JP3139276B2 - Overload protection circuit for power semiconductor devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for protecting a power semiconductor element for controlling a current flowing to a load connected in series to a power supply from an overload which is likely to be applied from a load side during use.
In particular, the present invention relates to a protection circuit suitable for being incorporated in an integrated circuit together with a power semiconductor element.

[0002]

2. Description of the Related Art As power semiconductor devices such as field effect transistors and insulated gate bipolar transistors have been expanded in use, semiconductor or hybrid integrated circuits have been used together with related circuits for driving and control in order to improve usability. In recent years, there has been a growing trend to provide intelligent power switches and intelligent power modules in the form of intelligent power switches and intelligent power modules. It has come to be required to additionally incorporate them.

FIG. 5 shows a conventional representative example of a protection circuit in accordance with the requirements in view of protection characteristics. FIG. 5 (a) shows the protection characteristic B of a simple overvoltage protection circuit. When the voltage V on the horizontal axis applied to the semiconductor element when the inductive load is cut off exceeds the maximum voltage Vm set higher than the power supply voltage Vs. Then, the semiconductor element is turned off to interrupt the current I on the vertical axis as shown in the figure. The value of the maximum voltage Vm is, of course, lower than the withstand voltage of the semiconductor element.
Usually, it is set within a range of 1.5 to 2 times the power supply voltage Vs.

FIG. 5B shows a protection characteristic C of an overpower protection circuit for preventing a semiconductor element from being thermally destroyed by excessive power when a load is short-circuited or the like. As shown in the figure, when the voltage V applied to the semiconductor element exceeds the voltage Va set lower than the power supply voltage Vs, the current I starts to be limited, and thereafter, the voltage V becomes the maximum voltage Vm while limiting the current I with a hyperbolic characteristic. 0 when reached
To turn off the semiconductor element. Maximum voltage
When Vm is set to 1.5 to 2 times the power supply voltage Vs as described above and the hyperbolic characteristic portion is substantially matched to the thermal characteristics of the semiconductor element, the current limit start voltage Va becomes 0.5 to 0.
It is usually in the range of seven times.

[0005]

The overvoltage protection circuit having the protection characteristics shown in FIG. 5 (a) has an advantage that the circuit configuration is very simple, but as will be easily understood, the semiconductor element is not easily damaged by thermal destruction. There is a problem that cannot be sufficiently protected. Even if the voltage V applied to the semiconductor device is less than the maximum voltage Vm, if the overload state in which the current I flowing therethrough is excessive continues, especially in a range where the voltage V exceeds the power supply voltage Vs, there is a risk of thermal destruction of the semiconductor device. Because there is.

On the other hand, the overpower protection circuit having the protection characteristic shown in FIG. 5 (b) has good protection against thermal destruction of the semiconductor element and also has protection performance against overvoltage exceeding the maximum voltage Vm. . However, the power limit start voltage Va becomes lower than the power supply voltage Vs as described above, so that the voltage V becomes
In the range of Va to Vs, even if the load side is normal, the current I is limited, so that there is a problem that the semiconductor element cannot sufficiently exhibit its inherent load driving ability. When a particularly important load is being driven, it may not be absolutely permitted that the load driving capability is reduced or lost even though the load is normal and the voltage V of the semiconductor element is lower than the power supply voltage Vs. In addition, in a protection circuit having a hyperbolic characteristic as shown in FIG. 5B, it is not always easy to speed up the current limiting operation at the time of overpower or the current interrupting operation at the time of overvoltage when the load suddenly changes. There is a problem that the configuration is complicated and the cost is high.

[0007] In view of the above problems of the prior art, the present invention provides an overload protection circuit that allows a semiconductor device to sufficiently exhibit the drive capability of a load and has a rapid protection operation including overvoltage protection. A second object is to simplify the circuit configuration so as to be easily incorporated into an integrated circuit.

