GB1484803A - Electronic flash unit - Google Patents

Abstract

1484803 Electronic flash units FRANKE & HELDECKE GmbH 1 Aug 1975 [10 Aug 1974] 32227/75 Heading G2A An electronic flash unit comprises a flash tube 2 in series with a thyristor 3, a flash measuring device 16 for blocking the thyristor 3 after receipt of a predetermined quantity of light from the tube 2, a capacitor 12 connected in parallel with the thyristor 3 so as to charge during the time between blocking of the thyristor 3 and quenching of the tube 2 and means, preferably a lamp 15, to indicate when the charge on capacitor 12 reaches a predetermined level lighting up of lamp 15 thus indicates that device 16 has worked properly. When thyristor 3 is turned on again for the next flash, capacitor 12 discharges through it, if it hasn't already discharged through resistors 13, 14, so that lamp 15 is extinguished and ready for use again. In Fig. 1 the ignition circuit 5 to 8 ignites tube 2 and thyristor 3 simultaneously. In Fig. 2 (not shown) the tube (22) is ignited first, and the resulting voltage pulse through capacitors (29, 33) turns on the thyristor (23). In this circuit a resistor (32) has to be connected in parallel with the thyristor (32) and as a consequence diodes (37, 42) are connected in the charging and discharging paths of the lamp control capacitor (38). A prior art arrangement is described in which the flash tube is short circuited by a quench tube which lights up for a few milliseconds, light being transmitted from the quench tube to a fluorescent disc by a light pipe for indication purposes. The afterglow of.the disc makes this indicator arrangement ineffective when a rapid succession of flashes is used.