CN111313709A - Synchronous rectification control circuit, control method thereof and flyback isolated conversion circuit - Google Patents
Synchronous rectification control circuit, control method thereof and flyback isolated conversion circuit Download PDFInfo
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- CN111313709A CN111313709A CN202010228227.7A CN202010228227A CN111313709A CN 111313709 A CN111313709 A CN 111313709A CN 202010228227 A CN202010228227 A CN 202010228227A CN 111313709 A CN111313709 A CN 111313709A
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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
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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
- H02M3/33561—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 more than one ouput with independent control
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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
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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
- 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
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- 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
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Abstract
The invention provides a synchronous rectification control circuit, a control method thereof and a flyback isolated conversion circuit, wherein the flyback isolated conversion circuit comprises a primary winding, a first secondary winding and a second secondary winding. The first secondary winding is coupled to the first voltage output end for providing a first output voltage, the second secondary winding is coupled to the second voltage output end for providing a second output voltage, the second secondary winding is coupled to the synchronous rectifier tube, and the synchronous rectifier control circuit is used for generating a driving signal for driving the synchronous rectifier tube. The synchronous rectification control circuit controls the synchronous rectification tube to work in a reverse conducting state under a set state so as to enable the second secondary winding to transmit energy to the first secondary winding, and the reverse conducting state is that current flows from the drain electrode to the source electrode of the synchronous rectification tube. The invention can improve the problem of load cross regulation rate in the multi-output isolation power supply, is suitable for primary side feedback control and secondary side feedback control, and can reduce the cost of the power supply.
Description
Technical Field
The invention belongs to the electronic field, relates to the technical field of switching power supplies, and particularly relates to a synchronous rectification control circuit, a control method thereof and a flyback isolated conversion circuit.
Background
In a traditional dual-output isolation power supply, one output is used as feedback, and the other output is used for regulating voltage by virtue of coupling of a transformer. Fig. 1 shows a two-way isolated power supply topology, wherein if the first output (Vout1) is fully loaded and the second output (Vout2) is unloaded, and the first output is used as feedback, a surge of the second output voltage Vout2 occurs; if the first output (Vout1) is unloaded and the second output (Vout2) is loaded with the first output as feedback, the second output voltage Vout2 will be too low.
One conventional solution is to use the weighted information of the first output and the second output as feedback, as shown in fig. 2, the feedback signal VFB is K1 Vout1+ K2 Vout 2. However, the method of outputting weighted feedback needs to detect Vout1 and Vout2 at the same time to provide feedback signals, and is only suitable for secondary feedback control (SSR), and additionally uses optical couplers and other devices. The method is not suitable for obtaining the feedback signal through a primary side feedback control (PSR) approach such as an auxiliary winding, because the primary side feedback cannot obtain the difference between the first output voltage and the second output voltage.
In view of the above, there is a need to provide a new structure or control method for solving at least some of the above-mentioned problems of load cross adjustment rate.
Disclosure of Invention
In order to solve at least part of the problems, the invention provides a synchronous rectification control circuit, a control method thereof and a flyback isolated conversion circuit.
The invention provides a synchronous rectification control circuit for a flyback isolated conversion circuit, which comprises a primary winding, a first secondary winding and a second secondary winding, wherein the first secondary winding is coupled with a first voltage output end and used for providing a first output voltage, the second secondary winding is coupled with a second voltage output end and used for providing a second output voltage, the second secondary winding is coupled with a synchronous rectifier tube, and the synchronous rectification control circuit is used for generating a driving signal for driving the synchronous rectifier tube. The synchronous rectification control circuit controls the synchronous rectification tube to work in a reverse conducting state under a set state so as to enable the second secondary winding to transmit energy to the first secondary winding, and the reverse conducting state is that current flows from the drain electrode to the source electrode of the synchronous rectification tube.
In an embodiment of the present invention, the synchronous rectification control circuit is configured to generate a synchronous rectification forward conduction pulse signal and a synchronous rectification reverse conduction pulse signal to drive the synchronous rectification tube; the synchronous rectification forward conducting pulse signal in an effective state controls the current in the second secondary side circuit to flow from the source electrode to the drain electrode of the synchronous rectification tube; the synchronous rectification reverse conducting pulse signal in the effective state controls the current in the second secondary side circuit to flow from the drain electrode to the source electrode of the synchronous rectification tube.
In an embodiment of the invention, a time window interval of the synchronous rectification reverse conduction pulse signal of the effective state controlled by the synchronous rectification control circuit is a first time window, a starting time point of the first time window is a time point when a current flowing from a source to a drain of the synchronous rectification tube in the second secondary circuit is reduced to zero, an ending time point of the first time window is a time point when all secondary circuits in the flyback isolated conversion circuit finish freewheeling, and the synchronous rectification reverse conduction pulse signal generates an effective state in the first time window.
In an embodiment of the present invention, the synchronous rectification control circuit includes a flip-flop, the time window control circuit sets the flip-flop in a set state according to a falling edge of the synchronous rectification forward conduction pulse signal, the time window control circuit controls whether the flip-flop is in a reset state according to a comparison result between a voltage across the second secondary winding and/or a drain voltage of the synchronous rectification tube and the first reference voltage, and the output terminal of the flip-flop outputs a pulse signal representing the first time window.