[0008]

A first object of the present invention is to provide an overload protection circuit according to the present invention, wherein when a voltage between main terminals of a semiconductor device reaches a predetermined maximum set value, a control input terminal of the semiconductor device is controlled. A maximum voltage protection circuit for controlling the voltage applied to the control input terminal of the semiconductor element when the voltage between the main terminals of the semiconductor element exceeds an intermediate set value lower than the maximum set value; The intermediate voltage protection circuit controls the voltage applied to the control input terminal of the semiconductor element so as to narrow the load current to the current limit value, and the maximum voltage protection circuit controls the control input terminal of the semiconductor element so as to cut off the load current. Achieved by: Note that the above-mentioned intermediate set value is preferably set to be approximately equal to or slightly higher than the power supply voltage value in order to cause the semiconductor element to exhibit load driving capability. In addition, a plurality of the intermediate set values are set as required and necessary, and each time the voltage between the main terminals of the semiconductor device exceeds each intermediate set value, the load current is gradually reduced to the set current limit value. It is advantageous to do so.

A second object of the present invention is to provide an intermediate voltage protection circuit of the overload protection circuit having the above-mentioned configuration, in which (a) a Zener diode for receiving a voltage between main terminals of a semiconductor element is incorporated.
The Zener breakdown voltage is set as an intermediate set value to narrow down the load current, and (b) a resistive voltage dividing circuit that receives the voltage between the main terminals and a threshold operation circuit element that receives the divided voltage are incorporated. And a threshold voltage of the threshold operation circuit element to set an intermediate set value to narrow down the load current when the threshold operation circuit element operates, or A comparator that compares the divided voltage with a predetermined reference voltage is provided, an intermediate set value is set based on the voltage division ratio of the resistance voltage divider circuit and the reference voltage value, and the load current is narrowed down according to the output of the comparator. Is done. As the threshold operation circuit element in the above item (b), a MOS transistor whose gate has a predetermined operation threshold, a logic gate having an operation threshold on the input side, or the like can be appropriately used. further,
As means for narrowing down the load current, a resistor voltage dividing circuit for receiving a control input voltage to the semiconductor element is provided in the intermediate voltage protection circuit, and when the voltage between the main terminals of the semiconductor element exceeds the intermediate set value, this resistance voltage dividing circuit is provided. Providing the divided voltage value by the circuit to the control input terminal of the semiconductor element is advantageous in simplifying the circuit configuration.

[0010]

According to the present invention, the overvoltage protection is assigned to the maximum voltage protection circuit, and the overpower protection is assigned to the intermediate voltage protection circuit, so that the protection for the semiconductor element is applied stepwise.
The intermediate voltage protection circuit operates so that the intermediate set value can be freely set to the optimum value according to the application or case so that the semiconductor device can sufficiently exhibit the load driving capability, and the maximum voltage protection circuit and the intermediate voltage protection circuit Are operated independently of each other to speed up and ensure the overvoltage protection operation and the overpower protection operation.

Therefore, in the overload protection circuit of the present invention, as described in the configuration of the preceding paragraph, the maximum set value is set for the maximum voltage protection circuit, and the voltage between the main terminals of the semiconductor element reaches this value. When the load current is cut off, the semiconductor element is protected from overvoltage, and the intermediate set value is set lower than the maximum set value for the intermediate voltage protection circuit. The voltage applied to the control input terminal of the semiconductor device is controlled so as to narrow down to the current limit value, thereby protecting the semiconductor device from overpower.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of an overload protection circuit according to the present invention together with a power semiconductor element and related circuits, and a diagram illustrating protection characteristics. FIGS. 2 to 4 show intermediate examples of different embodiments of the present invention. FIG. 3 is a circuit diagram illustrating a voltage protection circuit together with a power semiconductor element and main related circuits. In these embodiments, the power semiconductor element is a field-effect transistor. However, the present invention is not limited to this, and the present invention can be applied to general protection of elements such as an insulated gate bipolar transistor whose control input terminal can be voltage-controlled.

As shown in FIG. 1A, in order to protect the power semiconductor device 1 or the above-mentioned field-effect transistor, in the present invention, a maximum voltage protection circuit 10 and an intermediate voltage protection circuit 20, which are respectively enclosed by dashed lines, are provided. Before using the description, first, the related circuit shown in the figure will be described. Output terminal To of semiconductor element 1
A power supply 2 and a load 3 are connected in series between the power supply 2 and a ground terminal E.
Receiving the control input voltage Vc that specifies the current flowing through the control input voltage Vc. The drive circuit 4 includes, for example, a Schmitt circuit and an amplifier circuit, and outputs the control input voltage Vc in a high logic state of only 5 V in this embodiment according to a drive command Sd received from the outside.

