| 摘要 |
In an embodiment of the present invention, there is a ring control device comprising a switch, a voltage control device in electrical series with the switch, and a first plug for receiving a first electrical signal, the first electrical signal comprising a first voltage and a second voltage, the first plug disposed in series with and before the voltage control device. The ring control device also includes a second plug for outputting at least one of the first and second voltages of the first electrical signal, the second plug disposed in series with and after the switch. In the ring control device, the voltage control device prevents one of the first and second voltages from passing to the second plug when the switch is in a predetermined position.
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