JP2560811Y2 - Failure detection device for semiconductor sensor - Google Patents

Description

[Detailed description of the invention]

[0001]

[Industrial application fields]
A failure detection device for a semiconductor sensor that can reliably detect a short circuit or disconnection of a strain gauge.

[0002]

2. Description of the Related Art An airbag device for deploying an airbag in the event of a vehicle collision to protect an occupant detects the magnitude of the impact applied to the vehicle, and as shown in FIG. 2, changes in acceleration proportional to the impact. Is used.
The semiconductor sensor 1 has four strain gauges R1, R2, whose resistance values change according to the magnitude of the external force due to the piezoresistance effect.
R3 and R4 are connected to strain gauges R1 and R2 and R2 in series with each other.
3 and R4 are connected in parallel, a constant voltage Vc is applied from the constant voltage source 2 to the strain gauges R1 to R4 connected in a bridge, and the connection point P12 between the strain gauges R1 and R2 and the strain gauge R3
The magnitude of the acceleration is detected from the potential difference ΔV between the connection point P34 of the switch and R4. The resistance values of the strain gauges R1 to R4 when no external force is acting are all R, but they remain when the resistance values of the strain gauges R1 and R3 at diagonal positions change to R + ΔR due to acceleration. The resistance values of the strain gauges R2 and R4 at diagonal positions change to R-ΔR. For this reason, while the combined resistance of the semiconductor sensor 1 itself is kept at R, a potential difference of ΔRVc / R corresponding to the magnitude of the resistance change ΔR, that is, the magnitude of the acceleration is generated at the connection points P12 and P34,
The magnitude of the impact is determined.

[0003] By the way, these four strain gauges R1 to R1
The semiconductor sensor 1 in which R4 is bridge-connected has a strain gauge R
If any one of R1, R2, R3, and R4 is short-circuited or disconnected, the function as an acceleration sensor cannot be performed at all, so that this kind of failure needs to be monitored particularly closely. Therefore, conventionally, voltage monitoring window comparators 3 and 4 are respectively connected to a connection point P12 between the strain gauges R1 and R2 and a connection point P34 between the strain gauges R3 and R4, and the voltages at the connection points P12 and P34 are compared with the window comparator 3 respectively. , 4 respectively set the upper and lower reference voltages V
a, Vb, if any one of the connection points P12, P34 deviates from the fixed voltage range Vb-Va sandwiched between the upper and lower reference voltages Va, Vb, the failure notification circuit 5 outputs a lamp or a buzzer. Is operated to notify the occurrence of a failure.

[0004]

In the conventional semiconductor sensor failure detecting device 6, if only the strain gauge R1 is short-circuited, the voltage at the connection point P12 jumps up to Vc, and only the strain gauge R1 is connected. In the event of a disconnection, the potential of the connection point P12 drops to zero, so that any abnormality detection is performed by the window comparator 3. Similarly, when only the strain gauge R2 is short-circuited, the connection point P12
Is reduced to zero, or when only the strain gauge R2 is disconnected, the voltage at the connection point P12 jumps to Vc, so that any abnormality can be detected by the window comparator 3. Furthermore, when the strain gauges R1 and R4 or R2 and R3 at the diagonal positions are simultaneously short-circuited or disconnected, the window comparators 3 and 4 are similarly operated.
Abnormality is detected. However, if the strain gauges R1 and R2 or R3 and R4 in series with each other are disconnected at the same time, the potential of the connection point P12 or P34 becomes indefinite,
The window comparators 3 and 4 may not be able to detect anomalies, and therefore may not be able to monitor faults. Further, strain gauges R1 and R2 or R
If R3 and R4 are short-circuited at the same time, the constant-voltage source 2 is directly grounded via the short-circuited strain gauges R1 and R2 or R3 and R4. As a result, there is a problem that the constant voltage source 2 itself is adversely affected.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and comprises a semiconductor sensor comprising a strain gauge connected in a bridge, a fault detecting resistor connected in parallel to the semiconductor sensor, and a fault detecting device. A constant current source for driving the parallel connection circuit of the semiconductor sensor and the semiconductor sensor at a constant current; detecting a voltage applied to both ends of the failure detection resistor; and detecting the semiconductor when the voltage is out of a predetermined range. A first feature is to include a failure detecting means for notifying a failure of the sensor.

