Patent ID: 7345383
Filing Date: 2008-03-18
Classification: H03K

Abstract:
1. An abnormality detection apparatus for a power feed circuit in which a DC power supply, an electric load, and a power transistor, which is controlled to open and close by a switching control section, are connected in series with one another through a wiring circuit, wherein a constant current control circuit, an overheat interruption circuit and a state detection circuit are connected to said power transistor for cooperation therewith; said switching control section includes an abnormal state determination section and an abnormality processing section; said constant current control circuit comprises a negative feedback control circuit; said constant current control circuit includes a conduction control transistor that operates in response to a detected voltage of a current detection resistor; said constant current control circuit linearly controls the conductive state of said power transistor in such a manner that a current flowing through said power transistor does not become a value equal to or larger than the value of a limit threshold current which is larger than a predetermined reference current corresponding to a rated current of said power transistor, and maintains, upon occurrence of a short-circuit abnormality of said electric load, a voltage across opposite ends of said power transistor at a value equal to or higher than a predetermined logical determination voltage; said overheat interruption circuit comprises a comparison control circuit; said comparison control circuit includes a temperature detection element for detecting a temperature in the vicinity of said power transistor, and an interruption control transistor, and operates to interrupt said power transistor when the temperature in the vicinity of said power transistor exceeds a predetermined temperature; said state detection circuit includes a state detection transistor and an open-circuit detection resistor connected in parallel to said power transistor; said state detection transistor is operated to open and close in accordance with whether the voltage across the opposite ends of said power transistor becomes equal to or higher than said logical determination voltage; an output signal of said state detection transistor is input to said switching control section as a state detection signal; said abnormal state determination section comprises a logical determination section; when a control output signal from said switching control section is a close command for said power transistor, and when the voltage across the opposite ends of said power transistor continues to be equal to or higher than said logical determination voltage, said logical determination section generates a short-circuit abnormality determination signal indicating that a short-circuit abnormality has occurred in said electric load; when said control output signal is an open command for said power transistor, and when the voltage across the opposite ends of said power transistor continues to be lower than said logical determination voltage, said logical determination section generates an open-circuit abnormality determination signal indicating that an open-circuit abnormality has occurred in said electric load; and said abnormality processing section performs at least one of abnormality warning processing and stop processing of said control output signal in response to said short-circuit abnormality determination signal or said open-circuit abnormality determination signal.