EP4734664A1

EP4734664A1 - Load driving device

Info

Publication number: EP4734664A1
Application number: EP24825496.3A
Authority: EP
Inventors: Rohit Sharma; Naoya Yoda
Original assignee: Valeo Japan Co Ltd
Current assignee: Valeo Japan Co Ltd
Priority date: 2023-06-23
Filing date: 2024-02-06
Publication date: 2026-04-29
Also published as: JP2025003215A; WO2024262084A1; JP7519508B1

Abstract

[Problem] To determine the presence or absence of an abnormality in a circuit while suppressing an expansion of a circuit scale. [Solution] A switch device 1 comprises: switches SW (SWh, SWc, SWf) that each are on/off-controlled on the basis of a drive signal; light-emitting elements L (Lh, Lc, Lf) that are connected in series to the respective 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 which 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 a switch SW (SWh, SWc, SWf) to be driven is on and of a voltage acquired when a switch SW (SWh, SWc, SWf) to be driven is off.

Description

Technical field

The present invention relates to a load driving device having a function of detecting a failure in an LED circuit.

Background art

Patent Document 1 discloses a lighting control system.

Prior art literature

Patent literature

Patent Document 1: JP 2018-55795 A

Summary of the invention

Problems to be resolved by the invention

Patent Document 1 indicates that a PWM signal corresponding to control content is output to a circuit in which loads (lighting appliances) are connected in parallel, and the connection status of the loads and the presence or absence of an abnormality such as a short circuit are determined from a voltage value based on the PWM signal in the circuit.
Patent Document 1 indicates that the voltage value based on the PWM signal is acquired using the following method. (a) A current detection circuit is provided to detect the value of a current flowing through the circuit, and to convert the detected current value into a voltage value.
Here, if an integrated circuit (microcontroller) is used to realize these functions, a large microcontroller is required, increasing the scale of the circuit. Furthermore, if one attempts to use discrete circuits to realize these functions, in the case of (a), a shunt resistor and an operational amplifier are required, increasing the scale of the circuit.
Accordingly, there is a demand for a method that makes it possible to determine whether or not there is an abnormality in a circuit while suppressing an expansion of the circuit scale.

Disclosure of the invention

Means for overcoming the problem

Provided is a load driving device comprising a drive switch that is on/off controlled on the basis of a drive signal,

a load that is connected in series with the drive switch, and
a monitoring circuit that acquires a voltage at an arbitrarily defined point between a power supply source that supplies drive electric power for the load, and the drive switch, wherein
the monitoring circuit
detects an abnormality in at least one of the drive switch and the load on the basis of a voltage acquired when the drive switch is on and a voltage acquired when the drive switch is off.

Advantages of the invention

According to the present invention, it is possible to determine whether or not there is an abnormality in a circuit while suppressing an increase in the circuit scale.

Brief explanation of the drawings

[Fig. 1] is a schematic diagram of a switch device.
[Fig. 2] is a diagram illustrating a switch control signal.
[Fig. 3] is a diagram illustrating the waveform of a voltage value detected by a microcontroller of a monitoring circuit.
[Fig. 4] is a diagram illustrating a relationship between abnormality type and threshold value.
[Fig. 5] is a diagram illustrating a threshold value table.
[Fig. 6] is a flowchart of normal processing performed by the microcontroller.
[Fig. 7] is a flowchart of abnormality determination processing.
[Fig. 8] is a flowchart of abnormality determination processing according to a modified example.

