| 摘要 |
PURPOSE:To use the titled circuit for the calling device system of an exchange, by controlling turn on and off of a PNPN transistor (TR) from external. CONSTITUTION:A PNP TR9 and an NPN TR10 constitute a PNPN switch. When ''1'' is inputted to a terminal 41, TRs 38, 15 and 24 turn on to absorb a constant current from the base of the TR9. Therefore, the PNPN switch turns on. When ''0'' is inputted to the terminal 41, TRs for driving the PNPN switch turn off. The input level is inverted by a gate 39 and a TR36 turns on. Then, the constant current flows to the base of an NPN TR25, which turns on. The NPN TR10 is cut off and the PNPN switch is turned off. |
