Load drive device

Abstract

To provide a load drive device that can securely detect an increase in inductance of an inductive load even if a power supply voltage fluctuates.SOLUTION: In a load drive device 1, an integration circuit 8 integrates a difference voltage between a voltage VB of a DC power supply 2 and a drain voltage of an FET 4 via a resistance element 6 and a diode 7, with a predetermined time constant after the FET 4 is turned off. A microcomputer 9 detects an abnormality of an L load 3 when a result of the integration exceeds a predetermined range.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus for low-side driving of an inductive load. [Background technology]

[0002] For example, as disclosed in Patent Document 1, in a device that drives a coil such as a relay as an inductive load, it is required to detect a state in which the relay contact is turned off and stuck. When the relay contact is turned off and stuck, the inductance of the inductive load increases. In order to detect the state in which the inductance has increased, for example, it is conceivable to determine the length of the flyback time by observing the waveform of the flyback voltage that is generated when the low-side switch is turned off. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-10563 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the length of the flyback time depends on the power supply voltage, there is a risk of false detection occurring if the power supply voltage fluctuates. The present invention has been made in consideration of the above circumstances, and has an object to provide a load driving device that can reliably detect an increase in inductance of an inductive load even if the power supply voltage fluctuates. [Means for solving the problem]

[0005] According to the load driving device of claim 1, the integration execution unit (8) integrates the difference between the voltage of the power supply (2) and the load side voltage of the switch (4) that drives the inductive load (3) on the low side with a predetermined time constant after the low side switch is turned off. The abnormality detection unit (9, 25) detects an abnormality in the inductive load when the integration result exceeds a predetermined range. The integration result reflects the flyback energy, i.e., the energy of the flyback voltage generated when the low side switch is turned off. In this way, by evaluating the magnitude of the flyback energy, it is possible to detect an increase in the inductive load inductance without being affected by fluctuations in the power supply voltage.

[0006] According to the load driving device of claim 2, an integrating circuit consisting of a capacitor (5) and a resistive element (6), and a series circuit of a delayed current conducting unit (7, 22, 33) are connected in parallel to an inductive load. With this configuration, the flyback energy of the inductive load can be evaluated by the voltage charged to the capacitor. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a load driving device according to a first embodiment. [Diagram 2] The diagram shows the integral voltage waveform when the low-side switch is turned off and the inductance of the L load is normal. [Diagram 3] The diagram shows the integral voltage waveform when the inductance of the L load is abnormal when the low-side switch is turned off. [Figure 4] FIG. 13 is a diagram illustrating a configuration of a load driving device according to a second embodiment. [Diagram 5] Flowchart showing the control contents by the microcomputer [Figure 6] FIG. 13 is a diagram illustrating a configuration of a load driving device according to a third embodiment. [Figure 7] FIG. 13 is a diagram illustrating a process for setting a range for determining whether something is normal or abnormal according to the fourth embodiment. [Figure 8]FIG. 13 is a diagram illustrating a process for setting a range for determining whether something is normal or abnormal according to the fifth embodiment. [Figure 9] FIG. 13 is a diagram illustrating a process for setting a range for determining whether something is normal or abnormal according to the sixth embodiment. [Figure 10] FIG. 13 is a diagram illustrating a process for setting a range for determining whether something is normal or abnormal according to the seventh embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] (First embodiment) As shown in FIG. 1, the load driving device 1 of this embodiment drives an inductive load 3, one end of which is connected to the positive terminal of a DC power supply 2, by an N-channel MOSFET 4, which is a low-side switch. Hereinafter, the inductive load 3 is referred to as an L load 3. The DC power supply 2 is, for example, a vehicle battery, and the voltage frequently fluctuates while the vehicle is running. The L load 3 is, for example, a relay coil. A series circuit of a capacitor 5, a resistive element 6, and a reverse diode 7 is connected in parallel to the L load 3. The anode of the diode 7, which is a delayed current conducting part, is connected to the drain of the FET 4. The capacitor 5 and the resistive element 6 configure an integrating circuit 8.

