JPH06324701A - Abnormality detection circuit for drive circuit - Google Patents

Abstract

(57) [Summary] [Construction] The optical insulation circuit 7 inputs the drive command 1, performs insulation by light, and then outputs it to the comparison circuit 11. DC voltage 3
Is input to the filter circuit 9 having a time constant equal to or longer than the response time of the driven object 5 via the optical isolation circuit 8. Comparison circuit 11
Then, based on the drive command 1 and the filter output 10, the logic determination circuit 12 and the voltage comparison circuit 13 determine the abnormality of the drive circuit 2 and the decrease of the DC voltage 3, and the drive circuit abnormality detection signal 14 and the DC voltage decrease detection signal 15 are detected. Output. [Effect] Since the abnormality detection circuit is provided with a filter whose time constant is equal to or longer than the response time of the drive target, an erroneous detection signal is output even if the DC voltage is temporarily reduced due to the mixing of electrical noise. There is nothing to do.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects whether a drive circuit and a DC voltage are normal in a drive device which controls a drive target by turning a switch on and off according to a DC voltage value output from the drive circuit. Regarding the circuit.

[0002]

2. Description of the Related Art As an example of the prior art, there is a "fail safe load control device using a microcomputer" disclosed in Japanese Patent Laid-Open No. 60-229103. In this prior art,
The operation of the oscillator is controlled by the pulse signal output from the microcomputer, and when the pulse signal from the microcomputer stops, the output of the oscillator stops.
A DC voltage is obtained based on the pulse signal output from the oscillator. Although the load is driven by this DC voltage, if the pulse signal that is the output of the oscillator stops, the DC voltage cannot be obtained and the driving of the load stops. However, there is no means for detecting that the DC voltage is no longer available or for detecting an abnormality in the load control device.

[0003]

The prior art of Japanese Patent Laid-Open No. 60-229103 discloses that when an abnormality occurs in the load control device and the DC voltage necessary for driving the load cannot be obtained, this abnormality is detected. However, it is easily conceivable to provide an abnormality detection circuit that detects a DC voltage and determines a decrease in the DC voltage when the level of the DC voltage becomes a predetermined value or less. However, although it is possible that electric noise is mixed in the DC voltage, in such a case, it is important that the abnormality detection circuit does not output an erroneous detection signal. An object of the present invention is to provide an abnormality detection circuit that does not output an erroneous detection signal even if the DC voltage is temporarily reduced due to the mixing of electrical noise.

[0004]

To achieve the above object, the present invention provides a filter having a time constant equal to or longer than the response time of a driven object, and inputs a DC voltage to a comparison circuit via this filter. An abnormality detection circuit is provided for outputting a detection signal of DC voltage drop from the comparison circuit when the voltage level becomes equal to or lower than a predetermined value.

[0005]

[Operation] With the time constant of the filter provided in the output stage of the drive circuit set to be equal to or longer than the response time of the drive target, the DC voltage drops in a time shorter than the time until the drive target in the normally excited state operates and becomes non-excited. Since the detection signal is not output at this time, the abnormality detection circuit does not output an erroneous detection signal even if the DC voltage is temporarily reduced due to electrical noise.

[0006]

Embodiments of the present invention will be described in detail below with reference to FIGS.

In FIG. 1, a drive circuit 2 receives a drive command 1 and outputs a DC voltage 3. The drive target 5 is controlled by the switch 4 which is turned on and off according to the level of the DC voltage 3. The abnormality detection circuit 6 is provided to detect an abnormality in the drive circuit 2 and a decrease in the DC voltage 3. The optical isolating circuit 7 inputs the drive command 1, performs insulation by light, and then outputs it to the comparison circuit 11. The DC voltage 3 is input to the filter circuit 9 via the optical insulation circuit 8. The comparison circuit 11 inputs the filter output 10 to the voltage comparison circuit 13 and compares the voltage level of the filter output 10 with a predetermined value set by the voltage comparison circuit 13. Drive command 1 is logic judgment circuit 1
2 is input to the voltage comparison circuit 13 and the logic of the output of the voltage comparison circuit 13 is compared with the logic of the drive command 1. In this way, the logic determination circuit 12 and the voltage comparison circuit 13 determine whether the drive circuit 2 is abnormal or the DC voltage 3 is reduced, and the drive circuit abnormality detection signal 14 and the DC voltage reduction detection signal 15 are output.

