JP3182300B2 - Connection failure 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 a connection failure detecting circuit for detecting a connection failure of a connector connecting a current transformer.

[0002]

2. Description of the Related Art An electromagnetic cooker, which is a high-frequency heating device, is provided with a current transformer for detecting a circuit current. When an overcurrent is detected, an on / off operation is performed to supply a current to an induction heating coil. Stop the operation of the switching element
The current of the switching element is cut off to protect the switching element from overcurrent. The current transformer is connected to a control circuit via a detachable connector.

[0003]

By the way, such an electromagnetic cooker is shipped after the assembly state is carefully checked after the manufacture, but in the unlikely event that the connector to which the current transformer is connected is defective. If an overcurrent occurs, the overcurrent of the circuit cannot be detected, and the switching element that is turned on and off to supply current to the induction heating coil cannot be stopped, and the switching element may be damaged. This can occur and can induce high voltages on the secondary side of the current transformer, damaging the current transformer.

Therefore, when the operation is started, the electromagnetic cooker may be heated at an extremely low output to check whether or not the output voltage of the current transformer corresponding to the extremely low output can be obtained. In that case, a circuit for checking must be added, which complicates the circuit and increases the cost.
Therefore, a circuit for performing such a check is not employed. In order to prevent a high voltage from being induced on the secondary side of the current transformer, it is conceivable to add a dummy resistor or a varistor between the secondary terminals, but the versatility of the current transformer is lost. In addition, there are problems such as an increase in size.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a connection failure detection circuit that can reliably detect a connection failure when a connection failure occurs in a connector to which a current transformer is connected. .

[0006]

A connection failure detecting circuit according to a first aspect of the present invention compares a current transformer for detecting a circuit current with an output voltage of the current transformer and a reference voltage provided by a DC power supply. A faulty connection detecting means for detecting an overcurrent by providing a comparator and detecting a faulty connection of a connector interposed in a connection circuit between the current transformer and the DC power supply and the comparator; In the circuit, the DC power supply and the terminal to which the reference voltage of the comparator is to be input, and the current transformer and the other input terminal of the comparator to which the output voltage of the current transformer is to be input, are commonly used. It is configured to be connected by a connector.

A faulty connection detection circuit according to a second aspect of the present invention is a faulty connection detection circuit for detecting faulty connection of a connector to which a current transformer for detecting a circuit current is to be connected, the output of the current transformer being connected via the connector. A comparator to which a voltage is to be input, a DC power supply that supplies a reference voltage to be input to the comparator, and a resistor interposed between the output side of the comparator and the ground potential. The configuration is such that the signal is applied to the output side of the comparator via a connector.

In the connection failure detecting circuit according to a third aspect of the invention, a plurality of connection terminals are arranged in the connector in one direction, and one of the outermost connection terminals is connected to the DC power supply and the outermost one is connected to the outermost connection terminal. The other connection terminal to be connected is connected to the terminal to which the reference voltage of the comparator is to be input, or the output terminal of the comparator, and the one and the other connection terminals are connected in series, one connection terminal and the other The current transformer is connected to a connection terminal located inside the connection terminal.

According to a fourth aspect of the present invention, there is provided a connection failure detection circuit in which a plurality of connection terminals are arranged in one direction in the connector, and one of the connection terminals located outside the two connection terminals connected to the current transformer. A terminal is connected to the DC power supply, and the other connection terminal located outside is connected to a terminal to which a reference voltage is input to the comparator, or an output terminal of the comparator, and the one connection terminal and the other connection terminal are connected to each other. Are connected in series.

[0010]

In the first invention, the current transformer and the DC power supply are connected to the terminal of the comparator to which the current transformer is to be connected and the terminal to which the reference voltage is to be inputted, through a common connector. When the output voltage of the current transformer becomes equal to or higher than the reference voltage, the comparator outputs an overcurrent detection signal. When a connection failure occurs in the connector, the reference voltage is not input to the comparator, and the output of the comparator is inverted to output a connection failure detection signal. Thereby, an overcurrent can be detected. In addition, a connection failure of the connector can be reliably detected.

