| 摘要 |
<p>PURPOSE:To avoid a short break of the fee pulse and at the same time to decrease the area of package for the charging of a public telephone set, by converting a feeding circuit to a constant current source mode when the direction is switched for the feed current to a terminal and then supplying the switch holding current. CONSTITUTION:A call current supplying system contains a DC power supply 6, an equivalent internal resistance 52, an equivalent constant current source 53, and a feeding circuit 18 which has a fee filter of switch type between the constant current supply and the constant voltage/resistance supply as well as a switch with which the resistance and the current source are connected with switch to a line. The circuit 18 contains the fee filter function, the equivalent internal resistance and the constant current source function. Then the circuit 18 performs the operations of the charging filter and the constant voltage source having an equivalent internal resistance in the feeding mode to a terminal and then supplies a constant current to secure the minimum level to hold a PNPN switch 10 when the direction of current is switched is switched to the terminal.</p> |
