JP3466928B2 - Overcurrent detection circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent detection circuit, and more particularly, to an overcurrent generated in a load such as a motor or various actuators due to some abnormality of the load based on a sense current flowing in a sense transistor. The present invention relates to an overcurrent detection circuit for detecting.

[0002]

2. Description of the Related Art Conventionally, as an overcurrent detection circuit for detecting an overcurrent of a load based on a sense current, a circuit as shown in FIG. 3 is known. The outline of the configuration and operation will be described below.

In FIG. 3, the overcurrent detection circuit 20 is
It is composed of a current detection circuit 21 and a control circuit 22.
Here, the current detection circuit 21 is mainly composed of an operational amplifier (opamp) A and a detection resistor Rd for detecting the sense current Is. The output (hereinafter, referred to as a sense output) Vos of the sense transistor Trs included in the drive transistor 40 is input to the inverting input terminal of the operational amplifier A. Further, the output (hereinafter referred to as a drive output) Vod of the load drive transistor TRd which also constitutes the drive transistor 40 is input to the non-inverting input terminal of the operational amplifier A.

The load drive transistor TRd is
It is composed of n transistor arrays Tr1 to Trn.
And a load 50 is connected to the same load drive transistor TRd.
Has been done. In addition, the sense transistor Trs and the negative
Each transistor that constitutes the load driving transistor TRd
Have the same electrical characteristics. The "drain current I" is shown in FIG.
_D-Drain-source voltage V_DSCharacteristics ”. In addition,
This "drain current I _D-Drain-source voltage V_DS
"Characteristics" means the characteristics of those transistors in the saturation operation region.
In this region, the drain current I_DAnd drain saw
Voltage V_DSIs proportional to.

On the other hand, the operational amplifier A is a voltage follower connection whose output is directly fed back to the inverting input terminal, and the sense output Vos is connected by the operational amplifier A.
And the drive output Vod are maintained at the same voltage. That is, at this time, the voltage drop ΔV due to the sense transistor Trs
s (drain-source voltage V _DS ) and voltage drop ΔVd (drain-source voltage V _DS ) due to the load driving transistor TRd are made equal. In this state, theoretically, the load current I _L (drain current I _D of the load drive transistor TRd) becomes n times the sense current Is (drain current I _D of the sense transistor Trs), and as shown in FIG. , The sense current Is becomes proportional to the load current I _L. Therefore, from the detection voltage Vd by the detection resistor Rd, the sense current Is is obtained from the following equation Is = detection voltage Vd / detection resistor Rd (1), and the sense current Is is multiplied by n to obtain the load current. I _L is required. The exact correspondence is obtained in advance by experiments or the like.

Here, since the sense transistor Trs and the load drive transistor TRd are on / off controlled in the saturation operation region, the voltage drop ΔVs.
(V _DS ) is proportional to the sense current Is, and the above voltage drop ΔV
d is proportional to the load current I _L. In addition, these voltage drops Δ
The normal values of Vs and the voltage drop ΔVd are about 0.1 V (volt), and the sense output Vos and the drive output Vod are the same.
Is approximately equal to the power supply voltage Vcc.

Incidentally, these sense transistors Tr
s or the load drive transistor TRd, the relationship between the power supply Vcc, the drain-source voltage V _DS , and the sense output Vos (drive output Vod) is as follows.

Vcc = V _DS + Vos (Vod) (2) From the relationship of this equation (2) and the relationship shown in FIG. 4, the sense output Vos and the drive output Vod are shown in FIG. As described above, the load current I _L (or drain current I
It becomes inversely proportional to _D ).

On the other hand, the control circuit 22 controls the sense current I
While constantly monitoring s (detection voltage Vd), the same current Is (power
When the pressure Vd) exceeds a predetermined value, the load 50 receives an excessive load voltage.
Flow I _LIs determined to have flowed. At that time, for example, gate drive
Drive circuit 30 to turn off the operation of drive transistor 40.
Output a control signal or reduce the load on the load 50.
Output a control signal that causes
Flow I_LTo prevent the continuous
The controller 40 and the load 50 operate to be protected.

