Rectifier circuit and power supply using the same

Abstract

In rectifier circuits that use switching elements such as MOSFETs for synchronous rectification, the capacitance of the capacitor supplying power to the drive circuit of the switching element used for synchronous rectification can be reduced. A rectifier circuit having an anode and a cathode includes: a first switching element, whose first terminal is connected to the cathode of the rectifier circuit and whose second terminal is connected to the anode of the rectifier circuit; a first diode, whose cathode is connected to the first terminal and whose anode is connected to the second terminal; a second switching element, whose third terminal is connected to the first terminal; a second diode, whose anode is connected to the fourth terminal of the second switching element; a first capacitor, whose positive terminal is connected to the cathode of the second diode and whose negative terminal is connected to the second terminal; a comparator that detects the voltage between the fourth terminal and the second terminal and is powered by the first capacitor; and a gate driver. Its input terminal is connected to the output terminal of the comparator, and its output terminal is connected to the fifth terminal of the first switching element used to control the first switching element. The first switching element is controlled according to the output signal of the comparator. A control circuit is connected to the sixth terminal of the second switching element, which is used to input a signal to control the second switching element. The control circuit keeps the second switching element in a conducting state at all times. The current flowing from the third terminal to the fourth terminal of the second switching element is controlled by controlling the voltage between the sixth terminal and the fourth terminal of the second switching element, so that the voltage of the first capacitor does not exceed a specified target voltage.

Description

Technical Field

[0001] This invention relates to the structure of a rectifier circuit and a power supply using the rectifier circuit, and particularly to a technique for effectively applying to rectifier circuits that use switching elements such as MOSFETs to implement synchronous rectification. Background Technology

[0002] To rectify AC to DC, synchronous rectification using switching elements such as MOSFETs to replace diodes is employed. Rectification using diodes suffers from high losses due to the voltage drop caused by the diode's built-in potential. In contrast, synchronous rectification using MOSFETs, for example, results in low losses because the forward current rises from 0V without the MOSFET's built-in potential. Therefore, synchronous rectification utilizing MOSFETs is primarily used in switching power supplies with stringent efficiency constraints, especially in applications like front-end power supplies, to achieve even lower rectification losses.

[0003] As background technology in this field, there are technologies such as those in Patent Document 1 and Patent Document 2.

[0004] Rectifier circuits for implementing synchronous rectification are shown in Patent Documents 1 and 2.

[0005] These rectifier circuits mainly consist of MOSFETs and their driving circuits for synchronous rectification, capacitors that supply power to the driving circuits, and switching elements and their control circuits for controlling the voltage of the capacitors. The driving circuit controls the MOSFET's on / off state based on the threshold voltage of the driving circuit and the detected drain-source voltage of the MOSFET.

[0006] The capacitor supplying power to the drive circuit is charged after the MOSFET is turned off, using the current flowing through the path of the MOSFET's drain terminal, the capacitor, and the MOSFET's source terminal. When charging of the capacitor begins, the capacitor voltage increases in a manner that follows the drain-source voltage of the MOSFET.

[0007] Here, when the drain-source voltage of the MOSFET is much larger than the operating voltage of the drive circuit, etc., in order not to apply excessive voltage to the capacitor, drive circuit, MOSFET gate, etc., it is necessary to control the voltage of the capacitor to be below the target voltage.

[0008] In such a rectifier circuit, once the capacitor voltage reaches the target voltage, the switching element inserted between the drain terminal of the MOSFET and the positive terminal of the capacitor is turned off, thereby cutting off the capacitor's charging current. Thus, the capacitor voltage is controlled to be below the target voltage.

[0009] Subsequently, the power stored in the capacitor is consumed by the standby power of the drive circuit, thus reducing the capacitor voltage. Then, during the MOSFET's on-time until the MOSFET turns off again and the capacitor begins charging, the power stored in the capacitor is used for either power consumption by the drive circuit or for generating the gate-source voltage of the MOSFET, thus continuously reducing the capacitor voltage.

[0010] Thus, during the period from the completion of capacitor charging to the resumption of capacitor charging, the capacitance of the capacitor is selected such that the voltage of the capacitor is, for example, above the operating guarantee voltage of the drive circuit or the gate threshold voltage of the MOSFET.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Application Publication No. 2001-251861

[0014] Patent Document 2: US Patent No. 10,756,645 Summary of the Invention

[0015] The problem that the invention aims to solve

[0016] As mentioned above, in conventional rectifier circuits such as Patent Document 1 and Patent Document 2, a capacitor is required to supply power to the drive circuit of the MOSFET used for synchronous rectification. The size of this capacitor becomes an obstacle to the miniaturization and cost reduction of the rectifier circuit.