In the second invention, the current transformer and the DC power supply are separately connected to the input terminal and the output terminal of the comparator via a common connector. When the output voltage of the current transformer becomes equal to or higher than the reference voltage, the output of the comparator is inverted to output an overcurrent detection signal. When the connector is disconnected, the DC power supply is disconnected from the output side of the comparator, the voltage on the output side of the comparator is pulled down via a resistor, and the voltage on the output side of the comparator changes to detect a connection failure. Output a signal. Thereby, an overcurrent can be detected. In addition, a connection failure of the connector can be reliably detected.

In the third invention, the output voltage of the current transformer and the reference voltage or the voltage of the DC power supply are connected to one terminal of the comparator and the other through a common connector having a plurality of connection terminals arranged in one direction. Input to each terminal, or apply to the output terminal of the comparator. When the output voltage of the current transformer exceeds the reference voltage,
The output of the comparator is inverted to output an overcurrent detection signal.
When the connector becomes defective, a series circuit of one of the outermost connection terminals and the other of the outermost connection terminals is cut off. Then, the reference voltage is no longer input to the comparator, and the output of the comparator is inverted to output a connection failure detection signal, or the DC power supply and the output side of the comparator are disconnected and the voltage on the output side of the comparator is reduced. Pull down to output a connection failure detection signal. Thereby, an overcurrent can be detected. In addition, a connection failure of the connector can be detected more accurately.

In the fourth invention, the output voltage and the reference voltage of the current transformer or the DC power supply are connected to one terminal and the other terminal of the comparator through a common connector having a plurality of connection terminals arranged in one direction. To each other, or to the output terminal of the comparator. When the output voltage of the current transformer becomes equal to or higher than the reference voltage, the output of the comparator is inverted to output an overcurrent detection signal. If the common connector becomes defective, one connection terminal located outside the connection terminal connecting the current transformer and the other connection terminal located outside the connection terminal connecting the current transformer Is shut off. Then, the reference voltage is not input to the comparator, the voltage on the output side of the comparator changes to output a connection failure detection signal, or the DC power supply that provides the reference voltage and the output side of the comparator are disconnected, The voltage on the output side of the comparator is pulled down to output a connection failure detection signal. Thereby, an overcurrent can be detected. In addition, a connection failure of the connector can be detected more accurately.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a block diagram showing a configuration of an electromagnetic cooker provided with a connection failure detection circuit according to the present invention. The three-phase AC power supply 1 is connected to the AC input terminals 2au, 2av, 2aw of the rectifier bridge 2, and a smoothing capacitor 3 is interposed between the output terminals 2b and 2c. The smoothing capacitor 3 includes a series circuit of a switching element 4 and a switching element 5,
The series circuit of the resonance capacitor 6 and the resonance capacitor 7 is respectively connected in parallel. A heating coil 8 is interposed between the connection between the switching elements 4 and 5 and the connection between the resonance capacitors 6 and 7. A current transformer 10 for detecting a current flowing through the heating coil 8 is provided in the circuit connecting the heating coil 8.
Is provided.

In the circuit connecting the three-phase AC power supply 1 and the AC input terminal 2aw of the rectifier bridge 2, a rectifier bridge 2 is provided.
Current transformer 9 for detecting the input current of Current transformer 9
Is input to a connection failure detection circuit 15 having an input overcurrent detection function, and is input to one terminal of the error comparator 12 via the connection failure detection circuit 15. The detection output of the connection failure detection circuit 15 is input to the drive circuit 14 and the abnormality display circuit 17.
The output current of the current transformer 10 is input to a connection failure detection circuit 16 having a coil overcurrent detection function, and the detection output is input to a drive circuit 14 and an abnormality display circuit 17. Input current setting device
The output of 11 is input to the other terminal of the error comparator 12, and the comparison output of the error comparator 12 is input to the voltage controlled oscillator 13. The oscillation output of the voltage controlled oscillator 13 is input to the drive circuit 14, and the output of the drive circuit 14 is input to each gate of the switching elements 4 and 5.

