| 摘要 |
PROBLEM TO BE SOLVED: To reliably make overcurrent protection of a power transistor, by suppressing the dispersion in the maximum value of a load current. SOLUTION: A power PNP transistor 18 is fixed onto and electrically connected to a surface 16 of a metal radiating plate 15 through a platelike resistor 17. Further, a controlling integrated circuit device 20 is fixed onto the surface 16 through an electrically insulating paste 19, and the resistor 17, the transistor 18 and the device 20 are connected using thin metal wires 42 to 44. A load current Io from an input terminal flows from the emitter to the collector of the transistor 18, and further flows through the resistor 17 in a thickness direction to reach the plate 15. The device 20 detects a voltage across the resistor 17 corresponding to the current Io between the plate 15 and the surface of the resistor 17 on the side of the transistor 18. When such voltage becomes high, the device 20 excessively changes the impedance of the transistor 18 to suppress an overcurrent. |
