JP2005229713A - Step-up circuit and crew protecting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a step-up circuit, in which charging time of a backup capacitor is short and noise is not likely to be generated, when a transistor is turned on/off, and to provide a crew protection system comprising it. <P>SOLUTION: The step-up circuit comprises a DC-DC converter 20, and a backup circuit 60. The DC-DC converter comprises a step-up coil 23 for receiving energy from a DC power supply, a step-up switching transistor 55 being turned on/off in order to store energy in the step-up coil, a threshold alteration means 30 for detecting transistor current, having an alterable threshold and turning the step-up switching transistor off, when the transistor current reaches the threshold, and an off time determining circuit 45 for starting when the step-up switching transistor is turned off, and steps up the voltage of the DC power supply. Threshold of the transistor current is altered, depending on the magnitude of difference between a predetermined voltage and the output voltage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a booster circuit that boosts a voltage of a DC power supply, and an occupant protection system that includes the booster circuit and is installed in a vehicle.

  In recent years, vehicles equipped with vehicle occupant protection devices such as airbags and seat belt pretensioners are increasing in order to protect occupants from serious accidents. When the determination circuit determines a collision based on information from the acceleration sensor, the airbag is deployed via the ignition circuit and the inflator. Since loads such as an ignition circuit and an inflator are too low for the voltage of the on-vehicle DC power supply (battery), they are often driven by a boosted voltage boosted by a booster circuit. One type of booster circuit is a DC-DC converter. Further, a backup circuit is often provided in order to reliably supply power to the load even when the supply of power from the battery to the DC-DC converter is interrupted due to a vehicle collision.

  FIG. 5 shows a conventional airbag system. When the ignition switch 101 is turned on, the DC-DC converter 102 fed from the in-vehicle battery 100 starts to operate and the voltage is boosted to charge a backup capacitor (hereinafter referred to as “capacitor”) 103. When the collision detection circuit 106 determines that the acceleration signal detected by the acceleration sensor 104 is based on a serious collision, the switch circuit 107 is turned on, an ignition current is supplied from the capacitor 103 to the squib 108, and an airbag (not shown) is turned on. Be expanded. The mechanical acceleration switch 109 is set to be surely turned on at a level determined by the collision determination circuit 106 to be based on a serious collision.

  Next, the DC-DC converter 102 will be described. The switching transistor (hereinafter referred to as “transistor”) 116 is turned off until the charge voltage of the capacitor 103 reaches the output voltage of the in-vehicle battery 100 after the ignition switch 101 is turned on. Charged. The power supply voltage output from the in-vehicle battery 100 is supplied to the coil 114 via the first backflow prevention diode 112 and the current detection resistor 113, and the current flowing through the coil 114 is on / off controlled by the transistor 116.

  That is, the transistor 116 is turned on / off by receiving a supply of a clock pulse of a fixed period from the clock pulse generator 111, and the input voltage is boosted by the current flowing into the coil 114 when the on control is shifted to the off control. By repeating this, the capacitor 103 is gradually charged.

  The charging voltage generated in the capacitor 103 by the charging current is divided by the third resistance dividing circuit 118 and compared with the reference voltage V0 of the second comparison circuit 119. When the reference voltage VO is exceeded, it is determined that the charging is completed. Then, the output of the second comparison circuit 119 is set to a low level, the transistor 116 is turned off, the current flowing into the coil 114 is stopped, and the charging of the capacitor 103 is stopped.

On the other hand, when the transistor 116 is turned on, an excessive current flows through the coil 114, a large potential difference is generated in the current detection resistor 113, and the first and second resistance dividing circuits 121 and 122 connected to the input / output terminals thereof. The first comparison circuit 123 compares the output voltages from both of these. As a result, the transistor 116 is turned off to prevent an excessive current from flowing through the coil 114. By repeating this, the backup capacitor 103 is charged and boosted.
JP 2001-178118 A

  In general, when a voltage from a DC-DC converter is charged to a backup circuit, it is required that the backup circuit can be charged in a short time and that no noise is generated when a transistor is switched. However, in the airbag system, it takes a long time to charge the capacitor 103.