Further, in the present invention, the constant current source is connected to a grounding resistor for grounding the parallel connection circuit, and an inverting input terminal is connected to a connection point between the grounding resistor and the parallel connection circuit, so that the constant voltage source is not connected. A second feature is that it comprises an operational amplifier connected to an inverting input terminal and the parallel connection circuit is connected to an output terminal, and further comprises a pair of the fault detecting means connected to both ends of the fault detecting resistor. A voltage follower, a differential amplifier that differentially amplifies the outputs of the pair of voltage followers, a window comparator that compares and separates the output of the differential amplifier with reference to upper and lower thresholds that define the certain range, and A third feature is that an alarm circuit is provided for receiving the output of the window comparator and notifying the failure of the semiconductor sensor.

[0007]

According to the present invention, a fault detecting resistor is connected in parallel to a semiconductor sensor comprising a bridge-connected strain gauge, and a parallel connection circuit of the fault detecting resistor and the semiconductor sensor is driven at a constant current to provide a fault detecting resistor. Detects the voltage applied to both ends, and when this voltage goes out of the predetermined range,
By notifying the failure of the semiconductor sensor, a short circuit or a disconnection of the strain gauge is reliably detected regardless of the content of the failure.

[0008]

An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a circuit diagram showing an embodiment of the semiconductor sensor failure detection device according to the present invention.

FIG. 1 shows a failure detecting device 1 for a semiconductor sensor.
Reference numeral 1 denotes bridge-connected strain gauges R1, R2, R3.
A failure detection resistor r is connected in parallel to the semiconductor sensor 1 made of R4, and the parallel connection circuit 12 of the failure detection resistor r and the semiconductor sensor 1 is driven at a constant current to detect a voltage rI applied to both ends of the failure detection resistor r. When the voltage is out of a predetermined range, a failure of the semiconductor sensor 1 is notified. A constant current source 1 for supplying a constant current I to a parallel connection circuit 12 of the failure detection resistor r and the semiconductor sensor 1
Reference numeral 3 denotes a ground resistance R5 for grounding the parallel connection circuit 12, and an operational amplifier 14. The operational amplifier 14 has an inverting input terminal connected to the node between the ground resistor R5 and the parallel connection circuit 12, and a non-inverting input terminal connected to the constant voltage source 15. Further, the parallel connection circuit 12 is connected to the output terminal, and the potential at the connection point between the parallel connection circuit 12 and the ground resistor R5 is fixed to the output voltage Vc of the constant voltage source 15. Further, a pair of voltage followers 16 and 17 which are high input impedance buffers are connected to both ends of the failure detection resistor r, and the pair of voltage followers 16 and 17 are connected.
And a differential amplifier 18 for differentially amplifying the output, and a window comparator 19 for comparing and separating the output of the differential amplifier 18 with reference to upper and lower thresholds defining the certain range.
Further, an alarm circuit 20 which receives an output of the window comparator 19 and notifies a failure of the semiconductor sensor 1 constitutes a failure detecting means.

Incidentally, the semiconductor sensor 1 composed of the four bridge-connected strain gauges R1 to R4 is driven by a constant current, instead of being driven by a constant voltage as in the prior art. That is, the resistance Ra,
Since the constant voltage Vc divided by Rb is applied in a form backed up by the capacitor C, and the inverting input terminal is virtually short-circuited to the non-inverting input terminal, the connection point between the parallel connection circuit 12 and the ground resistor R5 is: The voltage is fixed at Vc. Therefore, the current I flowing into the ground resistor R5 is Vc /
R5 (= constant), and the current I is shunted by the semiconductor sensor 1 and the failure detection resistor r. The combined resistance value of the semiconductor sensor 1 obtained by combining the resistance values R of the individual strain gauges R1 to R4 is R, but here, the resistance value of the failure detection resistor r is also set to R. , The current flowing through the semiconductor sensor 1 and the current flowing through the failure detection resistor r are both I / 2.

