Research On The Design Techniques Of High Performance Charge Pump DC-DC Of White LED Driver

With decades of development, LED has draw increasing attention, and it is known as one of the fields with the most prospects. Thus improvement of the LED drive becomes a hot research subject. The paper focuses on the design technology of high performance white LED drive and its charge pump. Research results include:1. High precision controllable LED drive with constant currentIn order to improve the accuracy and efficiency of the LED drive output current, we propose a novel controllable LED drive with constant current. Using external resistance and enable terminals, high precision bandgap reference generates three low voltages in the constant-current LED drive. The lowest voltage is about 73mV, decreasing the ballast resistance and increasing the drive efficiency. The influence of offset on the output current becomes considerable when reference voltage is down to dozens of mV. To solve this problem and increase the precision of the output current, we adopt an auto-zeroing operational amplifier in the driver circuit of the LED driver. This approach could limit the effect of offset and increase the precision of the output current. Also, this could reduce the sensitivity of diver current to the technology.2. Large current and low noise charge pump DC-DCConventional charge pump always leads to huge peak input current and low frequency noise. It can be improved by applying current mode. However, normal current mode is based on the procedure by controlling the charge current with voltage. This would lower the drive ability. In this paper, a novel current-control charge pump is proposed that the regulator resistor and switch are substituted by current mirror and inverter. Continuous input current can be realized by only one charge pump, decreasing the input noise of charge pump and the output ripple, meanwhile drive ability is also improved.3. High efficiency adaptive LED drive of charge pumpMost of the existing adaptive charge pumps adopt drain dropout of the current source MOSFET and sensitive diode to detect maximum dropout. However, when MOSFET work at liner region, it would fail to detect dropout. Also, the diode is very sensitive to temperature. In this paper, we propose a novel high efficiency adaptive LED drive of charge pumps, which adopts digital circuit rather than diode, to directly detect dropout. The circuit uses double-feedback loop with outer voltage-loop and inner current-loop to control LED drive of charge pump. Voltage-loop guarantees the multi-mode automatic conversion of charge pump and current-loop ensures stable output of charger pump.4. Voltage reference working at sub-threshold levelWith the continuing down-scaling of CMOS process as well as the ongoing reduction of the supply voltage, the quiescent current becomes a most factor to the whole power dissipation. For this reason, the paper takes the reference circuit as a research object to study on the MOSFET in the non-traditional working area. With the research result of traditional band-gap reference, a CMOS reference based on sub-threshold MOSFET is presented. The simulation results show that our proposed circuit can satisfy the application requirements, with slightly increasing of minimum operation voltage.