JP5592073B2 - Bidirectional switch current detection circuit - Google Patents

Description

  The present invention relates to a current detection circuit for a bidirectional switch that monitors a charging / discharging current of a DC power supply such as a rechargeable battery and protects the DC power supply by cutting off an excessive charging current or discharging current, and more particularly to a bidirectional switch. The present invention relates to a current detection circuit for a bidirectional switch that detects the current of the current with a low loss and high accuracy without directly inserting a sense resistor into the current path of the bidirectional switch.

  FIG. 4 is a block diagram of the simplest current measuring circuit of this type in the prior art. In the figure, a current is detected by inserting a high-precision sense resistor Rs in series with a MOSFET Q1 as a main switch for opening and closing a load current Im to be measured, and observing a voltage generated at both ends thereof. However, in this circuit, when the current Im to be measured is particularly large, the power loss in the sense resistor Rs becomes large, which causes a problem.

  On the other hand, there is an apparatus shown in FIG. 5 as an apparatus for detecting the load current Im with low loss. In FIG. 5, a current mirror circuit is provided by providing an Nch • MOSFET Q3 as a mirror switch having the same gate potential as that of the Nch • MOSFET Q1 as a main switch through which the load current Im flows, and having a W length of the transistor 1 / n that of the FETQ1. And the output terminal of the operational amplifier Op1 by a negative feedback circuit using a high input impedance element (the operational amplifier Op1 in this example) so that the voltage generated across the main FET Q1 and the voltage generated across the mirror FET Q3 are equal. The mirror current Is of exactly Im × (1 / n) is made to flow through the sense resistor Rs connected between the drains of the mirror FET Q3.

Since the mirror current Is is sufficiently smaller than the load current Im, the loss when detecting the mirror current Is is very small. The mirror current Is can be accurately detected by the element having a low output impedance (the operational amplifier Op1 in this example) and the sense resistor Rs, and the current Im of the main FET Q1 can be accurately detected.
However, in the current detection method shown in FIGS. 4 and 5, the direction of the current Im flowing through the main switch is constant, and a bidirectional current that flows through the bidirectional switch as the charge / discharge protection switch cannot be detected as it is.

  FIG. 6 shows a normal configuration diagram of a main switch portion of a charge / discharge protection switch (bidirectional switch) that cuts off an excessive charge / discharge current of the battery E. In the figure, main switches M1 and M2 each consisting of two Nch MOSFETs originally incorporating parasitic diodes are connected in series with opposite polarities so that the source terminals of the main switches M1 and M2 are at both ends in this example. And inserted into the charge / discharge path on the cathode side of the battery E.

Here, for example, if the main switch M1 is turned on and M2 is turned off, the charging current of the battery E can be cut off, and if the main switch M1 is turned off and M2 is driven on, the discharging current of the battery E can be cut off. .
However, this method has a problem that it is necessary to select a sense resistor value according to the current output specification of the device in order to suppress the loss of the sense resistor and increase the sense voltage, and it is inserted into the charge / discharge current path. The loss of the sense resistor portion that remains is still a problem.

In order to solve these problems, Patent Document 1 discloses the following.
FIG. 7 is a circuit diagram showing the configuration described in Patent Document 1. In FIG. In FIG. 7, the main switches M1 and M2 composed of Nch MOSFETs constituting the bidirectional main switch similar to FIG. 6 are connected in series with the opposite polarity in parallel to each other, and the main switches M1 and M2 are gated respectively. There are provided mirror switches M3 and M4 composed of Nch.MOSFETs which form the mirror circuit of the main switches M1 and M2 with the same voltage. Here, the series connection of the mirror switches M3 and M4 is also referred to as a bidirectional mirror switch.

Strictly speaking, the main switches M1 and M2 are composed of Nch MOSFETs Q1 and Q2 and their parasitic diodes D1 and D2, respectively. Similarly, the mirror switches M3 and M4 are composed of Nch MOSFETs Q3 and Q4 and their parasitic diodes D3 and D4, respectively.
In this example, the source terminals (point c) of the main switch M1 and the mirror switch M3 are connected to the cathode of the battery E and maintained at the ground potential, and the source terminal (point a) of the main switch M2 is the negative external terminal VB. Connected to-. The anode terminal of the battery E is connected to the positive external terminal VB +, and a battery charger (not shown) is connected between the external terminals VB + and VB− when the battery E is charged (the positive electrode side is the external terminal VB +). When the battery E is discharged, a load (not shown) is connected.