[0010]

By the way, in general, the input voltage of an input transistor forming an operational amplifier or the like has an appropriate input voltage range, and the operation of the operational amplifier or the like is performed with respect to an input outside the appropriate input voltage range. Becomes unstable by itself. Therefore, as described above, the operational amplifier A is used to equalize the sense output Vos and the drive output Vod, and then the overcurrent detection circuit 2 for detecting the overcurrent of the load is performed.
When it is 0, the load 50 is short-circuited.
Occurs, and the drive output Vod of the load drive transistor TRd may drop to nearly zero V, the reliability of overcurrent detection will also drop significantly.

That is, when a voltage near zero V, which is an input voltage outside the proper input voltage range, is input to the non-inverting input terminal of the operational amplifier A as the load 50 is short-circuited, the operational amplifier A itself is This voltage cannot be recognized properly, and the sense output Vos cannot follow the drive output Vod as a voltage follower.

On the other hand, since the sense output Vos is not directly applied to the load 50 as is apparent from FIG. 3, the sense current Is is the same as the sense output Vos.
For example, some current as indicated by the chain double-dashed line continues to flow in the area S of FIG. 5 corresponding to s. Therefore, even if a short circuit occurs in the load 50, the value can be obtained as the above-mentioned detection voltage Vd within a normal range, and the control circuit 22 is not prompted to perform its protective operation, and an excessive load current is applied. The load 50 will continue to flow.

Conventionally, as a circuit for detecting an overcurrent, for example, a circuit described in Japanese Patent Application Laid-Open No. 3-27575 or a circuit described in Japanese Patent Application Laid-Open No. 4-261327 is known. However, there is no known circuit that solves such a problem in the circuit that detects the overcurrent of the drive current (load current) by feeding back the sense output to the same potential as the drive output.

The present invention has been made in view of such a situation of a circuit for detecting an overcurrent of a drive current (load current) by feeding back a sense output to the same potential as a drive output, and an object thereof. However, an object of the present invention is to provide an overcurrent detection circuit that can reliably detect an overcurrent resulting from this even when a load is short-circuited and maintain its reliability.

[0015]

In order to achieve the above object, in the invention of the overcurrent detection circuit according to claim 1, the sense transistor and the load drive transistor driven under the same drive condition are respectively connected. While inputting the output voltage and performing feedback control so that the voltages have the same potential, the presence or absence of excess current flowing in the load drive transistor connected to the load is determined by the sense current flowing in the sense transistor not connected to the load. An overcurrent detection circuit that detects the voltage based on a means for generating a reference voltage;
The output voltage of the transistor has dropped below the reference voltage
When the sense transistor of the sense transistor
The gist is to provide means for limiting the output voltage to this reference voltage .

In the same configuration, the load driving transistor
When the output voltage of is lower than the reference voltage,
The output voltage of the sense transistor is
Limited to pressure . Therefore, the load is ground (GND)
The output voltage of the short circuit to the load drive transistor is a case such that decrease near zero V and is also over-current is also reliably detect the load is detected based on the sense current flowing through the cell Nsu transistor.

Further, in the invention described in claim 2, the same
Sense transistor and load drive driven under drive conditions
Input its output voltage from each of the dynamic transistors
And feedback control so that the voltages are at the same potential while connecting to the load.
Excessive current flowing through the load drive transistor
With or without the sense transistor not connected to the load
In the overcurrent detection circuit for detecting on the basis of the sense current flowing through a reference voltage generating means for generating a group reference voltage, when the output voltage of the load drive transistor becomes lower than the reference voltage, on the basis of the same reference voltage The gist of the invention is that it is configured to include a limiting transistor that limits the output voltage of the sense transistor to this reference voltage.

In the same configuration, the load driving transistor
When the output voltage of the sense transistor is lower than the reference voltage , the output voltage of the sense transistor is preferably set to the reference voltage with an extremely simple configuration of the reference voltage generating means and the limiting transistor.
Can be limited to pressure.

According to the invention described in claim 3,
In the overcurrent detection circuit described in 1 or 2, the short circuit of the load is recognized based on the output voltage of the sense transistor reaching the reference voltage, and the driving of the load drive transistor is stopped based on the recognition of the short circuit. The gist of the present invention is to further include a control circuit for performing the operation.

