Research on Electrical Conduction Mechanism and Withstand Voltage Properties after Current Limiting of PTC (Positive Temperature Coefficient ) Device

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Positive temperature coefficient(PTC) devices are now used as over-current limiting device for secondary batteries of small electronic apparatuses such as mobile phone, note type personal computer and video camera. A number of PTC devices used at present have various issues to be tackled on improvement of withstand voltage after current limiting action, optimum composition of materials, electrode materials and the configuration etc. Aim of this project is to elucidate electrical conduction mechanism in high resistance region and the influence of partial discharges on the current limiting properties of ceramic type PTC devices, which are expected to have higher current rating and limiting voltage than conventional PTC devices such as polyethylene type and barium titanate type PTC devices. Besides, we proposed a new type hybrid PTC device where liquid or gel material is used as a matrix and solid conducting particles are used as filler, and performed experiments to verify the principle o … More f operation. Namely, the PTC device is proposed where on short circuit event the conducting particles are evaporated and dissipated to perform current limiting operation, and then dielectrophoresis force allows automatic collection of the conducting particles efficiently to realize switching on the circuit again. We made an application for patent for the new hybrid PTC decive.We measured resistance-temperature relation and current-voltage relation for 6 kinds of ceramic type PTC devices with different filler amounts and different ratios of gas content H_2 and N_2 on burning to form ceramic. Then, we compared the ratio of resistance jump from on-state to off-state of the ceramic type PTC devices, and the resistance after returning to on-state and the transition voltage. As a result, it was found that the higher the H_2 gas content on burning, the larger the resistance jump ratio and the transition voltage. Besides, as the filler amount increased, the transition voltage increased. It was also indicated that tunneling current or ionic hopping current is attributed to the conduction mechanism of ceramic type PTC device. It was also confirmed that on applying ac voltage to the PTC device, partial discharges took place. It was found that the instantaneous discharge inception voltage corresponded to the voltage giving the degradation of the return resistance on backing to on-state, suggesting the bad influence of partial discharges on the return resistance degradation. Less