Further, in the example shown in the figure, a current detecting resistor 1a is connected to the ground terminal E of the semiconductor element 1 for detecting a current flowing through the load 3, and the voltage drop of the current detecting resistor 1a is used as an actual current signal of the operational amplifier 5, Given to one input. The operational amplifier 5 has a reference voltage Vr applied to the other input and a resistor 27 in the example shown in FIG.
The control transistor 6 receives the target value signal of the load current as a target value signal via a, and supplies a difference signal between the target value signal and the actual current value to an input, which is a gate in the illustrated example of the control transistor 6 for analogly controlling the value of the control input voltage Vc. As can be easily understood, the load current is controlled by the high gain automatic control system including the semiconductor element 1, the operational amplifier 5 and the control transistor 6 so that the actual value of the current detection resistor 1a exactly matches the target value of the reference voltage Vr. Is controlled.

The maximum voltage protection circuit 10 may have a simple configuration comprising a single comparator 11 as shown in the figure. The maximum voltage protection circuit 10 is shown separately from the drive circuit 4 in the figure, but is preferably incorporated in the drive circuit 4 in practice. The comparator 11 receives, at one input, a maximum set value Vm, which is the maximum voltage allowable to the semiconductor element 1, and receives, at the other input, the voltage of the output terminal To as a voltage V between the main terminals of the semiconductor element 1. 1 is connected to the supply point of the control input voltage Vc. Although the voltage at the output terminal To includes a voltage drop of the current detection resistor 1a, an error caused by the voltage drop is insignificant, so that the voltage V between the main terminals of the semiconductor element 1 may be used practically. The maximum voltage protection circuit 10 operates under the power supply of the control power supply voltage Vd. When the main terminal voltage V reaches the maximum set value Vm, the output of the comparator 11 becomes low and the control input voltage Vd becomes low.
The semiconductor device 1 is turned off by lowering Vc to the ground potential.

In the intermediate voltage protection circuit 20 shown in FIG. 1A, a Zener diode receiving a voltage V between main terminals of the semiconductor element 1 is used.
An intermediate set value is set by the breakdown voltage of 21. When the voltage V between the main terminals exceeds this set value, the voltage divider circuit composed of a pair of resistors 27a and 27b and the operational amplifier 5 are connected to protect the semiconductor element 1 from overpower. The current of the load 3 is narrowed down to a low value by utilizing this. A current limiting resistor 21a and a ground-side detection resistor 22 are connected to the Zener diode 21, and a detection signal is applied from the detection resistor 22 to one input of a NAND gate 24 at the time of breakdown. The NAND gate 24 receives the control power supply voltage Vd at the other input, and when the detection signal is received, a low level of the output grounds the resistor 27b. Thereby, the operational amplifier 5 receives the divided voltage value of the reference voltage Vr by the voltage dividing circuit as a new control target value,
The current flowing through the load 3 is controlled to a lower constant value.

FIG. 1 (b) shows a protection characteristic A corresponding to the embodiment of FIG. 1 (a). The horizontal axis in the figure is the voltage V between the main terminals of the semiconductor device 1 and the vertical axis is the load current I. In the figure, in addition to this characteristic A, the above-mentioned conventional characteristic C in FIG. Shown. As shown, the protection characteristic A in the case of the present invention is divided into three voltage regions A1, A2, A3 divided by an intermediate set value Vi and a maximum set value Vm in a stepwise manner. The voltage region A1 in which the main terminal voltage V is lower than the intermediate set value Vi is a region where the intermediate voltage protection circuit 20 does not operate yet. Here, the load current I is set to the target value specified by the reference voltage Vr as described above. Constant control is performed accordingly. In the present invention, the intermediate set value Vi is preferably set to be equal to or slightly higher than the power supply voltage Vs as in this embodiment, so that the semiconductor element 1 can sufficiently exhibit its load driving capability in the voltage range A1. Can be.

When the voltage between the main terminals exceeds the intermediate set value Vi, the voltage enters the voltage region A2. In this region, the load current I must be set within a range where the semiconductor element 1 is not likely to be thermally damaged. However, in practice, it is reasonable to consider the characteristics of the load 3, especially the transient characteristics as an inductive load. The value of the load current is set by the voltage dividing ratio of the voltage dividing circuit including the resistors 27a and 27b in the intermediate voltage protection circuit 20 as described above, and the operational amplifier 5 controls the load current I to a constant value according to this setting. I do.

