| 摘要 |
<p>PURPOSE:To avoid the brightness from decreasing when a filament breaks, by providing a bypassing means, which invalidates a current limiting means connected in series to plural electric lamps, and turning on the lamps through the bypassing means when any of the electric lamps is detected in its filament breaking. CONSTITUTION:A passage, connecting electric lamps 1A, 1B through current limiting means 2A, 2B, provides a means 5 which compares a voltage drop in a voltage comparator circuit 5a detecting a filament to be broken. Now if the electric lamp 1A breaks its filament, a lighting current is halved. Then the voltage comparator circuit 5a, whose detection side input terminal voltage Vl decreases less than the standard side input terminal voltage VS, switches a relay coil 4a to a normally opened contact side. In this way, the electric lamp 1B, with no break of its filament, is turned on as a result in the original brightness through a bypassing means B which invalidates the current limiting means 2B. Accordingly, visibility can be prevented from decreasing by satisfying the specified brightness.</p> |
