JP6207669B2 - Synchronous rectifier circuit - Google Patents

Description

  The present invention relates to a synchronous rectifier circuit for turning on a switching element connected in parallel to a diode when a current flows in the forward direction of the diode of the power semiconductor element including the sense switching element in the synchronous rectifier circuit. It is.

  As a conventional synchronous rectifier circuit, for example, there is one disclosed in Patent Document 1. The synchronous rectification method is a method in which the switching element of the upper arm and the switching element of the lower arm are alternately turned on by using input signals at respective on / off timings with a dead time interposed therebetween. In this synchronous rectification method, when a switching element capable of switching in the forward direction and in the reverse direction is used, it is possible to reduce loss as much as possible by turning on the switching element even when a current flows in the reverse direction. However, when the dead time is short, the switching elements of the upper and lower arms are simultaneously turned on, and the loss may increase or the element may be destroyed in the worst case. If the dead time is too long, the voltage drop during that period becomes large, causing a problem such as an increase in loss, and it is necessary to optimize the dead time.

  Patent Document 1 relates to optimization of dead time in the synchronous rectification method, and includes first current detection means for detecting a current flowing in a MOSFET as a switching element and a second current detection for detecting a current flowing in a parasitic diode. There is shown a system in which a dead time is set so that both the through current detected by the first current detecting means and the recovery current detected by the second current detecting means are both reduced.

  Patent Document 2 describes a technique for solving the problem of causing deterioration or destruction when a body diode that is inherent in a switching element is used as a free-wheeling diode when silicon carbide, which is a wide band gap semiconductor, is used. Has been. A structure in which a Schottky barrier diode is connected in parallel to the switching element SiC-FET, and the voltage of the Schottky barrier diode is detected and the SiC-FET is turned on / off according to the voltage, and the current / current change A method is described in which the rate is detected and the switching element is turned on and off during the reflux period.

  Further, in Patent Document 3, in a synchronous rectifier circuit, a sense switching element is used to detect a current flowing backward from a load, that is, a forward current flowing through the switching element, and charge of a capacitor connected to the output terminal is detected. A technique for discharging is disclosed. In addition, regarding the sense switching element, there are many conventional techniques used for detecting the forward current of the switching element (for example, Patent Document 4).

JP 2007-14059 A JP 2008-17237 A JP 2007-244156 A JP-A-7-146722

  In Patent Document 1, the current flowing through the MOSFET and the current flowing through the parasitic diode connected in parallel with the MOSFET are separately detected and the dead time is adjusted, but the switching speed depends on the current, voltage, temperature, etc. When fluctuates, it is difficult to adjust the dead time. Further, since the two current detection means are required, the circuit configuration is complicated, and there is a possibility that the circuit becomes large. Patent Document 2 is a method of turning on and off the switching element so that the body diode is not energized in the reflux mode, and does not necessarily shorten the dead time. In addition, the current and the rate of change of current are detected by detecting the total current flowing through the semiconductor, which may increase the size of the apparatus.

  The present invention has been made to solve the above-described problems. In the synchronous rectifier circuit, the dead time is stably reduced as much as possible with a relatively simple circuit configuration, and a wide range of SiC or the like can be used. An object of the present invention is to obtain a synchronous rectifier circuit that suppresses deterioration and destruction of a body diode when a band gap semiconductor is used.

  The present invention includes a semiconductor element having a body diode in parallel and having a switching element capable of switching a bidirectional current in a forward direction and a reverse direction, and a control circuit for controlling on / off of the switching element. The power switching circuit provided is connected in series to the output of the DC power supply, and this connection point is used as an output terminal, and the switching elements of the power switching circuit connected in series are alternately turned on and off from the output terminal. In a synchronous rectifier circuit configured to flow current to an inductive load, a semiconductor element includes a main cell including a main switching element having a main body diode in parallel and a sense cell including a sense switching element having a sense body diode in parallel. And a detector for detecting the total current flowing through the sense cell In the power switching circuit, the control circuit of the power switching circuit has a period in which the current flows in the forward direction of the switching element based on a predetermined input signal input to the control circuit. During the period in which the switching element is controlled and the current flows in the reverse direction of the switching element in the power switching circuit, the control circuit of the power switching circuit is in the semiconductor element having the switching element to be controlled detected by the detecting means. The total current flowing through the sense cell is used to detect the value of the parameter during operation of the semiconductor element of the power switching circuit, and the switching of the power switching circuit is performed by the control signal created based on the detected parameter value. It is intended to control the element