  On the other hand, for the source terminal (point a) of the main switch M2 and the source terminal (point b) of the mirror switch M4, the voltages of the source terminals (points a and b) are respectively input to the (+) input terminal and the (-) input. A high input impedance is input to the terminal, and a current is applied to the series connection of the mirror switches M3 and M4 via the sense resistor Rs so as to amplify the deviation between the two source terminal voltages and to make this deviation zero. An operational amplifier Op1 is provided.

  In the circuit of FIG. 7, when the battery E is charged, a charging current flows through the path of the external terminal (VB +) → battery E → main switch M1 → M2 → external terminal (VB−), and the point a with respect to the ground potential (point c). When the battery E is discharged, a discharge current flows through the path of the external terminal (VB−) → the main switch M2 → the same M1 → the battery E → (VB +). The potential becomes positive.

  The operational amplifier Op1 that performs the feedback amplification operation needs to operate so that the potentials between the points a and b are equal during charging and discharging. Therefore, the operational amplifier Op1 is mirror-switched via the sense resistor Rs when the battery E is charged. It is necessary to sink current from M3 and M4, and to flow current to the mirror switches M3 and M4 via the sense resistor Rs when the battery E is discharged. That is, the output voltage of the operational amplifier Op1 needs to be a negative voltage with respect to the ground potential (point c) when the battery E is charged, and also needs to be a positive voltage when the battery E is discharged.

Therefore, in the present invention, the power supply voltage supplied to the operational amplifier Op1 is not a zero potential (0V) and a positive voltage (VDD) during normal use, but a positive and negative power supply such as a negative voltage (−VDD) and a positive voltage (VDD). By using it, the output voltage range of the operational amplifier Op1 extends over both positive and negative voltage ranges sandwiching 0V.
In FIG. 7, the voltage difference unit 11 obtains the difference between the voltages at both ends of the sense resistor Rs, whereby the current of the sense resistor Rs, and hence the current passing through the main switches M1 and M2, can be measured. At this time, the current direction of the main switch can also be detected by looking at the polarity of the differential voltage, and it can be determined whether the charging state or the discharging state.

  Then, the measured current (the output of the voltage differentiator 11, which is output separately as the current measurement value 11a in this example) is compared with a predetermined value by the comparator 12, and the measured current is changed to a predetermined current value. When exceeding, the gates G1 and G2 of the bidirectional main switch (and mirror switch) can be controlled by the output of the comparator 12 via the gate control circuit 13, and the bidirectional switch can be turned off.

  For example, when an excessive discharge current flows due to a short circuit of an external circuit or the like, the gate G1 (and therefore the switches M1 and M3) is driven to the off side while the gate G2 (and therefore the switches M2 and M4) are driven to the on side, or When the battery E is destroyed and short-circuited, the gate G1 (and therefore the switches M1 and M3) is driven on while the gate G2 (and therefore the switches M2 and M4) are driven off and an excessive current is generated. Can be prevented.

In the circuit configuration of Patent Document 1, it is possible to detect and block an overcurrent flowing through the parasitic diode of the main switch, which was not considered in FIGS. 4 and 5. FIGS. 8A and 8B are explanatory diagrams of such energization mode. In FIG. 8, only the bidirectional main switches M1 and M2 in FIG. 7 are shown for simplicity.
That is, FIG. 8A shows an overdischarge prohibited, chargeable mode, that is, the state where the gate G1 is driven to the off side and the gate G2 is driven to the on side. The current can flow through the path of the parasitic diode D1 → the main switch M2 of the main switch M1.

