JPH1178771A - Ignition current limiting circuit for air bag device and method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve precision of limitation of an ignition current and to reduce necessary capacity of a capacitor for back up. SOLUTION: A pull down resistor 21 is connected to the external part of a semiconductor integrated circuit 1, a current is fed from a reference source 15 in the semiconductor integrated circuit 11 and detected by a reference current detecting circuit 16. An ignition current to effect energization to a squib 12 is detected by an ignition current detecting circuit 20, and based on a detecting value from the reference current detecting circuit 16, an ignition transistor 14 is controlled to effect limitation of an ignition current. Since a pull down resistor 21 is connected to the outside of the semiconductor integrated circuit 11, the occurrence of unevenness in a resistance value is reduced, and precision of a reference current is improved. Since an ignition current is detected with high precision, capacity of a capacitor 19 to effect back up of a power fed to an air bag device from a battery 17 is reduced, and even when a part cost is reduced and the size of a substrate is reduced, the squib 12 is reliably ignited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an airbag device mounted on an automobile or the like and protecting an occupant in the event of a collision, and more particularly to an ignition current limiting circuit and method for an airbag device.

[0002]

2. Description of the Related Art Conventionally, an ignition current limiting circuit for an airbag device detects an ignition current according to the principle shown in FIG.
The ignition current is limited. A semiconductor integrated circuit (hereinafter sometimes abbreviated as “IC”) 1 controls an ignition current to be supplied to a squib 2 for inflating an airbag. An ignition drive circuit 3, an ignition transistor 4, a current detection resistor 5, and a voltage detection circuit 6 are provided in the semiconductor integrated circuit 1, and are integrally formed inside the semiconductor integrated circuit 1. An ignition current for igniting the squib 2 is supplied from a battery 7 mounted on an automobile or the like. In the airbag device 8 including the semiconductor integrated circuit 1, a capacitor 9 for storing a current supplied from the battery 7 or the like as electric charge is also provided. The ignition current detection circuit 6 detects only a potential difference based on a voltage drop across the current detection resistor 5 and controls the detected current value to be within a certain range.

Prior art techniques for limiting the ignition current of an air bag ignition squib using a resistor in a semiconductor integrated circuit include, for example, JP-A-8-282434 and JP-A-8-282434.
74159 discloses a configuration in which a current detection resistor is provided inside an IC. JP-A-9-39720 discloses I
A prior art of an ignition current limiting circuit that facilitates C conversion is disclosed. Japanese Unexamined Utility Model Publication No. 7-23672 discloses a prior art for reducing the size and weight of a control circuit for an airbag device.

[0004]

In the prior art shown in FIG. 7 and prior arts such as Japanese Unexamined Patent Publication No. 8-282434 and Japanese Unexamined Utility Model Publication No. 4-74159, the ignition current is limited by detecting only the voltage drop of the current detection resistor inside the IC. However, due to the initial variation of the resistance inside the IC and the poor temperature characteristics,
The variation in the ignition current value will inevitably increase. If this variation is large, the capacity of the capacitor 9 in FIG. 7 for backing up the ignition power supply becomes large, and it becomes necessary to use the backup capacitor 7 having a large capacity.
When the size of the capacitor 9 increases, the component cost increases and the area of the wiring board required as a current limiting circuit also increases.

[0005] In the airbag device, the duration of the ignition current is controlled by a microcomputer of an electronic control unit called an ECU. Therefore, it is necessary to add some means for notifying the microcomputer that the ignition current is flowing. by this,
The parts cost increases, the required area of the substrate increases, and the load on the microcomputer increases. Regarding these points, the prior arts of Japanese Patent Application Laid-Open No. 9-39720 and Japanese Utility Model Application Laid-Open No. 7-23672 are also the same.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ignition current limiting circuit and method for an airbag device that can limit the cost of parts and accurately limit the ignition current.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a circuit for limiting an ignition current supplied to a squib for inflating an airbag in an airbag apparatus, wherein a squib ignition drive circuit is formed. A reference power supply formed in the semiconductor integrated circuit, a pull-down resistor connected to the outside of the semiconductor integrated circuit and supplied with current from the reference power supply, and a pull-down resistor formed inside the semiconductor integrated circuit and supplied from the reference power supply to the pull-down resistor And a current limiting circuit for limiting an ignition current value to be supplied to the squib to a predetermined range based on the reference current value.

