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.