| 摘要 |
PROBLEM TO BE SOLVED: To provide a charger with low power consumption not having an analog/digital converter.SOLUTION: A charger for charging an accumulator battery includes: a circuit for extracting current corresponding to a charging current of the accumulator battery; a circuit for accumulating charges when current corresponding to the charging current is supplied periodically; and a circuit for outputting a signal instructing the end of the charging of the accumulator battery when the potential of the circuit that accumulates the charges is more than or equal to the reference potential. The circuit that accumulates the charges when a part of the charging current is periodically supplied includes: a transistor that is formed using an oxide semiconductor in a channel formation region and that is turned on or off according to the pulse signal input to a gate thereof; and a capacitor that is electrically connected to the transistor and that accumulates charges when a part of the charging current is supplied via the transistor in the ON state. |
