JP2799833B2 - Control device for electrical load - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for controlling on / off of a plurality of electric loads (hereinafter simply referred to as loads) in various electric devices, and more particularly to a control device for simplifying a circuit configuration while maintaining high safety. Regarding improvement.

[0002]

2. Description of the Related Art For example, a gas water heater or the like is also an electric device having a control circuit which operates by receiving operating power from a power supply, and a load which is turned on / off by a command from the control circuit is also a pump, a solenoid valve, or an ignition device. There are many devices and so on. The selective operation and non-operation (on / off) of each load is generally determined by a semiconductor switching element (hereinafter simply referred to as a switching element) connected in series to the load.
Is turned on and off. That is, when a voltage signal (also referred to as an ON voltage) in a predetermined voltage range in which the element is to be turned on is selectively given to the control input of the switching element, the switching element is turned on and its main current path is conducted, As a result, the power is supplied to the load and the load operates.

[0003] However, even when no on-voltage is applied to the switching element (in other words, a signal in a voltage range to be turned off is applied), a short circuit that keeps the switching element on remains. If a failure (also referred to as an ON failure) occurs and a load connected in series with the failure continues to operate unexpectedly, particularly in the above-described gas water heater or the like, the release of raw gas or the like occurs. However, in some cases, it does not necessarily lead to a dangerous state.

[0004] Conventionally, safety measures as shown in FIG. 3 have been established by the present applicant. To explain,
In the figure, for the sake of simplicity, the number of loads that may actually be larger is shown only as two as indicated by reference numerals 12a and 12b, but each of these loads 12a and 12b is respectively connected in series. The first and second switching elements 13a, 15a: 13b, 15b are connected, and these series circuits are connected to both ends of the power supply 11 in parallel with each other. Then, first and second switching elements 13 in each series circuit are driven by drive signals Sa and Sb selectively applied to input terminals Ta and Tb.
a, 15a: Both 13b and 15b are turned on at the same time, and conversely, the drive signal S
If a and Sb are lost (fall), they are both turned off at the same time. In the case shown, the first switching elements 13a and 13b are pnp type bipolar transistors, and the second switching elements 15a and 15b are npn bipolar transistors. Needs to be inverted. Here, the drive signal S
Since a and Sb are assumed to be signals for operating the loads 12a and 12b at the input terminals Ta and Tb when they are at the logic "H" (that is, a positive voltage level higher than a predetermined voltage value). , The drive signals Sa, Sb are the second switching elements 15a,
For 15b, the logic level remains significant,
Although the ON voltage for the second switching element applied to the base which is the control input can be itself, the drive signal to be given to the control input of the first switching elements 13a and 13b includes npn for high / low level inversion or logic level inversion. It is necessary to invert the voltage level range or the logic level of the drive signals Sa and Sb by the driver transistors 14a and 14b.

In the prior art, only one switching element, for example, one of the first switching elements 13a and 13b is provided for each series circuit including the loads 12a and 12b. , Sb are turned off, the loads 12a, 12b are not turned off, whereas in the control device configuration shown in FIG. 3, two switching elements 13 are provided for each load 12a, 12b.
a, 15a: Since 13b and 15b cooperate, if one of them does not turn off due to a short-circuit fault, the other can turn off, so it is necessary to turn off the loads 12a and 12b as expected. It is possible and the safety is surely enhanced. If both of the first and second switching elements 13a, 15a: 13b, 15b fail to turn on, this cannot be dealt with, but the probability of both turning on at the same time is extremely small.

[0006]

However, according to the configuration of FIG. 3, as the number of loads increases, the number of first and second switching elements connected in series to each load also increases in a simple proportional relationship. . If this is, for example, the first and second switching elements are small and inexpensive elements for so-called small signal amplification, there is no problem, but generally, the first and second switching elements are relatively large currents flowing to the load. Must be large and expensive, so-called power type. Therefore, as the number of loads increases, the cost as a control device increases. In addition, the space factor including installation of a radiator for each switching element also deteriorates, and the device itself increases in size.

