Load drive device

Abstract

To determine whether there is an abnormality in a circuit while suppressing an expansion of a circuit scale.SOLUTION: A switch device 1 includes switches SW (SWh, SWc, SWf) that are controlled to be turned on / off on the basis of a drive signal, light-emitting elements L (Lh, Lc, Lf) that are connected in series to the switches SW (SWh, SWc, SWf), and a monitoring circuit 43 that acquires a voltage between the switches SW (SWh, SWc, SWf) and a power supply source PS that supplies power for driving the light-emitting elements L (Lh, Lc, Lf). The monitoring circuit 43 detects an abnormality in at least one of the switches SW (SWh, SWc, SWf) and the light-emitting elements L (Lh, Lc, Lf) on the basis of a voltage Von acquired when the switches SW (SWh, SWc, SWf) to be driven are on and a voltage acquired when the switches SW (SWh, SWc, SWf) to be driven are off.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a load driving device having a function of detecting a failure in an LED circuit. [Background technology]

[0002] Patent Document 1 discloses a lighting control system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-55795 A Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses that a PWM signal corresponding to the control content is output to a circuit to which a load (lighting equipment) is connected in parallel, and the connection status of the load and the presence or absence of an abnormality such as a short circuit are determined from the voltage value based on the PWM signal in the circuit. Patent Document 1 discloses that a voltage value based on a PWM signal is obtained by the following method: (a) A current detection circuit is provided to detect the value of a current flowing through the circuit, and the detected current value is converted into a voltage value.

[0005] If an integrated circuit (microcontroller) is used to realize these functions, the microcontroller will become larger, resulting in a larger circuit scale. Also, if these functions are to be realized using discrete circuits, in the case of (a), shunt resistors and operational amplifiers will be required, resulting in a larger circuit scale. Therefore, there is a demand for making it possible to determine the presence or absence of an abnormality in a circuit while suppressing an increase in the circuit scale. DISCLOSURE OF THEINVENTION [Means for solving the problem]

[0006] A drive switch that is controlled to be on / off based on a drive signal; A load connected in series to the driving switch; a power supply source for supplying power for driving the load and a monitoring circuit for acquiring a voltage at an arbitrary point between the power supply source and the drive switch, The monitoring circuit, The load driving device is configured to detect an abnormality in at least one of the driving switch and the load based on the voltage acquired when the driving switch is on and the voltage acquired when the driving switch is off. Effect of the Invention

[0007] According to the present invention, it is possible to determine the presence or absence of an abnormality in a circuit while suppressing an increase in the circuit scale. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic diagram of a switch device. [Diagram 2] FIG. 4 is a diagram illustrating a control signal of a switch. [Diagram 3] 4A and 4B are diagrams illustrating waveforms of voltage values ​​detected by a microcomputer of a monitoring circuit. [Figure 4] FIG. 13 is a diagram illustrating the relationship between the type of abnormality and a threshold value. [Diagram 5] FIG. 13 is a diagram illustrating a threshold table. [Figure 6] 1 is a flowchart of normal processing performed by a microcomputer. [Figure 7] 4 is a flowchart of an abnormality determination process. [Figure 8] 13 is a flowchart of an abnormality determination process according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a description will be given of an example in which the load driving device according to the present invention is a switch device 1 used for switching the operation mode of an appliance. FIG. 1 is a schematic diagram of a switch device 1.

[0010] The switch device 1 is used by a user when switching the operation mode of a device. The device, the operation mode of which is to be switched, has a plurality of operation modes which can be alternatively selected. An example of this type of device is an air conditioner, which has several alternatively selectable operation modes, such as "heating," "cooling," "air blowing," and "stop." 1, the switch device 1 has a plurality of operation buttons P (Ph, Pc, Pf, Ps). Each of the operation buttons P (Ph, Pc, Pf, Ps) is assigned a function for specifying an operation mode such as heating (Heater), cooling (Cooler), fan (Fan), and stop (Stop). In the following description, when no particular distinction is required between operation buttons, they will simply be referred to as operation buttons P.

[0011] In the switch device 1, when an operation button P (Ph, Pc, Pf) corresponding to an operation mode for driving is turned on to drive the air conditioner, a light-emitting element L (Lh, Lc, Lf) for notifying the operation mode selected by the on operation is turned on. This allows the user to visually grasp the selected operation mode by checking the turned-on light-emitting element L (Lh, Lc, Lf). In addition, when another operation button P (Ph, Pc, Pf) corresponding to a driving operation mode is newly turned on, the light-emitting elements L (Lh, Lc, Lf) for notifying the already selected operation mode are turned off, and the other light-emitting elements L (Lh, Lc, Lf) for notifying the newly selected operation mode are turned on. In the following description, the light emitting elements will be simply referred to as light emitting elements L unless otherwise specified.

[0012] A printed circuit board and a power supply source PS (not shown) are housed inside a main body case (not shown) of the switch device 1. A circuit 3 on the printed circuit board has a first connection line 31 connected to the power supply source PS (DC power supply) and a second connection line 32 (32h, 32c, 32f) connected to ground GD.

[0013] The power supply source PS is, for example, a battery capable of charging and discharging power. The power supply source PS is a power supply source for supplying power to the circuit 3. The output voltage supplied from the power supply source PS to the circuit is the battery voltage or a voltage that varies in conjunction with the battery voltage. In the circuit 3, the first connection line 31 is connected to three second connection lines 32 (32h, 32c, 32f) in parallel.

[0014] In each of the second connection lines 32 (32h, 32c, 32f), the light-emitting elements L (Lh, Lc, Lf) and the switches SW (SWh, SWc, SWf) are arranged in series. In each of the second connection lines 32 (32h, 32c, 32f), the light-emitting elements L (Lh, Lc, Lf) are located closer to the first connection line 31 than the switches SW (SWh, SWc, SWf). In the circuit 3 (first connection line 31, second connection line 32), the light-emitting elements L (Lh, Lc, Lf) are located upstream of the switches SW (SWh, SWc, SWf) in the current flow direction. Here, the light emitting elements L (Lh, Lc, Lf) are, for example, light emitting diodes (LEDs). The light emitting elements L (Lh, Lc, Lf) are an example of a load to which driving power is supplied from the power supply source PS.

[0015] In the second connection line 32 (32h, 32c, 32f), the switches SW (SWh, SWc, SWf) are located between the light-emitting element L (Lh, Lc, Lf) and the ground GD. The switches SW (SWh, SWc, SWf) are drive switches used to switch between supplying and not supplying power to the light-emitting elements L (Lh, Lc, Lf). The switches SW (SWh, SWc, SWf) in this embodiment are, for example, NPN transistors. The switches SW (SWh, SWc, SWf) may be field effect transistors that are turned on when a drive voltage is input to the base B. In the circuit 3, when the switch SW (SWh, SWc, SWf) is turned on, a current flows from the collector C located on the power supply source PS side to the emitter E located on the ground GD side. This causes a current to flow through the light-emitting element L (Lh, Lc, Lf) located upstream of the turned-on switch SW (SWh, SWc, SWf), and the light-emitting element L (Lh, Lc, Lf) emits light with an amount of light corresponding to the amount of current.

[0016] In addition to the circuit 3, the printed circuit board is provided with a detection circuit 41 that detects the on-operation of an operation button P (Ph, Pc, Pf, Ps), a lighting control circuit 42 for lighting the light-emitting element L (Lh, Lc, Lf) corresponding to the operated operation button P (Ph, Pc, Pf), and a monitoring circuit 43 that acquires a voltage value at an arbitrary position on the first connection line 31 of the circuit 3.