Description of Embodiments

By way of example, a description will now be given of a case in which the load driving device according to the present invention is a switch device 1 used to switch the operating mode of an appliance.
Fig. 1 is a schematic diagram of the switch device 1.
The switch device 1 is used by a user to switch the operating mode of the appliance. The appliance of which the operating mode is to be switched has a plurality of operating modes that are selected mutually exclusively.
An air conditioner is one example of this type of appliance. Air conditioners have operating modes such as "heater," "cooler," "fan," and "stop" that are selected mutually exclusively.
As shown in fig. 1, the switch device 1 has a plurality of operating buttons P (Ph, Pc, Pf, Ps). Each of the operating buttons P (Ph, Pc, Pf, Ps) is individually assigned a function specifying the operating mode, such as heater, cooler, fan, or stop.
In the following description, when no particular distinction is being made between the operating buttons, they are simply referred to as operating buttons P.
In the switch device 1, when one of the operating buttons P (Ph, Pc, Pf) corresponding to a drive operating mode is turned on to drive the air conditioner, a light-emitting element L (Lh, Lc, Lf) for notifying the operating mode selected by the ON operation is lit. This allows the user to visually ascertain the selected operating mode by checking the lit light-emitting element L (Lh, Lc, Lf).
Furthermore, when another operating button P (Ph, Pc, Pf) corresponding to a drive operating mode is newly turned on, the light-emitting element L (Lh, Lc, Lf) for reporting the operating mode that was already selected is extinguished, and another light-emitting element L (Lh, Lc, Lf) for reporting the newly selected operating mode is lit.
In the following description, when no particular distinction is being made between the light-emitting elements, they are simply referred to as light-emitting elements L.
A printed circuit board (not shown) and a power supply source PS are accommodated inside a main body case (not shown) of the switch device 1. A circuit 3 on the printed circuit board has a first connecting line 31 connected to the power supply source PS (DC power supply) and second connecting lines 32 (32h, 32c, 32f) connected to ground GD.
The power supply source PS is, for example, a battery that can charge and discharge power. The power supply 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 a battery voltage or a voltage that varies in conjunction with the battery voltage.
In the circuit 3, three second connecting lines 32 (32h, 32c, 32f) are connected to the first connecting line 31 in parallel.
In each second connecting line 32 (32h, 32c, 32f), a light-emitting element L (Lh, Lc, Lf) and a switch SW (SWh, SWc, SWf) are arranged in series. In each second connecting line 32 (32h, 32c, 32f), the light-emitting element L (Lh, Lc, Lf) is located closer to the first connecting line 31 than the switch SW (SWh, SWc, SWf).
In the circuit 3 (first connecting line 31, second connecting lines 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, LEDs (light emitting diodes). The light-emitting elements L (Lh, Lc, Lf) are an example of a load to which drive electric power is supplied from the power supply source PS.
In the second connecting line 32 (32h, 32c, 32f), the switches SW (SWh, SWc, SWf) are located between the light-emitting elements L (Lh, Lc, Lf) and 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 the present embodiment are, for example, NPN-type transistors. The switches SW (SWh, SWc, SWf) may equally be field-effect transistors or the like that turn on when a drive voltage is input to a base B thereof.
In the circuit 3, when the switch SW (SWh, SWc, SWf) is turned on, a current flows from a collector C located on the power supply source PS side to an emitter E located on the ground GD side. As a result, a current flows through the light-emitting element L (Lh, Lc, Lf) located upstream of the switch SW (SWh, SWc, SWf) that has been turned on, causing the light-emitting element L (Lh, Lc, Lf) to emit light with a light emission amount corresponding to the amount of current.
In addition to the circuit 3, the printed circuit board is provided with a detecting circuit 41 that detects the ON operations of the operating buttons P (Ph, Pc, Pf, Ps), a lighting control circuit 42 for lighting the light-emitting element L (Lh, Lc, Lf) corresponding to the operating button P (Ph, Pc, Pf) that has been operated, and a monitoring circuit 43 that acquires a voltage value at an arbitrarily defined position on the first connecting line 31 of the circuit 3.
Fig. 2 is a diagram illustrating a control signal for the switches SW.
In the present embodiment, the switches SW (SWh, SWc, SWf) are controlled to be on or off by means of a PWM signal (pulse width modulation signal), serving as the drive signal. As shown in fig. 2, the PWM signal is a control signal in which a period (pulse width H) during which the voltage applied to the base B of the switch SW is at a high level and a period (pulse width L) during which the voltage is at a low level can be adjusted within the range of a pulse period T.
The ratio between the ON period and the OFF period of the switch SW (SWh, SWc, SWf) can be adjusted by changing a duty ratio D = (pulse width H/pulse period T) of the PWM signal, thereby enabling the amount of current flowing from the collector C side to the emitter E side of the switch SW (SWh, SWc, SWf) to be adjusted.
It should be noted that in the present embodiment, an average value V_ave of a feedback voltage, described hereinafter, is calculated using the feedback voltage (voltage value) during the period when the switch SW (SWh, SWc, SWf) is on and the feedback voltage (voltage value) during the period when the switch SW (SWh, SWc, SWf) is off.
Therefore, the duty ratio of the PWM signal is preferably set between a lower limit value greater than 0% and an upper limit value less than 100%. Furthermore, if upper and lower limit values of the duty ratio of the PWM signal are not set, the feedback voltage is preferably acquired while avoiding instances when the duty ratio is 0% or 100%.
Here, the light emission amount of the light-emitting elements L (Lh, Lc, Lf) can be adjusted by performing duty control of the amount of current flowing through the light-emitting elements L (Lh, Lc, Lf). In the case of fig. 2, a pulse width H' is greater than the pulse width H. Therefore, the duty ratio D' when the pulse width is H' is greater than the duty ratio D when the pulse width is H. Thus, a larger current flows through the light-emitting element L (Lh, Lc, Lf) when the pulse width is H' than when the pulse width is H, and therefore the light emission amount of the light-emitting element L (Lh, Lc, Lf) increases.
Input of the PWM signals to the bases B of the switches SW (SWh, SWc, SWf) is controlled by a control device such as a microcontroller MC (processor) on the printed circuit board.
In the present embodiment, when an operating button P (Ph, Pc, Pf, Ps) is turned on, an ON signal is input from the detecting circuit 41 corresponding to the operating button P (Ph, Pc, Pf, Ps) that has been turned on, to the microcontroller MC provided in the monitoring circuit 43. The microcontroller MC identifies the operating button P (Ph, Pc, Pf, Ps) that has been turned on. If the identified operating button P (Ph, Pc, Pf) is an operating button for an operating mode that drives the air conditioner, a PWM signal is output to the switch SW corresponding to the identified operating button P (Ph, Pc, Pf) to turn the switch SW on.
Furthermore, if the operating button Ps for stopping the air conditioner is turned on while a PWM signal is being output, the output of the PWM signal to the switch SW corresponding to the operating button P (Ph, Pc, Pf) that was turned on is stopped. As a result, the operation of the air conditioner stops.
The monitoring circuit 43 is connected to the circuit 3 to detect whether or not there is an abnormality in the circuit 3 on the basis of the voltage value while the switch SW is being on/off controlled (PWM controlled).
In the present embodiment, wiring 25 on the monitoring circuit 43 side is connected between the power supply source PS and a connection point Cn of the first connecting line 31 and the second connecting lines 32 (32h, 32c, 32f), in the circuit 3.
In the circuit 3, resistors Ra and 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 in the second connecting lines 32 (32h, 32c, 32f), respectively.
It is also possible to connect the monitoring circuit 43 side wiring 25 to the second connecting lines 32, but in the present embodiment, connecting the monitoring circuit 43 side wiring 25 to the first connecting line 31 allows one monitoring circuit 43 to detect whether or not there is an abnormality in the elements (light-emitting elements L, switches SW) on each second connecting line 32 (32h, 32c, 32f).
The monitoring circuit 43 has a microcontroller MC (processor) for performing abnormality detection processing. The microcontroller MC is connected to the first connecting line 31 via the wiring 25. A resistor Rc is provided between the microcontroller MC and the first connecting line 31. One end of a resistor Rd is connected to the wiring 25 between the resistor Rc and the microcontroller MC. The other end of the resistor Rd is connected to ground GD.
In the monitoring circuit 43, a resistive voltage-dividing circuit formed by the two resistors Rc and Rd is provided between the first connecting line 31 and the microcontroller MC. The power supply source PS described hereinabove can, for example, supply a predetermined voltage, such as 16V, to the circuit 3. The resistive voltage-dividing circuit is provided in order to reduce the voltage on the circuit 3 side to a voltage that can be detected by the microcontroller MC.