The maximum set value Vm for operating the maximum voltage protection circuit 10 is preferably set to a range of 1.5 to 2 times the power supply voltage Vs, as in the conventional example of FIG. In the voltage region A3 after the voltage V reaches this set value, the semiconductor element 1 is turned off and the load current I is cut off. In the conventional characteristic C corresponding to FIG. 5A, the decrease rate of the load current I decreases as the main terminal voltage V increases as shown in the figure, so that the maximum voltage value allowed for the semiconductor element 1 varies. Although it is easy to fluctuate and vary, in the present invention the maximum voltage protection circuit
By using 10, the voltage V between the main terminals can be suppressed to the maximum set value Vm or less, and the semiconductor element 1 can be reliably protected from overvoltage.

An embodiment of the present invention is shown in FIG. The power supply 2 and the load 3 in FIG. 1A are omitted for simplification of the drawing. Although the control system for the load current I comprising the current detection resistor 1a, the operational amplifier 5 and the control transistor 6 in FIG. 1A is omitted, the use of this current control system is not required in any of the following embodiments. Of course, it can be used together.

In the intermediate voltage protection circuit 20 of the embodiment shown in FIG.
Using a resistance voltage dividing circuit composed of a pair of resistors 23a and 23b for receiving the voltage V between the main terminals and a NAND gate 24 as a threshold operation circuit element for receiving the divided voltage, the voltage dividing ratio of the resistance voltage dividing circuit and the NAND gate The intermediate setting value Vi is set according to the input operation threshold value. For this reason, although the voltage divided by the resistance voltage dividing circuit is applied to one input of the NAND gate 24, the high of the control input voltage Vc is applied to the other input through a time constant circuit composed of a resistor 28 and a capacitor 29 in the example of FIG. . The output of the NAND gate 24 goes low when the voltage V between the main terminals exceeds the intermediate set value Vi and grounds the resistor 27b.
The voltage Vc is divided by a resistance voltage dividing circuit composed of a pair of resistors 27a and 27b and then applied to the control input terminal of the semiconductor element 1, so that the load current I is reduced. In the example shown in the drawing, the semiconductor element 1 is directly controlled by a resistance voltage dividing circuit including the resistors 27a and 27b, and the load current I is set by the voltage dividing ratio. (a)
Of the reference voltage Vr supplied to the operational amplifier 5 may be controlled.

In the intermediate voltage protection circuit 20 of the embodiment shown in FIG.
Set intermediate setting values. On the other hand, for example, the lower intermediate set value is set by a resistor voltage dividing circuit composed of resistors 23a and 23b and a transistor 25 having a gate operation threshold value. When the transistor 25 is turned on, the control input voltage Vc is changed by a resistor 27a.
The load current I is reduced by reducing the voltage by the voltage division due to the on-resistance of the transistor 25 and applying the reduced voltage to the semiconductor element 1. On the other hand, for example, a higher intermediate set value is set by a series circuit including a Zener diode 21, its current limiting resistor 21a, and a detection resistor 22, and when a transistor 25 different from the above is turned on by a detection signal of the detection resistor 22, The control input voltage Vc is divided and reduced by the resistor 27a and the on-resistance of the two transistors 25 connected in parallel, and the divided voltage is applied to the semiconductor element 1, so that the load current I is further reduced by one stage.

In the embodiment shown in FIG. 3, two intermediate setting values Vi shown in FIG. 1B are set and the load current I is narrowed down to two stages. Better adapted overpower protection can be provided. Further, by making the transistor 25 also function as a voltage-dividing resistor and a threshold operation circuit element, the entire circuit can be completed with a simple configuration irrespective of two-stage protection. The protection is not limited to the two stages, but may be further increased as necessary.

In the intermediate voltage protection circuit 20 of the embodiment shown in FIG. 4, an intermediate set value is set by a resistor voltage dividing circuit composed of resistors 23a and 23b and a comparator 26 receiving the divided voltage. The comparator 26 compares the divided voltage of the voltage V between the main terminals with the reference voltage Vr for the intermediate set value. When the former exceeds the latter, the output is made low. Also in this embodiment, the on-resistance of the transistor forming the comparator 26 is used together with the resistor 27a in the configuration of the resistor voltage dividing circuit. Accordingly, when the output of the comparator 26 becomes low, the control input voltage Vc is reduced by the voltage dividing circuit and then applied to the semiconductor element 1, whereby the load current I is reduced to a value set by the voltage dividing ratio.

