| 摘要 |
PURPOSE:To allow an expanded board to alternately switch internal power supply and external power supply by driving an external feed detecting circuit, by the internal power supply only when the internal power supply of a computer is fed to a normally fed terminal part. CONSTITUTION:On a expanded board 1 for the computer, the internal power supply of the computer is fed to normally-closed contacts (normally fed terminal parts) 5a, 5b and the external power supply is applied to normally-opened contacts 6a, 6b. A switch 4 connects power supply lines 13a, 13b on the board 1 to the contacts 5a, 5b with priority. An external feed detecting circuit 9 is driven by the power supply through the contact 5a, and only during the ON period of power supply for the computer, judges whether the external power supply is fed to the contacts 6a, 6b or not. In addition, the circuit 9 switches the switch 4 only when the external power supply is fed to connect the lines 13a, 13b to the contacts 6a, 6b. Only when the internal power supply of the computer is fed to the contacts 5a, 5b, the circuit 9 is driven by the internal power supply. |
