| 摘要 |
A low voltage lighting fixture connected to an isolation step-down transformer is protected from limited or maximum short circuit conditions by monitoring the secondary current of the step-down transformer until a fault is detected, whereupon the protection circuitry deenergizes the primary of the transformer by opening a relay. The protection circuitry is completely isolated such that a breakdown in voltage from the primary to secondary of the stepdown transformer, which would place 120 volts on the secondary side, cannot occur. Additionally, while monitoring the high current-low voltage secondary of the transformer, the relay is placed in the primary circuitry which is at line voltage, but at a much lower current rating. The relay is a normally open device which closes when either of a pair of redundant optoisolators conduct current.
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