[0017] FIG. 2 is a diagram for explaining a control signal for the switch SW. In this embodiment, the on / off of the switches SW (SWh, SWc, SWf) is controlled by a PWM signal (pulse width modulation signal) as a drive signal. As shown in Fig. 2, the PWM signal is a control signal in which the period (pulse width H) during which the voltage applied to the base B of the switch SW is at a high level and the period (pulse width L) during which the voltage is at a low level can be adjusted within the range of the pulse period T. By changing the duty ratio D = (pulse width H / pulse period T) of the PWM signal, the ratio of the on period to the off period of the switch SW (SWh, SWc, SWf) can be adjusted, and the amount of current flowing from the collector C side to the emitter E side of the switch SW (SWh, SWc, SWf) can be adjusted.

[0018] In this embodiment, the feedback voltage average value V_ave described below is calculated using the feedback voltage (voltage value) during the period when the switches SW (SWh, SWc, SWf) are on and the feedback voltage (voltage value) during the period when the switches SW (SWh, SWc, SWf) are off. Therefore, it is preferable that the duty ratio of the PWM signal is set between a lower limit value greater than 0% and an upper limit value less than 100%. Furthermore, if the upper and lower limits of the duty ratio of the PWM signal are not set, it is preferable to obtain the feedback voltage while avoiding the duty ratio being 0% and 100%.

[0019] Here, the amount of light emitted by the light-emitting elements L (Lh, Lc, Lf) can be adjusted by duty control of the amount of current flowing through the light-emitting elements L (Lh, Lc, Lf). In the case of FIG. 2, the pulse width H' is greater than the pulse width H. Therefore, the duty ratio D' when the pulse width H' is greater than the duty ratio D when the pulse width H is H. Therefore, more current flows through the light-emitting elements L (Lh, Lc, Lf) when the pulse width H' is greater than when the pulse width H is H, and the amount of light emitted by the light-emitting elements L (Lh, Lc, Lf) is greater.

[0020] The input of a PWM signal to the base B of each switch SW (SWh, SWc, SWf) is controlled by a control device such as a microcomputer MC (processor) on a printed circuit board. In this embodiment, when an operation button P (Ph, Pc, Pf, Ps) is turned on, an on signal is input from the detection circuit 41 corresponding to the turned-on operation button P (Ph, Pc, Pf, Ps) to the microcomputer MC provided in the monitoring circuit 43. The microcomputer MC identifies the turned-on operation button P (Ph, Pc, Pf, Ps). If the identified operation button P (Ph, Pc, Pf) is an operation button for an operation mode for driving an air conditioner, a PWM signal is output to the switch SW corresponding to the identified operation button P (Ph, Pc, Pf) to turn on the switch SW. Furthermore, when the operation button Ps for stopping the air conditioner is turned on while the PWM signal is being output, the output of the PWM signal to the switch SW corresponding to the operation button P (Ph, Pc, Pf) that was turned on is stopped, thereby stopping the operation of the air conditioner.

[0021] A monitoring circuit 43 is connected to the circuit 3 for detecting the presence or absence of an abnormality in the circuit 3 based on a voltage value during on / off control (PWM control) of the switch SW. In this embodiment, the wiring 25 on the monitoring circuit 43 side is connected between the power supply source PS in the circuit 3 and the connection point Cn between the first connection line 31 and the second connection line 32 (32h, 32c, 32f). In the circuit 3, resistors Ra, Rb (Rbh, Rbc, Rbf) are provided on the power supply source PS side (upstream side) and the ground GD side (downstream side) of the connection point Cn, respectively. The downstream resistors Rb (Rbh, Rbc, Rbf) are provided on the second connection lines 32 (32h, 32c, 32f), respectively. It is also possible to connect the wiring 25 on the monitoring circuit 43 side to the second connection line 32, but in this embodiment, by connecting the wiring 25 on the monitoring circuit 43 side to the first connection line 31, it is possible for one monitoring circuit 43 to detect the presence or absence of abnormalities in the elements (light-emitting element L, switch SW) on each second connection line 32 (32h, 32c, 32f).

[0022] The monitoring circuit 43 has a microcomputer MC (processor) for detecting an abnormality. The microcomputer MC is connected to the first connection line 31 via the wiring 25. A resistor Rc is provided between the microcomputer MC and the first connection line 31. The other end of a resistor Rd is connected to the wiring 25 between the resistor Rc and the microcomputer MC. One end of the resistor Rd is connected to the ground GD. In the monitoring circuit 43, a resistive voltage divider circuit composed of two resistors Rc and Rd is provided between the first connection line 31 and the microcomputer MC. The power supply source PS described above is capable of supplying a predetermined voltage, for example, 16 V, to the circuit 3. The resistive voltage divider circuit is provided to drop the voltage on the circuit 3 side to a voltage detectable by the microcomputer MC. In the following description, unless a particular distinction is made between resistors, they will simply be referred to as resistors R.

[0023] 1, the microcomputer MC has an input / output port I / O, a processing unit 50 such as a CPU, and a storage unit 60 configured with a RAM, a ROM, etc. The input / output port I / O, the processing unit 50, and the storage unit 60 are connected to each other via a bus 65.

[0024] A detection circuit 41 that detects the ON operation of the operation button P (Ph, Pc, Pf, Ps) is connected to the input / output port I / O. When any of the operation buttons P (Ph, Pc, Pf, Ps) is turned ON, a signal is input from a connection line that is connected to the operation button P (Ph, Pc, Pf, Ps) that is turned ON.

[0025] The input / output port I / O is connected to the base B of the switch SW (SWh, SWc, SWf) via a connection line 45. When any of the switches SW (SWh, SWc, SWf) is turned on to be driven, a PWM signal generated by the processing unit 50 is output to the connection line 45 of the switch SW to be driven. The input / output port I / O is connected to the wiring 25 of the monitoring circuit 43 via a resistor Rc. While any of the switches SW (SWh, SWc, SWf) is driven, a voltage stepped down by a resistive voltage divider circuit (resistors Rc, Rd) is input to the input / output port I / O.

[0026] A voltage sensor 46 that acquires the output voltage of the power supply source PS is connected to the input / output port I / O via a connection line 47. The voltage sensor 46 constantly monitors the output voltage of the power supply source PS. A signal indicating the output voltage of the power supply source PS detected by the voltage sensor 46 is input to the microcomputer MC (processing unit 50) via the input / output port I / O.

[0027] The processing unit 50 carries out arithmetic processing defined by a program stored in the storage unit 60 . The storage unit 60 stores programs for the arithmetic processing executed by the processing unit 50 and information generated during the arithmetic processing.

[0028] As described above, the on / off control of the switch SW is performed by adjusting the duty ratio D of the PWM signal. For example, in the circuit 3, when the switch SWh is turned on, a current flows from the power supply source PS to the ground GD of the second connection line 32h having the turned-on switch SWh. When a current flows through the circuit 3 to the ground GD, the voltage value detected by the microcomputer MC of the monitoring circuit 43 increases or decreases according to the output voltage of the power supply source PS and the voltage drop in each element of the circuit 3.

[0029] FIG. 3 is a diagram illustrating the waveform of a voltage value detected by the microcomputer MC of the monitoring circuit 43. As shown in FIG. Specifically, as shown in Figures 2 and 3, during the period when a High signal is input to the switch SW to turn on the switch SW (the on period of the switch SW), the voltage value Von detected by the microcontroller MC becomes lower due to a voltage drop than the voltage value Voff during the period when a Low signal is input to the switch SW (the off period of the switch SW).