  According to the present invention, during the period in which the current flows in the reverse direction of the switching element, the value of the parameter during operation of the semiconductor element is detected, and the switching element is controlled based on the detected parameter value. It is less affected by voltage, temperature, etc., and the dead time can be stably reduced.

It is a circuit diagram which shows the switching circuit for electric power used for the synchronous rectifier circuit by Embodiment 1 of this invention. It is a figure which shows an example of the power converter device to which the synchronous rectifier circuit by this invention is applied. It is a time chart explaining operation | movement of the synchronous rectification circuit by Embodiment 1 of this invention. It is a circuit diagram which shows the switching circuit for electric power used for the synchronous rectifier circuit by Embodiment 2 of this invention. It is a circuit diagram which shows the power switching circuit used for the synchronous rectifier circuit by Embodiment 3 of this invention. It is a circuit diagram which shows the power switching circuit used for the synchronous rectifier circuit by Embodiment 4 of this invention.

  As shown in Patent Documents 3 and 4, the sense switching element is often used to detect a current flowing through the main switching element, that is, a current flowing in the forward direction. In contrast, when the power switching element is an element having a parasitic diode such as a MOSFET, the present inventors can measure the forward current of the parasitic diode using a sense switching element. Pay attention. It has been found that a synchronous rectifier circuit with a short dead time can be realized by detecting the current flowing in the forward direction of the parasitic diode with a sense switching element and using it as a control signal. Hereinafter, the present invention will be described according to embodiments.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing a power switching circuit 100 used in a synchronous rectifier circuit according to Embodiment 1 of the present invention. Here, a power switching circuit 100 using a MOSFET as a switching element will be described as an example. The switching element constituting the semiconductor element 10 is composed of a main MOSFET 1 that is a main switching element and a sense MOSFET 2 that is a sense switching element. Each MOSFET includes a body diode in parallel. Here, the main MOSFET 1 and the main body diode 3 parallel to the main MOSFET 1 are collectively called a main cell 20, and the sense MOSFET 2 and the sense body diode 4 parallel to the main MOSFET 20 are collectively called a sense cell 30. Although the body diode is parasitic on the MOSFET, it is described as parallel for ease of understanding. The drive circuit is configured to control the main MOSFET 1, the control circuit 5 that performs the on / off operation of the sense MOSFET 2, the current including the sense MOSFET 2 and the sense body diode 4 in parallel therewith, that is, the total current flowing through the sense cell 30 and the current change rate. It comprises a sense resistor 6 for detection, a current detection circuit 7, and a current change rate detection circuit 8.

  The main cell 20 includes a larger number of cells than the sense cell 30, and the ratio is, for example, several thousand to several tens of thousands to one. Therefore, the current flowing through the semiconductor element 10 flows in a divided manner to the main cell 20 and the sense cell 30 according to the ratio. The current and current change rate flowing in the sense cell 30 are detected from the voltage of the sense resistor 6 connected in series to the sense cell 30 and the voltage change rate, and the current and current change flowing in the main cell 20 from the shunt ratio according to the cell ratio. The rate can be detected. Further, since the main MOSFET 1 and the sense MOSFET 2 include the main body diode 3 and the sense body diode 4, respectively, even when the main MOSFET 1 and the sense MOSFET 2 are in the off state, the current of the body diode and the current change are detected by detecting the current of the sense cell 30. The rate can also be detected.