Accordingly, the present invention first aims to provide a control device having a rational circuit configuration capable of suppressing the cost increase and the degree of space factor deterioration even when the number of loads increases, as a basic solution.

In addition, as a second object, a configuration for positively detecting a short-circuit failure of at least one or both of the first and second switching elements is proposed to further enhance safety.

[0009]

In order to achieve the above object, the present invention provides: (a) connecting a series circuit in which a first switching element is connected in series to each of a plurality of electric loads; Configuring a parallel circuit; (b) connecting one end of the parallel circuit to one end of a power supply;
The other end is connected to the other end of the power supply via the second switching element; (c) when the first switching element is selectively turned on by a dedicated drive signal, the second switching element is also turned on; The second switching element is turned off only when all of the one switching element is turned off; and (d) the first switching element is turned on even though no drive signal is supplied to the first switching element. A short-circuit detection circuit is provided for each of the first switching elements for detecting the short-circuit fault that has become: (e) The short-circuit detection circuit forcibly forces the second switching element upon detecting the short-circuit fault A control device for an electric load, characterized in that:

In this case, the first switching element is an element that conducts the main current path when a drive signal in a predetermined voltage range is applied to the control input, as seen in general bipolar transistors and field effect transistors. If there is, the short-circuit detection circuit described above can be configured to detect a short-circuit fault of the first switching element by comparing the voltage of the control input with the output voltage of the main current path, If the switching element is also an element that conducts the main current path when a voltage signal of a predetermined voltage range is given to the control input, the short-circuit detection circuit detects the short-circuit failure of the first switching element and the second short-circuit detection circuit. Can be configured as a circuit for applying a voltage signal outside the above-mentioned predetermined voltage range to the control input of the switching element.

Further, in the present invention, the above-mentioned constituent requirements (a) to
In addition to (e), (f) for the second switching element, a short circuit for the second switching element for detecting a short-circuit fault that is on when the second switching element should be off (G) the short-circuit detection circuit for the second switching element forcibly turns off all of the first switching element upon detecting a short-circuit failure of the second switching element; A control device is also proposed. Again, if the second switching element is an element that conducts the main current path when a voltage signal in a predetermined voltage range is given to the control input, as seen in a general bipolar transistor or a field effect transistor, The short-circuit detection circuit for the second switching element can be configured to detect the short-circuit fault by comparing the voltage of the second switching element control input with the output voltage of the main current path. If the element is also a general element that conducts the main current path when a drive signal of a predetermined voltage range is given to the control input, the second switching element short-circuit detection circuit detects a short-circuit failure of the second switching element. Upon detection, it can be configured as a circuit that applies a voltage signal outside a predetermined voltage range to the control input of the first switching element.

[0012]

FIG. 1 shows a schematic configuration of an electric load control device according to an embodiment of the present invention. In order to clarify the improvements of the present invention, the same reference numerals as those already used in FIG. 3 denote the same circuit components or components in this embodiment. In addition, in the case of the drawing, for simplicity, only two loads 12 a and 12 b are indicated as on-off controlled objects, but the subscripts a and b indicate that individual loads need to be distinguished from each other. Omitted in the text chapter except for, for example, if simply described as load 12, two loads 12a,
This is an explanation applicable to any of 12b. Similarly, members or components provided in connection with each of the loads 12a and 12b, but which may be the same circuit components, except when it is necessary to express each of them in a discriminative manner. Subscripts a and b are omitted in the text chapter.

However, in the conventional configuration of FIG. 3, the second switching elements 15a,
b is single and common as described below in the control device to which the present invention is applied, and the reference numeral 15 does not require a subscript as shown in the figure. In other words,
In the figure, components without subscripts can be used as common components regardless of the number of loads 12.

