CN108809097B - Synchronous rectifier applied to power converter and operation method thereof - Google Patents

Synchronous rectifier applied to power converter and operation method thereof Download PDF

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Publication number
CN108809097B
CN108809097B CN201710302246.8A CN201710302246A CN108809097B CN 108809097 B CN108809097 B CN 108809097B CN 201710302246 A CN201710302246 A CN 201710302246A CN 108809097 B CN108809097 B CN 108809097B
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control signal
attenuation
signal corresponding
current period
secondary side
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CN108809097A (en
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林崇伟
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Leadtrend Technology Corp
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Leadtrend Technology Corp
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
    • H02M7/2195—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration the switches being synchronously commutated at the same frequency of the AC input voltage
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention discloses a synchronous rectifier applied to a power converter and an operation method thereof. The operation method comprises the steps that when the secondary side of the power converter is started, a control signal generating circuit in the synchronous rectifier generates a control signal corresponding to a previous period according to a detection voltage corresponding to the previous period of the secondary side, a first reference voltage and a second reference voltage; the pre-attenuation circuit in the synchronous rectifier pre-attenuates the grid control signal corresponding to the current period of the secondary side and generates a pre-attenuation signal corresponding to the current period according to the discharge time corresponding to the previous period of the secondary side. Therefore, when the load coupled to the secondary side is light load, the synchronous rectifier does not pre-attenuate the gate control signal corresponding to the current period in advance, and when the load is very heavy load, the gate control signal corresponding to the current period is not directly turned off.

Description

Synchronous rectifier applied to power converter and operation method thereof
Technical Field
The present invention relates to a synchronous rectifier applied to a power converter and an operating method thereof, and more particularly, to a synchronous rectifier and an operating method thereof, which pre-attenuate a gate control signal corresponding to a current period of a secondary side of the power converter according to a discharge time corresponding to a previous period of the secondary side of the power converter.
Background
As shown in fig. 1, in a Continuous Conduction Mode (CCM) of the power converter 100, the synchronous rectifier 200 applied to the secondary side SEC of the power converter 100 generates the gate control signal GCS for controlling the synchronous switch 102 according to a detection voltage VDET (i.e. a source voltage of the synchronous switch 102) of the secondary side SEC of the power converter 100 when the secondary side SEC of the power converter 100 is turned on, wherein in the continuous conduction mode of the power converter 100, the prior art uses the synchronous rectifier 200 to rapidly turn off the gate control signal GCS according to the detection voltage VDET to prevent the primary side PRI of the power converter 100 and the secondary side SEC of the power converter 100 from being turned on simultaneously.
As shown in fig. 2, when the secondary side SEC of the power converter 100 is turned on, the detection voltage VDET gradually increases from the minimum value VMIM (about-0.7V). Therefore, at a time T1, the synchronous rectifier 200 pre-attenuates the gate control signal GCS when the detection voltage VDET increases to a first reference voltage VREF1 (about-50 mV), and then at a time T2, the synchronous rectifier 200 fully turns off the gate control signal GCS when the detection voltage VDET increases to a second reference voltage VREF2 (about-10 mV).
However, when the load 104 coupled to the secondary side SEC of the power converter 100 is very heavy, the synchronous rectifier 200 does not pre-attenuate the gate control signal GCS because the detection voltage VDET may not increase to the first reference voltage VREF1, so that the synchronous rectifier 200 must directly turn off the gate control signal GCS. In addition, when the load 104 coupled to the secondary side SEC of the power converter 100 is a light load, the synchronous switch 102 operates in a triode region (trio region) most of the time because the detection voltage VDET may quickly increase to the first reference voltage VREF1, resulting in a deterioration of the efficiency of the power converter 100.
Therefore, how to improve the above prior art has become an important issue for designers of the synchronous rectifier 200.
