TURN-OFF CIRCUIT FOR LDMOS WHEN REVERSE CURRENT EXISTS

摘要

PROBLEM TO BE SOLVED: To automatically switch off an LDMOS transistor by having a zener diode which is biased forward between a supply node and a source node of an LDMOS transistor and providing a 2nd zener diode in place of a charging diode. SOLUTION: A 1st Zener diode Z1 is used in place of a charging diode of a capacity Cp which exists at Vs supply voltage. A 2nd Zener diode Z2 is connected between a source node S of a transistor LD and the supply node Vs. When Zehner voltages VZ1 and VZ2 of the diodes Z1 and Z2 satisfy the condition Vs>VZ1, there holds VTH>VZ1-VZ2, and when VsVs+ Vbe-VZ2 holds. VTH is the threshold voltage of the transistor LD, and the difference between the source voltage of the transistor LD and the substrate voltage is equal to VZ2-nVbe.