| 摘要 |
PROBLEM TO BE SOLVED: To protect a load from an excessive voltage by allowing a depression type MOSFET, wherein a drain is connected to an input, a source to an output while a gate to a value of voltage to be saturated when an input voltage becomes excessive. SOLUTION: Normally, a pinch-off voltage Vp of a depression type MOSFET 50 is in the range 1 V-4 V. Assuming that, in normal operation, the device size and Vp of the MOSFET 50 are appropriately selected, while a diode D2 is in a breakdown state, and the MOSFET 50 behaves as a resistor. When a load dump takes place, the source voltage of MOSFET 50 rises, and if an input voltage continues to rise, even after reaching the breakdown voltage of the diode D2, the MOSFET 50 supports an increased voltage, and saturates, to start limiting of current. Thus, when the MOSFET 50 goes into a current limit mode, the amount of increase in the electric power consumed with the MOSFET 50 is equal only to the amount of voltage risen, resulting in protection of a load 51 from an excessive voltage. |