However, the first switching element 13 is provided in series with each load 12 as in the above-described conventional example, but in the case of the present invention, first, only the series circuit is provided in plurality. One end of the parallel circuit (the side provided with the first switching element 13 in the illustrated case) is connected to one end of the power supply 11 and the other end of the parallel circuit is connected to all the loads 12. Are connected to the other end of the power supply 11 via a second switching element 15 which is common to the power supply 11. Therefore, as the number of loads 12 increases, the first switching element 13
Increases, but the number of second switching elements 15 remains one without increasing. In this regard, the circuit is simplified and streamlined as compared with the conventional example on the premise that the safety by the two switching elements 13 and 15 is ensured. Naturally, since the number of switching elements used is reduced, the size of the entire device is also reduced.

In the case of the illustrated embodiment, the first switching element
13 is a pnp bipolar transistor, while the common second switching element 15 is an npn bipolar transistor. Therefore, the drive signals Sa and Sb for selectively operating (turning on) each load 12 are significant positive voltages at the input terminals Ta and Tb (this may be referred to as logic "H" for convenience). If this is the case, this can be a voltage signal for turning on the second switching element 15 for the second switching element 15, but an off signal for the control input of the first switching element 13 of the pnp type as it is. Becomes Therefore, for the first switching element 13, the drive signals Sa and Sb respectively applied exclusively are npn bipolar transistors for voltage range inversion or logic level inversion.
Is to be given through 14. In this case, in general, the first and second switching elements 13 and 15 need to be so-called power transistors in order to flow the load current as described above, but the transistors 14 and 15 as the logic level inversion driver transistors are required. May be for small and inexpensive small signal amplification. The other transistors, which will be described below in order, need not be used for power, but may be used for small and inexpensive small signal amplification.

However, the above is a complementary problem,
When inverting the logic level of the drive signal applied to the input terminals Ta and Tb, a switching element for inverting the logic level may be provided for the control input of the second switching element 15, and the first and second switching elements may be provided. If the two switching elements 13 and 15 have the same conductivity type, such a driver transistor for inverting the logic level becomes unnecessary. Instead of a bipolar transistor, a field effect transistor having a conductivity type different from that of a main current path (between a source and a drain) which is conducted by a significant voltage value applied to a control input (gate), such as an n-channel type or a p-channel type, is used. Although it is possible to do so, the same considerations should be taken in such a case.

However, any one of the drive signals Sa and Sb applied to the input terminals Ta and Tb is applied to the corresponding load 12.
When it becomes a significant voltage level in order to turn on, the corresponding first switching element 13 is turned on via the driver transistor 14 and at the same time, the second switching element 15 common to all loads 12 is also turned on. Otherwise, since the operating power from the power supply 11 is not supplied to the target load 12, the driving signal equal to the OR logic of the driving signals Sa and Sb is applied to the base which is the control input of the second switching element 15. Is given. That is, in the case shown in the figure, a diode-OR logic is employed, and the input terminal Ta of one drive signal Sa is input.
The cathode of the diode 25a whose anode is connected to the cathode of the diode 25b whose anode is connected to the input terminal Tb of the other drive signal Sb is connected to each other, and their connection points are both connected to the base of the second switching element 15. Have been.

When only the drive signal Sa is generated, it is supplied as it is to the base of the second switching element 15 as an on-voltage of the second switching element via the diode 25a, so that it is turned on. On the other hand, a driver transistor 14 for voltage level inversion or logic value inversion
Since the driving signal Sa is also applied to the base of the first switching element 15a, it is turned on, and the base which is the control input of the first switching element 15a is grounded via the main current path (between the emitter and the collector) of the driver transistor 14a. The first switching element, which is a pnp transistor
13a, a substantially significant voltage level, that is, a substantially ground level (logic "L") on-state voltage, which is inverted, is applied, which conducts, and accordingly the corresponding load 12a is turned on.
a is supplied with power from the power supply 11. However, even if the second switching element 15 conducts, the driver transistor 14b associated with the load 12b does not conduct unless the drive signal Sb is applied, so that the first switching element 13b also conducts. Without this, the operating power is not supplied from the power supply 11, and the sleep state is maintained as expected.

