JP5017179B2 - Digital output circuit with failure detection function - Google Patents

Description

  The present invention relates to a digital output circuit that constitutes a highly safe system that requires fail-safety, and more particularly to a digital output circuit that can detect a failure with a simple configuration without erroneous output to a load.

  In railway signal control systems that require high safety, it is indispensable to realize a fail-safe configuration that transitions the entire system to a safer state even if an unexpected situation such as a failure of the components that make up the system occurs. . Even in a digital output circuit that is used in a railway signal control system and plays a role of actually controlling field devices such as traffic lights and switches, it is not allowed to operate on the dangerous side due to a component failure. In order to achieve this fail-safety in the digital output circuit, the entire system is constructed so that the on-side output is on the dangerous side and the off-side output is on the safe side, and the components that make up the digital output circuit fail. In this case, it is necessary to configure the circuit so that the output is turned off.

  As means for realizing such a digital output circuit, a configuration in which two switch elements are connected in series is generally used. In a digital output circuit having a configuration in which two switch elements are connected in series, even if one switch element is short-circuited, a dangerous operation such as an erroneous ON output is not caused as long as the other switch elements are normal. However, if this short circuit failure of the switch element cannot be detected and the failure is made latent, an error is output when the other normal switch element has a short circuit failure. For this reason, in such a digital output circuit, a failure detection circuit is generally provided in each switch element, and failure detection is generally prevented by performing failure detection at all times.

  An example of this failure detection method is shown in FIG. In the digital output circuit of FIG. 3, a voltage detection circuit is connected to the output side of each of the two switch elements. In the case of detecting a failure of the switch element 2 in this circuit configuration, the switch element 2 is turned on and off while the switch element 3 is turned off. If the voltage detection circuit 4 detects a voltage with the switch element 2 turned on, and the voltage detection circuit 4 does not detect a voltage with the switch element 2 turned off, the switch element 2 is determined to be normal, and other states Is judged abnormal. The failure detection of the switch element 3 is performed at the timing when the digital output circuit is controlled to be turned on. When the digital output circuit is turned on, the switch element 2 and the switch element 3 are not turned on at the same time, but are turned on in the order of the switch element 2 and the switch element 3. If the voltage detection circuit 5 detects a voltage while the switch element 2 is on and the switch element 3 is off, it is judged abnormal, and if no voltage is detected, it is judged normal.

  However, in this method, the failure detection of the switch element 3 can be performed only at the timing when the digital output circuit is turned on, and the failure of the switch element 3 is made latent in an application where the digital output circuit is kept off for a long time. There is a risk that

  An object of the present invention is to provide a digital output circuit that has a simple configuration, does not erroneously output to a load, and can detect a failure of a switch element at an arbitrary timing.

Digital output circuit of the present invention is to connect two switching elements in series, a digital output circuit you apply a DC voltage to a load, the load side of the output end of the switching element, a diode and a DC power supply and A failure detection circuit having a voltage detection circuit is connected , and the diode has one end connected to the middle of two switch elements and the other end connected to the load; and It is characterized by comprising a reverse voltage application preventing diode connected between an output terminal on the load side and the load .
Also, the digital output circuit of the present invention, three or more switching elements may be connected in series.

  The digital output circuit of the present invention has a simple configuration, does not erroneously output to the load, and can detect a failure of the switch element at an arbitrary timing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing the configuration of the present invention. In FIG. 1, the digital output circuit includes two switch elements 2 and 3 connected in series, a voltage detection circuit 4 connected to the output terminal of the switch element 2, and a voltage connected to the output terminal of the switch element 3. It comprises a detection circuit 5, a DC power source 6, a diode 7 connected between the switch elements 2 and 3, and a diode 8 for preventing reverse voltage application to the load.

  Fault detection of the switch element 2 is performed with the switch element 3 turned off. When the switch element 2 is turned on with the switch element 3 turned off, it is determined that the voltage detection circuit 4 is normal if the voltage is detected, and is abnormal if the voltage is not detected. On the contrary, when the switch element 2 is turned off, the voltage detection circuit 4 is abnormal if the voltage is detected, and is normal if the voltage is not detected.