As can be seen from the embodiments shown in FIGS. 1 to 5, the maximum voltage protection circuit 10 and the intermediate voltage protection circuit 20 used in the present invention are composed of circuits such as a Zener diode, a resistor, a logic gate, a comparator and a control transistor. Since all of the combined elements have a very simple circuit configuration, the operation requires little time, and the operation is hardly disrupted. Therefore, the circuit of the present invention can provide high-speed and reliable overload protection for the power semiconductor device.

[0026]

As described above, in the power overload protection circuit according to the present invention, the maximum voltage protection circuit for controlling the control input terminal of the semiconductor element when the voltage between the main terminals of the semiconductor element reaches the maximum set value is provided. And an intermediate voltage protection circuit for controlling a control input voltage of the semiconductor element when the voltage between the main terminals exceeds an intermediate set value lower than the maximum set value. The following effects can be obtained by performing overpower protection by narrowing down to the limit value and then performing overvoltage protection by cutting off the load current by the maximum voltage protection circuit as necessary.

(A) The intermediate set value for operating the intermediate voltage protection circuit can be set to an optimum value according to the thermal characteristics of the semiconductor device and the characteristics of the load. This makes it possible to sufficiently exhibit the inherent drive capability of the load under the supply of the power supply voltage. (b) Speeding up and ensuring the operation of overpower protection and overvoltage protection by assigning overvoltage protection to the intermediate voltage protection circuit and overvoltage protection to the maximum voltage protection circuit, and performing protection operations independently of each other. be able to.

(C) By providing over-power protection and over-voltage protection for the semiconductor element in a stepwise manner, the protection characteristics are simplified as compared with a conventional protection circuit having a hyperbolic protection characteristic, and over-power and over-voltage protection are performed. Despite having the protection performance for both, the overall configuration of the circuit can be simplified to facilitate incorporation into an integrated circuit. The mode in which the intermediate set value is set to be approximately the same as or slightly higher than the power supply voltage value is more advantageous for sufficiently exhibiting the load driving capability of the semiconductor device. It is advantageous to improve the overpower protection performance by causing the intermediate voltage protection circuit to reduce the load current to a current limit value that decreases sequentially each time the intermediate voltage exceeds each intermediate set value.

Further, with respect to the intermediate voltage protection circuit, (a)
Incorporating a Zener diode that receives the voltage between the main terminals of the semiconductor element, narrows down the load current using the breakdown voltage as an intermediate set value, and Incorporating operating circuit elements,
An intermediate set value is set according to the former voltage dividing ratio and the latter threshold, and the load current is narrowed down when the threshold operation circuit element operates, or (c) a resistive voltage dividing circuit receiving the voltage between the main terminals. A comparator for comparing the divided voltage with a predetermined reference voltage is incorporated, an intermediate set value is set based on the former divided ratio and the reference voltage value, and the load current is narrowed according to the output of the comparator. This is advantageous in simplifying the configuration of the circuit and improving its operation reliability. Further, as a means for narrowing down the load current by the intermediate voltage protection circuit, a resistance voltage dividing circuit for receiving a control input voltage to the semiconductor element is provided, and the divided voltage of the control input voltage is applied to the semiconductor element to simplify the circuit configuration. It is particularly advantageous in doing so.

[Brief description of the drawings]

1 shows an embodiment of the present invention together with a power semiconductor device and related circuits. FIG. 1 (a) is a circuit diagram of an embodiment of an overload protection circuit according to the present invention, and FIG. 1 (b) is a protection characteristic thereof. It is a diagram showing an example.

FIG. 2 is a circuit diagram showing a different embodiment of the present invention for an intermediate voltage protection circuit together with main related circuits.

FIG. 3 is a circuit diagram showing still another embodiment of the present invention together with main related circuits for an intermediate voltage protection circuit.

FIG. 4 is a circuit diagram showing another different embodiment of the present invention for an intermediate voltage protection circuit together with main related circuits.

