Signal detection circuit

Abstract

To provide a signal detection circuit that detects a signal using a voltage from a power supply different from an operating voltage of a device without using a downconverter.SOLUTION: A signal detection circuit according to an embodiment comprises a resistor which is supplied with a voltage from a power supply via a relay, and an ECU connected to the resistor and configured to detect a state of an input signal being input to the relay via a voltage lowered by the resistor.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to a signal detection circuit. [Background technology]

[0002] Generally, when operating 12V equipment in a vehicle that uses a 24V power supply, it is common to use a down converter to step down the voltage from 24V to 12V, and then operate the 12V equipment using the stepped-down 12V (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-159642 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there is a problem in that the downconverter settings must be changed every time a vehicle model change is made and a new ECU is added, which is time-consuming.

[0005] The present invention has been made in light of the above-mentioned circumstances, and its object is to provide a signal detection circuit that can detect signals using a voltage from a power supply that is different from the operating voltage of the device, without using a down-converter. [Means for solving the problem]

[0006] A signal detection circuit according to one embodiment includes a resistor to which voltage is supplied from a power source via a relay, and an ECU connected to the resistor and capable of detecting a state in which an input signal has been input to the relay based on the voltage stepped down by the resistor. [Effects of the Invention]

[0007] According to the above-described signal detection circuit, it is possible to provide a signal detection circuit that detects a signal using a voltage from a power supply that is different from the operating voltage of the device, without using a down-converter. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the configuration of a signal detection circuit according to the prior art. [Figure 2] FIG. 2 is a diagram illustrating an example of a power detection circuit according to an embodiment. [Figure 3] FIG. 3 is a diagram showing a current flow when an ignition signal is not input to the IG relay according to one embodiment. [Figure 4] FIG. 4 is a diagram showing a current flow when an ignition signal according to one embodiment is input to an IG relay. [Figure 5] FIG. 5 is a circuit diagram showing an example of a case where a disconnection occurs between a resistor and an ECU. DETAILED DESCRIPTION OF THE INVENTION

[0009] The signal detection circuit will be described in detail below with reference to the drawings. In the following embodiments, parts with the same numbers perform the same operation, and redundant description will be omitted. For example, when there are multiple identical or similar elements, a common reference number may be used to describe each element without distinguishing between them, or a subnumber may be used in addition to the common reference number to describe each element with distinction between them.

[0010] [Embodiment] First, the prior art will be described. Vehicles such as commercial vehicles generally use 24V power supplies. However, these vehicles also use devices that operate on 12V (hereinafter referred to as 12V devices), which are used in general vehicles. For this reason, it is common to place a down converter between the 24V power supply and the 12V devices, and use the stepped-down voltage with the 12V devices.

[0011] FIG. 1 is a diagram showing the configuration of a signal detection circuit according to the prior art. As shown in FIG. 1, the signal detection circuit includes an ECU (Electronic Control Unit) 1, an IG relay 2, a DC-DC converter 3, and a relay 4.

[0012] The DC-DC converter 3 is, for example, a down converter that steps down an input voltage and outputs the stepped-down voltage to an output port. The input terminal VIN of the DC-DC converter 3 is connected to a 24V power supply. For example, the DC-DC converter 3 steps down a voltage of 24V to 12V and outputs the stepped-down voltage from each output port (in the example of FIG. 1, a first output port VOUT1 and a second output port VOUT2). The DC-DC converter 3 also grounds the stepped-down voltage via the port GND.

[0013] The ECU 1 is a control unit that controls, for example, the +B circuit and the ignition (IG) circuit using the power output from the DC-DC converter 3. For example, it is necessary to control the +B circuit so that power is constantly supplied to it. For this reason, the ECU 1 and the DC-DC converter 3 are directly connected, and the ECU 1 controls the +B circuit using the power output from the first output port VOUT1.

[0014] On the other hand, the IG circuit needs to be controlled when receiving an ignition signal. Therefore, the ECU 1 is connected to the second output port VOUT2 via the IG relay 2.

[0015] The IG relay 2 includes a switch and a coil. When an ignition signal IG is input to the coil (i.e., when current flows through the coil), the switch becomes conductive and power output from the DC-DC converter 3 is supplied to the ECU 1.

