AUTOMATIC_VOLTAGE_CONTROLLER

Published:2009/7/12 22:51:00 Author:May | From:SeekIC

Station dc voltage, a nominal 113.8 Vdc, is fed through the normally closed contacts of relay K2. This voltage also provides power for the protective circuit illustrated. The voltage appears across R1 and R2, 10-kΩ trimpots, the wipers of which are set to exactly midrange, measuring a nominal 16.9 V dc. As the station dc varies between 111.2 and 115 V, the voltage at the wipers will vary from 5.6 to 7.5 Vdc. Zener diode D2 controls the high-voltage limit of 115 Vdc. R5 and zener diode D4 control the low-volt-age limit of 111.2 Vdc. Avoltage is fed from the wiper of R1 directly to the base of Q1, relay K1 is not energized, and its normally open contacts prevent relay K2 from being energized, allowing station dc to flow through K2's normally closed contacts. Above 115 V, the voltage at the base of Q1 also rises to or above 17.5 V, energizing K1, whose normally open contacts close, energizing K2, whose normally closed contacts open, removing the voltage from the station equipment. Should the voltage fall to or below 111.2 Vdc, zener diode D4 ceases to conduct, cutting off Q2, which causes Q3 to conduct, energizing K3. K3 applies operation voltage through its contacts to the coil of relay K2, opening its normally closed contacts, removing voltage from D6, the station equipment, and applying power to LED D7 and the audible alert.



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