Abstract
Recently, there are step dimmer circuits for High Intensity Discharge (HID) lamps of 100% and 50% light output. But, a continuous dimmer circuit of wide range is not available. The reasons are pointed out as follows;
(1) Unstable lamp operation under a lower wattage condition.
(2) Extinguishment of the HID lamp when transient operation of dimming.
(3) Lower lamp efficiency lm/W under dimming.
(4) Shorter lamp life caused by dimming.
(5) Variation of spectral distribution under a lower wattage condition.
The authors have tried to develop a new continuous dimmer circuit by means of thyristors for HID lamps, with an auxiliary step-up transformer, in order to overcome the above mentioned difficulties of (1) and (2). The dimmer circuit can generate higher voltage enough for reignition and sustain the lamp current during the thyristor-off period. We can control the light output of HID lamp from 100% to about 1 % by the dimmer circuit.
In the paper, the principle of dimmer, the configuration of circuit, the characteristics of operation and discussions are dcscribed.