In the following description, when no particular distinction is being made between the resistors, they are simply referred to as resistors R.
As shown in fig. 1, the microcontroller MC has an input/output port I/O, a processing unit 50 such as a CPU, and a storage unit 60 configured by a RAM, a ROM, or the like. The input/output port I/O, the processing unit 50 and the storage unit 60 are connected to one another via a bus 65.
The detecting circuit 41 that detects the ON operations of the operating buttons P (Ph, Pc, Pf, Ps) is connected to the input/output port I/O. When any of the operating buttons P (Ph, Pc, Pf, Ps) is turned on, a signal is input from the connecting line connected to the operating button P (Ph, Pc, Pf, Ps) that has been turned on.
The bases B of the switches SW (SWh, SWc, SWf) are connected to the input/output port I/O via connecting lines 45. When any of the switches SW (SWh, SWc, SWf) is to be turned on and driven, a PWM signal generated by the processing unit 50 is output to the connecting line 45 of the switch SW to be driven.
The wiring 25 of the monitoring circuit 43 is connected to the input/output port I/O via the resistor Rc. While any one of the switches SW (SWh, SWc, SWf) is being driven, the voltage stepped down by the resistive voltage-dividing circuit (resistors Rc and Rd) is input to the input/output port I/O.
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 connecting 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 microcontroller MC (processing unit 50) via the input/output port I/O.
The processing unit 50 performs arithmetic processing defined by a program stored in the storage unit 60.
The storage unit 60 stores the program for the arithmetic processing executed by the processing unit 50 and information generated in the course of the arithmetic processing.
As described above, the on/off control of the switches SW is performed by adjusting the duty ratio D of the PWM signals.
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 connecting line 32h having the switch SWh that has been turned on. When a current flows through the circuit 3 toward the ground GD, the voltage value detected by the microcontroller MC of the monitoring circuit 43 increases or decreases in accordance with the output voltage of the power supply source PS and the voltage drop across each element of the circuit 3.
Fig. 3 is a diagram illustrating the waveform of the voltage value detected by the microcontroller MC of the monitoring circuit 43.
Specifically, as shown in fig. 2 and fig. 3, during the period when a High signal is being input to the switch SW to turn the switch SW on (the ON period of the switch SW), a voltage drop causes a voltage value Von detected by the microcontroller MC to be lower than a voltage value Voff during the period when a Low signal is being input to the switch SW (the OFF period of the switch SW).
In the processing unit 50, processing (abnormality determination processing) for determining whether or not there is an abnormality in the circuit 3 is executed while on/off control of the switches SW is being performed. That is, the abnormality determination processing is executed in parallel with the on/off control of the switches SW.
When performing the abnormality determination processing, the processing unit 50 acquires 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 acquires the voltage value at the midpoint of the period during which the switch SW is on as the voltage value Von. Furthermore, the processing unit 50 acquires the voltage value at the midpoint of the period during which the switch SW is off as the voltage value Voff.
In the case of fig. 3 (A), the processing unit 50 acquires the voltage value at a midpoint tb in a period from a timing ta at which the voltage drops due to the switch SW being turned on to a timing tc at which the voltage rises due to the switch SW being turned off as the voltage value Von.
Similarly, the processing unit 50 acquires the voltage value at a midpoint td in a period from a timing tc at which the voltage rises due to the switch SW being turned off to a timing te at which the voltage drops due to the switch SW being turned on as the voltage value Voff.
The detected voltage value may fluctuate greatly immediately after the switch SW is turned on/off. By acquiring the voltage values at the midpoints as the voltage values Von and Voff, the influence of fluctuations and delays in the voltage value immediately after switching can be reduced. Furthermore, instead of the voltage values at the midpoints, voltage values after a predetermined time required for the switch SW to be switched on/off, relative to the rising/falling edges of the PWM signal, may be acquired.
The processing unit 50 calculates the average value V_ave of the acquired voltage values Von and Voff as the 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. 3(A), the average value of the voltage value Voff at time tb and the voltage value Von at time td is calculated as the average value V_ave of the feedback voltage.
The processing unit 50 determines whether or not there is an abnormality in the circuit 3 by comparing the calculated average value V_ave with an abnormality determination threshold value Th.
Fig. 4 is a diagram illustrating a relationship between the abnormality category (type) 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 abnormality, and threshold values for distinguishing the abnormality category (type).
Fig. 5 is a diagram illustrating a threshold value table. Fig. 5 summarizes an example of the relationship between the output voltage of the power supply source PS and threshold values for determining an abnormality.
As described above, in the present embodiment, a plurality of elements (light-emitting elements L, switches SW, resistors R) are provided in the circuit 3 (see fig. 1). One light-emitting element L and one switch SW are provided in each second connecting line 32 (32h, 32c, 32f) of the circuit 3. One resistor Ra is provided in the first connecting line 31, upstream of a connection point Cn1 with the monitoring circuit 43.
In the present embodiment, the presence or absence of an abnormality in the plurality of elements (light-emitting elements L, switches SW, resistors Ra) is confirmed by the abnormality determination processing described above.
Here, "normal" and "abnormal" are prepared as labels indicating the determination result.
"Normal" means that no short-circuit failure or open-circuit failure has occurred in any of the three light-emitting elements L, the three switches SW, or the one resistor Ra.
"Abnormal" means that a short-circuit failure an open-circuit failure has occurred in any of the elements in the circuit (light-emitting elements L, switches SW, resistors Ra).
In the present embodiment, in order to distinguish which element (light-emitting element L, switch SW, resistor Ra) is experiencing such a failure, the "abnormality" category is subdivided into four categories: "abnormality 1," "abnormality 2," "abnormality 3," and "abnormality 4."
Here, a short-circuit failure means a state in which the upstream and downstream sides of the element (light-emitting element L, switch SW, resistor Ra) in which the short-circuit failure has occurred are electrically connected such that 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 failure means a state in which no current flows from the upstream side to the downstream side of the element (light-emitting element L, switch SW, resistor Ra) in which the open-circuit failure has occurred.
"Abnormality 1" is a category indicating a case in which an open-circuit failure has occurred in at least one of the light-emitting element being driven and the switch being driven.
Here, the switch being driven means the switch that is being on/off controlled by means of a PWM signal. The light-emitting element being driven means the light-emitting element that is arranged in series with the switch that is being on/off controlled, and is the light-emitting element that is being caused to emit light.
"Abnormality 2" is a category indicating a case in which a short-circuit failure has occurred in the light-emitting element being driven.
"Abnormality 3" is a category indicating a case in which a short-circuit failure has occurred in at least one of the switches.
"Abnormality 4" is a category indicating a case in which an open-circuit failure has occurred in the resistor Ra.
In the present 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, to thereby determine whether or not there is an abnormality, and, if there is an abnormality, to identify the category of the abnormality.
In the threshold table shown in fig 5, a plurality of thresholds are set in advance to determine whether or not there is an abnormality, and to identify the category (abnormality 1 to abnormality 4) if there is an abnormality.
As an example, in the threshold value table, threshold values (first threshold value Th1, second threshold value Th2, third threshold value Th3, fourth threshold value Th4) are set for the standard output voltage V_std of the power supply source PS.
Here, when an abnormality occurs in the circuit 3, the voltage value (feedback voltage) that can be detected by the monitoring circuit 43 will lie outside the range of voltage values when the circuit 3 is normal.
Therefore, the first threshold value Th1 (upper limit threshold value) and the second threshold value Th2 (lower limit threshold value) are set at the upper and lower ends of the range of voltage values when all elements are normal, to determine a deviation from the normal range.
