Here, the constant current diode is to input mains voltage changes to maintain the same output current, of course, can be eliminated due to the current caused by the household LED ceiling lights negative temperature coefficient increases. However, due to the pressure of the constant current diode to certain restrictions, so it can be absorbed by the supply voltage change is limited. 100V withstand voltage of the CRD, its operating voltage range is also minus its minimum operating voltage of 10V, the voltage range available, it was only 90V. 220V mains power supply, if the change of +10% to -20%, equivalent to the rectifier 290 ~ 211V, the voltage change of 79V in the range of its pressure. If the household LED ceiling lights 80, if the forward voltage of 3.3V, then the total voltage of 264V, exactly equivalent to 220V after bridge rectifier after the value. At this time there is no voltage drop across the constant current diode, but this time it is unable to work and need at least 10V voltage drop, which is required rectified voltage is 274V, the mains voltage is 228VAC. When the constant current diode voltage drop to a minimum, power consumption is minimum, only 0.03Ax10V = 0.3W, the overall efficiency of up to 96% (of course, but also consider the efficiency of the rectifier, in fact even lower). If power is increased to 242VAC, then the constant current diode voltage increased 26.4V, its power consumption is also increased to 0.79W, the efficiency of this time is equivalent to 91%.
Previously assumed that the led high bay light forward voltage drop of 3.3V, in fact even if its rated 3.3V, later in the boot of a period of time, the junction temperature increases, the forward voltage drop is reduced to 3.1V or even 3.0V.