Disclosure of Invention
An embodiment of the invention discloses a synchronous rectifier applied to a power converter. The synchronous rectifier comprises a control signal generating circuit, a pre-attenuation circuit and a grid driving circuit. The control signal generating circuit is used for generating a control signal corresponding to a previous period according to a detection voltage corresponding to the previous period of the secondary side, a first reference voltage and a second reference voltage when the secondary side of the power converter is started, wherein the control signal corresponding to the previous period is a discharge time corresponding to the previous period. The pre-attenuation circuit is coupled to the control signal generation circuit and configured to pre-attenuate the gate control signal corresponding to the current period of the secondary side and generate a pre-attenuation signal corresponding to the current period according to the discharge time corresponding to the previous period. The gate driving circuit is coupled to the control signal generating circuit and the pre-attenuation circuit, and configured to drive the gate control signal corresponding to the current period according to the control signal corresponding to the current period, and stop driving the gate control signal corresponding to the current period according to the pre-attenuation signal corresponding to the current period.
Another embodiment of the present invention discloses a method for operating a synchronous rectifier applied to a power converter, wherein the synchronous rectifier includes a control signal generating circuit, a pre-attenuation circuit and a gate driving circuit. The operation method comprises the steps that when a secondary side of the power converter is started, the control signal generating circuit generates a control signal corresponding to a previous period according to a detection voltage corresponding to the previous period of the secondary side, a first reference voltage and a second reference voltage, wherein the control signal corresponding to the previous period is a discharge time corresponding to the previous period of the secondary side; the pre-attenuation circuit pre-attenuates the gate control signal corresponding to the current period of the secondary side and generates a pre-attenuation signal corresponding to the current period according to the discharge time corresponding to the previous period.
The invention discloses a synchronous rectifier applied to a power converter and an operation method thereof. The synchronous rectifier and the operation method are that when a control signal generating circuit of the synchronous rectifier is started on a secondary side of the power converter, a control signal corresponding to a previous period is generated according to a detection voltage corresponding to the previous period of the secondary side, a first reference voltage and a second reference voltage, and a pre-attenuation circuit of the synchronous rectifier pre-attenuates a gate control signal corresponding to a next period of the secondary side according to a discharge time corresponding to the previous period (the control signal corresponding to the previous period). Because the synchronous rectifier and the operating method pre-attenuate the gate control signal corresponding to the current period according to the discharge time corresponding to the previous period, when the load coupled to the secondary side of the power converter is a light load, the synchronous rectifier does not pre-attenuate the gate control signal corresponding to the current period in advance to prevent the synchronous switch from operating in a triode region most of the time, and when the load is a heavy load, the synchronous rectifier does not need to directly turn off the gate control signal corresponding to the current period.
Drawings
Fig. 1 is a schematic diagram illustrating a synchronous rectifier applied to the secondary side of a power converter.
Fig. 2 is a timing diagram illustrating the detection voltage and the gate control signal.
Fig. 3 is a schematic diagram of a synchronous rectifier applied to the secondary side of a power converter according to a first embodiment of the present invention.
Fig. 4 is a timing diagram illustrating the detection voltage, control signal, gate control signal, and pre-attenuation pulse.
Fig. 5 is a flowchart of an operation method of a synchronous rectifier applied to a power converter according to a second embodiment of the present invention.
Wherein the reference numerals are as follows:
100 power converter
101 primary side winding
102 synchronous switch
103 power switch
104 load
200. 300 synchronous rectifier
302 control signal generating circuit
304 pre-attenuation circuit
306 gate drive circuit
308. 310 pin
3042 Pre-attenuation Signal Generator
3044 the pulse generator
3046 the pull-down circuit
30462A first N-type metal oxide semiconductor transistor
30464A second NMOS transistor
30466 the switch
CS control signal
Current pre-decay time of CT
GND ground terminal
GCS Gate control Signal
PAS pre-attenuation signal
PAP pre-attenuation pulses
PDT pseudo dead time
PRI Primary side
PV predetermined voltage value
SEC Secondary side
Time T1-T3
TDIS discharge time
VDET detection voltage
VREF1 first reference voltage
VREF2 second reference voltage
VREF3 third reference voltage
VMIM minimum value
500-508 step
Detailed Description
