The present invention relates to an electric power supply apparatus, etc., more particularly to an apparatus and a method for reducing the loss of electric power supplied to a notebook PC, etc.
At present, in such an electric device as an information terminal represented by a notebook PC, which is provided with an AC adapter and a battery, occurs a power conversion loss in the AC adapter when the device is powered off (almost no loaded) or suspended (slightly loaded). At this time, the electric power is consumed not only in the AC adapter, but also in the internal circuits of the device.
FIG. 6 shows how such electric power is consumed in a conventional AC adapter used for the electric device when the device is powered off. In particular, it is supposed here that the AC adapter is connected to a notebook PC or the like and the PC is prevented from being powered. In FIG. 6, the horizontal axis denotes a time and the vertical axis denotes electric power consumption. In this case, the total power loss means a total of the system power dissipation by the internal circuits of the subject electric device (a notebook PC or the like) and the power loss by the AC adapter. Because the controller, etc. must always be kept active in the inner circuits of the device, for example, so as to charge a battery even when the device is powered off, the device comes to consume electric power up to a certain value.
For example, for a computer, which is an example of an electric device in this specification, electric power is kept to be supplied to the timer, the keyboard/mouse controller, etc. so as to perform predetermined functions for activating the timer, etc. even when the device is powered off. (A component kept to be supplied with electric power in such a way even when the device is powered off is referred to as a power-off-time active component in this specification.) On the other hand, when the device is powered off, the electric powers to other components including the main CPU are shut off, so unnecessary power consumption is prevented. (A component to which the electric power supply is shut off in such a way when the device is powered off is referred to as a power-off-time inactive component”.)
To supply electric power to such a power-off-time active component when the subject electric device is powered off and shut off the electric power to such a power-off-time inactive component, there is a method proposed. According to the method, a DC/DC converter is used to supply electric power to a power-off-time inactive component and the output voltage from the DC/DC converter is shut off so as to achieve the above purpose. If the DC/DC converter is used to relay supply of electric power to both of a power-off-time inactive component and a power-off-time active component, an FET (field effect transistor) is powered off. The FET relays the output voltage of the DC/DC converter to the power-off-time inactive component; the output voltage of the DC/DC converter is not shut off at this time. The conventional method has been employed for such an object.
On the other hand, especially for a notebook PC or the like, if the PC is not accessed for a certain time the PC is suspended (loaded lightly) to prevent battery consumption, thereby shutting off the supply of the electric power to other components (the main CPU, the CRT, etc.) except for some components (the main memory, the keyboard/mouse controller, the VRAM, etc.), which are required to resume the PC from the suspended state. In this specification, a component supplied with electric power when the PC is loaded lightly is referred to as “a light-load-time active component” and a component to which supply of electric power is shut off when the PC is loaded lightly is referred to as “a light-load-time inactive component”.
The power consumption in such an electric device as a notebook PC is shown as the lower area in FIG. 6. Electric power is kept to be consumed there by about 0.35 W. When the AC adapter is activated, an electric power conversion loss occurs depending on the power conversion efficiency that varies among AC adapters and among PC types. The power loss by this AC adapter is, for example, shown as the upper area (raised portion) in FIG. 6. In this case, electric power is kept to be consumed there by about 1 W. In particular, in the conventional example shown in FIG. 6, a power loss of about 1.35 W is kept even when the user does not operate the electric device connected to the AC adapter.
On the other hand, Japanese Published Unexamined Patent Application No. 11-175174 discloses a technique that measures a voltage held in load power holding means at a voltage sensor circuit when an AC voltage is supplied to a stabilized source power supply circuit via switching means, thereby controlling the output of the stabilized source power supply circuit if the measured voltage exceeds a predetermined range so as to adjust the voltage to be under the predetermined value and save the power consumption. And, Japanese Published Unexamined Patent Application No. 2000-4547 discloses a technique that employs an MPU for determining whether to charge a subject backup capacitor if a switch for supplying AC electric power is powered off so as to turn on the switch and turns off the switch again if the charging of the backup capacitor is completed, thereby reducing the stand-by time power consumption endlessly up to zero.