[0009] A microcomputer 9 drives the gate of the FET 4 via a resistor element 10. The source of the FET 4 is connected to the ground, and the L load 3 is driven on the low side by the FET 4. When the FET 4 is turned off, a delay current generated by the L load 3 flows to the integrating circuit 8 side via a diode 7. The integrating circuit 8 corresponds to an integration execution unit.

[0010] Both ends of the capacitor 5 are connected to the inverting input terminal and non-inverting input terminal of an operational amplifier 13 via resistor elements 11 and 12, respectively. The output terminal of the operational amplifier 13 is connected to the input terminal of an A / D converter built into the microcomputer 9. A resistor element 14 is connected between the inverting input terminal and the output terminal of the operational amplifier 13. A resistor element 15 is connected between the non-inverting input terminal of the operational amplifier 13 and ground. This forms a differential amplifier 16.

[0011] The terminal voltage of the capacitor 5, which is input to the microcomputer 9 corresponding to the abnormality detection unit via the differential amplifier 16, is a voltage obtained by integrating the difference voltage between the voltage VB of the DC power supply 2 and the drain voltage of the FET 4 via the resistive element 6 and the diode 7, using the time constant of the integration circuit 8.

[0012] Next, the operation of this embodiment will be described below. Here, the parameters shown in Figs. Breakdown voltage BV: Flyback voltage VBa_max: Maximum voltage VB VBa_min: Minimum value of voltage VB Ta_max: Time when the flyback voltage occurs when the voltage VB=VBa_max and the inductance of L load 3 is normal Ta_min: Time when the flyback voltage occurs when the voltage VB=VBa_min and the inductance of L load 3 is normal Tb_max: Time when the flyback voltage occurs when the inductance of L load 3 is abnormal at voltage VB=VBa_max Tb_min: Time when the flyback voltage occurs when the inductance of L load 3 is abnormal at voltage VB=VBa_min

[0013] As shown in Figures 2 and 3, even if the voltage VB of the DC power supply 2 fluctuates within the range of VBa_max to VBa_min, the voltage integrated with a predetermined time constant equivalent to the flyback energy converges to a constant value. When the inductance of the L load 3 is normal, the integrated voltage V1 is higher than when the inductance is abnormal. This allows for a determination of normality or abnormality.

[0014] As described above, according to this embodiment, in the load driving device 1, the integrating circuit 8 integrates the difference voltage between the voltage VB of the DC power supply 2 and the drain voltage of the FET 4 via the resistive element 6 and the diode 7 with a predetermined time constant after the FET 4 is turned off. The microcomputer 9 detects an abnormality in the L load 3 when the result of the integration exceeds a predetermined range. In this way, by evaluating the magnitude of the flyback energy as the integration result, it is possible to detect an increase in the inductance of the L load 3 without being affected by fluctuations in the voltage VB.

[0015] More specifically, an integrator circuit 8 consisting of a capacitor 5 and a resistor 6, and a series circuit of a reverse diode 7 are connected in parallel to the L load 3. With this configuration, the flyback energy of the L load 3 is converted into the voltage charged in the capacitor 5. It can be evaluated.

[0016] Second embodiment Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted, and only the different parts will be described. As shown in Fig. 4, in a load driving device 21 of the second embodiment, the diode 7 is replaced with a constant current diode 22. Also, an N-channel MOSFET 23 is connected between the common connection point of the capacitor 5 and the resistive element 6 and the ground. The gate of the FET 23, which corresponds to the discharge section, is driven by a microcomputer 25, which replaces the microcomputer 9, via a resistive element 24.

[0017] Next, the operation of the second embodiment will be described. In the following, the names in parentheses correspond to those shown in the flow chart shown in FIG. 5. As shown in FIG. 2, when the microcomputer 25 turns the FET 4 (SW) on and then off (S1, S2), it A / D converts and measures the terminal voltage of the capacitor 5 (C1) (S3). Then, it applies a voltage to determine whether the measured voltage is within a predetermined range and performs an abnormality determination (S4).

[0018] If there is no abnormality, the microcomputer 25 stores the measured integral voltage value in memory (S6). Then, the FET 23 is turned on to discharge the charge of the capacitor 5 (S7), and if the result of the determination in step S4 is no abnormality (S8), the process returns to step S1. On the other hand, if the result of the determination in step S4 is an abnormality, the process notifies, for example, a higher-level control device (S5) and then proceeds to step S6. In the first embodiment, step S7 is omitted from the above process. The microcomputers 9 and 25 correspond to a drive stopping unit.

