Ab Electronic Components Limited

Graham J Legg

Stuart F Webb

Derek M Embrey

In order to provide a lamp failure warning in both illuminated and unilluminated states of the lamp, there is provided a resistance bridge circuit Rs, L, R2 and R3 which is substantially in balance if the lamp L is sound. An amplifier IC1 acts as a detection means if the bridge goes out of balance as a consequence of failure of the lamp L. In the unilluminated state a reduced current is fed to the bridge via a high value resistance R1, which is by-passed by a lamp switch SW1 if the lamp is to receive enough power to illuminate it.

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Camberley, United Kingdom

Graham J Legg