| 摘要 |
<p>A drive circuit (20) is disclosed for powering an LED chain 11 even if the chain presents an unusual high forward voltage drop. This may be due to extraordinary low temperature, connecting more LEDs in the chain, aging or the like. It is considered to raise the DC voltage for powering the LEDs at least if those unusual high voltage drop conditions occur. If so, however, the LED current otherwise kept constant will be reduced in that second mode of operation. The DC voltage source (23) can be designed for a maximum power which is equal to a constant power in the second mode II of operation. Preferably, the reduction of the LED current is such that the power applied to the LEDs will be kept at a given constant value.</p> |