In an embodiment of the invention, the synchronous rectification control circuit is coupled to the second output voltage, and the synchronous rectification control circuit controls a time length of the synchronous rectification reverse conducting pulse signal in an active state according to the second output voltage.
In an embodiment of the present invention, the synchronous rectification control circuit includes:
the synchronous rectification forward conduction pulse generating circuit is used for generating a synchronous rectification forward conduction pulse signal;
the reverse conducting time control circuit is used for generating a synchronous rectification reverse conducting pulse signal; and
and the input end of the first OR gate is respectively coupled with the output end of the synchronous rectification forward conduction pulse generating circuit and the output end of the reverse conduction time control circuit, and the output end of the first OR gate outputs a driving signal of the synchronous rectification tube.
In an embodiment of the invention, a first input terminal of the reverse conduction time control circuit is coupled to an output terminal of the synchronous rectification forward conduction pulse generation circuit, a second input terminal of the reverse conduction time control circuit is coupled to the second secondary winding and/or a drain of the synchronous rectification tube, and the synchronous rectification control circuit controls a time window interval of the synchronous rectification reverse conduction pulse signal in an effective state according to signals received by the first input terminal and the second input terminal.
In an embodiment of the present invention, the reverse on-time control circuit includes:
a time window control circuit, a first input end of which is coupled with the output end of the synchronous rectification forward conduction pulse generating circuit, a second input end of which is coupled with the second secondary winding and/or the drain electrode of the synchronous rectification tube, and is used for controlling the time window interval of the synchronous rectification reverse conduction pulse signal in an effective state;
a time length control circuit, a first input end of which is coupled with the second output voltage, and is used for controlling the time length of the synchronous rectification reverse conduction pulse signal in the effective state according to the second output voltage; and
and the first input end of the AND gate is coupled with the output end of the time window control circuit, the second input end of the AND gate is coupled with the output end of the time length control circuit, and the output end of the AND gate is coupled with the first OR gate.
In an embodiment of the present invention, the reverse on-time control circuit includes:
the input end of the falling edge acquisition circuit is coupled with the output end of the synchronous rectification forward conduction pulse generation circuit;
a first comparator, wherein a first input end of the first comparator is coupled with the second secondary winding and/or the drain electrode of the synchronous rectifier tube, and a second input end of the first comparator is coupled with a first reference voltage;
the setting end of the trigger is coupled with the output end of the falling edge acquisition circuit, and the output end of the trigger outputs a synchronous rectification reverse conduction pulse signal;
a first input end of the second or gate is coupled with the output end of the first comparator, and an output end of the second or gate is coupled with the reset end of the trigger;
the output end of the current source is coupled with the first end of the second switch;
a second switch, a second terminal of which is coupled to the first terminal of the third capacitor, and a control terminal of which is coupled to the output terminal of the trigger;
an error amplifier having a first input terminal coupled to the second output voltage and a second input terminal coupled to the second reference voltage;
a first input terminal of the second comparator is coupled to the first terminal of the third capacitor, a second input terminal of the second comparator is coupled to the output terminal of the error amplifier, and an output terminal of the second comparator is coupled to the second input terminal of the second or gate; and a third capacitance.
In an embodiment of the invention, a delay circuit is further coupled between the falling edge obtaining circuit and the flip-flop, and the delay circuit is used for delaying the set state of the flip-flop.
The invention provides a flyback isolated conversion circuit, which comprises a primary side circuit, a first secondary side circuit, a second secondary side circuit and any one of the synchronous rectification control circuits, wherein the primary side circuit comprises a primary side winding and a primary side switch, the first secondary side circuit comprises a first secondary side winding and a rectifying tube, and the first secondary side circuit provides a first output voltage; the second secondary side circuit comprises a second secondary side winding and a synchronous rectifier tube, and the second secondary side circuit provides a second output voltage; the synchronous rectification control circuit is coupled with the synchronous rectification tube, and the primary winding, the first secondary winding and the second secondary winding form a transformer winding.
In an embodiment of the invention, when the synchronous rectification reverse conducting pulse signal in the active state controls the current in the second secondary side circuit to flow from the drain to the source of the synchronous rectification tube, the second secondary side circuit transmits energy to the first secondary side circuit through the transformer winding.
The invention provides a synchronous rectification control method for a flyback isolated conversion circuit, the flyback isolated conversion circuit comprises a primary winding, a first secondary winding and a second secondary winding, the first secondary winding is coupled with a first voltage output end and used for providing a first output voltage, the second secondary winding is coupled with a second voltage output end and used for providing a second output voltage, the second secondary winding is coupled with a synchronous rectifier tube, the synchronous rectification control circuit is used for generating a driving signal for driving the synchronous rectifier tube, and the synchronous rectification control method comprises the following steps:
generating a synchronous rectification forward conduction pulse signal; and
and generating a synchronous rectification reverse conduction pulse signal according to the synchronous rectification forward conduction pulse signal, wherein the synchronous rectification reverse conduction pulse signal in an effective state is used for controlling the current in the second secondary side circuit to flow from the drain electrode to the source electrode of the synchronous rectification tube so as to promote the second secondary side winding to transfer energy to the first secondary side winding.
