JP2010132070A - Automobile electrical equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent malfunction related to switching of a load even if a direct current potential difference between earth lines occurs in automobile electrical equipment including a control circuit and an output circuit using a plurality of independent earth lines. <P>SOLUTION: The automobile electrical equipment includes: the control circuit 30 to output a control signal SG1; the output circuit 40 to perform load switching according to the control signal SG1; and a conversion circuit 50 connected between these circuits. The conversion circuit includes a first switching element TR1 whose control input is connected to the output of the control circuit when a first earth potential SGND and a second earth potential PGND are independent, and which turns on or off according to a potential difference between the first earth potential and the control signal; and a second switching element TR2 whose control input is connected to the output of the first switching element TR1, and which turns on or off according to a potential difference between the potential of a predetermined power line 61 and the output of the first switching element TR1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an automotive electrical device, and more particularly to an automotive electrical device including a control circuit and an output circuit that use a plurality of ground lines that are independent of each other.

  As shown in FIG. 2, for example, an automotive electrical device includes a control circuit 10 for performing complex control such as a microcomputer (CPU), and an output circuit 20 for on / off control of energization of various loads. There are many cases. Examples of the load include a display lamp, a light emitting diode, a solenoid, and an electric motor. A relatively large current flows through the load, and the current fluctuates greatly. Therefore, noise such as a relatively large potential fluctuation occurs in the power supply line and earth line (also referred to as ground side) connected to the load. It is likely to occur. However, such noise usually does not significantly affect the load control in the output circuit.

  On the other hand, for a control circuit such as a microcomputer, it is indispensable to supply a very stable and constant voltage as a power supply voltage so as not to cause a malfunction. For this reason, the ground line (SGND) on the control circuit side is often independent of the ground line (PGND) on the output circuit side. As a result, the potential of the ground line on the control circuit side is not affected by the noise generated when the load is turned on and off, and the operation of the control circuit is stabilized.

  For example, in the technique disclosed in Patent Document 1, it is assumed that a ground line (earth line) of an engine electronic control device is separated into a power ground line and a signal ground line. Patent Document 1 discloses a technique for reducing a potential difference between a power system ground line and a signal system ground line. Specifically, the capacitance of the capacitor is adjusted so that the potential variation of the ground line due to the voltage variation of the power supply line does not appear as a potential difference between a plurality of grounds.

  For example, in the technique disclosed in Patent Document 2, a circuit in which two Zener diodes are connected in series with opposite polarities is used to prevent a potential difference between a plurality of grounds from exceeding a predetermined value.

For example, Patent Document 3 discloses a level conversion circuit for converting a CML level signal into a TTL level signal.
JP-A-9-177597 JP 2001-157360 A Japanese Patent Laid-Open No. 9-107283

  In various automotive electrical equipment, for example, a binary level (high level / low level) control signal output from a control circuit composed of a microcomputer or the like is applied to the input of the output circuit, and a load is generated by this control signal. It is common to control the on / off of the power supply. However, if there is a potential difference between the ground line on the control circuit side (signal system ground line) and the ground line on the output circuit side (power system ground line), malfunction may occur. It was.

  That is, even when the control signal output from the control circuit is switched to the on level, the state of the switching element (eg, transistor) in the output circuit is not sufficiently switched due to the influence of the potential difference, and the energization of the load is not turned on. Alternatively, even when the control signal output from the control circuit is switched to the off level, the state of the switching element of the output circuit is not sufficiently switched due to the influence of the potential difference, and the energization of the load is not turned off.

  For example, when a long harness is used to connect the ground line of a power circuit to an automotive electrical device, a voltage drop (resistance of the line) occurs on the harness line according to the magnitude of the current flowing through each circuit. Value × current), and a potential difference (offset) is generated between a plurality of independent earth lines (signal system ground line, power system ground line).

  When such a potential difference occurs between the ground line (signal system ground line) of the control circuit and the ground line (power system ground line) of the output circuit, the control signal output from the control circuit is turned on or off (ground potential). Does not reach the threshold required for switching the switching element on the output circuit side, and a switching malfunction occurs.

  As a specific example, consider the operation of the apparatus shown in FIG. Here, the voltage of the control signal SG1 necessary for switching the switching element (FET1) in the output circuit 20 from OFF to ON is 4 V or more with respect to the power system ground line (PGND), and the switching element (FET1) is turned on. Assume that the voltage of the control signal SG1 necessary for switching from on to off is designed to be 0.4 V or less with respect to the power system ground line (PGND). Further, it is assumed that the (high level / low level) voltages of the control signal SG1 with respect to the signal system ground line (SGND) are (4.5 V / 0.1 V), respectively.

