current detection circuit

Abstract

According to an embodiment, a current detection circuit includes: a first switching element of a normally-on type, having a source, a drain, and a gate; a second switching element of a normally-off type, having a drain connected to the source of the first switching element, a source connected to the gate of the first switching element, and a gate; and a differential amplifier circuit outputting a voltage corresponding to a voltage between the drain and the source of the second switching element.

Description

[0001] This application is a divisional application of the application filed on July 31, 2019, application number 201910701064.7, with the title "Current detection circuit".

[0002] Related Application

[0003] This application claims priority from Japanese Patent Application No. 2018-243301 filed on December 26, 2018, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0004] The present embodiment generally relates to a current detection circuit. BACKGROUND

[0005] In the past, a semiconductor device obtained by connecting a normally-on switching element and a normally-off switching element in cascade has been disclosed. For example, the normally-on switching element is composed of a transistor using GaN (gallium nitride) or SiC (silicon carbide) as a material. By using the normally-on switching element composed of GaN or SiC, a semiconductor device with high withstand voltage and low loss is provided. On the other hand, since the normally-on switching element is provided, there is a case where, for example, the output current of the semiconductor device cannot be accurately detected in response to the leakage current of the normally-on switching element. It is desirable to provide a current detection circuit which can utilize the characteristics of a semiconductor device provided with a normally-on switching element and accurately detect the output current, and which is highly reliable. SUMMARY

[0006] One embodiment provides a current detection circuit which can accurately detect the output current of a semiconductor device provided with a normally-on switching element and a normally-off switching element connected in cascade, and which is highly reliable.

[0007] According to one embodiment, the current detection circuit includes a normally-on first switching element having a source, a drain, and a gate; a normally-off second switching element having a drain connected to the source of the first switching element, a source connected to the gate of the first switching element, and a gate; and a differential amplifier circuit which outputs a voltage corresponding to the voltage between the drain and the source of the second switching element. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 is a view showing a current detection circuit of a first embodiment.

[0009] Figure 2 is a view showing the characteristics of a normally-on switching element.

[0010] Figure 3 is a view showing a current detection circuit of a second embodiment.

[0011] Figure 4 FIG. 1 is a diagram showing a current detection circuit of a first embodiment.

[0012] Figure 5 FIG. 2 is a diagram showing a configuration example of an adjustment circuit.

[0013] Figure 6 FIG. 3 is a diagram showing a current detection circuit of a second embodiment.

[0014] Figure 7 FIG. 4 is a diagram showing another configuration example of an adjustment circuit.

[0015] Figure 8 FIG. 5 is a diagram showing another configuration example of an adjustment circuit.

[0016] Figure 9 FIG. 6 is a diagram showing another configuration example of an adjustment circuit.

[0017] Figure 10 FIG. 7 is a diagram showing another configuration example of an adjustment circuit.

[0018] Figure 11 FIG. 8 is a diagram showing a current detection circuit of a fifth embodiment.

[0019] Figure 12 FIG. 9 is a diagram showing a current detection circuit of a sixth embodiment.

[0020] Figure 13 FIG. 10 is a diagram showing a current detection circuit of a seventh embodiment.

[0021] Figure 14 FIG. 11 is a diagram showing a current detection circuit of an eighth embodiment.

[0022] Figure 15 FIG. 12 is a diagram showing a current detection circuit of a ninth embodiment. DETAILED DESCRIPTION

[0023] A current detection circuit relating to an embodiment will be described in detail below with reference to the drawings. In addition, the present application is not limited to these embodiments.

[0024] (First Embodiment)

[0025] Figure 1 FIG. 1 is a diagram showing a current detection circuit of a first embodiment. The current detection circuit of the present embodiment has a normally-on type switching element Ql. The switching element Ql is constituted by, for example, an N-channel type MOS transistor using GaN as a material. The main current path between the drain and the source of the MOS transistor using GaN as a material is constituted by GaN. Hereinafter, it is sometimes referred to as a GaN transistor.