On the other hand, both ends of the failure detecting resistor r are connected to a differential amplifier 18 via voltage followers 16 and 17, and the voltage followers 16 and 17 are connected to the output of operational amplifiers 16a and 17a serving as nuclei. Since the terminal is directly connected to the inverting input terminal, the input voltage applied to the non-inverting input terminal is amplified with an amplification factor of 1, and is directly taken out as an output voltage. Since the input impedances of the operational amplifiers 16a and 17a are very large, a part of the current I does not leak to the non-inverting input terminal thereof. Does not collapse. One Voltage Follower 1
6 is connected to a differential amplifier 18 via an input resistor r1.
, And the non-inverting input terminal is grounded via a resistor r2. The output terminal of the other voltage follower 17 is connected to the inverting input terminal of the differential amplifier 18 via the input resistor r3, and the inverting input terminal is connected to the output terminal via the feedback resistor r4. .
Since the non-inverting input terminal and the inverting input terminal of the differential amplifier 18 are virtually short-circuited, the applied voltages of both input terminals are equal,
Therefore, r2v1 / (r1 + r2) = (r3v3 + r4v2) / (r3 + r4) holds. Therefore, r1 = r3 = Rs, r2 = r4 =
By setting the condition of Rf, v3 = (v1−v2) Rs / Rf. That is, the voltage rI (= v1−v2) applied to both ends of the failure detection resistor r is amplified by the differential amplifier 18 with the gain Rs / Rf.

The output voltage v3 of the differential amplifier 18 is supplied to a window comparator 19 in which a pair of voltage comparators 19a and 19b are connected in parallel, and it is determined whether the output voltage v3 is in an area between upper and lower thresholds Ea and Eb. You. The threshold value Ea used as a comparison reference by the upper limit detection voltage comparator 19a is a resistance r
5, r6, the power supply voltage is divided and given, and the threshold Eb is used as a comparison reference by the lower-limit detection voltage comparator 19b.
Is supplied by dividing the power supply voltage by the resistors r7 and r8. However, for the threshold values Ea and Eb, a relationship of Eb (0.45 rIRs / Rf) <Ea (0.55 rIRs / Rf) is set. Therefore, when the output v3 of the differential amplifier 18 is sandwiched between the upper and lower thresholds Ea and Eb, that is, if Eb <v3 <Ea, the outputs of the voltage comparators 19a and 19b are both at the high level. It is. An alarm circuit 20 subsequent to the window comparator 19 includes a pull-up resistor r9, a Schmitt trigger circuit 20a, and an alarm lamp 20b.
The output terminals of the voltage comparators 19a and 19b are connected to the input terminal of the Schmitt trigger circuit 20a while being pulled up by a DC power supply by a pull-up resistor r9. For this reason,
When both the outputs of the voltage comparators 19a and 19b are at the high level, the output of the Schmitt trigger circuit 20a also becomes the high level, and the alarm lamp 20a connected between the Schmitt trigger circuit 20a and the DC power supply is turned off and abnormal. Indicates that there is no

If any one of the strain gauges R1 and R2 is short-circuited, the combined resistance of the semiconductor sensor 1 becomes 2
The current drops to R / 3, and the current flowing through the fault detection resistor r drops from I / 2 at normal time to 2I / 5. Therefore, the voltage comparator 19 for detecting the lower limit in the window comparator 19
The output of b is inverted to low level, and the output terminal of the Schmitt trigger circuit 20a also switches to low level. As a result, the power supply current flows through the alarm lamp 20b, and the alarm lamp 2
When 0b lights up, the occurrence of a failure is warned. If any one of the strain gauges R1 to R4 is disconnected, the combined resistance of the semiconductor sensor 1 increases to 2R, and the current flowing through the failure detection resistor r changes from I / 2 at normal time to 2I / 3. Increase. Therefore, the output of the voltage comparator 19a for detecting the upper limit in the window comparator 19 is inverted to low level, and the output terminal of the Schmitt trigger circuit 20a is also switched to low level. As a result, the power supply current flows through the warning lamp 20b, and the occurrence of a failure is warned by the lit warning lamp 20b.

