JP2009196541A - Airbag ignition circuit and airbag ignition unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an airbag ignition circuit eliminating the necessity of increase in the size of only a high side transistor element and in breakdown resistance by dispersing excessive loss of electric power generated only in a high side transistor to a low side transistor. <P>SOLUTION: The airbag ignition circuit 40 is provided with a first transistor Tr1 arranged between a squib 50 and a power source 21; a constant current control part 42 for performing constant current control by using the first transistor Tr1; a second transistor Tr2 arranged between the squib 50 and a GND; and a constant voltage control part 43 for performing constant voltage control so that the voltage of a power source side terminal of the squib 50 or the central voltage of the squib 50 becomes constant by using the second transistor Tr2. A unit 200 including the airbag ignition circuit 40 is provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an airbag ignition circuit and an airbag ignition unit, and more particularly to an airbag ignition circuit and an airbag ignition unit in an airbag device that protects an occupant when a collision accident occurs in an automobile or the like.

  The airbag ignition circuit is used to protect an occupant by causing an electric current to flow through the squib to ignite and explode the squib and deploy the airbag when a collision accident occurs.

  The squib 10 has a transistor 11 on the high side (power supply voltage side) and a transistor 12 on the low side (GND side), and is further ignited by the high side transistor so that no more current than necessary flows through the squib. An airbag ignition circuit having a constant current circuit 131 for performing constant current control of current is known (for example, Patent Document 1).

  In the airbag ignition circuit described in Patent Document 1, when the booster circuit 21 outputs a normal voltage, the constant current circuit 131 is connected to the high-side transistor 11 and the low-side transistor 12 is connected. When the booster circuit 21 outputs a high voltage due to a low dump surge, the constant current circuit 131 is connected to the high-side transistor 11 and the switching circuit 133 is connected to the low-side transistor 12. Is connected. That is, Patent Document 1 does not describe an example in which a constant current circuit is connected to a high-side transistor and a constant voltage circuit is connected to a low-side transistor.

  However, when trying to ignite the squib, a large current flows through the above-mentioned high-side transistor, so the element size is increased so that the transistor element is not destroyed by excessive power loss earlier than the squib ignition time. Therefore, it was necessary to increase the breakdown tolerance. Therefore, there is a problem that the size of the airbag circuit is increased and the cost is increased.

JP 2006-264491 A (FIG. 1)

  Therefore, an object of the present invention is to provide an airbag ignition circuit that can solve the above-described problems.

  In addition, the present invention makes it unnecessary to increase the size of only the high-side transistor element or increase the breakdown resistance by dispersing the excessive power loss that has occurred only in the high-side transistor to the low-side transistor. An object is to provide an airbag ignition circuit.

  In the airbag ignition circuit according to the present invention, the first transistor disposed between the squib and the power source, the constant current control unit performing constant current control using the first transistor, and disposed between the squib and GND. And a constant voltage control unit that performs constant voltage control using the second transistor so that the power source side terminal voltage of the squib or the center voltage of the squib becomes a constant voltage.

  In the airbag ignition unit according to the present invention, the first transistor disposed between the squib and the power source, the constant current control unit that performs constant current control using the first transistor, and the squib and GND And a plurality of airbag ignition circuits having a constant voltage control unit for performing constant voltage control so that the squib power supply side terminal voltage or the squib center voltage becomes a constant voltage by using the second transistor. It is characterized by having.

  In the airbag ignition circuit or the airbag ignition unit according to the present invention, the constant voltage control circuit 43 maintains at least the voltage between the terminals of the transistor Tr2, so that the power loss concentrated on the transistor Tr1 is reduced. It was possible to reduce the size of the transistor Tr1 that could be dispersed in the Tr2 and had to be increased in order to increase the breakdown resistance in the conventional case.

  Hereinafter, an airbag ignition circuit and an airbag ignition unit according to the present invention will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 1 is a diagram showing a schematic configuration of an airbag system 1 mounted on a vehicle or the like.

  The airbag system 1 includes a battery 20, a boost power source 21, an airbag control circuit 30, an airbag ignition circuit 40, a squib 50, a backup capacitor C1, a backflow prevention diode D1, and the like.

  The battery 20 is a chargeable / dischargeable battery having a rated output of 12 V, for example. The boosting power source 21 boosts the output voltage of the battery 20, and its rated output is 25V, for example. The step-up power supply 21 is connected to the airbag ignition circuit 40 via a backup capacitor C1 and a backflow prevention diode D1.