[0017] Therefore, the object of the present invention is to provide a rectifier circuit that reduces the capacitance of the capacitor supplying power to the drive circuit of the switching element used for synchronous rectification in a rectifier circuit that uses switching elements such as MOSFETs to perform synchronous rectification, and a power supply using the rectifier circuit.

[0018] Methods for solving problems

[0019] To address the aforementioned issues, the present invention provides a rectifier circuit having an anode and a cathode. The rectifier circuit comprises: a first switching element, the first terminal of which is connected to the cathode of the rectifier circuit, and a second terminal of which is connected to the anode of the rectifier circuit; a first diode, the cathode of which is connected to the first terminal, and the anode of which is connected to the second terminal; a second switching element, the third terminal of which is connected to the first terminal; a second diode, the anode of which is connected to a fourth terminal of the second switching element; a first capacitor, the positive terminal of which is connected to the cathode of the second diode, and the negative terminal of which is connected to the second terminal; and a comparator that detects the voltage between the fourth terminal and the second terminal, and is supplied by the first capacitor. The device includes: a power supply; a gate driver whose input terminal is connected to the output terminal of the comparator, and whose output terminal is connected to the fifth terminal of the first switching element for controlling the first switching element, controlling the first switching element according to the output signal of the comparator; and a control circuit connected to the sixth terminal of the second switching element for inputting a signal to control the second switching element, the control circuit keeping the second switching element always in an on state, and controlling the current flowing from the third terminal to the fourth terminal of the second switching element by controlling the voltage between the sixth terminal and the fourth terminal of the second switching element, so that the voltage of the first capacitor does not exceed a predetermined target voltage.

[0020] Invention Effects

[0021] According to the present invention, a rectifier circuit that reduces the capacitance of the capacitor supplying power to the drive circuit of the switching element for synchronous rectification, and a power supply using the rectifier circuit, can be realized in a rectifier circuit that performs synchronous rectification using switching elements such as MOSFETs.

[0022] This enables the miniaturization and low cost of the rectifier circuit and the power supply using the rectifier circuit.

[0023] Other issues, structures, and effects not mentioned above will be clarified through the following description of the implementation methods. Attached Figure Description

[0024] Figure 1 This is a diagram showing the structure of the rectifier circuit of Embodiment 1 of the present invention.

[0025] Figure 2 It means Figure 1 The diagram shows the waveform of the rectifier circuit in operation.

[0026] Figure 3 This is a diagram illustrating the structure of the rectifier circuits in Embodiments 2 and 5 of the present invention.

[0027] Figure 4This is a diagram showing the structure of the rectifier circuit of Embodiment 3 of the present invention.

[0028] Figure 5 This is a diagram showing the structure of the rectifier circuit of Embodiment 4 of the present invention.

[0029] Figure 6 This is a diagram illustrating the structure of the semiconductor package according to Embodiment 6 of the present invention.

[0030] Figure 7 This is a diagram illustrating the structure of the semiconductor package according to Embodiment 6 of the present invention.

[0031] Figure 8 This is a diagram illustrating the structure of the front-end power supply according to Embodiment 7 of the present invention.

[0032] Figure 9 It is a diagram showing the operating waveform of an existing rectifier circuit. Detailed Implementation

[0033] Hereinafter, embodiments of the present invention will be described using the accompanying drawings. Furthermore, the same reference numerals will be used to label the same structures in the drawings, and detailed descriptions of repeated parts will be omitted.

[0034] In addition, in the accompanying drawings, the drain terminal of MOSFET Q1 is represented as the first terminal 6, the source terminal of MOSFET Q1 is represented as the second terminal 7, the drain terminal of MOSFET Q2 is represented as the third terminal 8, the source terminal of MOSFET Q2 is represented as the fourth terminal 9, the gate terminal of MOSFET Q1 is represented as the fifth terminal 10, the gate terminal of MOSFET Q2 is represented as the sixth terminal 11, one terminal of resistor R1 is represented as the seventh terminal 12, the other terminal of resistor R1 is represented as the eighth terminal 13, one terminal of resistor R2 is represented as the ninth terminal 14, and the other terminal of resistor R2 is represented as the tenth terminal 15.

[0035] The following explanation is based on the above provisions.

[0036] Example 1

[0037] Reference Figure 1 as well as Figure 2 , Figure 9 This describes the structure of the rectifier circuit and its control method in Embodiment 1 of the present invention. Figure 1 This is a diagram showing the structure of the rectifier circuit in this embodiment. Figure 2 It means Figure 1 A diagram showing the operating waveforms of the rectifier circuit. Additionally, Figure 9 The diagram shows the operating waveforms of a conventional rectifier circuit as a comparative example, for the purpose of facilitating understanding of the present invention.

