Current detection circuit and current detection system

Abstract

To accurately detect the output current of a semiconductor device in which a normally-on type switching element and a normally-off type switching element are cascode-connected.SOLUTION: A current detection circuit according to an embodiment comprises a normally-on type first switching element, a normally-off type second switching element, a normally-off type third switching element, and a comparison circuit that compares the drain voltage of the second switching element with the drain voltage of the third switching element at current detection time and outputs a detection signal. A current source causes a current value to change by a control signal at current detection time, and the comparison circuit outputs a detection signal to the effect that the current value has exceeded a current flowing between the source and the drain of the first switching element, when the drain voltage of the third switching element exceeds the drain voltage of the second switching element.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present embodiment relates to a current detection circuit and a current detection system. [Background technology]

[0002] Conventionally, a semiconductor device in which a normally-on type switching element and a normally-off type switching element are cascode-connected has been disclosed. For example, the normally-on type switching element is composed of a transistor made of GaN (gallium nitride) or SiC (silicon carbide). The normally-on type switching element made of GaN or SiC has a high withstand voltage and low loss, and is therefore suitable for application to a power supply circuit that outputs a high voltage. On the other hand, since the normally-on type switching element is included, for example, the output current of the semiconductor device may not be accurately detected in response to a leakage current of the normally-on type switching element. For example, in an AC / DC converter that converts an AC voltage into a DC voltage, the power factor is increased by matching the phase of the input voltage and the output current, so a configuration including a current detection circuit that can accurately detect the output current is desired. A highly reliable current detection circuit and current detection system that can accurately detect the output current while taking advantage of the characteristics of a semiconductor device that includes a normally-on type switching element, and a power supply circuit that includes a current detection circuit that can accurately detect the output current are desired. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 166523 [Patent Document 2] Patent No. 5800986 Summary of the Invention [Problem to be solved by the invention]

[0004] One embodiment aims to provide a current detection circuit and a current detection system that can accurately detect the output current of a semiconductor device in which a normally-on switching element and a normally-off switching element are cascode-connected. [Means for solving the problem]

[0005] According to one embodiment, a current detection circuit includes a normally-on type first switching element having a source, a drain, and a gate, a drain connected to the source of the first switching element, a source connected to a reference potential, a normally-off type second switching element having a gate, a source connected to the source of the second switching element, a drain connected to a current source whose current value changes in response to a control signal, a normally-off type third switching element to whose gate a voltage applied to the gate of the second switching element during current detection is applied, and a comparison circuit that compares the drain voltage of the second switching element with the drain voltage of the third switching element during the current detection and outputs a detection signal, and the current source is ,before When the current is detected The control signal is generated in accordance with the switching operations of the first to third switching elements. The current value is changed, and when the drain voltage of the third switching element exceeds the drain voltage of the second switching element, the comparison circuit outputs the detection signal indicating that the current value has exceeded the current flowing between the source and drain of the first switching element. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram showing a current detection circuit according to a first embodiment. [Diagram 2] FIG. 2 is a diagram for explaining the operation of the current detection circuit according to the first embodiment. [Diagram 3] FIG. 3 is a diagram showing a configuration of a current detection system according to the second embodiment. [Figure 4] FIG. 4 is a diagram showing an example of the configuration of a current source. [Diagram 5] FIG. 5 is a diagram specifically illustrating an example of the configuration of the current source in FIG. [Figure 6] FIG. 6 is a diagram specifically illustrating another configuration example of a current source. [Figure 7] FIG. 7 is a diagram showing a current detection system according to the third embodiment. [Figure 8] FIG. 8 is a diagram showing a power supply circuit according to a fourth embodiment. [Figure 9] FIG. 9 is a diagram for explaining the operation of the power supply circuit according to the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] A current detection circuit, a current detection system, and a power supply circuit according to embodiments will be described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments.

[0008] (First embodiment) FIG. 1 is a diagram showing a current detection circuit of a first embodiment. This embodiment has a drive circuit 10 and a current detection circuit 20. The current detection circuit 20 has a normally-on switching element 21. The switching element 21 is composed of, for example, an N-channel MOS transistor made of GaN. For example, in a MOS transistor made of GaN, the main current path between the drain and source is composed of GaN.