  The backup capacitor C1 is provided to ignite the squib with the accumulated charge when the battery 20 and the boost power source 21 are disconnected due to the impact of a vehicle collision. It is comprised so that more electric charges may be charged.

  The airbag control circuit 30 includes a CPU, a ROM, a RAM, and the like, generates an ignition command for igniting the squib 50 based on outputs from various sensors (not shown), and sends the ignition command to the airbag ignition circuit 30. Output.

  The airbag ignition circuit 40 includes an ignition control circuit 41, a constant current control circuit 42, a constant voltage control circuit 43, an n-channel field effect transistor Tr1 and an n-channel field effect transistor Tr2 arranged on the high side, a resistor R1, etc. The squib 50 is ignited by applying a predetermined current, and an airbag (not shown) is deployed. The squib 50 is connected to the source of the transistor Tr1 and the drain of the transistor Tr2. The source electrode of the transistor Tr2 is grounded (GND) to the vehicle body.

  When the ignition control circuit 41 receives an ignition command from the airbag control circuit 30, the ignition control circuit 41 performs control so as to start the operations of the constant current control circuit 42 and the constant voltage control circuit 43.

  When the constant current control circuit 42 receives the operation start command from the ignition control circuit 41, the voltage across the terminal of the resistor R1 is such that a predetermined current required for the squib 50 to ignite flows to the squib 50 via the transistor Tr1. Based on the above, the voltage applied to the gate of the transistor Tr1 is controlled.

  When the constant voltage control circuit 43 receives the operation start command from the ignition control circuit 41, the voltage between the terminals of the transistor Tr2, that is, the voltage between the low-side terminal b of the squib 50 and GND is maintained at a predetermined voltage. The voltage applied to the gate of the transistor Tr2 is controlled.

  Hereinafter, the operation of the airbag ignition circuit 40 will be described.

  Since the squib 50 needs to deploy the airbag, the squib 50 is disposed in the steering wheel of the vehicle, and thus may be short-circuited with the metal part at the GND potential. In such a case, if the constant voltage control circuit 43 does not exist, the transistor Tr1 is subjected to constant voltage control, and there is no possibility of constant current control, which may destroy the transistor Tr1. Therefore, it is necessary to increase the size of the transistor Tr1 in order to increase the breakdown tolerance.

  However, in the airbag ignition circuit 40, the voltage between the terminals of the transistor Tr2 is maintained at a predetermined voltage by the constant voltage control circuit 43. Therefore, even if the squib 50 is short-circuited, power loss is caused to the transistor Tr2. Since it can be dispersed, it is not necessary to increase the size of the transistor Tr1 in order to increase the breakdown tolerance.

  Even if the squib 50 is short-circuited, a predetermined current flows to the squib 50 by the action of the constant current control circuit 42, and the squib 50 can be ignited.

  FIG. 2 is a diagram showing a schematic configuration of another airbag system 2 mounted on a vehicle or the like.

  The airbag system 2 includes a battery 20, a boost power source 21, an airbag control circuit 30, an airbag ignition circuit 100, a squib 50, a backup capacitor C1, a backflow prevention diode D1, and the like.

  The difference between the airbag ignition circuit 100 shown in FIG. 2 and the airbag ignition circuit 40 shown in FIG. 1 is that the constant voltage control circuit 43 of the airbag ignition circuit 100 has a voltage between the low-side terminal b of the squib 50 and GND. Is not controlled so as to be a predetermined voltage, but is only controlled such that the voltage between the terminal a on the high side of the squib 50 and the GND becomes a predetermined voltage. In the airbag system 2 shown in FIG. 2, the same components as those in the airbag system 1 shown in FIG.

  Hereinafter, the operation of the airbag ignition circuit 100 will be described.

  When the impedance of the squib 50 is increased (increased) due to disconnection of the wiring, deterioration of the squib, etc., if one end side of the squib 50 is voltage-controlled, the potential of the high-side terminal a becomes high, and the constant current control circuit 42 There was a possibility that the constant current control in would not operate sufficiently, and current sufficient to activate the airbag could not be passed through the slab 50.

  However, when the airbag ignition circuit 100 shown in FIG. 2 is used, the constant voltage control circuit 43 of the airbag ignition circuit 100 consequently maintains the high-side terminal a of the squib 50 at a predetermined potential. Since it operates, it is possible to increase the possibility that the airbag can be operated when the constant current control in the constant current control circuit 42 operates sufficiently.