The first threshold value Th1 is also the threshold value for checking whether or not there is an open-circuit failure in the switch SW being driven and the light-emitting element L (light-emitting element L being driven) provided in series with this switch SW.
For example, if an open-circuit failure has occurred in at least one of the switch SW being driven and the light-emitting element L being driven, the path from the power supply source PS to ground GD is not connected, and therefore no current flows through the circuit 3. In this case, no voltage drop occurs as a result of current flowing through the light-emitting element L and the switch SW, and therefore the feedback voltage (voltage value of the circuit 3) acquired by the monitoring circuit 43 is higher than when no open-circuit failure has occurred in the light-emitting element or switch (the normal case).
In the present embodiment, if 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 microcontroller MC recognizes the abnormality category to be "abnormality 1."
In the present embodiment, the first threshold value Th1 is determined on the basis of the upper limit of the feedback voltage when no failure (open-circuit failure or short-circuit failure) has occurred in either the light-emitting element L or the switch SW, and the lower limit of the feedback voltage when an open-circuit failure has occurred in the light-emitting element or the switch.
Specifically, the first threshold value Th1 is set to an intermediate value between the upper limit of the feedback voltage when no failure has occurred and the lower limit of the feedback voltage when an open-circuit failure has occurred in the light-emitting element or the switch.
Here, the upper limit of the feedback voltage when no failure has occurred and the lower limit of the feedback voltage when an open-circuit failure has occurred in the light-emitting element or the switch are values calculated by simulation or the like using a circuit model that takes into account variations in the elements (light-emitting elements L, switches SW, resistors R), for example.
The second threshold value Th2 is the lower limit threshold value at which it can be determined that the element is normal, and is also the threshold value for checking whether a short-circuit failure has occurred in the light-emitting element L being driven.
If the light-emitting element L being driven is short-circuited, the feedback voltage when the switch SW arranged in series with this light-emitting element L is turned on becomes a value that is lower by the forward voltage of the light-emitting element than the voltage when there is no short-circuit. In association therewith, the average value V_ave also becomes a lower value.
The extent of the drop in the feedback voltage at this time is less than that when the switch SW being driven experiences a short-circuit failure, or when a switch SW or light-emitting element L that is not being driven experiences a short-circuit failure. Therefore, the drop in the feedback voltage is smallest when the light-emitting element being driven experiences a short-circuit failure.
It should be noted that 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 the short circuit has occurred.
In the present embodiment, if the average value V_ave of the feedback voltage is less than or equal to the first threshold value Th1 (V_ave≤Th1) and greater than or equal to 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."
Meanwhile, if the average value V_ave of the feedback voltage is less than the second threshold value Th2 (Th2>V_ave), this indicates that an abnormality of some kind has occurred.
The third threshold value Th3 is a threshold value for determining whether the detected abnormality is a short-circuit failure in the light-emitting element L being driven (a failure having the category "Abnormality 2") or an abnormality ("Abnormality 3") belonging to a category other than "Abnormality 2".
If the light-emitting element (light-emitting element L being driven) provided in series with the switch SW being driven experience a short-circuit failure, the feedback voltage when the switch SW being driven is turned on (when the PWM signal is High) becomes a value that is lower by the forward voltage of the light-emitting element than the voltage when there is no short-circuit failure.
As shown in fig. 3, in comparison with a case in which the light-emitting element L being driven is not experiencing a short-circuit failure (see fig. 3 (A)), in a case in which there is a short-circuit failure (see fig. 3 (B)), the extent of the decrease in the voltage value Von when the switch SW is turned on is smaller by ΔV.
In contrast, in the case of a failure belonging to the "abnormality 3" category, the effect on the voltage value Von when the switch SW is turned on is approximately the same as the effect on the voltage value Voff when the switch SW is turned off. Therefore, the extent of the drop in the feedback voltage is less when the light-emitting element L being driven experiences a short-circuit failure (abnormality 2) than when the switch SW being driven experiences a short-circuit failure, or when a switch SW that is not being driven experiences a short-circuit failure (abnormality 3).
In other words, the extent of the drop in the feedback voltage is less for an abnormality belonging to the category of "abnormality 2" than for an abnormality belonging to the category of "abnormality 3".
In the present embodiment, if the average value V_ave of the feedback voltage is less than the second threshold value Th2 (V_ave<Th2) and greater than or equal to the third threshold value Th3 (Th3≤V_ave<Th2), the processing unit 50 of the microcontroller MC recognizes the abnormality category to be "abnormality 2."
Here, the extent of the drop in the feedback voltage when the switch SW being driven experiences a short-circuit failure is smallest. Then, as the number of short-circuit failures in the switches SW that are not being driven increases, the extent of the drop in the feedback voltage increases.
Therefore, in the present embodiment, the third threshold value Th3 is set to an intermediate value between the feedback voltage when a short-circuit failure has occurred in the light-emitting element L being driven and the feedback voltage when a short-circuit failure has occurred in the switch SW being driven.
It should be noted that the voltage values used to calculate the intermediate values are values calculated by a simulation or the like using a circuit model that takes into account variations in the elements (light-emitting elements L, switches SW, resistors R).
The fourth threshold value Th4 is a threshold value for determining whether the detected abnormality is an open-circuit failure in the upstream resistor Ra in the monitoring circuit 43 (a failure having the category "abnormality 4") or a short-circuit failure in at least one of the switches SW (a failure having the category "abnormality 3").
If an open-circuit failure has occurred in the resistor Ra in the first connecting line 31, the path from the power supply source PS to the monitoring circuit 43 is not connected. In such a case, the feedback voltage detected by the monitoring circuit 43 will be a low value close to 0 V regardless of whether the switch SW being driven is on or off.
The feedback voltage at this time is a value that is lower than the voltage value when all the plurality of switches that are not being driven are short-circuited.
In the present embodiment, the fourth threshold value Th4 is set to a value that is lower than the voltage value when all the plurality of switches that are not being driven are short-circuited, and that is higher than 0 V.
As an example, in the present embodiment, the fourth threshold value Th4 is set to an intermediate value between the feedback voltage value when all the plurality of switches that are not being driven are short-circuited, and 0 V.
Therefore, when the average value V_ave of the feedback voltage is less than the fourth threshold value Th4 (V_ave<Th4), the processing unit 50 of the microcontroller MC recognizes the abnormality category to be "abnormality 4."
Then, if the average value V_ave of the feedback voltage is less than the third threshold value Th3 (V_ave<Th2) and greater than or equal to the fourth threshold value Th4 (Th4≤V_ave<Th3), the processing unit 50 of the microcontroller MC recognizes the abnormality category to be "abnormality 3."
Here, the output voltage of the power supply source PS may fluctuate from a standard output voltage depending on the total number of loads to which drive power is being supplied from the power supply source PS and the amount of power being consumed by each load.
Therefore, in the present embodiment, the abovementioned threshold values Th1 to Th4 are prepared for different voltage values in consideration of the fluctuation range of the output voltage.
In the threshold value table shown in fig. 5, threshold values corresponding to fluctuations within a range of ±1.0 volts around a standard output voltage V_std are prepared in increments of 0.5 volts.
The threshold value table specifies thresholds (first threshold Th1±a, Th1±b, second threshold Th2±a, Th2±b, third threshold Th3±a, Th3±b, fourth threshold Th4±a, Th4±b) corresponding to a 0.5 volt or 1.0 volt shift to the positive side and a 0.5 volt or 1.0 volt shift to the negative side, in increments of 0.5 volts from the standard output voltage V_std.
The threshold values defined in the threshold table are set on the basis of values calculated by simulation or the like using a circuit model that takes into account variations in the elements (light-emitting elements L, switches SW, resistors R).
Fig. 6 is a flowchart of normal processing performed by the processing unit 50.
