A voltage supply circuit includes a charging circuit, a window adjustment circuit, a driving voltage adjustment circuit, a sampling and feedback circuit and a storage circuit. The charging circuit includes a modulation input terminal for receiving a control voltage; and an energy supply terminal for selectively outputting a charging energy according to the control voltage. The window adjustment circuit is used to adjust the control voltage according to a sampling output voltage corresponding to an output voltage signal, and output the control voltage. The driving voltage adjustment circuit is used to keep the control voltage within a clamping voltage according to the output voltage signal. The sampling and feedback circuit is used to generate the output voltage signal according to a voltage at the energy supply terminal. The storage circuit is used to store the charging energy to pull up the voltage at the energy supply terminal.