Next, the operation of the electromagnetic cooker will be described. A three-phase input current flows from the three-phase AC power supply 1 to the rectifier bridge 2 to perform full-wave rectification. This input current is detected by the current transformer 9, and the output current is input to the connection failure detection circuit 15. Then, the rectified DC voltage charges the smoothing capacitor 3. Here, when a predetermined input current value is set in the input current setter 11, the error comparator 12 sets the set input current value,
The input current detected by the current transformer 9 is compared in magnitude with the input current, and the comparison result is input to the voltage controlled oscillator 13. Thereby,
The voltage controlled oscillator 13 causes the detected input current to oscillate at an oscillation frequency corresponding to the set input current value in accordance with an error between the set input current value and the detected input current. The oscillation output is input to the drive circuit 14, and the switching elements 4 and 5 are alternately turned on and off according to the oscillation frequency by the drive signal output from the drive circuit 14. As a result, a resonance current alternately flows through a resonance circuit formed by the heating coil 8 and the resonance capacitor 6 and a resonance circuit formed by the heating coil 8 and the resonance capacitor 7, so that a heating output is obtained at the heating coil 8 and the heating coil 8 is placed on the heating coil 8. The not-shown pan is heated by high frequency. The high-frequency current flowing through the heating coil 8 is detected by the current transformer 10 and is input to the connection failure detection circuit 16.

On the other hand, the output current detected by the current transformer 9 is input to the connection failure detection circuit 15. Then, a heating output is obtained from the heating coil 8 according to the set input current value. Now, if the input current of the rectifier bridge 2 becomes an overcurrent, an overcurrent detection signal is input from the connection failure detection circuit 15 to the drive circuit 14, the drive signal of the drive circuit 14 is cut off, and the switching element 4 is turned off. , 5 are both turned off to cut off the current flowing through the switching elements 4, 5, to prevent the switching elements 4, 5 from being damaged by overcurrent, and to indicate that the input current has become overcurrent. Display by
If the current flowing through the heating coil 8 becomes an overcurrent, an overcurrent detection signal is output from the connection failure detection circuit 16 to the drive circuit.
14 and the switching elements 4 and 4
5 is prevented from being damaged by the overcurrent, and the fact that the current of the heating coil 8 has become an overcurrent is displayed. In this way, the switching element is protected from overcurrent. Current transformers 9,10
When a connection failure of a connector (not shown) connected to the power supply is detected, a connection failure detection signal is input to the drive circuit 14, and the switching elements 4 and 5 are both turned off to prevent the damage due to the above-described overcurrent beforehand. Prevents the occurrence of high voltage generated in the current transformer.

FIG. 2 is a block diagram showing the configuration of the connection failure detection circuit 15.
It is a lock figure. The secondary terminals 9a and 9b of the current transformer 9
Connection terminals 20a, 20b, 20c,
Connect separately to the connection terminals 20b and 20c located inside 20d.
Continued. The outermost connection terminals 20a and 20d
Are short-circuited by the short-circuit line 21. The connection terminal 20a is a resistor R ₁
Is connected to the DC power supply E via the. Connection terminal 20d is compared
The positive input terminal + is connected to the positive input terminal + of the
_TwoGrounded. The connection terminal 20b is a diode D₁
Anode and diode D_TwoConnected to the cathode and
You. Connection terminal 20c is diode D_ThreeAnode and die
Aether D_FourConnected to the cathode. diode
D₁, D_ThreeAre connected in common and a diode
D_Two, D_FourAre connected in common. diode
D₁, D_ThreeIs connected to a resistor R_Three, Conde
Connected to each terminal of the sensor C and the negative input terminal of the comparator 22.
It is. Diode D_Two, D_FourThe anode common connection of
Resistance R_Three, Capacitor C and other terminals.
_FourIs connected to a DC power supply E via a resistor R_FiveContact through
Ground. The negative input terminal of the comparator 22 is connected to the error comparator 11
The output terminal of the comparator 22 is connected to the drive circuit 14 (Fig.
1).