  There is no problem if there is no potential difference offset between the ground potential of the power system ground line (PGND) and the ground potential of the signal system ground line (SGND). That is, when the control signal SG1 becomes a high level, a voltage of 4.5 V is applied to the input of the output circuit 20, so that the switching element (FET1) is switched from OFF to ON. Further, when the control signal SG1 becomes low level, a voltage of 0.1 V is applied to the input of the output circuit 20, so that the switching element (FET1) is switched from on to off.

  However, as shown in FIG. 3, a problem occurs when the ground potential of the power system ground line (PGND) is higher by, for example, 1.0 V (offset) than the ground potential of the signal system ground line (SGND). To do. That is, when the control signal SG1 becomes high level, the voltage applied to the input of the output circuit 20 reaches only a voltage of 3.5V with respect to the ground potential of the power system ground line (PGND) due to the influence of the offset. Therefore, the switching element (FET1) cannot be switched from OFF to ON.

  Also, for example, as shown in FIG. 4, there is a problem even when the ground potential of the power system ground line (PGND) is lower by, for example, 1.0 V (offset) than the ground potential of the signal system ground line (SGND). Occurs. In other words, the voltage applied to the input of the output circuit 20 when the control signal SG1 becomes a low level is only lowered to a voltage of 1.1 V with respect to the ground potential of the power system ground line (PGND) due to the influence of the offset. Therefore, the switching element (FET1) does not switch from on to off.

  For example, in the technique disclosed in Patent Document 1, an increase in potential difference between a plurality of earth lines can be suppressed when an alternating potential fluctuation occurs in the power supply line. Moreover, in the technique disclosed in Patent Document 2, it is possible to suppress an increase in direct-current potential difference between a plurality of earth lines.

  However, even if the technique of Patent Document 1 or Patent Document 2 is adopted, the DC potential difference between the plurality of earth lines cannot be reduced to 0, and the switching malfunction as described above cannot be prevented.

  Further, if the technique of Patent Document 3 is adopted, signal level conversion can be performed between a plurality of circuits. However, in Patent Document 3, since the ground lines of a plurality of circuits connected like a CML circuit and a TTL circuit are common and no potential difference occurs between them, the above-described automotive electrical equipment Thus, it cannot be used in applications where an unknown potential difference may occur between the ground lines of a plurality of circuits.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a direct current between a plurality of ground lines in an automotive electrical device including a control circuit and an output circuit that use a plurality of independent ground lines. It is an object of the present invention to provide an automotive electrical device capable of preventing a malfunction related to load switching even when a potential difference of 2 is generated.

In order to achieve the above-described object, the automotive electrical apparatus according to the present invention is characterized by the following (1) to (4).
(1) A control circuit that generates a control signal for controlling energization to the load, an output circuit that switches energization to the load in accordance with a control signal output from the control circuit, an output of the control circuit, and the output A conversion circuit connected to the input of the circuit, and a first ground potential appearing at the ground terminal on the control circuit side and a second ground potential appearing at the ground terminal on the output circuit side are independent. Automotive electrical equipment
A first switching element having a control input terminal connected to an output of the control circuit and being turned on / off according to a potential difference between the first ground potential of the control circuit and the control signal; and a control input terminal being the first switching element A second switching element connected to the output terminal of the first switching element and turned on / off in accordance with a potential difference between a potential of a predetermined power supply line and an output terminal of the first switching element, and the second switching element Connected to the input terminal of the output circuit.
(2) In the automotive electrical equipment having the configuration described in (1) above,
One end of the second switching element is connected to a second power supply line in which a higher potential appears than the first power supply line that supplies power to the control circuit.
(3) In the automotive electrical equipment having the configuration described in (1) above,
Switching elements having different types or polarities are connected as the first switching element and the second switching element.
(4) In the electrical equipment for automobiles having the configuration described in (1) above,
The first switching element is constituted by a transistor, a base electrode of the first switching element is connected to an output terminal of a control circuit, and an emitter electrode of the first switching element is equal to the first ground potential. Be connected to the ground terminal of potential.

