Electronic firing circuit

A circuit for operating a load device comprising an operating circuit including an energy storage device for providing electrical energy for operating the device and a voltage responsive switch having a control terminal and connected between a voltage source and energy storage device of the operating circuit to provide energy to the storage device and opening when the stored energy causes the voltage on both sides of the switch to be essentially the same thereby disconnecting the source from the operating circuit so that any short circuit in the load does not affect the source or the remainder of the circuit associated therewith. The circuit can be in combination with a structure having a conducting path, the load device can have a conductive casing physically contacting the path of the structure, there can be a conducting element within the casing, the device can be susceptible to short circuit conditions between the conducting element and casing, and the voltage source can be in the structure and have positive and negative terminals, one of which is connected to the path of the structure as a common return for a circuit including the source. The circuit can be an electronic firing circuit for an electro-explosive device.