Referring to fig. 3, fig. 3 is a schematic diagram of a synchronous rectifier 300 applied to the secondary side SEC of the power converter 100 according to the first embodiment of the present invention, wherein the primary side PRI of the power converter 100 only includes the primary winding 101 and a power switch 103, and is shown in fig. 3, the power converter 100 is an ac/dc power converter, the synchronous rectifier 300 is suitable for a continuous conduction mode of the power converter 100, and GND represents a ground terminal. As shown in fig. 3, the synchronous rectifier 300 includes a control signal generating circuit 302, a pre-attenuation circuit 304 and a gate driving circuit 306, wherein the pre-attenuation circuit 304 is coupled to the control signal generating circuit 302, and the gate driving circuit 306 is coupled to the control signal generating circuit 302 and the pre-attenuation circuit 304. When the secondary side SEC of the power converter 100 is turned on, the control signal generating circuit 302 receives the detection voltage VDET (i.e. the source voltage of the synchronous switch 102 of the secondary side SEC of the power converter 100) corresponding to the current period of the secondary side SEC of the power converter 100 through the pin 308 of the synchronous rectifier 300. After the control signal generating circuit 302 receives the detection voltage VDET corresponding to the current period, the control signal generating circuit 302 may generate the control signal CS corresponding to the current period according to the detection voltage VDET corresponding to the current period, a first reference voltage VREF1 and a second reference voltage VREF2, wherein timing of the detection voltage VDET corresponding to the current period and the control signal CS corresponding to the current period may be referred to fig. 4. As shown in fig. 4, at a time T1, the control signal generating circuit 302 may enable the control signal CS corresponding to the current period according to the detection voltage VDET corresponding to the current period and the first reference voltage VREF1, and at a time T2, the control signal generating circuit 302 may turn off the control signal CS corresponding to the current period according to the detection voltage VDET corresponding to the current period and the second reference voltage VREF2, wherein the second reference voltage VREF2 is greater than the first reference voltage VREF 1. Therefore, as shown in fig. 4, the control signal CS corresponding to the current cycle is the discharge time TDIS corresponding to the current cycle. In addition, as shown in fig. 4, the gate driving circuit 306 is configured to drive the gate control signal GCS corresponding to the current period according to the control signal CS corresponding to the current period, the gate control signal GCS corresponding to the current period is transmitted to the synchronous switch 102 on the secondary side SEC of the power converter 100 through a pin 310, and the gate control signal GCS corresponding to the current period is used to control the synchronous switch 102 to be turned on and off.
As shown in fig. 3, the pre-attenuation circuit 304 includes a pre-attenuation signal generator 3042, a pulse generator 3044 and a pull-down circuit 3046, wherein the pre-attenuation signal generator 3042 is coupled to the control signal generating circuit 302, the pulse generator 3044 is coupled to the pre-attenuation signal generator 3042, the pull-down circuit 3046 is coupled to the pulse generator 3044 and the pre-attenuation signal generator 3042, and the pull-down circuit 3046 includes a first nmos transistor 30462, a second nmos transistor 30464 and a switch 30466. In addition, the coupling relationship among the control signal generating circuit 302, the gate driving circuit 306, the pre-attenuation signal generator 3042, the pulse generator 3044, the first nmos transistor 30462, the second nmos transistor 30464 and the switch 30466 can refer to fig. 3, and will not be described herein.
The pre-attenuation signal generator 3042 may generate a current pre-attenuation time CT (as shown in fig. 4) corresponding to the current period and a pre-attenuation signal PAS corresponding to the current pre-attenuation time CT (where the pre-attenuation signal PAS corresponding to the current pre-attenuation time CT also corresponds to the current period) according to the discharge time (corresponding to the control signal CS of the previous period of the secondary side SEC of the power converter 100) of the previous period of the secondary side SEC of the power converter 100. For example, the initial pre-attenuation signal generator 3042 may generate a first pre-attenuation time corresponding to the first period of the secondary side SEC of the power converter 100 and a pre-attenuation signal corresponding to the first pre-attenuation time according to the discharge time corresponding to the zero-th period of the secondary side SEC of the power converter 100 and a preset time value; then, the pre-attenuation signal generator 3042 may generate a second pre-attenuation time corresponding to a second period of the secondary side SEC of the power converter 100 and a pre-attenuation signal corresponding to the second pre-attenuation time according to the discharge time corresponding to the first period of the secondary side SEC of the power converter 100 and the first pre-attenuation time; then, the pre-attenuation signal generator 3042 may generate a third pre-attenuation time corresponding to a third period of the secondary side SEC of the power converter 100 and a pre-attenuation signal corresponding to the third pre-attenuation time according to the discharge time corresponding to the second period of the secondary side SEC of the power converter 100 and the second pre-attenuation time; and so on, wherein the third period is after the second period, the second period is after the first period, and the first period is after the zeroth period. Therefore, the pre-attenuation signal generator 3042 generates the pre-attenuation time CT corresponding to the current period of the secondary side SEC of the power converter 100 according to the discharge time corresponding to the previous period of the secondary side SEC of the power converter 100, but the pre-attenuation signal generator 3042 makes a pseudo dead time pdt (pseudo dead time) shown in fig. 4 not less than a predetermined time interval.
