Open base bipolar transistor protective device
AssigneeNational Semiconductor Corporation
InventorCharles P. Carinalli
Life of this patent
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Abstract
A transistor, used in the switching of current in an inductive load, is protected by a similar transistor connected between collector and base. The protective transistor has a lower breakdown voltage than the transistor being protected. When the inductive load produces a voltage surge, the protective transistor breaks down first and turns the protected transistor on so that the surge is absorbed in an active transistor not in breakdown and therefore capable of dissipating the surge without damage. Since the surge is arrested at high voltage the time required to complete the arrest is shortened.
Claims5
An integrated circuit for switching inductive load devices which generate transient voltages that may rise to levels in excess of transistor collector breakdown, said integrated including means for arresting said transient voltages to limit them to levels below said transistor collector breakdown and comprising:
- a semiconductor substrate;
- at least one isolated region in said substrate;
- an output transistor located in said isolated region, said output transistor having a base, a collector and an emitter made up of a plurality of individual small area emitter sections, the combination of which provides the total collector current capability, and
- a protective active transistor located in said substrate, said protective transistor having a floating, unconnected base, a collector coupled in common with said collector of said output transistor, and an emitter coupled to said base of said output transistor whereby said collector of said protective transistor in reverse biased when acting as a protective device, said emitter of said protective transistor being composed solely of a single emitter section having an area that is large in relation to the area of an individual one of said small area emitter sections to create a base region in said protective transistor that is thinner than the base region in said output transistor, said protective transistor having an active and higher base to collector current gain and a collector breakdown voltage that is close to but lower than the collector breakdown voltage of said output transistor.
Dependencies are inferred from the claim text.