[0009] The current detection circuit 20 has normally-off switching elements 22 and 23. The normally-off switching elements 22 and 23 are configured, for example, by N-channel MOS transistors made of Si. For example, in a MOS transistor made of Si, the main current path between the drain and source is made of Si.

[0010] The drain of the switching element 21 is connected to a terminal 26. The terminal 26 is connected to a power supply line (not shown) to which a voltage of, for example, 600 V is applied via a load (not shown). The source of the switching element 21 is connected to the drain of the switching element 22.

[0011] The source of the switching element 22 is connected to the terminal 27. That is, the drain-source path which is the main current path of the switching element 22 is connected in series with the drain-source path which is the main current path of the switching element 21. The terminal 27 is supplied with, for example, a ground potential.

[0012] The source of the switching element 23 is connected to the source of the switching element 22, and the drain of the switching element 23 is connected to the reference current I REF The reference current I REF The current value of the current source 24 is controlled by a current control signal Cont. The other end of the current source 24 is applied with a power supply voltage VDD.

[0013] The switching elements 22 and 23 are formed on a common semiconductor substrate (not shown). By forming them on a common semiconductor substrate, the element characteristics of both elements can be matched. Even if manufacturing variations occur, the element characteristics of the switching elements 22 and 23 fluctuate in the same way. For example, if the on-resistance of the switching element 22 fluctuates so as to increase, the on-resistance of the switching element 23 also fluctuates so as to increase.

[0014] The dimensions of the switching elements 22 and 23 are set such that the gate lengths are the same and the gate widths have a dimensional ratio of n:m. According to the dimensional ratio, the ratio of the on-resistance Ron2 of the switching element 22 to the on-resistance Ron3 of the switching element 23 is expressed by equation (1). Ron2:Ron3=1 / n:1 / m (1)

[0015] The drain voltages V1 and V2 of the switching elements 22 and 23 are expressed by the equations (2) and (3). The drain voltages V1 and V2 are expressed with respect to the ground potential applied to the terminal 27, zero (0) V. The same applies hereinafter.

[0016] V1 = Ron2 × Id (2) V2 = Ron3 × I REF ... (3) Here, Id indicates the drain current Id flowing through the switching element 21. The current flowing through the switching element 22 is approximately equal to the current flowing through the switching element 21, and therefore the current flowing through the switching element 22 is approximately equal to the output current Id. Hereinafter, the drain current Id of the switching element 21 may be referred to as the output current Id for the sake of convenience.

[0017] The drain voltage V1 of the switching element 22 is supplied to the non-inverting input terminal (+) of the comparison circuit 25, and the drain voltage V2 of the switching element 23 is supplied to the inverting input terminal (-). When the drain voltage V1 of the switching element 22 becomes higher than the drain voltage V2 of the switching element 23, the comparison circuit 25 outputs an H-level detection signal from the output terminal 28. That is, from the relationship between the equations (2) and (3), Ron2×Id>Ron3×I REF When the comparison circuit 25 detects that the output current Id is greater than the reference current I REF It is detected that

[0018] For example, the maximum allowable output current Id is MAX and the reference current I REF According to the value of and the setting of the size ratio m:n of the switching elements 22 and 23, the output current Id becomes the maximum current I MAX The detection signal from the comparison circuit 25 can be used to detect an overcurrent state that exceeds the maximum current I MAX By configuring the comparator circuit 25 to supply a detection signal indicating that an overcurrent state exceeding 10 has occurred to the drive circuit 10 and turn off the switching elements 21 and 22, it is possible to prevent the switching elements 21 and 22 from being in an overcurrent state.

[0019] The drive circuit 10 generates drive signals that control the on / off of the switching elements 21, 22, and 23, and supplies the drive signals to the gates of the switching elements 21, 22, and 23. For example, the drive circuit 10 applies a voltage to the gate of the switching element 22 that is equal to the voltage applied to the gate of the switching element 23 during current detection, thereby turning on the switching element 22. By making the gate-source voltages of the switching elements 22 and 23 the same when turning on the switching elements 22 and 23, the ratio of the on-resistances of the switching elements 22 and 23 is set by the ratio of the gate widths, and the ratio of the on-resistances Ron2 and Ron3 and the reference current I REF The output current Id can be detected accurately by the value of

[0020] Alternatively, the gate of switching element 21 may be connected to the source of switching element 22, and a drive signal having the same voltage as the signal applied to the gate of switching element 23 during current detection may be supplied to the gate of switching element 22 by drive circuit 10.

