| 摘要 |
A transformer T1 having a primary winding and a secondary winding each having a plurality of turns 12 and 14 and a plurality of taps 16, 18, 20, 22 and 24 for changing the number of effective turns 12 and 14 of the primary winding. An array of LEDs 36 produce a luminous output in response to power supplied by the transformer T1. The assembly is characterized by a controller 38 for automatically selecting one of the taps 16, 18, 20, 22 or 24 in response to an operating parameter of the LEDs 36 for maintaining the luminous output of said LEDs 36 above a predetermined level. The measurement of the operating parameter may be any one of or any combination of measuring voltage across the LEDs 36, measuring current through the LEDs 36, measuring the temperature of the LEDs 36, or measuring 40 the luminous output of the LEDs 36.
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