Four-Quadrant Dimmer

38 059 FOUR-QUADRANT DIMMER This very special mains-operated dim- mer for domestic or industrial lights is not available in proprietary form: it enables brightness control of two groups of lights in one operation. The possible combinations of brightness are shown in the table. It will be clear that it is not pos- sible to obtain continuous control of brightness in the two groups. Instead, the circuit affords the setting of four states of brightness in either group: full on, fully dim-med, 1/3 on and 2/3 on. Both sections of the circuit operate on the well-known principle of a triac being switched from the blocking state to the conducting state with the aid of an RC network and a diode. The RC network provides the necessary phase shift and determines when the triac is switched. The rotary switch selects the resistor in a given network and thus the brightness of the relevant group of lights. No resistor means that the group is off; a short-cir- cuit gives maximum brightness, and res...