Patent ID: 7208929

Claim:
A startup circuit used to activate a bandgap reference circuit, the startup circuit comprising: (a) a first transistor having a gate node coupled to a first interconnection of an interface between the startup circuit and the bandgap reference circuit used to provide startup current to the bandgap reference circuit, a source node coupled to a voltage supply, and a drain node; (b) a capacitor having a first end coupled to the drain node of the first transistor and a second end coupled to ground, wherein the capacitor is slowly charged by current provided by the drain node of the first transistor; (c) a second transistor configured to discharge the capacitor when the voltage supply is turned off, the second transistor having a gate node and a source node coupled to the voltage supply, and a drain node coupled to the first end of the capacitor and the drain node of the first transistor; and (d) a third transistor having a gate node coupled to the drain nodes of the first and second transistors and the first end of the capacitor, wherein the third transistor prevents current from flowing through at least one other electrical component of the startup circuit that is not required when a voltage level of the gate node of the third transistor exceeds a value equal to the difference between the voltage of the voltage supply when powered on and a voltage threshold of the gate node of the third transistor.