[0038] First, use Figure 1 The structure of the rectifier circuit in this embodiment will be described. For example... Figure 1 As shown, the rectifier circuit in this embodiment consists of MOSFET Q1 and its driving circuit 1, MOSFET Q2 and its control circuit 5, diode D, and capacitor C1.

[0039] The drive circuit 1 for MOSFET Q1 has a comparator Co and a gate driver GD.

[0040] In addition, Figure 1 In this context, MOSFET Q1 and MOSFET Q2 are represented by an n-channel enhancement-mode MOSFET and an n-channel depletion-mode MOSFET, respectively, but they can also be replaced by other switching elements or diodes along with the body diode built into the MOSFET.

[0041] Next, use Figure 2 right Figure 1 The control method of the rectifier circuit will be explained. Figure 2 Indicates the use of 4 Figure 1 The waveforms of each operation of the rectifier circuit are shown when a resistive load is connected to the bridge circuit formed by the rectifier circuit shown, and a sinusoidal voltage is input.

[0042] At time t0, the rectification period ends and the non-rectification period begins.

[0043] The period from time t0 to time t1 is the non-rectified period, during which MOSFET Q1 is turned off. Additionally, as the sinusoidal voltage input to the bridge increases, the drain-source voltage Vds1 of MOSFET Q1 increases.

[0044] In addition, the gate-source voltage Vgs2 of MOSFET Q2 is greater than the gate threshold voltage Vgth2 of MOSFET Q2, so MOSFET Q2 is in the on state.

[0045] When the drain-source voltage Vds1 of MOSFET Q1 is greater than the sum of the voltage Vc1 of capacitor C1 and the forward voltage Vf of diode D, charging begins to begin on capacitor C1, and the voltage Vc1 of capacitor C1 increases. The charging current of capacitor C1 flows through the path of the drain terminal of MOSFET Q1, MOSFET Q2, diode D, capacitor C1, and the source terminal of MOSFET Q1.

[0046] Time t1 is the time when the sum of the drain-source voltage Vds1 of MOSFET Q1, the target maximum voltage Vcref1 of capacitor C1, and the forward voltage Vf of diode D is equal. In order not to apply excessive voltage to capacitor C1, drive circuit 1, the gate of MOSFET Q1, etc., the target maximum voltage Vcref1 of capacitor C1 is selected, for example, in a manner that is the lowest of the maximum rated voltages of comparator Co constituting drive circuit 1, the maximum rated voltage of gate driver GD, and the maximum rated voltage of gate-source of MOSFET Q1.

[0047] The period from time t1 to time t2 is the non-rectified period, during which MOSFET Q1 is off. Additionally, as the sinusoidal voltage input to the bridge increases and decreases, the drain-source voltage Vds1 of MOSFET Q1 increases and then decreases.

[0048] During this period, the gate-source voltage Vgs2 of MOSFET Q2 is greater than the gate threshold voltage Vgth2 of MOSFET Q2, and MOSFET Q2 is always in the on state.

[0049] However, by controlling the gate-source voltage Vgs2 of MOSFET Q2, the voltage Vc1 of capacitor C1 is made not greater than the target maximum voltage Vcref1 of capacitor C1, thereby controlling the current flowing from the drain to the source of MOSFET Q2.

[0050] Specifically, the gate-source voltage Vgs2 of MOSFET Q2 is controlled near the gate threshold voltage Vgth2 of MOSFET Q2 to make the on-resistance of MOSFET Q2 high. At this time, the differential voltage between the drain-source voltage Vds1 of MOSFET Q1 and the voltage Vc1 of capacitor C1 is applied to the drain-source of MOSFET Q2.

[0051] During this period, the power stored in capacitor C1 is consumed as standby power for drive circuit 1. On the other hand, the charging current of capacitor C1 flowing in the path from the drain of MOSFET Q1 to MOSFET Q2, diode D, capacitor C1, and the source of MOSFET Q1 is not interrupted, and capacitor C1 is charged, thus suppressing the voltage drop of capacitor C1.

[0052] The period from time t2 to time t3 is the non-rectified period, during which MOSFET Q1 is turned off. Additionally, as the sinusoidal voltage input to the bridge decreases, the drain-source voltage Vds1 of MOSFET Q1 decreases.

[0053] During this period, the gate-source voltage Vgs2 of MOSFET Q2 is greater than the gate threshold voltage Vgth2 of MOSFET Q2, and MOSFET Q2 is in the on state. On the other hand, the drain-source voltage Vds1 of MOSFET Q1 is less than the sum of the voltage Vc1 of capacitor C1 and the forward voltage Vf of diode D, so capacitor C1 is not charged. At this time, the charge accumulated in capacitor C1 is prevented from flowing into the drain terminal of MOSFET Q1 through diode D.

