A Li-ion Battery Input 96.8% Peak Efficiency Single- Inductor Off-Chip-Capacitor-Free 2-Switch LED Driver with Two-Color Mixing Capability

Li-ion battery-powered LED illumination provides a wide range of potential applications for portable devices. It is always desirable to design an LED driver that uses the fewest off-chip components, operates with higher efficiency, and includes extra features such as color mixing. As shown in Fig. 1, the buck-boost topology is commonly adopted as the battery voltage (from 2.7 ~V to 4.2 ~V) can be either higher or lower than the forward voltage of LED. However, its power stage consists of four switches, each of which suffers from switching and conduction losses. In addition, it is not P C B area efficient to include at least three off-chip components (an inductor and input and output capacitors) [1-2]. The recent introduction of various hybrid buck-boost converters helps to improve efficiency by reducing effective resistance that the main current flow through, but at the expense of the extra off-chip flying capacitors [3-5]. Moreover, to drive LEDs for color mixing, these general-purpose converters need to pay additional power to regulate and balance the current, especially when the forward voltages of LEDs are unequal [6].