  When the airbag ignition circuit 100 shown in FIG. 2 is used, on the contrary, even when the impedance of the squib 50 is increased, the operation of the constant voltage control circuit 43 causes the high-side terminal a of the squib 50 to be connected. Since the potential can be kept low, a predetermined current can be passed through the squib 50.

  FIG. 3 is a diagram showing a schematic configuration of still another airbag system 3 mounted on a vehicle or the like.

  The airbag system 3 includes a battery 20, a boost power source 21, an airbag control circuit 30, an airbag ignition circuit 110, a squib 50, a backup capacitor C1, a backflow prevention diode D1, and the like.

  The airbag ignition circuit 110 includes an ignition control circuit 41, a constant current control circuit 42, a constant voltage control circuit 43, an n-channel field effect transistor Tr1 and an n-channel field effect transistor Tr2 arranged on the high side, a resistor R1, It consists of R2 and R3.

  The difference between the airbag ignition circuit 110 shown in FIG. 3 and the airbag ignition circuit 40 shown in FIG. 1 is that the constant voltage control circuit 43 of the airbag ignition circuit 110 has a voltage between the terminal b on the low side of the squib 50 and GND. Is not controlled so as to be a predetermined voltage, but is only controlled such that the center voltage between the terminals of the squib 50 and the voltage between the GND are controlled to a predetermined voltage. In the airbag system 3 shown in FIG. 3, the same components as those in the airbag system 1 shown in FIG.

  Hereinafter, the operation of the airbag ignition circuit 110 will be described.

  When the airbag ignition circuit 110 shown in FIG. 3 is used, as described with reference to FIG. 2, the balance of the applied voltage is made equal to the transistors Tr1 and Tr2 without being affected by the impedance of the squib 50. It becomes possible to control to.

  FIG. 4 is a diagram showing a schematic configuration of still another airbag system 4 mounted on a vehicle or the like.

  The airbag system 4 includes a battery 20, a boost power source 21, an airbag control circuit 30, an airbag ignition circuit 120, a squib 50, a backup capacitor C1, a backflow prevention diode D1, and the like.

  The airbag ignition circuit 120 includes an ignition control circuit 41, a constant current control circuit 42, a constant voltage control circuit 43, a control voltage generation circuit 44, an n-channel field effect transistor Tr1 and an n-channel field effect arranged on the high side. A transistor Tr2, a resistor R1, and the like are included.

  The difference between the airbag ignition circuit 120 shown in FIG. 4 and the airbag ignition circuit 100 shown in FIG. 2 is that the control voltage generation circuit 44 of the airbag ignition circuit 120 detects the output voltage of the boost power source 21 and depends on the output voltage. The control voltage is generated, and the constant voltage control circuit 43 performs constant voltage control so that the voltage between the high-side terminal a of the squib 50 and the GND becomes the generated control voltage. In the airbag system 4 shown in FIG. 4, the same components as those in the airbag system 2 shown in FIG.

  Hereinafter, the operation of the airbag ignition circuit 120 will be described.

  When the airbag ignition circuit 120 shown in FIG. 4 is used, the control value of the constant voltage control circuit 43 can be changed depending on the output voltage of the boost power source 21 as a power source. On the other hand, appropriate dispersion of power loss can be freely set by the transistors Tr1 and Tr2. As a result, high reliability of the airbag ignition circuit 120 can be obtained. If necessary, the size of the transistor Tr1 can be reduced within a range that does not cause a problem with respect to fluctuations in the output voltage of the power supply.

  In the example of FIG. 4, the control voltage generation circuit 44 is provided in the airbag ignition circuit 100 shown in FIG. 2 and the control value of the constant voltage control circuit 43 is set, but the airbag ignition circuit 40 shown in FIG. The control voltage generation circuit 44 may be provided in the airbag ignition circuit 110 shown in FIG. 3 so that the control value of the constant voltage control circuit 43 is set.

  FIG. 5 is a diagram showing an example of the relationship between the control voltage generated by the control voltage generation circuit 44 of the airbag ignition circuit 120 shown in FIG. 4 and the power supply voltage.

