Patent ID: 7990674
Filing Date: 2011-08-02
Classification: H03K

Abstract:
1. A load drive apparatus comprising a switching element connected in series to a DC power source and an electric load, a drive circuit for generating control signals to turn said switching element on and off, a thermal detection element for detecting a temperature of the switching element, an overheat protective circuit for generating an overheat detection signal when the thermal detection element detects the temperature of the switching element over a predetermined temperature level, and a disconnection detection circuit having a current mirror circuit connected to one and the other terminals in the thermal detection element to detect disconnection in wiring between the thermal detection element and overheat protective circuit by the current mirror circuit, wherein the disconnection detection circuit comprises a first amplifying element which has one of its main terminals connected to one of terminals in the thermal detection element, a constant current source connected to the other of its main terminals in the first amplifying element and ground, and a second amplifying element having one of its main terminal connected to the other of the terminals in the thermal detection element and a voltage source through a resistor, the one terminal and a control terminal of the first amplifying element are connected to each other, the control terminal of the first amplifying element is connected to a control terminal of the second amplifying element, the other main terminal of the second amplifying element is connected to ground, the level of voltage applied on one terminal of the second amplifying element indicates existence or absence of disconnection in wiring, and the overheat protective circuit or disconnection detection circuit produces an output signal to block transmission of control signals from the drive circuit to the switching element when the overheat protective circuit produces the overheat detection signal or when the disconnection detection circuit detects the disconnection in wiring between the thermal detection element and overheat protective circuit.