In addition, in an embodiment of the invention, the pre-attenuation signal generator 3042 averages the discharge time corresponding to the zero-th period and the preset time value to generate a first pre-attenuation time corresponding to the first period of the secondary side SEC of the power converter 100, but the invention is not limited to the pre-attenuation signal generator 3042 averaging the discharge time corresponding to the zero-th period and the preset time value to generate the first pre-attenuation time corresponding to the first period of the secondary side SEC of the power converter 100, that is, the pre-attenuation signal generator 3042 may also weight the discharge time corresponding to the zero-th period and the preset time value to generate the first pre-attenuation time corresponding to the first period of the secondary side SEC of the power converter 100. Therefore, it is within the scope of the present invention that the pre-attenuation signal generator 3042 utilizes the discharge time corresponding to the previous cycle of the secondary-side SEC of the power converter 100 to generate the current pre-attenuation time CT corresponding to the current cycle of the secondary-side SEC of the power converter 100.
As shown in fig. 3, after the pre-attenuation signal generator 3042 generates the pre-attenuation signal PAS corresponding to the current period, the gate driving circuit 306 stops driving the gate control signal GCS corresponding to the current period.
In addition, as shown in fig. 4, the pulse generator 3044 is configured to generate the pre-attenuation pulse PAP corresponding to the current period at a time T3 according to the pre-attenuation signal PAS corresponding to the current period. Therefore, as shown in fig. 3, after the pulse generator 3044 generates the pre-attenuation pulse PAP corresponding to the current period, the first nmos transistor 30462 is turned on, and the gate control signal GCS corresponding to the current period will be pre-attenuated because the gate driving circuit 306 stops driving the gate control signal GCS corresponding to the current period (as shown in fig. 4). In addition, since the switch 30466 is turned on according to the pre-attenuation signal PAS corresponding to the current period, the second nmos transistor 30464 is turned on according to a third reference voltage VREF3, so that the gate control signal GCS corresponding to the current period is regulated to a predetermined voltage value PV (as shown in fig. 4), wherein the predetermined voltage value PV can be determined by the third reference voltage VREF3, the threshold voltage VTH30464 of the second nmos transistor 30464, and the equation (1):
PV＝VREF3–VTH30464 (1)
in another embodiment of the present invention, the switch 30466 and the second nmos transistor 30464 may be replaced by a clamp circuit, which can regulate the gate control signal GCS to a predetermined voltage value PV according to the pre-attenuation signal PAS corresponding to the current period.
Because the synchronous rectifier 300 pre-attenuates the gate control signal GCS corresponding to the current period according to the discharge time corresponding to the previous period, when the load 104 coupled to the secondary side SEC of the power converter 100 is a light load, the synchronous rectifier 300 does not pre-attenuate the gate control signal GCS corresponding to the current period early to prevent the synchronous switch 102 from operating in the triode region most of the time, and when the load 104 is a very heavy load, the synchronous rectifier 300 does not need to directly turn off the gate control signal GCS corresponding to the current period.
Referring to fig. 3-5, fig. 5 is a flowchart illustrating an operation method of a synchronous rectifier applied to a power converter according to a second embodiment of the present invention. The operation method of fig. 5 is illustrated by using the power converter 100 and the synchronous rectifier 300 of fig. 3, and the detailed steps are as follows:
step 500: starting;
step 502: when the secondary-side SEC of the power converter 100 is turned on, the control signal generating circuit 302 generates the control signal CS corresponding to the previous cycle of the secondary-side SEC of the power converter 100 according to the detection voltage VDET corresponding to the previous cycle of the secondary-side SEC of the power converter 100, the first reference voltage VREF1, and the second reference voltage VREF 2;
step 504: the pre-attenuation signal generator 3042 generates a pre-attenuation signal PAS corresponding to the current period of the secondary side SEC of the power converter 100 according to the control signal CS corresponding to the previous period;
step 506: the pulse generator 3044 generates a pre-attenuation pulse PAP corresponding to the current period of the secondary side SEC of the power converter 100 according to the pre-attenuation signal PAS corresponding to the current period of the secondary side SEC of the power converter 100;
step 508: the pull-down circuit 3046 pre-attenuates the gate control signal GCS corresponding to the current period of the secondary side SEC of the power converter 100 according to the pre-attenuation pulse PAP corresponding to the current period of the secondary side SEC of the power converter 100, and jumps back to step 502.
