TWI871627B - Rectifier circuit and power supply using the same - Google Patents

Abstract

The present invention provides a rectifier circuit using a rectifier switching element, which can reduce the necessary capacitance of a capacitor for supplying power to a driving circuit for driving the rectifier switching element.

The present invention is a rectifier circuit 2 having an anode A and a cathode K, a rectifier switching element (MOSFET Q1), a diode (internal diode DQ1), a driving circuit 1 for driving the rectifier switching element (MOSFET Q1), and a capacitor C1 for supplying power to the driving circuit 1. The capacitor C1 has a first charging period and a second charging period during which the capacitor C1 is charged, and a charging stop period which is set between the first charging period and the second charging period and stops charging the capacitor C1.

Description

Rectifier circuit and power supply using the same

The present invention relates to a rectifier circuit and a power supply using the same.

As a rectifier circuit for rectifying AC to DC, there are known ones that use a diode or use a switching element such as MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) instead of a diode for synchronous rectification.

When using a diode for rectification, there are the following problems: the voltage drop caused by the built-in potential of the diode causes large losses. In contrast, synchronous rectification using MOSFET has the following advantages: since there is no built-in potential of the MOSFET and the forward current rises from 0V, the losses are lower. Therefore, especially for switching power supplies with strict efficiency regulations such as front-end power supplies, synchronous rectification using MOSFET is mainly used in order to perform rectification with lower losses.

As a rectifier circuit for realizing synchronous rectification, there are, for example, Patent Document 1 and Patent Document 2.

Generally speaking, a rectifier circuit for synchronous rectification has: a MOSFET as the first switching element for synchronous rectification, its driving circuit, a capacitor for supplying power to the driving circuit, a second switching element for controlling the voltage of the capacitor, and a control circuit for the second switching element. The driving circuit controls the on/off of the MOSFET based on a predetermined threshold voltage and the detected drain-source voltage of the MOSFET.

Figure 9 is a diagram showing the operating waveform of the previous rectifier circuit. In Figure 9, the vertical axis represents voltage or current, and the horizontal axis represents time t.

The capacitor that supplies power to the driving circuit is charged by a current flowing through the drain terminal of the MOSFET, the second switching element, the capacitor, and the source terminal of the MOSFET between time t1 and time t2 after the gate-source voltage Vgs1 of the MOSFET becomes 0 and the MOSFET is turned off at time t0. When the charging of the capacitor starts, the voltage Vc1 of the capacitor increases to follow the drain-source voltage Vds1 of the MOSFET.

In the rectifier circuit, when the capacitor voltage Vc1 reaches the target voltage Vcref1 at time t2, the second switch element inserted between the drain terminal of the MOSFET and the positive terminal of the capacitor is turned off, thereby blocking the charging current Ic of the capacitor. In this way, the capacitor voltage Vc1 is controlled to be below the target voltage Vcref1.

[Prior Art Literature] [Patent Literature]

[Patent document 1] Japanese Patent Publication No. 2001-251861

[Patent Document 2] U.S. Patent No. 10756645 Specification

Here, in the previous rectifier circuit, as shown in Figure 9, between time t2 and time t5, the power stored in the capacitor is consumed as standby power for the drive circuit, so the capacitor voltage Vc1 decreases. Furthermore, after the MOSFET is turned on from time t5, until the MOSFET is turned off again at the next time t0 and before the capacitor charging starts at time t1, the power stored in the capacitor is used to generate the consumption power of the drive circuit or the gate-source voltage of the MOSFET, so the capacitor voltage continues to decrease.

Therefore, the capacitor voltage Vc1 must be set to a lower limit value Vcref2 of the capacitor voltage, and the capacitor capacitance must be selected to meet this requirement, such as the action guarantee voltage of the drive circuit or the gate threshold voltage of the MOSFET, from the moment when the capacitor charging is completed to the next moment when the capacitor charging starts again at t1.

However, in the previous rectifier circuit, as mentioned above, since the capacitance of the capacitor that supplies power to the MOSFET driving circuit for synchronous rectification must be ensured, there is a limit in reducing the size of the capacitor, which hinders the miniaturization and cost reduction of the rectifier circuit.

The problem that the present invention aims to solve is to provide a rectifier circuit and a power source using the same. The rectifier circuit uses a switching element for rectification and can reduce the necessary capacitance of the capacitor for supplying power to the driving circuit for driving the switching element for rectification, thereby reducing the volume of the capacitor and achieving miniaturization and low cost.

