PURPOSE: To accurately control the sending of dial pulses by supplying power to a control part for controlling a dial pulse sending circuit through only either one of two transistors (TRs) connected by Darlington connection.
CONSTITUTION: When a DC loop is formed between a telephone set and an exchange by off-hook of the telephone set, a dial circuit 7 applies a signal to a TR 9 through a signal line 8, the TR 9 is turned on and TRs 3, 4 are also turned on to start power supply to a feeder circuit 5 and a calling circuit 6. Since power supply to the feeder circuit 5 is executed only through the TR 3, a higher voltage boosted by a voltage drop (0.6V) based upon the TR 4 is applied between lines 11, 12. Consequently, 1.2V is applied to the feeder circuit 5 and the dial circuit 7 receiving stable power supply can precisely control the sending of dial pulses.
TANAKA MASANORI
KARASUTANI SHIGEMITSU