[0016] Relay 4 is a relay connected to contact S in the wiring between ECU 1 and IG relay 2. Relay 4 includes a switch and a coil. One end of the coil is connected to contact S, and the other end is grounded. When the current value flowing through ECU 1 is extremely small, if it is below the rated current value of the contact of IG relay 2, repeated opening and closing will cause a contact coating to form, resulting in problems such as contact failure. Therefore, relay 4 is set to keep the current value within the rated current value range of the contact of IG relay 2.

[0017] As shown in Figure 1, ECU 1, which controls the IG circuit, receives voltage stepped down by DC-DC converter 1 via IG relay circuit 2. Furthermore, to reduce the current value supplied to ECU 1, a relay 4 must be installed downstream of IG circuit 2 (i.e., on the ECU 1 side). This relay 4 poses the problem of taking up space within the circuit. Furthermore, when installing a new 12V device, there may be no available ports on DC-DC converter 1.

[0018] Therefore, in one embodiment, a signal detection circuit capable of detecting a signal such as an IG signal using power from a 24V power supply without using a DC-DC converter 1 and a relay 4 is provided.

[0019] FIG. 2 is a diagram illustrating an example of a power detection circuit according to an embodiment. 2 includes an ECU 10, a resistor R, and an IG relay 20. The signal detection circuit is a circuit mounted on a vehicle that uses a 24V power supply, for example, a commercial vehicle such as a truck. However, the vehicle is not limited to commercial vehicles, and may be any vehicle that uses a 24V power supply.

[0020] The ECU 10 is connected to a 24V power supply via a resistor R and an IG relay 20. The ECU 10 includes a bidirectional Zener diode D1, a diode D2, a first resistor R1, a second resistor R2, a capacitor C1, a transistor Q1, a third resistor R3, and a fourth resistor R4. In one embodiment, the ECU 10 is capable of detecting, for example, ignition.

[0021] One end of the bidirectional Zener diode D1 is connected to the node S1 in the wiring between the resistor R and the diode D2, and the other end is grounded. The bidirectional Zener diode D1 is a diode that is placed to protect downstream devices from varying voltage values ​​or unexpected overvoltage from the 24V power supply.

[0022] The diode D2 is located downstream of the contact S1 as viewed from the 24V power supply, and is provided between the resistor R and the first resistor R1. The diode D2 is provided to prevent current from the constant power supply Vcc from flowing through the resistor R and other resistors.

[0023] The first resistor R1 has one end connected to the diode D2 and the other end connected to the base of the transistor Q1. For example, the first resistor R1 is a resistor having a resistance value R1.

[0024] The second resistor R2 and the capacitor C1 have one end connected to a node S2 and one end connected to a node S3 in the wiring between the first resistor R1 and the transistor Q1, respectively, and the other end connected to ground. For example, the second resistor R2 has a resistance value R2, and the capacitor C1 has a capacitance C1. As shown in FIG. 2, the second resistor R2 is located upstream of the capacitor C1 from the 24V power supply.

[0025] The collector of the transistor Q1 is connected to the power supply Vcc via a third resistor R3, and the emitter is grounded. For example, the third resistor R3 is a resistor having a resistance value R3.

[0026] The fourth resistor R4 has one end connected to a node S4 in the wiring between the collector of the transistor Q1 and the third resistor R3, and the other end connected to the CPU. For example, the fourth resistor R4 is a resistor having a resistance value R4.

[0027] The first resistor R1, the second resistor R2, the capacitor C1, the diode D2, the third resistor R3, and the fourth resistor R4 are used to detect a predetermined signal, for example, an ignition signal.

[0028] The resistor R is a resistor used to step down the voltage from the 24V power supply provided via the IG relay 20 to a voltage that allows the ECU 10 to detect a signal. For example, the resistor R is a resistor having a resistance value R. The resistor R is set to a resistance value that allows the ECU 10 to detect a signal. The setting conditions for the resistor R will be described later.