In order to solve the above problem, the rectifier circuit of the present invention has an anode and a cathode, and is characterized by having: 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 driving circuit, which drives the first switching element Component; and a first capacitor, which supplies power to the above-mentioned drive circuit; and the above-mentioned first capacitor has: a first charging period and a second charging period in which the above-mentioned first capacitor is charged; and a charging stop period set between the above-mentioned first charging period and the above-mentioned second charging period and stopping the charging of the above-mentioned first capacitor during the period from the above-mentioned first switching element being disconnected to the next time it is connected.

Furthermore, the power supply of the present invention is characterized in that, for example, it has the above-mentioned rectifier circuit.

According to the rectifier circuit and power supply of the present invention, the capacitor can be charged twice, in the first charging period and the second charging period, and at least a portion of the discharged power during the charging stop period after the first charging period can be replenished in the second charging period, so the necessary capacitance of the capacitor can be reduced. As a result, the volume of the capacitor can be reduced to achieve miniaturization and cost reduction of the rectifier circuit and power supply.

1: Driving circuit

2: Rectifier circuit

3:Semiconductor packaging

4:Semiconductor packaging

A: Anode

BPD: Backflow prevention diode

C1: Capacitor

C2: Capacitor

Co1: Comparator

Co2: Comparator

CRD1~CRD4: Commercial rectifier diodes

CTR: Control circuit

D:Diode

DQ1: Internal diode

DQ2: Internal diode

FWD: Reflux Diode

GD1: Gate driver

GD2: Gate driver

Ic: Charging current

K: cathode

Q1: MOSFET

Q2: MOSFET

R1: resistor

R2: resistor

R3: resistor

SSD1~SSD2: Secondary side rectifier diode

t: time

t0~t5: time

T1~T4: Terminals

Vc1: Capacitor voltage

Vcref1: Target voltage of capacitor C1

Vcref2: The lower voltage limit of capacitor C1

Vds1: Drain-source voltage of MOSFET Q1

Vds2: Drain-source voltage of MOSFET Q2

Vf: forward voltage of diode D

Vgs1: Gate-source voltage of MOSFET Q1

Vgs2: Gate-source voltage of MOSFET Q2

Vgth1: Gate threshold voltage of MOSFET Q1

Vgth2: Gate threshold voltage of MOSFET Q2

Vref1: Threshold voltage

Vref2: Threshold voltage

Figure 1 is a circuit diagram of the rectifier circuit of Example 1.

Figure 2 is a diagram showing the operating waveform of the rectifier circuit of Example 1.

Figure 3 is a circuit diagram of the rectifier circuit of Example 2.

Figure 4 is a circuit diagram of the rectifier circuit of Example 3.

Figure 5 is a circuit diagram of the rectifier circuit of Example 4.

FIG6 is a diagram showing an example of the configuration of the rectifier circuit of Example 5.

FIG. 7 is a diagram showing another example of the configuration of the rectifier circuit of Example 5.

Figure 8 is a circuit diagram of the power supply of Example 6.

Figure 9 shows the operation waveform of the previous rectifier circuit.

The following uses drawings to illustrate the embodiments of the present invention. In each drawing and each embodiment, the same or similar components are marked with the same symbols, and repeated descriptions are omitted.

[Implementation Example 1]

First, the basic principle of Example 1 is explained.

Figure 1 is a circuit diagram of the rectifier circuit of Example 1.

As shown in FIG1 , the rectifier circuit 2 of the embodiment 1 has an anode A, a cathode K, a MOSFET Q1 as a first switching element for rectification, an internal diode DQ1 of the MOSFET Q1, a driving circuit 1 for driving the MOSFET Q1, and a capacitor C1 for supplying power to the driving circuit 1. Furthermore, the rectifier circuit 2 of the embodiment 1 has: a MOSFET Q2 as a second switching element for controlling the voltage Vc1 of the capacitor C1, an internal diode DQ2 of the MOSFET Q2, a control circuit CTR for controlling the MOSFET Q2, and a diode D. The driving circuit 1 has a comparator Co1 and a gate driver GD1.

FIG1 shows that an n-channel enhancement MOSFET is used as MOSFET Q1 and an n-channel depletion MOSFET is used as MOSFET Q2, but the present invention is not limited thereto and other switching elements may be used. In addition, regarding the internal diode DQ1 and the internal diode DQ2, the internal diodes are not limited to the internal diodes built into the MOSFET and other diodes such as externally mounted diodes may be used.

MOSFET Q1 has a gate terminal as a control terminal, a drain terminal as a main terminal, and a source terminal as another main terminal. MOSFET Q1 is a switching element for rectification, the drain terminal is connected to the cathode K of the rectification circuit 2, the source terminal is connected to the anode A of the rectification circuit 2, and the gate terminal is connected to the driving circuit 1.