  That is, when an overcurrent flows through the current detection resistor 113 for some reason during the charging of the capacitor 103 and the current flowing through the coil 114 exceeds a certain value, the transistor 116 is turned off by the output of the second comparison circuit 119. When the charging voltage to the capacitor 103 exceeds the reference voltage VO and the transistor 116 is turned off, it is necessary to wait until the next clock pulse is generated in order for the transistor 116 to be turned on again. This is because the transistor 116 is turned on and off at a constant cycle.

  In addition, since the threshold value of the transistor current is fixed (there is no description that the threshold value is changed), the operation of the transistor 116 is ensured when the input voltage from the battery 100 reaches the minimum value in the guaranteed operating voltage range. A booster circuit must be designed. Even in the case of the minimum value, in order to ensure the necessary output capability of the transistor 116, it is necessary to constantly turn on and off at a relatively high threshold of the transistor current. Then, noise may occur in a normal state where the output voltage is close to or reaches the upper limit voltage.

  That is, the threshold value of the transistor current in the normal state is too high, and it takes time until the transistor current becomes zero from the peak. As a result, the transistor 116 is turned on at the timing when the forward current flows through the diode 117, and a large noise is generated due to the recovery current of the diode 116.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a booster circuit in which the charging time for the backup circuit is short and noise is not easily generated when the booster switching transistor is turned on and off, and an occupant protection system including the booster circuit. And

The inventor of the present application has come up with the idea of changing the threshold value of the transistor current according to the voltage difference between the predetermined voltage of the DC-DC converter and the output voltage, and has completed the present invention.
(1) The booster circuit according to the first invention of the present application is, as described in claim 1, (a) a booster coil into which energy from a DC power source flows, and an on / off switch for storing energy in the booster coil. Boosting switching transistor, threshold changing means for detecting a transistor current whose threshold can be changed and turning off the boosting switching transistor when the transistor current reaches the threshold, and off for determining an off time which starts when the boosting switching transistor is turned off A DC-DC converter that includes a time determination circuit and boosts the voltage of the DC power supply, and (b) a backup circuit that is connected to the output side of the DC-DC converter and is charged with the voltage. In this booster circuit, the threshold value changing means changes the threshold value of the transistor current according to the voltage difference between the predetermined voltage and the output voltage.

According to a second aspect of the present invention, in the booster circuit according to the first aspect, the threshold value changing means raises the threshold value when the voltage difference between the reference voltage and the output voltage is large, and lowers it when the voltage difference is small. According to a third aspect of the present invention, in the booster circuit according to the second aspect, the predetermined voltage is a reference voltage having a constant magnitude determined based on the output voltage.
(2) The occupant protection system according to the second aspect of the present invention includes, as described in claim 4, (a) an in-vehicle DC power supply, (b) a boosting coil, a boosting switching transistor, and a transistor current whose threshold can be changed. A DC-DC converter for boosting the voltage of the DC power supply, including threshold change means for turning off the boost switching transistor when the threshold is reached, and an off time determination circuit for determining the off time length of the boost switching transistor; A backup circuit charged with a voltage from the DC converter; (d) a collision determination means for determining a collision based on acceleration applied to the vehicle driven by a DC power supply or a power supply from the backup circuit; and (e) a DC power supply or backup. Driven by power supply from the circuit and protects the occupant during operation based on collision judgment by the collision judging means And personnel protection equipment, consisting of. In this passenger protection system, the threshold value changing means changes the threshold value of the transistor current in accordance with the voltage difference between the predetermined voltage of the DC-DC converter and the output voltage.