A description of normal processing and abnormality determination processing performed by the processing unit 50 will now be given, taking by way of example a case in which, in the switch device 1 equipped with the operating buttons P (Ph, Pc, Pf, Ps) for the operating modes of an air conditioner, the operating button Sc for selecting "cooler" as the operating mode is turned on.
When any of the operating 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 operating button that has been turned on (step S102).
If the operating button Pc for specifying "cooler" is turned on, a control signal is input from the processing unit 50 to the base B of the switch SWc corresponding to the operation button Pc. As described above, the control signal is a PWM signal in which a high signal and a low signal fluctuate with 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 source) and the ground GD are connected via the second connecting line 32c in which the switch SWc is provided (see fig. 1). As a result, current flows from the power supply source PS to the ground GD of the second connecting line 32c, and the light-emitting element Lc connected in series with the switch SWc emits light with a light emission amount corresponding to the duty ratio D.
When the PWM control (step S102) of the switch begins, abnormality detection processing is performed to detect whether or not there is an abnormality in the circuit 3 (step S103).
Fig. 7 is a flowchart of the abnormality determination processing performed by the processing unit 50.
In the abnormality determination processing, the processing unit 50 of the monitoring circuit 43 acquires a feedback voltage V_on during the period in which the switch SW is on (step S201).
Here, if the specification of the switch SW is for the switch SW to be on when a high signal is input, 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).
Furthermore, 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. 3 (A), the voltage value at the midpoint tb in the period from the timing ta at which the voltage drops due to the switch SW being turned on to the timing tc at which the voltage rises due to the switch being turned off is acquired as the voltage value Von.
Next, the processing unit 50 acquires a feedback voltage V_off during the period in which the switch SW is off (step S202).
Here, if the specification of the switch SW is for the switch SW to be off when a low signal is input, 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 a 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. 3 (A), the voltage value at the midpoint td in the period from the timing tc at which the voltage rises due to the switch SW being turned off to the timing te at which the voltage drops due to the switch being turned on is acquired as the voltage value Voff.
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).
Next, the control unit compares the average value V_ave of the feedback voltage with the 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), processing proceeds to step S205. This corresponds to a case in which the circuit 3 has an abnormality belonging to "abnormality 1", and therefore, in step S205, the processing unit 50 executes abnormality processing determined for the case of "abnormality 1".
Specifically, the processing unit 50 outputs, to an external control device or appliance connected to the microcontroller MC, a signal indicating that an abnormality belonging to "abnormality 1" has occurred. The processing unit 50 turns on all the light-emitting elements that can be turned on, and performs processing or the like to allow the occurrence of the abnormality to be recognized visually.
Meanwhile, if the average value V_ave is equal to or less than the first threshold value Th1 (Th1≥V_ave) (No in step S204), processing 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.
If the average value V_ave is greater than or equal to the second threshold value Th2 (Th2≤V_ave) (step S206, Yes), the average value V_ave is a value that is less than or equal to the first threshold value Th1 and greater than or equal to the second threshold value Th2, and the average value V_ave of the feedback voltage falls within a voltage range that can be considered normal.
This corresponds to a case in which there is no abnormality in the circuit 3, and therefore, in step S207, the processing for a case determined to be "normal" (normal processing) is carried out.
For example, in the normal processing, the microcontroller MC outputs, to the external control device or appliance connected thereto, a signal indicating that the circuit 3 is "normal." It should be noted that the processing of step S207 may be omitted.
Meanwhile, if the average value V_ave is less than the second threshold value Th2 (V_ave<Th2) (No in step S206), processing proceeds to step S208, and the processing unit 50 compares the average value V_ave of the feedback voltage with the third threshold value Th3.
If the average value V_ave is equal to or greater than the third threshold value Th3 (V_ave≥Th3) (Yes in step S208), processing proceeds to step S209. This corresponds to a case in which the circuit 3 has an abnormality belonging to "abnormality 2", and therefore, in step S209, the processing unit 50 executes abnormality processing determined for the case of "abnormality 2".
Meanwhile, if the average value V_ave is less than the third threshold value Th3 (V_ave<Th3) (No in step S208), processing proceeds to step S210.
In step S210, the processing unit 50 compares the average value V_ave of the feedback voltage with the fourth threshold value Th4.
If the average value V_ave is equal to or greater than the fourth threshold value Th4 (V_ave≥Th4) (Yes in step S210), processing proceeds to step S211. This corresponds to a case in which the circuit 3 has an abnormality belonging to "abnormality 3", and therefore, in step S211, the processing unit 50 executes abnormality processing determined for the case of "abnormality 3".
Meanwhile, if the average value V_ave is less than the fourth threshold value Th4 (V_ave<Th4) (No in step S210), processing proceeds to step S212. This corresponds to a case in which the circuit 3 has an abnormality belonging to "abnormality 4", and therefore, in step S212, the processing unit 50 executes abnormality processing determined for the case of "abnormality 4".
When the processing in any one of steps S205, S207, S209, S211, and S212 has been performed, the abnormality determination processing ends, and processing proceeds to step S104 in fig. 2.
Returning to the flowchart of fig. 6, in step S104, the processing unit 50 checks whether or not another operating button has been operated. If no other operation button has been operated (No in step S104), the cooler mode remains selected as the operating mode of the air conditioner.
In this case, the processing proceeds to step S103, and the abnormality detection processing described above is carried out. Thus, the abnormality determination processing is performed repeatedly until another operating button is operated.
Then, when another operating button is operated (Yes in step S104), in step S105 the processing unit 50 checks whether or not the operated operating button is the operation stop operating button Ps. If it is the operation stop operating button Ps, the PWM control of the switch SW is terminated (step S106). This terminates the operation of the air conditioner.
If an operating button other than the operation stop operation button Ps is operated (No in step S105), the processing proceeds to step S102. As a result, a control signal (PWM signal) is input from the microcontroller MC (processing unit 50) to the base B of the switch SW corresponding to the newly operated operating button.
For example, if the newly operated operating button is the operating button Pf corresponding to "fan," a control signal is input to the base B of the switch SWf, and PWM control of the switch SWf is performed.
In this way, the monitoring circuit 43 is used to calculate the average value V_ave of the feedback voltage from the voltage value Von when the switch SW being controlled is on and the voltage value Voff when the switch SW being controlled is off. Then, the calculated average value V_ave is compared with the threshold values Th1, Th2, Th3, and Th4 to determine whether or not there is an abnormality in the circuit 3. If there is an abnormality, the category of the abnormality is recognized.
When the drive of the light-emitting element is being controlled by on/off control (switching control) of the switch SW, the amount of current (current value) flowing through the circuit 3 varies in accordance with the on/off ratio. Therefore, if the presence or absence of an abnormality is to be detected on the basis of the current value, an amplification circuit is required so that cases in which the current value is low can also be handled.
As described above, in the case of voltage, although the voltage value differs between when the switch SW is on and off, it is less susceptible to the influence of load driving than in the current value case. This allows appropriate detection of the presence or absence of an abnormality.
It should be noted that it is not possible to distinguish between "abnormality 2" and "abnormality 3" if only the voltage value when the switch SW is off is considered. In the present embodiment, it is possible to distinguish between "abnormality 2" and "abnormality 3" by using both the voltage value Von when the switch SW being controlled is on and the voltage value Voff when the switch SW being controlled is off. That is, in the present embodiment, since the average value V_ave based on both of the two voltage values Von and Voff is used, subdivided abnormality categories can be recognized.

