JP2006208153A - Switch circuit with diagnostic functions - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switch circuit with diagnostic functions, using an FET switch in place of a relay and being capable of normally monitoring the state of the switch. <P>SOLUTION: This switch circuit, connected between the supply side of direct current voltage and the receiving side for receiving the direct current voltage, comprises an FET switch part having two lines of two switches which are connected in series; a control circuit which turns on the FET switch part for both the lines at normal times and which turns off the FET switching part for each line at diagnosis; a resistance for diagnosis connected between the FETs which are connected in series and GND; and a diagnostic circuit which recognizes the operation state of the control circuit and detects the voltage level of the resistance for diagnosis and which determines it as being normal, when detecting the voltage applied to the FET switching part at a normal time, and when detecting 0V at diagnostic time respectively, and determines it as being abnormal, when detecting voltage levels other than this. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a switch circuit with a diagnosis function capable of performing operation diagnosis during operation.

  In a circuit for supplying voltage to a load, etc., a switch circuit using a contact switch is provided between the supply voltage and the load, and it is normally on (ON), but in rare emergency situations, etc. Some are in an off state. In such a switch circuit, when it should be turned off in an emergency situation, etc., if the switch is stuck in the ON state and cannot be switched to the OFF state, the abnormality is detected in advance and an appropriate countermeasure is taken. Some have a self-diagnostic function for taking care of.

  Prior art documents related to this type of switch circuit include the following.

Japanese Patent Laying-Open No. 2005-3522 (paragraphs 0022 to 0039, FIGS. 1 to 5)

  FIG. 3 is a block diagram showing an example of a conventional switch circuit equivalent to the diagnostic circuit described in Patent Document 1. In FIG. This switch circuit includes two sets of c-contact relays (hereinafter simply referred to as relays) 1 and 2, a control circuit 3 for controlling each relay, resistors R1 and R2 connected to the b-contact of each relay, and this resistor R1. It comprises a diagnostic circuit 4 for diagnosing the voltage level generated at R2. The diagnostic circuit 4 is configured to operate in synchronization with the operation of the control circuit 3.

  This switch circuit is inserted and connected between the load 11 and the high-voltage side of the DC power supply 10 having a voltage E volts (hereinafter, V is expressed as V). The low-voltage side of the DC power supply 10, the other end of the load 11, and the other ends of the resistors R1 and R2 are connected in common.

In such a configuration, normally, the c contacts (common contacts) of the relays 1 and 2 are both turned on to the a contact side under the control of the control circuit 3. At the time of diagnosis, the relays 1 and 2 are turned on to the b contact side one by one under the control of the control circuit 3. The relays 1 and 2 are not turned ON to the b contact side at the same time.
If the switch circuit is normal, the diagnostic circuit 4 can observe a predetermined voltage generated in the resistor (R1 or R2) connected to the relay side when the a contact side is ON and 0V, and when the b contact side is ON. The diagnostic circuit 4 diagnoses that the relay is abnormal if the predetermined voltage value generated in the resistance is abnormal, and performs corresponding measures such as display and alarm output.

However, such a conventional switch circuit has the following problems.
(1) The use of relays has the following disadvantages.
・ Mounting area and volume are large, chattering occurs, and power consumption is large.
-It has a lifetime, a narrow operating temperature range, and low reliability.
・ Operation speed is slow.
·Price is high.
(2) Although it can be diagnosed that the relay operates, it is unclear whether or not the b contact side is normally touched.

  An object of the present invention is to solve such a problem. A switch circuit with a diagnostic function which can solve the above problem by using an FET switch instead of a relay and can always monitor the state of the switch is provided. It is to provide.

In order to achieve such a problem, the invention according to claim 1 of the present invention provides:
A switch circuit connected between a DC voltage supply side and a reception side receiving the DC voltage,
An FET switch unit having two systems of two FET switches connected in series;
A control circuit for turning on the FET switch part in both normal systems and turning off in one system unit at the time of diagnosis,
A diagnostic resistor connected between the series-connected FETs and GND;
Recognizing the operating state of the control circuit and detecting the voltage level of the diagnostic resistor, 0V is detected when the voltage applied to the FET switch section is detected during normal times and during diagnosis. A diagnostic circuit is provided that determines that each time is normal and determines that it is abnormal when any other voltage level is detected.

  With such a configuration, the following effects are exhibited. That is, the mounting area and volume are small, chattering does not occur, power consumption is small, life is long, the operating temperature range is wide, and reliability is high. It is also inexpensive and has a high operating speed. Furthermore, the state of the switch can be constantly monitored.

The invention described in claim 2
In the switch circuit with a diagnostic function according to claim 1,
Each of the two FET switches connected in series is an N-channel MOSFET in which source electrodes are connected to each other, and a P-channel MOSFET.
An insulating photoMOS driver is connected between the two systems of the MOSFET and the control circuit.

  According to such a configuration, the direction of the existing diode existing in the FET can be reversed, current wraparound can be eliminated, and the diagnostic detection rate can be increased.

