White LED can be used in series or parallel connection, both solutions have advantages and disadvantages. The disadvantage is that parallel the LED current and brightness do not automatically match.
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Series to maintain the inherent characteristics of the match, but requires a higher supply voltage. Because the white LED forward voltage drop of 3 ~ 4V (typ), either in parallel or in series, the battery voltage is most portable electronic devices are insufficient to drive the LED, so the need for a separate power supply. In a series configuration, the number of LED's that drive the highest voltage limit. If the maximum voltage of 40V, in a series configuration according to the white LED forward voltage, the maximum voltage that can drive up to 13 white LED, the drive current in the range of 10 ~ 350mA continuous state. Advantage of this configuration is a series of white LED can be used single-wire current; the disadvantage is that when the PCB space is limited (especially when high power), the current density on the copper wire is a problem, but if one in-line mode white LED fails, all white LED will be turned off. However, from a design point of view, if there is a knife only white LED, the battery voltage is necessary to enhance the n Vp, it must step-up structure. You can use inductance element accurately monitor current slope, limiting the EMI uncontrolled instantaneous current. A typical boost topology shown in Fig.
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