Inductive Boost Converter LED Driver

White LEDs can be connected in series or parallel, and both solutions have their own pros and cons. The disadvantage of the parallel connection method is that the LED current and brightness cannot be automatically matched. The series connection maintains the inherent matching characteristics, but requires a higher supply voltage. Because the forward voltage drop of white LEDs is 3 to 4V (typical value), the battery voltage of most portable electronic devices is not enough to drive LEDs, whether in parallel or in series, so an independent power supply is required.

In a series configuration, the number of LEDs is limited by the maximum voltage of the driver. If the maximum voltage is 40V, based on the forward voltage of the white LEDs in a series configuration, this maximum voltage can drive up to 13 white LEDs, and the driving current range is 10 to 350mA in a continuous state. The advantage of this configuration is that the white LEDs in series can carry current with a single wire; the disadvantage is that when PCB space is limited (especially at high power), the current density on the copper wire is a problem, and if one wire is used in series mode When a white LED fails, all white LEDs will be turned off. However, from a design perspective, if there is only a white LED , the battery voltage must be increased to n×Vp, so a boost structure must be used. Inductive components can be used to accurately monitor the current slope, thus limiting EMI generated by uncontrolled transient currents. A typical boost topology is shown in the figure.