Electronic device and power supply control method

Abstract

The present invention relates to an electronic apparatus and a power supply controlling method with which input power source is switched efficiently in accordance with a load of a device. A power controller 50 , upon detecting a USB connection, monitors power consumption of a CPU 44 based on the operation status of the CPU 44 , and controls a switch 42 in accordance with a current supplied from a USB cable 2 . When the current is less than or equal to 500 mA, the switch 42 is switched to a terminal a. Before configuration, when the current is less than or equal to 100 mA, the switch 42 is switched to the terminal a, and then a regulator 43 is controlled so that the current will not exceed 100 mA. In USB suspend, the switch 42 is switched to a terminal b, and a regulator 53 stops output to a backup battery 54 . The present invention can be applied to a digital still camera supporting USB.

1 . An electronic apparatus that can be connected to another electronic apparatus via a cable, the electronic apparatus comprising: 
 first switching means for switching between first electric power of the electronic apparatus and second electric power supplied from the another electronic apparatus via the cable, and supplying either the first electric power or the second electric power to a first power supply line;    second switching means for switching from the first electric power to the second electric power and supplying the second electric power to a second power supply line when the second electric power is supplied from the another electronic apparatus;    determining means for determining whether the second electric power supplied from the another electronic apparatus is less than or equal to a predetermined threshold value; and    controlling means for controlling the first switching means based on a result of determination by the determining means.    
   
   
       2 . An electronic apparatus according to  claim 1 , 
 further comprising detecting means for detecting a connection with the another electronic apparatus;    wherein the determining means determines whether the second electric power is less than or equal to the predetermined threshold value when the detecting means has detected a connection with the another electronic apparatus,    and wherein the controlling means controls switching of the first switching means so that the second electric power will be supplied to the first power supply line when the determining means has determined that the second electric power is less than or equal to the predetermined threshold value.    
   
   
       3 . An electronic apparatus according to  claim 1 , 
 further comprising setting processing means for executing processing for setting that is needed for connection with the another electronic apparatus,    wherein the determining means determines whether the second electric power is less than or equal to the predetermined threshold value when the setting processing means is finished,    and wherein the controlling means controls switching of the first switching means so that the second electric power will be supplied to the first power supply line when the determining means has determined that the second electric power is less than or equal to the threshold value.    
   
   
       4 . An electronic apparatus according to  claim 1 , further comprising charging means for charging a backup battery when the second electric power is being supplied from the another electronic apparatus via the cable.  
   
   
       5 . An electronic apparatus according to  claim 4 , 
 further comprising detecting means for detecting a suspend status of the electronic apparatus connected to the another electronic apparatus via the cable,    wherein when the detecting means has detected the suspend status, the charging means stops charging of the backup battery,    and wherein the controlling means controls switching of the first switching means so that the first electric power will be supplied to the first power supply line.    
   
   
       6 . An electronic apparatus according to  claim 1 , 
 wherein the cable is a USB cable or an IEEE 1394 cable.    
   
   
       7 . A power supply controlling method for an electronic apparatus that is connected to another electronic apparatus via a cable, the power supply controlling method comprising: 
 a first switching step of switching between first electric power of the electronic apparatus and second electric power supplied from the another electronic apparatus via the cable, and supplying either the first electric power or the second electric power to a first power supply line;    a second switching step of switching from the first electric power to the second electric power and supplying the second electric power to a second power supply line when the second electric power is supplied from the another electronic apparatus;    a determining step of determining whether the second electric power supplied from the another electronic apparatus is less than or equal to a predetermined threshold value; and    a controlling step of controlling processing in the first switching step based on a result of determination by processing in the determining step.