A DC-DC Step-up Converter Used On Thermoelectric Generator

Wireless sensor networks have been in development for many environmental,structural, medical, and military applications. Because sensing and transmittingcomponents continue to be scaled down, the size of nodes in wireless sensor networks ismainly determined by the size of the battery. Most commercial nodes for wirelesssensor networks use two AA batteries as the power source. The lifetime of each nodewill depend on the duty cycle and the amount of data being sensed and transmitted. Atthe end of this lifetime, the battery must be replaced or recharged. FOR wirelesssystems such as implantable medical sensors and animal tracking devices, batteryreplacement may be difficult or impossible. Emerging energy from wireless sensorworking environment has been research focus for many years, because this can not onlyavoid the limitation of battery but also extend the lifetime of wireless sensors. Withrecent advancements in thermoelectric material performance, thermoelectric generatorshave become a viable alternative for power generation using small temperaturedifferences with benefits that can not be found in other energy conversion methods. Thepower generated by a thermoelectric generator, using a small ΔT, is characterized by arelatively low voltage, which is often not suited for many practical applications. In orderto make use of the thermoelectric generated power, a DC-DC step up converter that canhandle low input voltage is needed, so that the output of converter can be used bywireless sensors.First, the thermoelectric effects should be studied, so that we can know theworking principle and character. Based on the character of working environment andoutputs of thermoelectric generator, the electrical model of thermoelectric generator canbe built, and used in the simulation of step-up converter.Second, choose an appropriate structure of DC-DC step-up converter. There aretwo kinds of step-up converter, one works with inductors, and one work with capacitors.In order to have high work efficiency, the Boost structure would use big inductors,which can not build easily in state of art CMOS technology, so the structure with chargepump would be the choice. The converter with charge pump can achieve high workefficiency when the capacitor is M-I-M structure, which can build in CMOStechnology.Third, design the structure of DC-DC step-up converter with charge pump. There are two stages of circuit in the structure of converter; every stage has a charge pump.The first stage works with the output of thermoelectric generator as voltage source, andputout a voltage about1V to second stage. The second stage works with the output offirst stage, and PFM oscillator of this stage controlled by voltage feedback circuit andover-temperature protection, so that the converter can putout stable voltage and avoidthe destruction of high temperature.Last, simulate the design with GSMC0.18μm CMOS technology, and design thelayout of this circuit.The simulation result shows:①This DC-DC step-up converter can turn the outputof thermoelectric generator0.3V to high voltage2.3V effectively.②Compare withother converter, this circuit is characterized by low power consumption, high efficiencyand high output voltage.③This circuit can work without external devices, and thelayout of this circuit only occupation489.6×693.4μm2, so it can be integratedconveniently.