Thyristor (auto thyristor).

A semiconductor (electronic component) used in photography to control electronic flash tubes.

Thyristors are switch devices which allow current to pass through when a third conductor has a control voltage applied. They’re commonly used in electronic flash units for this very purpose - they allow high-voltage electricity to pass into the flash tube, creating light, until the lower-voltage control voltage is dropped, at which point the light is extinguished. If the flash unit is not fired at full power then the main storage capacitor is not fully drained, unlike older units which wasted a full charge even if the flash was fired in a low power mode.

Most electronic flash units these days contain thyristors, but the term is generally associated with the first generation of automatic units which employed thyristors - auto-thyristor flashes (see automatic flash unit). Since there’s nothing particularly remarkable about thyristors today the term generally isn’t used as a marketing tool anymore.

cf. automatic flash unit, capacitor, flash unit.

Entry last updated 2002-05-20. Term 1225 of 1487.

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