Integrated circuit overvoltage protection circuit

A protection circuit for increasing the capability of a first transistor in an automotive electronic circuit including first and second terminals connected, respectively, to a B+ voltage conductor and a ground voltage conductor to withstand noise signals and load dump signals on said B+ conductor comprising:

• protection circuit means coupled between a base and an emitter of said first transistor and also connected to said first terminal for increasing the breakdown voltage of said first transistor from its BV.sub.CEO breakdown voltage to its BV.sub.CES breakdown voltage in response to said noise signals and load dump signals occurring on said B+ conductor, wherein said protection circuit means include;
• a second transistor;
• a plurality of diode-connected transistors connected in series with said resistor, said diode-connected transistors and said resistor being coupled in series between said first terminal and the base of said second transistor;
• said first transistor having an emitter coupled to said second terminal and a collector coupled to said first terminal, and a base coupled to a collector of said second transistor;
• said second transistor having an emitter coupled to said second terminal;
• said first transistor, said second transistor, said resistor, and said diode-connected transistors all being in a monolithic semiconductor die;
• a zener diode external to said monolithic semiconductor die;
• a second resistor external to said monolithic semiconductor die;
• said second resistor being coupled between said first terminal and said B+ conductor, said zener diode having a cathode coupled to said first terminal and its anode coupled to said second terminal;
• said zener diode and said second resistor acting to limit the noise voltage on said B+ conductor;
• wherein said first transistor is selected so that said BV.sub.CEO breakdown voltage is of sufficiently low magnitude that said first transistor would ordinarily be destroyed by said severe overvoltages in the absence of said protection circuit means, and said BV.sub.CEO breakdown voltage is of sufficiently high magnitude that said first transistor will not be destroyed by said severe overvoltage.