[0054] During this period, the power stored in capacitor C1 is consumed as standby power for drive circuit 1, but capacitor C1 is not charged, so the voltage Vc1 of capacitor C1 decreases.

[0055] The period from time t3 to time t0 is the rectification period, during which the rectified current flows from the anode A to the cathode K.

[0056] In addition, the gate-source voltage Vgs2 of MOSFET Q2 is greater than the gate threshold voltage Vgth2 of MOSFET Q2, so MOSFET Q2 is in the on state.

[0057] Comparator Co detects the drain-source voltage Vds1 of MOSFET Q1 from the source terminals of MOSFET Q2 and MOSFET Q1. Based on the detected voltage, drive circuit 1 turns MOSFET Q1 on and off.

[0058] The specific control method for MOSFET Q1 is explained.

[0059] The rectified current flowing from the anode A to the cathode K first flows through the body diode of MOSFET Q1. Due to the voltage drop across the body diode, the drain-source voltage Vds1 of MOSFET Q1 becomes negative.

[0060] When the voltage detected by comparator Co is less than the first threshold voltage of comparator Co, comparator Co outputs a turn-on signal, and the gate driver GD pulls up the gate-source voltage Vgs1 of MOSFET Q1 to the voltage Vc1 of capacitor C1, thereby turning on MOSFET Q1.

[0061] Subsequently, the drain-source voltage Vds1 of MOSFET Q1 becomes a voltage determined by the rectified current and the on-resistance of MOSFET Q1.

[0062] As time passes, the rectified current decreases. With the decrease in rectified current, the drain-source voltage Vds1 of MOSFET Q1 increases. When the voltage detected by comparator Co exceeds the second threshold voltage of comparator Co, comparator Co outputs a cutoff signal, and the gate driver GD pulls down the gate-source voltage Vgs1 of MOSFET Q1 to 0V, thus turning off MOSFET Q1.

[0063] The comparator Co has a first threshold voltage and a second threshold voltage that can be the same value, or the first threshold voltage can be smaller than the second threshold voltage. When the first threshold voltage is less than the second threshold voltage, it is possible to suppress the oscillation of the MOSFET repeatedly turning on and off in short cycles.

[0064] During this period, MOSFET Q2 is in the on state. On the other hand, the drain-source voltage Vds1 of MOSFET Q1 is less than the sum of the voltage Vc1 of capacitor C1 and the forward voltage Vf of diode D, so capacitor C1 is not charged.

[0065] As a result, during this period, the power stored in capacitor C1 is used to consume power in drive circuit 1 and generate the gate-source voltage Vgs1 of MOSFET Q1, but capacitor C1 is not charged, so the voltage of capacitor C1 decreases.

[0066] By repeating the above control, the rectifier circuit in this embodiment achieves synchronous rectification.

[0067] During the period from time t2 through time t3 to from time t0 through time t1, until the charging of capacitor C1 resumes, the voltage of capacitor C1 continuously decreases.

[0068] During this period, the capacitance of capacitor C1 needs to be selected so that the voltage Vc1 of capacitor C1 is greater than the target minimum voltage Vcref2 of capacitor C1. The target minimum voltage Vcref2 is, for example, the minimum operating voltage of drive circuit 1, or a value greater than the gate threshold voltage Vgth1 of MOSFET Q1 such that the on-resistance of MOSFET Q1 becomes sufficiently small.

[0069] Next, use Figure 9 The control methods of existing rectifier circuits are explained, and the effects of the rectifier circuit of the present invention are shown.

[0070] Although not illustrated, the conventional rectifier circuit and Figure 1The rectifier circuit shown in this embodiment is similarly composed of MOSFET Q1 and its driving circuit 1, MOSFET Q2 and its control circuit 5, diode D, and capacitor C1. However, MOSFET Q1 and MOSFET Q2 can also be replaced with other switching elements or diodes.

[0071] like Figure 2 and Figure 9 As shown, the control method of MOSFET Q2 during the period from time t1 to time t2 differs between the rectifier circuit of the present invention and the existing rectifier circuit.

[0072] like Figure 9 As shown, in a conventional rectifier circuit, capacitor C1 begins charging during the period from time t0 to time t1, and the voltage Vc1 of capacitor C1 increases. When the voltage of capacitor C1 reaches the target maximum voltage Vcref1 at time t1, MOSFET Q2 is turned off.

[0073] During the period from time t1 to time t2, MOSFET Q2 is in the off state, cutting off the charging current to capacitor C1, thereby controlling the voltage Vc1 of capacitor C1 to not exceed the target maximum voltage Vcref1. During the period from time t1 to time t2, the power stored in capacitor C1 is consumed as standby power for drive circuit 1, but capacitor C1 is not charged, so the voltage Vc1 of the capacitor decreases.

