Rectifier circuit and control method for rectifier circuit

Abstract

Provided is a rectifier circuit that can be controlled to reduce total power loss when a load current (rectified current) is relatively small.　The rectifier circuit having an anode and a cathode comprises: a first switching element in which a first terminal is connected to the cathode of the rectifier circuit and a second terminal is connected to the anode of the rectifier circuit; a first diode in which a cathode is connected to the cathode of the rectifier circuit and an anode is connected to the anode of the rectifier circuit; a first capacitor in which a third terminal is connected to the anode of the rectifier circuit; a reverse current prevention diode in which a cathode is connected to a fourth terminal of the first capacitor; a second switching element in which a fifth terminal is connected to the cathode of the rectifier circuit and a sixth terminal is connected to an anode of the reverse current prevention diode; a first comparison circuit for controlling the first switching element on the basis of the voltage between the anode and the cathode of the rectifier circuit; and a second comparison circuit for controlling the second switching element so as to control the voltage between the third terminal and the fourth terminal of the first capacitor to a target voltage.

Description

Rectifier circuit and control method for rectifier circuit

[0001] The present invention relates to the configuration of a rectifier circuit and a control method thereof, and more particularly to a technique that is effective when applied to semiconductor devices mounted on power supply devices and chargers for electric vehicles, which require low loss.

[0002] Diode rectifier circuits and synchronous rectifier circuits using MOSFETs are used as rectifier circuits in power supply devices to convert AC to DC. Synchronous rectifier circuits have low power loss because MOSFETs do not have a built-in potential like diodes and forward current rises from 0 V. Therefore, synchronous rectifier circuits are used in power supply devices that require low loss, such as front-end power supplies.

[0003] Known prior art related to synchronous rectification circuits includes, for example, techniques such as those disclosed in Patent Documents 1 and 2. Patent Documents 1 and 2 disclose rectification circuits that achieve synchronous rectification.

[0004] In the technology described in Patent Document 1, a control circuit and a MOSFET are mounted in a single package as a low-loss rectifier circuit used in an alternator. This rectifier circuit operates as a two-terminal semiconductor device with a unidirectional current flow function (rectification function), like a diode. Furthermore, the power required to operate the circuit that drives the MOSFET is generated within the package, and is sometimes called a self-powered synchronous rectifier circuit.

[0005] The rectifier circuit of Patent Document 1 is composed of a control circuit having a comparator and a gate driver, a capacitor that supplies power to the control circuit, and a MOSFET. The control circuit turns the MOSFET on and off using the gate driver in response to the drain-source voltage of the MOSFET detected by the comparator. When the MOSFET is off, the capacitor is charged by the drain-source voltage of the MOSFET.

[0006] In the technology described in Patent Document 2, multiple synchronous rectification MOSFETs are connected in parallel, and the number of MOSFETs that are turned on is set according to the magnitude of the load current, i.e., the rectified current, so as to reduce the total power loss.

[0007] JP 2015-116053 A JP 2010-213366 A

[0008] As described above, in power supply devices such as front-end power supplies that require low loss, a synchronous rectifier circuit is used to reduce loss that occurs in the diode.

[0009] Furthermore, in front-end power supplies that are redundant to improve reliability, the output power is shared among multiple front-end power supplies, so the proportion of light-load operation time for each front-end power supply tends to be large. Therefore, reducing the loss in the synchronous rectifier circuit during light-load operation is effective in improving the efficiency of the entire system.

[0010] Therefore, it is conceivable to configure a rectifier circuit with lower loss by combining the synchronous rectifier circuit of Patent Document 1 with the synchronous rectifier control of Patent Document 2.

[0011] However, the control technology described in Patent Document 2 is based on the premise that two or more synchronous rectification MOSFETs are connected in parallel, and therefore it is difficult to apply the control technology to the rectifier circuit described in Patent Document 1, which has only one synchronous rectification MOSFET.

[0012] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a rectifier circuit and a control method thereof that are capable of controlling the total power loss to be small when the load current (rectified current) is relatively small.