The cathode of the internal diode DQ1 is connected to the drain terminal of the MOSFET Q1, and the anode is connected to the source terminal of the MOSFET Q1.

Figure 2 is a diagram showing the operating waveform of the rectifier circuit of Example 1.

FIG2 is a diagram corresponding to FIG9, and is an operation waveform when a resistive load is connected to a bridge circuit formed by using four rectifier circuits 2 shown in FIG1, and a sine wave voltage is input. In FIG2, the vertical axis represents the drain-source voltage Vds1 of MOSFET Q1, the gate-source voltage Vgs1 of MOSFET Q1, the charging current Ic of capacitor C1, and the voltage Vc1 of capacitor C1, and the horizontal axis represents the time t. In addition, Vgth1 is the gate threshold voltage of MOSFET Q1. Furthermore, regarding the drain-source voltage Vds2 of MOSFET Q2, the gate-source voltage Vgs2 of MOSFET Q2, and the gate threshold voltage Vgth2 of MOSFET Q2, the illustration and detailed description are omitted.

As shown in FIG2 , in the rectifier circuit 2 of the embodiment 1, the capacitor C1 that supplies power to the driving circuit 1 has: a first charging period (from moment t1 to moment t2) and a second charging period (from moment t3 to moment t4) in which the first capacitor C1 is charged; and a charging stop period (from moment t2 to moment t3) in which the charging of the capacitor C1 is stopped, after the MOSFET Q1 is turned off at moment t0 and then turned on at moment t5; in this respect, it is different from the action waveform of the previous FIG9 .

In the previous FIG. 9, the charging period of the capacitor is only from time t1 to time t2. After that, the capacitance of the capacitor must be selected so that the voltage Vc1 of the capacitor can be maintained above the voltage lower limit Vcref2 until the next charging period, i.e., time t1. In contrast, according to the rectifier circuit 2 of the embodiment 1, the capacitor C1 can be charged twice, i.e., the first charging period and the second charging period, and at least a part of the discharged voltage during the charging stop period after the first charging period is replenished during the second charging period. Therefore, the necessary capacitance of the capacitor C1 can be reduced. As a result, the volume of the capacitor C1 can be reduced, thereby realizing the miniaturization and cost reduction of the rectifier circuit 2 and the power supply using the same. In addition, a driver circuit or control IC that consumes more power during the MOSFET's off period can be used.

In FIG. 2 , as an example, the first charging period and the second charging period are periods when the drain-source voltage Vds1 of the MOSFET Q1 is less than the predetermined threshold voltage Vref1, and the charging stop period is a period when the drain-source voltage Vds1 of the MOSFET Q1 is greater than the predetermined threshold voltage Vref1. Thus, the first charging period is a period when the drain-source voltage Vds1 of the MOSFET Q1 is increasing, and the second charging period is a period when the drain-source voltage Vds1 of the MOSFET Q1 is decreasing. In Figure 2, the threshold voltage Vref1 is set to the sum of the target voltage Vcref1 of capacitor C1 and the forward voltage Vf of diode D.

When the capacitor C1 is charged during the period when the drain-source voltage Vds1 of the MOSFET Q1 is large, the drain-source voltage Vds2 of the MOSFET Q2 located in the middle of the path also increases, and the loss (Vds2×Ic) generated by the MOSFET Q2 also increases. Therefore, in the rectifier circuit 2 of the embodiment 1, the period when the drain-source voltage Vds1 of the MOSFET Q1 is greater than the specified threshold voltage Vref1 is set as the charging stop period to suppress the generation of loss and improve the charging efficiency. Furthermore, since the second charging period is the period when the drain-source voltage Vds1 of MOSFET Q1 is decreasing, it can be shortened to the period until the next first charging period, which can effectively reduce the required capacitance of capacitor C1.

Next, the detailed structure and operation of Example 1 are described using Figures 1 and 2.

MOSFET Q2 has: a gate terminal as a control terminal, a drain terminal as a main terminal, and a source terminal as another main terminal. MOSFET Q2 is a switching element for controlling the voltage Vc1 of capacitor C1. The drain terminal is connected to the drain terminal of MOSFET Q1, the source terminal is connected to capacitor C1 via diode D, and the gate terminal is connected to the control circuit CTR.

The cathode of the internal diode DQ2 is connected to the drain terminal of MOSFET Q2, and the anode is connected to the source terminal of MOSFET Q2.

The anode of diode D is connected to the source terminal of MOSFET Q2, and the cathode is connected to the positive terminal of capacitor C1.