In an embodiment of the present invention, the process of generating the synchronous rectification reverse conduction pulse signal according to the synchronous rectification forward conduction pulse signal further includes: the time window interval of the synchronous rectification reverse conduction pulse signal for controlling the effective state is a first time window, the starting time point of the first time window is the time when the current flowing from the source electrode to the drain electrode of the synchronous rectification tube in the second secondary side circuit is reduced to zero, the ending time point of the first time window is the time when all secondary side circuits in the flyback isolated conversion circuit finish follow current, and the synchronous rectification reverse conduction pulse signal generates the effective state in the first time window.
In an embodiment of the present invention, the process of generating the synchronous rectification reverse conduction pulse signal according to the synchronous rectification forward conduction pulse signal further includes: and controlling the time length of the synchronous rectification reverse conduction pulse signal in the effective state according to the second output voltage.
In an embodiment of the invention, a time window interval of the synchronous rectification reverse conduction pulse signal in an effective state is controlled as a first time window according to the synchronous rectification forward conduction pulse signal and the voltage across the second secondary winding and/or the drain voltage of the synchronous rectification tube.
The invention provides a synchronous rectification control circuit, a control method thereof and a flyback isolated conversion circuit. The synchronous rectification control circuit is used for generating a driving signal for driving the synchronous rectification tube. The synchronous rectification control circuit controls the synchronous rectification tube to work in a reverse conduction state under a set state so as to enable the second secondary winding to transfer energy to the first secondary winding, and the reverse conduction state is that current flows from the drain electrode to the source electrode of the synchronous rectification tube. The synchronous rectification control circuit, the control method thereof and the flyback isolated conversion circuit provided by the invention can effectively improve the problem of load cross regulation rate in a multi-output flyback isolated power supply under the condition of not increasing the circuit cost, and can be suitable for primary side feedback control as well as secondary side feedback control, thereby reducing the power supply cost.
Drawings
Fig. 1 shows a circuit schematic diagram of a two-way flyback isolated converter circuit in the prior art.
Fig. 2 shows a circuit schematic diagram of a prior art weighted flyback isolated converter circuit.
Fig. 3 shows a circuit schematic diagram of a flyback isolated converter circuit according to an embodiment of the present invention.
Fig. 4 shows a circuit schematic diagram of a flyback isolated converter circuit according to another embodiment of the present invention.
Fig. 5 shows a waveform diagram of a signal in a conventional flyback isolated converter circuit.
Fig. 6 shows a schematic diagram of a flyback isolated converter circuit according to an embodiment of the invention.
Fig. 7 is a waveform diagram of signals in the flyback isolated converter circuit according to an embodiment of the present invention.
Fig. 8 shows a circuit schematic of a synchronous rectification control circuit according to an embodiment of the present invention.
Fig. 9 shows a circuit schematic of a reverse on-time control circuit according to an embodiment of the invention.
Fig. 10 shows a circuit schematic of a reverse on-time control circuit according to an embodiment of the invention.
Fig. 11 shows a circuit timing diagram of a flyback isolated converter circuit according to an embodiment of the present invention.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
The description in this section is for several exemplary embodiments only, and the present invention is not limited only to the scope of the embodiments described. It is within the scope of the present disclosure and protection that the same or similar prior art means and some features of the embodiments may be interchanged.
The term "coupled" or "connected" in this specification includes both direct and indirect connections. An indirect connection is a connection made through an intermediate medium, such as a connection made through an electrically conductive medium, which may have parasitic inductance or parasitic capacitance; indirect connections may also include connections through other active or passive devices, such as connections through switches, follower circuits, etc., that serve the same or similar functional purpose.
As shown in fig. 3, an embodiment of the present invention provides a flyback isolated converter circuit, which includes a primary side circuit, a first secondary side circuit, a second secondary side circuit, and a synchronous rectification control circuit. The primary side circuit comprises a primary side winding Np and a primary side switch S1, the first secondary side circuit comprises a first secondary side winding Ns1 and a rectifying tube D1, and the first secondary side circuit provides a first output voltage Vout 1; the second secondary circuit includes a second secondary winding Ns2 and a synchronous rectifier SR, and provides a second output voltage Vout 2. The first secondary circuit may further include a first capacitor Co1, a first terminal of the first capacitor Co1 is coupled to the first output voltage Vout1, and a second terminal of the first capacitor Co1 is grounded. The second secondary side circuit may further include a second capacitor Co2, a first terminal of the second capacitor Co2 is coupled to the second output voltage Vout2, and a second terminal of the second capacitor Co2 is grounded. The synchronous rectification control circuit 200 is coupled to the synchronous rectification transistor SR, and the primary winding Np, the first secondary winding Ns1 and the second secondary winding Ns2 form a transformer winding 100. Wherein the rectifier D1 may be a diode or a synchronous rectifier. The synchronous rectifier may be a switching transistor. In another embodiment, the flyback isolated converter circuit may include no less than two secondary side circuits. In another embodiment, the flyback isolated converter circuit may include at least two secondary side circuits, wherein at least two of the secondary side circuits have synchronous rectifiers. In an embodiment, the flyback isolated converter circuit comprises a secondary side circuit a1 and a secondary side circuit a2, the secondary side circuit a1 comprises a synchronous rectifier tube S100 and a first synchronous rectification control circuit, the secondary side circuit a2 comprises a synchronous rectifier tube S200 and a second synchronous rectification control circuit, and under a set condition, a circulating current and energy exchange can be created between the secondary side circuit a1 and the secondary side circuit a 2.
