What's the difference between the transformer in a camera flash and other sorts?

Shortly before I began university, I used to mess about (carefully) with the flash circuits from disposable cameras (mostly for BEAM robotics projects, although I did build a coilgun once, too. It fired paperclips). The other day I got the urge to pick up where I left off, but disposable cameras seem to have become rather scarce in the few years since I last looked.

I thought about just building the circuit from scratch, but I can’t seem to find any transformers that step up the voltage in the same way as the ones in camera flashes. Do they use some sort of special type of transformer, or am I missing something?

They are designed to run at much higher frequencies than the garden variety mains transformers. This allows them to be much smaller. You are looking for the sort of transformer used in a switched mode power supply or similar. These are wound on a ferrite core rather than iron laminates, in order to avoid crippling losses in the core (which go up with frequency.)

after hearing this I won’t be on my taking any pictures on my phone on 11.23


…what’s that got to do with the question?

Are they using capacitors in these tiny units?

Yes, the circuit’s basically a transformer connected to a capacitor (as far as I’m aware the transformer takes the lower voltage DC current from the battery and converts it to a higher voltage AC current and the capacitor stores the charge and releases it as a DC current).

I was wondering specifically about the transformer (the capacitors appear to just be the same sort of capacitors you can get in any hobbyist shop). All of the transformers I’ve been able to find are either step-down (taking the sort of current you get from the mains and reducing it to <12v) or do a similar thing but deal with much higher voltages (like the “trigger” transformers used in strobe lights, which go from 300v to multiple kV).

The modern way is to use a switch mode power supply.

An Inductor, a capacitor, and a 555 timer switching the low voltage power on and off.

The basic idea for increasing voltage is to charge an Inductor with a low voltage current, now switch off the current source, and the voltage across the inductor increases to keep the same current flow… Though the current doesn’t drop instantly, it may rapidly drop … so repeat… the charge and switch off.

Its the same principle as common car (petrol engine) ignition…

Hmm, can you provide a circuit diagram? I’ve only ever heard of switch mode power supplies using inductors to keep the power flow constant, not do the job of a transformer…

Depends which way the SMPS is regulating. One that takes - say - mains power and delivers low voltage DC - like the majority you use, can simply chop the input (essentially pulse width modulate it) and uses an inductor as part of the output. You can make one a very small number of components, with the caveat that there is no protection in the event something fails - at which point the entire circuit tends to spectacularly self destruct. Most of the complexity is in making sure the thing is not going to do this, and if something does fail, it shuts down and avoids pyrotechnics or delivering mains power on its output. However there are advantages in using a transformer, some of which include avoiding contaminating the input power with noise, smaller size, higher efficiency, a lot of which comes with operating at higher frequencies. The term SMPS is wide enough to encompass the basic PWM style with a diode, inductor and capacitor, to a system that is essentially a high frequency power converter with transformer.

You will often want to convert to higher voltages, from lower, and here you need a transformer anyway (at least if you intend delivering any useful amount of power.)

What is missing from the OP request is a use case or requirements. A coil gun needs a capacitor bank charged to reasonably high voltages, and a bag of disposable cameras is a great way of doing this. However I’m curious as to what sort of BEAM robot use such a circuit can be adapted to. Knowing the requirements would make it easier to give a useful answer.

All you need to do is find the winding ratio for the transformers in the flash circuit, one source suggested ~920:1. Then find a suitable transformer.

A better suggestion is multiple transformers:

Would a page about thyristors (SCRs) help?

Disclaimer: I am not a electronics expert by any means. I just remember this term from early ads about auto flashes. Continue on with all your informed geekinesses

Basically the robot in question (I tried to find a photo, but I didn’t have any to hand) was designed to move in short bursts (my aim was to create a “ninja bot” which scuttled from one hiding place to another when it went dark…it turned out to be very good at crashing into walls when the lights went off and not much else, but there we go). I used the flash circuit to power the motors so I could get more power for each burst (and because it made a cool whining noise).

I’m not really that well informed myself (then again, that’s why I’m here).