According to the present invention, a reference power supply is generated in a semiconductor integrated circuit on which a squib ignition drive circuit is formed, and a pull-down resistor to which a current is supplied from the reference power supply is connected outside the semiconductor integrated circuit. A current limiting circuit formed in the semiconductor integrated circuit limits an ignition current value to be supplied to the squib to a predetermined range based on a reference current value supplied from a reference power supply to a pull-down resistor. It is relatively easy to accurately adjust the output voltage of the reference power supply formed inside the semiconductor integrated circuit. Therefore, a reference current corresponding to the resistance value of the pull-down resistor can be accurately supplied to the pull-down resistor outside the semiconductor integrated circuit. Since the current limiting circuit controls the value of the ignition current supplied to the squib based on the reference current value, the control of the ignition current value can be performed with high accuracy. Since the ignition current value can be limited with high accuracy, it is possible to reduce the margin of the capacitance value of a power-up capacitor or the like, thereby reducing the cost of parts and the required board area.

In the present invention, the current limiting circuit includes a current mirror circuit for detecting the reference current value and the ignition current value.

According to the present invention, the reference current value and the ignition current value are detected by the current mirror circuit.
The current value can be accurately detected in the semiconductor integrated circuit. Since there is no need to insert a resistor into the current supply system and detect the current value from the voltage drop, the current can be accurately detected without being affected by variations in the resistance value.

Further, the present invention relates to a circuit for limiting an ignition current supplied to a squib for inflating an airbag in an airbag device, comprising: a squib ignition drive circuit; a current detection resistor through which the squib ignition current flows; A constant current source,
A pull-down resistor through which a current from a constant current source flows and a current limiting circuit that limits an ignition current value detected from a potential difference between both ends of the current detection resistor to a predetermined range based on a potential difference between both ends of the pull-down resistor are the same. An ignition current limiting circuit for an airbag device, which is included in a semiconductor integrated circuit.

According to the present invention, a squib ignition drive circuit,
Since the current detection resistor through which the squib ignition current flows and the pull-down resistor through which the constant current flows from the constant current source are formed inside the semiconductor integrated circuit including the constant current source and the current limiting circuit, the absolute value of the resistance value varies. Even if it occurs, the relative change between the current detection resistor and the pull-down resistor can be formed to be small, and the accuracy of current limitation based on the voltage drop of these resistors can be improved.

Further, the present invention relates to a circuit for limiting an ignition current to be supplied to a squib for inflating an airbag in an airbag apparatus, wherein the semiconductor integrated circuit includes a squib ignition drive circuit, and a semiconductor integrated circuit. An ignition current limiting circuit for an airbag device, comprising: a time limiter externally connected to limit an energization time of the ignition current to a preset time.

According to the present invention, a reference power supply is formed in the semiconductor integrated circuit in which the squib ignition drive circuit is formed, and the ignition current supply time is limited outside the semiconductor integrated circuit so as to be a preset time. Since the time limiting means is connected, the energizing time of the ignition current can be accurately controlled. Energize the ignition current as needed to ignite the squib,
By controlling the excess ignition current, for example, when it is necessary to ignite a plurality of squibs, the plurality of squibs can be reliably ignited by effectively utilizing the charge stored in the backup capacitor.

Further, the invention is characterized in that the time limiting means includes a resistor and a capacitor.

According to the present invention, since the time limiting means includes the resistor and the capacitor, the time can be easily set based on the time constant of the resistor and the capacitor.

Further, the present invention is characterized in that a change means for changing the value of the resistor or the capacitor from outside the semiconductor integrated circuit is provided.

According to the present invention, the value of the resistor or the capacitor can be changed by the changing means from outside the semiconductor integrated circuit, so that the ignition time can be flexibly changed according to the required specifications of the airbag. it can.

Further, the present invention is characterized in that there is provided an invalidating means for invalidating the time limit by the time limiting means from outside the semiconductor integrated circuit.

According to the present invention, by disabling the limitation of the ignition time by the time limiting means by the invalidating means, the time can be limited by a microcomputer or the like, and it is necessary to change the ignition time according to the type of collision or the like. Can be flexibly dealt with when there is.

Further, the present invention relates to an ignition current limiting method for energizing a squib for inflating an airbag in an airbag device, wherein a squib ignition drive circuit having a current limiting function is formed as a semiconductor integrated circuit. An ignition current limiting method for an airbag device, wherein a time period for supplying an ignition current is limited by circuits formed inside and outside an integrated circuit.

