US 7,888,976 B2 · Load-driving circuit having two transistors switched for heat dissipation

Abstract

A load-driving circuit supplies electric current to a load, such as a resistor of an airbag squib. The load-driving circuit includes high side and low side current control circuits, both connected in series. Each current control circuit is composed of a driving transistor, a resistor and a current mirror circuit for controlling operation of the driving transistor. The components in the load-driving circuit are positioned in an integrated circuit chip to generate different temperature gradients among the components. For example, the low side resistor is positioned close to the high side driving transistor, so that the low side resistor is heated by the high side driving transistor controlled under a constant current control. As the low side resistor is heated, the high side driving transistor is switched from the constant current control to a full-on control. In this manner, controls of both driving transistors are automatically switched thereby to avoid overheating of one of the driving transistors.

Claims18

Dependent claims

The load-driving circuit formed as an integrated circuit, comprising:

a high side driving transistor connected between a high potential terminal and a load;
a low side driving transistor connected between the load and a low potential terminal;
first means for controlling current supplied to the load via the high side driving transistor;
second means for controlling current supplied to the load via the low side driving transistor, wherein elements constituting the first and the second means are positioned in the load-driving circuit so that temperature gradients are formed among the elements due to heat generated in a heat source composed of the high side and/or the low side driving transistors;
and
means for switching the high side driving transistor to constant current control from full-on control based on the temperature gradients of the low side transistor and the low side driving transistor to the full-on control from the constant current control based on the temperature gradients of the high side transistor, the switching being performed one time or more than one time.

3 more elements

Dependencies are inferred from the claim text.

Load-driving circuit having two transistors switched for heat dissipation

Life of this patent

Load-driving circuit having two transistors switched for heat dissipation

Life of this patent

Abstract

Claims18