Patent ID: 8283705

Claim:
An integrated circuit (IC) for a switching power supply, the IC comprising: a start-up circuit comprising: a JFET having a first source electrode and a second source electrode electrically isolated from the first source electrode; a MOSFET of a second conductivity type having a drain terminal, a gate terminal, and a source terminal; and a resistor, wherein the drain terminal of the MOSFET is connected to the first source electrode of the JFET, wherein the gate terminal of the MOSFET is connected to the second source electrode of the JFET through the resistor, and is adapted to be connected to a control circuit for outputting a control signal for controlling a switching element, wherein the source terminal of the MOSFET is adapted to be connected to the control circuit and a capacitor, and wherein the JFET comprises: a semiconductor substrate of a first conductivity type; a drain region of a second conductivity type in the semiconductor substrate; a drain electrode electrically connected to the drain region; a drift region of the second conductivity type in the semiconductor substrate; a plurality of source regions of the second conductivity type in the semiconductor substrate; a plurality of source electrodes each electrically connected to one of the source regions; a gate region of the first conductivity in the semiconductor substrate in contact with the drift region and the source regions; and a gate electrode electrically connected to the gate region, wherein the drift region is between the drain region and the source regions, wherein the source electrodes are divided into at least a first source electrode group and a second source electrode group, which is electrically isolated from the first source electrode group, and wherein the first electrode comprises the first source electrode group and the second electrode comprises the second electrode group.