  FIG. 2 shows an example of a power converter using the synchronous rectifier circuit of the present invention. FIG. 2 shows a configuration of a three-phase inverter using six power switching circuits 100 shown in FIG. 1, that is, power switching circuits 100a, 100b, 100c, 100d, 100e, and 100f. Is an example of a power conversion device using a synchronous rectifier circuit that converts a current into an alternating current and supplies a current to the inductive load 14. In the arrangement in which the power switching circuits are arranged in series as shown in FIG. 2 (for example, the power switching circuits 100a and 100b) and an inductive load is connected to the connection point, current flows in the forward direction of a certain switching element. When the switching element is turned off and then turned on again, the power switching circuit on the opposite side of the series connection has a reverse direction to the forward direction of the switching element (the forward direction of the diode). ) Current. It is important to turn on the switching element connected in parallel with the diode during a period in which current flows in the forward direction of the diode. Note that the three-phase inverter of FIG. 2 is shown as an example of a power converter to which the present invention is applied, and the present invention can also be applied to a synchronous rectifier circuit other than an inverter, such as a converter or a chopper.

  The operation of the synchronous rectifier circuit according to the first embodiment will be described with reference to the simplified voltage, current waveform, and input signal to the control circuit shown in FIG. Here, the operation of a pair of the power switching circuit 100a and the power switching circuit 100b connected in series in FIG. 2 will be described as an example. In FIG. 2, two sets of the power switching circuit 100c and the power switching circuit 100d connected in series, and the two power switching circuits 100e and 100f connected in series are connected. Also, the operation of the pair of the power switching circuit 100a and the power switching circuit 100b is exactly the same as the pair of the power switching circuit 100a and the power switching circuit 100b except for the phase. FIG. 3 shows a case where, in the three-phase inverter shown in FIG. 2, the switching element is turned off and then turned on again from the state in which the current flows in the forward direction of the switching element in the upper arm power switching circuit 100a. Yes. The case where the current flows in the forward direction of the switching element is positive, and the current change rate dI / dt is described as positive when the forward current of the switching element increases.

  Hereinafter, portions corresponding to the respective portions in FIG. 1 in the power switching circuit 100a will be described by adding “a” to the reference numerals in FIG. Similarly, each part in the power switching circuit 100b will be described by adding b to the reference numeral. First, the switching element is turned off from time t1 when the input signal to the input terminal 50a of the control circuit 5a of the power switching circuit 100a is turned off. Looking at this state in detail, the input signal is switched from on to off, and the current Id1 of the power switching circuit 100a starts to decrease from time t2 with a slight delay, and is negative in the power switching circuit 100b of the lower arm. The current Id2 (current in the forward direction of the diode) starts to flow. The operation of the power switching circuit 100b will be described from the circuit shown in FIG. 1. Current flowing in the forward direction of the diode starts to flow through the main body diode 3b and the sense body diode 4b. When the current starts to flow, a voltage corresponding to the current value is generated in the sense resistor 6b. Since the voltage of the sense resistor 6b fluctuates according to the current change rate dId2 / dt, the current change rate detection circuit 8b detects that the current change rate is less than or equal to a predetermined value (absolute value is greater than or equal to a predetermined value) from the voltage change of the sense resistor 6b. ) And a detection signal is output to the control circuit 5b. In response to the signal, the control circuit 5b turns on the main MOSFET 1b and the sense MOSFET 2b. As a result, the current is shunted and flows to the main MOSFET 1b and the main body diode 3b, and the on-voltage is reduced. Depending on the characteristics, the current may not flow through the body diode but only through the MOSFET.