The current flowing through the parasitic diode D1 can be detected simultaneously by the current flowing through the sense resistor Rs through the path of the parasitic diode D3 on the side of the bidirectional mirror switch in parallel with the bidirectional main switch and the mirror switch M4 (see FIGS. 7 to 1). The overcurrent of the parasitic diode D1 can be blocked by further driving the gate G2 off.
Similarly, FIG. 8B shows an overcharge prohibited and dischargeable mode, that is, the gate G1 is driven on and the gate G2 is driven off, and the charging current is blocked but the discharge side Current can flow through the path of the parasitic diode D2 → main switch M1 of the main switch M2.

The current flowing through the parasitic diode D2 can also be detected by the current flowing from the sense resistor Rs to the path of the parasitic diode D4 on the side of the bidirectional mirror switch parallel to the bidirectional main switch → mirror switch M3 (see FIG. 7). The overcurrent of the parasitic diode D2 can be further blocked by driving the gate G1 off.
In this case, in order to make the current characteristics of the parasitic diode equal to the mirror ratio between the mirror path and the main path, the area of the source region and the drain region and the area of the substrate contact region corresponding to the mirror path and the main path are accurately determined. To mirror ratio.

That is, if the current characteristics of the transistors Q1 and Q3 (and Q2 and Q4) are proportional to each other, it is important to match the W length to the mirror ratio, but the currents of the parasitic diodes D1 and D3 (and D2 and D4) In order to make the characteristics proportional to each other, it is important to match the opposing area of the PN junction with the mirror ratio.
If diode characteristics that completely match the mirror ratio are obtained, the applied voltages applied to both terminals of the diodes D1 and D3 (or applied voltages applied to both terminals of the diodes D2 and D4) are the same. Since the diode current is also equal to the mirror ratio, the mirror path current is proportional to the main path current even if the transistor is off.

JP 2005-16481A

  However, when one end of the bidirectional switch is connected to the anode side of the battery E, the power supply VDD and −VDD of the operational amplifier Op1 must have positive and negative potentials with respect to the potential of the anode of the battery E, respectively. Therefore, when only a positive voltage is supplied from the outside, it is necessary to use another battery inside to obtain a negative voltage, or to incorporate a power supply circuit that generates a negative voltage from the positive voltage.

  The object of the present invention is to solve the above-mentioned problems and provide only a power supply circuit for generating a positive voltage without providing another battery or a power supply circuit for generating a negative voltage from a positive voltage, and accurately with low loss. A bidirectional switch current detection circuit capable of detecting a charge / discharge current is provided.

In order to achieve the above object, according to the first aspect of the present invention, the first external terminal directly connected to one end of the main DC power source and the bidirectional main switch at the other end are provided. A second external terminal connected in series, two main transistors connected in series with opposite polarities to form a bidirectional main switch, and connected in series with opposite polarities so as to correspond to the series connection, Two sets of two mirror transistors formed so as to flow a current having a predetermined mirror ratio smaller than the current flowing through the corresponding main transistor under the condition that the potentials of the main electrodes corresponding to the main transistor are equal,
The other end of the main DC power supply is connected to a ground potential;
One end corresponding to the series connection of the main transistors and the series connection of one set of mirror transistors is connected to the second external terminal, and the series connection of the main transistors is inserted into the current path of the main DC power supply. And
Power is supplied from one power source having a positive potential with respect to the ground potential, its own positive terminal is connected to the ground potential, and its own negative terminal is connected to the other end of the series connection of the one set of mirror transistors. Its output terminal is connected to the other end of the series connection of the one set of mirror transistors via the first sense resistor, and the potential of the other end of the series connection of the one set of mirror transistors is grounded. A first feedback amplifying means for outputting a current of the mirror ratio so as to become a potential;
One end corresponding to the series connection of the main transistor and the series connection of the other set of mirror transistors are both connected to the ground potential,
Power is supplied from one power source having a positive potential with respect to the ground potential, its own positive terminal is connected to the second external terminal, and its negative terminal is the other of the series connection of the other set of mirror transistors. And connected to the other end of the series connection of the other pair of mirror transistors via the second sense resistor, and connected to the other end of the other series connection of the other pair of mirror transistors . Second feedback amplifying means for outputting the current of the mirror ratio so that the potential becomes the potential of the second external terminal;
The charging current of the bidirectional main switch is detected from the voltage across the first sense resistor, and the discharging current of the bidirectional main switch is detected from the voltage across the second sense resistor.

