| 摘要 |
PURPOSE:To reduce the power consumption by increasing a current to drive a lamp of a key telephone set for a prescribed time so as to light the lamp and facilitating to observe the lamp lighting state even at a location difficult to see. CONSTITUTION:In depressing a key telephone set operating button 1, the depression of the key telephone set operating button 1 is detected by a button depression circuit 2 and a lamp drive circuit 3 lights a key telephone set display lamp 4 by a lamp drive circuit 3. When the key telephone set display lamp 4 is difficult to see depending on the surrounding state, the lamp current variable button 5 is depressed and the button depression detecting circuit 2 detects the depression of the lamp current variable button 5, a timer circuit 6 is activated, the lamp drive circuit 3 varying the lamp current is controlled timewise, the lamp drive circuit 3 is operated for a prescribed time only to increase the lamp current. Thus, the key telephone set display lamp 4 is lighted for a prescribed time.
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