| 摘要 |
PURPOSE:To prevent a change in an initial setting when a power supply is turned on by a method wherein a voltage at an input terminal is set to a ground voltage when the power supply is turned on and fixed to a power-supply voltage after the power supply is turned on and a part between the input terminal and the power supply is opened when the power supply voltage exceeds a prescribed voltage. CONSTITUTION:Since a pull-up resistor R1 is formed by n<+>, a voltage at a node (b) and a node (c) is at the same voltage as a ground of an IC when a power supply is turned on. Immediately after that, a pull-up transistor Q1 becomes conductive; the voltage of the node (b) is increased through the pull-up resistor R1 as soon as a power supply voltage rises. Accordingly, a node (a) keeps the same voltage as the node (c). When the voltage of the node (b) exceeds a threshold voltage X of the pull-up transistor Q1, the pull-up transistor Q1 is turned off; a part between the power supply and the node (a) becomes a high impedance. |