The positive terminal of capacitor C1 is connected to the cathode of diode D, and the negative terminal is connected to the source terminal of MOSFET Q1.

The driver circuit 1 has: a comparator Co1, which is supplied with power by a capacitor C1 and detects the voltage between the source terminal of the MOSFET Q2 and the source terminal of the MOSFET Q1; and a gate driver GD1, whose input terminal is connected to the output terminal of the comparator Co1 and whose output terminal is connected to the gate terminal of the MOSFET Q1, which is supplied with power by the capacitor C1 and controls the MOSFET Q1 based on the output signal of the comparator Co1.

The control circuit CTR inputs a signal for controlling MOSFET Q2 to the control terminal of MOSFET Q2. Furthermore, the control circuit CTR controls MOSFET Q2 to be turned on when the drain-source voltage Vds1 of MOSFET Q1 is less than the total voltage (threshold voltage Vref1) of the target voltage Vcref1 of capacitor C1 and the forward voltage Vf of diode D, and controls MOSFET Q2 to be turned off when the drain-source voltage Vds1 of MOSFET Q1 is greater than the total voltage (threshold voltage Vref1) of the target voltage Vcref1 of capacitor C1 and the forward voltage Vf of diode D, thereby controlling the charging current Ic flowing to capacitor C1.

Here, the target voltage Vcref1 of capacitor C1 is set to be sufficiently greater than the gate threshold voltage Vgth1 of MOSFET Q1 so that the driver circuit 1 can drive MOSFET Q1. In addition, the target voltage Vcref1 of capacitor C1 is set to be less than the minimum of the maximum rated voltage of comparator Co1, the maximum rated voltage of gate driver GD1, and the maximum rated voltage of gate-source voltage Vgs1 of MOSFET Q1. In this way, damage to the driver circuit 1 or MOSFET Q1 can be prevented.

Furthermore, the control circuit CTR can also be configured to have a differential circuit for determining the timing of controlling the MOSFET Q2. For example, the charging timing can be determined based on the slope of the drain-source voltage Vds1 of the MOSFET Q1.

As an example, in FIG. 2 , by detecting that the slope of the drain-source voltage Vds1 of the MOSFET Q1 is within a specified range, for example, a period when the slope is larger than the slope at time t3 and smaller than the slope at time t2, it is possible to detect that the period is a period when the drain-source voltage Vds1 of the MOSFET Q1 is larger than the threshold voltage Vref1 (from time t2 to time t3), and the MOSFET Q2 can be controlled based on this. Furthermore, without limitation to this, the slope of the drain-source voltage Vds1 of the MOSFET Q1 can be detected to be within a specified range, such as a specified range corresponding to the slope from time t0 to time t2 or from time t1 to time t2, or a specified range corresponding to the slope from time t3 to time t5 or from time t3 to time t4, and the period can be detected to be the first charging period or the second charging period, and the MOSFET Q2 can be controlled based on this.

As another example, control can also be performed in the following manner, that is, the magnitude of the drain-source voltage Vds1 of the MOSFET Q1 is detected, and its slope is also detected by a differential circuit. When the drain-source voltage Vds1 of the MOSFET Q1 is below the threshold voltage Vref1 and its slope is within a range of a prescribed slope that is not too steep, the capacitor C1 is charged. For example, when the drain-source voltage Vds1 of the MOSFET Q1 is not a complete sine wave but is mixed with noise, it may be lower than the threshold voltage Vref1 for only a moment and immediately return to its original state. In this case, if the slope is not considered, the MOSFET Q2 will be turned off immediately after it is turned on, resulting in loss. In this case, the slope is steeper than usual, so by using a differential circuit to detect the slope and use it for control, it is possible to prevent false actions caused by noise.

Next, the operation of the rectifier circuit 2 of Embodiment 1 is explained based on FIG. 2 .

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

The period from time t0 to time t1 is a non-rectification period, and MOSFET Q1 is turned off. Also, as the sine wave voltage input to the bridge circuit increases, the drain-source voltage Vds1 of MOSFET Q1 increases. Also, during this period, the drain-source voltage Vds1 of MOSFET Q1 is less than the threshold voltage Vref1, so the control circuit CTR controls MOSFET Q2 to be turned on. At this time, although the drain-source voltage Vds1 of MOSFET Q1 is less than the voltage Vc1 of capacitor C1, the diode D prevents the current from the positive terminal of capacitor C1 from flowing back to the drain terminal of MOSFET Q1.