In an embodiment of the invention, the flyback isolated converter circuit includes a primary winding, a first secondary winding and a second secondary winding, the first secondary winding is coupled to the first voltage output terminal for providing a first output voltage, the second secondary winding is coupled to the second voltage output terminal for providing a second output voltage, the second secondary winding is coupled to the synchronous rectifier tube, the synchronous rectifier control circuit is configured to generate a driving signal for driving the synchronous rectifier tube, the synchronous rectifier control circuit controls the synchronous rectifier tube to operate in a reverse conduction state under a set state to enable the second secondary winding to transmit energy to the first secondary winding, and the reverse conduction state is that a current flows from a drain to a source of the synchronous rectifier tube. The setting state refers to that the synchronous rectification control circuit controls the synchronous rectification tube to work in a reverse conduction state in a proper time window. In an embodiment of the invention, the synchronous rectification control circuit selects a certain time length within a time range of the first time window to control the synchronous rectification tube to operate in a reverse conduction state.
In an embodiment of the invention, the synchronous rectification control circuit is configured to generate a synchronous rectification forward conduction pulse signal and a synchronous rectification reverse conduction pulse signal to drive the synchronous rectification tube. The synchronous rectification forward direction conducting pulse signal in the effective state controls the current in the second secondary side circuit to flow from the source electrode to the drain electrode of the synchronous rectification tube. The synchronous rectification reverse conducting pulse signal in the effective state controls the current in the second secondary side circuit to flow from the drain electrode to the source electrode of the synchronous rectification tube. In an embodiment of the present invention, in the synchronous rectification control circuit, the synchronous rectification forward conduction pulse signal and the synchronous rectification reverse conduction pulse signal generate the driving signal in a logical phase or relationship.
As shown in fig. 4 and 5, in an embodiment of the present invention, the synchronous rectification control circuit of the flyback isolated converter circuit generates a synchronous rectification forward conduction pulse signal, and the synchronous rectification forward conduction pulse signal in an active state controls the current Is2 in the second secondary circuit to flow from the source to the drain of the synchronous rectification tube. As shown in fig. 5, when the switching signal of the primary switch S1 is active in the primary circuit, the primary current Ip increases accordingly. When the switching signal of the side switch S1 is in an inactive state, the first and second sub-side circuits start demagnetization. The current Is1 in the first secondary circuit and the current Is2 in the second secondary circuit decrease accordingly. Under the effect of the load cross regulation, the time for the synchronous rectifier SR to flow current is shorter than the time for the rectifier D1 to flow current. The voltage Vsec2 across the second secondary winding gradually decreases and oscillates after the freewheeling ends, which causes a problem of load cross regulation in the flyback isolated converter circuit.
In an embodiment of the invention, the synchronous rectification control circuit generates a synchronous rectification reverse conduction pulse signal to drive the synchronous rectification tube after the time when the current flowing from the source to the drain of the synchronous rectification tube in the second secondary circuit is reduced to zero, so that the synchronous rectification reverse conduction pulse signal in an effective state controls the current in the second secondary circuit to flow from the drain to the source of the synchronous rectification tube. As shown in fig. 6 and 7, after the time when the current Is2 in the second secondary circuit drops from positive to zero, the synchronous rectification control circuit controls to output a synchronous rectification reverse conduction pulse signal to drive the synchronous rectifier tube, at this time, the current Is2 in the second secondary circuit increases in a reverse direction, the current Is2 Is a negative value, that Is, the current Is2 Is reversed (as shown by a dotted arrow in fig. 6, the current Is in a counterclockwise direction), at this time, the second secondary circuit transmits energy to the first secondary circuit through the transformer winding, and the problem of load cross regulation rate of the multi-path flyback isolated conversion circuit can be effectively solved.
In an embodiment of the invention, a time window interval of the synchronous rectification reverse conduction pulse signal of which the synchronous rectification control circuit controls the effective state is a first time window, a starting time point of the first time window is a time point when a current flowing from a source to a drain of the synchronous rectification tube in the second secondary side circuit is reduced to zero, an ending time point of the first time window is a time point when a follow current of all secondary side circuits in the flyback isolated conversion circuit is ended, and the synchronous rectification reverse conduction pulse signal generates the effective state in the first time window.