[0021] According to the first embodiment, the reference current I REF The value of is changed by the current control signal Cont, and the drain voltages V1 and V2 of the switching elements 22 and 23 are compared by the comparison circuit 25. The H-level detection signal of the comparison circuit 25 indicates that the output current Id is equal to or lower than the reference current I REF Therefore, the reference current I REF If the value of the output current Id is set as a target value, then the detection signal of the comparison circuit 25 at H level indicates that the output current Id has reached the target current value.

[0022] The reference current I when the detection signal becomes H level REF The value of the output current Id is detected based on the value of the reference current I REF By varying the reference current I, a current detection circuit is provided that detects the value of the output current Id. The output voltage Vout at the terminal 26 is the sum of the voltage drops caused by the output current Id across the on-resistances of the switching elements 21 and 22 when the switching elements 21 and 22 are in the on-state. Therefore, the reference current I REFThe value of the output current Id indicated by can be used as data indicating the output voltage Vout of the terminal 26.

[0023] The operation of the first embodiment will be described with reference to FIG. 2. The horizontal axis of FIG. 2 represents time, and the vertical axis represents the reference current I REF The solid line 15 indicates the reference current I REF The reference current I REF The value of the output current Id is increased over time by the current control signal Cont. When the detection signal of the comparator circuit 25 becomes H level at the timing t1, the value of the output current Id is equal to the reference current I REF Value of I t1 When the detection signal of the comparison circuit 25 becomes H level at the timing t2, the value of the output current Id is equal to or greater than the reference current I REF Value of I t2 It is detected that:

[0024] Second embodiment FIG. 3 is a diagram showing the configuration of a current detection system according to a second embodiment. The same reference numerals are used for configurations corresponding to the previously described embodiments, and duplicated descriptions are given only when necessary. The same applies hereinafter. This embodiment has a control circuit 100, a modulator 101, a demodulator 103, and isolators 102, 105, and 106. A current detection circuit 20 has a DA converter 104 and a current source 24. Although the DA converter 104 and the current source 24 are shown separately, the DA converter 104 and the current source 24 cooperate to form one current source. A specific configuration example of the current source will be described later.

[0025] The control circuit 100 controls the reference current I REFand supplies the basic data for controlling the modulator 101. The basic data is, for example, digital signal data indicating an amplitude value corresponding to a sine wave. The basic data can be approximated to a sine wave by an approximation curve such as a zero-order curve (Y=C) based on a constant or a linear curve based on a constant and a variable (Y=a×X+b). By increasing the order of the approximation curve, basic data approximating a sine wave can be obtained. The control circuit 100 outputs the basic data discretely, for example, in accordance with the on / off switching operation of the switching elements 21, 22, and 23. By outputting the basic data discretely, the amount of data can be reduced.

[0026] The modulator 101 generates a modulated signal by encoding the digital signal from the control circuit 100 with a Manchester code or the like. The modulated signal from the modulator 101 is supplied to the isolator 102. The isolator 102 is configured using a transformer, a photocoupler, a capacitor, or the like. The isolator 102 electrically insulates and separates a low-voltage side including the control circuit 100 biased with a low voltage of, for example, about 5 V, from a high-voltage side to which a high voltage of, for example, more than 400 V is applied. The isolators 105 and 106 can be configured in the same manner as the isolator 102.

[0027] The demodulator 103 demodulates the modulated signal supplied from the isolator 102, generates a current control signal Cont, and supplies it to the DA converter 104. The DA converter 104 converts the current control signal Cont into an analog signal and supplies it to the current source 24. The current source 24 cooperates with the DA converter 104 to generate a reference current I REF Output.