[0019] In FIG. 2, the connection terminals 20a of the conventional connector 21, without providing the 20d, connected to the positive input terminal + of the comparator 22 via the resistor R ₁ to the DC power source E, a current transformer The circuit for detecting the overcurrent of the input current of the rectifier bridge 2 by the output current of 9 is provided in the electromagnetic cooker.
The present invention uses the circuit to constitute a connection failure detection circuit for preventing the switching element from being damaged due to the connection failure of the connector 20 and the high voltage generated in the current transformer.

Next, the operation of the connection failure detection circuit will be described with reference to FIGS. 3 and 4 which are timing charts of a voltage related to the output current of the current transformer, an overcurrent detection signal, and voltages of respective parts. The voltage of the DC power supply E is divided by the resistors R ₁ and R _2, and the divided voltage, that is, the reference voltage _Vref is compared with the comparator 22.
Is input to the positive input terminal +. On the other hand, the voltage of the DC power supply E is divided by the resistors R ₄ and R _5, and the offset voltage V _{OFS as the divided} voltage is _divided by the diodes D ₁ , D ₂ , D ₃ , D
₄ superimposed on the rectified voltage by the charging voltage V _C next to capacitor C, the charging voltage V _C is the negative input terminal of the comparator 22 - is fed. Then, the reference voltage V _ref and the offset voltage V _OFS have the voltage levels shown in FIG.

On the other hand, the current transformer 9 detects the input current of the rectifier bridge 2 (see FIG. 1), and the output current is subjected to full-wave rectification by diodes D ₁ , D ₂ , D ₃ and D ₄ , and is charged capacitor C is the wave rectified direct current, the charging voltage V _C is the negative input terminal of the comparator 22 - is input to. Thus comparator 22 compares the charging voltage V _C and the reference voltage V _ref. The comparison output when the charging voltage V _C is less than the reference voltage V _ref is the comparator 22 becomes H level as shown in FIG. 3 (b), it does not detect an overcurrent.

When the output current of the current transformer 9 increases and the charging voltage V _C of the capacitor C rises as shown in FIG. 3A, when the charging voltage V _C exceeds the reference voltage V _ref. , the comparison output of the comparator 22 is inverted to L level as shown in FIG. 3 (b), continued period L level charge voltage V _C is above the reference voltage V _ref, the overcurrent comparator 22 of L level The detection signal #OC is output.

By the way, when the connector 20 is not completely connected and a connection failure occurs, that is, when the connector 20 is not connected, the voltage of the DC power supply E is applied to the comparator 22 via the connector 20. The signal is not input to the positive input terminal +, and the reference voltage _Vref becomes zero. On the other hand, the negative input terminal-of the comparator 22 has an offset voltage V _OF as shown in FIG.
Only _S is entered. As a result, the charging voltage V _C becomes higher than the reference voltage, and the comparison output of the comparator 22 remains inverted to the L level. As shown in FIG. NG is output, and the connection failure of the connector 20 is detected.

FIG. 5 is a block diagram showing the structure of the connection failure detection circuit 16. The secondary terminals 10a, 10b of the current transformer 10 are connected to the connection terminals 20a, 20b, 20
They are separately connected to the connection terminals 20b, 20c located inside c, 20d. Outermost connection terminals 20a and 20d
Is short-circuited by the short-circuit line 21. The connection terminal 20a is a resistor R
It is connected to the DC power supply E via ₁₁ . The connection terminal 20d is connected to the positive input terminal + of the first comparator 23. Connection terminal 20
resistor R ₁₂ between b and 20c is interposed, the connection terminal 20c is grounded. The connection terminal 20b is connected to the negative input terminal-of the comparator 23 and the positive input terminal + of the second comparator 24. Negative DC power source -E through a series circuit of a connection point between the positive input terminal + of the comparator 23 and the connecting terminal 20d is a resistor R ₁₃ and the resistor R ₁₄
Connected to The connection point between the resistor R ₁₃ and the resistor R ₁₄ is the negative input terminal of the comparator 24 - is connected to. Comparators 23, 24
Are commonly connected and connected to the drive circuit 14 (see FIG. 1).