In the configuration, the control circuit recognizes a short circuit of the load based on the output voltage of the sense transistor reaching the reference voltage, and stops driving the load driving transistor. Also, it is possible to surely prevent the load driving transistor from being destroyed by a short circuit generated in the load and the load from being damaged by a short circuit current.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an overcurrent detection circuit according to the present invention will be described in detail below with reference to FIGS. The configuration of the overcurrent detection circuit of this embodiment is shown in FIG. Note that, in FIG. 1, the same elements as those shown in FIG. 3 above are denoted by the same reference numerals, and a duplicate description of those elements will be omitted.

In the circuit shown in FIG. 1, the overcurrent detection circuit 10 is mainly composed of a current detection circuit 11, a control circuit 12 and a reference voltage generator 13. Hereinafter, the configuration of the overcurrent detection circuit 10 will be described focusing on the configuration of the current detection circuit 11.

In the current detection circuit 11, the reference voltage generator 13 is connected to the base of the input transistor Q1, and the reference voltage V _REF generated by the reference voltage generator 13 is input to the base of the input transistor Q1. It The reference voltage generating unit 13 is, for example, a power supply voltage Vcc.
Is divided into a predetermined ratio by two voltage _dividing resistors (not shown). At that time, the reference voltage V _REF becomes a divided value of the power supply voltage Vcc. The reference voltage V _REF is, for example, 3V,
It is set to a value within the appropriate input voltage range described later.

The base of the input transistor Q2 is connected to the source of the load driving transistor TRd, and the output Vod of the load driving transistor TRd is input to the base of the transistor Q2. On the other hand, the base of the input transistor Q3 is connected to the source of the sense transistor Trs, and the output Vos of the sense transistor Trs is input to the base of the transistor Q3. The appropriate base input voltage range of these input transistors Q1, Q2, Q3 is approximately "1.6 V to power supply voltage Vcc".
+ 0.4V ", and for example, if the power supply voltage Vcc is 12V, the same voltage range is" 1.6V to 12.4V " .

Incidentally, the lower limit value "1.6 V" is determined as follows, for example, in the case of the input transistor Q3. 1.6 V ≈ V _BEQ9 + V _CEQ6 + V _BEQ3 where V _BEQ9 is the base-emitter voltage of the transistor Q9, V _CEQ6 is the collector-emitter voltage of the transistor Q6, and V _BEQ3 is the base-emitter voltage of the transistor Q3. Indicates.

Similarly, the upper limit value "12.4V" is determined as follows. _{12.4V≈12V−} V _CEQ3 + V _BEQ3 where V _CEQ3 represents the collector-emitter voltage of the transistor Q3.

Further, these input transistors Q1 and Q
The emitters of Q2 and Q3 are transistors Q4 and Q, respectively.
It is connected to the emitters of Q5 and Q6. The bases of these transistors Q4, Q5, Q6 are commonly connected, and their collectors are formed in a multi-collector structure consisting of two collectors. One of the collectors is commonly connected and is connected to the commonly connected base, and is also connected to the constant current source IG2. The other collectors of the transistors Q4 and Q5 are commonly connected and connected to the collector of the transistor Q7.
The other collector of the transistor Q6 is connected to the collector of the transistor Q8 and the base of the transistor Q9.

The bases of the transistors Q7 and Q8 are commonly connected to the collector of the transistor Q7, and the emitters of the transistors Q7 and Q8 are both grounded. The transistors Q7 and Q8
Is a well-known current mirror circuit, and transistor Q
7 is equal to the collector current I _CQ8 the collector current I _CQ7 the transistor Q8 of.

The collector of the transistor Q9 is connected to the base of the transistor Q10 and also to the constant current source IG1, and the emitter thereof is grounded. A capacitor C is connected between the collector and base of the transistor Q9.

Further, the transistor Q10 and the transistor Q11 are Darlington connected, and the transistor Q1
The emitter of 0 and the collector of the transistor Q11 are connected to the base of the transistor Q3. The emitter of the transistor Q11 has a detection resistor Rd for detecting the sense current Is of the sense transistor Trs.
And the control circuit 12 as well. Here, the transistors Q1 and Q4 form a limiting transistor that limits the lower limit of the input of the transistor Q3.

Next, the electrical characteristics and operation of the overcurrent detection circuit 10 thus constructed will be described with reference to FIG. Prior to the description of the overcurrent detection circuit 10, an outline of the feedback operation by the current detection circuit 11 that makes the sense output Vos the same potential as the drive output Vod will be described.