According to the automotive electrical equipment having the configuration of (1) above, malfunction occurs even when a direct-current potential difference (potential offset) is generated between the first ground potential and the second ground potential. Can be prevented from occurring. That is, since the first switching element provided in the conversion circuit is turned on / off with the potential difference between the control signal and the first ground potential as an input, the influence of the potential difference between the first ground potential and the second ground potential is affected. Will not receive. Also, the second switching element is turned on / off according to the potential difference between the potential of the power supply line and the output terminal of the first switching element, so that the potential difference between the first ground potential and the second ground potential is reduced. Not affected. Therefore, when the potential of the power supply line is sufficiently high, even when the offset exists in the second ground potential, the control signal causes the input circuit to be connected between the input terminal of the output circuit and the second ground potential. A potential change sufficient for switching can be given.
According to the automotive electrical equipment having the configuration of (2) above, the second switching element is connected to the second power supply line in which a higher potential appears than the first power supply line. When the switching element is turned on, a potential higher than the high level of the control signal can be supplied to the input terminal of the output circuit, and is less susceptible to the offset of the second ground potential. Accordingly, switching malfunction is unlikely to occur.
According to the automotive electrical equipment having the configuration (3), since switching elements having different types or polarities such as PNP transistors and NPN transistors can be used, a desired switching operation can be easily realized. That is, by using, for example, an NPN transistor as the first switching element, an operation of turning on / off with the potential difference between the control signal and the first ground potential as an input can be realized. In addition, by using, for example, a PNP transistor as the second switching element, it is possible to realize an operation of turning on / off using a potential difference between the potential of the power supply line and the output of the first switching element as an input.
According to the automotive electrical equipment having the configuration of the above (4), the first switching element provided in the conversion circuit is turned on / off using the potential difference between the control signal and the first ground potential as an input. It is not affected by the potential difference between the ground potential and the second ground potential. When a transistor is used as the switching element, the on / off state can be switched with a small potential change (about 0.7 V) compared to the level change of the control signal (for example, the difference between the high level and the low level is 5 V). This is possible, and more reliable switching is possible.

  As described above, according to the present invention, in an automotive electrical device including a control circuit and an output circuit that use a plurality of independent ground lines, a direct current potential difference is generated between the plurality of ground lines. Also, malfunctions related to load switching can be prevented.

  The present invention has been briefly described above. Furthermore, the details of the present invention will be further clarified by reading through the best mode for carrying out the invention described below with reference to the accompanying drawings.

  A specific embodiment relating to the automotive electrical equipment of the present invention will be described below with reference to FIG.

  FIG. 1 shows a basic configuration example of an automotive electrical device according to the present embodiment. Specifically, this automobile electrical equipment is a part of an illumination device for illuminating an instrument panel mounted on the automobile. Needless to say, the present invention can be applied to various automotive electrical equipment other than such a lighting device.

  The automobile electrical device shown in FIG. 1 has a light emitting diode LED1 serving as a light source for illumination as a load to be controlled. An output circuit 40 is provided in order to switch on / off the energization of the light emitting diode LED1. In the output circuit 40, a field effect transistor FET1 is provided as a switching element. An ordinary transistor may be used instead of the field effect transistor FET1.

  The light emitting diode LED1 has an anode terminal connected to the power supply line 61 and a cathode terminal connected to the output terminal 40a of the output circuit 40 via the resistor RL. In the field effect transistor FET1, the gate electrode as a control input is connected to the input terminal 40b of the output circuit 40 via the resistor R1, the source electrode is connected to the power system ground line (PGND) 63, and the drain electrode is output. The output terminal 40a of the circuit 40 is connected. A resistor R2 is connected between the gate electrode and the source electrode of the field effect transistor FET1.

  In this example, since the output circuit 40 handles a relatively large current, the power system ground line 63 is used as the ground. A DC voltage of about 12 V (potential difference with respect to the potential of PGND) is supplied to the power supply line 61 from a power supply (not shown).

  A control circuit 30 is provided to generate a control signal SG1 for controlling on / off of the light emitting diode LED1, which is a load to be controlled. The control circuit 30 is configured using a microcomputer (CPU). The control signal SG1 is a binary signal that changes to one of two states of high level / low level.

  The control circuit 30 is supplied with a predetermined DC voltage (5 V: potential difference with respect to the potential of SGND) stabilized from the power supply line 60. The ground terminal of the control circuit 30 is connected to a signal system ground line (SGND) 62.