  Fault detection of the switch element 3 is performed with the switch element 2 turned off. When the switch element 3 is turned on in this state, a closed circuit including the power source 6, the diode 7, the switch element 3, and the voltage detection circuit 5 is established. If the voltage detection circuit 5 detects a voltage by this closed circuit, the switch element 3 is normal, and if the voltage is not detected, the switch element 3 is abnormal. Conversely, when the switch element 3 is turned off, the switch element 3 is abnormal if the voltage detection circuit 5 detects the voltage, and the switch element 3 is normal if the voltage is not detected.

  In a state in which the switch element 2 is turned off, a negative voltage is applied to the output terminal of the switch element 3 by the power supply 6, but is not applied to the load by the diode 8 and does not affect the load.

  FIG. 2 is an electronic circuit diagram of a digital output circuit using the present invention. In the circuit of FIG. 2, the output to the load 9 is controlled by turning on and off the switch elements 2 and 3. This switch element may be a semiconductor or a mechanical contact type relay.

  The failure detection of the switch elements 2 and 3 is performed according to the following procedure. First, the switch elements 2 and 3 and the failure detection switch element 14 are controlled to be off. At this time, if the switch element 2 has a short-circuit failure, a current flows through the resistor 11 and the photocoupler 10, the terminal 17 becomes the same potential as GND (hereinafter referred to as LOW level), and failure detection is performed. Is possible. Next, the switch element 2 is turned on while the switch element 3 is turned off. If the switch element 2 has an open failure, no current flows through the photocoupler 10, so that the terminal 17 is not at the LOW level and is determined to be in failure.

  After confirming the soundness of the switch element 2 by the above procedure, the failure of the switch element 3 is detected. In a state where the switch elements 2 and 3 are turned off, the failure detection switch element 14 is turned on. If the switch element 3 has a short circuit failure, a current flows from the power source 6 to the diode 7, the switch element 3, the resistor 13, the photocoupler 12, and the switch element 14. As a result of the current flowing through the photocoupler 12, the terminal 18 becomes the LOW level, and the failure can be detected. At this time, a negative voltage is applied to the output terminal of the switch element 3 by the power supply 6 but is interrupted by the diode 8 so that the load is not affected. Next, the switch element 3 is turned on while the switch element 2 is turned off. If the switch element 3 has an open failure, no current flows through the photocoupler 12, so that the terminal 18 does not go to the LOW level and the failure can be detected.

  The failure detection of the switch elements 2 and 3 can be realized by the above procedure. In addition, there is no erroneous output to the load during this failure detection.

  When failure detection is not performed, the switch element 14 is turned off. At this time, the resistor 13, the photocoupler 12, the resistor 16, and the diode 15 function as an output readback circuit that captures the output of the digital output circuit. If the ratio of the resistor 13 and the resistor 16 is set appropriately, the current flowing through the photocoupler 12 can be kept constant even if the voltages of the power supply 1 and the power supply 6 are different, and the circuit design becomes easy.

  In the above embodiment, an example in which the two switch elements 2 and 3 are connected in series has been described. However, the number of switch elements connected in series is not limited to two, and the same applies to the case of three or more switch elements. The present invention can be applied to.

FIG. 1 is a circuit diagram showing the configuration of the present invention. FIG. 2 is an electronic circuit diagram showing an embodiment of the present invention. FIG. 3 is a general digital output circuit diagram with a failure detection function.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Switch element 3 Switch element 4 Voltage detection circuit 5 Voltage detection circuit 6 DC power supply 7 Diode 8 Diode 9 Load 10 Photocoupler 11 Resistance
12 Photocoupler 13 Resistor 14 Switch element 15 Diode 16 Resistor 17 Terminal 18 Terminal

Claims (2)

Connect the two switch elements in series, a digital output circuit you apply a DC voltage to a load, the load side of the output end of the switching element, and a diode and a DC power supply and the voltage detection circuit failure A detection circuit is connected , and the diode has one end connected in the middle of the two switch elements and the other end connected to the load, and an output end on the load side of the switch element and the load A digital output circuit comprising a diode for preventing reverse voltage application connected between and . In the digital output circuit according to claim 1, the digital output circuit three or more switch elements, characterized in that it is connected to the series.

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