[0030] While the on / off control of the switch SW is being performed, the processing unit 50 executes a process (abnormality determination process) for determining the presence or absence of an abnormality in the circuit 3. That is, the abnormality determination process is executed in parallel with the on / off control of the switch SW. When performing the abnormality determination process, the processing unit 50 obtains the voltage value Von while the switch SW is on and the voltage value Voff while the switch SW is off in the same pulse period T. As an example, the processing unit 50 obtains the voltage value at the midpoint of the period during which the switch SW is on as the voltage value Von, and further obtains the voltage value at the midpoint of the period during which the switch SW is off as the voltage value Voff.

[0031] In the case of FIG. 3A, the processing unit 50 acquires, as the voltage value Von, the voltage value at the midpoint tb in the period from the timing ta when the voltage drops due to the switch SW being turned on to the timing tc when the voltage rises due to the switch SW being turned off. Similarly, the processing unit 50 obtains, as the voltage value Voff, the voltage value at the midpoint td in the period from the timing tc when the voltage rises due to the switch SW being turned off to the timing te when the voltage drops due to the switch SW being turned on.

[0032] Immediately after the switch SW is switched on / off, the detected voltage value may fluctuate significantly. By acquiring the voltage value at the midpoint as the voltage values ​​Von and Voff, the effects of fluctuation and delay in the voltage value immediately after switching can be reduced. In addition, instead of the voltage value at the midpoint, the voltage value after a predetermined time required for switching the switch SW on / off may be acquired based on the rising / falling edges of the PWM signal.

[0033] The processing unit 50 calculates an average value V_ave of the acquired voltage values ​​Von and Voff as an average value of the feedback voltage of the circuit 3 during the on / off control of the switch SW. In the case of the pulse period from time ta to time te in FIG. 3A, the average value of the voltage value Voff at time tb and the voltage value Von at time td is calculated as the average feedback voltage V_ave. The processing unit 50 determines whether or not an abnormality exists in the circuit 3 by comparing the calculated average value V_ave with a threshold value Th for determining an abnormality.

[0034] Fig. 4 is a diagram for explaining the relationship between the category (type) of anomaly and the threshold value. Fig. 4 summarizes an example of the relationship between the average value V_ave of the feedback voltage, the presence or absence of an anomaly, and each threshold value for distinguishing the category (type) of anomaly. Fig. 5 is a diagram illustrating a threshold value table, which shows an example of the relationship between the output voltage of the power supply source PS and each threshold value for determining an abnormality.

[0035] As described above, in this embodiment, a plurality of elements (light-emitting element L, switch SW, resistor R) are provided on the circuit 3 (see FIG. 1). Each of the second connection lines 32 (32h, 32c, 32f) of the circuit 3 is provided with one light-emitting element L and one switch SW. One resistor Ra is provided upstream of the connection point Cn1 with the monitoring circuit 43 in the first connection line 31. In this embodiment, the presence or absence of an abnormality in a plurality of elements (light-emitting element L, switch SW, resistor Ra) is confirmed by the abnormality determination process described above.

[0036] Here, "normal" and "abnormal" are provided as labels indicating the judgment results. "Normal" means that no short circuit or open circuit fault occurs in any of the three light-emitting elements L, the three switches SW, and the one resistor Ra. "Abnormal" means that a short circuit or an open circuit has occurred in any of the elements on the circuit (the light-emitting element L, the switch SW, or the resistor Ra). In this embodiment, in order to distinguish which element (light-emitting element L, switch SW, resistor Ra) is experiencing a similar fault, the "abnormality" category is subdivided into four categories: "abnormality 1," "abnormality 2," "abnormality 3," and "abnormality 4." Here, a short-circuit fault means a state in which the upstream and downstream sides of an element (light-emitting element L, switch SW, resistor Ra) in which a short-circuit fault has occurred are electrically connected, and current can always flow from the upstream side to the downstream side of the element (light-emitting element L, switch SW, resistor Ra). An open circuit fault refers to a state in which no current flows from the upstream side to the downstream side of an element (light-emitting element L, switch SW, or resistor Ra) in which an open circuit fault occurs.

[0037] "Abnormality 1" is a category indicating a case where an open fault occurs in at least one of the light emitting element to be driven and the switch to be driven. Here, the switch to be driven refers to a switch that is on / off controlled by a PWM signal, and the light-emitting element to be driven refers to a light-emitting element that is arranged in series with the switch that is on / off controlled and is the target light-emitting element to be made to emit light.

[0038] "Abnormality 2" is a category indicating a case where a short circuit occurs in the light emitting element to be driven. "Abnormality 3" is a category that indicates a case where a short circuit fault occurs in at least one switch. "Abnormality 4" is a category that indicates a case where an open fault occurs in resistor Ra.

[0039] In this embodiment, the processing unit 50 compares the average value V_ave of the feedback voltage acquired during PWM control of the switch SW with a threshold value, thereby determining whether or not an abnormality exists and, if an abnormality exists, identifying the category of the abnormality.

[0040] In the threshold value table shown in FIG. 5, a plurality of threshold values ​​are set in advance for determining the presence or absence of an abnormality and, if an abnormality is present, for specifying a category (abnormality 1 to abnormality 4). As an example, in the threshold table, thresholds (a first threshold Th1, a second threshold Th2, a third threshold Th3, and a fourth threshold Th4) are set for the output voltage V_std serving as a reference of the power supply source PS.

[0041] Here, when an abnormality occurs in the circuit 3, the voltage value (feedback voltage) that can be detected by the monitoring circuit 43 will be outside the range of voltage values ​​when the circuit 3 is normal. Therefore, a first threshold value Th1 (upper limit threshold value) and a second threshold value Th2 (lower limit threshold value) for determining a deviation from the normal range are set above and below the range of voltage values when all the elements are normal. The first threshold value Th1 is also a threshold value for checking the presence or absence of an open fault in the switch SW to be driven and the light emitting element L (light emitting element L to be driven) provided in series with this switch SW.

[0042] For example, when an open fault occurs in at least one of the switch SW to be driven and the light emitting element L to be driven, since the path from the power supply PS to the ground GD is not connected, no current flows through the circuit 3. Then, since no voltage drop occurs in the light emitting element L or the switch SW due to the flow of current, the feedback voltage (voltage value of the circuit 3) acquired by the monitoring circuit 43 becomes a higher value than when no open fault occurs in the light emitting element or the switch (normal case). In the present embodiment, when the average value V_ave of the feedback voltage is greater than the first threshold value Th1 (Th1 < V_ave), the processing unit 50 of the microcomputer MC determines that the category of the abnormality is "abnormality 1".

[0043] In the present embodiment, the first threshold value Th1 is determined based on the upper limit of the feedback voltage when no fault (open fault, short circuit fault) occurs in any of the light emitting element L and the switch SW, and the lower limit of the feedback voltage when an open fault occurs in the light emitting element or the switch. Specifically, the intermediate value between the upper limit of the feedback voltage when no fault occurs and the lower limit of the feedback voltage when an open fault occurs in the light emitting element or the switch is set as the first threshold value Th1. Here, the upper limit of the feedback voltage when no fault occurs and the lower limit of the feedback voltage when an open fault occurs in the light emitting element or the switch are values calculated by simulation or the like using a circuit model that takes into account the variations of the elements (light emitting element L, switch SW, resistor R) as an example.

