Conventionally, an alternator such as a commercial power or the like supplied through a household outlet has been widely used. On the other hand, an electronic apparatus such as a computer or the like generally operates with the direct current. Accordingly, an AC adapter is used to convert an alternating current into a direct current and supply the direct current to an electronic apparatus (hereinafter, called “main device”).
The AC adapter has a different rated current, a different type, and the like depending on its size or the like. By these different features, power to be supplied becomes different. However, since it is not possible to determine the rated current, the different type, and the like of the AC adapter at a side of the main device, a relationship between the main device and the AC adapter has been fixed. Accordingly, there is no compatibility between models, or manufacturers, and the AC adapter has not been standardized between different models, or manufacturers.
Also, in a state of supplying power from the AC adapter to the main device, in an order of a state of a smaller power consumption, the state of the power supply may be one of the following states: (1) a state of conducting power supply only to charge an internal battery of the main device, (2) a state of conducting power supply only for an actual operation of the main device. Moreover, as a state in which the power consumption is great, the power supply may be in (3) a state of conducting power supplies for a charge of the internal battery and for an actual operation of the main device. However, there is no guarantee that the AC adapter supports all states by its possible power to supply.
Technologies related to the above described problems have been known as follows.
Japanese Laid-open Patent Application No. 2004-341592 discloses a system including the main device capable of detecting power supply capacity information of an external power source device. In this system, a terminal other than a regular terminal for supplying power is provided. By detecting, in the main device, a range in which a voltage supplied from a side of the main device is dropped due to a resistor provided at a side of an external power source, a power supply ability of the external device is detected.
Also, Japanese Laid-open Patent Application No. H07-143749 discloses an AC adapter which includes an oscillation part for generating a signal voltage of an oscillation frequency corresponding to a current value possible to supply, and the signal voltage is superimposed with an original DC voltage. In the main device disclosed in Japanese Laid-open Patent Application No. H07-143749, an operation state of the main device is changed by separating the signal voltage from the original voltage and measuring the signal voltage.
Moreover, Japanese Laid-open Patent Application No. H05-184065 discloses that connections of various types of power sources such as an AC adapter, an external battery, and the like are assumed, and the main device determines which type of the power source is connected based on the power voltage. In the main device, based on the determined type of the power source, the power consumption is adjusted in one of the above states (1) to (3).
Furthermore, Japanese Laid-open Patent Application No. 2000-134816 discloses a system in which when the AC adapter is connected, an impedance on a power source output line is changed in a certain time, and a power source input specification of the main device itself is informed to the AC adapter. The AC adapter, which is disclosed in Japanese Laid-open Patent Application No. 2000-134816, generates the power source for an operation based on the informed power source input specification.
However, in a system disclosed in Japanese Laid-open Patent Application No. 2004-341592, since the number of output terminals of the AC adapter is increased, there is a problem in which the expense and the size of the AC adapter are increased.
Also, in the AC adapter disclosed in Japanese Laid-open Patent Application No. H07-143749, since the oscillation part for generating the signal voltage is additionally included, there is a problem in which the expense and the size of the AC adapter are increased.
Moreover, in the AC adapter disclosed in Japanese Laid-open Patent Application No. H05-184065, it is difficult to determine the same power source as an output voltage. Accordingly, there is a problem in which a different type of the AC adapter may not be determined.
Furthermore, in the system disclosed in Japanese Laid-open Patent Application No. 2000-134816, since the AC adapter generates the power source for the operation of the AC adapter based on the specification of the main device, as a result, the AC adapter depends on the specification of the main device. Accordingly, it is not possible for the AC adapter including the above described mechanism to connect to the main device, and the main device does not allow AC adapters which are based on various specifications.