According to the invention of claim 2, the first external terminal directly connected to one end of the main DC power source and the second external terminal connected to the other end via the bidirectional main switch A main electrode corresponding to the corresponding main transistor, connected in series with the opposite polarity so as to correspond to the series connection, and two main transistors constituting a bidirectional main switch connected in series with the terminal and opposite polarity Two mirror transistors formed so as to flow a current having a predetermined mirror ratio smaller than the current flowing through the corresponding main transistor under the condition where the potentials are equal to each other, and the other end of the main DC power supply is set to the ground potential. One end of the main transistor connected in series and one end of the mirror transistor connected in series are both connected to the second external terminal, and the main transistor Series connection of static are inserted into the current path of the main DC power source,
Power is supplied from one power source having a positive potential with respect to the ground potential, its own positive terminal is connected to the ground potential, its own negative terminal is connected to the other end of the series connection of the mirror transistors , the output terminal is connected to the other end of the series connection of said one set of the mirror transistor through the sense resistor, wherein as the potential of the other end of the series connection of the one set of the mirror transistor is ground potential Provided with feedback amplification means for outputting a mirror ratio current,
The current of the bidirectional main switch is detected from the voltage across the sense resistor.

According to the invention described in claim 3 of the claims, in the invention described in claim 1 or 2, the four or six transistors may be N-channel MOSFETs.

Further, according to the invention of claim 4, wherein the appended claims, the invention of claim 3, wherein the parasitic diode of the mirror transistor, a current flowing through the parasitic diode, simultaneously flows through the parasitic diode of the main transistor It is preferable to form the mirror ratio with respect to the current.

According to the present invention, by providing a charging current detection circuit and a discharge current detection circuit composed of a bidirectional mirror switch, a sense resistor, and an operational amplifier, only a circuit that generates a positive voltage can be provided as a power supply circuit for the operational amplifier. . As a result, it is possible to eliminate the need for a separate battery or a power supply circuit that generates a negative voltage from a positive voltage as a power supply for the operational amplifier.
Further, a small current (mirror current) having a predetermined mirror ratio with respect to the current of the bidirectional main switch is supplied to the bidirectional main switch having a role of cutting off an excessive charging / discharging current of a DC power source such as a battery. In addition, the bidirectional mirror switch is mirrored through a sense resistor so that both ends of the bidirectional main switch and the bidirectional mirror switch are equalized by being fed from a positive power source. An operational amplifier that allows current to flow is provided, and the mirror current, and hence the bidirectional main switch current, is measured from the voltage across the sense resistor, so the bidirectional main switch current (battery charge / discharge current) is detected with high accuracy and low loss. be able to.

  In addition, the element layout on the semiconductor substrate of the main switch and the mirror switch is performed so that the currents of the respective parasitic diodes of the MOSFETs constituting the bidirectional main switch and the bidirectional mirror switch also accurately flow in the mirror ratio. Even in the operation mode in which the parasitic diode is energized, the parasitic diode current can be accurately detected, and an excessive parasitic diode current can be cut off.

  Further, when only the detection of the charging current or the detection of the discharging current is performed, the loss is reduced in the power supply circuit for generating the positive voltage by using the charging current detecting circuit or the discharging current detecting circuit of the present invention. The accurate charging current or discharging current can be detected.

It is a current detection circuit diagram of the bidirectional switch of the first embodiment of the present invention. It is a current detection circuit diagram of the bidirectional switch of the second embodiment of the present invention. It is a current detection circuit diagram of the bidirectional switch of the third embodiment of the present invention. It is a block diagram of the conventional simplest current measurement circuit of this kind. Configuration diagram of a device that detects load current Im with low loss 2 is a normal configuration diagram of a main switch portion of a charge / discharge protection switch (bidirectional switch) that cuts off an excessive charge / discharge current of a battery E. FIG. 2 is a configuration diagram of a current detection circuit described in Patent Document 1. FIG. Illustration of energization mode

  Embodiments will be described in the following examples.