[0026] The switch element Q2 of the always-off type is constituted by, for example, an N-channel MOS transistor of which the material is Si. The main current path between the drain and the source of the MOS transistor of which the material is Si is constituted by Si. Hereinafter, this is sometimes referred to as a Si transistor. The drain of the switch element Ql is connected to a terminal 11. The terminal 11 is connected to a power supply line (not shown) to which a voltage of, for example, 600 V is applied. The source of the switch element Ql is connected to the drain of the switch element Q2.

[0027] The source of the switch element Q2 is connected to a terminal 12. The terminal 12 is supplied with, for example, a ground potential. The gate of the switch element Q2 is connected to a terminal 10. The terminal 10 is applied with a drive signal V G .

[0028] The drain of the switch element Q2 is connected to the non-inverting input (+) of a differential amplification circuit Al, and the source is connected to the inverting input (-) of the differential amplification circuit Al. The differential amplification circuit Al outputs an output voltage V C to a terminal 13.

[0029] The current detection operation of the present embodiment becomes as follows. By making the drive signal V G applied to the gate of the switch element Q2 "High", the switch element Q2 is turned on. At this time, the voltage V DS between the drain and the source of the switch element Q2 is represented by the following equation (1).

[0030] V DS = R ON x I D ... (1)

[0031] Here, R ON represents the on-resistance of the switch element Q2, and I D represents the output current I D flowing through the switch element Ql. Since the current flowing through the switch element Q2 is approximately equal to the current flowing through the switch element Ql, the current flowing through the switch element Q2 becomes a current approximately equal to the output current I D . In addition, hereinafter, the drain current I D of the switch element Ql is simply used as the output current I D .

[0032] Also, the output voltage V C of the differential amplification circuit Al can be represented by the following equation (2).

[0033] V C = A x R ON x I D ... (2)

[0034] Here, A is the voltage gain of the differential amplifier circuit A1.

[0035] For example, by using the gate-source voltage V of the switching element Q2 GS With the drain-source voltage V DS The relationship becomes V GS >>V DS The method is to set the drive signal V applied to the gate of the switching element Q2. G The voltage is supplied to the switching element Q2 to turn it on, enabling the switching element Q2 to operate in the linear region. By making the switching element Q2 operate in the linear region, the drain-source voltage V of the switching element Q2... DS Becomes with the output current I D The voltage is proportional, and therefore, as a result, it is possible to make the output current I... D Proportional output voltage V C The output is from the differential amplifier circuit A1. Therefore, the output current I when the switching element Q2 is driven can be accurately detected. D .

[0036] According to this embodiment, the drain-source voltage V between the differential amplifier circuit A1 and the switching element Q2 operating in the linear region is output. DS The corresponding voltage can accurately detect the output current I flowing through the normally open switching element Q1 when the switching element Q2 is driven. D .

[0037] Figure 2 This is a graph showing the characteristics of a normally open switching element. Specifically, it shows the characteristics of the switching element Q1 in the first embodiment described above. The horizontal axis shows the gate-source voltage V. GS The vertical axis shows the drain current I. D Through the gate-source voltage V GS Even when the voltage is zero (0)V, the drain current I also flows. D The gate-source voltage V GS Negative threshold voltage V TH Drain current I D The characteristic curve 100 represents approximately zero (0)A.

[0038] (Second Implementation)

[0039] Figure 3 This is a diagram showing the current detection circuit of the second embodiment. Configurations corresponding to the previously described embodiments are given the same reference numerals, and will be repeated only where necessary. The same applies hereinafter. In this embodiment, a drive signal V applied to the gate of the switching element Q2 is provided. G The differential amplifier circuit A11 is used to control the on / off state.

[0040] Specifically, when the drive signal V G is "high", the switch element Q2 becomes an active state (on), and when the drive signal V G is "low", the switch element Q2 becomes an inactive state (off). For example, when the drive signal V G is "low", control is performed to turn off the bias circuit (not shown) of the differential amplification circuit A11.