  In the case shown in FIG. 5, the control voltage generation circuit 44 of the airbag ignition circuit 120 outputs a control voltage 61 that always becomes a predetermined ratio of the output voltage 60 of the power supply. As a result, the ratio of the voltage applied to the high-side transistor Tr1 and the voltage applied to the low-side transistor Tr2 can be made constant (in this case, 1/2), and the range of the entire output voltage of the power supply It is possible to maintain a state in which the transistor Tr1 has the highest breakdown resistance.

  In the case of FIG. 5, the ratio of the voltage applied to the high-side transistor Tr1 and the voltage applied to the low-side transistor Tr2 is ½, but the present invention is not limited to this. It is also possible to generate the control value by the control voltage generation circuit 44 so that the voltage ratio is as follows.

  FIG. 6 is a diagram illustrating another example of the relationship between the control voltage generated by the control voltage generation circuit 44 of the airbag ignition circuit 120 shown in FIG. 4 and the power supply voltage.

  In the case shown in FIG. 6, the control voltage generation circuit 44 of the airbag ignition circuit 120 outputs a control voltage 62 so that the applied voltage to the high-side transistor Tr1 is always a predetermined value regardless of the power supply voltage 60. . As a result, the power loss of the high-side transistor Tr1 can be kept constant without depending on the output voltage of the power supply.

  When an n-channel MOSFET is used for the high-side transistor Tr1, the transistor Tr1 can raise the source voltage only to a voltage lower than the output voltage of the power source by the gate-source voltage VGS. By the way, it is conceivable that the low-side transistor Tr2 can be advantageously operated down to a low voltage by increasing the size, but the high-side transistor Tr1 does not have such an advantage. In this way, even if the size of the high-side transistor Tr1 is reduced, there is little influence. Therefore, by setting the applied voltage to the transistor Tr1 within a voltage range of the power supply output, the transistor Tr1 is set to a predetermined value. It is possible to reduce the size of Tr1.

  FIG. 7 is a diagram showing a schematic configuration of still another airbag system 5 mounted on a vehicle or the like.

  The airbag system 5 includes a battery 20, a boost power source 21, an airbag control circuit 30, an airbag ignition circuit 130, a squib 50, a backup capacitor C1, a backflow prevention diode D1, and the like.

  The airbag ignition circuit 130 includes an ignition control circuit 41, a constant current control circuit 42, a constant voltage control circuit 43, a control voltage generation circuit 44, a switch 45, an n-channel field effect transistor Tr1 and an n-channel arranged on the high side. It comprises a field effect transistor Tr2 and a resistor R1.

  The difference between the airbag ignition circuit 130 shown in FIG. 7 and the airbag ignition circuit 120 shown in FIG. 4 is that the airbag ignition circuit 130 uses the transistor Tr2 in accordance with the switch signal 132 output from the ignition control circuit 41. It is only a point having a switch 45 for switching between control and switch control. In FIG. 7, the ignition control circuit 41 outputs a switching signal 132 according to a signal received via the airbag control circuit 30 based on an arbitrary signal from the outside. In the airbag system 5 shown in FIG. 7, the same components as those in the airbag system 4 shown in FIG.

  Hereinafter, the operation of the airbag ignition circuit 130 will be described.

  In the airbag ignition circuit 130, when the switch 45 connects the output from the constant voltage control circuit 43 to the gate of the transistor Tr2, the constant voltage circuit 43 is connected to the airbag system 4 shown in FIG. Constant voltage control is performed so that the voltage between the terminal a on the high side of the squib 50 and GND becomes a predetermined voltage. Further, when the switch 45 connects the output from the ignition control circuit 41 to the gate of the transistor Tr2, switch control for turning on the transistor Tr2 is performed by a predetermined voltage output from the ignition control circuit 41.

  As described above, the airbag ignition circuit 130 shown in FIG. 7 can switch the control method of the low-side transistor Tr2 by outputting a switching signal from the ignition control circuit 41 by an arbitrary signal from the outside. .

  FIG. 8 is a diagram showing a schematic configuration of still another airbag system 6 mounted on a vehicle or the like.

  The airbag system 6 includes a battery 20, a boost power source 21, an airbag control circuit 30, an airbag ignition circuit 140, a squib 50, a backup capacitor C1, a backflow prevention diode D1, and the like.

  The airbag ignition circuit 140 includes an ignition control circuit 41, a constant current control circuit 42, a constant voltage control circuit 43, a control voltage generation circuit 44, a switch 45, an n-channel field effect transistor Tr1 and an n-channel arranged on the high side. It comprises a field effect transistor Tr2, a resistor R1, a voltage monitor output 141, and the like.