[0019] As described above, according to the second embodiment, when an abnormality is detected in the L load 3, the FET 23 is turned on to discharge the charge in the capacitor 5, so that the next integration operation can be performed promptly. Moreover, since the flyback energy also depends on the current, the measurement accuracy can be further improved by using the constant current diode 22.

[0020] Third embodiment 6 shows a load driving device 31 of the third embodiment, in which the constant current diode 22 in the configuration of the second embodiment is replaced with a voltage buffer circuit 33 configured with an operational amplifier 32. With this configuration, there is no effect of voltage drop due to forward voltage, as in the case of using the diode 7 or the constant current diode 22, and therefore the measurement accuracy can be further improved.

[0021] (Fourth embodiment) The fourth to seventh embodiments described below show variations of the abnormality determination in step S4. In the fourth embodiment shown in Fig. 7, for example, the integral voltage of the load driving device 1 is measured before it is shipped from the factory, and a range for determining normality is set based on the measurement result.

[0022] Fifth embodiment In the fifth embodiment shown in FIG. 8, a range within which the next voltage is determined to be normal is set based on the previously measured integral voltage.

[0023] Sixth embodiment In the sixth embodiment shown in FIG. 9, an average value is calculated every time integral voltage is measured since shipment from the factory, and a range within which the next measurement will be determined as normal is set based on the average value.

[0024] Seventh embodiment In the seventh embodiment shown in FIG. 10, after the DC power supply 2 is initially charged, the slope of the previously measured integral voltage and the current integral result is calculated, and a range within which the slope is determined to be normal the next time is set.

[0025] (Other embodiments) The low-side switch is not limited to an N-channel MOSFET. When an abnormality is detected, the process of stopping the driving of the inductive load by the low-side switch may be performed as necessary. The fourth to seventh embodiments may be applied to the second and third embodiments. Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure. [Explanation of symbols]

[0026] In the drawing, reference numeral 1 denotes a load driver, 2 denotes a DC power supply, 3 denotes an inductive load, 4 denotes an N-channel MOSFET, 5 denotes a capacitor, 6 denotes a resistive element, 7 denotes a diode, 8 denotes an integrating circuit, 9 denotes a microcomputer, and 16 denotes a differential amplifier.

Claims

1. A low-side switch (4) connected in series with an inductive load (3) between a power supply (2) and ground; an integration execution unit (8) that integrates a difference between a voltage of the power supply and a load side voltage of the low-side switch with a predetermined time constant after the low-side switch is turned off; and an abnormality detection unit (9, 25) that detects an abnormality in the inductive load when the result of the integration exceeds a predetermined range.

2. The integration execution unit includes an integration circuit including a capacitor (5) and a resistor element (6), 2. The load driving device according to claim 1, wherein a series circuit of the integrating circuit and the delay current conducting unit (7, 22, 33) is connected in parallel with the inductive load.

3. 3. The load driving device according to claim 2, wherein the delayed current conducting portion is a diode (7).

4. 4. The load driver according to claim 3, wherein the diode is a constant current diode (22).

5. 3. The load driving device according to claim 2, wherein the delayed current supplying section is a voltage buffer circuit (33).

6. 6. The load driving device according to claim 2, further comprising a discharge unit (23) for discharging the electric charge stored in the capacitor.

7. 2. The load driving device according to claim 1, wherein the predetermined range is determined based on the result of integration previously performed by the integration execution unit.

8. 2. The load driving device according to claim 1, wherein the predetermined range is determined based on a result of integration previously performed by the integration execution unit.

9. 2. The load driving device according to claim 1, wherein the predetermined range is determined based on an average value of a plurality of integration results that have been executed by the integration execution unit up to the present time.

10. The power source is a secondary battery.

2. The load driving device according to claim 1, wherein the predetermined range is set for a difference between two successive integration results executed by the integration execution unit after the power supply is initially charged.

11. 2. The load driving device according to claim 1, further comprising a drive stopping unit (9, 25) that stops driving of the inductive load by the low-side switch when the abnormality is detected.

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