Patent ID: 7531999

Claim:
A startup circuit, for activating a bandgap voltage generator, the bandgap voltage generator comprising a first terminal for providing a first voltage level and a second terminal for providing a second voltage level, the startup circuit comprising: a switching circuit, coupled to the bandgap voltage generator; an activating circuit, coupled to the switching circuit, for conducting the switching circuit to activate the bandgap voltage generator; and a controlling circuit, coupled to the switching circuit, for monitoring the variation of the first voltage level and the second voltage level to control the conductivity of the switching circuits; wherein the controlling circuit comprises: a differential circuit, coupled to the first terminal, for generating a first output current and a second output current at a first output terminal and a second output terminal respectively according to the second voltage level and the first voltage level; wherein the controlling circuit controls the conductivity of the switching circuit according to the first output current and the second output current.