Constant current control circuit

#The present application is based on Japanese Patent Applications No. 2008-160258 filed on Jun. 19, 2008 and No. 2009-056417 filed on Mar. 10, 2009, the disclosures of which are incorporated herein by reference.

#1. Field of the Invention

#The present invention relates to a constant current control circuit having a built-in shunt resistor for detecting a constant current flowing toward a load, more specifically relates to a squib drive circuit for use in a vehicle to control a constant current flowing toward a squib resistor for airbag inflation.

#The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

#FIG. 1 is a block diagram illustrating a squib drive circuit according to a first exemplary embodiment;

#FIG. 2 is a diagram illustrating a circuit configuration of the squib drive circuit illustrated in FIG. 1;

#In embodiments, a constant current control circuit is illustrated by using a squib drive circuit for use in a vehicle to control airbag inflation.

#Referring to FIGS. 10 to 14, a squib drive circuit 100 according to one embodiment is described below as comparison examples. FIG. 10 illustrates a squib drive circuit 100 that employs a Pch type MOS transistor as a semiconductor switching element functioning as a high-side switch. FIG. 11 illustrates a squib drive circuit 100 that employs an Nch type MOS transistor as a high-side switch. FIG. 12 illustrates a specific circuit configuration of the squid drive circuit shown in FIG. 10. FIG. 13 illustrates a specific circuit configuration of the squib drive circuit shown in FIG. 11. It should be noted that, among multiple circuit systems of the squib drive circuit shown in FIGS. 10, 11, only a circuit system for driving a squib resistors is shown in FIGS. 12, 13. Another circuit system of the squib drive circuit 100 may have a circuit configuration similar to that shown in FIGS. 12, 13.

#The squib drive circuit 100 shown in each of FIGS. 10 and 11 performs constant current control by converting of currents flowing toward squib resistors 1, 2 into voltages by using shunt resistors 3, 4, transferring the voltages to the first and second drive circuits 5, 6, and feedback-controlling gate voltages of the Pch type MOS transistors. The squib resistors 1, 2 respectively acts as first and second external load and correspond to airbags, which can be equipped in various parts of the vehicle. The squib resistors 1, 2 can cause explosion for the airbags to inflate.