In step 502, when the secondary-side SEC of the power converter 100 is turned on in the previous cycle of the secondary-side SEC of the power converter 100, the control signal generating circuit 302 receives the detection voltage VDET corresponding to the previous cycle through the pin 308 of the synchronous rectifier 300. After the control signal generating circuit 302 receives the detection voltage VDET corresponding to the previous period, the control signal generating circuit 302 may generate the control signal CS corresponding to the previous period according to the detection voltage VDET corresponding to the previous period, the first reference voltage VREF1 and the second reference voltage VREF 2. Similarly, when the secondary-side SEC of the power converter 100 is turned on in the current period of the secondary-side SEC of the power converter 100, the control signal generating circuit 302 may also generate the control signal CS corresponding to the current period according to the detection voltage VDET corresponding to the current period, the first reference voltage VREF1, and the second reference voltage VREF 2.
In step 504, as shown in fig. 3, the pre-attenuation signal generator 3042 may generate a current pre-attenuation time CT (shown in fig. 4) corresponding to the current period and a pre-attenuation signal PAS corresponding to the current pre-attenuation time CT according to the discharge time (the control signal CS corresponding to the previous period of the secondary side SEC of the power converter 100) corresponding to the previous period of the secondary side SEC of the power converter 100. Therefore, the pre-attenuation signal generator 3042 generates the pre-attenuation time CT of the current period of the secondary side SEC of the corresponding power converter 100 according to the discharge time of the previous period of the secondary side SEC of the corresponding power converter 100, and the pre-attenuation time CT of the current period of the secondary side SEC of the corresponding power converter 100 gradually approaches the discharge time of the previous period of the secondary side SEC of the corresponding power converter 100, but the pre-attenuation signal generator 3042 makes the pseudo dead time PDT shown in fig. 4 not less than the predetermined time interval.
In steps 506 and 508, as shown in fig. 4, the pulse generator 3044 generates the pre-attenuation pulse PAP corresponding to the current period at time T3 according to the pre-attenuation signal PAS corresponding to the current period. Therefore, as shown in fig. 3, after the pulse generator 3044 generates the pre-attenuation pulse PAP corresponding to the current period, the first nmos transistor 30462 is turned on, and the gate control signal GCS corresponding to the current period will be pre-attenuated because the gate driving circuit 306 stops driving the gate control signal GCS corresponding to the current period (as shown in fig. 4). In addition, since the switch 30466 is turned on according to the pre-attenuation signal PAS corresponding to the current period, the second nmos transistor 30464 is turned on according to the third reference voltage VREF3, so that the gate control signal GCS corresponding to the current period is regulated to the predetermined voltage value PV (as shown in fig. 4).
In addition, as shown in fig. 3 and 4, the gate driving circuit 306 can drive the gate control signal GCS corresponding to the current period according to the control signal CS corresponding to the current period, and after the pre-attenuation signal generator 3042 generates the pre-attenuation signal PAS corresponding to the current period, the gate driving circuit 306 will stop driving the gate control signal GCS corresponding to the current period.