Similarly, when only the drive signal Sb is applied, the second switching element 15 receives the drive signal Sb as an ON voltage via the diode 25b also in this case. However, as for the first switching elements 13a and 13b, only the first switching element 13b related to the drive signal Sb is turned on, so that only the corresponding load 12b operates.

In this manner, the loads 12a and 12b are selectively turned on and off by the selective application of the drive signals Sa and Sb (of course, when both the drive signals Sa and Sb are applied, both loads are turned on). ), The second switching element 15
Conversely, regarding the second switching element 15,
Only when both drive signals Sa and Sb are falling, they are turned off.

As described above, when the first and second switching elements 13, 15 are functioning normally, each of the loads 12a, 12
b is the input terminal Ta, Tb is the drive signal associated with itself
Only when Sa and Sb are selectively received, it operates by receiving power supply from the power supply 11. However, during the long use period, although the voltage to be turned on is not given to the respective control inputs of the first and second switching elements 13 and 15 (in other words, the voltage to be turned off is given to the control input). However, it is conceivable that a short-circuit fault (on fault) occurs in which the main current paths maintain a conductive state. According to the circuit configuration shown in FIG. 1, such a failure is more likely to occur in the first switching element 13 provided exclusively for each load 12. Since the second switching element 15 common to all the loads 12 is on when any one of the loads 12 is to be turned on, the second switching element 15 must be turned on and off every time to control the on / off of the load 12. This is because, compared with the first switching element 13 which has to operate, the number of times of ON / OFF is small when integrated over time. The smaller the number of on / off operations, the lower the failure probability.

Therefore, in this embodiment, first, a short-circuit detection circuit 21 for detecting an ON failure of each of the first switching elements 13 is provided. Various configurations of the short-circuit detection circuit 21 can be considered by those skilled in the art, but as will be seen in a specific circuit configuration example described with reference to FIG.
The control input voltage and the output voltage of the main current path are monitored and compared, and if they do not have a predetermined relationship, it is possible to determine a short circuit failure. That is, if the first switching element 13 is a pnp bipolar transistor as shown, the control input is the base of the transistor 13 and the main current path output voltage is the collector voltage, but the base potential is the off voltage If the potential of the power supply 11 appears as the collector voltage despite the fact that the pnp transistor 13 should be at the "H" level, it can be clearly determined that the pnp transistor 13 has an ON failure. Therefore, in this embodiment, any one of the short-circuit detecting circuits provided for each of the first switching elements 13 is provided.
Even at 21, when the short-circuit fault is detected as a result of such voltage comparison, the second switching element common to all loads 12
15 is forcibly turned off.
That is, since the second switching element 15 is an npn bipolar transistor 15 in the drawing, an npn bipolar transistor 23 is provided as a control element that can be forcibly turned off by selectively grounding its base. Is turned on by the output of the short-circuit detection circuit 21, thereby applying a substantially ground level to the base of the second switching element 15 as a voltage outside a predetermined voltage range in which the second switching element 15 is to be turned on. It is.

As described above, in the circuit of the illustrated embodiment, if the first switching element 13 related to any one of the loads 12 is short-circuited, the second switching element 15 is forcibly turned off. All 12 are in a resting state to ensure safety and at the same time make it easy for the user to understand that a failure has occurred. In a situation where operation continues at any load, it may be difficult to appeal to the user that a failure has occurred, but this is not the case with the present circuit.

Further, as the most desirable mode of the present invention, the circuit of the illustrated embodiment discloses a configuration capable of detecting a short-circuit fault of the second switching element 15. That is,
Regarding the second switching element 15 as well, in this case, similarly to the first switching element 13 described above, the control input voltage and the output voltage of the main current path are monitored and compared, and they are in a predetermined relationship. A short-circuit detection circuit 22 for generating a short-circuit fault detection signal when not present is provided. In the case shown, the second switching element 15 is formed of an npn bipolar transistor, so that the short-circuit detecting circuit 22 can control the main current path between the emitter and the collector even though the control input (base) voltage is logic "L". As a result, the short-circuit fault detection signal is issued when the output voltage (collector voltage) has dropped to almost the ground level.

