Simple few transistors generator and transformer A transforms 1. 5V battery voltage to few hundred of volts. This is quite high voltage. Then this high-voltage current passes through a diode, which rectifies current to DC. This DC current is stored in quite big capacitor. The capacitor is connected to the two electrodes on the flash tube at all tim
es, but unless the xenon gas is ionized, the tube can`t conduct the current, so the capacitor can`t discharge and tube didn`t flash. The capacitor is also connected to a small gas discharge tube via a resistor. When the voltage in the capacitor is high enough, the small tube lights up. This acts as an indicator light, telling you when the flash is ready for action. When you press trigger of camera, the trigger closes briefly, connecting the capacitor to a second transformer. This transformer boosts the 290-volt current from the storage capacitor up to between 1, 000 and 10, 000 volts, and passes the high-voltage current pulse onto the metal plate next to the flash tube. The momentary high voltage on the metal plate provides the necessary energy to ionize the xenon gas, making the gas conductive. And the flash tube discharge.