FIG. 5 shows a typical example of a conventional protection circuit in terms of protection characteristics. FIG. 5 (a) is a diagram showing the protection characteristics of a conventional overvoltage protection circuit, and FIG. 5 (b) is a conventional overpower protection circuit. FIG. 3 is a diagram illustrating protection characteristics of a circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power semiconductor element to be protected 2 Power supply 3 Load 4 Drive circuit 5 Operational amplifier for load current control 6 Control transistor for load current control 10 Maximum voltage protection circuit 11 Comparator 20 Intermediate voltage protection circuit 21 Zener diode 22 Detection resistor 23a, 23b Resistor for resistor divider circuit 24 NAND gate 25 Transistor 26 Comparator 27a, 27b Resistor for resistor divider circuit A Protection characteristic according to the present invention B Conventional overvoltage protection characteristic C Conventional overpower protection characteristic I Load current V Semiconductor Element main terminal voltage Vc Semiconductor element control input voltage Vd Control power supply voltage Vi Intermediate set value Vm Maximum set value Vs Power supply voltage

Continuation of front page (56) References JP-A-5-327440 (JP, A) JP-A-3-40517 (JP, A) JP-A-5-275999 (JP, A) JP-A-5-267580 (JP) JP-A-3-293814 (JP, A) JP-A-3-106217 (JP, A) JP-A-2-128205 (JP, A) JP-A-5-299990 (JP, A) 6-291631 (JP, A) Japanese Utility Model Hei 6-16884 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03K 17/00-17/70

Claims (7)

(57) [Claims] A circuit for protecting a power semiconductor element for controlling a current flowing to a load connected in series to a power supply from an overload, wherein a voltage applied between main terminals of the semiconductor element is a predetermined maximum set value. A maximum voltage protection circuit that controls the control input terminal of the semiconductor element when the voltage reaches the intermediate input value that is set lower than the maximum set value. An intermediate voltage protection circuit for controlling the applied voltage, the voltage applied to the control input terminal of the semiconductor element is controlled by the intermediate voltage protection circuit so as to reduce the load current to the current limit value, and the load current is interrupted by the maximum voltage protection circuit An overload protection circuit for a power semiconductor device, wherein a control input terminal of the semiconductor device is controlled. 2. The circuit according to claim 1, wherein a plurality of intermediate set values are set, and the load current is sequentially reduced by the intermediate voltage protection circuit whenever the voltage between the main terminals of the semiconductor device exceeds each intermediate set value. An overload protection circuit for a power semiconductor device, wherein the overload protection circuit is limited to a current limit value. 3. The overload protection of a power semiconductor device according to claim 1, wherein the intermediate set value is set to be equal to or slightly higher than the value of the power supply voltage. circuit. 4. A circuit according to claim 1, wherein a Zener diode for receiving a voltage between main terminals of the semiconductor element is provided in the intermediate voltage protection circuit, and a control operation for narrowing down a load current is performed by using the Zener breakdown voltage as an intermediate set value. An overload protection circuit for a power semiconductor device, characterized in that: 5. The circuit according to claim 1, further comprising a resistor voltage dividing circuit for receiving a voltage between the main terminals of the semiconductor element and a threshold voltage operation circuit element for receiving the divided voltage in the intermediate voltage protection circuit. An intermediate set value is set based on a voltage dividing ratio of a voltage dividing circuit and a threshold value of a threshold operation circuit element, and a control operation for reducing a load current is performed when the threshold operation circuit element operates. Characteristic overload protection circuit for power semiconductor devices. 6. The circuit according to claim 1, further comprising a resistor voltage dividing circuit for receiving a voltage between the main terminals of the semiconductor element and a comparator for comparing the divided voltage with a predetermined reference voltage value in the intermediate voltage protection circuit. An overload protection circuit for a power semiconductor element, wherein an intermediate set value is set based on a voltage dividing ratio of a resistance voltage dividing circuit and a reference voltage value, and an operation of narrowing a load current according to an output of a comparator is performed. . 7. The circuit according to claim 1, further comprising a resistor voltage dividing circuit for receiving a control input voltage for the semiconductor element in the intermediate voltage protection circuit, wherein a voltage between main terminals of the semiconductor element exceeds an intermediate set value. A load current is narrowed by applying the divided voltage to a control input terminal of the semiconductor element.