FIG. 2 shows a circuit diagram of an embodiment of the present invention.
The optical insulation circuits 7 and 8 convert the predetermined voltage V1 of the drive command 1 and the predetermined voltage V2 of the DC voltage 3 into a TTL voltage level V3 (5v), respectively. The optical insulation circuits 7 and 8 are composed of light emitting elements 7B and 8B on the input side and resistors 7C and 8C for obtaining a drive current of the light emitting element, and light receiving circuits 7A and 8A on the output side which receive an optical signal from the light emitting element. It is composed of. The filter circuit 9 is composed of, for example, a resistor 9A and a capacitor 9B. The filter circuit 9 is
Even if the DC voltage 3 is temporarily reduced, if the drive target 5 does not operate and is not in the non-excitation state, the time constant τ of the filter circuit 9 is set to the response of the drive target 5 in order to prevent the abnormality determination. It is set in advance as time ΔT or more.
Therefore, the detection signals 14 and 15 are not output when the DC voltage 3 drops in a time shorter than the time until the driven object 5 operates and enters the non-excitation state, and the DC voltage 3 temporarily drops due to electrical noise. However, the abnormality detection circuit 6 does not erroneously output the detection signals 14 and 15. here,
The detection signals 14 and 15 output from the abnormality detection circuit 6 are logic "0" to indicate normality and logic "1" to indicate abnormality.

The voltage comparison circuit 13 of the comparison circuit 11 is composed of a voltage comparator 13A and a NOT circuit 13B. If the DC voltage 3 via the optical isolation circuit 8 is higher than the reference voltage V _th of the voltage comparator 13A, the voltage comparison circuit 13 outputs a logic "0" indicating normality, and if it is lower than the reference voltage V _th , a logic "1". Is output to indicate an abnormality. The drive command 1 converted to the voltage level V3 of TTL is input to the logic determination circuit 12 via the output of the voltage comparison circuit 13 and the optical insulation circuit 7. The logical determination circuit 12 is a NOT circuit 12A and an exclusive OR circuit 12
It consists of B and. The exclusive OR circuit 12B outputs a logic "0" if the two inputs are the same logic signal, and outputs a logic "1" if the two inputs are different logic signals. That is, the output signal of the voltage comparison circuit 13 indicates normality only when the signal through the NOT circuit 12A and the drive command 1 through the optical isolation circuit 7 are the same logic signal, and abnormal when they are different logic signals. Will be shown.

The abnormality detection circuit 6 uses the drive circuit abnormality detection signal 1
4, Regarding the operation until the DC voltage drop detection signal 15 is output, when normal, when electric noise is mixed, when the drive circuit is abnormal,
Each case will be described separately. When the drive circuit is abnormal, in case 1 the drive command 1 is the predetermined voltage V1 but the DC voltage 3 drops, and in case 2 the drive command 1 is cut off, the DC voltage 3 is output. The explanation will be divided into two cases in which it is continued.

The operation of the abnormality detection circuit 6 in the normal state will be described with reference to FIG. First, the drive command 1 is the predetermined voltage V1.
When the DC voltage 3 is the predetermined voltage V2, the outputs of the optical isolation circuits 7 and 8 in FIG. 2 are logic "1", and the voltage level of the filter output 10 is V3 as shown in FIG. This is a "1" signal. The output of the voltage comparator 13A shown in FIG.
Since it is higher than the reference voltage _{Vth of} 3A, it becomes a logic "1". This signal is inverted by the NOT circuit 13B of FIG. 2, the output of the voltage comparison circuit 13 becomes a signal of logic "0", and the DC voltage drop detection signal 15 of FIG. 3 indicates normal.