In response to this, in this circuit, an npn bipolar transistor is used as a control element which can selectively lower the base of the transistor 14 provided for inverting the logic of the drive signal to the first switching element 13 to ground. The control transistor 24 is provided, and the control transistor 24 is turned on by the short-circuit failure detection output of the short-circuit detection circuit 22, and the first switching element 15 is forcibly turned off by forcibly turning off the logic level inversion transistor 14. And so on.

As described above, according to this circuit, a short-circuit fault occurs in any one of the first switching elements 13 dedicated to each load, or a short-circuit fault occurs in the second switching element 15 common to each load. Occurs, the entire load 12 is put into a halt state, and the occurrence of a failure can be reported in an easy-to-understand state, and safety can be ensured. Of course, although not shown, when the short-circuit failure detection circuits 21 and 22 generate the short-circuit failure detection signal, the notification device based on the generation of audible sound or visible light may be driven. Further, in some cases, when the short-circuit detection circuit 22 only needs to be provided for the second switching element 15, the short-circuit detection circuit 21 provided for the first switching element 13 can be omitted.

The number of loads 12 is arbitrary. In the case where the number is larger than that shown in the figure, circuit elements 13, 14, 21, 24, and 25 with subscripts a and b are similarly provided for each load 12x. In addition, the drive signal Sx to those additional loads 12x
Also connected to the connection point to which the cathodes of the diodes 25a and 25b are connected via 25x, the short-circuit detection signals from the short-circuit detection circuits 21x provided for the other loads 12x are the short-circuit detection circuits 21a and 21b. Similarly, after the voltage is applied to the control element 23, the output of the common short-circuit detection circuit 22 for the second switching element 15 is wired so as to be sent to the control element 24x provided for the other load 12x. Good.

FIG. 2 shows a more specific circuit configuration example of the control device constructed according to the circuit configuration principle shown in FIG. The circuit elements or signals having the same reference numerals as those in FIG. 1 are the same as those used in the description already given with reference to FIG. 1, and therefore, the re-description here may be omitted.

In the circuit of FIG. 2, reference numerals 26, 27, 28, 29
1 are circuit elements included in the short-circuit detection circuit 21 for the first switching element 13 in FIG. 1, and the short-circuit detection circuit 21 selectively and forcibly turns off the second switching element 15. The control transistor 23 to be used is composed of a pair (23a, 23b) in the circuit of FIG. 2 for convenience of the circuit. Similarly, circuit elements denoted by reference numerals 30, 31, 32, 33, 34, and 35 are circuit elements included in the short-circuit detection circuit 22 for the second switching element 15 in FIG. The operations involving these circuit element groups can be described as follows.

Now, when the drive signal Sa or Sb falls, the corresponding driver transistor 14 is turned off, so that the corresponding pnp bipolar transistor 13 as the first switching element should also be turned off. If a short-circuit fault has occurred, the base of the bipolar transistor 13 having the short-circuit fault has been pulled up to the voltage of the power supply 11 to be turned off, but the main current path between the emitter and the collector remains conductive. , The collector voltage is pulled up to the power supply voltage 11, so that the collector voltage is applied from the resistor 26 to the base of the control transistor 23 via the resistors 28 and 29, and the control transistor 23 is turned on to Two switching elements 15
The power supply to the load 12 is cut off by forcibly lowering the base of the power supply to almost the ground level and turning it off.

The diode 27 included in the short-circuit detection circuit 21 does not directly participate in the short-circuit detection, and may cause the short-circuit detection circuit 21 to malfunction if the first switching element 13 does not have a short-circuit fault. It is to prevent. In other words, when the drive signal Sa or Sb rises, the first switching element 13 is turned on. As a result, when the collector voltage goes to the “H” level, this is a normal operation, and the control transistor 23 is turned off. It is bad if you turn on. Therefore, when the drive signals Sa and Sb at the input terminal Ta or Tb are at the "H" level, the corresponding logic value inversion driver transistor 14 is turned on. Therefore, the control transistor 23 through the conductive main current path is turned on. The diode 27 is provided in order to prevent the control transistor 23 from being turned off by pulling the base potential of the control transistor 23 to almost the ground level.