In summary, the synchronous rectifier applied to the power converter and the operating method thereof disclosed by the present invention generate the control signal corresponding to the previous period according to the detection voltage corresponding to the previous period of the secondary side, the first reference voltage and the second reference voltage when the control signal generating circuit is turned on at the secondary side of the power converter, and pre-attenuate the gate control signal corresponding to the current period of the secondary side according to the discharging time (corresponding to the control signal of the previous period) corresponding to the previous period by using the pre-attenuation circuit. Because the synchronous rectifier and the operating method pre-attenuate the gate control signal corresponding to the current period according to the discharge time corresponding to the previous period, when the load coupled to the secondary side of the power converter is a light load, the synchronous rectifier does not pre-attenuate the gate control signal corresponding to the current period in advance to prevent the synchronous switch from operating in a triode region most of the time, and when the load is a heavy load, the synchronous rectifier does not need to directly turn off the gate control signal corresponding to the current period.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (9)

1. A synchronous rectifier for a power converter, comprising:
a control signal generating circuit for turning on a control signal corresponding to a previous period according to a detection voltage corresponding to the previous period of the secondary side and a first reference voltage when the secondary side of the power converter is turned on, and turning off the control signal corresponding to the previous period according to the detection voltage corresponding to the previous period of the secondary side and a second reference voltage, wherein the control signal corresponding to the previous period is a discharge time corresponding to the previous period;
a pre-attenuation circuit, coupled to the control signal generation circuit, for pre-attenuating the gate control signal corresponding to the current period of the secondary side and generating a pre-attenuation signal corresponding to the current period according to the control signal corresponding to the previous period; and
a gate driving circuit, coupled to the control signal generating circuit and the pre-attenuation circuit, for driving the gate control signal corresponding to the current period according to the control signal corresponding to the current period, and stopping driving the gate control signal corresponding to the current period according to the pre-attenuation signal corresponding to the current period.
2. The synchronous rectifier of claim 1, wherein: the detection voltage is a source voltage of the synchronous switch on the secondary side.
3. The synchronous rectifier of claim 1, wherein: the grid control signal of the current period is used for controlling the opening and closing of the synchronous switch of the secondary side.
4. The synchronous rectifier of claim 1, wherein: the pre-attenuation circuit includes:
a pre-attenuation signal generator, coupled to the control signal generating circuit, for generating a pre-attenuation signal corresponding to the current period according to the control signal corresponding to the previous period;
a pulse generator, coupled to the pre-attenuation signal generator, for generating a pre-attenuation pulse corresponding to the current period according to the pre-attenuation signal corresponding to the current period; and
a pull-down circuit, coupled to the pulse generator and the pre-attenuation signal generator, for pre-attenuating the gate control signal corresponding to the current cycle according to the pre-attenuation pulse corresponding to the current cycle.
5. A method for operating a synchronous rectifier for a power converter, wherein the synchronous rectifier comprises a control signal generating circuit, a pre-attenuation circuit and a gate driving circuit, the method comprising:
when the secondary side of the power converter is started, the control signal generating circuit starts a control signal corresponding to a previous period according to a detection voltage corresponding to the previous period of the secondary side and a first reference voltage, and closes the control signal corresponding to the previous period according to the detection voltage corresponding to the previous period of the secondary side and a second reference voltage, wherein the control signal corresponding to the previous period is a discharge time corresponding to the previous period of the secondary side; and
the pre-attenuation circuit pre-attenuates the gate control signal corresponding to the current period of the secondary side and generates a pre-attenuation signal corresponding to the current period according to the control signal corresponding to the previous period.
6. The method of claim 5, further comprising:
the grid driving circuit drives the grid control signal corresponding to the current period according to the control signal corresponding to the current period; and
and the grid driving circuit stops driving the grid control signal corresponding to the current period according to the pre-attenuation signal corresponding to the current period.
7. The operating method of claim 5, wherein the detection voltage is a source voltage of a synchronous switch of the secondary side.
8. The method of operation of claim 5, wherein: the grid control signal of the current period is used for controlling the opening and closing of the synchronous switch of the secondary side.
9. The method of operation of claim 5, wherein: the pre-attenuating circuit pre-attenuates the gate control signal corresponding to the current period and generates a pre-attenuated signal corresponding to the current period according to the discharge time corresponding to the previous period, including:
a pre-attenuation signal generator of the pre-attenuation circuit generates a pre-attenuation signal corresponding to the current period according to the control signal corresponding to the previous period;
a pulse generator of the pre-attenuation circuit generates a pre-attenuation pulse corresponding to the current period according to the pre-attenuation signal corresponding to the current period; and
and the pull-down circuit of the pre-attenuation circuit pre-attenuates the gate control signal corresponding to the current period according to the pre-attenuation pulse corresponding to the current period.
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