VOLTAGE LEVEL DETECTION CIRCUIT

PURPOSE:To make it possible to detect the change in the voltage of a power source with high accuracy, by comparing the voltage of the power source whose level is shifted by the PN junction diode of a forward direction bias with the voltage of the power source set to a proper voltage dividing level by resistance-type potential dividing. CONSTITUTION:In such a process that a power source is closed and the power source voltage level supplied to the terminal VCC of the power source rises to operation guarantee voltage or more, the output node N2 of a resistance-type potential dividing circuit 3 is raised in a level at a change ratio smaller than that of power source voltage corresponding to the power source voltage supplied from the terminal VCC and the resistance-type potential dividing ratio by resistors R2, R3. The output node N1 of a level shift circuit 1 is set to voltage shifted by the value corresponding to the forward direction voltage drop by three PN junction diodes 2A-2C with respect to the power source voltage supplied from the terminal VCC and raised in a level at the change ratio equal to the power source voltage with potential difference corresponding to level shift with respect to the power source voltage. When the levels of the nodes N1, N2 are raised, the level of the output voltage Vout from a comparing circuit 4 is reversed to a low level when the level of the node N1 exceeded that of the node N2.