[0041] The switch element Q1 has a normally-on characteristic, and thus a drain current I D flows even when the gate thereof is supplied with a ground potential applied to the terminal 12. Therefore, when the drive signal V G applied to the gate of the switch element Q2 is "low", that is, when the switch element Q2 is off, the drain voltage V X of the switch element Q2 rises.

[0042] According to the present embodiment, when the drive signal V G applied to the gate of the switch element Q2 is "low", control is performed to turn off the operation of the differential amplification circuit A11. Thus, even when the drive signal V G is "low", the drain voltage V X of the switch element Q2 rises, but since the differential amplification circuit A11 is off, for example, 0 V is output. Thus, it is possible to avoid a situation in which overcurrent state is erroneously detected in response to the leakage current of the normally-on switch element Q1. Further, since the switch element Q2 performs control to activate the differential amplification circuit A11 only when the drive state is active, it is possible to reduce power consumption.

[0043] (Third Embodiment)

[0044] Figure 4 is a diagram showing a current detection circuit according to the third embodiment. The present embodiment is provided with an adjustment circuit 20 that adjusts the voltage between the drain and the source of the switch element Q2 and supplies the differential amplification circuit A11. The adjustment circuit 20, for example, divides the drain voltage V X of the switch element Q2 and supplies the differential amplification circuit A11.

[0045] The switch element Q1 has a normally-on characteristic, and thus the drain voltage V X of the switch element Q2 rises when the switch element Q2 is off. Sometimes, the characteristic of the normally-on switch element Q1 is utilized, and for example, a high voltage of 600 V is applied to the terminal 11. Thus, sometimes the drain voltage V X of the switch element Q2 becomes a high voltage when the switch element Q2 is off.

[0046] According to the present embodiment, the drain voltage V X of the switching element Q2 is adjusted and supplied to the differential amplification circuit A11. Thus, it is possible to avoid application of an overvoltage to the differential amplification circuit A11, and therefore it is possible to avoid damage to the differential amplification circuit A11 due to application of an overvoltage, and the reliability is improved. Further, since the drain voltage V X of the switching element Q2 is adjusted and supplied to the differential amplification circuit A11, it is possible to make the differential amplification circuit A11 into a configuration with low withstand voltage, and thus it is possible to simplify the circuit configuration and the manufacturing process.

[0047] Figure 5 is a diagram showing a configuration example of the adjustment circuit 20. The adjustment circuit 20 of the present configuration example has: a fixed resistor R1 of which one end is applied with the drain voltage V X of the switching element Q2 and the other end is connected to the non-inverting input terminal (+) of the differential amplification circuit A11; and a fixed resistor R2 of which one end is connected to the non-inverting input terminal (+) of the differential amplification circuit A11 and the other end is connected to the terminal 12.

[0048] The drain voltage V X of the switching element Q2 is adjusted by voltage division using the series circuit of the fixed resistor R1 and the fixed resistor R2, and is supplied to the non-inverting input terminal (+) of the differential amplification circuit A11. Thus, by adjusting the voltage division ratio by setting the resistance values of the fixed resistor R1 and the fixed resistor R2 to desired values, it is possible to avoid application of an overvoltage to the non-inverting input terminal (+) of the differential amplification circuit A11.

[0049] (Fourth Embodiment)

[0050] Figure 6 is a diagram showing a current detection circuit of the fourth embodiment. The present embodiment has an adjustment circuit 30 that adjusts the drain voltage V G of the switching element Q2 in accordance with the drive signal V X applied to the gate of the switching element Q2 and supplies it to the differential amplification circuit A11.

[0051] The adjustment circuit 30 adjusts as follows: when the drive signal V G applied to the gate of the switching element Q2 is "high", that is, in the drive state in which the switching element Q2 is on, the amount of attenuation of the drain voltage V X supplied to the differential amplification circuit A11 is reduced, and when the drive signal V G applied to the gate of the switching element Q2 is "low", that is, in the state in which the switching element Q2 is off, the amount of attenuation of the drain voltage V X supplied to the differential amplification circuit A11 is increased.