  The signal system ground line 62 is independent of the power system ground line 63. That is, the control circuit 30 and the output circuit 40 use grounds independent of each other. In many cases, the potential of the signal ground line 62 and the potential of the power ground line 63 are almost the same, but they are not always the same. For example, when a relatively large direct current flows through the power system ground line 63, the direct current potential of the power system ground line 63 changes due to the influence of a voltage drop that occurs on wiring such as a harness. Therefore, there is a possibility that a DC potential difference (potential offset) occurs between the signal system ground line 62 and the power system ground line 63.

  Therefore, if the output terminal of the control circuit 30 is directly connected to the input terminal 40b of the output circuit 40, the influence of offset as shown in FIGS. 3 and 4 appears. For example, when the control signal SG1 becomes a high level (about 5V), the voltage at the input terminal 40b of the output circuit 40 (potential difference with respect to PGND) greatly falls below 5V due to the offset, and the field effect transistor FET1 is turned off. It becomes a state that does not transition to ON. Alternatively, when the control signal SG1 becomes a low level (about 0V), the voltage of the input terminal 40b of the output circuit 40 (potential difference with respect to PGND) greatly exceeds 0V due to the offset, and the field effect transistor FET1 is turned on. It will be in a state that does not transition off. That is, an operation failure occurs in the switching of the output circuit 40 due to the offset of the ground potential.

  Therefore, in the automotive electrical equipment shown in FIG. 1, a special conversion circuit 50 is connected between the output of the control circuit 30 and the input of the output circuit 40. The conversion circuit 50 is provided with an NPN transistor TR1 and a PNP transistor TR2 as switching elements. As shown in FIG. 1, the NPN transistor TR1 has a base electrode that is a control input connected to the output terminal of the control circuit 30 via a resistor R3, and an emitter electrode that is connected to a signal system ground line 62 that is a ground. . A resistor R4 is connected between the base electrode and the emitter electrode of the NPN transistor TR1.

  The collector electrode that is the output of the NPN transistor TR1 is connected to the base electrode of the PNP transistor TR2 via the resistor R5. The emitter electrode of the PNP transistor TR2 is connected to the power supply line 61. A resistor R6 is connected between the base electrode and the emitter electrode of the PNP transistor TR2. The collector electrode, which is the output of the PNP transistor TR2, is connected to the input terminal 40b of the output circuit 40.

  The conversion circuit 50 uses a signal system ground line 62 common to the control circuit 30 as ground. Therefore, the conversion circuit 50 is not affected by the potential difference between the signal system ground line 62 and the power system ground line 63. That is, when the control signal SG1 becomes a high level (5V) and the input voltage (base-emitter voltage) of the NPN transistor TR1 exceeds a predetermined threshold value VBE (for example, 0.6V), the NPN transistor TR1 is turned on. , The collector-emitter of TR1 becomes conductive. Further, when the control signal SG1 becomes low level (0V) and the input voltage (base-emitter voltage) of the NPN transistor TR1 becomes equal to or lower than the threshold value, the NPN transistor TR1 is turned off and the collector-emitter between TR1 is not connected. It becomes conductive.

  When the NPN transistor TR1 is turned on, a current flows through the resistors R5 and R6, and a potential difference is generated between the terminals of the resistor R6. When this potential difference exceeds a threshold (for example, 0.6 V) of the input voltage (base-emitter voltage) of the PNP transistor TR2, the PNP transistor TR2 is turned on, and the emitter-collector of the PNP transistor TR2 is conducted. When the potential difference falls below the threshold value of the input voltage (base-emitter voltage) of the PNP transistor TR2, the PNP transistor TR2 is turned off, and the emitter-collector of the PNP transistor TR2 becomes non-conductive.

  That is, when the control signal SG1 becomes high level, both the NPN transistor TR1 and the PNP transistor TR2 are turned on, and when the control signal SG1 becomes low level, both the NPN transistor TR1 and the PNP transistor TR2 are turned off.

  When the PNP transistor TR2 is turned on, the potential of the power supply line 61 (12V: corresponding to the high level) is applied to the input terminal 40b of the output circuit 40. Further, when the PNP transistor TR2 is turned off, a high potential is not applied to the input terminal 40b of the output circuit 40.