(A) Vod> Vos (> V
_REF ) then the collector current I _{CQ5 of} transistor Q5
_Becomes larger than the collector current I _{CQ6 of the} transistor Q6. Also, the collector current I _CQ5 of the transistor Q5,
Collector current I _CQ7 of the transistors Q7, and a collector current I _CQ8 of the transistor Q8 for is equal, the _{I CQ6 <I CQ8 (= I} CQ7 = I CQ5). Therefore, no current is supplied to the base of the transistor Q9, the transistor Q9 is turned off, and the collector voltage V _CQ9 of the transistor Q9 rises.

[0033] In addition, the sense output Vos from the following relationship: _{Vos = V CQ9 + V BEQ10 .........} (3) is increased, the equilibrium become a sense output Vos = drive output Vod.

(B) (V _REF <) Vod <V
If it becomes os at this time, the collector current I _CQ5 of the transistor Q5 is opposite to the collector current I of the transistor Q6, contrary to the above.
_It is smaller than _CQ6 . Similarly, the transistor Q5
The collector current I _CQ5, the collector current I _CQ8 the collector current I _CQ7, and the transistor Q8 of the transistor Q7
_Are equal, therefore I _CQ6 > I _CQ8 (= I _CQ7 = I _CQ5 ). At this time, since the base current of the transistor Q9 increases, the collector current I _{CQ9 of} the transistor Q9 also increases and the collector voltage V _{CQ 9} of the transistor Q9 decreases. Therefore, the sense output Vos drops from the relationship of the above equation (3), and the sense output Vos = the drive output Vod is balanced.

(C) Vod <V _REF <Vos
When (the load current I _L greatly increases and the drive output V
At this time, the transistor Q2 does not operate and the collector current I _CQ1 does not flow at this time. Therefore, it can be considered as “when V _REF <Vos” in the current detection circuit 11. In this case, the above-mentioned "Vod <Vo
When s is reached, the sense output Vos is equal to the reference voltage V _REF and balanced.

In this way, the sense output Vos is set to the same potential as the drive output Vod or the reference voltage V _REF by the current detection circuit 11. That is, in the present embodiment, the sense output Vos does not drop below the reference voltage V _REF , eg, 3 V, which is the same as the transistor Q1.
And the operation of transistor Q4. Therefore, even if a short circuit (short to the ground) occurs in the load 50 and the drive output Vod is about to drop to around zero V, the current detection circuit 11 does not malfunction and the accurate sense current Is is obtained. Can be detected. .

Now, as shown in the electrical characteristics of the overcurrent detection circuit 10 in FIG. 2, the sense current Is increases in proportion to the increase of the load current I _L (drain current I _D of the load drive transistor TRd). At this time, as described above, the drive output Vod and the sense output Vos are maintained at the same voltage, and decrease as the load current I _L increases as described above. Then, as shown in FIG. 2, when the load current I _L further increases to the current value I _Lth and the drive output Vod decreases to the reference voltage V _REF (3V), the sense output Vos is as described above. The reference voltage V
_When it reaches _REF (3V), it is fixed to the same reference voltage V _REF . At this time, the sense current Is also has a predetermined constant value Isc.
Becomes That is, in this embodiment, the sense output Vos becomes the reference voltage V _REF and the sense current Is
Is equivalent to a predetermined constant value Isc.

Then, when the control circuit 12 constantly monitors the sense current Is and detects that the sense current Is (detection voltage Vd) reaches the predetermined value Isc, for example, a short circuit occurs in the load 50. To judge. At this time, the control circuit 12 outputs a control signal for turning off the operation of the load driving transistor TRd to the gate driving circuit 30 to turn off the operation of the load driving transistor TRd and protects the transistor TRd. Therefore, even when a short circuit (short to the ground) occurs in the load 50, the short circuit is reliably detected and the protection function comes to work. As a result, it is possible to reliably prevent the load driving transistor TRd from being destroyed by a short circuit generated in the load 50 and the load 50 from being damaged by a short circuit current.