[0029] The IG relay 20 includes a switch 21 and a coil unit 22. When an ignition signal IG (input signal) is input to the coil unit 22, the switch 21 becomes conductive, and power from the 24V power supply is supplied to the ECU 10 via a resistor R.

[0030] In the signal detection circuit configured as described above, the following conditions must be satisfied for the ECU 10 to detect the ignition signal (i.e., to detect that the IG signal (input signal) has been input to the IG relay 20) and to use it safely: (1) (When the ignition signal is not input to the coil portion 22 of the IG relay 20, i.e., when power from the 24V power supply is not being supplied to the ECU 10, the voltage value V applied to the second resistor R2 is R2_OFF )<(Voltage value V applied to the second resistor R2 when an ignition signal is input to the coil portion 22 of the IG relay 20, i.e., when power is supplied from the 24V power supply to the ECU 10 R2_ON ) Also, (2) even if a wire breaks between the resistor R and the ECU 10, the upper limit of the fuse and overvoltage are not applied to the wiring. Here, a general fuse is used, so details such as the upper limit are omitted.

[0031] As described above, the resistor R must be set to have a resistance value and capacitance that satisfy at least the two conditions described above.

[0032] First, in the above-mentioned condition (1), when power is not supplied to the ECU 10 from the 24V power supply, the voltage value V applied to the second resistor R2 is R2_OFF We will consider the following.

[0033] FIG. 3 is a diagram showing the flow of current when an ignition signal is not input to the IG relay 20 according to one embodiment. 3, when no IG signal is input to the coil 22 of the IG relay 20, the switch 21 is not conductive. Therefore, power from the 24V power supply is not supplied to the ECU 10. Therefore, only power from the constant power supply Vcc is supplied to the ECU 10.

[0034] In this case, as shown by the dotted line in Figure 3, a current flows through the third resistor R3, the transistor Q1, and the second resistor R2. Then, the voltage V applied to the second resistor R2 is R2_OFF From Kirchhoff's law, it is expressed as the following formula 1.

[0035] V R2_OFF =R2 / (R3+R2)*Vcc (Equation 1)

[0036] For example, if the second resistance is 470 [Ω], the third resistance is 47 [kΩ], and the voltage supplied by the constant power supply Vcc is 5 [V], the voltage value V R2_OFF is 0.05[V].

[0037] Next, in the above-mentioned condition (1), the voltage value V applied to the second resistor R2 when power is supplied to the ECU 10 from a 24V power supply is R2_ON We will consider the following.

[0038] FIG. 4 is a diagram showing a current flow when an ignition signal is input to the IG relay 20 according to one embodiment. As shown in FIG. 4, an IG signal is input to the coil 22 of the IG relay 20. In this case, the switch 21 is conductive. Therefore, power is supplied from the 24V power supply to the ECU 10. In this case, as shown by the dotted line in FIG. 4, a current flows through the resistor R, the first resistor R1, and the second resistor R2. Then, a voltage value V applied to the second resistor R2 is R2_ON From Kirchhoff's law, it is expressed as follows:

[0039] V R2_ON =R2 / (R+R1+R2)*V 24V (Formula 2) where V 24V represents the operating voltage value of a 24V power supply. For example, the operating voltage value of a 24V power supply is V 24V is in the range of 12 [V] to 28.5 [V], the resistance value of resistor R is 2 [kΩ], the resistance value of first resistor R1 is 470 [Ω], and the resistance value of second resistor R2 is 47 [kΩ].

[0040] Maximum operating voltage of 24V power supply V 24V_MAX and the minimum operating voltage V 24V_MIN Even in this case, the voltage value V R2_ON >Voltage value VR 2_OFF For example, the maximum operating voltage V 24V_MAX The maximum voltage value V when R2_ON_MAX is 3.13 [V], and the minimum operating voltage value V 24V_MIN The minimum voltage value V when is 12[V] R2_ON_MIN Therefore, under the above conditions, the maximum operating voltage of the 24V power supply is V 24V_MAX and the minimum operating voltage V 24V_MIN Even in this case, the voltage value V R2_ON >Voltage value VR 2_OFF It meets the following criteria.

