Abstract: The present invention relates to a constant voltage control device for preventing parasitic transistors from operating, which comprises a constant voltage generating section, an undervoltage lock-out section, an operation control section, and a supply voltage control section. According to the present invention, parasitic transistors induced during the operation of a switching transistor made of a lateral transistor are prevented from operating by feedback of a signal derived from the Vref signal output from the constant voltage generating section to the operation control section. Unwanted power consumption by the parasitic transistors is reduced and malfunction resulting therefrom is prevented.

Abstract: A hysteresis system with constant threshold voltage, regardless of an increase or decrease of an output signal by detecting the increase/decrease state of the input signal, and includes a second voltage signal generator for generating a second voltage signal which is gradually increased when a first voltage signal inputted is high and is gradually reduced when the first voltage signal inputted is low, a voltage comparator for comparing the reference threshold voltage signal with the second voltage signal generated from the second voltage signal generator and producing a corresponding value; a threshold voltage initialization circuit for comparing reference voltage with the first voltage signal inputted and producing a threshold voltage initialization signal in accordance with a corresponding value; and a threshold voltage generator to which an output signal produced from the voltage comparator and the threshold voltage initialization signal produced from the threshold voltage initialization circuit are fed ba