[0013] In order to solve the above problem, the present invention provides a rectifier circuit having an anode and a cathode, comprising: a first switching element having a first terminal connected to the cathode of the rectifier circuit and a second terminal connected to the anode of the rectifier circuit; a first diode having a cathode connected to the cathode of the rectifier circuit and an anode connected to the anode of the rectifier circuit; a first capacitor having a third terminal connected to the anode of the rectifier circuit; a backflow prevention diode having a cathode connected to the fourth terminal of the first capacitor; a second switching element having a fifth terminal connected to the cathode of the rectifier circuit and a sixth terminal connected to the anode of the backflow prevention diode; a first comparison circuit that controls the first switching element based on a voltage between the anode and cathode of the rectifier circuit; and a second comparison circuit that controls the second switching element so as to control the voltage between the third terminal and the fourth terminal of the first capacitor to a target voltage.

[0014] The present invention also provides a method for controlling a self-powered rectifier circuit using one synchronous rectifier MOSFET, characterized in that the voltage of a capacitor that supplies power to a gate drive circuit of the synchronous rectifier MOSFET is controlled based on the magnitude of the current flowing from the anode to the cathode of the rectifier circuit.

[0015] According to the present invention, it is possible to realize a rectifier circuit and a control method thereof that can perform control so as to reduce total power loss when the load current (rectified current) is relatively small.

[0016] This makes it possible to reduce the gate charge loss of the rectifier circuit when the power supply device is operating under a light load, for example, and to improve the efficiency of the power supply device.

[0017] Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0018] FIG. 1 is a circuit diagram showing the configuration of a rectifier circuit according to a first embodiment of the present invention. FIG. 2 is a current and voltage waveform diagram showing an example of the operation of the rectifier circuit of FIG. 1. FIG. 3 is a diagram showing the relationship between the total loss of the rectifier circuit and the rectified current Is and the gate-source voltage Vgs. FIG. 4 is a circuit diagram showing the configuration of a rectifier circuit according to a second embodiment of the present invention. FIG. 5 is a circuit diagram showing the configuration of a rectifier circuit according to a third embodiment of the present invention. FIG. 6 is a circuit diagram showing the configuration of a rectifier circuit according to a fourth embodiment of the present invention. FIG. 7 is a circuit diagram showing the configuration of a semiconductor device according to a fifth embodiment of the present invention. FIG. 8 is a circuit diagram showing the configuration of a power supply device according to a sixth embodiment of the present invention. FIG. 9 is a circuit diagram showing the configuration of a conventional rectifier circuit. FIG. 10 is a current and voltage waveform diagram showing an example of the operation of the conventional rectifier circuit.

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or similar components are designated by the same reference numerals, and detailed descriptions of overlapping parts will be omitted.

[0020] In addition, symbols indicating current and voltage (the arrows indicate the direction) in the figure, Is, Vds1, Vgs1, and Vc1, respectively, represent the rectified current, the voltage between the main terminals of the MOSFET Q1, i.e., the drain-source voltage, the gate-source voltage of the MOSFET Q1, and the voltage of the capacitor C1. These symbols will be used appropriately in the following explanation.

[0021] First Embodiment A circuit configuration of a rectifier circuit according to a first embodiment of the present invention and a control method thereof will be described with reference to FIGS. 1 to 3, 9 and 10. FIG.

[0022] Fig. 1 is a circuit diagram showing the configuration of a rectifier circuit of this embodiment. Fig. 2 is a current and voltage waveform diagram showing an example of the operation of the rectifier circuit of Fig. 1. Fig. 3 is a diagram showing the relationship between the total loss of the rectifier circuit and the rectified current Is and the gate-source voltage Vgs1. Figs. 9 and 10 are circuit diagrams of a conventional rectifier circuit shown as a comparative example to make the present invention easier to understand, and current and voltage waveform diagrams showing an example of its operation.

[0023] 1, in the rectifier circuit of this embodiment, a MOSFET Q1 is connected between an anode (A) and a cathode (K) as a semiconductor switching element for synchronous rectification. The drain of the MOSFET Q1 is connected to the cathode (K), and the source is connected to the anode (A).

[0024] The MOSFET Q1 is turned on and off based on the drain-source voltage of the MOSFET Q1 detected by the comparator circuit Co1. The MOSFET Q1 is turned on during the rectification period (rectification current Is≧0), that is, when the AC voltage applied between the anode (A) and cathode (K) is in the forward direction.

[0025] In this embodiment, an enhancement type n-channel MOSFET is used as the MOSFET Q1.

