JP3045219B2 - Power backup circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply backup circuit, and more particularly to a power supply backup circuit for supplying power to a microcomputer system.

[0002]

2. Description of the Related Art In recent years, airbags are often mounted to protect occupants in the event of a vehicle collision. In this airbag, when a collision detection sensor detects a collision, a current flows through the squib and the priming agent is ignited. The explosion heat generates nitrogen gas to instantaneously inflate an airbag incorporated in a steering wheel or the like.

As a collision detection sensor for detecting a collision of a vehicle, a so-called G sensor for detecting a rapid change in acceleration is generally installed in addition to a safing sensor and a front sensor for mechanically detecting a collision. It is a target. Then, the squib ignition circuit is directly turned on by the safing sensor, and the front sensor is turned on and G
The control unit detects sudden deceleration by the sensor and turns on the squib ignition switching element to supply energy to the squib.

Therefore, it is necessary to provide a structure capable of supplying sufficient electric power to the squib and the control unit even when the connection between the squib and the control unit and the battery is disconnected at the time of collision. In order to solve the above problem, the battery voltage is set to DC /
A circuit that charges a backup capacitor after boosting by a DC converter has been proposed.

[0005]

However, DC / D
When a C converter is used, D is used to cut off high frequency noise due to choppering of the switching element.
It is necessary to insert filters upstream and downstream of the C / DC converter, which is not only physically large, but also has economical problems. Further, it is necessary to take measures against heat generation of the DC / DC converter.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a power supply backup capable of maintaining a normal operation of a control unit even when a DC / DC converter is not used, when the battery is disconnected. It is intended to provide a circuit.

[0007]

According to a first aspect of the present invention, a power supply backup circuit includes a battery, a first backup capacitor having one terminal connected to one electrode of the battery, and a first backup capacitor. A first charging resistor in which one terminal is connected to one terminal and another terminal is connected to another terminal of the battery, and a second charging resistor is connected to one electrode of the battery. And a second backup capacitor in which one terminal is connected to the other terminal of the second charging resistor and the other terminal is connected to the other terminal of the battery. And a control unit connected between the other terminal of the first backup capacitor and the other terminal of the second charging resistor, and the control unit is connected to a predetermined threshold. A switching element controlled in a closed state by the control unit when the control unit is controlled to the open state is detected the following battery voltage predetermined threshold voltage by the control unit when it detects a voltage higher than the battery voltage, the
The control unit controls the battery voltage detection cycle to
Switching is performed in two stages according to the voltage of the battery.

[0008] A power supply backup circuit according to a second invention
Has one terminal on the battery and one electrode on the battery.
A first backup capacitor to be connected and a first
One terminal is connected to the other terminal of the backup capacitor.
The other terminal is connected to the other terminal of the battery.
Connected to the first charging resistor connected to one electrode of the battery
A second charging resistor to which one terminal is connected, and a second charging
One terminal is connected to the other terminal of the resistor and the other terminal
Is connected to the other terminal of the battery.
Connected in parallel with the backup capacitor and the battery
A control unit receiving power supply from the battery, the first back
The other terminal of the up capacitor and the second charging resistor
The control unit is connected between the other terminal and a predetermined threshold.
When a battery voltage equal to or higher than the value voltage is detected,
The control unit is controlled to be more open, and the control unit is below a predetermined threshold voltage.
Is closed by the control unit when the battery voltage is detected.
Anda switching element is controlled to the control unit
Changes the battery voltage detection cycle to the battery voltage.
It will be changed accordingly.

[0009]

In the power supply backup circuit according to the present invention , for example, when the connection between the battery and the control unit is disconnected and the control unit detects that the battery voltage has dropped, the switching element is turned on and the backup capacitor is connected in series. together, the voltage monitoring period according to the battery-voltage is changed in two stages or multiple stages.

