Saturation limit circuit for junction isolated PNP transistor and method
AssigneeNational Semiconductor Corporation
InventorMichael Maida
Life of this patent
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Abstract
A transistor saturation control circuit for controlling saturation of a PNP transistor. The control circuit includes current sense circuitry which produces a control output in response to a change in current of an N well associated with the PNP transistor. Base drive control circuitry operates to limit base drive to the PNP transistor in response to the control output.
Claims22
A transistor circuit having saturation control circuitry, said circuit comprising:
- a main PNP transistor;
- current sense circuitry configured to provide a control output in response to a change in current of an N well associated with the main PNP transistor;
- and
- base drive circuitry coupled to a base of the main PNP transistor and configured to limit base drive to the main PNP transistor in response to the control output.
A transistor circuit with saturation control, said circuit comprising:
- a desired bipolar transistor of a first conductivity type having an emitter region, a base region and a collector region;
- a parasitic bipolar transistor of a second conductivity type, opposite the first conductivity type, said parasitic bipolar transistor having a base region, at least a part of which is formed in common with the collector region of the desired bipolar transistor, and an emitter region, at least part of which is formed in common with the base region of the desired bipolar transistor;
- current sense circuitry configured to provide a control output in response to a change in collector current of the parasitic bipolar transistor;
- and
- drive circuitry for driving the desired bipolar transistor and configured to limit drive to the desired bipolar transistor in response to the control output.
A method of controlling the saturation level of a first transistor of a first conductivity type having an associated second parasitic transistor of a second conductivity type, opposite the first conductivity type, wherein the first transistor has a base region which is formed at least partially in common with an emitter region of the second transistor and wherein the first transistor has a collector region which is formed at least partially in common with an base region of the second transistor, said method comprising:
- sensing a change in collector current of the second transistor;
- and
- limiting drive to the first transistor in response to said sensing.
Dependencies are inferred from the claim text.