| 摘要 |
Current to a relay causes a telephone to be connected to a SLIC. Following LOOP, a sleep switch opens to interrupt current to the power supply converter after a first predetermined period expires. If the telephone is on-hook, loss of current to the relay causes disconnection from the SLIC, but causes connection to a battery. Current sensed from the battery through an off-hook hook switch generates a current signal. The current signal closes a current switch, which is in parallel with the open sleep switch, thereby providing a current path to the converter. The sleep switch then makes and then the current switch breaks. After awakening, a ring-back signal informs a user that telephony service has been restored and a message may indicate that telephony service is being sought. When the telephone is placed back on-hook, counting of a second predetermined period starts, after which the sleep switch opens again.
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