  During the period in which the current flows in the forward direction of the diode, the current detection circuit 7b detects the energization of the current from the voltage of the sense resistor 6b, and outputs a detection signal to the control circuit 5b, thereby maintaining the on state. Thereafter, when the main MOSFET 1a and the sense MOSFET 2a of the upper arm power switching circuit 100a are turned on after time t6, which is slightly delayed from time t5 when the input signal of the control circuit 5a is turned on, the lower arm power switching circuit 100b The current starts to increase (absolute value decreases). The current change rate detection circuit 8b detects from the voltage change of the sense resistor 6b that the current change rate is equal to or higher than a predetermined value, and outputs a detection signal to the control circuit 5b. The control circuit 5b The MOSFET 2b is turned off.

  The control of the switching element of the lower arm power switching circuit 100b in the conventional synchronous rectifier circuit is performed based on a predetermined input signal to the control circuit 5b. In FIG. 3, this input signal is indicated by a broken line as an input signal 100b. This input signal has a sufficient dead time so that the switching time of the upper and lower arms does not turn on at the same time, so that the dead time can be secured even if the switching characteristics of the element change due to the current value or the temperature change of the element. The input signal is predetermined so as to be controlled at the timing. For example, the dead time as the input signal is from time t1 when the input signal of the upper arm changes from on to off to time t3 when the input signal of the lower arm changes from off to on. Thus, when controlling a switching element with a predetermined input signal, it is necessary to ensure a sufficient dead time.

  On the other hand, in the synchronous rectifier circuit according to the first embodiment, since the current change rate is detected and the switching element is turned on / off, even if there is a characteristic change due to a current value, a temperature change of the element, or the like, By being able to turn on and off according to the characteristics, it is possible to shorten the dead time during which both the switching elements of the upper and lower arms are turned off, compared to the case where the switching is turned on and off by a predetermined input signal. Here, the case where the power switching circuit 100a is turned off and on from the state where the forward current flows in the power switching circuit 100a of the upper arm has been described as an example, but conversely the power switching circuit 100b of the lower arm. Even when the power switching circuit 100b is turned off and on from the state where the forward current is flowing in the upper arm, the upper arm power switching circuit 100a performs the same operation as the power switching circuit 100b described above.

  The current detection circuit 7 detects whether or not a current is flowing based on the voltage of the sense resistor 6, and can be constituted by, for example, a comparator that compares the reference voltage with the voltage of the sense resistor. The reference voltage may be 0 V or less (the absolute value is 0 V or more), but is set in consideration of malfunction caused by noise. The current change rate detection circuit 8 detects whether the positive and negative current change rates are greater than or less than a reference value based on voltage fluctuations of the sense resistor 6. For example, an operational amplifier for differentiating the sense voltage is used. An output of the differentiation circuit, positive and negative reference voltages, and a comparator for comparing them can be used. The reference voltage is set so as not to be detected by a current change when switching is not performed, but to be detected by a current change at the time of switching. Further, a filter or the like may be provided to prevent malfunction due to noise. Further, when the current change due to the recovery operation of the diode is large, a filter that ignores the negative current change immediately after the positive current change may be provided.

  Also, as indicated by dId1 / dt in FIG. 3, a current change occurs even when the switching element is turned off when a current flows in the forward direction and when the current flows in a forward direction. In order to prevent the control circuit 5 from operating with this current change, filter circuits such as not turning on immediately after an off signal is input from an input signal, and not turning off immediately after an on signal is input from an input signal are provided. It may be provided. In addition to the output of the current detection circuit 7, the on / off operation may be performed only when the current detection circuit 7 detects the forward current of the diode, that is, the reverse current of the switching element. . Further, the current change rate detection circuit 8 is used to detect the start of the forward flow of the diode. However, when the current detection circuit 7 detects the current flow using the current detection circuit 7, the switching element is detected. You may turn on. In short, a control signal for causing a current in the reverse direction to flow through the switching element of the power switching circuit 100 detects a current in the reverse direction of the switching element that flows through the sense cell 30 of the semiconductor element 10 having the switching element to be controlled. Then, it is created based on the detected current value and the current change rate obtained from the detected current. Here, the sense resistor is used to convert the current flowing through the sense body diode into a voltage. However, it is sufficient that the current flowing through the sense body diode and the current change rate can be detected, and the circuit must always use the sense resistor. There is no.

