V capacitor inside these disposable cameras. Is there a specific chip designed to act as a voltage amplifier and diode or do capacitors act as a sponge of sorts and directly connecting them to lower power sources allow for saturation?

After previous answers I have more questions.

1. you state the current is transformed to AC with a transistor* embedded in the chip. Does this mean I could get the same result with a suitable market transistor (and other components*)?

As my direct intentions for the hack are to use an increased voltage supply to drive a motor from a smaller set of cells (18650 to be exact) and I am aware that power is always lost during any conversion, would it maybe be best to use an AC motor such as a furnace fan I have rather than the 12 V scooter motor I intended to use?

Assuming I were to go with the AC alternative I would presume I would substantially be building an inverter, while I have had trouble with these being limited in their output to under 100 W, I suspect this may be mostly due to compenent costs and limits to ensure certain commercial safety ranges for delicate electronics's safety, as the whole point of this circuit will be to drive a motor some of those parts may be omitted?

I have APX30 18650 cells at my disposal and I prefer to keep them in smaller banks of 2-4 cells per set. I have an Arduino with relays I could use to switch banks.

What would be the easiest method (i.e. specific parts and general wiring preferred) to deliver the energy to get this motor running as well as possible?

Particularly, as I believe the fan motor calls for something like 20 A, I would presume I may need multiple transistors in parallel. If so, would I then need to bridge one of the legs on each to ensure they are all switched at the same time to the same phase, or would it need to be more complicated than that?

The intent is to build a motorized cart from bikes and other materials.

Answer 1

Its not even a chip - its a single transistor oscillator.

Here's a fairly typical circuit. Q1 (NPN BJT) forms an oscillator with T1,R1 and C1. (If you listen carefully you can usually hear its high frequency whine).

The primary of T1 is 6 turns, the output is 1750 with a feedback tapping of 15 turns. In otherwords a step up transformer. This high voltage AC is then converted to DC by D1 and used to charge up C2. After several seconds the voltage across C2 is high enough and triggers the small neon indicator (ready light). The other (trigger) coil produces a very short high voltage pulse for the flash tube causing the Xenon gas inside it to conduct and short out the capacitor - Very quickly the charge on the capacitor is used up and the flash stops.

What about the AA cell providing the energy?

The cell provides current at 1.5V. It can't supply any more than 1.5V, that's why you need the oscillator circuit to boost the voltage. The oscillator circuit draws quite a large current from the cell (that's why batteries don't last long in flash guns). As voltage is stepped UP by the transformer the current is stepped DOWN. That's why it takes several seconds to charge the capacitor.

Simply connecting an AA cell to any capacitor would only allow it to charge to (nearly) 1.5V. To charge up your microwave oven capacitor you could use it to replace C2 - in which case it might get up to about 100V.

To get to 1900V you would have to build a circuit capable of supplying that voltage.

SAFETY WARNING: High voltages and charged capacitors are quite capable of killing you, even when the circuit power has been switched off. Unless you wish to put yourself forward for the Darwin Awards (taking yourself out of the gene pool by your own stupidity) I suggest you leave hacking microwave ovens well alone.

One small slip for screwdriver, one giant blue flash for man.

Answer 2

Inside the camera there's a little chip that turns the small battery voltage into AC (but still at the same voltage), the AC feeds a step-up transformer that cranks it up to around 350V AC (pretty much all xenon camera flashes use ~300-350V). The AC from the step-up transformer gets rectified to DC and that's used to charge the capacitor. You can only charge up a capacitor to the voltage of your power supply (in exactly the same way as you can't get boiling water from a hot water heater set to 60°C, you get what you give). Hooking up a microwave oven capacitor to a 1.5V battery will charge it to 1.5V, no more, no less. Now if you had 1200 AA batteries in series... then you'd get 1800+ volts but that'd be more dangerous than a microwave cap at 1800+ V.