[0028] The comparator circuit 25 compares the drain voltage V1 of the switching element 22 with the drain voltage V2 of the switching element 23, and outputs a detection signal of H level or L level according to the comparison result. The detection signal is supplied to the isolator 105. The isolator 105 supplies a signal in response to the detection signal to the control circuit 100. The control circuit 100 determines whether the output current Id is equal to or lower than the reference current I REFIt is detected whether it has been reached.

[0029] The control circuit 100 supplies a control signal to the drive circuit 10 via the isolator 106. The control signal supplied to the drive circuit 10 is, for example, a PWM control signal. The drive circuit 10 adjusts the duty ratio of the drive signal supplied to the switching elements 21, 22, and 23 in response to the PWM control signal.

[0030] According to this embodiment, the reference current I REF The drain voltage V1 of the switching element 22 and the reference current I REF The drain voltage V1 of the switching element 23 generated by the drain voltage V2 is compared with the reference current Id. The detection signal of the comparator circuit 25 at H level indicates that the drain voltage V1 has reached the drain voltage V2. REF It is also detected that the output current Id has reached the reference current I REF If the switching elements 21 and 22 are turned off when the reference current I REF Therefore, it is possible to control the output current Id so that the upper limit value of the output current Id is set to Id.

[0031] By connecting the control circuit 100 side and the current detection circuit 20 side with isolators 102, 105, and 106, it is possible to insulate and separate the low voltage side biased with a low voltage from the high voltage side to which a high voltage is applied. Also, a comparison circuit 25 is provided on the high voltage side, and a detection signal of the comparison circuit 25 is supplied to the control circuit 100 via the isolator 105. In other words, instead of data indicating the current value of the output current Id, a reference current I REF A 1-bit detection signal based on the result of comparing the output current Id with the output current Id is supplied to the control circuit 100. This makes it possible to reduce the amount of data supplied to the control circuit 100.

[0032] In addition, since the isolator 105 only needs to transmit a one-bit detection signal from the comparison circuit 25, it can be configured with an isolator with a relatively slow transmission speed. The control circuit 100 judges the detection signal from the comparison circuit 25 at a timing that includes the delay time caused by the isolators 102 and 105. The timing at which the basic data is output from the control circuit 100 and the reference current I REF By taking into consideration the timing at which the output current Id is compared with the output current Ii and the timing at which the detection signal of the comparator circuit 25 is supplied to the control circuit 100, the output current Id can be detected accurately.

[0033] FIG. 4 shows a switching element 23 supplied with a reference current I REF The current source 120 includes current sources 124 and 125 connected to the drain of the switching element 23. The current source 124 cooperates with the DA converter 114 to supply a reference current I REFp The current source 125 cooperates with the DA converter 115 to output a reference current I REFn A power supply voltage VDD supplied to one end of the current source 124 is a positive voltage with respect to the source voltage of the switching element 23, and a power supply voltage VSS supplied to one end of the current source 125 is a negative voltage with respect to the source voltage of the switching element 23.

[0034] Reference current I of current source 125 REFn is the reference current I REFp Since the reference current I REF I REFp -I REFn Therefore, the reference current I REFp , I REFn By controlling the reference current I REF The value of can be varied from positive to negative values. Thus, for example, a reference current I that varies according to a sine wave can be REF It is possible to generate

[0035] Fig. 5 is a diagram showing a specific example of the configuration of the current source of Fig. 4. The current source of this example has a DA converter 114 that cooperates with a current source 124. The DA converter 114 has a diode-connected PMOS transistor 300. The source of the PMOS transistor 300 is connected to a terminal 220 to which a power supply voltage VDD is applied, and the drain is connected to one end of the current source 124. The other end of the current source 124 is connected to a terminal 221 to which a power supply voltage VSS is applied.

[0036] The DA converter 114 has PMOS transistors 301 to 304 connected in parallel between the terminal 220 and the drain of the switching element 23. The PMOS transistors 301 to 304 have a capacitance of 2.0 V to 1.0 V. N Specifically, PMOS transistor 301 has the same dimensions as PMOS transistor 300, and PMOS transistors 302, 303, and 304 have dimensions that are weighted by a factor of two. 1 , 2 2 , 2 3 The dimensions correspond to the weighting of the

[0037] A switch 311 is connected between the source and gate of the PMOS transistor 301, and a switch 312 is connected between the gate and a node ND1. A control signal P0 is supplied to the switch 311 via an inverter 320, and a control signal P0 is supplied to the switch 312. When the control signal P0 is at an H level, the switch 312 is in a connected state, and the PMOS transistor 301 is turned on. Control signals P1, P2, and P3 are supplied to the switches 313, 315, and 317 via inverters 321, 322, and 323.