[0026] A diode D1 is connected in antiparallel to the MOSFET Q1. In this embodiment, the diode D1 is a body diode built into the MOSFET. Alternatively, an externally connected separate diode may be used as the diode D1.

[0027] The rectifier circuit of this embodiment detects a voltage drop when a rectified current (load current) Is flowing from the anode (A) to the cathode (K) of the rectifier circuit flows through the MOSFET Q1 or the diode D1, and realizes synchronous rectification by controlling the MOSFET Q1 to be on during the rectification period.

[0028] The comparator circuit Co1 compares the drain-source voltage Vds1 of the MOSFET Q1 (i.e., the voltage between the anode (A) and cathode (K) of the rectifier circuit) with the threshold voltage generated by the threshold voltage generator circuit Rv1, and controls the on / off of the MOSFET Q1.

[0029] For example, if the threshold voltage generating circuit Rv1 generates a negative threshold voltage Vth1, and Vds1≦Vth1, the comparator circuit Co1 controls the MOSFET Q1 to be on, and if Vds1>Vth1, the comparator circuit Co1 controls the MOSFET Q1 to be off.

[0030] In order to suppress chattering, which occurs when the MOSFET Q1 repeatedly turns on and off in a short cycle, the threshold voltage generation circuit Rv1 may generate a negative threshold voltage Vth2 that is greater than the threshold voltage Vth1, and when Vds1>Vth2 (i.e., when Vds1>Vth2>Vth1), the comparison circuit Co1 may control the MOSFET Q1 to be turned off.

[0031] The rectifier circuit of this embodiment reduces losses in the rectifier circuit by controlling the maximum value of the voltage Vc1 of the capacitor C1 during the period in which the capacitor C1 is being charged, based on the magnitude of the detected rectified current Is.

[0032] The capacitor C1 is charged by the drain-source voltage Vds1 of the MOSFET Q1 that occurs when the MOSFET Q1 is off. The maximum value of the voltage Vc1 of the capacitor C1 is controlled by controlling the on / off of the switching element Q2.

[0033] The on / off of MOSFET Q2 is controlled by a comparator circuit Co2. The comparator circuit Co2 compares the drain-source voltage Vds1 of MOSFET Q1 with the threshold voltage generated by the threshold voltage generator circuit Rv2, and controls the switching element Q2 to be on when Vds1 is equal to or less than the threshold voltage generated by the threshold voltage generator circuit Rv2, and controls the switching element Q2 to be off when Vds1 is greater than the threshold voltage generated by the threshold voltage generator circuit Rv2. Therefore, if the maximum value of the drain-source voltage Vds1 applied to MOSFET Q1 while MOSFET Q1 is off is greater than the threshold voltage generated by the threshold voltage generator circuit Rv2, the voltage Vc1 of the charged capacitor C1 increases to the threshold voltage generated by the threshold voltage generator circuit Rv2.

[0034] The threshold voltage generating circuit Rv2 generates at least two different threshold voltages.

[0035] As an example, the threshold voltage generation circuit Rv2 generates two different threshold voltages Vcref1 and Vcref2, and the maximum value of the voltage Vc1 of the charged capacitor C1 is controlled to Vcref1 or Vcref2, thereby reducing the loss of the rectifier circuit. However, Vcref1 and Vcref2 are positive values, and Vcref1 > Vcref2. Furthermore, Vcref1 and Vcref2 are sufficiently larger than the gate threshold voltage Vgsth1 of the MOSFET Q1 and smaller than the rated voltages of the comparator circuits Co1, Co2, and Co3.

[0036] Vcref1 and Vcref2 generated by the threshold voltage generating circuit Rv2 are determined, for example, as follows.

[0037] The losses occurring in the rectifier circuit include the conduction loss of the MOSFET Q1 caused by the load current (rectified current) Is, the gate charge loss when driving the MOSFET Q1, and the loss of the control circuit (gate driver).

[0038] The conduction loss is estimated as the product of the square of the effective value of the load current (rectified current) Is and the on-resistance of the MOSFET Q1, the gate charge loss is estimated as the product of the square of the gate-source voltage Vgs1 of the MOSFET Q1, the input capacitance of the MOSFET Q1, and the switching frequency of the MOSFET Q1, and the loss of the control circuit (gate driver) is estimated as the product of the voltage Vc1 of the capacitor C1 and the current consumption of the control circuit (gate driver).