In the logic judgment circuit 12 of FIG. 2, the signal of logic "1" obtained by inverting the output of the voltage comparison circuit 13 by the NOT circuit 12A and the signal of logic "1" of the drive command 1 via the optical isolation circuit 7 are exclusive. It is input to the logical OR circuit 12B. The output of the exclusive OR circuit 12B is a logic "0" because the inputs are the same logic signal, and the drive command detection signal 14 in FIG. 3 indicates normal. That is, the abnormality detection circuit 6 outputs the detection signals 14 and 15 indicating the normal state.

A case in which the drive command 1 is cut off in order to operate the drive target 5 and the DC voltage 3 drops will be described with reference to FIG. After the DC voltage 3 drops at time t1,
After time t2, the drive target 5 operates and is in a non-excitation state. That is, the response time of the driven object 5 in FIG. 1 is ΔT. Figure 3
As shown in, the filter output 10 gradually decreases,
This voltage level is the reference voltage V of the voltage comparator 13A in FIG.
_The time to reach _th is t3. The time constant τ of the filter circuit 9 of FIG. 2 is set so that the voltage level of the filter output 10 is longer than the time to reach V _th, the time to reach V _th than the response time of the driven object 5 [Delta] T long. This is because when the drive target 5 is in the excited state, the abnormality detection circuit 6
This is to prevent the determination of abnormality.

As shown in FIG. 3, when the voltage level of the filter output 10 reaches V _th , the output of the voltage comparator 13A of FIG. 2 becomes logic "0". The output of the voltage comparison circuit 13 via the NOT circuit 13B of FIG. 2 becomes a logic "1", and the DC voltage drop detection signal 15 of FIG. 3 indicates that the DC voltage has dropped.

In the logic decision circuit 12 of FIG. 2, the signal of logic “0” obtained by inverting the output of the voltage comparison circuit 13 by the NOT circuit 12A and the signal of logic “0” of the drive command 1 via the optical isolation circuit 7 are exclusive. It is input to the logical OR circuit 12B. The output of the exclusive OR circuit 12B becomes a logic "0" because the inputs are the same logic signal, and the drive circuit abnormality detection signal 14 in FIG. 3 indicates normal. That is, the abnormality detection circuit 6 only indicates that the DC voltage has dropped.

Next, with reference to FIG. 4, the operation of the abnormality detection circuit 6 in the case where the DC voltage 3 is temporarily reduced by the electrical noise and the DC voltage 3 is temporarily reduced will be described. When the time width of the decrease of the DC voltage 3 is shorter than the response time ΔT of the driven object 5, the voltage level of the filter output 10 does not reach the reference voltage V _th of the voltage comparator 13A in FIG. The output of 13 becomes logic "0", and the DC voltage drop detection signal 1 of FIG.
5 means normal.

In the logic judgment circuit 12 of FIG. 2, the signal of logic “1” obtained by inverting the output of the voltage comparison circuit 13 by the NOT circuit 12A and the signal of logic “1” of the drive command 1 via the optical isolation circuit 7 are exclusive. It is input to the logical OR circuit 12B. The output of the exclusive OR circuit 12B becomes a logic "0" because the inputs are the same logic signal, and the drive circuit abnormality detection signal 14 in FIG. 4 indicates normal. That is, the abnormality detection circuit 6 indicates a normal state.

When the drive circuit is abnormal, first of all, Case 1
Although the drive command 1 is the predetermined voltage V1, the DC voltage 3
The operation of the abnormality detection circuit 6 in the case of decrease of will be described with reference to FIG. When the DC voltage 3 decreases, the filter output 10 gradually decreases, and when this voltage level reaches the reference voltage V _th of the voltage comparator 13A in FIG. 2, the output of the voltage comparison circuit 13 becomes logic "1", The DC voltage drop detection signal 15 in FIG. 5 indicates an abnormality.

In the logic decision circuit 12 of FIG. 2, the signal of logic “0” obtained by inverting the output of the voltage comparison circuit 13 by the NOT circuit 12A and the signal of logic “1” of the drive command 1 via the optical isolation circuit 7 are exclusive. It is input to the logical OR circuit 12B. The output of the exclusive OR circuit 12B is a logic "1" because the inputs are different logic signals, and the drive circuit abnormality detection signal 14 in FIG. 5 indicates abnormality. That is, the abnormality detection circuit 6 shows both a drive circuit abnormality and a DC voltage drop.

