| 摘要 |
<p>1528369 Signalling over power lines AMERICAN SCIENCE & ENG Inc 12 Dec 1975 [20 Feb 1975] 51056/75 Heading H4R In an arrangement for signalling over power lines a unidirectional voltage is derived from the power line by rectifiers 501 and 502, and drive signals applied in antiphase to transistors 504 and 505 at a carrier frequency modulated by digital data to be transmitted. Switching on of transistor 504 causes capacitor 510 to charge and slowly switch on transistors 511 and 512 so that capacitor 528 is able to charge from the supply line 526, charging current flowing through resistor 527 turning on triac 529. When the carrier signal turns transistor 504 off transistors 511 and 512 are turned off as capacitor 510 discharges. Turning on of transistor 505 by the carrier signal on terminal 136' transistor 515 is turned on to allow capacitor 519 to charge up turning transistor 520 on slowly to connect line 525 to the power supply line 24<SP>1</SP> capacitor 528 is therefore discharged and the discharge current in resistor 527 again makes triac 529 conduct. Switching off of transistor 505 by the carrier signal allows transistor 520 to be turned off slowly as capacitor 519 discharges. Diodes 514 and 522 are provided to clip reverse voltage spikes produced by the inductance of the power line and its transformer when the transistors 512 or 520 are turned off. The voltage transitions of line 525 are coupled to the power supply line via capacitor 109.</p> |