[0041] In a signal detection circuit having a resistor R set to satisfy the above-mentioned condition (1), when an IG signal is input to the coil portion 22 of the IG relay 20, a base current I flows through the transistor Q1. BThis allows the voltage change to the CPU to be detected, and therefore the IG state to be detected.

[0042] Next, we consider the above-mentioned condition (2), that is, the upper limit value of the fuse and whether or not an overvoltage is being applied to the wiring.

[0043] FIG. 5 is a circuit diagram showing an example in which a disconnection occurs between the resistor R and the ECU 10. In FIG. For example, the example in FIG. 5 shows a case where a wire break occurs between the resistor R and the ECU 10, resulting in the resistor R being grounded.

[0044] In this case, the current flowing downstream of resistor R is V 24V / R. In this case, the power value is V 24V 2 If the resistor R has a power capacity larger than this value, the resistor R will not burn out even if the wire between the resistor R and the ECU 10 is broken.

[0045] For example, if 28.5V, the maximum operating voltage of a 24V power supply, is supplied and R is 2kΩ, the current value is 0.01425 [A]. In this case, the power is 0.01425A * 28.5V = 0.406 [W]. Therefore, if the power capacity of resistor R is set to about 0.5 [W], resistor R will not burn even if a break occurs between resistor R and ECU 10. Furthermore, the current value under the above conditions is less than the upper limit of a typical fuse.

[0046] (Effects of the embodiment) The signal detection circuit of the embodiment described above uses the resistor R, allowing the ECU 10 to detect that the IG signal has been input to the IG relay 20 (i.e., the ignition state). The signal detection circuit does not use a DC-DC converter, so it is possible to provide a free port for the DC-DC converter. Furthermore, the signal detection circuit does not require the placement of a relay, which was previously required. This reduces space consumption and reduces design constraints.

[0047] Furthermore, by appropriately setting the capacitance of the resistor R, even if a wire breaks between the resistor R and the ECU 10, the resistor R will not burn out and can be used safely.

[0048] Furthermore, when a model change or the like is implemented, it is only necessary to change the setting of the resistor R arranged in the wiring between the 24V power supply and the ECU 10. In other words, it is no longer necessary to change the settings of the ECU 10, etc., thereby reducing the amount of work required.

[0049] [Other embodiments] In short, this invention is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the invention. Furthermore, the embodiments may be implemented in combination as appropriate as possible, and in such cases, the combined effects can be obtained. Furthermore, the above-described embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining the disclosed multiple constituent elements. [Explanation of symbols]

[0050] 1...ECU 2...IG relay 3. DC-DC converter 4...Relay 10...ECU 20...IG Relay 21...Switch 22...Coil section R…Resistance R1,R2,R3,R4…Resistance C1...Capacitor D1: Bidirectional Zener diode D2...Diode Q1...Transistor S1, S2, S3, S4…Contacts

Claims

1. A resistor to which voltage from the power supply is supplied via a relay; an ECU connected to the resistor and capable of detecting a state in which an input signal is input to the relay based on a voltage stepped down by the resistor; A signal detection circuit comprising:

2. The ECU a transistor having a base connected to the resistor via a first resistor and an emitter grounded; a second resistor having one end connected to a wiring between the first resistor and the transistor and the other end grounded; a capacitor having one end connected to a wiring between the first resistor and the transistor and the other end grounded; a third resistor having one end connected to the collector of the transistor and the other end connected to a constant power supply; wherein the resistor is set so that a voltage applied to the second resistor when the relay is in an ON state is greater than a voltage applied to the second resistor when the relay is in an OFF state.

2. The signal detection circuit according to claim 1.

3. the resistor is set so that the voltage applied to the second resistor when the relay is in an ON state is greater than the voltage applied to the second resistor when the relay is in an OFF state, at both the maximum operating voltage value and the minimum operating voltage value of the power supply.

3. The signal detection circuit according to claim 2.

4. The resistor is set to have an electric capacity that will not burn out even if a wire breaks between the resistor and the ECU.

2. The signal detection circuit according to claim 1.

5. The capacitance of the resistor is set to be greater than a power value obtained by dividing the square of the maximum operating voltage of the power source by the resistance value of the resistor.

5. The signal detection circuit according to claim 4.

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