Analytical features - LED series and parallel drive circuit China lighting network

LED series configuration in the series configuration, the number of the LED drive maximum voltage limit, if the highest voltage 40 v. In the series configuration based on white LED the forward voltage, the highest voltage can only white LED drive 10 ~ 13, the scope of the drive current is a continuous state of 10 ~ 350 ma. This configuration has the advantage of series of white LED can use the single wire transfer current. Disadvantage is when the PCB space is limited, Especially when high power) , the current density on the copper wire is a problem, and if in the series model only white LED fails, all white LED will go out. However, from the design point of view, if there are n white LED, only is to upgrade the battery voltage to n * VF, so must use booster structure, can use inductive components accurately monitor the current slope, limiting the uncontrolled instantaneous current produced by EMI, typical booster topology structure as shown in figure 1. Leds in parallel configuration in parallel configuration, the number of white LED in particular array by drive encapsulation level and the limitation of the connector pin number, in addition, when the white LED in parallel, must be conducted for each white LED current control, to ensure that the matching between the white LED is very suitable for a particular application. In fact, two white LED current exceeds more than 10%, will affect the quality of the color LCD display images ( White LED as the LCD back light) 。 In addition, the parallel configuration can use the electric charge pump technology, with the two ceramic capacitors to transmit energy from the battery to white LED array. Based on the charge pump LED driver block diagram as shown in figure 2, based on the special battery and current source for energy conversion and adjustment of charge pump, after the current source optimization design can make the white LED current is not affected by the forward voltage and input power change. LED series and parallel drive circuit is the LED driver circuit topology is the boost converter or two charge pump circuit topology selection, selection of the key is to consider two solutions of all specific factors. White LED drive circuit based on charge pump is an important parameter is the LED drive to produce noise, because the capacitor to charge and discharge, so the charge pump is large current burr. If you would like to reduce this effect, you must set the input filter circuit with high performance. Based on inductive step-up converter white LED drive, due to inductance, can cause electromagnetic interference ( EMI) 。 Under normal circumstances, change the switch frequency can decrease interference, but the frequency values depends on the working conditions of the converter. 2 v, but at the same time for up to five white LED power supply, each white LED to 20 ma current. Using TPS61062 booster converter drive white LED typical circuit as shown in figure 4. As shown in figure 4 of the boost converter is one of the latest development results of IC technology, as a comprehensive integration of synchronous boost converter, without external schottky diode can realize the solution of least size, number of external components required to a minimum.

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