Power-Efficiency and Current-Accuracy Enhancement Techniques for High-Voltage Automotive LED Drivers
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The light-emitting diodes (LEDs) have been widely used in commercial automotive lighting applications. However, the lighting implementations are still a mixture of both traditional filament-based lamps and LED light sources due to the unit price of LEDs and reliability of LED driver considerations. For LED drivers, the single-stage solution is preferred because the higher efficiency can be achieved. However, the LED driver is required to withstand high voltage because of the large battery voltage spike caused by load dump. Moreover, the high voltage (HV) LED drivers are suffered from the significant power efficiency degradation due to large switching power losses when the input voltage is high. Also, the reliability is another problem if the conventional hard-switching (HS) mechanism is applied for high voltage (HV) LED drivers. On the other hand, the brightness of LEDs is tightly related to average current accuracy of LEDs. This thesis proposes the power efficiency and current accuracy enhancement techniques to optimize the power efficiency and average LED current accuracy of the HV-LED drivers. At first, the soft-switching (SS) technique is adopted for the buck type LED driver. An auxiliary LC resonant branch is paralleled between the drain and source terminal of the high side switch to alleviate the large current stress on main power inductor, which improves the reliability of the HV-LED driver. Secondly, an adaptive peak & valley reference compensator (APVC) is proposed to improve the average LED main inductor current accuracy. The APVC is able to compensate the current deviation caused by non-ignorable system propagation delays when the LED driver operates at high frequency. With the APVC, the peak & valley reference can be adjusted adaptively according to the amount of system propagation delays and thus the average current is adjusted to pre-set value. To verify the functionality of the proposed power efficiency and current accuracy enhancement techniques, the HV-LED driver is simulated with 0.5-μm 120-V CMOS process. Simulation results show that the HV-LED driver can achieve the peak efficiency of 92% in HS mode and 91.1% in SS mode, respectively. And the current accuracy is improved to ±1.5% in HS mode and ±3.0% in SS mode, respectively. The HV-LED driver is able to drive 1–25 LEDs with different input voltage of 5–100 V, which is suitable for automotive lighting applications.