[0074] During the period from time t1 through time t2 and time t3 until the charging of capacitor C1 resumes during the period from time t0 to time t1, the power stored in capacitor C1 is used to drive the power consumption of circuit 1 and generate the gate-source voltage Vgs1 of MOSFET Q1. Therefore, the voltage Vc1 of capacitor C1 continuously decreases.

[0075] During this period, the capacitance of capacitor C1 needs to be selected so that the voltage Vc1 of capacitor C1 is above the target minimum voltage Vcref2 of capacitor C1.

[0076] On the other hand, in the rectifier circuit of the present invention, such as Figure 2 As shown, compared with the conventional rectifier circuit, it can reduce the period from time t1 to time t2 during which capacitor C1 is not charged.

[0077] That is, it can suppress the voltage drop of capacitor C1 during the off period of MOSFET Q1 and reduce the necessary capacitance of capacitor C1.

[0078] As an advantage of this embodiment, by suppressing the voltage drop of the capacitor supplying power to the drive circuit of the switching element for synchronous rectification during non-rectification, the required capacitance of the capacitor can be reduced.

[0079] As a result, reducing the size of capacitor C1 helps to miniaturize and reduce the cost of the rectifier circuit. Additionally, it enables the use of drive circuits and control ICs that consume significant power during the MOSFET's off-time.

[0080] Example 2

[0081] Reference Figure 3 The structure of the rectifier circuit and its control method in Embodiment 2 of the present invention will be described. Figure 3 This is a diagram showing the structure of the rectifier circuit in this embodiment.

[0082] like Figure 3 As shown, the rectifier circuit of this embodiment includes a resistor R1 connected between the source terminal and the gate terminal of MOSFET Q2 and a resistor R2 connected between the gate terminal of MOSFET Q2 and the source terminal of MOSFET Q1 as a control circuit 5 for MOSFET Q2. Resistors R1 and R2 are connected in series between the source terminal of MOSFET Q2 and the source terminal of MOSFET Q1.

[0083] In addition, compared with Example 1 ( Figure 1 Similarly, MOSFET Q1 and MOSFET Q2 use an n-channel enhancement-mode MOSFET and an n-channel depletion-mode MOSFET, respectively.

[0084] One terminal of resistor R1 is connected to the source terminal of MOSFET Q2, and the other terminal of resistor R1 is connected to the gate terminal of MOSFET Q2. Additionally, one terminal of resistor R2 is connected to the gate terminal of MOSFET Q2, and the other terminal of resistor R2 is connected to the source terminal of MOSFET Q1.

[0085] use Figure 2 This embodiment is described in detail. Figure 3 The operation of the rectifier circuit. Operations identical to those described in Example 1 are omitted as they are repetitive descriptions.

[0086] During the period from time t0 to time t1, the drain-source voltage Vds1 of MOSFET Q1 is applied to MOSFET Q2, resistor R1, and resistor R2. At time t0, the drain-source voltage Vds1 of MOSFET Q1 is 0, therefore the voltage applied to resistor R1, i.e., the gate-source voltage Vgs2 of MOSFET Q2, is 0. Since MOSFET Q2 is an n-channel depletion-mode MOSFET, the gate threshold voltage Vgth2 of MOSFET Q2 is negative, and MOSFET Q2 is in the on state.

[0087] Subsequently, as the drain-source voltage Vds1 of MOSFET Q1 increases, the current flowing from the drain terminal of MOSFET Q2 through the source terminal to resistor R1 increases. At this time, the voltage applied to resistor R1, i.e., the gate-source voltage Vgs2 of MOSFET Q2, decreases, thus increasing the on-resistance of MOSFET Q2 and reducing the current flowing through resistor R1. As a result, at time t1, the current flowing through resistor R1 reaches a certain value and no longer increases.

[0088] During the period from time t1 to time t2, the voltage generated between the sources of MOSFET Q2 and MOSFET Q1 is determined by the product of the current flowing through resistors R1 and R2 and the combined resistance of resistors R1 and R2. During this period, assuming Vgth2 is constant, the voltage generated between the sources of MOSFET Q2 and MOSFET Q1 is constant. When the resistance of resistor R1 is set to R1 and the resistance of resistor R2 is set to R2, its magnitude can be approximated as |Vgth2|×(R1+R2) / R1.

[0089] Therefore, during this period, the voltage Vc1 of capacitor C1 is fixed at |Vgth2|×(R1+R2) / R1-Vf. Thus, MOSFET Q2, resistor R1, resistor R2, and diode D are selected to make this value the desired target maximum voltage Vcref1 of capacitor C1.