[0052] The drain voltage V G of the switching element Q2 is adjusted in accordance with the drive signal V X applied to the gate of the switching element Q2 and is supplied to the differential amplification circuit A11.G to control the adjustment circuit 30 to reduce the attenuation amount of the drain voltage V X to the differential amplifier circuit Al l, thereby being able to supply the output current I D to the differential amplifier circuit Al l in proportion to the drive state of the switching element Q2 after the switching element Q2 is turned on.

[0053] Figure 7 is a diagram showing a configuration example of the adjustment circuit 30. This configuration example has a variable resistor VRl that adjusts the resistance value in accordance with the drive signal V G , and a fixed resistor R2. The variable resistor VRl reduces the resistance value when the drive signal V G is "high", and increases the resistance value when the drive signal V G is "low". Thus, when the drive signal V G is "high" and the switching element Q2 is in the drive state, control is performed to reduce the attenuation amount of the drain voltage V X , and when the drive signal V G is "low", the resistance value of the variable resistor VRl is increased to attenuate the drain voltage V X and supply it to the differential amplifier circuit Al l, thereby being able to avoid a situation in which an overvoltage is supplied to the differential amplifier circuit Al l.

[0054] When the drive signal V G is "high", that is, when the switching element Q2 is in the drive state, control is performed to reduce the attenuation amount of the drain voltage V X . That is, since the ratio of the division ratio (=resistance value of the fixed resistor R2 / (resistance value of the variable resistor VRl + resistance value of the fixed resistor R2)) of the resistance value of the variable resistor VRl to the resistance value of the fixed resistor R2 becomes large, the attenuation amount of the drain voltage V X can be reduced and supplied to the differential amplifier circuit Al l. Thus, the output voltage V D that is correctly reflected by the drain-source voltage V DS of the switching element Q2 generated in proportion to the output current I C can be output. Accordingly, the output current I D when the switching element Q2 is in the drive state can be accurately detected.

[0055] Further, by reducing the resistance value of the variable resistor VRl, the change in the drain voltage V X can be rapidly communicated to the differential amplifier circuit Al l, so the response speed of the differential amplifier circuit Al l can be improved, and the change in the output current I D can be rapidly detected.

[0056] Furthermore, through the driving signal V G When the value is "low", the resistance of the variable resistor VR1 is increased, thus reducing the voltage division ratio between the variable resistor VR1 and the fixed resistor R2. Therefore, the drain voltage V X The voltage is attenuated and supplied to the differential amplifier circuit A11. This prevents overvoltage from being supplied to the differential amplifier circuit A11 when the switching element Q2 is off.

[0057] For example, it can be configured as follows: by connecting a switch (not shown) in parallel with a resistor and applying a drive signal V... G When it is "high", the switch is turned on, thereby driving the signal V. G When it is "high", the resistance value of the variable resistor VR1 is reduced.

[0058] Figure 8 This diagram illustrates another configuration example of the adjustment circuit 30. This configuration example includes a fixed resistor R1 and a drive signal V. G The variable resistor VR2 is used to adjust its resistance value. The variable resistor VR2 is driven by signal V. G When the value is "high", the resistance value will increase, and the driving signal V G When the value is "low", the resistance value will decrease.

[0059] That is, when the driving signal V is made G When the switching element Q2 is driven to "high", the resistance value of the variable resistor VR2 increases, thereby increasing the voltage division ratio between the fixed resistor R1 and the variable resistor VR2 (=resistance value of variable resistor VR2 / (resistance value of fixed resistor R1 + resistance value of variable resistor VR2)). This increases the drain voltage V. X The attenuation is reduced and supplied to the differential amplifier circuit A11. Therefore, it can output the same current as the output current I. D The drain-source voltage V of the switching element Q2 is generated proportionally. DS The output voltage V obtained by correctly reflecting the data C Therefore, it is possible to accurately detect the output current I when the switching element Q2 is in the driving state. D .

