The invention relates to a PCI bus interface circuit for supplying power to a PCI plug-in card that is connected to a PCI bus. The inventive PCI bus interface circuit comprises a first input (2) for connection to a main voltage supply line of the PCI bus and a second input (3) for connection to an auxiliary voltage supply line of the PCI bus. The circuit further comprises an output (4) for delivering a supply voltage to the PCI plug-in card and a first switching means (6) for switching a main supply voltage supplied at the first input (2) to the output (4) when no auxiliary supply voltage Vaux is supplied at the second output (3). A second switching means (7) switches an auxiliary supply voltage Vaux supplied at the second input (3) to the output (4) when no main supply voltage VCC is supplied at the first input (2). The inventive circuit further comprises a third switching means (20) that switches the second switching means (7) to switch the auxiliary supply voltage to the output (4) when a main supply voltage is supplied at the first input (2) while an auxiliary supply voltage is simultaneously supplied at the second input (3).
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