During the period from time t1 to time t2, the drain-source voltage Vds1 of MOSFET Q1 is less than the threshold voltage Vref1, so the control circuit CTR then controls MOSFET Q2 to be turned on. In addition, 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. As a result, charging of capacitor C1 starts, and the voltage Vc1 of capacitor C1 increases. The charging current Ic 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.

At time t2, the drain-source voltage Vds1 of MOSFET Q1 is equal to the threshold voltage Vref1.

During the period from time t2 to time t3, the drain-source voltage Vds1 of MOSFET Q1 is greater than the threshold voltage Vref1, so the control circuit CTR controls MOSFET Q2 to be disconnected, thereby becoming a charging stop period. As a result, the charging current Ic of capacitor C1 is blocked. During this period, the power stored in capacitor C1 is consumed as standby power for driving circuit 1, and capacitor C1 is not charged, so the capacitor voltage Vc1 decreases. In addition, during this period, the sine wave voltage input to the bridge circuit increases in the first half and decreases in the second half. Along with this, the drain-source voltage Vds1 of MOSFET Q1 also increases in the first half and decreases in the second half.

At time t3, the drain-source voltage Vds1 of MOSFET Q1 is equal to the threshold voltage Vref1.

During the period from time t3 to time t4, the drain-source voltage Vds1 of MOSFET Q1 is less than the threshold voltage Vref1, so the control circuit CTR controls MOSFET Q2 to be turned on. In addition, during the period from time t2 to time t3, the voltage Vc1 of capacitor C1 decreases, so 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. As a result, the charging current Ic 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, and the voltage Vc1 of capacitor C1 increases. The capacitor C1 is also charged during this period, which is different from the previous Figure 9.

The moment t4 is the moment when the sum of the voltage of MOSFET Q1, the voltage Vc1 of capacitor C1, and the forward voltage Vf of diode D are not equal.

During the period from time t4 to time t5, the drain-source voltage Vds1 of MOSFET Q1 is less than the threshold voltage Vref1, so the control circuit CTR then controls MOSFET Q2 to be turned on. At this time, the diode D prevents the charge from flowing from the positive terminal of the capacitor C1 to the drain terminal of the MOSFET Q1.

Finally, during the period from moment t5 to moment t0, it becomes a rectification period again, and the driving circuit 1 turns on MOSFET Q1, and the rectified current flows from the anode A to the cathode K.

Here, the operation of the driver circuit 1 and the control method of the MOSFET Q1 are explained.

The comparator Co1 of the driver circuit 1 detects the drain-source voltage Vds1 of the MOSFET Q1 from the source terminal of the MOSFET Q2 and the source terminal of the MOSFET Q1. Based on the detected voltage, the driver circuit 1 turns the MOSFET Q1 on and off.

The rectified current flowing from anode A to cathode K first flows through the internal diode DQ1 of MOSFET Q1. Due to the voltage drop of the internal diode DQ1, the drain-source voltage Vds1 of MOSFET Q1 becomes negative.

When the voltage detected by comparator Co1 is less than the first threshold voltage of comparator Co1, comparator Co1 outputs a connection signal, and gate driver GD1 pulls up the gate-source voltage Vgs1 of MOSFET Q1 to the voltage Vc1 of capacitor C1, thereby turning on MOSFET Q1.

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

As time goes by, the rectified current decreases. As the rectified current decreases, the drain-source voltage Vds1 of MOSFET Q1 increases. When the voltage detected by comparator Co1 is greater than the second threshold voltage of comparator Co1, comparator Co1 outputs a disconnection signal, and gate driver GD1 pulls down the gate-source voltage Vgs1 of MOSFET Q1 to 0V, thereby turning off MOSFET Q1.

The first threshold voltage and the second threshold voltage of the comparator Co1 can be the same value, or the first threshold voltage can be smaller than the second threshold voltage. When the first threshold voltage is smaller than the second threshold voltage, the vibration of the MOSFET repeatedly turning on and off in a short period of time can be suppressed.

Let’s go back to the description of Figure 2.

During the period from time t5 to time t0, the drain-source voltage Vds1 of MOSFET Q1 is less than the threshold voltage Vref1, so the control circuit CTR then controls MOSFET Q2 to be turned on. 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 drain-source voltage Vds1 of MOSFET Q1 is less than the voltage Vc1 of capacitor C1, but diode D prevents the current from flowing back from the positive terminal of capacitor C1 to the drain terminal of MOSFET Q1.

As a result, during this period, the power stored in capacitor C1 is used to generate the power consumption of driving circuit 1 and the gate-source voltage Vgs1 of MOSFET Q1, so the voltage Vc1 of capacitor C1 decreases.