[0010]

FIG. 1 is a circuit diagram of an embodiment in which a power supply backup circuit according to the present invention is applied to an on-vehicle microcomputer system. A negative electrode of a battery 101 is grounded to a vehicle body. The positive electrode of the battery 101 is connected to a power supply bus 106 via an accessory switch 102 and a backflow prevention diode 103 or an ignition switch 104 and a backflow prevention diode 105.

[0011] Note that the battery voltage detecting upstream resistor 109 and a downstream resistor 110 via the reverse current preventing diode 107 and 108 in order to detect the battery voltage V _B
Is connected. The power supply bus 106 is connected with a power supply bus voltage detection upstream resistance 111 and a downstream resistance 112 for detecting the power supply bus voltage V _S.

The positive electrode of the first backup capacitor 113 is connected to the power supply bus 106, and the negative electrode is grounded via the first charging resistor 114. The positive electrode of the second backup capacitor 115 is connected to the power supply bus 106 via the second charging resistor 116, and the negative electrode is directly grounded. The power bus 106 is further connected to a positive electrode of a microcomputer 118 via a regulator 117, and a negative electrode is grounded.

The negative electrode of the first backup capacitor 113 is connected to the collector of the switching transistor 119,
The positive electrode of the second backup capacitor 115 is connected to the emitter of the switching transistor element 119. The base of the switching transistor 119 is connected to the collector of the control transistor 120, and the emitter of the control transistor 120 is grounded.

The connection point between the battery voltage detection upstream resistance 109 and the downstream resistance 110 and the connection point between the power supply bus voltage detection upstream resistance 111 and the downstream resistance 112 are connected to the microcomputer 118 for detecting the battery voltage. Connected to the power bus voltage detection input terminal. The backup command output terminal output from the microcomputer 118 is connected to the base of the control transistor 120.

FIG. 2 is a flowchart of a main routine executed by the microcomputer 118, which is executed at relatively long intervals (for example, every 5 milliseconds). At step 21, a flag setting routine is executed, at step 22, a control voltage monitoring routine is executed, and at step 23, a backup reset routine is executed. Figure 3 is a detailed flowchart of the flag setting routine executed in step 21 of the main routine reads the battery voltage V _B and the power supply bus voltage V _S at step 211.

In step 212, the battery voltage V _B is set to the first
Is determined to be equal to or lower than the reference voltage V _B1 (for example, 8 V). When a negative determination is made in step 212, the process proceeds to step 213, where the flag F8 indicating that the battery voltage is equal to or lower than the lower limit battery voltage is reset, and this routine ends. If an affirmative determination is made in step 212, step 214
To determine whether the flag F8 is "1".

If a negative determination is made in step 214, the process proceeds to step 215, in which the flag F8 is set and the routine ends. If an affirmative determination is made in step 214, the process proceeds to step 216, in which a flag FDGDI indicating that the flag F8 is continuously "1" twice.
S is set to "1" and this routine ends.

FIG. 4 is a flowchart of a precision monitoring routine executed by the microcomputer 118. In the first embodiment, the period is shorter (for example, 500 microseconds) than the execution period of the main routine shown in FIG. It is executed as an interrupt routine for each. That is, the interrupt processing routine is executed in a short execution cycle to monitor when the battery voltage V _B falls below the first reference voltage V _B1, the voltage in a short time period.

In step 41, the flag FDGDIS is
Is "1", and this routine is immediately terminated if a negative determination is made. If an affirmative determination is made in step 41, the process proceeds to step 42, where it is determined whether the flag FBK indicating that the power supply is being backed up is "1". If a negative determination is made in step 42, step 4
Proceed to 3 to execute the backup set routine, and end this routine.

If an affirmative determination is made in step 42, the process proceeds to step 44, where a backup processing routine is executed, and this routine is terminated. Figure 5 is a detailed flowchart of a backup set routine executed at step 43 of the interrupt processing routine of FIG. 4, reads a battery voltage V _B at step 431.

[0021] The battery voltage V _B is the second in step 432
Is determined to be equal to or lower than the reference voltage V _B2 (for example, 6 V). If the determination is affirmative, that is, if the battery voltage V _B decreases to the second reference voltage V _B2 or lower, the process proceeds to step 433. At step 433, the flag FBK is set to "1", and at step 434, the flag FBK is output to make the control transistor 120 conductive.