In an embodiment of the invention, the synchronous rectification control circuit includes a flip-flop, the time window control circuit sets the flip-flop in a set state according to a falling edge of the synchronous rectification forward conduction pulse signal, the time window control circuit controls whether the flip-flop is in a reset state according to a comparison result of a voltage across the second secondary winding and/or a drain voltage of the synchronous rectification tube and a first reference voltage, and an output end of the flip-flop outputs a pulse signal representing the first time window. In an embodiment of the invention, when the voltage across the second secondary winding is greater than the first reference voltage, or the drain voltage of the synchronous rectifier is greater than the first reference voltage, the time window control circuit controls the flip-flop to be in the reset state.
In an embodiment of the invention, the synchronous rectification control circuit is coupled to the second output voltage, and the synchronous rectification control circuit controls a time length of the synchronous rectification reverse conducting pulse signal in an active state according to the second output voltage.
In an embodiment of the present invention, as shown in fig. 8, the synchronous rectification control circuit 200 includes a synchronous rectification forward conducting pulse generating circuit 210, a reverse conducting time control circuit 220 and a first or gate. The synchronous rectification forward conduction pulse generating circuit 210 is used for generating a synchronous rectification forward conduction pulse signal SR _ PWM. The Reverse conduction time control circuit 220 is used for generating a synchronous rectification Reverse conduction Pulse signal SR _ Reverse _ Pulse. The input end of the first or Gate is coupled to the output end of the synchronous rectification forward conducting pulse generating circuit 210 and the output end of the reverse conducting time control circuit 220, respectively, and the output end of the first or Gate outputs the driving signal SR Gate of the synchronous rectification tube. In another embodiment of the present invention, a first input terminal of the reverse conduction time control circuit 220 is coupled to the output terminal of the synchronous rectification forward conduction pulse generating circuit 210, a second input terminal of the reverse conduction time control circuit 220 is coupled to the second secondary winding and/or the drain of the synchronous rectifier SR, and the synchronous rectification control circuit controls a time window interval of the synchronous rectification reverse conduction pulse signal in an active state according to signals received by the first input terminal and the second input terminal. The received signals are respectively a synchronous rectification forward direction conducting pulse signal SR _ PWM and a voltage Vsec2 at two ends of the second secondary winding, and the received signals also can be respectively the synchronous rectification forward direction conducting pulse signal SR _ PWM and a drain voltage Vdrain of the synchronous rectifier tube.
In an embodiment of the invention, as shown in fig. 9, the reverse on-time control circuit 220 includes a time window control circuit 221, a time length control circuit 222, and an and gate. A first input terminal of the time window control circuit 221 is coupled to the output terminal of the synchronous rectification forward conducting pulse generating circuit to receive the synchronous rectification forward conducting pulse signal SR _ PWM. The second input terminal of the time window control circuit 221 is coupled to the second secondary winding and/or the drain of the synchronous rectifier, and the time window control circuit 221 is configured to control a time window interval of the synchronous rectification reverse conducting pulse signal in an active state. The first input terminal of the time length control circuit 222 is coupled to the second output voltage Vout2, and the second input terminal of the time length control circuit 222 is coupled to the output terminal of the and gate. A first input terminal of the and gate is coupled to the output terminal of the time window control circuit 221, a second input terminal of the and gate is coupled to the output terminal of the time length control circuit 222, an output terminal of the and gate is coupled to the first or gate, and an output terminal of the and gate outputs the synchronous rectification Reverse conduction Pulse signal SR _ Reverse _ Pulse. The time length control circuit 222 is used for controlling the time length of the synchronous rectification reverse conducting pulse signal of the active state according to the second output voltage Vout 2.
In an embodiment of the invention, as shown in fig. 10, the reverse conducting time control circuit 220 includes a falling edge obtaining circuit, a first comparator COM1, a flip-flop, a second or gate, a current source I1, a second switch S2, an error amplifier, a second comparator COM2, and a third capacitor C3. The input end of the falling edge acquisition circuit is coupled with the output end of the synchronous rectification forward conduction pulse generation circuit. In the embodiment of fig. 10, the falling edge acquisition circuit includes a not gate and a rising edge acquisition circuit. A first input terminal of the first comparator COM1 is coupled to the second secondary winding and/or the drain of the synchronous rectifier, and a second input terminal of the first comparator COM1 is coupled to the first reference voltage Vref 1. The setting end S of the trigger is coupled with the output end of the falling edge acquisition circuit, and the output end Q of the trigger outputs a synchronous rectification Reverse conduction Pulse signal SR _ Reverse _ Pulse. A first input terminal of the second or-gate is coupled to the output terminal of the first comparator COM1, and an output terminal of the second or-gate is coupled to the reset terminal R of the flip-flop. An output terminal of the current source I1 is coupled to a first terminal of the second switch S2. The second terminal of the second switch S2 is coupled to the first terminal of the third capacitor C3. The output terminal Q of the flip-flop is coupled to the control terminal of the second switch S2 to control the switching state of the second switch S2, and when the synchronous rectified Reverse conducting Pulse signal SR _ Reverse _ Pulse is in an active state, the output terminal Q of the flip-flop controls the second switch S2 to maintain the closed conducting state. When the synchronous rectification Reverse conduction Pulse signal SR _ Reverse _ Pulse is in an inactive state, the second switch S2 is controlled to maintain an off state. The first input terminal of the error amplifier is coupled to the second output voltage Vout2, and the second input terminal of the error amplifier is coupled to the second reference voltage Vref 2. A first input terminal of the second comparator COM2 is coupled to the first terminal of the third capacitor C3, a second input terminal of the second comparator COM2 is coupled to the output terminal of the error amplifier, and an output terminal of the second comparator COM2 is coupled to the second input terminal of the second or gate. When the synchronous rectification Reverse conduction Pulse signal SR _ Reverse _ Pulse is in an active state, the synchronous rectification Reverse conduction Pulse signal in the active state controls the second switch S2 to be switched on and off, at this time, the current source I1 charges the third capacitor C3, at this time, the voltage VC3 at the same-direction input end of the second comparator COM2 gradually rises, and when the voltage VC3 is greater than the voltage at the opposite-direction input end of the second comparator COM2, the trigger is controlled to be in a reset state, so that the time length of the synchronous rectification Reverse conduction Pulse signal in the active state is controlled. As shown in fig. 10, the first input terminal of the error amplifier EA is a non-inverting input terminal, and the second input terminal thereof is an inverting input terminal. In an embodiment of the invention, a first resistor R1 is further coupled between the first input terminal of the error amplifier EA and the second output voltage Vout2, a first end of the first resistor R1 is coupled to the second output voltage Vout2, a second end of the first resistor R1 is coupled to the first input terminal of the error amplifier EA and a first end of the second resistor R2, respectively, and a second end of the second resistor R2 is grounded.