  The occupant protection system according to claim 5 is the occupant protection system according to claim 4, wherein the threshold value changing means detects a voltage difference between the predetermined voltage and the output voltage, a converter for converting the voltage into current, and a second predetermined voltage and transistor current. A comparison unit that compares the output voltage obtained by converting the voltage into the output voltage. A passenger protection system according to a sixth aspect is the occupant protection system according to the fourth aspect, wherein the threshold value changing means increases the threshold value when the voltage difference between the predetermined voltage and the output voltage is large, and decreases it when the voltage difference is small. According to a seventh aspect of the present invention, in the passenger protection system according to the sixth aspect, the predetermined voltage is a reference voltage having a constant magnitude determined based on the output voltage. An occupant protection system according to an eighth aspect of the present invention is the occupant protection system according to the fourth aspect, wherein the off-time determination circuit fixes the off-time length to a predetermined value.

(1) According to the booster circuit of the first aspect of the invention, first, noise due to a recovery current from the diode can be suppressed. That is, when the output voltage is away from the predetermined voltage and approaches or reaches the upper limit voltage, the time required from the peak to zero is shortened by changing (lowering) the threshold value of the transistor current. As a result, the transistor is turned on after forward current stops flowing in the diode.

  Second, the booster circuit can be designed assuming a state where the input voltage is higher than a certain level. While the output voltage is far from the reference voltage and lower than the upper limit voltage, the battery voltage can be boosted in a short time by changing (increasing) the transistor current threshold, and the input voltage is extremely short. Because it doesn't last.

According to the booster circuit of the second and third aspects, the noise due to the recovery current can be suppressed, and the booster circuit designed on the assumption that the input voltage is higher than a certain level can be more reliably performed.
(2) According to the occupant protection system of the second invention, in the occupant protection system including the booster circuit, basically the same effects as those of the booster circuit can be obtained.

  According to the passenger protection system of the fifth aspect, the threshold value of the transistor current can be reliably changed with a simple configuration. According to the occupant protection system of claims 6 and 7, it is possible to more reliably perform the suppression circuit noise suppression and the booster circuit design assuming a state where the input voltage is higher than a certain level. According to the occupant protection system of the eighth aspect, noise due to the recovery current can be more reliably suppressed.

<Boost circuit>
The booster circuit includes a DC-DC converter and a backup circuit. There are no particular restrictions on the use of the booster circuit, and it can be widely used in devices and devices that are driven using a DC power supply and require a backup function for operational safety.
(A) The DC-DC converter includes a known and general-purpose boosting coil, a boosting switching transistor, a diode, and the like. In addition, it includes a threshold value changing means for outputting a signal for turning off the transistor when the threshold value of the transistor current is variable and the transistor current reaches the threshold value, and an off time determination circuit having a timer that starts at the time of turning off and determines the off time. . The DC-DC converter boosts a voltage supplied from a DC power source.

  The threshold value changing means sets the threshold value of the transistor current to be high when the voltage difference between a predetermined voltage (for example, a reference voltage determined based on the output voltage) and the output voltage is large and to be low when the voltage difference is small. For this purpose, a detection unit that detects a voltage difference between the predetermined voltage and the output voltage, a conversion unit that converts the voltage into a current, and a comparison unit that compares the second predetermined voltage with an output voltage obtained by converting the transistor current into a voltage are included.

The off-time determining circuit determines the off-time of the transistor to a predetermined value, and the off-time can be made variable or fixed.
(B) The backup circuit includes a known and general-purpose backup capacitor, and is connected to the output side of the DC-DC converter to charge the voltage.
<Crew protection system>
(B) The DC power supply is mounted on a vehicle (onboard) and moves together with the vehicle. The power supply voltage can be set in the range of 6V to 16V, for example. The DC-DC converter boosts the voltage of the DC power supply to, for example, 24V.
(B) The collision determination circuit includes an acceleration sensor and the like, is driven by power supplied from a DC power supply or a backup circuit, that is, boosted power, and determines a collision based on acceleration applied to the vehicle. The occupant protection device includes an air bag and a seat-balt pretensioner, is driven by power supplied from a DC power supply or a backup circuit, that is, driven by boosted power, and is operated based on a collision determination by a collision determination unit.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
(Constitution)
(A) Occupant protection system The occupant protection system shown in FIG. 1 includes a direct current power source (battery) 10, an ignition switch 12, a DC-DC converter 20, a backup circuit 50, a collision determination device 55, and an occupant protection device 60. It consists of. The DC-DC converter 20 connected to the battery 10 via the backflow prevention diode 13 boosts the voltage of the battery 10 (details will be described later). The backup circuit 60 including the backup capacitor 61 is connected to the output side of the DC-DC converter 20 via the backflow prevention diode 14 and supplies power to the collision determination device 65 and the occupant protection device 70 instead of the battery 10 in the event of a disconnection due to a collision or the like. To supply.

