A Design of Cold Start Charge Pump for Flexible Thermoelectric Generator with High Output Impedance

This paper proposes a practical control circuit design of power converter for energy transducer with high output impedance. In conventional control circuit systems, the input voltage of the power converter is set so that the output power becomes maximum. However, this operating point voltage can be lower than the lower limit of the supply voltage at which the power converter can work. The proposed control circuit enables the power converter to operate when the output voltage is lower than a target voltage Vpp and the input voltage is higher than a specified voltage VDD. As a result, the input impedance ZCPin of the power converter can be low enough to extract power from the energy transducer via a power supply capacitor CDD when the power converter is enabled. On the other hand, ZCPin can be high enough to charge up CDD via the energy transducer when the power converter is disabled. As a result, 1) the operating point of the input voltage can be controlled to be higher than the minimum supply voltage, 2) a maximum power can be extracted, and 3) the output voltage is controlled to be the target voltage. The proposed circuit system was fabricated in 65nm 1V CMOS and its operation was verified. The proposed integrated circuit converts an output power of 50µW at an output voltage of 2.5V from a thermoelectric energy transducer with an open circuit voltage of 0.9V and an output impedance of 400Ω.