  In the present invention, since the switching element is turned on by the current flowing in the forward direction of the diode and the rate of change of the current, even when a predetermined input signal for turning on the switching element is input with a delay when performing synchronous rectification, Since the switching element is turned on, the dead time can be shortened. Even in the off operation, even if an input signal for turning off the switching element is input first, the on state is maintained until the diode forward voltage changes, so that the dead time can be shortened. Even when an input signal that does not consider synchronous rectification is input, since the switching element is turned on, there is an effect such as loss reduction. In addition, since the switching element is turned on / off depending on the current and the rate of change of the current, it is hardly affected by the current value, voltage, temperature, etc., and the dead time can be stably reduced.

  In the above, the current that flows in the forward direction of the diode and the method of turning on and off the switching element according to the rate of change of the current have been shown, but one of on or off is controlled according to a predetermined input signal, and only the above control Even if the method is applied, there is an effect of reducing the dead time. This method can be applied not only to the first embodiment but also to other embodiments.

Embodiment 2. FIG.
FIG. 4 shows a circuit diagram of a power switching circuit used in the synchronous rectifier circuit according to the second embodiment of the present invention. In Patent Document 1, the dead time is adjusted so that both the through current and the recovery current become small. However, in the present invention, since the on / off operation is performed based on the current and the current change rate, the switching speed of the switching element is set. Is fast, there is a possibility that the on / off of the switching element on the side where the current flows through the body diode is delayed. The second embodiment corresponds to such a case, and is different from the first embodiment in that the control circuit 5 includes a switching speed adjustment circuit 11.

  The switching speed adjustment circuit 11 switches the switching speed between when the switching element is turned on / off when a current flows in the reverse direction of the switching element and when the switching element is turned on / off based on a predetermined input signal. Is. That is, the switching speed adjustment circuit 11 is turned on based on the input signal input to the input terminal 50 when switching on and off based on the outputs of the current detection circuit 7 and the current change rate detection circuit 8. Compared to the case of turning off, the switching is performed at a higher speed. As a circuit, for example, a gate resistor for performing switching based on an input signal from the input terminal 50, a gate resistor for performing switching based on the outputs of the current detection circuit 7 and the current change rate detection circuit 8, and a gate It consists of a resistance changeover switch. The gate resistance for turning on and the gate resistance for turning off may be the same or different. By switching the gate resistance with the changeover switch, the switching speed is adjusted, and switching can be performed without delay.

Embodiment 3 FIG.
FIG. 5 shows a circuit diagram of a power switching circuit used in the synchronous rectifier circuit according to the third embodiment of the present invention. In the case where a wide band gap semiconductor such as SiC is used for the semiconductor element 10, there is a possibility that deterioration or destruction will occur if the body diode is energized. The third embodiment corresponds to such a case, and is obtained by adding a freewheeling diode 12 to the second embodiment, that is, the circuit of FIG.

  In the first and second embodiments, the semiconductor element that turns on the switching element when a current flows in the forward direction of the diode and the drive circuit thereof are described. However, depending on the characteristics of the switching element and the body diode, the switching element is turned on. Even so, current flows through the body diode. In the present invention, since the freewheeling diode 12 is connected in parallel with the semiconductor element 10, the current also flows in parallel with the freewheeling diode 12, further reducing the current flowing through the body diode and suppressing deterioration and destruction of the body diode. Is possible. Reference 2 describes examples of current-voltage characteristics of SiC-FETs, Schottky barrier diodes, and body diodes. Switching elements, free-wheeling diodes are used so that the body diodes are not energized when the switching elements are turned on. The characteristics of the Schottky barrier diode may be set. In that case, the effect of suppressing deterioration and destruction of the body diode is further enhanced.