The collision determination device 65 includes a constant voltage power supply circuit 66, a collision determination circuit 67, and an acceleration sensor 68. The acceleration sensor 67 detects acceleration applied to the vehicle at a constant voltage supplied from the constant voltage power supply circuit 66, and the collision determination circuit 68 determines the risk of collision based on the detection result. The occupant protection device 70 includes a safing sensor 71, an ignition drive circuit 72, a squib 73, an airbag (not shown), and the like. The ignition drive circuit 72 is turned on by the output from the collision determination circuit 68, and the squib 73 is operated to deploy the airbag.
(B) DC-DC converter The details of the DC-DC converter 20 are shown in FIG. The DC-DC converter 20 includes an input smoothing capacitor 21, a reference voltage circuit 22, a boosting coil (hereinafter referred to as “coil”) 26, a diode 27, an output smoothing capacitor 28, and a current detection variable control circuit (threshold changing means) 30. , An off timer circuit (off time determination circuit) 45, a drive circuit 50, a boosting switching transistor (hereinafter referred to as "transistor") 55, and the like.

  The reference voltage circuit 22 includes a resistor 23 and a Zener diode 24, sets a reference voltage having a constant magnitude based on the output voltage Vout, and a coil 26 is connected in series with the battery 10 to store energy from the battery 10. The transistor 55 is turned on and off by a driver circuit 50 to be described later, and charges the backup circuit 60 through the diode 27 with the energy flowing into the coil 26 from the battery 10.

  The current detection variable control circuit 30 changes the threshold value of the transistor current of the transistor 55 according to the voltage difference between the reference voltage and the output voltage Vout from the output terminal 29. For this purpose, a shunt resistor 41, an operational amplifier 31, a pair of current mirrors 33 and 35, and a comparator 39 are included. Among them, the output voltage and the reference voltage are input to the operational amplifier 31, a constant gain is provided with respect to the reference voltage, and the result is fed back to the comparator 39. The pair of current mirrors 33 and 35 converts a voltage into a current. The comparator 39 compares the reference voltage corrected by the output of the operational amplifier 31 input through the current mirrors 33 and 35 with the output obtained by converting the transistor current by the shunt resistor 41.

The off timer circuit 45 sets an off time of the transistor 55, and includes a constant current circuit 46, a timer 47 composed of a capacitor and a transistor, a comparator 48, and a NOR gate 49. The comparator 48 compares the reference voltage with the output of the low current circuit 46. The NOR gate 49 receives an output from the comparator 48 and a signal from the drive circuit 50.
As described above, the off-timer circuit 45 includes an oscillation circuit, and is configured to fix the off-time to a predetermined value.

The drive circuit 50 controls on / off of the gate of the transistor 55. Signals are input from the current detection variable control circuit 30 and the off-timer circuit 45, and 1 is output to the transistor 55 when these outputs are both 0, and 0 is output when either one is 1.
(Function)
(A) Boosting and charging In FIGS. 3A, 3B, and 3C, while the output voltage Vout from the output terminal 29 is lower than the upper limit voltage Vth and not far from the reference voltage, the off-timer variable control circuit 35 The transistor 55 is repeatedly turned on and off by this signal. As the transistor 55 is turned off, the timer 47 of the off timer circuit 45 starts and measures the off time length. The transistor 55 remains off until the timer off time ends, and is turned on again when the timer expires.