According to the present invention, since a circuit for limiting the time for supplying the ignition current inside and outside the semiconductor integrated circuit in which the squib ignition drive circuit is formed is constituted, the ignition is performed without control by the microcomputer. The current supply time can be limited.

[0023]

FIG. 1 shows a schematic configuration of an ignition current limiting circuit 10 according to a first embodiment of the present invention. The semiconductor integrated circuit 11 includes an ignition drive circuit 1 for the squib 12.
3 inclusive. The ignition drive circuit 13 includes an NPN-type ignition transistor 14. The semiconductor integrated circuit 11 further includes a reference power supply 15 and a reference current detection circuit 16. The electric power supplied to the ignition current limiting circuit 10 is:
It is supplied from a battery 17 mounted on the vehicle. In an airbag device for protecting an occupant in the event of a collision of a vehicle, the battery 17 may be detached in the event of a collision. Can be supplied.

The ignition drive circuit 13 of the present embodiment includes an ignition current detection circuit 20. The reference current when the reference voltage from the reference voltage source 15 is supplied to the pull-down resistor 21 connected to the outside of the semiconductor integrated circuit 11 is detected by the reference current detection circuit 16 and is used for comparing the ignition current with the reference current. The ignition transistor 14 is controlled on the basis of the control so that the ignition current falls within a predetermined range.

FIG. 2 shows a configuration in which the reference current detection circuit 16 and the ignition current detection circuit 20 of FIG. 1 are realized by a current mirror circuit. The comparison circuit 25 compares the outputs of the two current mirror circuits, and controls the ignition transistor 14 based on the comparison. Reference current detection circuit 16
The current mirror circuit 30 operating as a PNP transistor 31, whose emitter and base are commonly connected,
32. The reference current is one PNP transistor 3
1 flows between the emitter and the collector. Since this collector is connected to the base that is connected in common, the other P
An emitter-collector current corresponding to the emitter-collector current of one PNP transistor 31 also flows through the NP transistor 32, and a voltage corresponding to this current is generated across the resistor 33. The current mirror circuit 40 as the ignition current detection circuit 20 also includes PNP transistors 41 and 42.
, And the emitter and the base are commonly connected. Since an ignition current flows between the emitter and the collector of one PNP transistor 41, and the collector is connected to the base commonly connected, the current corresponding to the ignition current also flows between the emitter and the collector of the other PNP transistor 42. Flows. This current value is detected as a voltage drop of the resistor 43.

In the current mirror circuits 30, 40, one of the transistors 31, 32; 41, 42 has one of the transistors 31, 4 based on the ratio of the emitter-base junction area.
Since the emitter-collector current corresponding to one emitter-collector current flows through the other transistors 32 and 42, the comparison circuit 25 can be configured by appropriately setting the ratio of the junction area and the ratio of the resistances of the resistors 33 and 43. The reference current and the ignition current can be compared. Since the resistors 33 and 43 are formed inside the semiconductor integrated circuit 11, although the variation in the absolute value of the resistance value is large, the variation in the relative resistance value can be reduced, and the difference between the reference current and the ignition current can be accurately determined. A comparison can be made.

FIG. 3 shows a schematic configuration of an ignition current limiting circuit 50 according to a second embodiment of the present invention. The semiconductor integrated circuit 51 of the present embodiment includes an ignition drive circuit 53, a current detection resistor 55, and a voltage detection circuit 56. In the semiconductor integrated circuit 51, a constant current source 57, a pull-down resistor 58, and a voltage detection circuit 59 are also formed. A constant current flows from a constant current source 57 in the semiconductor integrated circuit 51 to a pull-down resistor 58 in the semiconductor integrated circuit 51, and a voltage value is detected by a voltage detection circuit 59. Based on this voltage value, the voltage drop value of the current detection resistor 55 through which the ignition current flows is read by the voltage detection circuit 56 to limit the ignition current. Since the current detection resistor 55 and the pull-down resistor 58 are formed in the same semiconductor integrated circuit 51, the variation in the resistance value is large, but the relative variation can be suppressed, and the ignition current can be accurately limited. .