[0060] Furthermore, through the driving signal V G When the value is "low", the resistance of the variable resistor VR2 is reduced, thus decreasing the voltage division ratio between the fixed resistor R1 and the variable resistor VR2. Therefore, the drain voltage V X The voltage is significantly attenuated before being supplied to the differential amplifier circuit A11. This prevents overvoltage from being supplied to the differential amplifier circuit A11 when the switching element Q2 is off.

[0061] Figure 9 This diagram illustrates another configuration example of the adjustment circuit 30. This configuration example includes a circuit controlled by a drive signal V.G variable resistor VR1 and variable resistor VR2. The variable resistor VR1 decreases the resistance value when the drive signal V G is "high", and increases the resistance value when the drive signal V G is "low". The variable resistor VR2 increases the resistance value when the drive signal V G is "high", and decreases the resistance value when the drive signal V G is "low".

[0062] According to this configuration, the following control is performed: when the drive signal V G is "high" and the switching element Q2 is driven, the resistance value of the variable resistor VR1 is decreased and the resistance value of the variable resistor VR2 is increased, the voltage division ratio of the variable resistor VR1 and the variable resistor VR2 (= the resistance value of the variable resistor VR2 / (the resistance value of the variable resistor VR1 + the resistance value of the variable resistor VR2)) is made large to decrease the attenuation amount of the drain voltage V X , and the drain voltage V G is supplied to the differential amplifier circuit Al l. When the drive signal V X is "low", the resistance value of the variable resistor VR1 is increased and the resistance value of the variable resistor VR2 is decreased, the voltage division ratio of the variable resistor VR1 and VR2 is made small to increase the attenuation amount of the drain voltage V G , and the drain voltage V X is supplied to the differential amplifier circuit Al l.

[0063] The attenuation amount of the drain voltage V G by the adjustment circuit 30 corresponding to the drive signal V X , when the drive signal V G is "high" and the switching element Q2 is driven, the drain-source voltage V D of the switching element Q2 generated in proportion to the output current I DS is accurately reflected and the output voltage V C is obtained. Also, when the drive signal V G is "low", the drain voltage V X is largely attenuated and supplied to the differential amplifier circuit Al l, so that the case where an overvoltage is supplied to the differential amplifier circuit Al l when the switching element Q2 is turned off can be avoided.

[0064] For example, it can be configured as follows: the variable resistor VR1 has a parallel circuit of a fixed resistor and a switch (not shown), and the variable resistor VR2 has a parallel circuit of a fixed resistor and a switch (not shown). It can be configured that, when the drive signal V G is "high", the switch configuring the variable resistor VR1 is turned on so that the resistance value of the variable resistor VR1 is decreased, and when the drive signal V G is "low", the switch configuring the variable resistor VR2 is turned on so that the resistance value of the variable resistor VR2 is decreased.

[0065] Figure 10 is a view showing another configuration example of the adjustment circuit 30. This configuration example has switches S1, S2 which control on-off by a drive signal V G . The switch S1 becomes on when the drive signal V G is "high", and the switch S2 becomes on when the drive signal V G is "low".

[0066] By this configuration, when the switch element Q2 is driven by making the drive signal V G "high", the switch S1 becomes on and the switch S2 becomes off. When the switch S1 is on, the resistance value of the switch S1 can be ignored, and when the switch S2 is off, the resistance value of the switch S2 becomes infinite, so when the switch element Q2 is driven by making the drive signal V G "high", the drain voltage V X can be directly supplied to the non-inverting input terminal (+) of the differential amplifier circuit A11 without being attenuated.

[0067] Thus, when the switch element Q2 is driven by making the drive signal V G "high", the drain voltage V X is applied to the non-inverting input terminal (+) of the differential amplifier circuit A11 as it is, so by using the differential amplifier circuit A11, the drain voltage V D correspondingly generated by the output current I X is detected, and the output current I D when the switch element Q2 is driven can be accurately detected.