[0090] During this period, the power stored in capacitor C1 is consumed as standby power for drive circuit 1, but at the same time, capacitor C1 is charged with the voltage of capacitor C1 fixed at the target maximum voltage Vcref1, thus suppressing the decrease in voltage of capacitor C1.

[0091] The period from time t3 to time t0 is the rectification period, during which the rectified current flows from the anode A to the cathode K. By selecting the resistances of resistors R1 and R2 such that their combined resistance is sufficiently greater than the on-resistance of MOSFET Q1, the rectified current flows through MOSFET Q1.

[0092] The drain-source voltage Vds1 of MOSFET Q1 is applied to MOSFET Q2, resistor R1, and resistor R2. At time t3, the drain-source voltage Vds1 of MOSFET Q1 is 0, therefore the voltage applied to resistor R1, i.e., the gate-source voltage Vgs2 of MOSFET Q2, is also 0. Because MOSFET Q2 is an n-channel depletion-mode MOSFET, MOSFET Q2 is in the on state.

[0093] In addition, the voltage detected by comparator Co is 0.

[0094] This embodiment ( Figure 3 The rectifier circuit of Example 1 is the same as that of Example 2. Figure 1 Similarly, MOSFET Q2 is always in the on state. By controlling the current flowing through MOSFET Q2, the voltage Vc1 of capacitor C1 is controlled to ensure that it does not exceed the target maximum voltage Vcref1. Furthermore, the voltage drop of capacitor C1 during the off period of MOSFET Q1 is suppressed.

[0095] As an advantage of this embodiment, since the control circuit 5 of MOSFET Q2 is constructed with fewer components, it can help reduce the cost of the rectifier circuit.

[0096] Example 3

[0097] Reference Figure 4 The structure of the rectifier circuit and its control method in Embodiment 3 of the present invention will be described. Figure 4 This is a diagram showing the structure of the rectifier circuit in this embodiment.

[0098] like Figure 4 As shown, the rectifier circuit of this embodiment has a resistor R3 inserted between the drain of MOSFET Q1 and the drain of MOSFET Q2.

[0099] In the rectifier circuits of Embodiments 1 and 2, when capacitor C1 is charged, the charging current of capacitor C1 flows through the path of the drain terminal of MOSFET Q1, MOSFET Q2, diode D, capacitor C1, and the source terminal of MOSFET Q1.

[0100] In particular, the charging current increases sharply after the charging of capacitor C1 has just begun. As a result, there are sometimes reduced rectifier circuit efficiency due to increased losses in the charging current path, and temperature rises exceeding the ratings of MOSFET Q2 or diode D.

[0101] Therefore, in the rectifier circuit of this embodiment, by inserting a resistor R3 in series in the charging current path, a sharp increase in the charging current of capacitor C1 is suppressed. That is, resistor R3 functions as a surge current preventer.

[0102] As an advantage of this embodiment, it can suppress the decrease in efficiency of the rectifier circuit and the temperature rise of MOSFET Q2 and diode D caused by the increase in losses in the charging current path.

[0103] Example 4

[0104] Reference Figure 5 The structure of the rectifier circuit and its control method in Embodiment 4 of the present invention will be described. Figure 5 This is a diagram showing the structure of the rectifier circuit in this embodiment.

[0105] like Figure 5 As shown, the rectifier circuit of this embodiment has a capacitor C2, the positive terminal of which is connected to the source terminal of MOSFET Q2, and the negative terminal is connected to the source terminal of MOSFET Q1.

[0106] In the rectifier circuits of Examples 1 to 3, comparator Co may malfunction due to high-frequency noise in the voltage detected by comparator Co. As a result, for example, MOSFET Q1 may be turned off during rectification, impairing the loss reduction effect based on synchronous rectification.

[0107] Therefore, in the rectifier circuit of this embodiment, a low-pass filter is formed by the on-resistance of MOSFET Q2, resistor R3 and capacitor C2, thereby suppressing high-frequency noise contained in the voltage detected by comparator Co.

[0108] Furthermore, even without inserting resistor R3, a low-pass filter can be formed by the on-resistance of MOSFET Q2 and capacitor C2, thus suppressing high-frequency noise contained in the voltage detected by comparator Co.

[0109] As an advantage of this embodiment, by suppressing malfunctions of the comparator Co and unexpected switching on and off of the MOSFET, the loss reduction effect based on synchronous rectification is not compromised.

[0110] Example 5

[0111] Reference Figure 3The structure of the rectifier circuit and its control method in Embodiment 5 of the present invention will be described. Figure 3 The structure of the rectifier circuit of this embodiment is shown together with Example 2.

