Patent ID: 8138735

Claim:
A start up circuit for assisting start up of an inductive boost circuit including a switch transistor coupled to the inductor rises to a predetermined input voltage level, the boost circuit generating a first voltage indicative of a current flowing in the inductor, the start up circuit comprising: (a) oscillator circuitry including 1) delay circuitry having an input coupled to a first conductor and an output coupled to a second conductor, 2) the second conductor being coupled to a first terminal of a first capacitor, a second terminal of the first capacitor being coupled by the second conductor to a first terminal of a first resistor, a first terminal of a second resistor, and a first terminal of a second capacitor, the first resistor having a second terminal coupled to a drain of a first transistor, the second resistor having a second terminal coupled to a drain of a second transistor, the first transistor having a source coupled to a first supply voltage and a gate coupled to the first terminal of the first capacitor, values of the first and second resistors and values of the first and second capacitors being determinative of a duty cycle of the oscillator circuitry, the second transistor having a source coupled to a second supply voltage and a gate coupled to the gate of the first transistor; and (b) amplifier circuitry having a first input coupled to receive the first voltage and also having an output coupled to turn off the switch transistor if the first voltage exceeds a predetermined level to prevent the inductor current from exceeding a predetermined inductor current level.