Embodiment 4 FIG.
FIG. 6 shows a circuit diagram of a power switching circuit used in the synchronous rectifier circuit according to the fourth embodiment of the present invention. Although the freewheeling diode 12 is provided in the third embodiment, depending on the characteristics of the freewheeling diode 12 and the characteristics of the body diode, when the forward current of the diode starts to flow, it flows only to the freewheeling diode 12 and flows to the body diode. There may be no case. The fourth embodiment corresponds to such a case, and includes a voltage detection circuit 13 instead of the current detection circuit 7 of the third embodiment. The voltage detection circuit 13 outputs a detection signal when the voltage of the parallel body of the main switching element 1, the main body diode 3, and the freewheeling diode 12 falls below a certain value. Even when the freewheeling diode 12 is added, as in FIG. 2, when the upper arm power switching circuit 100a is switched, the voltage Vds2 of the lower arm power switching circuit 100b decreases and current flows in the forward direction of the diode. start. When the voltage decreases and falls below a predetermined value, the voltage detection circuit 13 outputs a detection signal to the control circuit 5, and the control circuit 5 turns on the main MOSFET 1 and the sense MOSFET 2. The voltage detection circuit 13 outputs a detection signal while the voltage is equal to or lower than a predetermined value, and the main MOSFET 1 and the sense MOSFET 2 are kept on. In addition, a current detection circuit may be provided separately, and the output of the current detection circuit may be used to keep the on state.

  When the current starts to increase (decreases as an absolute value), the current change rate detection circuit 8 detects that the current change rate is equal to or higher than a predetermined value, and outputs a detection signal to the control circuit 5 to control the current. The circuit 5 turns off the main MOSFET 1 and the sense MOSFET 2. In the first embodiment, an example in which the off operation is performed only when the current detection circuit detects energization in the reverse direction of the switching element (forward direction of the diode) together with the output of the current detection circuit (for example, AND circuit). However, together with the output of the voltage detection circuit 13, the OFF operation may be performed only when the voltage detection circuit 13 detects a voltage drop.

  The voltage detection circuit 13 includes, for example, a voltage dividing circuit, a reference voltage, and a comparator that compares the output of the voltage dividing circuit with the reference voltage. The reference voltage is preferably 0 V or less, but is set in consideration of noise, operating conditions, and the like. By adopting such a circuit configuration, even when the forward current of the diode starts to flow, even when it flows only to the freewheeling diode 12 and does not flow to the body diode, the energization of the freewheeling diode 12 is detected and the switching element is turned on. It becomes possible to do.

  In addition, the configuration of the present system to which the voltage detection circuit 13 for detecting the voltage generated in the semiconductor element having the switching element to be controlled is added regardless of the presence or absence of the freewheeling diode or the current flowing through the body diode. Applicable.

  In the first to fourth embodiments described above, an example in which a MOSFET is used as the switching element has been described. However, the switching element may be any element that can switch bidirectionally, and is not necessarily a MOSFET. The switching element may be formed of a wide band gap semiconductor having a band gap larger than that of silicon, in addition to the switching element formed of silicon. Examples of the material of the wide band gap semiconductor include silicon carbide, a gallium nitride material, and diamond. When a wide bandgap semiconductor is used, the allowable current density is high and the power loss is low, so that a device using the power semiconductor element can be downsized. In addition, when a wide band gap semiconductor is used for the switching element, the withstand voltage of an element that can be switched bidirectionally, such as a MOSFET, is increased, and it can be applied to a high voltage region. In addition, when a wide band gap semiconductor is used, if there is a possibility of causing deterioration or destruction when the body diode is energized, this can be suppressed, and the effect of the present invention is particularly great.

  As described above, according to the present invention, as described in the first to fourth embodiments, in the synchronous rectifier circuit, the control signal of the switching element in the period in which the current flows in the reverse direction of the switching element is detected as the current flowing in the sense cell. It is created based on a current change rate which is a current value or a differential value of the current value, or a voltage of a semiconductor element is detected and created based on the detected voltage. That is, since the parameter value during operation of the semiconductor element is detected and the switching element is controlled based on the detected parameter value, it is hardly affected by the current value, voltage, temperature, etc. Can be shortened.

