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Therefore, LED dimming,[link widoczny dla zalogowanych], to get transferred to a fixed brightness LED, it is necessary to ensure a fixed,[link widoczny dla zalogowanych], constant current control to be used is to say. There is another way: constant power control. It is also currently on the market generally used ASIC dimming way. But the constant power control has the inherent disadvantage.
2 Constant power control LED dimming 2.1 theoretical basis for constant power control using single-stage FLYBACK general topology, the basic block diagram shown in Figure 2.1. Figure 2.1 Diagram of constant power control can be seen from the diagram of switching power supply FLYBACK general than constant power program more than a dimmer signal control circuit for detecting the input SCR conduction angle and input voltage, thus gives the corresponding dimming signal.
Meanwhile, the program is no feedback signal, completely open-loop control, the size of the original edge of the control duty cycle to control the size of the output power. Theoretical basis for its control are as follows: Where: constant power control mode are the first to predict the output power of LED P, in theory, once after a good transformer design, have determined that as long as the change in the size of the primary current, you can change the output power size.
Since then: where: U is added to the transformer primary voltage, the input voltage; D is the duty cycle; is the switching frequency; for the transformer primary inductance. According to equation 2.2 we can see, and D is proportional to the duty cycle D can be changed as long as the change in primary current size,[link widoczny dla zalogowanych], it can change the size of the output power. 2.2 The advantages and disadvantages of theory, this topology is simple,[link widoczny dla zalogowanych], low cost, but careful analysis will find that this approach has many drawbacks.