  When a high potential (12V) is applied to the input terminal 40b of the output circuit 40, the voltage between the gate and the source of the field effect transistor FET1 exceeds its threshold (for example, 0.6V), and the field effect transistor FET1 is turned on. To do. Further, when the PNP transistor TR2 is off, no high potential is applied to the input terminal 40b of the output circuit 40, so that the voltage between the gate and the source of the field effect transistor FET1 becomes lower than the threshold and the field effect transistor FET1 is turned off. .

  Therefore, the potential difference between the signal system ground line 62 and the power system ground line 63 does not affect the switching operation of the field effect transistor FET1 of the output circuit 40. That is, the potential (corresponding to the high level of SG1 (about 5V)) when switching the field effect transistor FET1 from OFF to ON is converted to a potential equivalent to the potential (12V) of the power supply line 61. Further, the potential (corresponding to the low level of SG1 (about 0V)) when switching the field effect transistor FET1 from on to off is equivalent to the potential of the power system ground line 63 because the PNP transistor TR2 is non-conductive. . Therefore, regardless of the DC potential offset between the signal ground line 62 and the power ground line 63, the field effect transistor FET1 is reliably turned on and off according to the level of the control signal SG1.

  The high level (about 5V) potential of the control signal SG1 is determined according to the potential (5V) of the power supply line 60 that supplies power to the control circuit 30. On the other hand, since the potential (about 12 V) for turning on the field effect transistor FET1 is supplied from the power supply line 61, a potential sufficiently higher than the control signal SG1 can be applied to the input terminal 40b of the output circuit 40. . Therefore, even when the offset becomes very large, the field effect transistor FET1 can be reliably turned on.

  When the field effect transistor FET1 of the output circuit 40 is off, no current flows through the light emitting diode LED1, and when the field effect transistor FET1 is turned on, the light emitting diode LED1, the resistor RL, and the field effect transistor are turned on from the power supply line 61. A current flows through the power system ground line 63 through the FET 1. The light emitting diode LED1 emits light when a current flows.

  1 is assumed to be a lighting device for an instrument panel. In addition to the light emitting diode LED1, for example, an output for turning on / off a load such as a lamp, a solenoid, or an electric motor is provided. The present invention can be similarly applied to an automotive electrical device having a circuit.

  As described above, the present invention is assumed to be applied to various automotive electrical devices that perform wiring using a long harness or the like as a representative example. In other words, when a relatively large offset (potential difference) occurs in the DC potential between the signal system ground and the power system ground due to the influence of the voltage drop of the wiring, it can be used to prevent switching malfunctions in the output circuit. it can.

It is an electric circuit diagram which shows the basic structural example of the electrical equipment for motor vehicles in embodiment. It is an electric circuit diagram which shows the basic structural example regarding the general electrical equipment for motor vehicles. It is a wave form diagram which shows the specific example of the waveform and electric potential of control signal SG1. It is a wave form diagram which shows the specific example of the waveform and electric potential of control signal SG1.

Explanation of symbols

10, 30 Control circuit 20, 40 Output circuit 40a Output terminal 40b Input terminal 50 Conversion circuit 60, 61 Power supply line 62 Signal system ground line 63 Power system ground line TR1 NPN transistor TR2 PNP transistor SG1 Control signal

Claims (4)

A control circuit that generates a control signal for controlling energization to the load, an output circuit that switches energization to the load in accordance with the control signal output from the control circuit, an output of the control circuit, and an input of the output circuit A first ground potential appearing at the ground terminal on the control circuit side and a second ground potential appearing at the ground terminal on the output circuit side are independent of each other. Automotive electrical equipment,
A control input terminal is connected to the output of the control circuit, a first switching element that is turned on / off according to a potential difference between the first ground potential of the control circuit and the control signal, and a control input terminal is the first switching element A second switching element connected to the output terminal of the first switching element and turned on / off according to a potential difference between a potential of a predetermined power supply line and a potential of the output terminal of the first switching element. The output terminal is connected to the input terminal of the output circuit.   2. The automobile use according to claim 1, wherein one end of the second switching element is connected to a second power supply line in which a higher potential appears than the first power supply line supplying power to the control circuit. Electrical equipment.   The automotive electrical device according to claim 1, wherein switching elements having different types or polarities are connected as the first switching element and the second switching element.   The first switching element is constituted by a transistor, a base electrode of the first switching element is connected to an output terminal of a control circuit, and an emitter electrode of the first switching element is equal to the first ground potential. The vehicle electrical equipment according to claim 1, wherein the vehicle electrical equipment is connected to a ground terminal of potential.

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