CN111669033A - Synchronous rectifier tube control circuit, flyback voltage conversion circuit and control method - Google Patents
Synchronous rectifier tube control circuit, flyback voltage conversion circuit and control method Download PDFInfo
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- CN111669033A CN111669033A CN202010647360.6A CN202010647360A CN111669033A CN 111669033 A CN111669033 A CN 111669033A CN 202010647360 A CN202010647360 A CN 202010647360A CN 111669033 A CN111669033 A CN 111669033A
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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
- 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
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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
Abstract
The invention provides a control circuit for controlling a synchronous rectifier tube, a flyback voltage conversion circuit and a control method. The synchronous rectifier control circuit includes: the selection control circuit comprises a first comparison circuit, and generates a selection control signal at least based on the comparison between a detection signal representing the pressure difference between two ends of the synchronous rectifier tube and a first threshold signal; a second comparator circuit having a first input terminal, a second input terminal and an output terminal, wherein the second input terminal is coupled to a second threshold signal; and a switch that selectively inputs the detection signal to the first input terminal of the second comparison circuit based on the selection control signal; the output end of the second comparison circuit provides a conduction control signal for controlling the conduction of the synchronous rectifier tube. The control circuit for controlling the synchronous rectifier tube, the flyback voltage conversion circuit and the control method are used for improving the accuracy of the synchronous rectification conduction time and are suitable for adjustment under different conditions.
Description
Technical Field
The present invention relates to the field of electronics, and in particular, but not exclusively, to a control circuit for controlling a synchronous rectifier, a flyback voltage converter circuit, and a control method thereof.
Background
With the development of electronic technology, synchronous rectification circuits are widely used in situations where high conversion efficiency is required due to their high conversion efficiency. A synchronous rectification circuit generally refers to a circuit that receives an input voltage on the primary side of a transformer and converts the input voltage to a desired output voltage on the secondary side of the transformer using a synchronous rectification switch.
In the secondary side synchronous rectification scheme, the on and off of the synchronous rectification switch are usually controlled directly according to the drain-source voltage of the synchronous rectification switch. However, in this control method, if the power supply operates in a DCM Mode (discontinuous conduction Mode), when the synchronous rectification switch is turned off, the circuit may oscillate, and parasitic oscillation of the circuit may also cause the body diode of the synchronous rectification switch to be turned on, which may cause the synchronous rectification switch to be turned on erroneously. If the parasitic oscillation time is directly blanked, the blanking time (Blank time) may hinder the normal turn-on of the synchronous rectification switch in the QR (quasi-resonant Mode) and CCM (Continuous Conduction Mode) operation modes, thereby reducing the efficiency of the power supply. Therefore, the existing synchronous rectification circuit cannot accurately control the conduction of the synchronous rectification switch, and the power supply efficiency is low.
In view of the above, there is a need to provide a new structure or control method to solve at least some of the above problems.
Disclosure of Invention
The invention provides a control circuit for controlling a synchronous rectifier tube, a flyback voltage conversion circuit and a control method, which aim at one or more problems in the prior art.
According to one aspect of the invention, a control circuit for controlling a synchronous rectifier tube comprises: the selection control circuit comprises a first comparison circuit, and generates a selection control signal at least based on the comparison between a detection signal representing the pressure difference between two ends of the synchronous rectifier tube and a first threshold signal; a second comparator circuit having a first input terminal, a second input terminal and an output terminal, wherein the second input terminal is coupled to a second threshold signal; and a switch that selectively inputs the detection signal to the first input terminal of the second comparison circuit based on the selection control signal; the output end of the second comparison circuit provides a conduction control signal for controlling the conduction of the synchronous rectifier tube.
In one embodiment, the selection control circuit further comprises: a time signal generating circuit that generates a time control signal based on at least a comparison of the detection signal with a first threshold signal; and the input end of the trigger circuit respectively receives the output signal and the time control signal provided by the first comparison circuit, and the output end of the trigger circuit provides a selection control signal.
In one embodiment, the selection control signal controls the switch to be turned on when the output signal of the first comparison circuit jumps from the first state to the second state, the time signal generation circuit starts to time when the output signal of the first comparison circuit jumps from the second state to the first state, and the time control signal controls the switch to be turned off after the preset time elapses.
