| 摘要 |
PURPOSE:To light up a message lamp of a telephone set without using a booster power supply by connecting one contact to a DC voltage and the other contact to a voltage of an opposite polarity when a message lamp drive relay is actuated. CONSTITUTION:A message lamp drive circuit 14 is an extension circuit of an exchange lighting a message lamp of a telephone set 40 with message lamp accommodated in the exchange. Then the drive circuit 14 has a message lamp drive M relay having plural contacts m1, m2 driven when the message lamp of the telephone set 40 is lighted. Then a call signal transmission circuit 12 of an exchange is provided with a DC voltage generating means comprising a diode D and a capacitor C, and the means rectifies and smoothes a signal of the call signal generator 13 sending a call signal to the telephone set 40 to be a DC voltage. Then the contact m1 of the M relay is connected to a DC generating means and the contact m2 is connected to a feeding power supply 18 to be opposite in the polarity and a speech current is supplied. Thus, no booster current is required. |