[0038] Similarly, the on / off of the PMOS transistors 302 to 304 is controlled by the control signals P1 to P3 supplied to the switches 313 to 318. The PMOS transistors 301 to 304 output a current according to the weighting for the PMOS transistor 300. The combination of the PMOS transistors 301 to 304 that are turned on by the control signals P0 to P3 is changed to control the reference current I REFp It is possible to adjust the value of the current control signal Cont1. The demodulator 103 outputs the control signals P0 to P3 as a current control signal Cont1.

[0039] The current source of this configuration example has a DA converter 115 that cooperates with a current source 125. The DA converter 115 has a diode-connected NMOS transistor 400. The source of the NMOS transistor 400 is connected to a terminal 225 to which a power supply voltage VSS is applied, and the drain is connected to one end of the current source 125. The other end of the current source 125 is connected to a terminal 224 to which a power supply voltage VDD is applied. The current sources 124 and 125 are formed of, for example, a bandgap circuit, and output a current Io.

[0040] The DA converter 115 has NMOS transistors 401 to 404 connected in parallel between the terminal 225 and a node ND4. N Specifically, NMOS transistor 401 has the same dimensions as NMOS transistor 400, and NMOS transistors 402, 403, and 404 have dimensions that are weighted by a factor of two. 1 , 2 2 , 2 3 The dimensions correspond to the weighting of the

[0041] A switch 411 is connected between the source and gate of the NMOS transistor 401, and a switch 412 is connected between the gate and a node ND3. A control signal N0 is supplied to the switch 411 via an inverter 420, and a control signal N0 is supplied to the switch 412. When the control signal N0 is at an H level, the switch 412 is turned on, and the NMOS transistor 401 is turned on. Control signals N1, N2, and N3 are supplied to the switches 413, 415, and 417 via inverters 421, 422, and 423.

[0042] Similarly, the NMOS transistors 402 to 404 are controlled to be turned on / off by control signals N1 to N3 supplied to the switches 413 to 418. The NMOS transistors 401 to 404 output a current according to the weighting for the NMOS transistor 400. The combination of the NMOS transistors 401 to 404 that are turned on by the control signals N0 to N3 is changed to control the reference current I REFn It is possible to adjust the value of the current control signal Cont2. The demodulator 103 outputs the control signals N0 to N3 as the current control signal Cont2. The current source of this configuration example can supply a current according to the current control signals Cont1 and Cont2.

[0043] FIG. 6 is a diagram specifically illustrating another configuration example of a current source. The current source of this embodiment has a resistor ladder circuit 500 configured with an R-2R ladder resistor. The resistor ladder circuit 500 has resistors 511-514 with a resistance value R and resistors 521-523 with twice the resistance value 2R. With respect to the current Io flowing through the right-end resistor 514, the current flowing through the adjacent resistor 523 is 2×Io. Similarly, the current flowing through resistor 522 is 4×Io, and the current flowing through resistor 521 is 8×Io. The connection destinations of the switches S0-S3 are switched in response to a control signal D to change the combination of currents supplied to the output terminal 501, thereby changing the reference current I REF You can adjust the value of .

[0044] The connection destination of the input terminal 504 of the resistor ladder circuit 500 is switched between a terminal 502 to which +VREF is applied and a terminal 503 to which -VREF is applied by a switch S17 controlled by a switching signal S. By switching the voltage applied to the input terminal 504 between +VREF and -VREF, the reference current IREF can be changed from positive to negative values. Therefore, the reference current I corresponding to a sine wave that changes from positive to negative current values ​​is REF The control signal D and the switching signal S are supplied as current control signals Cont1 and Cont2 from the demodulator 103, for example. The current source of this configuration example can supply a current according to the current control signals Cont1 and Cont2.