[0039] Assuming that the gate-source voltage of MOSFET Q1 when MOSFET Q1 is on and the voltage of capacitor C1 are approximately equal, the sum of these losses can be expressed as a variable representing the maximum voltage when capacitor C1 is charged to voltage Vc1, i.e., the effective value of load current (rectified current) Is for each of Vcref1 and Vcref2. Therefore, as shown in Figure 3, when the sum of losses is plotted on the vertical axis and the effective value of load current (rectified current) Is is plotted on the horizontal axis, the graph when the threshold voltage generated by threshold voltage generation circuit Rv is Vcref1 and the graph when it is Vcref2 intersect at a certain effective value of load current (rectified current) Is. Therefore, when the effective value of the load current (rectified current) Is that actually flows is smaller than the effective value of the load current (rectified current) Is, the threshold voltage generated by the threshold voltage generation circuit Rv2 is switched to Vcref2, and when it is larger, the threshold voltage generated by the threshold voltage generation circuit Rv2 is switched to Vcref1, thereby reducing losses in the rectifier circuit.

[0040] The threshold voltages Vcref1 and Vcref2 generated by the threshold voltage generating circuit Rv2 are switched based on the magnitude of the detected rectified current Is.

[0041] In the rectifier circuit of this embodiment, in order to detect the rectified current (load current) Is, the voltage drop caused by the rectified current (load current) Is and the on-resistance of the MOSFET Q1, i.e., the drain-source voltage Vds1 of the MOSFET Q1 during the on-period of the MOSFET Q1, is detected.

[0042] The comparator circuit Co3 compares the detected Vds1 with the threshold voltage generated by the threshold voltage generator circuit Rv3, and inputs a signal to the threshold voltage generator circuit Rv2 to switch the threshold voltage generated by the threshold voltage generator circuit Rv2.

[0043] The threshold voltage generated by the threshold voltage generation circuit Rv3 is determined, for example, as follows. Assuming that the waveform of the rectified current Is is a sine wave, the maximum value of the rectified current Is is uniquely determined for the effective value of the load current (rectified current) Is at the intersection of the graph in Figure 3. Also, assuming that the voltage of the capacitor C1 and the gate-source voltage of the MOSFET Q1 are approximately equal and that the MOSFET Q1 is driven under conditions where it is sufficiently cooled, the on-resistance of the MOSFET Q1 is uniquely determined when the threshold voltage generated by the threshold voltage generation circuit Rv2 is Vcref1 or Vcref2. Therefore, for the effective value of the load current (rectified current) Is at the intersection of the graph in FIG. 3, when the threshold voltage generated by the threshold voltage generation circuit Rv2 is Vcref1 or Vcref2, the minimum value Vds1onmin of the drain-source voltage of the MOSFET Q1 during the on-period of the MOSFET Q1 is uniquely determined.

[0044] The threshold voltage generation circuit Rv3 generates two threshold voltages Vthl1 and Vthl2, and when the threshold voltage generated by the threshold voltage generation circuit Rv2 is Vcref1, the corresponding Vds1onm is set to Vthl1, and when the threshold voltage generated by the threshold voltage generation circuit Rv2 is Vcref2, the corresponding Vds1onm is set to Vthl2. Furthermore, when the threshold voltage generated by the threshold voltage generation circuit Rv2 is Vcref1, the threshold voltage generation circuit Rv3 generates the threshold voltage Vthl1, and when the threshold voltage generated by the threshold voltage generation circuit Rv2 is Vcref2, the threshold voltage generation circuit Rv3 generates the threshold voltage Vthl2.

[0045] 2 shows the operating waveforms of the rectifier circuit of this embodiment when the threshold voltage generated by the threshold voltage generator Rv2 switches from Vcref1 to Vcref2. The comparator circuit Co3 detects the drain-source voltage Vds1 during the on-period of the MOSFET Q1, compares the minimum value Vdsonm of the detected drain-source voltage with the threshold voltage Vthl1 generated by the threshold voltage generator Rv3, determines that Vdsonm > Vthl1, and inputs a signal to the threshold voltage generator Rv2. As a result, the threshold voltage generated by the threshold voltage generator Rv2 switches to Vcref2. Similarly, the threshold voltage generated by the threshold voltage generation circuit Rv2 switches from Vcref2 to Vcref1 when the comparison circuit Co3 determines that Vdsonm<Vthl2, and this is achieved by the comparison circuit Co3 inputting a signal to switch the threshold voltage generated by the threshold voltage generation circuit Rv2 from Vcref2 to Vcref1.

