| 摘要 |
PURPOSE:To secure a proper calling state on any condition, by arranging a constant voltage element between a transistor (TR) constituting of a DC separating circuit and a transformer coupling with a transmitting and receiving circuit. CONSTITUTION:To obtain the sufficient collector-base voltage of a TR201 used in the DC separating circuit 42, diodes 421 and 422 as constant voltage elements are connected in a loop containing the transformer 21. Consequently, even when the current amplification factor hFE of the TR201 is large, a forward voltage by the diodes 421 and 422 compensate the collector-base voltage of the TR201. Thus, an enough dynamic range for adequate calling is obtained. Consequently, when the TR201 turns off owing to a voltage drop between the collector of the TR201 and the negative line of the diode bridge, a fine current flows to the diode bridge through a resistance 425, so calling is compensated even while a DC component is consumed by another telephone set. |
