Development of a small-size and light-weight AC adaptor

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In this research, a small-size and light-weight AC/DC adaptor using switched-capacitor (SC) circuit is presented which can carry out voltage conversion by using only capacitors and IC switches without using a coil and a transformer.The transient response showed that the inrush current of the proposed circuit is less than half of the conventional SC power supply (refer to the IEICE of Japan, vol.J76-C-II, no.6, pp.422-431, June 1993). Since in the conventional SC power supply, four 300μF capacitors are connected to a commercial power line simultaneously through a full wave rectifier circuit, the inrush current becomes large. On the other hand, in the proposed circuit the large inrush current can be suppressed without using a soft start circuit, since the value of the charge transfer capacitors is only 30μF. However, the proposed circuit can not keep the output voltage at the nominal load when a power failure is occurred during a half period of a commercial power line, because the time constant of the output is shorter than 1/7 of the conventional circuit, namely, the total capacitance of the proposed circuit is about 180μF and that of the conventional circuit is 1,200μF.The power supply block of the proposed circuit is easy to generate noise and the control block is sensitive for noise, since the experiment circuit is composed of discrete parts and its wiring is long. Therefore, a control circuit may malfunction when the input voltage is high. The verification by experiment is not finished yet.Although the circuit operations using discrete parts are verified normally by experiments and the excellent characteristics are obtained by Hspice simulations, in future, the proposed circuit will be implemented in an IC form except capacitors in order to prevent malfunction of the control circuit and the experimental characteristics will be verified.