[0068] Further, since the resistance value when the switch S1 is on can be ignored, the change of the drain voltage V X when the switch element Q2 is in the driven state can be rapidly transmitted to the differential amplifier circuit A11, so the change of the output current I D can be rapidly detected.

[0069] Further, since the switch S1 becomes off when the drive signal V G is "low", the supply path of the drain voltage V X to the differential amplifier circuit A11 is cut off. Therefore, when the switch element Q2 is off, the case where an overvoltage is applied to the differential amplifier circuit A11 can be avoided.

[0070] The switches S1, S2 are configured by, for example, a switching element such as a MOS transistor, or a bipolar transistor, and can be configured to control on-off by a drive signal V G .

[0071] (Fifth Implementation)

[0072] Figure 11 This is a diagram illustrating the current detection circuit of the fifth embodiment. This embodiment includes a circuit that detects the drain voltage V. X With the specified reference voltage V REF The comparison circuit C11 is used for comparison. The comparison circuit C11 has, for example, a higher gain and faster response speed compared to the differential amplifier circuit A11. For example, the comparison circuit C11 can be configured without a feedback loop.

[0073] The inverting input terminal (-) of comparator circuit C11 is supplied with a reference voltage V. REF The non-inverting input (+) of comparator circuit C11 is supplied with drain voltage V via adjustment circuit 30-1. X The adjustment circuit 30-1 has the same configuration as the adjustment circuit 30 and can be configured as described above. Figures 7 to 10 Any one of the components.

[0074] In the driving signal V G The voltage supplied via the adjustment circuit 30-1 becomes "high" and is higher than the reference voltage V. REF When the comparator circuit C11 outputs a "high" signal V, F Supply to terminal 14. That is, in relation to the output current I D The corresponding drain voltage V X The corresponding voltage becomes higher than the reference voltage V. REF When the comparator circuit C11 outputs a "high" signal V, F Output.

[0075] Drain voltage V X With output current I D Proportional. Therefore, by utilizing the comparator circuit C11, the drain voltage V is proportional. X The corresponding voltage and the reference voltage V set as the threshold for overcurrent detection. REF By making comparisons, overcurrent detection can be performed.

[0076] Furthermore, the drain voltage V is adjusted via the adjustment circuit 30-1. X The configuration supplied to the comparator circuit C11 can be configured such that: in the drive signal V G When the voltage is "high" and the switching element Q2 is in the driving state, the drain voltage V will be... X The reduced attenuation is supplied to the comparator circuit C11, thereby accurately detecting the output current I when the switching element Q2 is in the driving state. D In the drive signal V GWhen the signal is "low" and the switching element Q2 is off, overvoltage is avoided from being applied to the comparator circuit C11. Alternatively, it can be configured such that the output signal V from the comparator circuit C11 is... F Supply to the control circuit (not shown) to the output signal V indicating the overcurrent state. F To respond, for example, to make the drive signal V G The application of stop control.

[0077] (Sixth Implementation Method)

[0078] Figure 12 This diagram illustrates the current detection circuit of the sixth embodiment. This embodiment includes a constant current source 16 connected to the power supply terminal 15, and a constant current I supplied to the constant current source 16. REF The switching element Q3. The constant current source 16 is constructed, for example, using a bandgap circuit (not shown). The drain of the switching element Q3 is connected to the inverting input (-) of the comparator circuit C11, the source is connected to terminal 12, and the gate is applied with a drive signal V. G .

[0079] Switching element Q3 is formed on a semiconductor substrate (not shown) on which switching element Q2 is formed. By forming switching elements Q2 and Q3 on the same semiconductor substrate, the characteristics of the two switching elements Q2 and Q3 can be made consistent, thus compensating for, for example, characteristic deviations.