  FIG. 1 is a current detection circuit diagram of a bidirectional switch according to a first embodiment of the present invention. The current detection circuit includes a charging current detection circuit 2a and a discharge current detection circuit 3a. The charging current detection circuit 2a includes a first Nch bidirectional mirror switch 2, a first sense resistor Rs11, a first AD converter 4, and a first operational amplifier Op11. The first Nch bidirectional mirror switch 2 includes first mirror switches M13 and M14. M13 includes a first mirror MOSFET Q13 and a parasitic diode D13, and M14 includes a first mirror MOSFET Q14 and a parasitic diode D14. Incidentally, Op11 and Rs11 constitute the first feedback amplification circuit 2b.

  On the other hand, the discharge current detection circuit 3a includes the second Nch bidirectional mirror switch 3, the second sense resistor Rs12, the second AD converter 5, and the second operational amplifier Op12. The second Nch bidirectional mirror switch 3 includes second mirror switches M15 and M16. M15 includes a second mirror MOSFET Q15 and a parasitic diode D15, and M16 includes a second mirror MOSFET Q16 and a parasitic diode D16. Note that Op12 and Rs12 constitute the second feedback amplifier circuit 3b.

The high potential side of the battery E is connected to the external terminal VB +, and the ground side of the battery E is connected to the external terminal VB− via the Nch bidirectional main switch 1. The Nch bidirectional main switch 1 includes main switches M11 and M12. M11 includes a main MOSFET Q11 and a parasitic diode D11. M12 includes a main MOSFET Q12 and a parasitic diode D12.
M11 and M12, M13 and M14, and M15 and M16 are connected so that their drains face each other.

  The first and second AD converters 4 and 5 convert the analog value of the voltage generated by the first and second sense resistors R11 and R12 into a digital value, and after data processing, the signal is the gate G11 of M11, M13, and M15. And input to the gate G12 of M12, M14, and M16. Further, the first and second AD converters 4 and 5 are replaced with a comparator (not shown), and the output of the comparator is input to a gate control circuit (not shown), and an output signal from the gate control circuit is input to G11 and G12. May be. When Im1 or Im2 becomes an excessive current, an off signal is sent to G11 and G12, the Nch bidirectional main switch 1 is turned off, and the battery E and the load are protected.

In FIG. 1, G11 is a common gate terminal for Q11, Q13, and Q15, and G12 is a common gate terminal for Q12, Q14, and Q16. A circuit operation may be performed by supplying a predetermined gate signal to an independent gate terminal.
Next, circuit operation will be described. First, the case where the battery E is charged by connecting the positive terminal and the negative terminal of the charger to the external terminal VB + and the external terminal VB− will be described. In this mode, the charging current Im1 flows toward the external terminal VB− via the Nch bidirectional main switch 1. At this time, the potential at the point e becomes lower than the potential at the point d on the ground side of the battery E.
First, after connecting a charger (not shown), an on signal is input to G11 and G12, and Q11 and Q12 are turned on. At this time, Q13 and Q14 are also turned on.

Since the + terminal of Op11 constituting the first feedback amplifier circuit 2b is fixed to the ground potential, the potential at the point g of the negative terminal of OP11 is also the ground potential. The potential at point g is transmitted to point i via point f, and the potential at point i becomes the ground potential.
Therefore, the voltage at both ends of the first Nch bidirectional mirror switch 2 (voltage between points i and j) is exactly the same as the voltage at both ends of the Nch bidirectional main switch 1 (voltage between points d and e). It becomes the same voltage.

As a result, a current having a mirror ratio (1 / n) of the current (Im1) flowing through the Nch bidirectional main switch 1 flows through the first Nch bidirectional mirror switch 2 as a mirror current. This mirror current becomes a detection current Is1 that flows from the point h which is the output of Op11 to the first Nch bidirectional mirror switch 2 through the sense resistor Rs11.
Since Is1 is 1 / n of the large current Im1, the power consumed by Rs1 can be extremely reduced. However, n is about 100 to 10,000, and 1: n is a mirror ratio. Also, Im1 can be detected accurately with the mirror ratio.