By repeatedly performing the above control, the rectifier circuit 2 of Example 1 realizes synchronous rectification.

In the above control, capacitor C1 is not charged during the period from moment t2 to moment t3 and from moment t4 to the next moment t1, so the voltage Vc1 of capacitor C1 decreases. The capacitance of capacitor C1 must be selected so that the minimum value of the voltage Vc1 of capacitor C1 in any period is greater than the lower limit value Vcref2 of the voltage of capacitor C1. The lower limit value Vcref2 of the voltage of capacitor C1 is, for example, a value greater than the minimum operating voltage of the drive circuit 1 and greater than the gate threshold voltage Vgth1 of MOSFET Q1 when the on-resistance of MOSFET Q1 is sufficiently small.

As described above, according to the rectifier circuit 2 of embodiment 1, the necessary capacitance of the capacitor C1 can be reduced, and as a result, the volume of the capacitor C1 can be reduced to achieve miniaturization and low cost of the rectifier circuit 2 and the power supply.

[Example 2]

Figure 3 is a circuit diagram of the rectifier circuit of Example 2.

Embodiment 2 is a variation of Embodiment 1. Embodiment 2 shows an example of a specific structure of the control circuit CTR, which is different from Embodiment 1. The effects of other structures are basically the same as those of Embodiment 1. Therefore, in Embodiment 2, the explanation is centered on the differences from Embodiment 1, and the explanations repeated in Embodiment 1 are omitted.

The control circuit CTR of the rectifier circuit 2 of the embodiment 2 has: resistors R1 and R2, which divide the drain-source voltage Vds1 of the MOSFET Q1; a comparator Co2, which is supplied with power by the capacitor C1 and detects the voltage of the resistor R2; and a gate driver GD2, whose input terminal is connected to the output terminal of the comparator Co2, whose output terminal is connected to the gate terminal of the MOSFET Q2, and which is supplied with power by the capacitor C1 and controls the MOSFET Q2 based on the output signal of the comparator Co2.

Here, resistors R1 and R2 are set so that the voltage of resistor R2 is lower than the rated voltage of comparator Co2. Comparator Co2 compares the detected voltage of resistor R2 with the threshold voltage Vref2 and outputs the signal to gate driver GD2. At this time, when the drain-source voltage Vds1 of MOSFET Q1 is not equal to the threshold voltage Vref1, the threshold voltage Vref2 is selected so that the voltage of resistor R2 is equal to the threshold voltage Vref2.

According to the rectifier circuit 2 of embodiment 2, the action described in FIG. 2 of embodiment 1 can be realized.

[Implementation Example 3]

Figure 4 is a circuit diagram of the rectifier circuit of Example 3.

Embodiment 3 is a variation of Embodiment 1. Embodiment 3 has a resistor R3, which is different from Embodiment 1. The effects of other components are basically the same as those of Embodiment 1. Therefore, in Embodiment 3, the explanation is centered on the differences from Embodiment 1, and the explanations repeated with Embodiment 1 are omitted. Furthermore, Embodiment 3 can also be applied to Embodiment 2.

The rectifier circuit 2 of Embodiment 3 has a resistor R3 having one terminal connected to the drain terminal of MOSFET Q1 and the other terminal connected to the drain terminal of MOSFET Q2. In other words, the resistor R3 is inserted between the drain terminal of MOSFET Q1 and the drain terminal of MOSFET Q2.

In the rectifier circuit 2 of Examples 1 to 2, when the capacitor C1 is charged, the charging current Ic of the capacitor C1 flows in the path of the drain terminal of the MOSFET Q1, the MOSFET Q2, the diode D, the capacitor C1, and the source terminal of the MOSFET Q1. In particular, the charging current Ic increases rapidly after the charging of the capacitor C1 begins. As a result, the efficiency of the rectifier circuit 2 may decrease due to the increase in the loss in the path of the charging current Ic, or the temperature may rise beyond the rated temperature of the MOSFET Q2 or the diode D.

According to the rectifier circuit 2 of the embodiment 3, by inserting the resistor R3 in series in the path of the charging current Ic, the rapid increase of the charging current Ic of the capacitor C1 can be suppressed. That is, the resistor R3 functions as a surge current prevention resistor. In this way, the efficiency reduction of the rectifier circuit 2 caused by the increase of the loss in the path of the charging current Ic and the temperature increase of the MOSFET Q2 or the diode D can be suppressed.

[Implementation Example 4]

Figure 5 is a circuit diagram of the rectifier circuit of Example 4.