Then, the switching transistor 119
Also become conductive, and the first backup capacitor 11
The third and second backup capacitors 115 are connected in series to supply power to the microcomputer 118. Next, in step 435, clears the timer A for determining the time until the start of monitoring the backup start after power bus voltage V _S, the process proceeds to step 436.

If a negative determination is made in step 432, the flow directly proceeds to step 436. In step 436, it clears the timer B defining the time until the battery voltage V _B to reset the recovery after switching transistor 119 terminates this routine.

FIG. 6 is a detailed flowchart of the backup processing routine executed in step 44 of the interrupt processing routine of FIG. 4. In step 441, it is determined whether or not timer A has passed 5 milliseconds after shifting to the backup state. . Ends this routine directly when a negative determination is made in step 441, it reads the power bus voltage V _S proceeds to step 442 when a positive determination is made.

In step 443, the power supply bus voltage V
It is determined whether _S is equal to or lower than the first power supply bus reference voltage V _S1 (for example, 5 V). When an affirmative determination is made in step 443, the process proceeds to step 444, where the power supply bus voltage V
Flag F indicating that _S is equal to or less than the first reference voltage V _S1
It is determined whether or not 5 is “1”.

When an affirmative determination is made in step 444, the process proceeds to step 445, in which a flag FF indicating that the voltage is equal to or lower than the first power supply bus reference voltage V _S1 is detected twice consecutively.
Set to "1" to DIS, the battery voltage V _B is clears the timer C to determine the time to allow recovery after squib ignition at step 446 the routine is terminated. If a negative determination is made in step 444, step 447
To set the flag F5 to "1" and end this routine.

If a negative determination is made in step 443, the flow advances to step 448 to reset the flag F5 and end this routine. FIG. 7 is a flowchart of a control voltage monitoring routine executed in step 22 of the main routine of FIG.
It is determined whether or not S is "1". If the determination is affirmative, the process proceeds to step 222.

[0028] The power supply bus voltage V _S in step 222 is the first
To determine whether the power supply is bus reference voltage V _S1 or more, the process proceeds to step 223 as if it is affirmative determination power bus voltage V _S is restored. In step 223, it is determined whether or not the timer C has elapsed for 3 seconds, that is, whether or not the time in which the squib ignition can be permitted after the recovery of the power supply bus voltage has elapsed. If the determination is affirmative, the flag FF is determined in step 224.
DIS is reset and this routine ends.

If a negative determination is made in step 221, step 222 or step 223, this routine is directly terminated. FIG. 8 is a flowchart of a backup reset routine executed in step 23 of the main routine of FIG. 2. In step 231, it is determined whether or not the microcomputer 118 is performing a self-diagnosis. Proceed to step 232.

In step 232, it is determined whether or not the flag FBK is "1", that is, whether or not the microcomputer 118 is outputting a backup command. If the determination is affirmative, the process proceeds to step 233. It determines whether or not the battery voltage V _B becomes a second reference voltage V _B2 above in step 233, the process proceeds to step 234 if it is affirmative determination.

At step 234, it is determined whether or not the timer B has elapsed for 5 milliseconds, that is, whether or not the time for releasing the backup after the recovery of the battery voltage has elapsed. If the determination is affirmative, the process proceeds to step 235. In step 235, the flag FBK indicating that backup is to be performed is reset, and in step 236, output is performed to release the backup state, and this routine ends.

If a negative determination is made in any of steps 231 to 234, this routine is directly terminated. In the first embodiment, the voltage monitoring cycle is switched between two stages depending on whether the battery voltage is equal to or higher than the first reference voltage. However, the monitoring cycle can be changed according to the battery voltage. is there.

FIG. 9 is a flowchart of a second main routine executed by the microcomputer 118 in the second embodiment. Steps 91 to 93 and step 4 are added to the main routine of FIG.
That is, after executing the flag setting routine of step 21, the process proceeds to step 91, and the variation ΔV _B of the battery voltage V _B is calculated by the following equation.