[0046] In the above explanation, assumptions are used such that the voltage of capacitor C1 and the gate-source voltage of MOSFET Q1 are approximately equal, the waveform of rectified current Is is a sine wave, and MOSFET Q1 is driven under conditions where it is sufficiently cooled. However, these assumptions are used merely to simply determine the threshold voltage generated by threshold voltage generation circuit Rv3, and the threshold voltage generated by threshold voltage generation circuit Rv3 may be determined taking into consideration the waveform of rectified current Is under actual driving conditions and the temperature characteristics of the on-resistance of MOSFET Q1.

[0047] Furthermore, if the switching loss occurring in the MOSFET Q1 is large, the switching loss may be added to the loss occurring in the rectifier circuit, and Vcref1 and Vcref2 may be determined by the same means.

[0048] As shown in Figure 9, in a conventional rectifier circuit, the voltage Vc1 of the capacitor C1 increases to the voltage between the cathode (K) and anode (A) of the rectifier circuit. However, the voltage drop of the backflow prevention diode Dr is ignored. Therefore, as shown in Figure 10, the voltage Vc1 of the capacitor C1 and the gate-source voltage Vgs1 of the MOSFET Q1 are constant regardless of the magnitude of the rectified current (load current) Is.

[0049] As shown in FIGS. 2 and 10, the present invention differs from conventional rectifier circuits in that the magnitudes of Vc1 and Vgs1 are controlled in accordance with the magnitude of the rectified current (load current) Is.

[0050] 9, conventional rectifier circuits also have a configuration in which a switching element is inserted between the blocking diode Dr and the cathode (K) of the rectifier circuit, and the charging current of capacitor C1 is controlled by controlling the switching element, thereby controlling the magnitude of Vc1 to a desired value equal to or less than the voltage between the cathode (K) and anode (A) of the rectifier circuit. However, this conventional rectifier circuit does not control Vc1 according to the magnitude of the rectified current (load current) Is.

[0051] As described above, the rectifier circuit of this embodiment is a rectifier circuit having an anode (A) and a cathode (K), and includes a first switching element (MOSFET Q1) having a first terminal connected to the cathode (K) of the rectifier circuit and a second terminal connected to the anode (A) of the rectifier circuit, a first diode (diode D1) having a cathode connected to the cathode (K) of the rectifier circuit and an anode connected to the anode (A) of the rectifier circuit, a first capacitor (capacitor C1) having a third terminal connected to the anode (A) of the rectifier circuit, a backflow prevention diode Dr having a cathode connected to the fourth terminal of the first capacitor (capacitor C1), a second switching element (switching element Q2) having a fifth terminal connected to the cathode (K) of the rectifier circuit and a sixth terminal connected to the anode of the backflow prevention diode Dr, and a first switching element (MOSFET Q2) having a sixth terminal connected to the anode of the backflow prevention diode Dr based on the voltage between the anode (A) and cathode (K) of the rectifier circuit. The first comparison circuit (comparison circuit Co1) controls a first switching element (switching element Q2) so as to adjust the voltage between the third terminal and the fourth terminal of the first capacitor (capacitor C1) to a target voltage.

[0052] The target voltages are at least two different values, and are controlled based on the magnitude of the current flowing from the anode (A) to the cathode (K) of the rectifier circuit.

[0053] Furthermore, according to this embodiment, in a self-powered synchronous rectifier circuit using one synchronous rectifier MOSFET, when the load current, i.e., the rectified current, is small, the voltage of the power supply that supplies power to the drive circuit that drives the MOSFET is controlled to be reduced so that the total power loss of the rectifier circuit is reduced.

[0054] Second Embodiment A circuit configuration of a rectifier circuit according to a second embodiment of the present invention will be described with reference to FIG.