[0080] The gate width of switching element Q3 is set to, for example, 1 / N (where N is any positive number) of the gate width of switching element Q2. Under this setting, when the drain current of switching element Q2 is N times the drain current of switching element Q3, the drain-source voltage V between the two switching elements Q2 and Q3... DS They become equal. Therefore, it is possible to configure the voltage distribution so that the drain voltage of the switching element Q3 is used as the reference voltage V. REF The power supply to the comparator circuit C11 is such that the drain current flowing through the switching element Q2 exceeds the constant current I. REF When the value is N times the value, the comparator circuit C11 outputs a "high" output signal V. F .

[0081] According to this embodiment, the output voltage V of the differential amplifier circuit A11 can be controlled. C To detect the drive signal V G The output current I when it is "high" and the switching element Q2 is in the activated state D Meanwhile, by using constant current I REF The value is set to, for example, the threshold current used for overcurrent detection, and the output signal V of the comparator circuit C11 can be used. F To detect the output current ID exceeding the constant current I REF by N times the current value of the overcurrent state.

[0082] (Seventh Embodiment)

[0083] Figure 13 is a diagram showing the current detection circuit of the seventh embodiment. This embodiment is a configuration in which the adjustment circuit 30 is shared by the differential amplification circuit Al and the comparison circuit Cl. As the adjustment circuit 30, any one of the configurations of the adjustment circuits 20, 20-1, 20-2, 20-3, 20-4, 20-5, 20-6, and 20-7 described above can be provided. By sharing the adjustment circuit 30, the number of circuit elements can be reduced and cost reduction can be sought. Figures 7 to 10

[0084] In this embodiment, the control of the on-off of the differential amplification circuit Al and the comparison circuit Cl by the drive signal V G is not performed. As described above, by providing a configuration in which the drain voltage V X is supplied to the differential amplification circuit Al and the comparison circuit Cl via the adjustment circuit 30, the attenuation of the drain voltage V G is suppressed when the drive signal V X is "high" and the drain voltage V G is supplied to the differential amplification circuit Al and the comparison circuit Cl, and the amount of attenuation of the drain voltage V X is increased or the supply path to the differential amplification circuit Al and the comparison circuit Cl is cut off when the drive signal V X is "low", it is possible to avoid a situation in which an overvoltage is applied to the differential amplification circuit Al and the comparison circuit Cl.

[0085] (Eighth Embodiment)

[0086] Figure 14 is a diagram showing the current detection circuit of the eighth embodiment. This embodiment has a comparison circuit Cll that compares the drain voltage V X supplied via the adjustment circuit 30-1 and the reference voltage V REF1 , and a comparison circuit C12 that compares the drain voltage V X supplied via the adjustment circuit 30-2 and the reference voltage V REF2 .

[0087] The inverting input terminal (-) of the comparison circuit C12 is supplied with the drain voltage V X via the adjustment circuit 30-2, and the non-inverting input terminal (+) is supplied with the reference voltage V REF2 . Thus, when the drain voltage V X supplied via the adjustment circuit 30-2 is lower than the reference voltage V REF2 , the comparison circuit C12 supplies a signal V F2Supply is made to terminal 17. Thus, it is possible to detect the reverse drain current flowing through the switching element Q2, and the drain voltage V due to the voltage drop generated by the switching element Q2. X Compared to the reference voltage V REF2 The reduced state, i.e., the reverse overcurrent state. Reference voltage V. REF2 It can be set to any negative voltage corresponding to the threshold value of the current value set as an overcurrent state.

[0088] According to this embodiment, the drive signal V can be accurately detected by the differential amplifier circuit A11. G The output current I when it is "high" and the switching element Q2 is in the driving state D At the same time, it can detect the output current I. D The system exhibits both positive and negative overcurrent states. Furthermore, in this embodiment, the operating states of the differential amplifier circuit A11, comparator circuits C11 and C12 are driven by the signal V. G The control structure. Therefore, since it only applies to the drive signal V... G When the differential amplifier circuit A11 and comparator circuits C11 and C12 are in a "high" state, the power consumption can be reduced. Alternatively, the differential amplifier circuit A11 and comparator circuits C11 and C12 can be configured so that the power consumption is not based on the drive signal V. G Control of on / off states.