  It should be noted that the present invention can be freely combined with each other within the scope of the invention, or each embodiment can be appropriately modified or omitted.

1: Main MOSFET (Main switching element)
2: Sense MOSFET (sense switching element)
3: Main body diode 4: Sense body diode 5: Control circuit 6: Sense resistor 7: Current detection circuit 8: Current change rate detection circuit 9: DC power supply 10: Power semiconductor element 11: Switching speed adjustment circuit 12: Freewheeling diode 13: Voltage detection circuit 14: Inductive load 20: Main cell 30: Sense cells 100, 100a, 100b, 100c, 100d, 100e, 100f: Power switching circuit

Claims (9)

Electric power provided with a semiconductor element having a body diode in parallel and having a switching element capable of switching forward and reverse currents in both directions and a control circuit for controlling on / off of the switching element The switching circuit for power is connected in series, the connection point is used as an output terminal, the other terminal of the power switching circuit is used as an input terminal connected to a DC power supply, and the switching elements of the power switching circuit connected in series are alternately arranged. In the synchronous rectifier circuit configured to flow current from the output terminal to the inductive load by turning on and off,
The semiconductor element comprises a main cell comprising a main switching element having a main body diode in parallel and a sense cell comprising a sense switching element having a sense body diode in parallel, and detecting means for detecting the total current flowing through the sense cell With
During the period in which a current flows in the forward direction of the switching element in the power switching circuit, the control circuit of the power switching circuit controls the switching element in the power switching circuit based on a predetermined input signal input to the control circuit. Control
During the period in which current flows in the reverse direction of the switching element in the power switching circuit, the control circuit of the power switching circuit flows through the sense cell in the semiconductor element having the switching element to be controlled, which is detected by the detection means. Using all the currents, the value of the parameter during operation of the semiconductor element of the power switching circuit is detected, and the switching element of the power switching circuit is controlled by the control signal created based on the detected parameter value A synchronous rectifier circuit.   The detection means is composed of a resistor arranged in series with a sense cell in a semiconductor element having the switching element to be controlled, and the control circuit controls a switching element that causes a current to flow in the reverse direction of the switching element. The synchronous rectifier circuit according to claim 1, wherein the synchronous rectifier circuit is generated based on a voltage drop caused by a current flowing through a resistor arranged in series with the sense cell.   The control circuit creates a control signal for controlling a switching element that allows a current to flow in a direction opposite to the switching element, based on a rate of change in voltage drop due to a current flowing through a resistor arranged in series with the sense cell. The synchronous rectifier circuit according to claim 2.   The synchronous rectifier circuit according to claim 1, further comprising a free-wheeling diode in parallel with the semiconductor element.   The control circuit generates a control signal for controlling a switching element that allows a current to flow in a direction opposite to the switching element, based on a voltage generated in a semiconductor element having the switching element to be controlled. 5. The synchronous rectifier circuit according to any one of 1 to 4.   The control circuit generates either one of an ON signal and an OFF signal among control signals generated in order to flow current in the reverse direction of the switching element based on a predetermined input signal input to the control circuit. The synchronous rectifier circuit according to claim 1, wherein the synchronous rectifier circuit is provided. When the control circuit controls the switching element by a control signal created based on the value of the operating parameter detected in the semiconductor element including the switching element to be controlled, based on a predetermined input signal 7. A switching speed adjustment circuit for increasing a switching speed for turning on / off a switching element to be controlled as compared with a case of controlling the switching element. Synchronous rectifier circuit.   The synchronous rectifier circuit according to claim 1, wherein the switching element is formed of a wide band gap semiconductor.   The synchronous rectifier circuit according to claim 8, wherein the material of the wide band gap semiconductor is any one of silicon carbide, a gallium nitride material, and diamond.

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