  As indicated by D in FIG. 4, when the transistor 55 is turned on, the transistor current Itr gradually increases with a predetermined time constant, and the energy of the battery 10 flows into the coil 26. When it is detected that the transistor current Ttr has reached the threshold value based on a voltage drop at the shunt resistor 41, the transistor 55 is turned off by a signal from the current detection circuit 30. When the transistor 55 is turned off, a current flows through the diode 27 as indicated by E, and the energy of the battery 10 is first charged to the backup capacitor 61 of the backup circuit 60 through the diode 27 and boosted. When the backup capacitor 61 is fully charged, energy is stored in the coil 26 by the on / off of the transistor 55, and the voltage is boosted.

The boosted voltage is supplied from the output terminal 29 of the DC-DC converter 20 or the backup circuit 60 to the collision determination circuit 65 and the occupant protection device 70, and determination of collision and occupant protection at the time of collision are executed. When the wiring between the battery 21 and the DC-DC converter 20 is disconnected due to a collision or the like, power is supplied from the backup circuit 60 to the collision determination circuit 65 and the occupant protection device 70. As can be seen, the DC-DC converter 20 and the backup circuit 60 constitute a booster circuit 15 with a backup function.
(B) Changing the threshold value of the transistor current If the output voltage supplied from the DC-DC converter 20 or the like to the collision determination circuit 65 or the like increases excessively, there is a concern about problems such as heating. In order to prevent over boosting, an upper limit voltage Vth is defined. Further, noise is likely to occur at the upper limit voltage and in the vicinity thereof. Considering these, the threshold Ith of the transistor current Itr is changed according to the voltage difference between the reference voltage and the output voltage.

  That is, as shown by A in FIG. 3A, when the output voltage V does not rise sufficiently and is far from the upper limit voltage Vth, a relatively large voltage difference is output from the operational amplifier 37 of the current detection variable control circuit 30. The corrected reference voltage is input to the comparator 39 via the pair of current mirrors 33 and 35. The comparator 39 compares this reference voltage with the output obtained by converting the transistor current by the shunt resistor 41 and outputs the comparison result to the driver circuit 50. On the other hand, in the off-timer circuit 45, the off-time of the transistor is fixed to a constant value by inserting the constant current circuit 46.

As shown in FIG. 3A, the current detection variable control circuit 30 sets a high threshold value Ia of the transistor current, and the time from zero to the threshold (peak) and the time from peak to zero are long. Become. The time from zero to peak of transistor current becomes longer, the energy stored in the coil 23 is much, and the output voltage rises rapidly in a short time. As the output voltage Vout moves away from the reference voltage and approaches the upper limit voltage Vth, The voltage difference output from the operational amplifier 31 decreases, and the signal level from the operational amplifier 31 to the comparator 39 decreases. As a result, as shown in FIG. 3C, a threshold value Ib slightly lower than the threshold value Ia is set. When the output voltage Vout further rises and reaches the upper limit voltage Vth, the voltage difference output from the operational amplifier 31 is further reduced, and the signal level from the operational amplifier 31 to the comparator 39 is further reduced. Thereby, as shown in FIG.3 (c), the threshold value Ic lower than the threshold value Ib is set.
(effect)
According to the embodiment, first, generation of noise accompanying switching of the transistor 55, particularly noise due to the recovery current of the diode 27 is suppressed. This is because the threshold Ith of the transistor current Itr is high when the voltage difference between the upper limit voltage and the output voltage is large, that is, when the voltage difference between the reference voltage and the output voltage is small, and is usually indicated by B and C in FIG. Due to the low in the state.