[0112] Typically, the gate threshold voltage decreases as the temperature of the MOSFET rises. In the rectifier circuits shown in Examples 2 to 4, the target maximum voltage Vcref1 of capacitor C1 can be approximated as |Vgth2|×(R1+R2) / R1-Vf. Therefore, if the temperature of the rectifier circuit rises, the temperature of MOSFET Q2 rises, the gate threshold voltage Vgth2 (negative value) of MOSFET Q2 decreases while its absolute value |Vgth2| increases, and the target maximum voltage Vcref1 of capacitor C1 increases. As a result, the voltage Vc1 of capacitor C1 is greater than the maximum rated voltage of drive circuit 1 or the maximum rated gate-source voltage of MOSFET Q1, posing a problem of damage to drive circuit 1 or MOSFET Q1.

[0113] Therefore, in the rectifier circuit of this embodiment, in Figure 3 In the rectifier circuit shown, the configuration can be such that (R1+R2) / R1 decreases as the temperature rises. For example, resistor R1 can be a resistor with a positive temperature coefficient, and resistor R2 can be a resistor with a negative temperature coefficient.

[0114] In the rectifier circuit of this embodiment, when the temperature of the rectifier circuit rises, the absolute value of the gate threshold temperature of MOSFET Q2, |Vgth2|, increases due to the temperature rise of MOSFET Q2. However, the resistance value of resistor R1 increases due to the temperature rise of resistor R1, and the resistance value of resistor R2 decreases due to the temperature rise of resistor R2. Therefore, (R1+R2) / R1 decreases, which can suppress the increase of the target maximum voltage Vcref1 of capacitor C1.

[0115] As an advantage of this embodiment, it can suppress the increase in capacitor voltage caused by the temperature rise of the rectifier circuit, thus preventing damage to the rectifier circuit.

[0116] Alternatively, at least one of resistors R1 and R2 can be set as a variable resistor.

[0117] Example 6

[0118] Reference Figure 6 and Figure 7 The semiconductor package of Embodiment 6 of the present invention will be described.

[0119] Figure 6 The diagram shows a structure in which the rectifier circuit described in Examples 1 to 5 is integrated into a semiconductor package 3. The semiconductor package 3 has a cathode K and an anode A as external terminals.

[0120] Figure 7 This indicates a structure in which a bridge circuit, constructed using four rectifier circuits 2 as described in Examples 1 to 5, is integrated into a semiconductor package 4. The semiconductor package 4 has terminals T1 to T4 as external terminals.

[0121] exist Figure 6 and Figure 7 Example 2 is shown in the figure. Figure 3 The rectifier circuit described in the embodiment may be used, but other rectifier circuits may also be used.

[0122] As an advantage of this embodiment, when designing and manufacturing products that require the use of rectifier circuits, it is only necessary to purchase and assemble a rectifier circuit with built-in drive circuit and capacitors as in this embodiment, without having to assemble the control circuit into the design and manufacturing process. Therefore, it has the effect of reducing design and installation time.

[0123] Example 7

[0124] Reference Figure 8 The front-end power supply of Embodiment 7 of the present invention will be described.

[0125] Figure 8 Examples of power supplies that are the objects of application of the rectifier circuit of the present invention described in Examples 1 to 6 are shown.

[0126] The scope of this invention is applicable to all rectifier circuits used in power converters. For example, in Figure 8 The front-end power supply shown can be replaced with a rectifier circuit that uses commercial rectifier diodes CRD1 to CRD4, return diode FWD, secondary-side rectifier diodes SSD1 and SSD2, and anti-reverse diode BPD.

[0127] By applying the rectifier circuit of the present invention to power supplies such as front-end power supplies, it is possible to improve the power density of the power supply and reduce its cost.

[0128] Furthermore, the present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are examples that have been explained in detail for the purpose of easily understanding the present invention, and are not necessarily limited to having all the described structures. In addition, a part of the structure of one embodiment can be replaced with the structure of another embodiment, and it is also possible to add the structure of another embodiment to the structure of one embodiment. Furthermore, with respect to a part of the structure of each embodiment, other structures can be added, deleted, or replaced.