FIG. 4 shows a schematic configuration of an ignition current limiting circuit 60 according to a third embodiment of the present invention. In the present embodiment, a current detection circuit 62 for detecting an ignition current and controlling the current of the ignition transistor 14 is provided in the semiconductor integrated circuit 61.
A current limiting switch 63 for starting current limiting when the reference power supply 15 and the current detecting circuit 62 detect a current exceeding the limiting current; and a current limiting switch 63 connected to the outside of the semiconductor integrated circuit 61 and operated by the current limiting switch 63. Reference power supply 15
And a voltage detecting circuit 65 for detecting an output voltage of the time limiting means 64.

The time limiting means 64 of the present embodiment comprises a resistor 6
6 and a capacitor 67 form an integrating circuit in which the resistor 6 is connected in series.
6 and the charging voltage of the capacitor 67 charged by the time constant of the capacitor 67 is detected. When the charging voltage of the capacitor 67 exceeds a preset threshold, the voltage detection circuit 65
Shuts off the ignition transistor 14. Time limiter 64
By changing the resistance value of the resistor 66 or the capacitance value of the capacitor 67, the time can be changed.

FIG. 5 shows a schematic configuration of an ignition current limiting circuit 70 according to a fourth embodiment of the present invention. In this embodiment,
Portions corresponding to the embodiment of FIG. 4 are denoted by the same reference numerals, and redundant description will be omitted. In the present embodiment, the time limiter 74 includes a plurality of capacitors 76, 77, 78, and the semiconductor integrated circuit 71 also includes a changeover switch 79. The time limiter 73 is connected to the outside of the semiconductor integrated circuit 71 as an integrating circuit, and includes capacitors 76, 77,
The time constant can be changed according to the combination set by the changeover switch 79 of 78, and the energization time of the ignition transistor 14 can be freely changed. If the changeover switch 79 is controlled by a microcomputer, it is possible to flexibly cope with a collision mode or the like.

FIG. 6 shows a schematic configuration of an ignition current limiting circuit 80 according to a fifth embodiment of the present invention. In this embodiment,
Parts corresponding to the embodiment of FIG. 4 are denoted by the same reference numerals, and redundant description will be omitted. In this embodiment, the semiconductor integrated circuit 81 is provided with an invalidation switch 82 for invalidating the time control of the ignition current conduction time by the externally connected time limiting means 64 by an external input. For example, when an enable input of the invalidation switch 82 is given from a microcomputer that controls the entire airbag device, the time control based on the time limiter 64 connected to the outside is invalidated.
Only the “ignition OFF” command for terminating ignition of the squib 12 from the microcomputer is valid. Depending on the type of collision, it is possible to flexibly cope with a case where the ignition time needs to be changed.

In each of the embodiments described above, although an NPN transistor is used as the ignition transistor 14, other switching elements such as a PNP transistor and a MOS FET can be used depending on the circuit system. Although the current mirror circuits 30 and 40 using PNP transistors are used as the reference current detection circuit 16 and the ignition current detection circuit 20, the current mirror circuit can be formed using other types of transistors.

[0033]

As described above, according to the present invention, a pull-down resistor is connected to the outside of a semiconductor integrated circuit, a variation in resistance value is reduced, an accurate ignition current is detected, and an external resistor is added. This makes it possible to suppress the variation in the ignition current value. As a result, the capacity of the capacitor for ignition backup can be reduced, and the reliability can be increased and the cost of parts can be reduced.

According to the present invention, the ignition current value and the reference current value are detected by the current mirror circuit.
The current value can be accurately detected in the semiconductor integrated circuit.

Further, according to the present invention, based on a current detection resistor and a pull-down resistor formed in a semiconductor integrated circuit,
Since the ignition current is limited, even if there is an absolute variation in the resistance value, the relative variation in the resistance value can be reduced, and the current can be accurately limited.

Further, according to the present invention, the time for energizing the ignition current is limited to a preset time by the time limiting means connected to the outside of the semiconductor integrated circuit.
There is no need to control the duration of the ignition current by software such as a microcomputer, so that the load on the microcomputer can be reduced, the number of parts can be reduced, and the cost of parts can be reduced.

Further, according to the present invention, since the time is limited by the resistor and the capacitor, the values of the resistor and the capacitor can be set according to the required specifications of the airbag, and the required time can be easily set.

Further, according to the present invention, the value of the resistor or the capacitor can be changed by the changing means, and the time limit can be changed according to the required specification of the airbag. If the change means is controlled by a microcomputer, the setting value of the ignition current energization time can be changed by the microcomputer, and it is possible to flexibly respond to the case where the ignition current energization time needs to be changed depending on the type of collision Can be done.