Further, the control circuit 12 controls the sense current I
While constantly monitoring s, when it is detected that the same sense current Is (detection voltage Vd) reaches a predetermined value Isa which is set separately before reaching the predetermined value Isc, the load 50
It is determined that an abnormal load current I _L has flowed to the. The predetermined value Isa is set as a value smaller than the predetermined value Isc in order to detect the overcurrent of the load 50. Then, for example, a control signal is output to the gate drive circuit 30 to limit the operation of the load drive transistor TRd, or a control signal for reducing the load is output to the load 50 to perform a protective operation. Therefore, even when an overcurrent (excluding a short circuit) occurs in the load 50, it is reliably detected and the protection function comes to work. As a result, it is possible to surely prevent the load driving transistor TRd from being destroyed by the overcurrent and the load 50 from being damaged by the overcurrent.

That is, in the overcurrent detection circuit of this embodiment, the load drive transistor TRd and the load 50 are reliably protected not only when the load 50 is overcurrent but also when the load 50 is short-circuited. The control circuit 1
Such a function as 2 can be realized by a known circuit including a comparison circuit, an AND circuit, and the like.

As described above, according to the overcurrent detection circuit of this embodiment, the following effects can be obtained. (1) In the present embodiment, by entering the criteria voltage V _REF to the current detecting circuit 11, the abnormal load current I _L flows drive output V
When od drops below this reference voltage V _REF , the sense output Vos is fixed to the same reference voltage V _REF and the sense current I
Let s be a constant value Isc. Then, by detecting the sense current Is that becomes the constant value Isc, it is detected that an abnormal load current _IL (short-circuit current) has flowed in the load 50.
Therefore, even if a short circuit (short to the ground) occurs in the load 50 and the drive output Vod drops to around zero V, the short circuit can be reliably detected. By operating the protection function based on the detection of the short circuit, it is possible to surely prevent the load driving transistor TRd from being destroyed by the short circuit of the load and the load 50 from being damaged by the short circuit current.

(2) In the present embodiment, the control circuit 12
Determines that an abnormal load current I _L has flowed to the load 50 when detecting that the predetermined value Isa, which is separately set before reaching the predetermined value Isc, is detected. Then, for example, a control signal is output to the gate drive circuit 30 to limit the operation of the load drive transistor TRd, or a control signal for reducing the load is output to the load 50 to perform a protective operation. Therefore, even if an overcurrent occurs in the load 50, it is reliably detected and the protection function comes to work. As a result, the load drive transistor TR
It is surely prevented that d is destroyed by an overcurrent or the load 50 is damaged by the overcurrent.

(3) In this embodiment, the limiting transistor (transistor Q) is added to the current detection circuit 11 whose input stage is composed of a differential amplifier (transistors Q2, Q3, etc.).
1, Q4) is added, the sense output Vos is preferably set to the reference voltage V _{RE F} with a very simple configuration.
It may be limited to.

The above embodiment can be implemented by changing the configuration as follows. In the above-described embodiment, an example in which the transistors Q1 to Q11 of the current detection circuit 11 are configured by bipolar transistors has been shown, but the present invention is not limited to this. For example, these transistors may be configured by field effect transistors (FET). , Bipolar transistor and F
It may be composed of a mixture of ETs.

In the above embodiment, the reference voltage V
_{An example in which REF} is set by two voltage dividing resistors for dividing the power supply voltage Vcc to a predetermined ratio has been shown, but the present invention is not limited to this, and may be set by using a Zener diode, or the bandgap voltage may be set, for example. It may be set by utilizing it. Also, the value of the reference voltage V _REF may be any value within the proper input voltage range of the system.

[0046]

In the above embodiment, the example in which the sense transistor Trs and the load drive transistor TRd that form the drive transistor 40 are N-MOS transistors has been shown, but the present invention is not limited to this. It may be composed of a P-MOS transistor or a bipolar transistor. In short, it is sufficient that the sense transistor and the load drive transistor are driven under the same drive condition.

In the above embodiment, the control circuit 1
2 is the same sense current Is (detection voltage Vd) is a predetermined value Is
Although it is determined that a short circuit has occurred in the load 50 when the reaching of c is detected, the present invention is not limited to this. For example, the control circuit 12 may determine that a short circuit has occurred in the load 50 when detecting that the sense current Is reaches the predetermined value Isc and is maintained at the predetermined value Isc for the predetermined time. At this time, erroneous recognition of a short circuit due to noise or the like is prevented.

