/diy/ - Do It Yourself

>>1205942
The basic idea is to compare the capacitor voltage (or some fraction of it) to your target voltage and throttle or turn off the capacitor charger when the limit is reached.
Pic related does this using a transistor (Q1), a neon bulb (NE) and a zener diode (D2). The neon bulb can be omitted, but it doubles as a "flash ready" indicator. The strike voltage of the neon bulb and the zener diode voltage set the voltage limit.
This is a bit unusual circuit in the sense that you push S1 only momentarily and the power supply then runs until the cap is charged.
There's at least one typo in it: Q2 and Q3 should be swapped. Stuff to the right of C2 is not needed in your case.

>How can the + side of C2 be connected to GND
If you want to see the battery's negative terminal as GND, then it is a positive ground circuit. Capacitor is charged to a negative voltage in comparison to that point.
The circuit itself is a blocking oscillator and the transformer is an integral part of it.
https://en.wikipedia.org/wiki/Blocking_oscillator

Typical disposable camera capacitor chargers are unregulated and just rely on the component dimensioning and battery voltage to keep the output voltage below the capacitor's maximum voltage.

>>1205935
Okay.