  The difference between the airbag ignition circuit 140 shown in FIG. 8 and the airbag ignition circuit 130 shown in FIG. 7 is that the airbag ignition circuit 140 sends a signal indicating the voltage of the high-side terminal a of the squib 50 to the airbag control circuit 30. It has a voltage monitor output 141 for transmission to the point. In the airbag system 6 shown in FIG. 8, the same components as those of the airbag system 5 shown in FIG.

  Hereinafter, the operation of the airbag ignition circuit 140 will be described.

  Based on the voltage at the high-side terminal a of the squib 50, it is possible to detect whether the constant-voltage control using the low-side transistor Tr2 is normally performed by the constant-voltage control circuit 43. Therefore, the airbag control circuit 30 monitors the voltage of the high-side terminal a of the squib 50 via the voltage monitor output 141, and if an abnormality occurs in the constant voltage control circuit 43, the airbag control circuit 30 proceeds to the ignition control circuit 41. A predetermined signal is transmitted, and the switching signal 142 is output from the ignition control circuit 41 to the switch 45. Thus, the transistor Tr2 is subjected to switch control by applying a predetermined voltage from the ignition control circuit 41 to the gate. As described above, in the airbag system 6 shown in FIG. 8, even if the operation of the constant voltage control circuit 43 is uncertain, the operation of the airbag ignition circuit itself can be performed reliably.

  Note that, in anticipation of power distribution to the low-side transistor Tr2 by the constant voltage control circuit 43, the size of the transistor Tr1 is reduced at the expense of the power breakdown tolerance of the high-side transistor Tr1. When the transistor Tr2 shifts to switch control due to an abnormality in the voltage control circuit 43, the airbag control circuit 30 controls the airbag Tr to operate safely by shortening the energization time to the transistor Tr1. It is preferable.

  FIG. 9 is a diagram showing a schematic configuration of still another airbag system 7 mounted on the vehicle.

  The airbag system 7 includes a battery 20, a boost power source 21, an airbag control circuit 30, an airbag ignition circuit 150, a squib 50, a backup capacitor C1, a backflow prevention diode D1, and the like.

  The airbag ignition circuit 150 includes an ignition control circuit 41, a constant current control circuit 42, a constant voltage control circuit 43, a control voltage generation circuit 44, a switch 45, an n-channel field effect transistor Tr1 and an n-channel arranged on the high side. It comprises a field effect transistor Tr2, a resistor R1, a constant current source 151, a first output 152 for monitoring, a second output 153 for monitoring, and the like.

  The difference between the airbag ignition circuit 150 shown in FIG. 9 and the airbag ignition circuit 130 shown in FIG. 7 is that the airbag ignition circuit 150 includes a constant current source 151 and has a closed circuit shown as a dotted line 154 in FIG. It is a point. In the airbag system 7 shown in FIG. 9, the same components as those of the airbag system 5 shown in FIG. The constant current source 151 can also be used as the constant current source 151 used for self-diagnosis of the squib 50.

  Hereinafter, the operation of the airbag ignition circuit 150 will be described.

  In the airbag control circuit 30, the current supplied from the boosted power source or the like by the constant current source 151 first flows to the squib 50, and then flows to the GND via the transistor Tr2. Also, the switching signal 155 is output from the ignition control circuit 41 to control the switch 45, the constant voltage control using the low-side transistor Tr2 is performed by the constant voltage control circuit 43, the first output 152 for monitoring and the monitoring Based on the voltage value of the second output 153, it can be detected whether the constant voltage control is operating normally. In addition, simultaneously with the detection of whether or not the constant voltage control is operating normally, the self-diagnosis of the resistance value of the squib 50 can be performed from the voltage drop across the squib 50.

  The detection of the constant voltage control by the airbag control circuit 30 is performed after the ignition switch (not shown) is turned on to supply the output voltage of the battery 20 and the operation of the airbag control circuit 30 is started. As one of the diagnostic procedures, it is preferably programmed to be performed along with the resistance value of the squib 50. If an abnormality is found in the constant voltage control circuit 43 as a result of self-diagnosis, the switching signal 155 can be used to switch the transistor Tr2.

  FIG. 10 is a diagram showing a schematic configuration of still another airbag system 8 mounted on a vehicle or the like.