Embodiment 4 is a variation of Embodiment 3. Embodiment 4 has a capacitor C2, which is different from Embodiment 3. The other structures and effects are basically the same as those of Embodiment 3. Therefore, in Embodiment 4, the explanation is centered on the differences from Embodiment 3, and the explanations repeated with Embodiment 3 are omitted. Furthermore, Embodiment 4 can also be applied to Embodiments 1 to 2.

The rectifier circuit 2 of Embodiment 4 has a capacitor C2 whose positive terminal is connected to the source terminal of MOSFET Q2 and whose negative terminal is connected to the source terminal of MOSFET Q1.

In the rectifier circuits of Examples 1 to 3, there is a situation where the comparator Co1 malfunctions due to the high-frequency noise contained in the voltage detected by the comparator Co1. As a result, for example, the MOSFET Q1 is turned off during the rectification period, which reduces the loss caused by the synchronous rectification.

According to the rectifier circuit 2 of Embodiment 4, by using the on-resistance of MOSFET Q2, resistor R3, and capacitor C2 to form a low-pass filter, the high-frequency noise contained in the voltage detected by the comparator Co1 can be suppressed. Furthermore, even when the resistor R3 is not inserted, the high-frequency noise contained in the voltage detected by the comparator Co1 can be suppressed by using the on-resistance of MOSFET Q2 and capacitor C2 to form a low-pass filter. In this way, the malfunction of the comparator Co1 and the unexpected conduction and shutdown of the MOSFET Q1 can be suppressed without affecting the loss reduction effect caused by synchronous rectification.

[Implementation Example 5]

FIG. 6 is a diagram showing an example of the configuration of the rectifier circuit of Example 5. FIG. 7 is a diagram showing another example of the configuration of the rectifier circuit of Example 5.

Embodiment 5 is a variation of Embodiment 1. Embodiment 5 places the rectifier circuit 2 inside the semiconductor package, which is different from Embodiment 1. The effects of other components are basically the same as those of Embodiment 1. Therefore, in Embodiment 5, the explanation is centered on the differences from Embodiment 1, and the explanations repeated with Embodiment 1 are omitted. Furthermore, in FIG. 6 and FIG. 7 of Embodiment 5, the explanation is based on FIG. 1 applied to Embodiment 1, but it can also be applied to various variations described in Embodiment 1, or Embodiments 2 to 4.

FIG6 shows a structure in which the rectifier circuit 2 is built into the semiconductor package 3. The semiconductor package 3 has a cathode K and an anode A as external terminals.

FIG. 7 shows a structure in which a plurality of rectifier circuits 2, such as a bridge circuit formed by using four rectifier circuits 2, are built into a semiconductor package 4. The semiconductor package 4 has terminals T1 to T4 as external terminals.

According to Example 5, when designing and manufacturing products using rectifier circuits, it is sufficient to purchase and assemble rectifier circuits with built-in drive circuits and capacitors as in this example, thereby eliminating the steps of designing and installing the drive circuits and capacitors, thereby having the effect of reducing the number of overall design and installation steps.

[Implementation Example 6]

Figure 8 is a circuit diagram of the power supply of Example 6.

Embodiment 6 is an embodiment of a power source as an application object of the rectifier circuit 2 described in Embodiments 1 to 5.

The application scope of the rectifier circuit 2 of Examples 1 to 5 is all rectifier circuits used in power supplies. For example, in the front-end power supply shown in FIG8 , the rectifier circuit 2 of Examples 1 to 5 can be used as commercial rectifier diodes CRD1 to CRD4, return diodes FWD, secondary side rectifier diodes SSD1 to SSD2, and backflow prevention diodes BPD.

By applying the rectifier circuit 2 of Examples 1 to 5 to a power source such as a front-end power source, it can help to miniaturize the power source and reduce costs.

The above describes the embodiments of the present invention, but the present invention is not limited to the structures described in the embodiments, and various changes can be made within the technical scope of the present invention. In addition, part or all of the structures described in each embodiment can also be combined and applied.