ΔV _B = V _BB −V _B where V _BB indicates the previous battery voltage. Step 92
Then, the battery voltage V _B is stored in V _BB in preparation for the next execution. In step 93, the execution cycle t of the second main routine is calculated as a function of ΔV _B.

T = t (ΔV _B ) Specifically, a function is used in which the execution cycle t becomes smaller as the variation ΔV _B of the battery voltage V _B becomes larger, that is, as the battery voltage decreases. For example, the execution period t can be a first-order decreasing function of the variation ΔV _B. Next, the precise monitoring routine shown in FIG. 4 is executed, then the control voltage monitoring routine is executed in step 22 and the backup reset routine is executed in step 23, and this routine is ended.

[0036]

According to the power supply backup circuit according to the present invention, when the control unit detects that the battery voltage has dropped, the switching element is turned on and the backup capacitor is connected in series, so that the drive power of the control unit is reduced. Can be secured.

Further, by changing the voltage monitoring cycle to two or more steps according to the battery voltage, it is possible to reliably detect a drop in the battery voltage and to shift to the backup state.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment.

FIG. 2 is a flowchart of a main routine.

FIG. 3 is a flowchart of a flag setting routine.

FIG. 4 is a flowchart of a precise monitoring routine.

FIG. 5 is a flowchart of a backup set routine.

FIG. 6 is a flowchart of a backup processing routine.

FIG. 7 is a flowchart of a control voltage monitoring routine.

FIG. 8 is a flowchart of a backup reset routine.

FIG. 9 is a flowchart of a second main routine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 ... Battery 113 ... 1st backup capacitor 115 ... 2nd backup capacitor 118 ... Microcomputer 119 ... Switching transistor 120 ... Controlling transistor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-193041 (JP, A) JP-A-3-2267 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02J 9/00-11/00 G01R 19/00-19/32 G01R 31/32-31/36

Claims (2)

(57) [Claims] 1. A battery, a first backup capacitor having one terminal connected to one electrode of the battery, and one terminal connected to another terminal of the first backup capacitor. A first charging resistor having one terminal connected to the other terminal of the battery; a second charging resistor having one terminal connected to one electrode of the battery; and the second charging. A second backup capacitor having one terminal connected to the other terminal of the resistor and the other terminal connected to the other terminal of the battery; and a battery connected in parallel with the battery. And a control unit that receives power supply from the other of the first backup capacitor and the other terminal of the second charging resistor, and the control unit is connected to a predetermined threshold value. A switching element that is controlled to an open state by the control unit when a battery voltage equal to or higher than a voltage is detected, and is controlled to a closed state by the control unit when the control unit detects a battery voltage equal to or lower than a predetermined threshold voltage. The power supply backup circuit comprising: a control unit , wherein the control unit changes a detection cycle of the battery voltage to a voltage of the battery.
Power backup circuit that switches between two stages
Road. 2. A battery having a first terminal connected to one terminal of one electrode of the battery.
1 backup capacitor and the other terminal of the first backup capacitor.
One terminal is connected and the other terminal is
A first charging resistor connected to the other one of the terminals; and a first charging resistor connected to one of the electrodes of the battery.
2 and one terminal is connected to the other terminal of the second charging resistor.
Connected to the other terminal of the battery.
A second backup capacitor connected to the battery ; a second backup capacitor connected in parallel to the battery;
A control unit receiving the supply, and another terminal of the first backup capacitor.
Connected to another terminal of the second charging resistor.
The control unit controls the battery power to be equal to or higher than a predetermined threshold voltage.
When the pressure is detected, it is controlled to the open state by the control unit.
The control unit controls the battery power below a predetermined threshold voltage.
When the pressure is detected, the controller is controlled to the closed state.
Power supply with switching element
A circuit, wherein the control unit changes a detection cycle of the battery voltage to a voltage of the battery.
A power supply backup circuit that changes accordingly.