Next, consider a case where an ON failure that does not turn off occurs when the second switching element 15 is to be turned off. As described above, the second switching element 15 is an element that is turned off only when both of the drive signals Sa and Sb are at the “L” level. However, if an on-failure occurs at this time, the collector voltage falls to almost the ground level via the conducting main current path between the emitter and the collector. In such a case, in the circuit of the present embodiment, the control element 33 of the npn transistor whose base is almost dropped to the ground level via the resistor 31 is turned off, and the main current path is opened. Then, the current supplied from the power supply 11 via the resistor 30 is commutated via the resistor 34 to the base of the control element 24 composed of an npn transistor, turning them on, thereby forcing the driver transistor 14 Is generated, and a power supply voltage 11 as a voltage signal “H” to be turned off is applied to the base of the first switching element 13.

An anode is connected to each cathode connection point of the diode 25 in the diode OR circuit for turning on the second switching element 15 by taking the OR logic of the driving signals Sa and Sb, and connecting the anode to the base of the control element 33. The diode 35 to which the cathode is connected is for preventing malfunction of the short-circuit detection circuit 22 for the second switching element 15. That is, when the second switching element 15 is normal, at least one of the drive signals Sa and Sb goes to the “H” level, so that the second switching element 15 must be turned on. At this time, the control element 33 must be turned on to maintain the control element 24 in the off state by pulling the base of the control element 24 to approximately the ground level through its main current path. Therefore, the diode 35
When either one of Sa and Sb is at the “H” level, it works to apply the ON voltage by this to the base of the control element 33.

In the specific circuit configuration shown in FIG. 2, only two loads 12 are shown. However, when three or more loads 12 are provided, as shown in FIG. The same circuit elements as those having the subscripts in FIG. 2 are provided in the same relationship as for the loads 12a and 12b with respect to the loads of FIG.
The collectors of the transistors connected to the connection node A in FIG. 2 through the same diodes as the transistors 25a and 25b and selectively forcibly turned off by the short-circuit detection circuit for the first switching element of the load circuits are the same as those of the transistors 23a and 23b shown. Connect to the connection node B in the same manner as Further, from a connection node C which is an output point of the common second switching element short-circuit detecting circuit 22, a control element (for the first switching element forcibly off) for forcibly turning off the driver transistor of each load circuit (hence, the control element for illustration) 24a, 24b equivalent) base resistance
Connect via resistors corresponding to 34a and 34b.

In the case of the configuration shown in FIG. 2, as described above, unlike the configuration shown in FIG.
The control element 23 selectively forcibly driven by the output of the short-circuit detection circuit 21 for 13 is distinguished by reference numerals 23a and 23b,
Although each of the resistors 26a and 26b is composed of an individual element whose base is connected exclusively, if the diode OR of the output of each of the resistors 26a and 26b is removed, the control element 23 is provided in the same manner as shown in FIG. May be common to each load circuit and may be a single one. In addition, modifications according to the gist of the present invention can be freely made by those skilled in the art.

[0036]

According to the present invention, by providing a pair of serial switching elements for each of a plurality of electric loads, it is possible to reduce the probability of occurrence of the inconvenience of a load malfunction due to an ON failure of the switching elements. However, since at least one of the switching elements is a common switching element for all loads, the number of switching elements does not have to be simply increased even if the number of loads increases, and is a reasonable, simple, inexpensive, and compact control device. Can be constructed.

In a specific embodiment of the present invention, a circuit for detecting a short-circuit fault is provided for at least a first switching element dedicated to each load, and when this detects a short-circuit fault, the second switching element is forcibly forced. Since it is turned off, even when each load is a load in a gas water heater or the like, a serious accident can be prevented from occurring. Generally speaking, it is possible to reduce the risk of a malfunction of the load when it is not allowed to operate, and also to ensure safety in various senses.