In one embodiment, the time signal generating circuit includes: a current source; a control end of the second switch is coupled with an output end of the first comparison circuit; when the detection signal is smaller than the first threshold value, the second switch controls the current source to charge the capacitor, and the voltage of the capacitor end is increased; and a third comparison circuit, wherein a first input end of the third comparison circuit is coupled with the capacitor, the other end of the third comparison circuit receives the time threshold signal, and an output end of the third comparison circuit provides the time control signal.
In one embodiment, the time signal generating circuit is coupled to the threshold configuration component for adjusting the time threshold signal.
In one embodiment, the control circuit further comprises: the turn-off control circuit provides a turn-off control signal based on the comparison of the detection signal and the third threshold signal and is used for controlling the turn-off of the synchronous rectifier tube; and the second trigger circuit controls the on and off of the synchronous rectifier tube based on the on control signal and the off control signal.
In one embodiment, the control circuit further comprises a third switch coupled to the first input of the second comparison circuit, the third switch being configured to ground the first input of the second comparison circuit when the detection signal is disconnected from the first input of the second comparison circuit.
According to another aspect of the present invention, a control circuit for controlling conduction of a synchronous rectifier includes: the first input end of the first comparison circuit receives a detection signal representing the voltage difference between two ends of the synchronous rectifier tube, and the second input end of the first comparison circuit receives a first threshold signal; the switch is provided with a first end, a second end and a control end, wherein the first end of the switch receives the detection signal, the control end of the switch is coupled with a selection control signal, and the selection control signal is generated at least based on an output end signal of the first comparison circuit; and the second comparison circuit is provided with a first input end, a second input end and an output end, wherein the first input end of the second comparison circuit is coupled with the second end of the switch, the second input end of the second comparison circuit receives a second threshold signal, and the output end of the second comparison circuit is used for providing a conduction control signal for controlling the conduction of the synchronous rectifier tube.
In one embodiment, the control circuit further comprises: a current source; the second switch is coupled with the current source; the capacitor is coupled with the second switch; a third comparison circuit, a first input terminal of which is coupled to (a first terminal of) the capacitor, and the other terminal of which receives the time threshold signal; and a trigger circuit, wherein a first input terminal of the trigger circuit is coupled to the output terminal of the first comparison circuit, a second input terminal of the trigger circuit is coupled to the output terminal of the third comparison circuit, and an output terminal of the trigger circuit is coupled to the control terminal of the switch.
According to another aspect of the present invention, a flyback voltage converter circuit includes a primary switch, a transformer, a secondary synchronous rectifier and a control circuit as described in any of the above embodiments, wherein the primary switch is coupled to a primary winding of the transformer, the secondary synchronous rectifier is coupled to a secondary winding of the transformer, and the control circuit is coupled to a control terminal of the secondary synchronous rectifier.
According to another aspect of the present invention, a method for controlling conduction of a synchronous rectifier includes: comparing the difference signal at two ends of the synchronous rectifier tube with a first threshold value; determining an allowed time interval for which the comparison of the difference signal with the second threshold value is allowed, based at least on a result of the comparison of the difference signal with the first threshold value; and in the allowed time interval, if the difference signal is smaller than a second threshold value, controlling the synchronous rectifier tube to be conducted, wherein the first threshold value is larger than the second threshold value.
In one embodiment, a method of determining an allowed time interval includes: determining a starting point of an allowable time interval at any time of the time interval when the difference signal is greater than the first threshold value; when the difference signal jumps from being larger than the first threshold value to being smaller than the first threshold value, determining the end point of the allowable time interval after the preset time; and if the difference signal is smaller than the second threshold value in the allowed time interval, controlling the synchronous rectifier tube to be conducted.
In one embodiment, the control method further comprises adjusting the preset time by an external configuration element.
In one embodiment, the control method further comprises: when the difference signal jumps from being larger than a first threshold value to being smaller than the first threshold value, the capacitor is charged by adopting a current source; comparing the capacitor voltage to an adjustable time threshold; when the difference signal jumps from being smaller than a first threshold value to being larger than the first threshold value, determining the starting point of the allowable time interval; and when the capacitor voltage is larger than the adjustable time threshold, determining the end point of the allowable time interval.