[Modified example 1]

Fig. 8 is a flowchart of abnormality determination processing according to a modified example.
The abnormality determination processing according to modified example 1 differs from the abnormality determination processing shown in fig. 7 in that the threshold values Th1 to Th4 for determining abnormality are changed in accordance with the actual output voltage of the power supply source PS.
Therefore, in the abnormality determination processing according to modified example 1, between step S303 for calculating the average value V_ave of the feedback voltage and step S306 for comparing the average value V_ave with the first threshold value, there is provided a step S304 for acquiring the actual output voltage of the power supply source PS, and a step S305 for determining the threshold values (first threshold value to fourth threshold value) on the basis of the acquired actual output voltage.
Steps S301 to S303 and S306 to S314 of the abnormality determination processing according to modified example 1 are the same as steps S201 to S203 and S204 to S212, respectively, of the abnormality determination processing shown in fig. 7, so steps S304 and S305 will be specifically described here.
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 microcontroller.
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 present time on the basis of the signal input from the voltage sensor 46 (step S304).
Next, the processing unit 50 refers to the threshold value table (fig. 5) to determine the threshold values (first threshold value to fourth threshold value) 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 a threshold value Th1-a, a threshold value Th2-a, a threshold value Th4-a, and a threshold value Th4-a, respectively, as the threshold values (first threshold value, second threshold value, third threshold value, and fourth threshold value) for determining whether or not there is an abnormality in the circuit 3.
As described above, the output voltage of the power supply source PS may fluctuate from the standard output voltage depending on the total number of loads to which drive power is being supplied from the power supply source PS and the amount of power being consumed by each load.
When the output voltage of the power supply source PS fluctuates from the standard output voltage, the fluctuation in the output voltage also affects the feedback voltage detected by the monitoring circuit 43 (microcontroller MC).
As described above, the adjustment threshold values for suppressing the influence of fluctuations in the output voltage are determined in advance by simulation or the like, and the adjustment threshold values are defined in association with the degree of fluctuation in a threshold value table. This allows the optimum threshold values to be selected at a given time by referring to the threshold value table on the basis of the actual output voltage.
This makes it possible to determine more appropriately whether or not there is an abnormality, and to perform the abovementioned categorization if an abnormality occurs.
In the switch device 1 of the embodiment and modified example described hereinabove, the monitoring circuit 43 is configured to include the wiring 25 connecting the first connecting line 31 and the microcontroller MC (control device), the resistive voltage-dividing circuit (resistors Rc, Rd) provided in the wiring 25, and the pair of resistors Ra and Rb (Rbh, Rbc, Rbf).
That is, the function as the monitoring circuit 43 is realized by a combination of individual elements (resistors R, switches SW, light-emitting elements L) rather than by an integrated circuit created collectively.
These individual elements, in particular 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 and placed in the available space on the printed circuit board, and the monitoring circuit 43 can be provided as a discrete circuit. That is, the degree of installation freedom on the printed circuit board is improved.
In the case of an integrated circuit, a large area is required for installation, and therefore the printed circuit board and the switch device 1 may become large. As described above, since the monitoring circuit 43 can be provided as a discrete circuit, it is possible to prevent the printed circuit board and the switch device 1 from becoming large.
Furthermore, since the voltage is detected by the monitoring circuit 43, it is not necessary to provide a shunt resistor or an operational amplifier, which would be required when detecting a current. Therefore, when detecting a current, the circuit scale increases. As described above, the monitoring circuit 43 is configured to detect a voltage and is realized as a discrete circuit, and it is therefore possible to determine whether or not there is an abnormality in the circuit 3 while suppressing an increase in the circuit scale.
Since the unit cost of the individual elements (resistors R, switches SW, light-emitting elements L) is lower than that of an integrated circuit, a reduction in the manufacturing cost of the switch device 1 can be expected.
In the embodiment and modified example described hereinabove, a case was described by way of example in which the average value V_ave of the feedback voltage value 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 value V_ave of the feedback voltage value may equally be calculated from a value obtained by adding voltage values during the period when the switch SW is on and adding voltage values during the period when the switch SW is off. That is, in the case of fig. 3 (A), the average value V_ave of the feedback voltage value may be calculated from the sum of the voltage values Von acquired between time ta and time tc and the sum of the voltage values Voff acquired between time tc and time te.
Alternatively, the average value V_ave of the feedback voltage value may be obtained by calculating and summing the average value V_ave of the feedback voltage value for each pulse period T, and dividing the summed value by the total number of pulse periods T.
It should be noted that the present invention is not limited to only the average value V_ave of the feedback voltage value, provided that 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.
For example, instead of the average value V_ave, an added value (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 a threshold value. Furthermore, the ratio between 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 a threshold value.
Furthermore, 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 each be compared individually with a 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 final abnormality content can also be determined by combining these provisional determinations.