[0044] The second threshold value Th2 is a lower limit threshold value at which it can be determined that the element is normal, and is also a threshold value for checking the occurrence of a short circuit failure in the light-emitting element L to be driven. When the light-emitting element L to be driven is short-circuited, the feedback voltage when the switch SW arranged in series with the light-emitting element L is turned on becomes lower by the forward voltage of the light-emitting element compared to when no short circuit occurs. Accordingly, the average value V_ave also becomes lower. The degree of drop in the feedback voltage at this time is smaller than when the switch SW to be driven fails short-circuited or when the switch SW or the light-emitting element L that is not the target to be driven fails short-circuited. Therefore, when the light-emitting element to be driven fails short-circuited, the drop in the feedback voltage is the smallest. The feedback voltage when the switch SW is turned on is the feedback voltage (voltage value) of the circuit 3 when a High PWM signal is input to the switch arranged in series with the light-emitting element L in which a short circuit has occurred.

[0045] In this embodiment, when the average value V_ave of the feedback voltage is equal to or less than the first threshold value Th1 (V_ave≦Th1) and equal to or greater than the second threshold value Th2 (Th2≦V_ave), the processing unit 50 of the microcontroller MC determines that no abnormality has occurred, i.e., that the system is “normal.” On the other hand, if the average value V_ave of the feedback voltage is smaller than the second threshold value Th2 (Th2>V_ave), it means that some abnormality has occurred.

[0046] The third threshold value Th3 is a threshold value for determining whether the detected abnormality is a short-circuit fault in the light-emitting element L to be driven (a fault whose category is "Abnormality 2") or an abnormality belonging to a category other than "Abnormality 2" ("Abnormality 3").

[0047] When a light-emitting element (light-emitting element L to be driven) provided in series with a switch SW to be driven has a short-circuit failure, the feedback voltage when the switch SW to be driven is turned on (when the PWM signal is High) is lower by the forward voltage of the light-emitting element than when no short-circuit failure occurs. As shown in FIG. 3, when no short-circuit failure occurs in the light-emitting element L to be driven (see (A) in FIG. 3), the degree of decrease in the voltage value Von when the switch SW is turned on is smaller by ΔV than when a short-circuit failure occurs (see (B) in FIG. 3).

[0048] On the other hand, in the case of a failure belonging to the category of "abnormality 3", the influence on the voltage value Von when the switch SW is turned on and the influence on the voltage value Voff when the switch SW is turned off are substantially the same. Therefore, the degree of decrease in the feedback voltage is smaller when the light-emitting element L to be driven has a short-circuit failure (abnormality 2) than when the switch SW to be driven has a short-circuit failure or when a switch SW not to be driven has a short-circuit failure (abnormality 3). In other words, the degree of decrease in the feedback voltage is smaller for an abnormality belonging to the category of "abnormality 2" than for an abnormality belonging to the category of "abnormality 3".

[0049] In the present embodiment, when the average value V_ave of the feedback voltage is smaller than the second threshold Th2 (V_ave < Th2) and equal to or greater than the third threshold Th3 (Th3 ≤ V_ave < Th2), the processing unit 50 of the microcomputer MC determines that the category of the abnormality is "abnormality 2".

[0050] Here, the degree of decrease in the feedback voltage is the smallest when the switch SW to be driven has a short-circuit failure. And as the number of short-circuit failure locations of the switch SW not to be driven increases, the degree of decrease in the feedback voltage increases. Therefore, in the present embodiment, the intermediate value between the feedback voltage when a short-circuit failure occurs in the light-emitting element L to be driven and the feedback voltage when the switch SW to be driven has a short-circuit failure is set as the third threshold Th3. The voltage value used for calculating the intermediate value is a value calculated by simulation or the like using a circuit model that takes into account the variations of the elements (light-emitting element L, switch SW, resistor R).

[0051] The fourth threshold Th4 is a threshold for determining whether the detected abnormality is an open failure of the upstream resistor Ra in the monitoring circuit 43 (a failure with the category of "abnormality 4") or a short-circuit failure of at least one of the switches SW (a failure with the category of "abnormality 3").

[0052] If an open failure occurs in the resistor Ra on the first connection line 31, the path from the power supply PS to the monitoring circuit 43 is not connected. In such a case, the feedback voltage detected by the monitoring circuit 43 becomes a low value close to 0V regardless of the on / off state of the switch SW to be driven. The feedback voltage at this time becomes a lower value than the voltage value when all of the plurality of switches that are not the drive target are short-circuited. In the present embodiment, a value that is lower than the voltage value when all of the plurality of switches that are not the drive target are short-circuited and higher than 0V is set as the fourth threshold Th4. As an example, in the present embodiment, the intermediate value between the feedback voltage value when all of the plurality of switches that are not the drive target are short-circuited and 0V is set as the fourth threshold Th4.

[0053] Therefore, when the average value V_ave of the feedback voltage is smaller than the fourth threshold Th4 (V_ave < Th4), the processing unit 50 of the microcomputer MC determines that the category of the abnormality is "abnormality 4". When the average value V_ave of the feedback voltage is smaller than the third threshold Th3 (V_ave < Th2) and equal to or greater than the fourth threshold Th4 (Th4 ≤ V_ave < Th3), the processing unit 50 of the microcomputer MC determines that the category of the abnormality is "abnormality 3".

[0054] Here, the output voltage of the power supply source PS may vary from a reference output voltage depending on the total number of loads to which driving power is supplied from the power supply source PS and the power consumption of each load. Therefore, in this embodiment, the above-mentioned threshold values ​​Th1 to Th4 are prepared for each different voltage value taking into consideration the fluctuation range of the output voltage.

[0055] In the threshold table shown in FIG. 5, thresholds corresponding to fluctuations within a range of ±1.0 volts centered around the reference output voltage V_std are provided in increments of 0.5 volts. This threshold table specifies thresholds (first thresholds Th1±a, Th1±b, second thresholds Th2±a, Th2±b, third thresholds Th3±a, Th3±b, fourth thresholds Th4±a, Th4±b) in increments of 0.5 volts from the reference output voltage V_std, corresponding to 0.5 volts and 1.0 volts on the positive side and 0.5 volts and 1.0 volts on the negative side. The threshold values ​​defined in this threshold table are values ​​set based on values ​​calculated by a simulation using a circuit model that takes into account variations in elements (light-emitting element L, switch SW, resistor R).

[0056] FIG. 6 is a flowchart of the normal process performed by the processing unit 50. Below, we will explain the normal processing and abnormality determination processing performed by the processing unit 50, using as an example a case in which the operation button Sc for selecting "cooling" as the operation mode is turned on in a switch device 1 equipped with operation buttons P (Ph, Pc, Pf, Ps) for the operation modes of an air conditioner.

[0057] When any of the operation buttons for operating the air conditioner is turned on (Yes in step S101), the processing unit 50 starts PWM control of the switch corresponding to the operation button that has been turned on (step S102).

[0058] When the operation button Pc specifying "cooling" is turned on, a control signal is input from the processing unit 50 to the base B of the switch SWc corresponding to this operation button Pc. As described above, the control signal is a PWM signal in which a High signal and a Low signal fluctuate at a set duty ratio D within a predetermined pulse period T (see FIG. 2). When the switch SWc is turned on, the power supply source PS (DC power supply) and the ground GD are connected via the second connection line 32c on which the switch SWc is provided (see FIG. 1). As a result, a current flows from the power supply source PS to the ground GD through the second connection line 32c, and the light-emitting element Lc provided in series with the switch SWc emits light with an amount of light corresponding to the duty ratio D.

[0059] When the PWM control of the switch (step S102) is started, an abnormality detection process is carried out to detect the presence or absence of an abnormality in the circuit 3 (step S103).