Such a function as the control circuit 12 can be realized by a known circuit including a delay circuit, a timer circuit and the like in addition to the comparison circuit and the like. This determination method can also be applied when determining overcurrent based on the predetermined value Isa.

In the above embodiment, the configuration example in which the predetermined value Isa for detecting the overcurrent is provided separately from the predetermined value Isc of the sense current Is for detecting the short circuit is shown, but only the predetermined value Isc is set. It may be configured to detect an overcurrent including a short circuit.

Next, technical ideas other than the invention described in the claims, which can be grasped from the above-described embodiments, will be described below together with their effects. (1) In the overcurrent detection circuit according to claim 3, the control circuit recognizes an excess current flowing through the load driving transistor before the output voltage of the sense transistor reaches the reference voltage, and the overcurrent is detected. The overcurrent detection circuit is configured to limit the drive of at least one of the load drive transistor and the load based on the recognition.

According to the configuration described in (1), the load driving transistor can be protected from the short circuit of the load, and
Even when an overcurrent is generated in the load, it is possible to suitably cope with it by limiting the load.

[0053]

According to the invention of claim 1, even when the load is short-circuited with the ground (GND) and the output voltage of the load driving transistor is reduced to around zero V ,
Se overcurrent detection of load is performed based on the sense current flowing through the Nsu transistor also made reliable.

According to the second aspect of the invention, the load driving torque
When the output voltage of the transistor drops below the reference voltage,
With the extremely simple structure of the reference voltage generating means and the limiting transistor, the output voltage of the sense transistor is preferably
The pressure can be limited to the reference voltage. According to the third aspect of the present invention, even when the load is short-circuited, it is possible to surely prevent the load driving transistor from being destroyed by the short-circuit generated in the load and the load from being damaged by the short-circuit current.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an overcurrent detection circuit according to the present invention.

FIG. 2 is a graph showing electrical characteristics of the overcurrent detection circuit.

FIG. 3 is a circuit diagram showing an outline of a conventional overcurrent detection circuit.

FIG. 4 is a graph showing the relationship between drain current and drain-source voltage.

FIG. 5 is a graph showing electrical characteristics of a conventional overcurrent detection circuit.

[Explanation of symbols]

10 ... Overcurrent detection circuit, 11 ... Current detection circuit, 12 ... Control circuit, 13 ... Reference voltage generator, Q1, Q4 ... Limiting transistor, Trs ... Sense transistor, TRd ... Load driving transistor.

Continuation of the front page (56) Reference JP-A-3-27575 (JP, A) JP-A-1-174987 (JP, A) JP-A-61-294415 (JP, A) JP-A-62-109409 (JP , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02H 3/08-3/10 G05F 1/56 H02P 5/00

Claims (3)

(57) [Claims] 1. The output voltage of each of a sense transistor and a load driving transistor driven under the same driving condition is input and feedback control is performed so that the voltages become the same potential, and the output voltage is connected to the load. In an overcurrent detection circuit for detecting the presence / absence of excess current flowing through a load drive transistor based on a sense current flowing through the sense transistor not connected to a load, a means for generating a reference voltage, and an output voltage of the load drive transistor Reference voltage
If the voltage drops below
A means to limit the output voltage of the transistor to this reference voltage
Overcurrent detection circuit comprising: a. 2.Sense drive driven under the same drive condition
Output from each transistor and load drive transistor
Feedback control is applied so that voltages are input and they have the same potential.
Control the load drive transistor connected to the load
Excess current flowing through the load is not connected to the load.
Detection based on the sense current flowing through the sense transistor.
RuIn the overcurrent detection circuit,Basis Reference voltage generating means for generating a quasi-voltage, The output voltage of the load driving transistor is higher than the reference voltage.
If the voltage drops below
A limiter that limits the output voltage of the transistor to this reference voltage.
Overcurrent characterized by being configured with a transistor
Flow detection circuit. 3. The overcurrent detection circuit according to claim 1 , wherein a short circuit of the load is recognized based on an output voltage of the sense transistor reaching the reference voltage, and the short circuit is recognized based on the recognition of the short circuit. An overcurrent detection circuit further comprising a control circuit for limiting driving of a load drive transistor.