Next, the operation of the connection failure detection circuit thus configured will be described with reference to FIGS. 6 and 7, which are timing charts of the voltage related to the output current of the current transformer, the overcurrent detection signal, and the voltages of various parts. DC power supply E and negative DC power supply-
And voltage resistance R ₁₁ between the E, and the resistor R _13, is divided by the resistors R _14, the voltage serving as the reference voltage + V _ref connection point between the resistor R ₁₁ and R ₁₃ is a comparator 23 is input to the positive input terminal +, and the resistor R _13, a voltage serving as a reference voltage -V _ref connection point between the resistor R ₁₄ is the negative input terminal of the comparator 24 - is input to.

On the other hand, the current transformer 10 is detects a current flowing through the heating coil 8 (see FIG. 1), flows an output current to the resistor R _12, the terminal voltage V _T is a comparator that occurs in the resistor R ₁₂
The negative input terminal 23 of the comparator 23 and the positive input terminal + of the comparator 24 are input. As a result, the comparator 23 outputs the positive-side reference voltage + V _ref
And the terminal voltage V _T and the magnitude comparator, comparator 24 compares the reference voltage -V _ref and the terminal voltage V _T of the negative side. Then, the terminal voltage V _T as shown in FIG. 6 (a) positive and negative side voltage level positive reference voltage + V _ref on the negative side, if in the range of -V _ref of the comparator 23 Fig. 6 (b)
As shown in (1), all become H level, and no overcurrent is detected.

By the way, the output current of the current transformer 10 increases.
And the resistance R₁₂Terminal voltage V_TIs on the top as shown in Fig. 6 (a).
Terminal voltage V_TOf the positive reference voltage
Pressure + V _refAt this point, the comparison output of the comparator 23 is as shown in FIG.
(b) As shown in FIG._TIs positive
Side reference voltage + V_refContinue L level for the above period
And outputs the L-level overcurrent detection signal #OC from the comparator 23.
Will do. Also, the terminal voltage V_TNegative voltage level
Is negative reference voltage -V_refCompare if:
The comparison output of the detector 24 is inverted to the L level, and as described above,
An L-level overcurrent detection signal #OC is output.

By the way, when the connector 20 is not connected, the positive input terminal + of the comparator 23 and the comparator
The voltage of the negative DC power supply -E is input to the negative input terminal 24. The terminal voltage V _T will not occur in the resistor R _12, it becomes 0V. As a result, the terminal voltage _VT and the reference voltage + _Vref change as shown in FIG. As a result, the comparison output of the comparator 23 is inverted to L level, and the comparison output of the comparator 24 is inverted to H level, and the L level connection failure detection signal #NG shown in FIG. Output, and a connection failure of the connector 20 is detected.

When a pair of connectors are connected in a non-parallel state and a connection failure occurs only in the outermost connection terminal 20a or 20d, the reference voltage + V _ref , -V
_ref changes to the voltage of the negative DC power supply -E, and the terminal voltage V _T
Is input to the comparators 23 and 24. In this case as well, the comparison output of the comparator 23 is inverted to the L level, and the L level connection failure detection signal #NG is output.