Further, if the strain gauges R1 and R2 or R
When both R2 and R3 are short-circuited, the combined resistance of the semiconductor sensor 1 becomes zero, so that no current flows through the failure detection resistor r, and the output of the lower limit detection voltage comparator 19b in the window comparator 19 becomes low level. Flip to As a result, the output terminal of the Schmitt trigger circuit 20a is also switched to a low level, and the alarm lamp 20b is turned on to warn of the occurrence of a failure. Also, the strain gauges R1 and R2 or R3 and R2
When the wires 4 are both disconnected, the combined resistance of the semiconductor sensor 1 increases to 2R. As a result, the current flowing through the failure detection resistor r increases from I / 2 at normal time to 2I / 3, and the occurrence of the failure is warned by the lit alarm lamp 20a as described above.

Furthermore, the strain gauges R1 and R
When both 4 (or R2 and R3) are short-circuited, the combined resistance of the semiconductor sensor 1 decreases to R / 2. Therefore, the current flowing through the failure detection resistor r is changed from I / 2 at normal time to I
/ 3. As a result, the window comparator 1
The output of the voltage comparator 19a for detecting the lower limit in 9 is inverted to a low level, and the occurrence of a failure is warned by the lit alarm lamp 20a. When the strain gauges R1 and R4 or R2 and R3 at the diagonal positions are both disconnected, the semiconductor sensor 1
Becomes infinite, and no current flows there. For this reason, the current flowing through the failure detection resistor r increases from I / 2 at normal time to I, and the window comparator 19
When the output of the upper limit detection voltage comparator 19a is inverted to a low level, the alarm lamp 20a is turned on.

As described above, in the semiconductor sensor failure detecting device 11, the combined resistance of the semiconductor sensor 1 composed of the bridge-connected strain gauges R1 to R4 is constant irrespective of the sensor input. Since a constant current I is always supplied to the parallel connection circuit 12 of the semiconductor sensor 1, a change in the combined resistance of the semiconductor sensor 1 caused when one or two or more strain gauges R1 to R4 are disconnected or short-circuited is
A conventional constant voltage that can be reliably detected based on a change in the current flowing through the failure detection resistor r, that is, a change in the voltage (v1−v2) applied across the failure detection resistor r, and the diagnosis becomes confused depending on the failure content. Unlike the driving method, the short circuit and the disconnection of the strain gauges R1 to R4 can always be reliably detected irrespective of the number of the failure points, whereby the failure of the semiconductor sensor 1 may lead to a serious accident. By applying this method to the like, dangerous buds that lead to the occurrence of an accident can be eliminated at an early stage.

The operational amplifier 1 used for the constant current source 13
In No. 4, since the inverting input terminal and the non-inverting input terminal are in a virtual short-circuit state, the connection point between the parallel connection circuit 12 and the ground resistor R5 is maintained at the same voltage Vc as the constant voltage source 15 connected to the non-inverting input terminal. As a result, the current I flowing through the parallel connection circuit 12 of the failure detection resistor r and the semiconductor sensor 1 can be
The current value Vc / R5 obtained by dividing the voltage Vc of the constant voltage source 15 by the resistance value of the ground resistor R5 can be fixed, and the parallel connection circuit 12 can be driven at a constant current with a stable current.

Furthermore, since the voltage followers 16 and 17 are connected as high input impedance buffers to both ends of the failure detecting resistor r, current leakage can be almost completely ignored, and a constant current driving method is adopted. There is no need to worry about the leakage current from the parallel connection circuit 12 between the failure detection resistor r and the semiconductor sensor 1 which is an important key above.
Furthermore, since the outputs of the pair of voltage followers 16 and 17 are differentially amplified by the differential amplifier 18 and then compared and separated by the window comparator 19, the separation accuracy in the window comparator 19 is extremely high, and therefore flows through the failure detecting resistor r. The change in the current is detected by the failure detection resistor r.
Can be accurately and reliably detected as a change in the voltage applied to both ends of the device.

[0019]

As described above, according to the present invention, a fault detection resistor is connected in parallel to a semiconductor sensor comprising a bridge-connected strain gauge, and a parallel connection circuit of the fault detection resistor and the semiconductor sensor is connected to a constant current. It is configured to detect the voltage applied to both ends of the failure detection resistor and to notify the failure of the semiconductor sensor when this voltage is out of a predetermined range. Since the combined resistance of the semiconductor sensor is constant irrespective of the sensor input, and a constant current is always supplied to the parallel connection circuit of the failure detection resistor and the semiconductor sensor, one or more strain gauges are disconnected or short-circuited. The change in the combined resistance of the semiconductor sensor caused by the change is determined by the change in the current flowing through the fault detection resistor, that is, the change in the voltage across the fault detection resistor. Unlike the conventional constant-voltage drive method, which can actually detect and cause the diagnosis to be lost depending on the content of the fault, whether the strain gauge is short-circuited or disconnected, or whether there is only one However, it can always be detected reliably, and by applying it to devices where the failure of the semiconductor sensor can lead to a serious accident, dangerous buds that lead to the occurrence of an accident can be eliminated early. And so on.

