Patent ID: 7362161
Filing Date: 2008-04-22
Classification: G06F,H02J

Abstract:
1. A power supply switching circuit for switching power supplied to an internal power supply node in a data processing device from a main power supply to a subordinate power supply, the data processing device including an internal circuit which receives power via the internal power supply node, the power supply switching circuit comprising: a detection circuit which detects a reduction in a voltage level of the main power supply to a predetermined detection level, the detection circuit outputting a detection signal for causing the internal circuit to perform data backup when the reduction in the voltage level to the predetermined detection level is detected by the detection circuit; a first switch circuit disposed between the main power supply and the internal power supply node, wherein the first switch circuit connects the main power supply to the internal power supply node before the reduction in the voltage level to the predetermined detection level is detected by the detection circuit and disconnects the main power supply from the internal power supply node when the reduction in the voltage level to the predetermined detection level is detected by the detection circuit; and a second switch circuit disposed between the subordinate power supply and the internal power supply node, wherein the second switch circuit disconnects the subordinate power supply from the internal power supply node before the reduction in the voltage level to the predetermined detection level is detected by the detection circuit, connects the subordinate power supply to the internal power supply node from when the reduction in the voltage level to the predetermined detection level is detected by the detection circuit to when the data backup is completed in the internal circuit, and subsequently disconnects the subordinate power supply from the internal power supply node when the data backup is completed in the internal circuit.