Initially the neon and xenon lamps are not conducting and act like a very high (almost infinite) resistance. Capacitors Cl and C4 in conjunction with DI and D2 form a voltage doubler circuit, which can charge C2 up to about 300 Vdc after several ac cycles. Voltage increases as current is supplied through Rl and R2. Neon bulb II will all of a sudden start to conduct when the voltage across C3 reaches II's ionization potential. While conducting, the resistance of the bulb will be relative low. Â£)ue to this sudden conduction, a pulse of current will pass through the primary of Tl.
The turns ratio is such that about 400 V will be developed at the secondary. The xenon tube is similar to the neon bulb in that it produces light when the gas ionizes and conducts. However, it is designed so that an external signal (the 4 kV on the metal ring around the tube) ionizes the gas and initiates the conduction. When F1 conducts, it discharges C2. At this point, the whole cycle starts over again. The purpose of R2 is to vary the rate at which C3 charges, and hence the repetition rate of the strobe.