The present invention relates to a variable voltage regulating device for modulating output voltage, comprising the implementation means of duty cycle modulation and control signal modulation. The duty cycle modulation mechanism entails the use of pulse signals with different duty cycles to produce different voltage signals in the resistor-capacitor network, which are regulated to obtain a control voltage. The original output voltage is then modulated by the control signal and the resistor network based on the Kirchhoff's current law to produce a new output voltage. The control signal modulation mechanism uses the field effect transistor switch to control the resistor network and then uses the resistor network and the Kirchhoff's current law to modulate the original output voltage and deliver a new output voltage.