| 摘要 |
PURPOSE:To reduce the used number of high-power transistors so as to reduce the cost of a telephone set circuit, by controlling a line-output transistor by means of a transmitting preamplifier output when a talking circuit is formed by the output of a PD dialer and on/off controlling the line-output transistor at the time of sending pulse dials. CONSTITUTION:During talking, the PD output of a PD dialer 1 is at a high level and forms a transmitting circuit similar to conventional circuits. During the period when dial pulses are set, dial pulses are outputted from the PD terminal of the PD dialer 1 and, when a transistor Q4 is in the 'off' state, no electric current is supplied to a transmitting preamplifier 2 and antiside tone circuit 3 and a transistor Q3 is turned on and another transistor Q1is turned off. When the transistor Q$4 is turned on, the transistor Q3 is turned off and transistor Q1 is turned on. Since the line output transistor Q1 is commonly used to sending transmitting output and dial pulse in such way, one of high- power transistors can be eliminated and the DC resistance of a telephone circuit becomes smaller.
|