  The airbag system 8 includes a battery 20, a boost power source 21, an airbag control circuit 30, an airbag ignition circuit 160, a squib 50, a backup capacitor C1, a backflow prevention diode D1, and the like.

  The difference between the airbag ignition circuit 160 shown in FIG. 10 and the airbag ignition circuit 130 shown in FIG. 7 is that the airbag ignition circuit 160 sends a signal indicating the voltage at the low-side terminal b of the squib 50 to the airbag control circuit 30. It has a voltage monitor output 161 for transmission. In the airbag system 8 shown in FIG. 10, the same components as those in the airbag system 5 shown in FIG.

  Hereinafter, the operation of the airbag ignition circuit 160 will be described.

  Based on the voltage at the low-side terminal b of the squib 50, it is possible to detect whether or not the squib 50 and the battery wiring are short-circuited. Therefore, the airbag control circuit 30 monitors the voltage of the low-side terminal b of the squib 50 via the voltage monitor output 161, and when the squib 50 and the battery wiring are short-circuited, that is, the voltage monitor output 161 is When the voltage is substantially the same as that of the battery 20, a predetermined signal is transmitted to the ignition control circuit 41, and the switching signal 162 is output from the ignition control circuit 41 to the switch 45. Thus, the transistor Tr2 is subjected to switch control by applying a predetermined voltage from the ignition control circuit 41 to the gate. Whether the squib 50 and the battery wiring are short-circuited may be determined independently by the airbag ignition circuit 41 detecting the voltage at the low-side terminal b of the squib 50.

  If the output voltage of the battery 20 is lower than the control voltage of the low-side transistor Tr2, the transistor Tr2 does not operate, so that there is a possibility that the squib 50 cannot be ignited to deploy the airbag. Further, when the squib 50 and the battery wiring are short-circuited, the effect of the constant current control by the constant current control circuit 42 is lost, and therefore unnecessary control is stopped from the viewpoint of reducing the power loss of the high-side transistor Tr1. It is necessary to ensure that the airbag can be operated. Therefore, in the airbag ignition circuit 160 shown in FIG. 10, when the squib 50 and the battery wiring are short-circuited, the switch 45 is switched by the switching neighborhood 162 and the transistor Tr2 is switch-controlled.

  FIG. 11 is a diagram showing a schematic configuration of still another airbag system 9 mounted on a vehicle or the like.

  The airbag system 9 includes a battery 20, a boost power source 21, an airbag control circuit 30, an airbag ignition circuit 170, a squib 50, a backup capacitor C1, a backflow prevention diode D1, and the like.

  The airbag ignition circuit 170 includes an ignition control circuit 41, a constant current control circuit 42, a constant voltage control circuit 43, a control voltage generation circuit 44, a switch 45, an n-channel field effect transistor Tr1 and an n-channel arranged on the high side. It comprises a field effect transistor Tr2 and a resistor R1.

  The difference between the airbag ignition circuit 170 shown in FIG. 11 and the airbag ignition circuit 120 shown in FIG. 4 is that the airbag ignition circuit 170 is controlled by the constant voltage control by the reduced voltage detection signal 172 output from the control voltage generation circuit 44. It is only a point having a switch 45 for switching between switch control. In the airbag system 9 shown in FIG. 11, the same components as those of the airbag system 4 shown in FIG.

  Hereinafter, the operation of the airbag ignition circuit 170 will be described.

  In the airbag ignition circuit 170, when the switch 45 connects the output from the constant voltage control circuit 43 to the gate of the transistor Tr2, the constant voltage control circuit 43 is configured as described in the airbag system 4 shown in FIG. The constant voltage control is performed so that the voltage between the terminal a on the high side of the squib 50 and the GND becomes constant. When the switch 45 connects the output from the ignition control circuit 41 to the gate of the transistor Tr2, the transistor Tr2 is turned on by applying a predetermined voltage output from the ignition control circuit 41 to the gate of the transistor Tr2. Switch control is performed.

  When the output of the boosting power source 21 decreases, the constant current control by the constant current control circuit 42 is saturated, and a predetermined current cannot be supplied to the high-side transistor Tr1. Along with this, the constant voltage control circuit 43 is also turned OFF, and the entire airbag ignition circuit 170 may not operate normally. Therefore, in the airbag ignition circuit 170 shown in FIG. 11, a threshold voltage higher than the voltage at which the constant current control circuit 42 saturates is provided in the control voltage generation circuit 44, and the output voltage of the boosting power supply 20 is lower than that. Controls the switch 45 to switch the transistor Tr2 by outputting the reduced voltage detection signal 172.

