Patent ID: 7038522

Claim:
A system for connecting a receiving circuit ( 120 ) to a first and a second power supply units ( 116 , 118 ), each power supply unit having a high potential terminal and a low potential terminal to be respectively connected to a high potential terminal and a low potential terminal of the receiving circuit, the system comprising; a first control switch device ( 102 ), said first control switch device being connected in series between the first power supply unit ( 116 ) and the receiving circuit ( 120 ); a second control switch device ( 104 ), said second control switch device being connected in series between the second power supply unit ( 118 ) and said receiving circuit ( 120 ); comparison means ( 106 , 108 , 110 , 112 ) having a first input and a second input respectively coupled to said first power supply unit and to said second power supply unit to select said first or said second power supply unit as having the higher difference of potential between its respective high and low voltage terminals, and to output a corresponding high or low level; controlling means ( 114 ) connected to said first and second control switch devices to close either said first or said second control switch device based on the high or low level of the comparison means; a first isolation switch device ( 202 ) being connected in series between said first power supply and said first control switch device; and a second isolation switch device ( 204 ) being connected in series between said second power supply and said second control switch device; wherein said first and second isolation switch devices being gated by the output of said comparison means.