In another embodiment of the present invention, a delay circuit is further coupled between the falling edge acquisition circuit and the flip-flop, the delay circuit for delaying the set state of the flip-flop. As shown in fig. 11, after the time when the current Is2 in the second secondary circuit drops from positive to zero, unlike fig. 7, the synchronous rectification control circuit does not immediately control to output the synchronous rectification reverse conduction pulse signal in the active state, and after the delay time period a, the synchronous rectification control circuit outputs the synchronous rectification reverse conduction pulse signal in the active state to drive the synchronous rectifier tube. At this time, the current Is2 in the second secondary side circuit increases reversely, Is2 Is a negative value, namely, the current Is2 reverses, and the synchronous rectification reverse conduction pulse signal in an effective state stops being output before all secondary side circuits finish freewheeling. As shown in fig. 11, the voltage Vsec2 across the second secondary winding changes in section B in response to the voltage signal change in response to the synchronous rectified reverse conducting pulse signal in the active state. As shown in fig. 11, the range of the time window interval of the synchronous rectification reverse conduction pulse signal is the effective state indicated by the double-headed arrow. The time length of the synchronous rectification Reverse conducting Pulse signal with the range indicated by an arrow on the coordinate axis of the synchronous rectification Reverse conducting Pulse signal SR _ Reverse _ Pulse as an effective state. In another embodiment of the present invention, the synchronous rectification control circuit further includes a time period selection circuit, and the time period selection circuit is configured to select a specific time period within the time window interval to output the synchronous rectification reverse conduction pulse signal in an active state.
The invention provides a flyback isolated conversion circuit which comprises a primary side circuit, a first secondary side circuit, a second secondary side circuit and the synchronous rectification control circuit. The primary side circuit comprises a primary side winding and a primary side switch, the first secondary side circuit comprises a first secondary side winding and a rectifying tube, and the first secondary side circuit provides a first output voltage. The second secondary side circuit includes a second secondary side winding and a synchronous rectifier, the second secondary side circuit providing a second output voltage. The synchronous rectification control circuit is coupled with the synchronous rectification tube, and the primary winding, the first secondary winding and the second secondary winding form a transformer winding.
In an embodiment of the invention, when the synchronous rectification reverse conducting pulse signal in an active state controls the current in the second secondary side circuit to flow from the drain to the source of the synchronous rectification tube, the second secondary side circuit transmits energy to the first secondary side circuit through the transformer winding.
An embodiment of the present invention further provides a synchronous rectification control method for a flyback isolated conversion circuit, where the flyback isolated conversion circuit includes a primary winding, a first secondary winding and a second secondary winding, the first secondary winding is coupled to a first voltage output terminal for providing a first output voltage, the second secondary winding is coupled to a second voltage output terminal for providing a second output voltage, the second secondary winding is coupled to a synchronous rectifier tube, the synchronous rectification control circuit is configured to generate a driving signal for driving the synchronous rectifier tube, and the synchronous rectification control method includes:
s1, generating a synchronous rectification forward direction conducting pulse signal; and
and S2, generating a synchronous rectification reverse conduction pulse signal according to the synchronous rectification forward conduction pulse signal, wherein the synchronous rectification reverse conduction pulse signal in an effective state is used for controlling the current in the second secondary side circuit to flow from the drain electrode to the source electrode of the synchronous rectification tube so as to promote the second secondary side winding to transfer energy to the first secondary side winding.