In addition, according to a further preferred aspect of the present invention, a circuit capable of detecting a short-circuit fault of the second switching element can be provided, and when this detects a short-circuit fault, all the first switching elements are forcibly forced. The safety is further improved because the power is turned off.

The short-circuit detection circuit may be provided only for the first switching element, alternatively, or in addition to the short-circuit detection circuit provided for the second switching element. Turning off all loads upon detection of a short-circuit fault is not only effective from a safety point of view, but also significant in notifying the user of the occurrence of the fault.
As described above, it is difficult to immediately recognize that a failure has occurred in a state where another load can continue to operate even if one of the loads fails.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an electric load control device configured according to the present invention.

FIG. 2 is a configuration diagram showing a more specific circuit configuration example of the control device shown in FIG. 1;

FIG. 3 is a schematic configuration diagram of an electric load control device considered to enhance safety in a process leading to the present invention.

[Explanation of symbols]

 11 power supply, 12 load, 13 first semiconductor switching element, 14 logic level inversion driver transistor, 15 second semiconductor switching element, 21 short circuit detection circuit for first semiconductor switching element, 22 short circuit detection circuit for second semiconductor switching element, 23 control elements, 24 control elements, 25 diodes, 26 resistors, 27 diodes, 30 resistors, 31 resistors, 33 control elements, 35 diodes.

Claims (6)

(57) [Claims] 1. A parallel circuit is formed by connecting a series circuit in which a first semiconductor switching element is connected in series to each of a plurality of electric loads in parallel with each other; one end of the parallel circuit is connected to one end of a power supply. On the other hand, the other end of the parallel circuit is connected to the other end of the power supply via a second semiconductor switching element; when the first semiconductor switching element is selectively turned on by a dedicated drive signal, The second semiconductor switching element is also turned on, and only when all of the first semiconductor switching elements are turned off, the second semiconductor switching element is turned off; A short-circuit detection circuit for detecting a short-circuit fault in which the first semiconductor switching element is turned on even when no drive signal is supplied is provided. A controller provided for each of the switching elements; wherein the short-circuit detection circuit forcibly turns off the second semiconductor switching element upon detecting the short-circuit failure. 2. The control device according to claim 1, wherein the first semiconductor switching element is an element that conducts a main current path when the drive signal in a predetermined voltage range is given to a control input; The short-circuit detection circuit detects a short-circuit failure of the first semiconductor switching element by comparing a voltage of the control input with an output voltage of the main current path. 3. The control device according to claim 2, wherein the second semiconductor switching element is an element that conducts a main current path when a voltage signal in a predetermined voltage range is applied to a control input; The short-circuit detection circuit, upon detecting the short-circuit fault, applies a voltage signal outside the predetermined voltage range to the control input of the second semiconductor switching element. 4. The control device according to claim 1, wherein a short-circuit fault that is turned on when the second semiconductor switching element is to be turned off is provided to the second semiconductor switching element. A second semiconductor switching element short-circuit detection circuit for detecting; the second semiconductor switching element short-circuit detection circuit forcibly turning off all of the first semiconductor switching elements upon detecting the short-circuit fault; A control device characterized by the following. 5. The control device according to claim 4, wherein the second semiconductor switching element is an element that conducts a main current path when a voltage signal in a predetermined voltage range is applied to a control input. The second semiconductor switching element short-circuit detection circuit detects a short-circuit fault of the second semiconductor switching element by comparing the voltage of the control input with the output voltage of the main current path; apparatus. 6. The control device according to claim 5, wherein the first semiconductor switching element is an element that conducts a main current path when the drive signal in a predetermined voltage range is given to a control input; The second semiconductor switching element short-circuit detection circuit, upon detecting the short-circuit fault, applies a voltage signal outside the predetermined voltage range to the control input of the first semiconductor switching element. Control device.