| 摘要 |
<p>PURPOSE:To solve the problem of heating and to make small the size of an exchanger, by controlling the transistors provided with a DC call circuit according to the duty and controlling the duty through the detection of AC of the said circuit, to make use it to present telephone system. CONSTITUTION:To a voltage source E, a transistor 10, inductor 12 and capacitor 13 are connected in series, and a voltage E0 is output across the capacitor 13 in proportion to the conduction time of the transistor 10. This voltage E0 is fed to subscriber lines to detect the DC current IL of the subscriber line, which is converted into a voltage Vt and a saw tooth voltage is produced 20 in the amplitude corresponding to the DC voltage E. The conduction time of the transistor 10 is controlled based on the result of comparison between this saw tooth voltage and the output voltage Vt.</p> |