[0129] Explanation of reference numerals in the attached figures

[0130] 1… (MOSFET Q1) drive circuit, 2… rectifier circuit, 3, 4… semiconductor package, 5… (MOSFET Q2) control circuit, 6… first terminal (MOSFET Q1 drain terminal), 7… second terminal (MOSFET Q1 source terminal), 8… third terminal (MOSFET Q2 drain terminal), 9… fourth terminal (MOSFET Q2 source terminal), 10… fifth terminal (MOSFET Q1 gate terminal), 11… sixth terminal (MOSFET Q2 source terminal). Q2 gate terminal), 12… seventh terminal (one terminal of resistor R1), 13… eighth terminal (the other terminal of resistor R1), 14… ninth terminal (one terminal of resistor R2), 15… tenth terminal (the other terminal of resistor R2), T1~T4… terminals, K… cathode, A… anode, C1, C2… capacitors, R1, R2, R3… resistors, Q1, Q2… MOSFETs, D… diode, Co… comparator, GD… gate driver, t0~t3… time, Vcref1… target maximum voltage of capacitor C1 supplying power to drive circuit 1, Vcref2… target minimum voltage of capacitor C1 supplying power to drive circuit 1, Vf… forward voltage of diode D, Vds1, Vds2… drain-source voltage of MOSFETs Q1 and Q2, Vgs1, Vgs2… gate-source voltage of MOSFETs Q1 and Q2, Vgth1, Vgth2… MOSFETs Gate threshold voltages of Q1 and Q2, CRD1 to CRD4… commercial rectifier diodes, FWD… recirculation diodes, SSD1 and SSD2… secondary rectifier diodes, BPD… anti-reverse current diodes.

Claims

1. A rectifier circuit having an anode and a cathode, characterized in that, The rectifier circuit includes: A first switching element has a first terminal connected to the cathode of the rectifier circuit and a second terminal connected to the anode of the rectifier circuit; The first diode has its cathode connected to the first terminal and its anode connected to the second terminal; The second switching element has its third terminal connected to the first terminal; The anode of the second diode is connected to the fourth terminal of the second switching element; The positive terminal of the first capacitor is connected to the cathode of the second diode, and the negative terminal is connected to the second terminal. A comparator that detects the voltage between the fourth terminal and the second terminal and is powered by the first capacitor; A gate driver, whose input terminal is connected to the output terminal of the comparator, and whose output terminal is connected to the fifth terminal of the first switching element for controlling the first switching element, controls the first switching element according to the output signal of the comparator; as well as A control circuit, which is connected to the sixth terminal of the second switching element, which receives a signal that controls the second switching element. The control circuit keeps the second switching element in a conducting state at all times, and controls the current flowing from the third terminal to the fourth terminal of the second switching element by controlling the voltage between the sixth terminal and the fourth terminal of the second switching element, so that the voltage of the first capacitor does not exceed the specified target voltage.

2. The rectifier circuit according to claim 1, characterized in that, The first switching element is a first MOSFET whose drain terminal, source terminal, and gate terminal respectively correspond to the first terminal, second terminal, and fifth terminal of the first switching element. The first diode is the body diode of the first MOSFET.

3. The rectifier circuit according to claim 1, characterized in that, The second switching element is a second MOSFET whose drain terminal, source terminal, and gate terminal are respectively equivalent to the third terminal, the fourth terminal, and the sixth terminal of the second switching element.

4. The rectifier circuit according to claim 3, characterized in that, The second MOSFET is an n-channel depletion-mode MOSFET. The control circuit has: A first resistor, the seventh terminal of which is connected to the source terminal of the second MOSFET, and the eighth terminal of which is connected to the gate terminal of the second MOSFET; and The second resistor has its ninth terminal connected to the gate terminal of the second MOSFET and its tenth terminal connected to the second terminal.

5. The rectifier circuit according to claim 4, characterized in that, When the resistance value of the first resistor is set to R1 and the resistance value of the second resistor is set to R2, (R1+R2) / R1 decreases as the temperature rises.

6. The rectifier circuit according to claim 1, characterized in that, The rectifier circuit has a third resistor, one terminal of which is connected to the first terminal and the other terminal of which is connected to the third terminal.

7. The rectifier circuit according to claim 1, characterized in that, The rectifier circuit includes: a second capacitor, the positive terminal of which is connected to the fourth terminal, and the negative terminal of which is connected to the second terminal.

8. The rectifier circuit according to claim 1, characterized in that, The comparator has a first threshold and a second threshold. When the comparator detects that the voltage between the fourth terminal and the second terminal is less than the first threshold, it generates a turn-on signal for the first switching element. When the comparator detects that the voltage between the fourth terminal and the second terminal is greater than the second threshold, it generates a cut-off signal for the first switching element.

9. The rectifier circuit according to claim 1, characterized in that, The specified target voltage of the first capacitor is the lowest of the following maximum rated voltages: the maximum rated voltage of the comparator, the maximum rated voltage of the gate driver, and the maximum rated voltage between the fifth terminal and the second terminal of the first switching element.

10. The rectifier circuit according to claim 1, characterized in that, One or more of the aforementioned rectifier circuits are built into the same semiconductor package.

11. The rectifier circuit according to claim 4, characterized in that, At least one of the first resistor and the second resistor is a variable resistor.

12. A power supply, characterized in that, The power supply includes a rectifier circuit as described in any one of claims 1 to 11.

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