[0060] FIG. 7 is a flowchart of the abnormality determination process performed by the processing unit 50. In the abnormality determination process, the processing unit 50 of the monitoring circuit 43 acquires the feedback voltage V_on during the period in which the switch SW is on (step S201). Here, if the switch SW is designed to be turned on by the input of a High signal, the period during which the switch SW is on corresponds to the period during which the PWM signal input to the switch SW is High (see FIG. 2). Moreover, the feedback voltage V_on is a voltage value acquired by the monitoring circuit 43 (processing unit 50) at the midpoint of the period during which the switch SW is on. For example, in the case of FIG. 3A, the voltage value at the midpoint tb in the period from the timing ta when the voltage drops due to the switch SW being turned on to the timing tc when the voltage rises due to the switch being turned off is acquired as the voltage value Von.

[0061] Next, the processing unit 50 obtains the feedback voltage V_off during the period in which the switch SW is off (step S202). Here, in the case where the switch SW is designed to be turned off by input of a Low signal, the period during which the switch SW is off corresponds to the period during which the PWM signal input to the switch SW is Low. Here, the feedback voltage V_off is the voltage value acquired by the monitoring circuit 43 at the midpoint of the period during which the switch SW is off. For example, in the case of FIG. 3A, the voltage value at the midpoint td in the period from the timing tc when the voltage rises due to the switch SW being turned off to the timing te when the voltage drops due to the switch being turned on is acquired as the voltage value Voff.

[0062] Next, the processing unit 50 calculates an average value V_ave of the feedback voltage V_on during the period in which the switch SW is on and the feedback voltage V_off during the period in which the switch SW is off (step S203).

[0063] Next, the control unit compares the average value V_ave of the feedback voltage with a first threshold value Th1 (step S204). If the average value V_ave is greater than the first threshold value Th1 (V_ave>Th1) (Yes in step S204), the process proceeds to step S205. In this case, since the circuit 3 has an abnormality that is attributed to "abnormality 1", in step S205, the processing unit 50 performs the abnormality process determined for the case of "abnormality 1". Specifically, the processing unit 50 outputs a signal indicating that an abnormality belonging to "abnormality 1" has occurred to an external control device or device connected to the microcomputer MC. The processing unit 50 turns on all light-emitting elements that can be turned on, and performs processing for visually grasping the occurrence of the abnormality.

[0064] On the other hand, if the average value V_ave is equal to or less than the first threshold value Th1 (Th1≧V_ave) (No in step S204), the process proceeds to step S206. In step S206, the processing unit 50 compares the average value V_ave of the feedback voltage with the second threshold value Th2.

[0065] When the average value V_ave is equal to or greater than the second threshold Th2 (Th2 ≦ V_ave) (step S206, Yes), the average value V_ave is a value that is equal to or less than the first threshold Th1 and equal to or greater than the second threshold Th2, which means that the average value V_ave of the feedback voltage falls within a voltage range that can be regarded as normal. In such a case, since there is no abnormality in circuit 3, in step S207, the process for the case where it is determined as "normal" (normal-time process) is executed. As an example, in the normal-time process, an output indicating that circuit 3 is "normal" is sent to an external control device or equipment to which the microcomputer MC is connected. Note that the process of this step S207 may be omitted.

[0066] On the other hand, when the average value V_ave is smaller than the second threshold Th2 (V_ave < Th2) (step S206, No), the process proceeds to step S208, and the processing unit 50 compares the average value V_ave of the feedback voltage with the third threshold Th3.

[0067] When the average value V_ave is equal to or greater than the third threshold Th3 (V_ave ≧ Th3) (step S208, Yes), the process proceeds to step S209. In this case, it means that there is an abnormality attributed to "abnormality 2" in circuit 3, so in step S209, the processing unit 50 executes the abnormal-time process determined for the case of "abnormality 2". On the other hand, when the average value V_ave is smaller than the third threshold Th3 (V_ave < Th3) (step S208, No), the process proceeds to step S210.

[0068] In step S210, the processing unit 50 compares the average value V_ave of the feedback voltage with the fourth threshold Th4. When the average value V_ave is equal to or greater than the fourth threshold Th4 (V_ave ≧ Th4) (step S210, Yes), the process proceeds to step S211. In this case, it means that there is an abnormality attributed to "abnormality 3" in circuit 3, so in step S211, the processing unit 50 executes the abnormal-time process determined for the case of "abnormality 3".

[0069] On the other hand, when the average value V_ave is smaller than the fourth threshold Th4 (V_ave < Th4) (step S210, No), the process proceeds to the process of step S212. In this case, since there is an abnormality attributed to "abnormality 4" in circuit 3, in step S212, the processing unit 50 performs the abnormality processing determined for the case of "abnormality 4".

[0070] When any of the processes of steps S205, S207, S209, S211, and S212 is performed, the abnormality determination process ends and the process proceeds to the process of step S104 in FIG. 2.

[0071] Returning to the flowchart of FIG. 6, in step S104, the processing unit 50 checks whether any other operation button has been operated. If no other operation button has been operated (step S104, No), the selection of the cooling mode in the operation mode of the air conditioner continues. In such a case, the process proceeds to the process of step S103, and the above-described abnormality detection process is executed. Therefore, the abnormality determination process is repeatedly performed until any other operation button is operated.

[0072] Then, when any other operation button other than the operation stop button Ps is operated (step S104, Yes), in step S105, the processing unit 50 checks whether the operated operation button is the operation stop button Ps. If it is the operation stop button Ps, the PWM control of the switch SW is terminated (step S106). As a result, the operation of the air conditioner ends.

[0073] When any other operation button other than the operation stop button Ps is operated (step S105, No), the process proceeds to the process of step S102. As a result, a control signal (PWM signal) is input from the microcomputer MC (processing unit 50) to the base B of the switch SW corresponding to the newly operated other operation button. For example, if the newly operated operation button is the operation button Pf corresponding to "blow air," a control signal is input to the base B of the switch SWf, and the PWM control of the switch SWf is performed.

[0074] In this way, the monitoring circuit 43 is used to calculate the average feedback voltage V_ave from the voltage value Von when the switch SW to be controlled is on and the voltage value Voff when the switch SW to be controlled is off. Then, the calculated average value V_ave is compared with the thresholds Th1, Th2, Th3, and Th4 to determine whether or not there is an abnormality in the circuit 3. Then, if there is an abnormality, the category of the abnormality is determined.

[0075] When controlling the driving of the light-emitting element by on / off control (switching control) of the switch SW, the amount of current (current value) flowing through the circuit 3 varies according to the on / off ratio. Therefore, when detecting the presence or absence of an abnormality based on the current value, an amplifier circuit is required to be able to handle cases where the current value is low. As described above, in the case of voltage, although the voltage value differs when the switch SW is on and when it is off, it is less susceptible to the effect of the load drive than the case of current value. This makes it possible to properly detect the presence or absence of an abnormality. It should be noted that if one looks only at the voltage value when the switch SW is off, it is not possible to distinguish between "Abnormality 2" and "Abnormality 3." In this embodiment, it is possible to distinguish between "Abnormality 2" and "Abnormality 3" by using both the voltage value Von when the switch SW to be controlled is on and the voltage value Voff when the switch SW to be controlled is off. That is, in this embodiment, the average value V_ave based on both the two voltage values ​​Von and Voff is used, so that the categories of abnormalities can be subdivided and recognized.