Ic: Charging current

t: time

t0~t5: time

Vc1: Capacitor voltage

Vcref1: Target voltage of capacitor C1

Vcref2: The lower voltage limit of capacitor C1

Vds1: Drain-source voltage of MOSFET Q1

Vf: forward voltage of diode D

Vgs1: Gate-source voltage of MOSFET Q1

Vgth1: Gate threshold voltage of MOSFET Q1

Vref1: Threshold voltage

Claims (16)

A rectifier circuit having an anode and a cathode, characterized by comprising: 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 driving circuit, which drives the first switching element; and a first capacitor, which supplies power to the driving circuit; and The first capacitor has a first charging period and a second charging period during which the first capacitor is charged, and a charging stop period which is set between the first charging period and the second charging period and stops charging the first capacitor, during the period from when the first switching element is turned off to when the first switching element is turned on next. The rectifier circuit of claim 1, wherein the first charging period and the second charging period are periods during which the voltage between the first terminal and the second terminal of the first switching element is below a specified voltage, and the charging stop period is a period during which the voltage between the first terminal and the second terminal of the first switching element is greater than the specified voltage. The rectifier circuit of claim 2, wherein the first charging period is a period during which the voltage between the first terminal and the second terminal of the first switching element is increasing, and the second charging period is a period during which the voltage between the first terminal and the second terminal of the first switching element is decreasing. The rectifier circuit of claim 2 comprises: a second switching element, whose third terminal is connected to the first terminal of the first switching element; a second diode, whose anode is connected to the fourth terminal of the second switching element and whose cathode is connected to the third terminal of the second switching element; a third diode, whose anode is connected to the fourth terminal of the second switching element; the first capacitor, whose positive terminal is connected to the cathode of the third diode and whose negative terminal is connected to the second terminal of the first switching element; and a control circuit, which inputs a signal for controlling the second switching element to the control terminal of the second switching element; and The driving circuit comprises: a first comparator, which is supplied with power by the first capacitor and detects the voltage between the fourth terminal of the second switching element and the second terminal of the first switching element; and a first gate driver, whose input terminal is connected to the output terminal of the first comparator, whose output terminal is connected to the control terminal of the first switching element, and which is supplied with power by the first capacitor and controls the first switching element based on the output signal of the first comparator; The control circuit controls the second switching element to be in the on state when the voltage between the first terminal and the second terminal of the first switching element is less than the total voltage of the target voltage of the first capacitor and the forward voltage of the third diode; and controls the second switching element to be in the off state when the voltage between the first terminal and the second terminal of the first switching element is greater than the total voltage of the target voltage of the first capacitor and the forward voltage of the diode, thereby controlling the charging current flowing into the first capacitor. The rectifier circuit of claim 4, wherein the first switching element is a first MOSFET in which the first terminal is a drain terminal, the second terminal is a source terminal, and the control terminal is a gate terminal, and the first diode is an internal diode of the first MOSFET. The rectifier circuit of claim 4, wherein the second switching element is a second MOSFET in which the third terminal is a drain terminal, the fourth terminal is a source terminal, and the control terminal is a gate terminal. As in the rectifier circuit of claim 6, wherein the second MOSFET is an n-channel depletion MOSFET. A rectifier circuit as claimed in claim 4, wherein the target voltage of the first capacitor is less than the minimum of the maximum rated voltage of the first comparator, the maximum rated voltage of the first gate driver, and the maximum rated voltage between the control terminal and the second terminal of the first switching element. A rectifier circuit as claimed in claim 4, wherein the control circuit has a differential circuit, which is used to determine the timing of controlling the second switching element. The rectifier circuit of claim 4, wherein the first comparator has a first threshold voltage and a second threshold voltage, and generates a connection signal when the voltage detected between the fourth terminal of the second switching element and the second terminal of the first switching element is less than the first threshold voltage, and generates a disconnection signal when the voltage is greater than the second threshold voltage, and the first threshold voltage is less than the second threshold voltage. A rectifier circuit as claimed in claim 4, wherein the control circuit comprises: a first resistor and a second resistor, which divide the voltage between the first terminal and the second terminal of the first switching element; a second comparator, which is supplied with power by the first capacitor and detects the voltage of the second resistor; and a second gate driver, whose input terminal is connected to the output terminal of the second comparator, whose output terminal is connected to the control terminal of the second switching element, which is supplied with power by the first capacitor and controls the second switching element based on the output signal of the second comparator. The rectifier circuit of claim 4 has a third resistor, the fifth terminal of the third resistor is connected to the first terminal of the first switching element, and the sixth terminal is connected to the third terminal of the second switching element. The rectifier circuit of claim 4 has a second capacitor, the positive terminal of the second capacitor is connected to the fourth terminal of the second switching element, and the negative terminal is connected to the second terminal of the first switching element. A rectifier circuit as claimed in any one of claims 1 to 13, wherein the rectifier circuit is built into a semiconductor package, and the anode and cathode of the rectifier circuit are external terminals of the semiconductor package. A rectifier circuit as claimed in any one of claims 1 to 13, wherein a plurality of the rectifier circuits are built into a semiconductor package. A power supply having a rectifier circuit as described in any one of claims 1 to 13.