The energy for the trigger pulse is usually derived from a capacitor, which may be charged from the power source of the trigatron's own circuit. In this regard, the entire circuit is very similar to a flashtube based photoflash, where the trigger transformer provides the ionization in the tube and the tube functions simultaneously as the light source and the power switching element for itself. An air-gap flash type, where the flash gap itself contains a trigger electrode and acts as a switch, is a form of a trigatron with the same dual function.