Brightness control of groups of discharge lamps - employing load sensitive regulating circuit allowing successful lamp starting at times of reduced brightness

摘要

A typical application for the control circuit is to ceiling mounted lighting in offices where the general brightness level of the lamps is regulated w.r.t. the intensity of natural daylight entering the room. The regulator controls a block of individually switched lamps. In order to ensure that, at a time when the regulator has turned the lamp voltage down, a further lamp can be successfully switched on, it is necessary to make the regulator load sensitive. This is achieved by having two input signals to the regulator circuit taken from separate points (A,B) on the supply line. These tapping points are typically between 30 and 50 cms apart. Of the two input channels to the amplifier (V) of the regulator one has a time delay (C3). By this means, step change changes in load, for example caused by switching on a lamp, are detected and a suitable transient step change made in the regulating device (LG) setting. In this example, it is a transient voltage increase to ensure that the incoming lamp strikes, after which the voltage across the total load returns to the original level.