[0055] 4 is a circuit diagram showing the configuration of a rectifier circuit of this embodiment, which corresponds to a modification of embodiment 1 (FIG. 1). In the rectifier circuit of embodiment 1 (FIG. 1), a switching element Q2 for controlling the charging current of capacitor C1 in accordance with the magnitude of rectified current (load current) Is is arranged between backflow prevention diode Dr and the cathode (K) of the rectifier circuit, whereas in the rectifier circuit of this embodiment (FIG. 4), the switching element Q2 is arranged between capacitor C1 and the anode (A) of the rectifier circuit, which is different.

[0056] As in this embodiment (FIG. 4), even if a switching element Q2 for controlling the charging current of capacitor C1 in accordance with the magnitude of the rectified current (load current) Is is disposed between capacitor C1 and the anode (A) of the rectifier circuit, the same effect as in embodiment 1 (FIG. 1) can be obtained.

[0057] Third Embodiment With reference to FIG. 5, a circuit configuration of a rectifier circuit according to a third embodiment of the present invention will be described.

[0058] 5 is a circuit diagram showing the configuration of a rectifier circuit of this embodiment, which corresponds to a modification of embodiment 1 (FIG. 1). In the rectifier circuit of embodiment 1 (FIG. 1), one of the input terminals of the comparator circuit Co2 is connected between the switching element Q2 and the cathode (K) of the rectifier circuit, whereas in the rectifier circuit of this embodiment (FIG. 5), it is connected between the blocking diode Dr and the capacitor C1, i.e., to the terminal of the capacitor C1 to which a positive voltage is applied.

[0059] By adopting the configuration of this embodiment (FIG. 5), the voltage Vc1 of the capacitor C1 can be controlled to the target voltage without including the voltage drop fluctuation of the backflow prevention diode Dr.

[0060] Fourth Embodiment With reference to FIG. 6, a circuit configuration of a rectifier circuit according to a fourth embodiment of the present invention will be described.

[0061] 6 is a circuit diagram showing the configuration of a rectifier circuit of this embodiment, which corresponds to a modification of embodiment 1 (FIG. 1). In the rectifier circuit of embodiment 1 (FIG. 1), one of the input terminals of the comparator circuit Co1 and one of the input terminals of the comparator circuit Co2 are connected between the switching element Q2 and the cathode (K) of the rectifier circuit, whereas in the rectifier circuit of this embodiment (FIG. 6), they are connected between the switching element Q2 and the backflow prevention diode Dr.

[0062] In the rectifier circuit of this embodiment, the on / off state of the switching element Q2 is controlled by a threshold voltage generated by a threshold voltage generation circuit Rv4. The threshold voltage generated by the threshold voltage generation circuit Rv4 is controlled based on the output signal of a comparison circuit Co2 so as to achieve the desired on / off control of the switching element Q2.

[0063] By configuring the present embodiment (FIG. 6), the rectifier circuit of the present invention can be applied even when a voltage equal to or greater than the rated voltage of the comparator circuits Co1 and Co2 is applied between the cathode (K) and anode (A) of the rectifier circuit.

[0064] A semiconductor device according to a fifth embodiment of the present invention will be described with reference to FIG.

[0065] 7 is a circuit diagram showing the configuration of a semiconductor device of this embodiment, which is a configuration example of a semiconductor device equipped with the rectifier circuit of the present invention described in embodiments 1 to 4. FIG. 7 shows an example in which the rectifier circuit of embodiment 1 (FIG. 1) is equipped.

[0066] 7, a four-terminal semiconductor device can be configured by configuring a bridge circuit using, for example, four rectifier circuits 1 and incorporating it into one semiconductor package 2. The semiconductor package 2 has terminals T1 to T4 as external terminals.

[0067] The configuration is not limited to that shown in FIG. 7, and the rectifier circuit 1 may be built into a semiconductor package having a cathode (K) and an anode (A) as external terminals.

[0068] According to the semiconductor device of this embodiment, when designing and manufacturing a product that uses a rectifier circuit, it is sufficient to purchase and incorporate a rectifier circuit with a built-in drive circuit and capacitor like that of this embodiment, and since the labor required for designing and implementing the drive circuit and capacitor is eliminated, the overall labor required for design and implementation can be reduced.

[0069] A power supply device according to a sixth embodiment of the present invention will be described with reference to FIG.