In an embodiment of the present invention, the process of generating the synchronous rectification reverse conduction pulse signal according to the synchronous rectification forward conduction pulse signal further includes: the time window interval of the synchronous rectification reverse conduction pulse signal for controlling the effective state is a first time window, the starting time point of the first time window is the time when the current flowing from the source electrode to the drain electrode of the synchronous rectification tube in the second secondary side circuit is reduced to zero, the ending time point of the first time window is the time when all secondary side circuits in the flyback isolated conversion circuit finish follow current, and the synchronous rectification reverse conduction pulse signal generates the effective state in the first time window.
In an embodiment of the present invention, the process of generating the synchronous rectification reverse conduction pulse signal according to the synchronous rectification forward conduction pulse signal further includes: and controlling the time length of the synchronous rectification reverse conduction pulse signal in the effective state according to the second output voltage.
In an embodiment of the invention, a time window interval of the synchronous rectification reverse conduction pulse signal for controlling an effective state according to the synchronous rectification forward conduction pulse signal and the voltage across the second secondary winding and/or the drain voltage of the synchronous rectification tube is a first time window.
The synchronous rectification control circuit, the control method thereof and the flyback isolated conversion circuit can effectively improve the problem of load cross regulation rate in a multi-output flyback isolated power supply under the condition of not increasing the circuit cost, are suitable for primary side feedback control and secondary side feedback control, and can reduce the power supply cost because the multi-output circuit can be isolated or grounded.
The above description and applications of the invention herein are illustrative and are not intended to limit the scope of the invention to the above described embodiments. The descriptions related to the effects or advantages mentioned in the embodiments may not be reflected in the experimental examples due to the uncertainty of the specific condition parameters, and are not used for limiting the embodiments. Variations and modifications of the embodiments disclosed herein are possible, and alternative and equivalent various components of the embodiments will be apparent to those skilled in the art. It will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, and with other components, materials, and parts, without departing from the spirit or essential characteristics thereof. Other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention.
Claims (16)
1. A synchronous rectification control circuit for a flyback isolated conversion circuit comprises a primary winding, a first secondary winding and a second secondary winding, wherein the first secondary winding is coupled with a first voltage output end and used for providing a first output voltage, the second secondary winding is coupled with a second voltage output end and used for providing a second output voltage, the second secondary winding is coupled with a synchronous rectifier tube, and the synchronous rectification control circuit is used for generating a driving signal for driving the synchronous rectifier tube.
2. The synchronous rectification control circuit of claim 1 wherein the synchronous rectification control circuit is configured to generate a synchronous rectification forward conduction pulse signal and a synchronous rectification reverse conduction pulse signal to drive the synchronous rectification transistor; the synchronous rectification forward conducting pulse signal in an effective state controls the current in the second secondary side circuit to flow from the source electrode to the drain electrode of the synchronous rectification tube; the synchronous rectification reverse conducting pulse signal in the effective state controls the current in the second secondary side circuit to flow from the drain electrode to the source electrode of the synchronous rectification tube.
3. The synchronous rectification control circuit of claim 2, wherein the synchronous rectification reverse conduction pulse signal time window interval of the synchronous rectification control circuit controlling the effective state is a first time window, the starting time point of the first time window is the time when the current flowing from the source to the drain of the synchronous rectification tube in the second secondary side circuit drops to zero, the ending time point of the first time window is the time when all secondary side circuits in the flyback isolated conversion circuit finish freewheeling, and the synchronous rectification reverse conduction pulse signal generates the effective state in the first time window.
4. The synchronous rectification control circuit of claim 3, wherein the synchronous rectification control circuit comprises a flip-flop, the time window control circuit sets the flip-flop to be in a set state according to a falling edge of the synchronous rectification forward conduction pulse signal, the time window control circuit controls whether the flip-flop is in a reset state according to a comparison result of a voltage across the second secondary winding and/or a drain voltage of the synchronous rectification tube and a first reference voltage, and an output end of the flip-flop outputs a pulse signal representing the first time window.
5. The synchronous rectification control circuit of claim 2, wherein the synchronous rectification control circuit is coupled to the second output voltage, and the synchronous rectification control circuit controls the time length of the synchronous rectification reverse conduction pulse signal in an active state according to the second output voltage.
6. The synchronous rectification control circuit of claim 2, wherein the synchronous rectification control circuit comprises: the synchronous rectification forward conduction pulse generating circuit is used for generating a synchronous rectification forward conduction pulse signal;
the reverse conducting time control circuit is used for generating a synchronous rectification reverse conducting pulse signal; and
and the input end of the first OR gate is respectively coupled with the output end of the synchronous rectification forward conduction pulse generation circuit and the output end of the reverse conduction time control circuit, and the output end of the first OR gate outputs a driving signal of the synchronous rectification tube.
7. The synchronous rectification control circuit of claim 6, wherein a first input terminal of the reverse conduction time control circuit is coupled to an output terminal of the synchronous rectification forward conduction pulse generation circuit, a second input terminal of the reverse conduction time control circuit is coupled to the second secondary winding and/or the drain of the synchronous rectification tube, and the synchronous rectification control circuit controls a time window interval of the synchronous rectification reverse conduction pulse signal in an active state according to signals received by the first input terminal and the second input terminal.