Further, according to the present invention, the ignition current energizing time can be invalidated from outside the semiconductor integrated circuit by the invalidating means. Therefore, when it is necessary to change the ignition current energizing time depending on the type of collision, The time limit by the time limit means can be invalidated, and the energization time can be controlled by software from the microcomputer.

Further, according to the present invention, the current is limited by the squib ignition drive circuit in the semiconductor integrated circuit, and the time for supplying the ignition current is limited by the circuits formed inside and outside the semiconductor integrated circuit. The ignition current of the squib can be controlled accurately, the capacity of the backup capacitor can be reduced, and the load on the microcomputer can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a first embodiment of the present invention.

FIG. 2 is a simplified electric circuit diagram showing the configurations of a reference current detection circuit 16 and an ignition current detection circuit 20 of FIG. 1 in further detail.

FIG. 3 is a block diagram showing a schematic configuration of a second embodiment of the present invention.

FIG. 4 is a block diagram showing a schematic configuration of a third embodiment of the present invention.

FIG. 5 is a block diagram showing a schematic configuration of a fourth embodiment of the present invention.

FIG. 6 is a block diagram showing a schematic configuration of a fifth embodiment of the present invention.

FIG. 7 is a block diagram showing a schematic configuration of a conventional ignition current limiting circuit.

[Explanation of symbols]

 10, 50, 60, 70, 80 Ignition current limiting circuit 11, 51, 61, 71, 81 Semiconductor integrated circuit 12 Squib 13, 53 Ignition drive circuit 14 Ignition capacitor 15 Reference power supply 16 Reference current detection circuit 17 Battery 19 Capacitor 20 Ignition Current detection circuit 21, 58 Pull-down resistor 25 Comparison circuit 30, 40 Current mirror circuit 31, 32; 41, 42 Transistor 33, 43, 66 Resistance 62 Current detection circuit 63 Current limiting switch 64, 74 Time limiting means 65 Voltage detecting circuit 67 , 76,77,78 Capacitor 79 Changeover switch 82 Invalid switch

Claims (8)

[Claims] 1. A circuit for limiting an ignition current supplied to a squib for inflating an airbag in an airbag device, comprising: a semiconductor integrated circuit in which a squib ignition drive circuit is formed; and a circuit formed in the semiconductor integrated circuit. A reference power supply, a pull-down resistor connected to the outside of the semiconductor integrated circuit and supplied with current from the reference power supply, and a reference current value formed inside the semiconductor integrated circuit and supplied to the pull-down resistor from the reference power supply. A current limiting circuit for limiting the value of the ignition current supplied to the squib to a predetermined range. 2. The ignition current limiting circuit according to claim 1, wherein the current limiting circuit includes a current mirror circuit that detects the reference current value and the ignition current value. 3. A circuit for limiting an ignition current supplied to a squib for inflating an airbag in an airbag device, comprising: a squib ignition drive circuit; a current detection resistor through which the squib ignition current flows; and a constant current source. A pull-down resistor through which a current from a constant current source flows, and a current limiting circuit that limits an ignition current value detected from a potential difference between both ends of the current detection resistor to a predetermined range based on a potential difference between both ends of the pull-down resistor. An ignition current limiting circuit for an airbag device, which is included in the same semiconductor integrated circuit. 4. A circuit for limiting an ignition current supplied to a squib for inflating an airbag in an airbag device, the semiconductor integrated circuit having a squib ignition drive circuit formed therein, and a circuit connected to the outside of the semiconductor integrated circuit. An ignition current limiting circuit for an airbag device, the time limiting means limiting an energizing time of the ignition current to a preset time. 5. An ignition current limiting circuit for an airbag device according to claim 4, wherein said time limiting means includes a resistor and a capacitor. 6. The value of the resistor or the capacitor,
6. The ignition current limiting circuit for an airbag device according to claim 5, further comprising changing means for changing the value from outside the semiconductor integrated circuit. 7. The ignition current for an airbag device according to claim 4, further comprising invalidating means for invalidating the time limit by said time limiting means from outside the semiconductor integrated circuit. Limit circuit. 8. An ignition current limiting method for energizing a squib for inflating an airbag in an airbag device, wherein a squib ignition drive circuit with a current limiting function is formed as a semiconductor integrated circuit. An ignition current limiting method for an airbag device, wherein a time period for supplying an ignition current is limited by circuits formed inside and outside.