FIG. 8 is a block diagram showing the configuration of another embodiment of the connection failure detecting circuit according to the present invention. Current transformer CT2
The secondary terminals CTa and CTb are connected to the connection terminals 20b and 20c of the connection terminals 20a, 20b, 20c and 20d arranged in one direction on the connector 20. The connection terminals 20a and 20d are connected by a short-circuit line 21, and the connection terminal 20a is connected to a DC power supply V _CC . A resistor _RL is interposed between the connection terminals 20b and 20c, and the connection terminal 20b is connected to the negative input terminal-of the comparator CMP. Connection terminal 20c is connected to the DC power supply V _CC through a resistor R _21,
Connection point between the connecting terminal 20c and the resistor R ₂₁ is grounded through a resistor R _22. Resistors R ₂₁ and R ₂₂ are selected as R ₂₁ ≒ R _22, resistor R _21, the divided voltage serving offset voltage V _OFS by R ₂₂ is are no substantially 1/2 of the voltage of the DC power supply V _CC. DC power supply V _CC is grounded through a series circuit of a resistor R ₂₃ and the resistor R _24, the connection portion of the resistor R ₂₃ and R ₂₄ comparator
Connected to positive input terminal + of CMP. Connection terminals 20d of the connector 20 is grounded via the resistor R _G, an output terminal CMP ₀ ungrounded terminal of the resistor R _G via a resistor R _P comparator CMP
Connected to From the output terminal CMP ₀ of the comparator CMP overcurrent detection signal #OC and connection failure detection signal #NG is output.

Next, the operation of the connection failure detection circuit thus configured will be described with reference to FIG. 9 showing a timing chart of a voltage related to the output current of the current transformer and an overcurrent detection signal. DC power supply V voltage _CC is the resistance R _P via the comparator CM
Given to an output terminal CMP ₀ of P, an output terminal CMP ₀ is H
Become a level. On the other hand, when the current transformer CT detects the current, the output current of the current transformer CT is flowing through the resistor R _L, the terminal voltage V _T of the resistor R _L to be varied in accordance with the output current of the current transformer CT Become. Voltage by dividing the voltage of the DC power supply V _CC by the resistors R ₂₁ and R ₂₂ in the terminal voltage V _T serving offset voltage V _OFS
There superimposed, the terminal voltage V _T of the offset voltage V _OFS is present I pressurizing the negative input terminal of the comparator CMP - is input to, its positive input terminal + and the DC power supply V _CC of the resistor voltage R ₂₃ R ₂₄ And the reference voltage _Vref is input. Also provided by dividing the offset voltage V _OFS the voltage of the DC power supply V _CC by the resistors R ₂₁ and R ₂₂ is one terminal of the resistor R _L, given the offset voltage V _OFS to the terminal voltage V _T, FIG. 9 (a)
The terminal voltage V _T as shown in changes on the basis of the offset voltage V _OFS.

The comparator CMP receives the input terminal voltage V
The _T and reference voltage V _ref and compares, when the terminal voltage V _T is equal to or less than the reference voltage V _ref, the comparison output of the comparator CMP, as shown in FIG. 9 (b) becomes H level, an overcurrent Not detected. By the way, the output current of the current transformer CT increases, and FIG. 9 (a)
When the terminal voltage V _T is equal to or higher than the reference voltage V _ref as shown in, the comparison output of the comparator CMP becomes L level inverted as shown in Figure 9 (b). The terminal voltage _VT is equal to the reference voltage V.
_The L level is maintained for a period longer than _ref , and the comparator CMP outputs the overcurrent detection signal #OC.

Further, when the connector 20 is not in a connected state, the terminal voltage V _T negative input terminal of the comparator CMP - no longer input to, also, the voltage of the DC power supply V _CC is interrupted by the connector 20 And the output terminal CMP of the comparator CMP
₀ becomes the ground voltage via a series circuit of the resistors _RP and _RG . As a result, the voltage of the output terminal CMP ₀ of the comparator CMP changes to L level, and the L-level connection failure detection signal #NG
Will continue to be output.

As a result, the overcurrent detection signal #OC and the connection failure detection signal #NG can be output, and the switching elements 4 and 5 are damaged due to the connection failure of the current transformer CT, and the high voltage generated in the current transformer CT is generated. Voltage can be prevented beforehand. In the present embodiment, the case where the present invention is applied to an electromagnetic cooker has been described. However, this is merely an example, and similar effects can be obtained by applying the present invention to a device other than the electromagnetic cooker.