[Modified example 2]

In the first modification described hereinabove, a case was described by way of example in which the threshold values are changed on the basis of the actual output voltage of the power supply source PS. The duty ratio of the control signal for the switch SW being driven may equally be changed on the basis of the actual output voltage of the power supply source PS.
For example, as the output voltage of the power supply source PS decreases, 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, the amount of current supplied to the LED element may decrease depending on the extent of the drop in the output voltage, resulting in a drop in the brightness of the LED element. By adjusting the duty ratio so that the ON period of the switch is lengthened in accordance with the extent of the drop in the output voltage, fluctuations in brightness can be suppressed.

[Modified example 3]

In the case of modified example 2 described hereinabove, if the duty ratio is changed in accordance with fluctuations 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 is also large.
Consequently, for example, if the ON period of the switch SW being driven suddenly decreases, light emission amount of the light-emitting element L suddenly decreases, and if the ON period of the switch SW being driven suddenly increases, the light emission amount of the light-emitting element L suddenly increases.
Accordingly, if the amount of change ΔV in the output voltage of the power supply source PS is greater than a predetermined threshold Thx, the duty ratio may be changed in steps from the duty ratio at the present time 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 (B-A) 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 changes rapidly to the duty ratio D_B when the output voltage is B volts.
In contrast, if the duty ratio is to be changed in steps, 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.
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 change amount ΔF, so that the amount of change ΔV used to determine the duty ratio D is 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 with a predetermined gradient so as to approach zero (=0).
This allows the duty ratio D to be gradually changed from the duty ratio D_A when the output voltage is A volts to the duty ratio D_B when the output voltage is B volts, thereby making it possible to suppress a sudden change in the light emission amount of the light-emitting element.
In the embodiment and modified examples described hereinabove, a case was described by way of example in which the switch SW is on when the PWM signal is high, and the switch SW is off when the PWM signal is low. The specification of the switch may be such that the switch SW is on when the PWM signal is low and the switch SW is off when the PWM signal is high.
In the embodiment and modified examples described hereinabove, the load is an LED. The load in the present invention is not limited only to a light-emitting element. The load may be a resistive element, a solenoid, a heating wire for a heater, or the like, which is an electronic component used in order to obtain a fixed electrical resistance value.
Therefore, in this specification, if the load is a "heater wire" the term "supply of drive electric power" means supplying power to the heater wire. If the load is a "resistive element", it means supplying power to the resistive element. If the load is a "light-emitting element", it means supplying power to the light-emitting element.
Furthermore, in the embodiment and modified examples described hereinabove, an example of application to an air conditioner was illustrated, but the present invention is not limited to this. The present invention is also applicable to other appliances having a load, such as a shift button.
In the embodiment and modified examples described hereinabove, a case was described by way of example in which, in each second connecting line 32 (32h, 32c, 32f), the light-emitting element L (Lh, Lc, Lf) is located closer to the first connecting line 31 than the switch SW (SWh, SWc, SWf). The switches SW (SWh, SWc, SWf) may equally be located closer to the first connecting line 31 than the light-emitting elements L (Lh, Lc, Lf).
Furthermore, a case was described by way of example in which the monitoring circuit 43 is connected to the first connecting line 31. A monitoring circuit 43 may be connected to each of the second connecting lines 32 (32h, 32c, 32f).
In the embodiment and modified examples described hereinabove, a case was described by way of example in which the processing unit 50 performs processing up to the determination of whether or not there is an abnormality in the circuit 3, and, if there is an abnormality, the identification of the type of 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 determination or identifying the type of abnormality. In this case, the external processing device (control device) determines whether or not there is an abnormality in the circuit 3, and if there is an abnormality, identifies the type of abnormality.
The external processing device does not need to be mounted on the same printed circuit board, but may be any device that can exchange information with the microcontroller MC via wire or wirelessly, for example.
As described above, the switch device 1 (load driving device) according to the embodiment has the following configuration.

(1) The switch device 1 comprises
- switches SW (drive switch) that are on/off controlled on the basis of a drive signal,
- light-emitting elements L that are connected in series with the switches SW, and
- a monitoring circuit 43 that acquires a voltage at an arbitrarily defined point between a power supply source PS (drive power source) that supplies drive electric power for the light-emitting elements L (loads), and the switches SW.

The monitoring circuit 43 performs abnormality detection processing to detect an abnormality in at least one of the switches SW and the light-emitting elements L on the basis of a voltage value Von acquired when the switch SW being driven is on and the voltage acquired when the switch SW being driven is off.
When the drive of the light-emitting element is being controlled by on/off control (switching control) of the switch SW, the amount of current (current value) flowing through the circuit 3 varies in accordance with the on/off ratio. Therefore, if the presence or absence of an abnormality is to be detected on the basis of the current value, an amplification circuit is required so that cases in which the current value is low can also be handled.
When the presence or absence of an abnormality is detected using a voltage, as described above, although the voltage value differs between when the switch SW is on and off, it is less susceptible to the influence of load driving than in the current value case. This allows appropriate detection of the presence or absence of an abnormality.
(2) In (1) above,
the circuit 3 of the switch device 1 has a first connecting line 31 connected to the power supply source PS, and second connecting lines 32 (32h, 32c, 32f) in which the light-emitting elements L and the switches SW are arranged in series.
A plurality of second connecting lines 32 (32h, 32c, 32f) are connected to the first connecting line 31 in parallel.
The monitoring circuit 43 performs abnormality detection processing on the basis of a voltage value during on/off control of one switch SW among the plurality of the switches SW (SWh, SEc, SWf).
The voltage detected by the monitoring circuit 43 has a different value depending on the location of the element (light-emitting element L, switch SW, resistor Ra) in which an abnormality occurs and the number of elements (light-emitting elements L, switches SW, resistors Ra) in which an abnormality occurs.
Therefore, by preparing a plurality of thresholds to be used for determining whether or not there is an abnormality and for categorizing the abnormality if there is an abnormality, depending on the location of the element in which an abnormality occurs and the total number of elements in which an abnormality occurs, it is possible to appropriately determine whether or not an abnormality has occurred and identify the category of the abnormality, indicating the kind of abnormality.
In particular, since the plurality of second connecting lines 32 (32h, 32c, 32f) are connected to the first connecting line 31 in parallel, it is possible to detect whether or not there is an abnormality in the light-emitting elements L and switches SW in all of the second connecting lines 32 (32h, 32c, 32f) on the basis of the voltage value during on/off control of one of the plurality of switches SW.
(3) In (1) or (2) above,
In the abnormality detection processing, (a) the average value V_ave of the acquired voltages is compared with the threshold values Th1 to Th4, or (b) the added value V_total of the acquired voltages is compared with the threshold values Th1 to Th4.
The average value V_ave of the acquired voltages is the average value 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 added value V_total of the acquired voltages is a value obtained by adding the voltage value Von acquired when the switch SW is on and the voltage value Voff acquired when the switch SW is off.
For example, when an open-circuit failure occurs in an element (switch SW, light-emitting element L) in the circuit 3, the voltage value Von acquired when the switch is on is high, and when a short-circuit failure occurs in an element (switch SW, light-emitting element L), the voltage value Voff acquired when the switch is off is low.
Furthermore, the acquired voltage value varies depending on which element of the circuit 3 (switch SW, light-emitting element L, resistor Ra) is experiencing an abnormality and what type of abnormality has occurred.
Therefore, by comparing values such as the average value V_ave based on both Von and Voff with the thresholds Th1, Th2, Th3, and Th4, which also serve as thresholds for identifying the abnormality category, it is possible to identify which element in the circuit 3 is experiencing the abnormality and what type of abnormality has occurred.
(4) In any one of (1) to (3) above,
the output voltage of the power supply source PS is a battery voltage or a voltage that varies in conjunction with the battery voltage. The threshold values are changed in accordance with the output voltage.
By changing the threshold values in accordance with the output voltage, it is possible to improve the accuracy of determining whether or not there is an abnormality, while suppressing the effect of fluctuations in the output voltage.
(5) In any one of (1) to (4) above,
the drive signal is a PWM signal output by a microcontroller MC (control device) provided in the monitoring circuit 43.
The light emission amount of the light emitting elements L, which are loads, changes in accordance with the duty ratio of the PWM signal.
When configured as described above, although the amount of current (current value) flowing through circuit 3 fluctuates in accordance with the light emission amount of the light-emitting element L, since the presence or absence of an abnormality can be detected on the basis of the voltage, which is almost unaffected by the light emission amount of the light-emitting element L, the presence or absence of an abnormality can be detected appropriately.
(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%.
With such a configuration, the lower limit value and the upper limit value are set on the basis of the minimum period required to acquire the voltage value, and therefore the voltage value used to determine whether or not there is an abnormality can be acquired appropriately whether the switch is on or the switch is off.
Here, if the duty ratio D becomes too close to 0% or 100%, the accuracy of acquiring the feedback voltage in the monitoring circuit 43 (microcontroller MC) may be affected, and the switch SW may not respond in time. Therefore, by setting the duty ratio D between a lower limit value of 5% or more and an upper limit value of 95% or less, the voltage value Von when the switch SW is on and the voltage value Voff when the switch SW is off can be acquired with high accuracy while reliably performing on/off control of the switch SW. In addition, even if the duty ratio D is changed significantly, both the voltage values Von and Voff required to determine whether or not there is an abnormality can be reliably acquired, thereby making it possible to secure opportunities for determining whether or not there is an abnormality.
(7) In (5) or (6) above,
as the output voltage of the power supply PS decreases, the duty ratio is 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, the amount of current supplied to the LED element may decrease depending on the extent of the drop in the output voltage, resulting in a drop in the brightness of the LED element.
By adjusting the duty ratio so that the ON period of the switch is lengthened in accordance with the extent of the drop in the output voltage, as described above, fluctuations in brightness can be suppressed.
With the above configuration, even if a sudden change occurs in the output voltage of the power supply source, it is possible to suppress a change in the brightness of the light-emitting element.
(8) In any one of (1) to (7) above,
the same number of the second connecting lines 32 (32h, 32c, 32f) are provided as the number of operating buttons P, which are turned on mutually exclusively.
For example, the switch device 1 used to switch the operating mode of an air conditioner has heater, cooler, fan, etc., as operating modes that are selected mutually exclusively.
When the loads of the second connecting lines 32 (32h, 32c, 32f) are light-emitting elements L, the light-emitting elements L are lit to identify the operating mode ("heater", "cooler", "fan") that has been selected mutually exclusively. Then, in order to light the light-emitting element L, the switch SW is turned on upon input of a drive signal from the microcontroller MC (processing unit 50) of the monitoring circuit 43 in conjunction with the operating button P being turned on.
Therefore, if 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 switch device 1, any one of the operating buttons P is turned on mutually exclusively. By detecting the feedback voltage when the switch SW corresponding to the operating button P that has been turned on is on/off, it is possible to quickly identify which of the plurality of switches SW and the plurality of light-emitting elements L is experiencing an abnormality.
(9) In any one of (1) to (9) above,
in the first connecting line 31, wiring 25 of the monitoring circuit 43 is connected between a connection point Cn with the second connecting lines 32 (32h, 32c, 32f), and the power supply source PS.
With this configuration, whichever switch SW of the second connecting lines 32 (32h, 32c, 32f) is being driven on/off, abnormalities in the switches SW and light-emitting elements L provided in all the second connecting lines 32 (32h, 32c, 32f) can be detected.
(10) In (9) above,
in the circuit 3, resistors Ra and Rb (Rbh, Rbc, Rbf) are respectively provided upstream and downstream of the connection point Cn between the first connecting line 31 and the second connecting lines 32 (32h, 32c, 32f).
In the circuit 3, the monitoring circuit is connected between the resistor Ra on the upstream side of the connection point Cn and the connection point Cn.
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 resistors Rb (Rbh, Rbc, Rbf) on the downstream side. As a result, by detecting the voltage when the switch SW is on/off using the monitoring circuit 43 including the microcontroller MC, it is possible to detect abnormalities in the switches SW and light-emitting elements L provided in all the second connecting lines 32 (32h, 32c, 32f), and the resistor Ra.
Embodiments and modified examples of the present invention have been described above, but the present invention is not limited thereto, and modifications can be made as appropriate within the scope of the technical concept of the invention.