  By controlling the switch of the transistor Tr2, the voltage between the terminals of the high-side transistor Tr1 can be increased, so that the constant current control by the constant current control circuit 42 is prevented from being saturated, and the airbag ignition circuit It became possible to avoid the abnormal operation of the entire 170.

  FIG. 12 is a diagram showing a schematic configuration of still another airbag system 10 mounted on a vehicle or the like.

  The airbag system 10 includes a battery 20, a boosting power source 21, an airbag control circuit 30, an airbag ignition unit 200, a plurality of squibs 50 and 51, a backup capacitor C1, a backflow prevention diode D1, and the like.

  The airbag ignition unit 200 includes an ignition control circuit 41, a control voltage generation circuit 44, a plurality of airbag ignition circuits 201 and 202, and the like.

  Although not specified, each airbag ignition circuit includes a constant current control circuit 42, a constant voltage control circuit 43, an n-channel field effect transistor Tr1 and an n-channel field effect transistor Tr2 arranged on the high side, a resistor R1 etc. are comprised.

  That is, the airbag system 10 shown in FIG. 12 has a plurality of sets of airbag ignition circuits 120 shown in FIG. 4, but each of the airbag ignition circuits is not provided with an ignition control circuit and a control voltage generation circuit. The control circuit 41 and the control voltage generation circuit 44 are shared. Since it is less necessary to set a reference voltage for constant voltage control for each airbag ignition circuit, since the ignition control circuit 41 and the control voltage generation circuit 44 are shared, the airbag ignition unit 200 can be configured at low cost. It became.

  Therefore, the airbag system 10 shown in FIG. 12 is effectively used as a means for deploying a vehicle airbag having a plurality of airbags, such as a driver airbag, a passenger airbag, and a side curtain airbag. can do. In FIG. 12, two airbag ignition circuits 201 and 202 and squibs 50 and 51 corresponding to the airbag ignition circuits 201 and 202, respectively, are described. However, the set of airbag ignition circuits and squibs is not limited to two sets. Can be provided.

  In the airbag system 10 shown in FIG. 12, the ignition control circuit 41 and the control voltage generation circuit 44 are shared, and a plurality of sets of the airbag ignition circuit 120 shown in FIG. In the airbag ignition circuits 40, 100, and 110 shown in FIGS. 1 to 3, the ignition control circuit 41 can be shared to make a plurality of sets as one unit.

  Further, in FIG. 12, the airbag ignition unit 200 may be integrated as an IC. The integration enables the airbag system to be reduced in size, priced, highly accurate, and highly reliable.

  FIG. 13 is a diagram showing a schematic configuration of still another airbag system 11 mounted on a vehicle or the like.

  The airbag system 11 includes a battery 20, an inductor L1, a Zener diode TD1, a backup capacitor C1, a backflow prevention diode D1, an airbag control circuit 30, an airbag ignition unit 210, a plurality of squibs 50 and 51, and the like.

  The airbag ignition unit 210 includes an ignition control circuit 41, a control voltage 44, a boost control circuit 211, a plurality of airbag ignition circuits 201 and 202, and the like.

  Although not specified, each airbag ignition circuit includes a constant current control circuit 42, a constant voltage control circuit 43, an n-channel field effect transistor Tr1 and an n-channel field effect transistor Tr2 arranged on the high side, a resistance R1 etc. are comprised.

  The airbag system 11 shown in FIG. 13 has a configuration in which at least a part or all of the boost power source 21 in the airbag system 10 shown in FIG. 12 is incorporated in the airbag ignition unit 210 as the boost control circuit 211.

  Therefore, the airbag system 11 shown in FIG. 13 is similar to the airbag system 9 shown in FIG. 12 in vehicles having a plurality of airbags such as a driver airbag, a passenger airbag, and a side curtain airbag. It can be effectively used as a means for deploying an airbag. In FIG. 13, two airbag ignition circuits 201 and 202 and squibs 50 and 51 corresponding to the airbag ignition circuits 201 and 202 are described. However, the set of airbag ignition circuits and squibs is not limited to two, Can be provided.