[0045] (Third embodiment) FIG. 7 is a diagram showing a current detection system according to the third embodiment. This embodiment includes a DA converter 601, a modulator 602, an isolator 603, and a demodulator 604. The DA converter 601 converts a digital signal from the control circuit 100 into an analog signal and supplies the analog signal to the modulator 602. The modulator 602 is configured, for example, by an AM modulator or an FSK modulator. The output signal of the modulator 602 is supplied to the isolator 603. The output signal of the isolator 603 is supplied to the demodulator 604. The demodulator 604 is configured corresponding to the modulator 602. For example, if the modulator 602 is an AM modulator, the demodulator 604 is configured by an AM demodulator. The demodulator 604 generates a current control signal Cont and supplies it to the current source 24. The current source 24 receives a reference current I, which changes in response to the current control signal Cont. REF For example, the gate voltage of a MOS transistor (not shown) constituting the current source 24 is controlled by the current control signal Cont to generate a reference current I REF can be configured to change in an analog manner.

[0046] A detection signal from a comparator circuit 25 that compares a drain voltage V1 of the switching element 22 with a drain voltage V2 of the switching element 23 is supplied to a control circuit 100 via an isolator 606. The control circuit 100 supplies a control signal to a drive circuit 10 via an isolator 605.

[0047] In this embodiment, the basic data from the control circuit 100 is converted to analog by a DA converter 601 and is supplied to the high voltage side via an isolator 603. The isolator 603 can be configured with a relatively narrow frequency band because it only needs to supply an analog signal directly to the high voltage side. A comparison circuit 25 that compares the drain voltage V1 of the switching element 22 with the drain voltage V2 of the switching element 23 is provided on the high voltage side, and its detection signal is supplied to the control circuit 100 via an isolator 606. The detection signal of the comparison circuit 25 is a 1-bit digital signal based on the comparison result between the drain voltage V1 of the switching element 22 and the drain voltage V2 of the switching element 23. Therefore, the isolator 606 that transmits the detection signal of the comparison circuit 25 can be configured with an isolator with a relatively slow transmission speed.

[0048] (Fourth embodiment) 8 is a diagram showing a power supply circuit of the fourth embodiment. This embodiment constitutes an AC / DC converter that converts AC voltage into DC voltage. This embodiment has current detection circuits 20-1 and 20-2, a capacitor 704 connected between output terminals 712 and 713, and diodes 702 and 703. An AC power supply 700 and a boost inductor 701 are connected between input terminals 710 and 711. The diode 702 is connected in the forward direction from the input terminal 711 to the output terminal 712, and the diode 703 is connected in the forward direction from the output terminal 713 to the input terminal 711.

[0049] The current detection circuit 20-1 detects an output current Id1 flowing through the switching elements 21-1 and 22-1 by comparing the drain voltage V1-1 of the switching element 22-1 with the drain voltage V2-1 of the switching element 23-1 using a comparison circuit 25-1. REF1 The current source 24-1 that supplies the current control signal Cont 11 is controlled by.

[0050] The current detection circuit 20-2 detects an output current Id2 flowing through the switching elements 21-2 and 22-2 by comparing the drain voltage V1-2 of the switching element 22-2 with the drain voltage V2-2 of the switching element 23-2 using a comparison circuit 25-2. REF2 The current source 24-2 that supplies the current control signal Cont 12 The detection signals of the comparison circuits 25-1 and 25-2 are supplied to the control circuit 100 via isolators 105-1 and 105-2, respectively.

[0051] The control circuit 100 calculates a reference current I REF1 , I REF2 The control circuit 100 supplies a digital signal of basic data for controlling the current control signal Cont to the modulator 101. The basic data is, for example, a digital signal generated based on the sine wave of the AC power supply 700. The modulator 101 generates a modulated signal by encoding the digital signal from the control circuit 100 using Manchester code or the like, and supplies the modulated signal to the demodulators 103-1 and 103-2 via the isolators 102-1 and 102-2. The demodulators 103-1 and 103-2 receive the current control signal Cont 11 , Cont 12 The current sources 24-1 and 24-2 cooperate with the DA converters 104-1 and 104-2 to generate a reference current I REF1 , I REF2 Output.