Next, a case where a load is connected to the external terminal VB + and the external terminal VB− to discharge from the battery E will be described. In this mode, the discharge current Im2 flows from the external terminal VB− toward the ground side of the battery E via the Nch bidirectional main switch 1. At this time, the potential at the point k is higher than the potential at the point d on the ground side of the battery E.
First, a load (not shown) is connected and an ON signal is input to G11 and G12, so that Q11 and Q12 are turned on. At this time, Q15 and Q16 are also turned on. Since the + terminal of Op12 constituting the second feedback amplifier circuit 3b is fixed at the potential of the k point, the potential of the q point of the − terminal of OP12 is also the potential of the k point.

Therefore, the voltage at both ends of the second Nch bidirectional mirror switch 3 (voltage between the points p and n) is exactly the same as the voltage at both ends of the Nch bidirectional main switch 1 (voltage between the points e and d). It becomes the same voltage.
As a result, a current having a mirror ratio (1 / n) of the current (Im2) flowing through the Nch bidirectional main switch 1 flows through the second Nch bidirectional mirror switch 3 as a mirror current. This mirror current becomes a detection current Is2 that flows from the point r which is the output of Op12 to the second Nch bidirectional mirror switch 3 through the sense resistor Rs12.

Since Is2 is 1 / n of Im2, the power consumed by Rs12 can be extremely reduced. However, n is about 100 to 10,000, and 1: n is a mirror ratio. Also, Im2 can be accurately detected with the mirror ratio.
By adopting the above circuit configuration, Im1 and Im2 are monitored from the voltage across Rs11 and Rs12 via Is1 and Is2, so that the charge / discharge current of the battery can be detected with high accuracy and low loss. it can.

Further, by adopting the configuration of the present invention, it is possible to detect both Im1 and Im2 by setting the power supply voltages of Op11 and Op12 to only normal voltages from 0 V to VDD (that is, positive voltages).
Further, by selecting the resistance values of Rs11 and Rs12 as large as possible, the potentials output from Op11 and Op12 (potentials at points H and r) can be set to potentials that are separated from the ground potential and the vicinity of the high potential. Therefore, the operations of Op11 and Op12 are stabilized. However, in order to allow the mirror current to flow accurately, the resistance values of Rs11 and Rs12 need to be smaller than the resistance values of the Nch bidirectional mirror switches 2 and 3.

  Further, the main switch and the mirror so that the currents of the parasitic diodes (D11 to D16) of the MOSFETs (Q11 to Q16) constituting the Nch bidirectional main switch 1 and the Nch bidirectional mirror switches 2 and 3 also flow accurately at a mirror ratio. By performing the element layout on the semiconductor substrate of the switch, it is possible to accurately detect the parasitic diode current even in the operation mode in which the parasitic diode is energized, and to block the excessive parasitic diode current. .

  As shown in FIG. 1, as the bidirectional switch, not only a type in which the drain is shared and the source is connected to the external terminal VB−, but also a type in which the source is shared and the drain is connected to the external terminal is possible. In addition to the type in which the Nch bidirectional main switch 1 is inserted at the cathode (ground potential side) with respect to the battery E, it is possible to insert the Pch bidirectional main switch at the anode.

  FIG. 2 is a current detection circuit diagram of the bidirectional switch according to the second embodiment of the present invention. This is a case where only the charging current detection circuit 2a including the first Nch bidirectional mirror switch 2 is provided. In particular, it is the case where only the charging current is monitored or the case where the discharging current is monitored by a configuration other than the discharging current detection circuit 3a including the second Nch bidirectional mirror switch 3.

  FIG. 3 is a current detection circuit diagram of the bidirectional switch according to the third embodiment of the present invention. This is a case where only the discharge current detection circuit 3a including the second Nch bidirectional mirror switch 3 is provided. In particular, it is a case where only the discharge current Im2 is monitored or a case where the charge current Im1 is monitored by a configuration other than the charge current detection circuit 2a including the first Nch bidirectional mirror switch 2.