[0076] [Variation 1] FIG. 8 is a flowchart of an abnormality determination process according to a modified example. The abnormality determination process according to the first modification differs from the abnormality determination process shown in FIG. 7 in that the abnormality determination thresholds Th1 to Th4 are changed in accordance with the actual output voltage of the power supply source PS. Therefore, in the abnormality determination process of the first modification, between step S303 of calculating the average feedback voltage V_ave and step S306 of comparing the average feedback voltage V_ave with the first threshold, there is provided step S304 of acquiring the actual output voltage of the power supply source PS and step S305 of determining thresholds (first to fourth thresholds) based on the acquired actual output voltage.

[0077] Steps S301 to S303 and S306 to S314 of the abnormality determination process according to the first modification are the same as steps S201 to S203 and S204 to S212 of the abnormality determination process shown in FIG. 7, so steps S304 and S305 will be specifically described here.

[0078] As described above, a signal indicating the actual output voltage of the power supply source PS is continuously input from the voltage sensor 46 to the input / output port I / O of the microcomputer. Therefore, when the average value V_ave of the feedback voltage is calculated in step S303, the processing unit 50 acquires the actual output voltage of the power supply source PS at the current time point based on the signal input from the voltage sensor 46 (step S304).

[0079] Next, the processing unit 50 refers to the threshold value table (FIG. 5) and determines the threshold values ​​(first to fourth threshold values) from the current output voltage. For example, if the current output voltage is 0.5 V lower on the negative side than the standard output voltage V_std of the power supply source PS, the processing unit 50 determines thresholds Th1-a, Th2-a, Th4-a, and Th4-a as the thresholds (first threshold, second threshold, third threshold, and fourth threshold) for determining whether or not there is an abnormality in the circuit 3, respectively.

[0080] As described above, the output voltage of the power supply source PS may vary from the reference output voltage depending on the total number of loads to which driving power is supplied from the power supply source PS and the power consumption of each load. When the output voltage of the power supply source PS deviates from the reference output voltage, the fluctuation in the output voltage also affects the feedback voltage detected by the monitoring circuit 43 (microcomputer MC). As described above, the adjustment threshold value for suppressing the effect of the fluctuation of the output voltage is determined in advance by simulation or the like, and the adjustment threshold value is specified in association with the degree of the fluctuation in the threshold value table. In this way, by referring to the threshold value table based on the actual output voltage, the optimum threshold value at that time can be selected. This makes it possible to more appropriately determine whether an abnormality exists and to more appropriately categorize the abnormality if it does occur.

[0081] In the switch device 1 of the above-described embodiment and modified example, the monitoring circuit 43 is configured to include a wiring 25 connecting the first connection line 31 and a microcontroller MC (control device), a resistive voltage divider circuit (resistors Rc, Rd) provided on the wiring 25, and a pair of resistors Ra, Rb (Rbh, Rbc, Rbf). That is, the function of the monitoring circuit 43 is realized by a combination of individual elements (resistor R, switch SW, and light-emitting element L) rather than by an integrated circuit fabricated as a whole. These single elements, particularly the resistors Ra, Rb, Rc, and Rd, require a small area for installation and can be distributed and placed at any desired positions on the printed circuit board. Therefore, the components of the monitoring circuit 43 can be distributed in the available space on the printed circuit board, and the monitoring circuit 43 can be provided as a discrete circuit, which improves the degree of freedom in placement on the printed circuit board. In the case of an integrated circuit, a large area is required for installation, which may result in an increase in size of the printed circuit board and the switch device 1. As described above, the monitoring circuit 43 can be provided as a discrete circuit, which can prevent the printed circuit board and the switch device 1 from becoming larger. Furthermore, because the monitoring circuit 43 is configured to detect voltage, a shunt resistor or operational amplifier is not required as in the case of detecting current. Therefore, the circuit size becomes large when detecting current. As described above, because the monitoring circuit 43 is configured to detect voltage and is realized with a discrete circuit, it is possible to determine whether or not there is an abnormality in the circuit 3 while suppressing an increase in the circuit size. Since the unit cost of the individual elements (resistor R, switch SW, light-emitting element L) is lower than that of an integrated circuit, the manufacturing cost of the switch device 1 can be expected to be reduced.

[0082] In the above-described embodiment and modified example, the average feedback voltage value V_ave is calculated from the voltage value Von at the midpoint of the period during which the switch SW is on and the voltage value Voff at the midpoint of the period during which the switch SW is off. The average feedback voltage value V_ave may be calculated from the sum of the voltage values ​​during the period when the switch SW is on and the sum of the voltage values ​​during the period when the switch SW is off. That is, in the case of (A) in FIG. 3, the average feedback voltage value V_ave may be calculated from the sum of the voltage values ​​Von acquired from time ta to time tc and the sum of the voltage values ​​Voff acquired from time tc to time te.

[0083] Alternatively, the average value V_ave of the feedback voltage values ​​may be calculated for each pulse period T, added up, and the sum may be divided by the total number of pulse periods T to obtain the average feedback voltage V_ave.

[0084] Note that, if both the voltage value during the period when the switch SW is on and the voltage value during the period when the switch SW is off can be used, the feedback voltage is not limited to the average value V_ave. For example, instead of the average value V_ave, a sum (total) V_total of the voltage value during the period when the switch SW is on and the voltage value during the period when the switch SW is off may be used for comparison with the threshold value. Also, a ratio of the voltage value during the period when the switch SW is on to the voltage value during the period when the switch SW is off may be used for comparison with the threshold value. Also, the voltage value during the period when the switch SW is on and the voltage value during the period when the switch SW is off may be individually compared with the threshold value. For example, the voltage value during the period when the switch SW is on is used to provisionally determine that one of abnormalities 1, 2, or 4 has occurred, and the voltage value during the period when the switch SW is off is used to provisionally determine that one of abnormalities 3 or 4 has occurred. The type of abnormality can also be finally identified by combining these provisional determinations.

[0085] [Variation 2] In the above-described first modification, the threshold value is changed based on the actual output voltage of the power supply source PS. The duty ratio of the control signal for the switch SW to be driven may be changed based on the actual output voltage of the power supply source PS. For example, as the output voltage of the power supply source PS becomes lower, the duty ratio may be set to a higher value that lengthens the on-period of the switch SW. For example, if the output voltage of the power supply source drops, depending on the degree of the drop in the output voltage, the amount of current supplied to the LED element may drop, causing the brightness of the LED element to drop. By adjusting the duty ratio so that the switch's on period is lengthened according to the degree of the drop in the output voltage, the fluctuation in brightness can be suppressed.

[0086] [Variation 3] In the case of the above-mentioned modification 2, if the duty ratio is changed following the fluctuation in the output voltage of the power supply source PS, when the fluctuation range of the output voltage is large, the change range of the duty ratio also becomes large. In this case, for example, if the on-period of the switch SW to be driven suddenly becomes shorter, the amount of light emitted by the light-emitting element L suddenly decreases, and if the on-period of the switch SW to be driven suddenly becomes longer, the amount of light emitted by the light-emitting element L suddenly increases.

[0087] Therefore, when the change amount ΔV of the output voltage of the power supply source PS is larger than a predetermined threshold value Thx, the duty ratio may be changed in stages from the current duty ratio to a duty ratio corresponding to the output voltage after the change. Here, an example will be described in which the output voltage of the power supply source PS drops from A volts to B volts and the amount of change in the output voltage ΔV(BA) is equal to or greater than the threshold value Thx (ΔV≧Thx). In this case, if the duty ratio is not changed in steps, the duty ratio D_A when the output voltage is A volts will be quickly changed to the duty ratio D_B when the output voltage is B volts. In contrast, when changing the duty ratio in a stepwise manner, a filter Fx that suppresses the amount of change ΔV is used, and the filter Fx is set to gradually become zero (=0), so that the duty ratio D gradually changes toward the duty ratio after the change in the output voltage.