[0052] The switching elements 21-1, 22-1, and 23-1 of the current detection circuit 20-1 are driven by a drive circuit 10-1, and the switching elements 21-2, 22-2, and 23-2 of the current detection circuit 20-2 are driven by a drive circuit 10-2. The control circuit 100 generates control signals in response to detection signals from the comparison circuits 25-1 and 25-2 and supplies them to the drive circuits 10-1 and 10-2.

[0053] In response to a control signal from the control circuit 100, the drive circuits 10-1 and 10-2 control the on / off of the switching elements 21-1 and 22-1 of the current detection circuit 20-1 and the switching elements 21-2 and 22-2 of the current detection circuit 20-2. L becomes an output current Id1 flowing through the switching elements 21-1 and 22-1 of the current detection circuit 20-1 and an output current Id2 flowing through the switching elements 21-2 and 22-2 of the current detection circuit 20-2. By alternately turning on / off the switching elements 21-1 and 22-1 of the current detection circuit 20-1 and the switching elements 21-2 and 22-2 of the current detection circuit 20-2, an output voltage Vout with the output terminal 712 as the + side and the output terminal 713 as the - side is charged to the capacitor 704.

[0054] The operation of the fourth embodiment will be described with reference to FIG. 9. FIG. 9(A) shows a case where the input voltage Vin is positive, that is, the voltage on the input terminal 710 side is higher than the voltage on the input terminal 711 side. The horizontal axis shows time. The upper part shows the inductor current I L 11A, the next line indicates the output current Id1 flowing through the switching elements 21-1 and 22-1 of the current detection circuit 20-1, and the lower line indicates the output current Id2 flowing through the switching elements 21-2 and 22-2 of the current detection circuit 20-2. The dashed line 720 in the upper line of FIG. 11A indicates the reference current I REF1 Shows.

[0055] When the input voltage Vin is positive, the reference current I REF1 The current control signal Cont 11The output current Id1 flowing through the switching elements 21-1 and 22-1 is equal to the reference current I REF1 At the timings t11, t13, t15, and t17 when the current reaches the threshold, the switching elements 21-1 and 22-1 are turned off, and the switching elements 21-2 and 22-2 of the current detection circuit 20-2 are turned on.

[0056] When the input voltage Vin is positive, the reference current I REF2 is the current control signal Cont 12 At timings t12, t14, t16, and t18 when the output current Id2 flowing through the switching elements 21-2 and 22-2 of the current detection circuit 20-2 becomes zero, the switching elements 21-2 and 22-2 of the current detection circuit 20-2 are turned off, and the switching elements 21-1 and 22-1 of the current detection circuit 20-1 are turned on.

[0057] The output current Id1 flowing through the switching elements 21-1 and 22-1 of the current detection circuit 20-1 is a reference current I REF1 By controlling the on / off of the switching elements 21-1, 22-1, 21-2, and 22-2 of the current detection circuits 20-1 and 20-2 at the timings t11, t13, t15, and t17 when the upper limit of the output current Id1 is reached, the upper limit of the inductor current I L can be controlled by basic data based on a sine wave supplied by the control circuit 100. That is, the inductor current I L The envelope of the input signal can be matched to the sine wave of the AC power supply 700.

[0058] FIG. 9B shows a case where the input voltage Vin is negative, that is, the voltage on the input terminal 711 side is higher than the voltage on the input terminal 710 side. Since the input voltage Vin is inverted, the inductor current I L The direction of the reference current I is inverted, but for convenience, the upper side is shown as positive. The upper dashed line 721 in FIG. 9B represents the reference current I REF2 The horizontal axis indicates time. The upper part of Fig. 9(B) shows the inductor current I LThe next row shows the output current Id1 flowing through the switching elements 21-1 and 22-1 of the current detection circuit 20-1, and the lower row shows the output current Id2 flowing through the switching elements 21-2 and 22-2 of the current detection circuit 20-2.

