Power transistor device including power transistors in darlington connection and zener diode which is coupled between collector and base of power transistors and which is formed in polysilicon film

A power transistor device for an ignition system of an internal combustion engine mounted on an automobile, comprising:

• a power transistor having a collector to be coupled to an inductive load for selectively making a switching current in response to an input signal;
• a Zener diode coupled between said collector and a base of said power transistor and constituted by a plurality of Dn-junctions formed in a film of polycrystalline silicon;
• and
• a MOSFET which is switch-controlled by a control voltage formed based on a Zener current flowing through said Zener diode, and which constitutes a current path in parallel to said Zener diode,
• wherein a voltage generated in said inductive load based on the switching current is clamped by a Zener voltage of said Zener diode,
• wherein a temperature characteristic coefficient with respect to said Zener voltage of said Zener diode is substantially zero, so that said voltage generated in the inductive load is set to a stable voltage in spite of temperature variation,
• wherein said MOSFET uses a semiconductor domain constituted integrally with a collector domain of the transistor as a drain domain, uses a semiconductor domain formed within said drain domain as a channel domain, and uses a semiconductor domain formed within said channel domain as a source domain, and
• wherein a gate electrode of said MOSFET is provided over the channel domain interposed between said source domain and said drain domain through a gate insulation film.

A power device comprising:

• a terminal;
• a power transistor having an input coupled to receive an input signal and a current path coupled to the terminal, wherein the power transistor performs switching operations in response to the input signal to selectively form a current at the current path thereof;
• first and second Zener diodes coupled in series between the terminal and the input of the power transistor;
• and
• a transistor having an input coupled to a common connection point of the first and second Zener diodes and a current path coupled between the terminal and the input of the power transistor.