  That is, in the normal state where the threshold is low, the time for the transistor current to drop from the peak to zero is short. For this reason, the off-time is fixed and the on / off period of the transistor 55 is relatively short, but since the peak returns to zero in a short time, the transistor 55 is turned on at the timing when the forward current of the diode 27 becomes sufficiently small (see F). This is because the recovery current hardly flows.

  Second, the booster circuit can be designed in consideration of a relatively small state, not the minimum input voltage from the battery 10. For example, the inductance value, switching peak current, and the like of the coil 26 can be designed based on a periodic state in which the input voltage indicated by B in FIG. 3A is higher than a certain level, the off time is long, and the period is long. As described above, the state where the input voltage indicated by A does not sufficiently increase does not continue for a long time.

1 is a block diagram showing an occupant protection system according to an embodiment of the present invention. It is a circuit diagram which shows the detail of the DC-DC converter of FIG. (A) is a graph showing changes in output voltage, (b) is a graph showing ON / OFF of a transistor, and (c) is a graph showing a threshold value of transistor current. FIG. 4 is an enlarged view of FIG. It is a block diagram which shows the conventional airbag system.

Explanation of symbols

10: DC power supply 15: Booster circuit 20: DC-DC converter 23: Reference voltage circuit 30: Current detection variable control circuit 31: Operational amplifier 41: Shunt resistor 37: Operational amplifier 39: Comparator 45: Off timer circuit 50: Drive circuit 60: Backup Circuit 65: Collision determination circuit 70: Crew protection device

Claims (8)

When a boosting coil into which energy from a DC power source flows in, a boosting switching transistor that is turned on / off to store energy in the boosting coil, and a transistor current whose threshold value can be changed are detected and the transistor current reaches the threshold value A DC-DC converter for boosting the voltage of the DC power supply, including threshold value changing means for turning off the boosting switching transistor; and an off time determining circuit for determining an off time to be started when the boosting switching transistor is turned off;
A backup circuit connected to the output side of the DC-DC converter and charged with a voltage;
And the threshold value changing means changes the threshold value of the transistor current according to the voltage difference between the predetermined voltage and the output voltage.   2. The booster circuit according to claim 1, wherein the threshold value changing means increases the threshold value when the voltage difference between the reference voltage and the output voltage is large and decreases the voltage difference when the voltage difference is small.   3. The booster circuit according to claim 2, wherein the predetermined voltage is a reference voltage having a constant magnitude determined based on the output voltage. In-vehicle DC power supply,
A step-up coil, a step-up switching transistor, a threshold value changing means for turning off the step-up switching transistor when a transistor current whose threshold value can be changed reaches the threshold value, and an off-time determining circuit for determining an off-time length of the step-up switching transistor A DC-DC converter that boosts the voltage of the DC power supply,
A backup circuit in which the voltage is charged from the DC-DC converter;
Collision determination means that is driven by power supply from the DC power supply or backup circuit and determines a collision based on acceleration applied to the vehicle;
An occupant protection device that is driven by power supply from the DC power supply or a backup circuit and protects the occupant in operation based on a collision determination by the collision determination means;
The occupant protection system is characterized in that the threshold value changing means changes the threshold value of the transistor current in accordance with a voltage difference between a predetermined voltage of the DC-DC converter and an output voltage.   The threshold changing means of the DC-DC converter includes a detection unit that detects a voltage difference between the predetermined voltage and the output voltage, a conversion unit that converts a voltage into a current, and a second predetermined voltage and a voltage obtained by converting the transistor current into a voltage. The occupant protection system according to claim 4, further comprising a comparison unit that compares the two.   The occupant protection system according to claim 4, wherein the threshold value changing means of the DC-DC converter increases the threshold value when the voltage difference between the predetermined voltage and the output voltage is large and decreases the threshold value when the voltage difference is small.   The occupant protection system according to claim 6, wherein the predetermined voltage is a reference voltage having a constant magnitude determined based on the output voltage.   The occupant protection system according to claim 4, wherein the off-time determination circuit of the DC-DC converter fixes the off-time length to a predetermined value.

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