[0035]

As described in detail above, according to the first aspect, the circuit for detecting overcurrent, which is already provided, is used to
Poor connector connection can be reliably detected at low cost.

According to the second aspect, the connection failure of the connector to which the current transformer is connected can be reliably and inexpensively detected by directly changing the output side of the comparator.

According to the third invention, when one of the outermost one or the other of the plurality of connection terminals arranged side by side in one direction becomes defective, a connection failure detection signal is output. Can be output, and even if a connection failure occurs at one end of the connector, the connection failure state can be detected.

According to the fourth aspect, one of the one or the other connection terminal located outside the connection terminal connecting the current transformers of the plurality of connection terminals arranged in one direction is connected. When a connection failure occurs, a connection failure detection signal can be output,
The connection failure detection circuit according to the present invention has an excellent effect such that a connection failure state can be detected even if a connection failure occurs at one end of the connector.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an electromagnetic cooker to which a connection failure detection circuit according to the present invention is applied.

FIG. 2 is a block diagram showing a configuration of a first embodiment of a connection failure detection circuit.

FIG. 3 is a timing chart of a voltage related to an output current of a current transformer and an overcurrent detection signal.

FIG. 4 is a state diagram of an offset voltage and a connection failure detection signal.

FIG. 5 is a block diagram illustrating a configuration of a connection failure detection circuit according to a second embodiment;

FIG. 6 is a timing chart of a voltage related to an output current of a current transformer and an overcurrent detection signal.

FIG. 7 is a state diagram of a voltage related to an output current of a current transformer and a connection failure detection signal.

FIG. 8 is a block diagram showing a configuration of a connection failure detection circuit according to a third embodiment of the present invention.

FIG. 9 is a timing chart of a voltage related to an output current of the current transformer and an overcurrent detection signal.

[Explanation of symbols]

 9, 10 Current transformer 20 Connector 20a, 20b, 20c, 20d Connection terminal 21 Short-circuit line 22 Comparator E DC power supply -E Negative power supply CT Current transformer CMP comparator

Claims (4)

(57) [Claims] An overcurrent is detected by providing a current transformer for detecting a circuit current and a comparator for comparing the output voltage of the current transformer and a reference voltage provided by a DC power supply. A connection failure detection circuit for detecting a connection failure of a connector interposed in the connection circuit between the current transformer and the DC power supply and the comparator, wherein the DC power supply and a reference voltage of the comparator are input; Connection, and a common connector for connecting the current transformer and the other input terminal of the comparator to which the output voltage of the current transformer is to be inputted. Failure detection circuit. 2. A connection failure detection circuit for detecting a connection failure of a connector to which a current transformer for detecting a circuit current is to be connected, comprising: a comparator to which an output voltage of the current transformer is input via the connector; A DC power supply that supplies a reference voltage to be input to the comparator; and a resistor interposed between an output side of the comparator and a ground potential. The voltage of the DC power supply is supplied to the comparator through a connector. A connection failure detection circuit, wherein the connection failure detection circuit is provided to an output side. 3. A plurality of connection terminals are arranged in the connector in one direction, one of the outermost connection terminals is connected to the DC power supply, and the other outermost connection terminal is connected to the comparator. A terminal to which the reference voltage is to be input, or the output terminal of the comparator, the one and the other connection terminals are connected in series, and the connection terminal located inside the one connection terminal and the other connection terminal 3. The faulty connection detection circuit according to claim 1, wherein the current transformer is connected to the current transformer. 4. A plurality of connection terminals are arranged in the connector in one direction, and one connection terminal located outside the two connection terminals connected to the current transformer is connected to the DC power supply and the outside. The other connection terminal located is connected to a terminal to which a reference voltage is input to the comparator or an output terminal of the comparator, and the one connection terminal and the other connection terminal are connected in series. The connection failure detection circuit according to claim 1 or 2.