Next, with reference to FIG. 6, the operation of the abnormality detection circuit 6 when the DC voltage 3 continues to be output although the drive command 1 is cut off in order to bring the drive target 5 into the non-excitation state Explain. Since the DC voltage 3 is the predetermined voltage V2, the filter output 10 does not decrease, and this voltage level is V3. Therefore, the voltage level of the filter output 10 does not reach the reference voltage V _th of the voltage comparator 13A of FIG. 2, the output of the voltage comparison circuit 13 becomes a logic “0”, and the DC voltage drop detection signal 15 of FIG. Will indicate normality.

In the logic decision circuit 12 of FIG. 2, the signal of logic “1” obtained by inverting the output of the voltage comparison circuit 13 by the NOT circuit 12A and the signal of logic “0” of the drive command 1 via the optical isolation circuit 7 are exclusive. It is input to the logical OR circuit 12B. Since the output of the exclusive OR circuit 12B is a logical signal having different inputs,
It becomes a logic "1", and the drive circuit abnormality detection signal 14 in FIG. 6 indicates an abnormality. That is, the abnormality detection circuit 6 indicates an abnormal state of the drive circuit.

As described above, in the abnormality detection circuit 6, the filter circuit 9 having a time constant equal to or longer than the response time ΔT of the driven object 5
Is provided. Therefore, even if electrical noise is mixed and the DC voltage 3 is temporarily reduced, it is not erroneously determined that the DC voltage is reduced. Further, since the optical isolation circuits 7 and 8 are provided in the signal input stage of the abnormality detection circuit 6, the drive circuit 2
The abnormality detection circuit 6 and the abnormality detection circuit 6 can be electrically insulated, and even if an abnormality occurs in the abnormality detection circuit 6, the abnormality does not affect the drive circuit 2.

[0023]

According to the present invention, an abnormality is detected by an abnormality detection circuit having a filter whose time constant is equal to or longer than the response time of the driven object, so that a temporary drop in the DC voltage due to the mixing of electrical noise occurs. Even if it occurs, if the drive target does not operate and it is in the excited state, it is not judged as abnormal. Further, even if an abnormality occurs in the abnormality detection circuit, the drive circuit is not affected because optical isolation is achieved at the signal input stage of the abnormality detection circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram embodying an embodiment of the present invention.

FIG. 3 is a time chart showing the operation of the abnormality detection circuit under normal conditions.

FIG. 4 is a time chart showing the operation of the abnormality detection circuit when electric noise is mixed.

FIG. 5 is a time chart showing the operation of the abnormality detection circuit of Case 1 when the drive circuit is abnormal.

FIG. 6 is a time chart showing the operation of the abnormality detection circuit in Case 2 when the drive circuit is abnormal.

[Explanation of symbols]

1 ... Drive command, 2 ... Drive circuit, 3 ... DC voltage, 4 ... Switch, 5 ... Drive target, 6 ... Abnormality detection circuit, 7, 8 ... Optical isolation circuit, 9 ... Filter circuit.

Claims (3)

[Claims] 1. A drive device in which a drive target is controlled by a drive circuit which inputs a drive command and outputs a direct current voltage, and a switch which is turned on and off according to a direct current voltage value output from the drive circuit. A filter with a time constant longer than the target response time is provided in the output stage of the drive circuit, and the DC voltage is input to the comparison circuit via the filter.When the DC voltage is below a predetermined value, the DC voltage drop detection signals are compared. An abnormality detection circuit for a drive circuit, comprising a voltage detection means for outputting from the circuit. 2. An abnormality determining means for detecting whether or not the drive circuit is normal by adding a drive instruction and determining the output state of the voltage detecting means based on the instruction according to claim 1. Abnormality detection circuit of the drive circuit. 3. An abnormality detection circuit for a drive circuit according to claim 1, wherein an optical insulation circuit is provided at the input stage of the filter of the voltage detecting means and the input stage of the comparison circuit for fetching the drive command.