Further, according to the present invention, a constant current source is connected to a grounding resistor for grounding a parallel connection circuit, and an inverting input terminal is connected to a connection point between the grounding resistor and the parallel connection circuit. Connected to the terminal, the output terminal is configured with the operational amplifier connected to the parallel connection circuit, the operational amplifier having a large gain, the inverting input terminal and the non-inverting input terminal are in a virtual short circuit state, the parallel connection resistance and The connection point of the ground resistor can be maintained at the same voltage as that of the constant voltage source connected to the non-inverting input terminal, so that the current flowing through the parallel connection circuit of the fault detection resistor and the semiconductor sensor is reduced to the voltage of the constant voltage source. Can be fixed to the current value obtained by dividing the resistance value by the resistance value of the ground resistance, and the parallel connection circuit can be driven at a constant current with a stable current.

Still further, according to the present invention, a failure detecting means includes a pair of voltage followers connected to both ends of a failure detecting resistor, a differential amplifier for differentially amplifying the outputs of the pair of voltage followers, and a differential amplifier. A window comparator that compares and separates the output of the amplifier with reference to upper and lower thresholds that define the certain range, and an alarm circuit that receives the output of the window comparator and notifies the semiconductor sensor of a failure. Even if there is concern about the effect of leakage current from the parallel connection circuit of the fault detection resistor and the semiconductor sensor on the fault detection accuracy, which is an important key in adopting the fault detection resistor, as a high input impedance buffer at both ends of the fault detection resistor Since the voltage follower is connected, current leakage can be almost completely ignored, and what is the fault detection accuracy? In addition, the output of a pair of voltage followers is differentially amplified by a differential amplifier and then compared and separated by a window comparator, so that the separation accuracy of the window comparator is extremely high. Changes in
The change in the voltage applied to both ends of the failure detection resistor can be detected accurately and reliably.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a semiconductor sensor failure detection device according to the present invention.

FIG. 2 is a circuit diagram illustrating an example of a conventional semiconductor sensor failure detection device.

[Explanation of symbols]

 R1 to R4 Strain gauge r Failure detection resistor 11 Semiconductor sensor failure detection device 12 Parallel connection circuit 13 Constant current source 16, 17 Failure detection means (voltage follower) 18 Failure detection means (differential amplifier) 19 Failure detection means (window) Comparator) 20 Failure detection means (alarm circuit)

Claims (3)

(57) [Scope of request for utility model registration] 1. A semiconductor sensor comprising a strain gauge connected in a bridge, a failure detection resistor connected in parallel to the semiconductor sensor, and a constant current for driving a parallel connection circuit of the failure detection resistor and the semiconductor sensor in a constant current. And a failure detection means for detecting a voltage applied to both ends of the failure detection resistor, and reporting a failure of the semiconductor sensor when the voltage is out of a predetermined range. Failure detection device for semiconductor sensors. 2. The constant current source has a grounding resistor for grounding the parallel connection circuit, an inverting input terminal connected to a connection point between the grounding resistor and the parallel connection circuit, and a constant voltage source connected to a non-inverting input terminal. 2. The failure detecting device for a semiconductor sensor according to claim 1, further comprising an operational amplifier connected to said output terminal and connected to said parallel connection circuit. 3. The failure detection means includes: a pair of voltage followers connected to both ends of the failure detection resistor; a differential amplifier for differentially amplifying outputs of the pair of voltage followers; and an output of the differential amplifier. 2. A window comparator for comparing and classifying the semiconductor sensor with reference to upper and lower thresholds that define the predetermined range, and an alarm circuit that receives an output of the window comparator and notifies a failure of the semiconductor sensor. Semiconductor sensor failure detection device.