Electronic photographic flash generating circuit - uses discharge lamp, triggering circuit, photodetector switch and thyristors

摘要

An electronic photographic flash generating circuit which controls the duration of the flash consists basically of a gas discharge tube (FT1) in series with a thyristor (SC R1) both supplied from a high voltage condenser (C1) and triggered by a triggering circuit (16) of known type. A known light detection circuit (18) fires a second thyristor (SCR2) when the reflected light exceeds a chosen threshold and this extinguishes the discharge tube (FT1) and produces a light pulse lasting 1-2 seconds from a light emitting diode, to show that the sequence has occurred correctly. Two alternative forms of the circuit with transistor drives for the light emitting diode (LED1) include a separate supply in one case and the high voltage condenser supply (C1) in the other.