| 摘要 |
<p>PURPOSE:To eliminate the need for the special supplying of power in a telephone exchange, by using a ringing signal for the lighting of a message waiting lamp. CONSTITUTION:When the ringing signal is applied to a supply terminal, this signal is rectified at a diode 11 and charged in a capacitor 15 via a protecting resistor 12. When a lighting signal of a message waiting lamp 3 is applied to a signal terminal 21, it is fed to a main transistor (TR)13 via a TR20, and resistors 19 and 16. Thus, the TR13 is made conductive, a voltage charged in the capacitor 15 is applied to the message waiting lamp 3 of a telephone set 1 via a limit resistor 17 and a terminal 5, and the lamp 3 is lighted.</p> |