Explanation of the reference numbers

1: Switching device (load driving device)
25: Wiring
3: Circuit
31: First connecting line
32 (32c, 32f, 32h): Second connecting line
41: Detecting circuit
42: Lighting control circuit
43: Monitoring circuit
45, 47: Connecting line
46: Voltage sensor
50: Processing unit
60: Storage unit
Cn, Cn1: Connection point
L (Lc, Lf, Lh): Light-emitting element
SW (SWc, SWf, SWh): Switch (drive switch)
P (Pc, Pf, Ph): Operating button
MC: Microcontroller
PS: Power supply source (drive power source)
V_ave: Average value of feedback voltage
V_off: Voltage (voltage when switch is off)
V_on: Voltage (voltage when switch is on)
V_std: Standard output voltage

Claims

A load driving device comprising a drive switch that is on/off controlled on the basis of a drive signal,
a load that is connected in series with the drive switch, and

a monitoring circuit that acquires a voltage at an arbitrarily defined point between a power supply source that supplies drive electric power for the load, and the drive switch, wherein

the monitoring circuit

detects an abnormality in at least one of the drive switch and the load on the basis of a voltage acquired when the drive switch is on and a voltage acquired when the drive switch is off.
The load driving device as claimed in claim 1, including
a first connecting line that is connected to the power supply source, and

a second connecting line in which the load and the drive switch are arranged in series, wherein

a plurality of the second connecting lines are connected in parallel to the first connecting line, and

the monitoring circuit

detects the abnormality on the basis of a voltage value during on/off control of one drive switch among a plurality of the drive switches.
The load driving device as claimed in claim 1 or claim 2, wherein:
the detection of the abnormality is performed by comparing an average value of the acquired voltages with a threshold value, or by comparing the added values of the acquired voltages with a threshold value;

the average value of the voltages is the average value of the voltage acquired when the drive switch is on and the voltage acquired when the drive switch is off; and

the average value of the voltages is a value obtained by adding the voltage acquired when the drive switch is on and the voltage acquired when the drive switch is off.
The load driving device as claimed in claim 3, 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 in accordance with the output voltage.
The load driving device as claimed in claim 4, wherein
the drive signal is a PWM signal, and

the load includes an LED element having a light emission amount that changes in accordance with the duty ratio of the PWM signal.
The load driving device as claimed in claim 5, wherein
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%.
The load driving device as claimed in claim 6, wherein
as the output voltage of the power supply source decreases, the duty ratio is set to a higher value that lengthens the ON period of the drive switch.
The load driving device as claimed in claim 2, wherein
the same number of the second connecting lines are provided as the number of operating buttons, which are turned on mutually exclusively.
The load driving device as claimed in claim 2 or claim 8, wherein,
the monitoring circuit is connected to the first connecting line between a connection point of the first connecting line and the second connecting lines, and the power supply source.
The load driving device as claimed in claim 9, wherein
resistors are provided on one side and the other side of the connection point of the first connecting line and the second connecting lines, and

a processing device of the monitoring circuit is connected between the resistor of the first connecting line and the connection point.