[0059] When the input voltage Vin is negative, the reference current I REF2 The current control signal Cont 12 The output current Id2 flowing through the switching elements 21-2 and 22-2 is equal to the reference current I REF2 At the timings t21, t23, t25, and t27 when the current reaches the threshold, the switching elements 21-2 and 22-2 of the current detection circuit 20-2 are turned off, and the switching elements 21-1 and 22-1 of the current detection circuit 20-1 are turned on.

[0060] When the input voltage Vin is negative, the reference current I REF1 is the current control signal Cont 11 At timings t22, t24, t26, and t28 when the output current Id1 flowing through the switching elements 21-1 and 22-1 of the current detection circuit 20-1 becomes zero, the switching elements 21-1 and 22-1 of the current detection circuit 20-1 are turned off, and the switching elements 21-2 and 22-2 of the current detection circuit 20-2 are turned on.

[0061] The output current Id2 flowing through the switching elements 21-2 and 22-2 of the current detection circuit 20-2 is the reference current I REF2 At the timings t21, t23, t25, and t27 when the lower limit of the output current Id2, and therefore the inductor current I L can be controlled by basic data based on a sine wave supplied by the control circuit 100. That is, the inductor current I L The envelope of the input signal can be matched to the sine wave of the AC power supply 700.

[0062] According to this embodiment, the inductor current I L is a reference current I generated according to basic data based on the sine wave of the AC power supply 700 output by the control circuit 100. REF1 , I REF2 This controls the inductor current I L The envelope of the output current Id1 can be made to coincide with the sine wave of the AC power supply 700. In other words, the phase of the input voltage Vin can be made to coincide with the phase of the output current, thereby improving the power factor of the power supply circuit. L Since it is possible to detect the inductor current I L There is no need to provide a separate circuit for detecting the voltage Vin. Furthermore, by providing isolators 102-1, 102-2, 105-1, 105-2, 106-1, and 106-2 between the low-voltage side where the control circuit 100 is provided and the high-voltage side to which the input voltage Vin is applied, the low-voltage side and the high-voltage side can be electrically insulated and separated and coupled. Since the detection signals of the comparison circuits 25-1 and 25-2 are 1-bit signals indicating the comparison results between the drain voltages V1-1 and V2-1, and the drain voltages V1-2 and V2-2 outputted for each switching cycle of the switching elements 21-1, 22-1, 21-2, and 22-2, the isolators 105-1 and 105-2 can be configured with isolators having a relatively slow transmission speed.

[0063] The normally-on switching element may be configured by a JFET (Junction Field Effect Transistor).

[0064] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0065] 10 drive circuit, 20, 20-1, 20-2 current detection circuit, 21 to 23 switching element, 24 current source, 25 comparison circuit, 100 control circuit, 700 AC power source, 701 boost inductor, 702, 703 diode, 704 capacitor.

Claims

1. a normally-on type first switching element having a source, a drain, and a gate; a normally-off type second switching element having a drain connected to a source of the first switching element, a source connected to a reference potential, and a gate; a source connected to the source of the second switching element, a drain connected to a current source whose current value changes in response to a control signal, and a normally-off third switching element, the gate of which is applied with a voltage applied to the gate of the second switching element during current detection; a comparison circuit that compares a drain voltage of the second switching element with a drain voltage of the third switching element during the current detection and outputs a detection signal; Equipped with the current source changes the current value according to the control signal in accordance with switching operations of the first to third switching elements when detecting the current; when the drain voltage of the third switching element exceeds the drain voltage of the second switching element, the comparison circuit outputs the detection signal indicating that the current value has exceeded the current flowing between the source and drain of the first switching element.

2. A current detection circuit comprising:

2. 2. The current detection circuit according to claim 1, wherein the current value of the current source varies from a positive value to a negative value.

3. the second switching element and the third switching element are formed on a common semiconductor substrate; The gate length is the same and the gate width is set to a predetermined dimension ratio.

2. The current sensing circuit of claim 1.

4. A current detection circuit according to any one of claims 1 to 3, A control circuit for generating basic data for the control signal; a first isolator that insulates and separates the control circuit and the current detection circuit and supplies a signal based on the basic data to the current detection circuit; a second isolator that insulates and separates the comparison circuit and the control circuit and supplies the detection signal to the control circuit; A current detection system comprising:

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