DESCRIPTION OF SYMBOLS 1 Nch bidirectional main switch 2 1st Nch bidirectional mirror switch 2a Charging current detection circuit 2b 1st feedback amplifier circuit 3 2nd Nch bidirectional mirror switch 3a Discharge current detection circuit 3b 2nd feedback amplification circuit 4 1st AD converter 5 2nd AD Converter E Battery VB +, VB− External terminal Rs1 First sense resistor Rs2 Second sense resistor Op11 First operational amplifier Op12 Second operational amplifier VDD Power supply of operational amplifier (positive voltage)

Claims (4)

A first external terminal directly connected to one end of the main DC power source and a second external terminal connected to the other end via a bidirectional main switch are connected in series with opposite polarities to form a bidirectional main switch. From the current flowing through the corresponding main transistor under the condition that the two main transistors are connected in series with opposite polarities so as to correspond to the series connection, and the potentials of the corresponding main transistors and the corresponding main electrodes are equal. Two sets of two mirror transistors formed to pass a current having a small predetermined mirror ratio,
The other end of the main DC power supply is connected to a ground potential;
One end corresponding to the series connection of the main transistors and the series connection of one set of mirror transistors is connected to the second external terminal, and the series connection of the main transistors is inserted into the current path of the main DC power supply. And
Power is supplied from one power source having a positive potential with respect to the ground potential, its own positive terminal is connected to the ground potential, and its own negative terminal is connected to the other end of the series connection of the one set of mirror transistors. Its output terminal is connected to the other end of the series connection of the one set of mirror transistors via the first sense resistor, and the potential of the other end of the series connection of the one set of mirror transistors is grounded. A first feedback amplifying means for outputting a current of the mirror ratio so as to become a potential;
One end corresponding to the series connection of the main transistor and the series connection of the other set of mirror transistors are both connected to the ground potential,
Power is supplied from one power source having a positive potential with respect to the ground potential, its own positive terminal is connected to the second external terminal, and its negative terminal is the other of the series connection of the other set of mirror transistors. And connected to the other end of the series connection of the other pair of mirror transistors via the second sense resistor, and connected to the other end of the other series connection of the other pair of mirror transistors . Second feedback amplifying means for outputting the current of the mirror ratio so that the potential becomes the potential of the second external terminal;
The bidirectional switch is characterized in that a charging current of the bidirectional main switch is detected from a voltage across the first sense resistor, and a discharging current of the bidirectional main switch is detected from a voltage across the second sense resistor. Current detection circuit. A first external terminal directly connected to one end of the main DC power source and a second external terminal connected to the other end via a bidirectional main switch are connected in series with opposite polarities to form a bidirectional main switch. From the current flowing through the corresponding main transistor under the condition that the two main transistors are connected in series with opposite polarities so as to correspond to the series connection, and the potentials of the corresponding main transistors and the corresponding main electrodes are equal. Comprising two mirror transistors formed to pass a current with a small predetermined mirror ratio;
The other end of the main DC power supply is connected to a ground potential;
One end corresponding to the series connection of the main transistor and the series connection of the mirror transistor are both connected to the second external terminal, and the series connection of the main transistor is inserted into the current path of the main DC power supply,
Power is supplied from one power source having a positive potential with respect to the ground potential, its own positive terminal is connected to the ground potential, its own negative terminal is connected to the other end of the series connection of the mirror transistors , the output terminal is connected to the other end of the series connection of said one set of the mirror transistor through the sense resistor, wherein as the potential of the other end of the series connection of the one set of the mirror transistor is ground potential Provided with feedback amplification means for outputting a mirror ratio current,
A bidirectional switch current detection circuit, comprising: detecting a current of the bidirectional main switch from a voltage across the sense resistor. 3. The bidirectional switch current detection circuit according to claim 1, wherein the four or six transistors are N-channel MOSFETs. Parasitic diode of the mirror transistor, the current flowing through the parasitic diode, according to claim 3, characterized in that are formed so as simultaneously with the mirror ratio to the current flowing through the parasitic diode of the main transistor Bidirectional switch current detection circuit.

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