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| ulv481x0p |
 Wysłany: Nie 4:43, 20 Mar 2011 Temat postu: Reading Street Lighting Design Montreal show techn |
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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, it can change the size of the output power. 2.2 The advantages and disadvantages of theory,display boards, this topology is simple, low cost, but careful analysis will find that this approach has many drawbacks.
The first is difficult to control, often large deviations, together with open-loop control, precision is difficult to ensure, in the volume, use the same power output duty cycle will result in significant bias, is directly reflected in the LED lights on the great brightness bias, it is difficult to ensure consistency.
Second, the constant power control is to presuppose a constant power output,business signs, such as using nine 1W (= 3.4V, = 350MA) of the LED in series with the PAR to be a 9W lamp,LED display board, then the design time to be with P = 9W calculation. But in fact the will of each LED deviation deviation shown in Table 2.1: Tab2.1 LED Electrical characteristic (T = 25 �� C) can be seen from the table 2.1,electric signs, although the deviation of each LED are not too large, But when the LED in series, the total deviation can not be ignored. |
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