[0088] Specifically, the value of the filter Fx immediately after the output voltage of the power supply source PS changes is set to the maximum value in the direction of suppressing the amount of change ΔF, so that the amount of change ΔV used to determine the duty ratio D becomes a small value. Then, the duty ratio is reset at predetermined time intervals, and each time the duty ratio is reset, the value of the filter Fx is changed at a predetermined gradient so as to approach zero (=0). This allows the duty ratio D to be gradually changed from a duty ratio D_A when the output voltage is A volts to a duty ratio D_B when the output voltage is B volts, thereby suppressing a sudden change in the amount of light emitted by the light-emitting element.

[0089] In the above-described embodiment and modified example, the switch SW is turned on when the PWM signal is high and turned off when the PWM signal is low. However, the switch may be designed so that the switch SW is turned on when the PWM signal is low and turned off when the PWM signal is high.

[0090] In the above-described embodiment and modified example, the load is an LED. The load in the present invention is not limited to a light-emitting element. The load may be a resistive element, which is an electronic component used to obtain a certain electrical resistance value, a solenoid, a heating wire for a heater, or the like. Therefore, the term "supply of driving power" in this specification means supplying power to a heater wire when the load is a heater wire, means supplying power to a resistor element when the load is a resistive element, and means supplying power to a light-emitting element when the load is a light-emitting element.

[0091] In addition, in the above-described embodiment and modified example, the application to an air conditioner has been shown as an example, but the present invention is not limited to this. It is also possible to apply the present invention to other devices having a load, such as a shift button.

[0092] In the above-described embodiment and modified example, a case has been illustrated in which the light-emitting element L (Lh, Lc, Lf) is located closer to the first connection line 31 than the switch SW (SWh, SWc, SWf) in each second connection line 32 (32h, 32c, 32f). The switch SW (SWh, SWc, SWf) may be located closer to the first connection line 31 than the light-emitting element L (Lh, Lc, Lf). In addition, the above embodiment illustrates a case in which the monitoring circuit 43 is connected to the first connection line 31. The monitoring circuit 43 may be connected to each of the second connection lines 32 (32h, 32c, 32f).

[0093] In the above-described embodiment and modified example, the processing unit 50 judges whether or not there is an abnormality in the circuit 3, and if there is an abnormality, identifies the type of the abnormality. The processing unit 50 may output the comparison result between the average value V_ave of the feedback voltage and the threshold values ​​Th (first threshold value Th1, second threshold value Th2, third threshold value Th3, fourth threshold value Th4) to an external processing device (control device) connected via the input / output port I / O, without making a judgment or identifying the type of abnormality. In this case, the external processing device (control device) judges whether or not there is an abnormality in the circuit 3, and if there is an abnormality, identifies the type of abnormality. This external processing device does not need to be provided on the same printed circuit board, and may be any device that can exchange information with the microcomputer MC via a wired or wireless connection.

[0094] As described above, the switch device 1 (load driving device) according to the embodiment has the following configuration. (1) The switch device 1 is A switch SW (drive switch) that is controlled to be on / off based on a drive signal; A light-emitting element L connected in series to a switch SW; The light emitting element L includes a power supply source PS (driving power source) that supplies driving power to the light emitting element L (load), and a monitoring circuit 43 that acquires the voltage at any point between the light emitting element L and the switch SW. The monitoring circuit 43 performs an abnormality detection process to detect an abnormality in at least one of the switch SW and the light-emitting element L based on the voltage value Von acquired when the switch SW to be driven is on and the voltage acquired when the switch SW to be driven is off.

[0095] When controlling the driving of the light-emitting element by on / off control (switching control) of the switch SW, the amount of current (current value) flowing through the circuit 3 varies according to the on / off ratio. Therefore, when detecting the presence or absence of an abnormality based on the current value, an amplifier circuit is required to be able to handle cases where the current value is low. As described above, when detecting the presence or absence of an abnormality using voltage, although the voltage value differs when the switch SW is on and off, it is less susceptible to the influence of the load drive than when using current values, which allows the presence or absence of an abnormality to be detected appropriately.

[0096] (2) In (1) above, The circuit 3 of the switch device 1 has a first connection line 31 connected to a power supply source PS, and a second connection line 32 (32h, 32c, 32f) in which a light emitting element L and a switch SW are arranged in series. The first connection line 31 is connected in parallel to a plurality of second connection lines 32 (32h, 32c, 32f). The monitoring circuit 43 performs an abnormality detection process based on a voltage value during on / off control of one of the multiple switches SW (SWh, SEc, SWf).

[0097] The voltage detected by the monitoring circuit 43 varies depending on the location of the element (light-emitting element L, switch SW, resistor Ra) where an abnormality occurs and the number of elements (light-emitting element L, switch SW, resistor Ra) where an abnormality occurs. Therefore, by preparing multiple thresholds for determining whether or not an abnormality exists and for categorizing the abnormality if one exists, depending on the location of the element where an abnormality exists and the total number of elements where an abnormality exists, it is possible to appropriately determine whether or not an abnormality has occurred and identify the category of the abnormality that indicates the type of abnormality. In particular, since the multiple second connection lines 32 (32h, 32c, 32f) are connected in parallel to the first connection line 31, the presence or absence of abnormalities in the light-emitting elements L and switches SW on all of the second connection lines 32 (32h, 32c, 32f) can be detected based on the voltage value during on / off control of one of the multiple switches SW.

[0098] (3) In (1) or (2) above, In the abnormality detection process, (a) the average voltage V_ave obtained is compared with the threshold values ​​Th1 to Th4, or (b) the sum V_total of the obtained voltages is compared with the threshold values ​​Th1 to Th4. The average voltage value V_ave is the average of the voltage value Von acquired when the switch SW is on and the voltage value Voff acquired when the switch SW is off. The sum V_total of the acquired voltages is the sum of the voltage value Von acquired when the switch SW is on and the voltage value Voff acquired when the switch Sw is off.

[0099] For example, when an open circuit fault occurs in an element (switch SW, light-emitting element L) on circuit 3, the voltage value Von acquired when the switch is on becomes high, and when a short circuit fault occurs in the element (switch SW, light-emitting element L), the voltage value Voff acquired when the switch is off becomes low. The acquired voltage value varies depending on which element (switch SW, light-emitting element L, or resistor Ra) of the circuit 3 has an abnormality and what kind of abnormality has occurred therein. Therefore, by comparing values ​​such as the average value V_ave based on both Von and Voff with thresholds Th1, Th2, Th3, and Th4, which also serve as thresholds for identifying the category of abnormality, it is possible to identify which element has an abnormality that has occurred in circuit 3 and what type of abnormality is occurring.

[0100] (4) In any one of (1) to (3) above, The output voltage of the power supply PS is the battery voltage or a voltage that varies in conjunction with the battery voltage. The threshold value is changed according to the output voltage.

[0101] By changing the threshold value in accordance with the output voltage, it is possible to improve the accuracy of determining whether or not an abnormality exists while suppressing the effects of fluctuations in the output voltage.

[0102] (5) In any one of (1) to (4) above, The drive signal is a PWM signal that is output by a microcomputer MC (control device) included in the monitoring circuit 43. The light emission amount of the light emitting element L, which is a load, changes according to the duty ratio of the PWM signal.