8. The synchronous rectification control circuit of claim 6, wherein the reverse conduction time control circuit comprises:
a time window control circuit, a first input end of which is coupled with the output end of the synchronous rectification forward conduction pulse generating circuit, a second input end of which is coupled with a second secondary winding and/or a drain electrode of the synchronous rectification tube, and is used for controlling the time window interval of the synchronous rectification reverse conduction pulse signal in an effective state;
a time length control circuit, a first input end of which is coupled to the second output voltage, for controlling the time length of the synchronous rectification reverse conduction pulse signal in the effective state according to the second output voltage; and
and the first input end of the AND gate is coupled with the output end of the time window control circuit, the second input end of the AND gate is coupled with the output end of the time length control circuit, and the output end of the AND gate is coupled with the first OR gate.
9. The synchronous rectification control circuit of claim 6, wherein the reverse conduction time control circuit comprises:
a falling edge obtaining circuit, the input end of which is coupled with the output end of the synchronous rectification forward conduction pulse generating circuit;
a first comparator, wherein a first input end of the first comparator is coupled with the second secondary winding and/or the drain electrode of the synchronous rectifier tube, and a second input end of the first comparator is coupled with a first reference voltage;
the setting end of the trigger is coupled with the output end of the falling edge acquisition circuit, and the output end of the trigger outputs the synchronous rectification reverse conduction pulse signal;
a second or gate, a first input terminal of which is coupled to the output terminal of the first comparator, and an output terminal of which is coupled to the reset terminal of the flip-flop;
the output end of the current source is coupled with the first end of the second switch;
a second switch, a second terminal of which is coupled to the first terminal of the third capacitor, and a control terminal of which is coupled to the output terminal of the trigger;
an error amplifier having a first input terminal coupled to the second output voltage and a second input terminal coupled to the second reference voltage;
a first input terminal of the second comparator is coupled to the first terminal of the third capacitor, a second input terminal of the second comparator is coupled to the output terminal of the error amplifier, and an output terminal of the second comparator is coupled to the second input terminal of the second or gate; and
and a third capacitor.
10. The synchronous rectification control circuit of claim 9, wherein a delay circuit is further coupled between the falling edge acquisition circuit and the flip-flop, the delay circuit configured to delay a set state of the flip-flop.
11. A flyback isolated converter circuit, comprising a primary circuit, a first secondary circuit, a second secondary circuit and a synchronous rectification control circuit as claimed in any one of claims 1 to 10, wherein the primary circuit comprises a primary winding and a primary switch, the first secondary circuit comprises a first secondary winding and a rectifying tube, and the first secondary circuit provides a first output voltage; the second secondary side circuit comprises a second secondary side winding and a synchronous rectifier tube, and the second secondary side circuit provides a second output voltage; the synchronous rectification control circuit is coupled with the synchronous rectification tube, and the primary winding, the first secondary winding and the second secondary winding form a transformer winding.
12. The flyback isolated converter circuit of claim 11 wherein the second secondary circuit transfers energy to the first secondary circuit through the transformer winding when the active synchronous rectification reverse conduction pulse signal controls the current in the second secondary circuit to flow from the drain to the source of the synchronous rectifier.
13. A synchronous rectification control method for a flyback isolated conversion circuit, the flyback isolated conversion circuit includes a primary winding, a first secondary winding and a second secondary winding, the first secondary winding is coupled to a first voltage output end for providing a first output voltage, the second secondary winding is coupled to a second voltage output end for providing a second output voltage, the second secondary winding is coupled to a synchronous rectifier tube, the synchronous rectification control circuit is used for generating a driving signal for driving the synchronous rectifier tube, the synchronous rectification control method includes:
generating a synchronous rectification forward conduction pulse signal; and
and generating a synchronous rectification reverse conduction pulse signal according to the synchronous rectification forward conduction pulse signal, wherein the synchronous rectification reverse conduction pulse signal in an effective state is used for controlling the current in the second secondary side circuit to flow from the drain electrode to the source electrode of the synchronous rectification tube so as to promote the second secondary side winding to transfer energy to the first secondary side winding.
14. The synchronous rectification control method of claim 13, wherein the generating of the synchronous rectified reverse conduction pulse signal from the synchronous rectified forward conduction pulse signal further comprises: the time window interval of the synchronous rectification reverse conduction pulse signal for controlling the effective state is a first time window, the starting time point of the first time window is the time when the current flowing from the source electrode to the drain electrode of the synchronous rectification tube in the second secondary side circuit is reduced to zero, the ending time point of the first time window is the time when all secondary side circuits in the flyback isolated conversion circuit finish follow current, and the synchronous rectification reverse conduction pulse signal generates the effective state in the first time window.
15. The synchronous rectification control method of claim 13, wherein the generating of the synchronous rectified reverse conduction pulse signal from the synchronous rectified forward conduction pulse signal further comprises: and controlling the time length of the synchronous rectification reverse conduction pulse signal in the effective state according to the second output voltage.
16. The synchronous rectification control method of claim 14, wherein a time window interval of the synchronous rectification reverse conduction pulse signal for controlling the active state according to the synchronous rectification forward conduction pulse signal and the voltage across the second secondary winding and/or the drain voltage of the synchronous rectification tube is a first time window.
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