  In the airbag system 11 shown in FIG. 13, the ignition control circuit 41 and the control voltage generation circuit 44 are shared, and a plurality of sets of the airbag ignition circuit 120 shown in FIG. In the airbag ignition circuits 40, 100, and 110 shown in FIGS. 1 to 3, the ignition control circuit 41 can be shared to make a plurality of sets as one unit.

  Further, the airbag ignition unit 210 in FIG. 13 may also be integrated as an IC. The integration enables the airbag system to be reduced in size, priced, highly accurate, and highly reliable.

  FIG. 14 is a diagram showing a schematic configuration of still another airbag system 11 mounted on a vehicle.

  The airbag system 11 includes a battery 20, an airbag ignition unit 220, a plurality of squibs 50 and 51, and the like.

  The airbag ignition unit 220 includes an airbag ignition IC 230, an inductor L1, a Zener diode TD1, a backup capacitor C1, a backflow prevention diode D1, and an airbag control circuit 30 that are integrated as shown in FIG. And the acceleration sensor 21 and the like.

  The acceleration sensor 31 detects gravity acceleration and outputs a signal corresponding to the detected acceleration to the airbag control circuit 30. The airbag control circuit 30 detects a vehicle collision or the like based on a signal corresponding to the detected acceleration from the acceleration sensor 31, and transmits an ignition command to the airbag ignition IC 230, whereby the squib 50, 51, etc. The airbag will be deployed.

  The airbag ignition unit 220 as shown in FIG. 14 can be easily attached to the vehicle simply by electrical wiring with the battery 20 and a plurality of squibs 50 and 51 arranged at necessary places. .

1 is a schematic configuration diagram of an airbag system 1. FIG. It is a schematic block diagram of the other airbag system 2. FIG. FIG. 5 is a schematic configuration diagram of still another airbag system 3. FIG. 6 is a schematic configuration diagram of still another airbag system 4. It is a figure which shows an example of the relationship between a control voltage and a power supply voltage. It is a figure which shows the other example of the relationship between a control voltage and a power supply voltage. FIG. 6 is a schematic configuration diagram of still another airbag system 5. FIG. 6 is a schematic configuration diagram of still another airbag system 6. FIG. 6 is a schematic configuration diagram of still another airbag system 7. FIG. 6 is a schematic configuration diagram of still another airbag system 8. FIG. 6 is a schematic configuration diagram of still another airbag system 9. 3 is a schematic configuration diagram of still another airbag system 10. FIG. FIG. 5 is a schematic configuration diagram of still another airbag system 11. FIG. 5 is a schematic configuration diagram of still another airbag system 12.

Explanation of symbols

21 Booster Power Supply 30 Airbag Control Circuit 40, 100, 110, 120, 130, 140, 150, 160, 170, 201, 202 Airbag Ignition Circuit 41 Ignition Control Circuit 42 Constant Current Control Circuit 43 Constant Voltage Control Circuit 44 Control Voltage Generation circuit 45 Switch 50 Squib 151 Constant current source 200, 210, 220 Airbag ignition unit Tr1 High side transistor Tr2 Low side transistor

Claims (6)

A first transistor disposed between the squib and the power source;
A constant current control unit that performs constant current control using the first transistor;
A second transistor disposed between the squib and GND;
A constant voltage control unit that performs constant voltage control using the second transistor so that the power source side terminal voltage of the squib or the center voltage of the squib becomes a constant voltage;
An air bag ignition circuit comprising:   The airbag ignition circuit according to claim 1, further comprising a generation unit that generates a control value for performing constant voltage control by the constant voltage control unit based on a power supply voltage.   3. The airbag ignition circuit according to claim 2, wherein the generation unit determines the control value such that a voltage between terminals of the first transistor is substantially constant.   The air according to any one of claims 1 to 3, further comprising a switching unit that switches between constant voltage control by the constant voltage control unit using the second transistor and switch control for turning on the second transistor. Bag ignition circuit.   A switching signal for switching to switch control for turning on the second transistor by the switching unit based on the detection result of detecting the power supply voltage, and the switching unit based on the detection result of detecting the operation of the constant voltage control unit A switching signal for switching to switch control for turning on the second transistor, or a switching signal for switching to switch control for turning on the second transistor by the switching unit based on a detection result of detecting the state of the squib, The airbag ignition circuit according to claim 4, further comprising a switching control unit that outputs   An airbag ignition unit comprising a plurality of airbag ignition circuits according to any one of claims 1 to 5.

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