[0103] When configured as described above, although the amount of current (current value) flowing through circuit 3 fluctuates depending on the amount of light emitted by the light-emitting element L, the presence or absence of an abnormality is detected based on a voltage that is almost unaffected by the amount of light emitted by the light-emitting element L, so that the presence or absence of an abnormality can be appropriately detected.

[0104] (6) In (4) above, The duty cycle of the PWM signal is set between a lower limit value greater than 0% and an upper limit value less than 100%, preferably between 5% and 95%.

[0105] With this configuration, the lower limit and upper limit are set based on the minimum period required to obtain a voltage value, so that the voltage value used to determine whether or not there is an abnormality can be appropriately obtained whether the switch is on or off. Here, if the duty ratio D becomes too close to 0% or 100%, it may affect the accuracy of obtaining the feedback voltage in the monitoring circuit 43 (microcomputer MC) and may affect the response of the switch SW in time. Therefore, by setting the duty ratio D between a lower limit of 5% or more and an upper limit of 95% or less, the switch SW can be reliably controlled on / off while the voltage value Von when the switch SW is on and the voltage value Voff when the switch SW is off can be obtained with high accuracy. Furthermore, even if the duty ratio D is changed significantly, both the voltage values ​​Von and Voff required for determining whether or not there is an abnormality can be reliably obtained, so that the opportunity to determine whether or not there is an abnormality can be secured.

[0106] (7) In (5) or (6) above, As the output voltage of the power supply source PS becomes lower, the duty ratio is set to a higher value that lengthens the on-period of the switch SW.

[0107] For example, when the output voltage of the power supply source drops, depending on the degree of the drop in the output voltage, the amount of current supplied to the LED element may drop, causing the brightness of the LED element to drop. As described above, by adjusting the duty ratio so that the on-period of the switch is lengthened according to the degree of the drop in the output voltage, it is possible to suppress fluctuations in luminance. With the above configuration, even if a sudden change occurs in the output voltage of the power supply source, the change in luminance of the light emitting element can be suppressed.

[0108] (8) In any one of (1) to (7) above, The second connection lines 32 (32h, 32c, 32f) are provided in the same number as the operation buttons P which are selectively turned on.

[0109] For example, a switch device 1 used to switch the operating mode of an air conditioner may be The system has heating, cooling, ventilation, etc. as operating modes that can be selected alternatively. When the load of the second connection line 32 (32h, 32c, 32f) is the light-emitting element L, the light-emitting element L is turned on to specify the alternatively selected operation mode ("heating", "cooling", "air blowing"). In order to turn on the light-emitting element L, the switch SW is turned on by receiving a drive signal from the microcomputer MC (processing unit 50) of the monitoring circuit 43 in conjunction with the ON operation of the operation button P. Therefore, when an abnormality occurs in the switch SW or the light-emitting element L, it is preferable to be able to quickly detect the occurrence of the abnormality and identify the content of the abnormality. In the above-mentioned switch device 1, any one of the above-mentioned operation buttons P is selectively turned on. By detecting the feedback voltage when the switch SW corresponding to the turned-on operation button P is turned on / off, it is possible to quickly identify which of the multiple switches SW or the multiple light-emitting elements L has an abnormality.

[0110] (9) In any one of (1) to (9) above, In the first connection line 31, a wiring 25 of a monitoring circuit 43 is connected between a connection point Cn with the second connection line 32 (32h, 32c, 32f) and the power supply source PS.

[0111] With this configuration, even if the switch SW of any second connection line 32 (32h, 32c, 32f) is driven on / off, abnormalities in the switches SW and light-emitting elements L provided in all second connection lines 32 (32h, 32c, 32f) can be detected.

[0112] (10) In (9) above, In the circuit 3, resistors Ra, Rb (Rbh, Rbc, Rbf) are provided upstream and downstream of a connection point Cn between the first connection line 31 and the second connection line 32 (32h, 32c, 32f), respectively. In circuit 3, between the resistor Ra upstream of the connection point Cn and the connection point Cn, The monitoring circuit is connected.

[0113] With this configuration, the wiring 25 of the monitoring circuit 43 is connected between the resistor Ra on the upstream side of the connection point Cn and the resistor Rb (Rbh, Rbc, Rbf) on the downstream side. This allows the monitoring circuit 43 having the microcomputer MC to detect the voltage when the switch SW is on / off, thereby making it possible to detect abnormalities in the switches SW, the light-emitting elements L, and the resistors Ra provided on all of the second connection lines 32 (32h, 32c, 32f).

[0114] Although the embodiment and modifications of the present invention have been described above, the present invention is not limited to these and can be modified as appropriate within the scope of the technical concept of the invention. [Explanation of symbols]

[0115] 1: Switch device (load driver) 25: Wiring 3: Circuit 31: First connecting line 32(32c, 32f, 32h): Second connecting line 41: Detection circuit 42: Lighting control circuit 43: Monitoring circuit 45, 47: Connection lines 46: Voltage sensor 50: Processing section 60: Storage section Cn, Cn1: Connection points L (Lc, Lf, Lh): Light emitting element SW (SWc, SWf, SWh): Switch (drive switch) P (Pc, Pf, Ph): Operation buttons MC: Microcomputer PS: Power supply source (driving power source) V_ave: Average value of feedback voltage V_off: Voltage (when the switch is off) V_on: Voltage (when the switch is on) V_std: Standard output voltage

Claims

1. A drive switch that is controlled to be on / off based on a drive signal; A load connected in series to the driving switch; a power supply source for supplying power for driving the load and a monitoring circuit for acquiring a voltage at an arbitrary point between the power supply source and the driving switch, The monitoring circuit The load driving device detects an abnormality in at least one of the drive switch and the load based on a voltage acquired when the drive switch is on and a voltage acquired when the drive switch is off.

2. In claim 1, a first connection line for connecting to the power supply source; a second connection line in which the load and the driving switch are arranged in series, a plurality of the second connection lines are connected in parallel to the first connection line, The monitoring circuit includes: The load driving device detects the abnormality based on a voltage value during on / off control of one of a plurality of driving switches.

3. In claim 1 or 2, The detection of the abnormality is performed by comparing an average value of the acquired voltages with a threshold value, or by comparing a sum of the acquired voltages with a threshold value; the average voltage value is an average value of a voltage acquired when the drive switch is on and a voltage acquired when the drive switch is off, The load driving device, wherein the added voltage value is a value obtained by adding together a voltage acquired when the driving switch is on and a voltage acquired when the driving switch is off.

4. In claim 3, A load driving device, wherein the output voltage of the power supply source is a battery voltage or a voltage that varies in conjunction with the battery voltage, and the threshold value is changed according to the output voltage.

5. In claim 4, the drive signal is a PWM signal, The load driving device includes an LED element whose light emission amount changes according to a duty ratio of the PWM signal.

6. In claim 5, A load driving device, wherein a duty ratio of the PWM signal is set between a lower limit value greater than 0% and an upper limit value less than 100%.

7. In claim 6, A load driving device, wherein the duty ratio is set to a higher value that lengthens an on-period of the driving switch as the output voltage of the power supply source decreases.

8. In claim 2, The load driving device, wherein the second connection lines are provided in the same number as the operation buttons that are selectively turned on.

9. In claim 2 or claim 8, The load driving device, wherein the monitoring circuit is connected in the first connection line between a connection point with the second connection line and the power supply source.

10. In claim 9, a resistor is provided on one side and the other side of a connection point between the first connection line and the second connection line, A load driving device, wherein the processing device of the monitoring circuit is connected between the resistor and the connection point on the first connection line.

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