In this case, as in claim 3, a photo MOS relay in which the FET switch unit and the photo MOS driver are integrated can be used.
According to a fourth aspect of the present invention, the connection reference for the diagnostic resistor can be connected to the voltage supply side instead of the GND.
According to a fifth aspect of the present invention, the diagnosis resistor can be configured to be divided into a plurality of resistors. As a result, the operating voltage of the diagnostic circuit can be reduced.

As is apparent from the above description, the present invention has the following effects.
Small mounting area and volume, no chattering, low power consumption, long life, wide temperature range, and high reliability. In addition, it is inexpensive, has a high operating speed, and can constantly monitor the state of the switch.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a switch circuit with a diagnostic function according to the present invention. 1 is different from FIG. 3 in the FET switch portion. The description of the same components as those in FIG. 3 is omitted.

The FET switch unit replaces the conventional relays 1 and 2 and has two systems of two FET switches connected in series. One set is two switches SW11 and SW12 connected in series, and the other set is two switches SW21 and SW22 connected in series. The two sets of switches are connected in parallel.
The resistor R1 is connected to the common connection point of the switches SW11 and SW12, and the resistor R2 is connected to the common connection point of the switches SW21 and SW22.

The operation in such a configuration will be described next. The group of switches SW11 and SW12 and the group of switches SW21 and SW22 are both ON in normal times. At this time, the voltage levels of the resistors R1 and R2 are measured by the diagnostic circuit 4.
At the time of diagnosis, one of the switches SW11 and SW12 or SW21 and SW22 is turned off. The voltage level of the resistor (R1 or R2) connected to the switch that is turned OFF becomes 0V, and is observed by the diagnostic circuit 4.

  If a voltage level other than the above is observed when the switch is fixed to ON or OFF, this means that a failure has occurred, and the diagnostic circuit 4 can detect the occurrence of the failure from the measured voltage.

  The present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.

  For example, it is good also as a structure as shown in FIG. A difference from the configuration of FIG. 1 is that a photo MOS driver is used to insulate the switch unit from the control circuit 3.

In this case, the switches SW11 and SW12 are N-type MOSFETs, and SW21 and SW22 are also N-type MOSFETs. Note that all switches may be P-type, or switches SW11 and SW12 may be N-type, and SW21 and SW22 may be P-type or vice versa.
The series-connected FETs (SW11 and SW12, and SW21 and SW22) are connected to each other so that the directions of the source and drain are reversed, so that the direction of the existing diode in the FET is reversed. . As a result, current wraparound can be eliminated and the diagnostic detection rate can be increased.
Further, the operating voltage of the diagnostic circuit 4 can be reduced by dividing each of the diagnostic resistors into two as shown in the figure.

1 and 2 is not limited to GND, and may be connected to the voltage supply side, for example.
In the embodiment, an example in which a DC power source is connected to the input of the switch circuit of the present invention and a load is connected to the output is used. However, the present invention is not limited to this example. The voltage or output may be a circuit or device that receives the DC voltage.

It is a block diagram which shows one Example of the switch circuit with a diagnostic function based on this invention. It is a block diagram which shows the other Example of this invention. It is a block diagram which shows an example of the conventional switch circuit.

Explanation of symbols

3 Control Circuit 4 Diagnostic Circuit 10 DC Power Supply 11 Load 7, 8 Photo MOS Driver SW11, SW12, SW21, SW22 Switch R1, R2 Resistance R11, R12, R21, R22 Resistance

Claims (5)

A switch circuit connected between a voltage supply side and a reception side receiving the voltage,
An FET switch unit having two systems of two FET switches connected in series;
A control circuit for turning on the FET switch part in both normal systems and turning off in one system unit at the time of diagnosis,
A diagnostic resistor connected between the series-connected FETs and GND;
Recognizing the operating state of the control circuit and detecting the voltage level of the diagnostic resistor, 0V is detected when the voltage applied to the FET switch section is detected during normal times and during diagnosis. A switch circuit with a diagnosis function, characterized in that a diagnosis circuit is provided that determines that each time is normal and determines that it is abnormal when a voltage level other than that is detected, so that operation diagnosis during operation is possible. In the switch circuit with a diagnostic function according to claim 1,
Each of the two FET switches connected in series is an N channel MOSFET in which source electrodes are connected to each other, or a P channel MOSFET.
A switch circuit with a diagnostic function, wherein an insulating photoMOS driver is connected between the two systems of the MOSFET and the control circuit.   3. The switch circuit with a diagnostic function according to claim 2, wherein a photo MOS relay in which the FET switch unit and the photo MOS driver are integrated is used.   4. The switch circuit with a diagnostic function according to claim 1, wherein a connection reference of the diagnostic resistor is connected not to the GND but to the supply side of the voltage. 5. 5. The diagnostic function according to claim 1, wherein the diagnostic resistor is configured to be divided into a plurality of voltages so that an operating voltage of the diagnostic circuit can be lowered. Switch circuit.

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