[0070] FIG. 8 is a circuit diagram showing the configuration of the power supply device of this embodiment, which is an example of the configuration of a power supply device equipped with the rectifier circuits and semiconductor devices of the present invention described in the first to fifth embodiments.

[0071] The rectifier circuits and semiconductor devices of Examples 1 to 5 are applicable to all rectifier circuits used in power supplies. For example, in a front-end power supply as shown in Fig. 8, the rectifier circuits and semiconductor devices of Examples 1 to 5 can be applied as commercial rectifier diodes CRD1 to CRD4, a freewheeling diode FWD, secondary-side rectifier diodes SSD1 and SSD2, and a backflow prevention diode BPD.

[0072] By applying the rectifier circuits and semiconductor devices according to the first to fifth embodiments to a power supply device such as a front-end power supply, it is possible to contribute to improving the efficiency and miniaturization of the power supply device.

[0073] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0074] 1: Rectifier circuit 2: Semiconductor package T1 to T4: Terminal K: Cathode A: Anode Q1: MOSFET Q2: Switching element D1, D2: Diode Dr: Reverse current prevention diode C1: Capacitor Co1 to Co3: Comparator circuit Rv1 to Rv4: Threshold voltage generation circuit Vth1, Vth2, Vthl1, Vthl2: Threshold voltage Is: Rectified current (load current) Vds1: Drain-source voltage of MOSFET Q1 (voltage between the cathode and anode of the rectifier circuit) Vds1onmin: Minimum drain-source voltage during the on period of MOSFET Q1 Vc1: Voltage of capacitor C1 Vgs1: Gate-source voltage of MOSFET Q1 Vgsth1: Gate threshold voltage of MOSFET Q1 Vcref1, Vcref2: Target voltage of capacitor C1 t, T1, T2, T1a, T1b, T2a: Time CRD1 to CRD4: Commercial rectifier diodes FWD: Freewheel diode SSD1 to SSD2: Secondary side rectifier diodes BPD: Backflow prevention diode.

Claims

1. A rectifier circuit having an anode and a cathode, comprising: a first switching element having a first terminal connected to the cathode of the rectifier circuit and a second terminal connected to the anode of the rectifier circuit; a first diode having a cathode connected to the cathode of the rectifier circuit and an anode connected to the anode of the rectifier circuit; a first capacitor having a third terminal connected to the anode of the rectifier circuit; a reverse current prevention diode having a cathode connected to a fourth terminal of the first capacitor; a second switching element having a fifth terminal connected to the cathode of the rectifier circuit and a sixth terminal connected to the anode of the reverse current prevention diode; a first comparison circuit that controls the first switching element based on a voltage between the anode and cathode of the rectifier circuit; and a second comparison circuit that controls the second switching element so as to control the voltage between the third terminal and the fourth terminal of the first capacitor to a target voltage.

2. A rectifier circuit as claimed in claim 1, wherein the target voltage has at least two different values, and the target voltage is controlled based on the magnitude of a current flowing from the anode to the cathode of the rectifier circuit.

3. A rectifier circuit as claimed in claim 1, characterized in that the first input terminal of the first comparator circuit is connected to the cathode of the rectifier circuit, and the second input terminal is connected to a first threshold voltage generating circuit.

4. A rectifier circuit according to claim 3, wherein the first threshold voltage generating circuit generates at least two different threshold voltages.

5. A rectifier circuit according to claim 1, characterized in that the first input terminal of said second comparator circuit is connected to the cathode of said rectifier circuit.

6. A rectifier circuit according to claim 5, wherein the second input terminal of the second comparator circuit is connected to a second threshold voltage generating circuit.

7. A rectifier circuit as claimed in claim 6, wherein the second threshold voltage generating circuit generates at least two different threshold voltages, and changes the generated threshold voltage based on the magnitude of the current flowing from the anode to the cathode of the rectifier circuit.

8. A rectifier circuit according to any one of claims 1 to 7, characterized in that the rectifier circuit is built into a semiconductor package.

9. A rectifier circuit according to any one of claims 1 to 7, characterized in that it is mounted on a power supply device.

10. A control method for a self-powered rectifier circuit using one synchronous rectifier MOSFET, comprising controlling the voltage of a capacitor that supplies power to the gate drive circuit of the synchronous rectifier MOSFET based on the magnitude of the current flowing from the anode to the cathode of the rectifier circuit.

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