[0089] (Ninth Implementation)

[0090] Figure 15 This is a diagram illustrating the current detection circuit of the ninth embodiment. This embodiment has a drain voltage V. X The comparator circuit C11 is supplied to the non-inverting input terminal (+) via the adjustment circuit 30-1, and the inverting input terminal (-) is connected to terminal 12. The adjustment circuit 30-1 can be configured as described above. Figures 7 to 10 The configuration of any of the adjustment circuits shown.

[0091] When the voltage supplied to the non-inverting input terminal (+) is higher than the voltage supplied to the inverting input terminal (-), the comparator circuit C11 outputs a "high" signal V. P Output to terminal 14: When the voltage supplied to the non-inverting input terminal (+) is lower than the voltage supplied to the inverting input terminal (-), output a "low" level signal V. POutput. When the flow direction of the drain current of the switching element Q2 is forward, the voltage of the non-inverted input (+) of the comparison circuit C11 becomes higher than the voltage of the inverted input (-), and when the flow direction of the drain current of the switching element Q2 is reverse, the voltage of the non-inverted input (+) of the comparison circuit C11 becomes lower than the voltage of the inverted input (-). Thus, since the flow direction of the drain current can be discriminated by the level of the output signal V P of the comparison circuit C11, the comparison circuit C11 can be used as a zero-crossing detection circuit.

[0092] According to the present embodiment, the output voltage V C of the differential amplification circuit A11 can be used to accurately detect the driving signal V G is "high" and the switching element Q2 is in the driving state, the output current I D , and at the same time, the zero-crossing detection can be performed by the output signal V P of the comparison circuit C11.

[0093] In addition, in the above-described embodiment, the differential amplification circuits A1, A11 which output the voltage corresponding to the drain-source voltage V DS of the switching element Q2 are configured to output one output voltage V C , but can be configured to output differential signals of the positive side and the negative side.

[0094] Also, the normally open switching element Q1 can be configured by a JFET (Junction Field Effect Transistor).

[0095] The present application has been described with reference to several embodiments, but these embodiments are presented by way of example only, and are not intended to limit the scope of the application. These new embodiments can be implemented in other various ways, and various omissions, substitutions, and changes can be made without departing from the spirit of the application. These embodiments and modifications thereof are included in the scope or spirit of the application, and are included in the scope of the application and its equivalents as recited in the claims.

Claims

1. A current sensing circuit, wherein, Possessing: a first switching element of normally-on type having a source, a drain, and a gate; a second switching element of normally-off type having a drain connected to the source of the first switching element, a source connected to the gate of the first switching element, and a gate; a differential amplification circuit outputting a voltage corresponding to the voltage between the drain and the source of the second switching element; a first comparison circuit comparing the voltage corresponding to the drain voltage of the second switching element with a first reference voltage; and an adjustment circuit provided between the drain of the second switching element and an input terminal of the differential amplification circuit, adjusting the drain voltage of the second switching element and supplying it to the differential amplification circuit, the adjustment circuit having a variable resistor connected to the drain of the second switching element and the input terminal of the differential amplification circuit, the resistance value of which being changed by a drive signal applied to the gate of the second switching element, the current detection circuit controlling the on-off of the differential amplification circuit and the first comparison circuit by the drive signal applied to the gate of the second switching element.

2. The current detection circuit according to claim 1, wherein the source voltage of the second switching element is supplied to the first comparison circuit as the first reference voltage.

3. The current detection circuit according to claim 1, wherein a second comparison circuit comparing the voltage corresponding to the drain voltage of the second switching element with a second reference voltage is provided.

4. The current detection circuit according to claim 3, wherein the second reference voltage is an arbitrary negative voltage. ​

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