Title:
DC LOOP CLOSING CIRCUIT
Document Type and Number:
Japanese Patent JP3158943
Kind Code:
B2
Abstract:
PURPOSE: To store the content of a memory backed up by a battery by preventing the reduction in a power supply voltage when a door of a public telephone set box is open, the battery power supply closes the DC loop of the channel, and a station power supply is supplied to the public telephone set to detect the opened door.
CONSTITUTION: The circuit is provided with a photocoupler 3 turned on by a low current pulse signal (a) from a one-shot pulse generating circuit 4 when a door is open, the output of the photocoupler is given to a thyristor SCR to close a DC loop comprising lines L1, L2. As a result, a CPU 9 is started by a station power supply based on the closing of the DC loop to detect an opened door, then the output current from a battery E to the DC loop closing circuit is decreased and then the destruction of the content of an SRAM 10 backed up by the battery E is prevented.
Inventors:
Wataru Iwasaki
So Noto
Katsuhiko Hayashi
So Noto
Katsuhiko Hayashi
Application Number:
JP7580295A
Publication Date:
April 23, 2001
Filing Date:
March 31, 1995
Export Citation:
Assignee:
Tamura Electric Co., Ltd.
International Classes:
H04M1/00; H04M17/00; (IPC1-7): H04M17/00
Domestic Patent References:
| JP58157249A |
Attorney, Agent or Firm:
Masaki Yamakawa