The control circuit for controlling the synchronous rectifier tube, the flyback voltage conversion circuit and the control method are used for improving the accuracy of synchronous rectification conduction time, optionally adjusting conduction conditions through external elements and are suitable for conduction control under different conditions.
Drawings
FIG. 1 shows a block diagram schematic of a control circuit for controlling a synchronous rectifier according to an embodiment of the invention;
FIG. 2 illustrates a circuit schematic of a control circuit for controlling a synchronous rectifier according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a conduction control circuit for controlling conduction of the synchronous rectifier SR according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a flyback voltage converter circuit according to an embodiment of the invention;
FIG. 5 shows a waveform diagram according to an embodiment of the invention;
fig. 6 is a flowchart illustrating a method for controlling the conduction of a synchronous rectifier according to an embodiment of the invention.
The same reference numbers in different drawings identify the same or similar elements or components.
Detailed Description
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. Combinations of different embodiments, and substitutions of features from different embodiments, or similar prior art means may be substituted for or substituted for features of the embodiments shown and described.
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 conductor, wherein the electrically conductive medium may contain parasitic inductance or parasitic capacitance, or through an intermediate circuit or component as described in the embodiments in the specification; indirect connections may also include connections through other active or passive devices that perform the same or similar function, such as connections through signal amplification circuitry, follower circuitry, logic processing circuitry, and so on. "plurality" or "plurality" means two or more.
Fig. 1 shows a schematic diagram of a control circuit 100 for controlling a synchronous rectifier SR according to an embodiment of the invention. The control circuit 100 includes an on control circuit 10 that controls the synchronous rectifier SR to be on, an off control circuit 13, a flip-flop circuit 14, and a drive circuit 15. The on-control circuit 10 provides an on-control signal Con, the off-control circuit 13 provides an off-control signal Coff, and the trigger circuit 14 controls the on and off of the synchronous rectifier SR based on the on-control signal Con and the off-control signal Coff. The conduction control circuit 10 includes a selection control circuit 11, a switch K1, and a second comparison circuit 12. Wherein the selection control circuit 11 comprises a first comparison circuit 111, the first comparison circuit 111 compares a detection signal Vds representing a voltage difference between the two ends D and S of the synchronous rectifier with a first threshold signal Vth1, the selection control circuit 11 generates the selection control signal SEL at least based on the comparison of the detection signal Vds representing the voltage difference between the two ends D and S of the synchronous rectifier with the first threshold signal Vth 1. In one embodiment, the selection control circuit 11 generates the time signal based on the comparison of the detection signal Vds with the first threshold signal Vth1, and further generates the selection control signal SEL based on the output of the first comparison circuit 111 and the time signal. The selection control signal SEL is used to control the switch K1. The first terminal of the switch K1 receives the detection signal Vds, the second terminal of the switch is coupled to the first input terminal of the second comparing circuit 12, and the second input terminal of the second comparing circuit 12 receives the second threshold signal Vth 1. The switch K1 selectively inputs the detection signal Vds to the second comparison circuit 12 based on the selection control signal SEL so that the detection signal Vds is compared with the second threshold signal Vth2 only in the allowable time interval. The output of the second comparator circuit 12 provides a conduction control signal Con for controlling the conduction of the synchronous rectifier. In one embodiment, in the allowed time interval generated by the first comparing circuit 111, if the detection signal Vds is smaller than the second threshold signal Vth2, the comparator 12 outputs a high level, and the trigger circuit 14 outputs a high level for turning on the synchronous rectifier SR.
Fig. 2 shows a circuit schematic of a control circuit 200 for controlling a synchronous rectifier SR according to an embodiment of the invention. The control circuit 200 includes a selection control circuit 21, a switch K1, a second comparison circuit 22, a turn-off control circuit 23, a trigger circuit 24, and a drive circuit 25. The selection control circuit 21 includes a first comparison circuit 211, a time signal generation circuit 212, and a trigger circuit 213. The first comparison circuit 211 has a first input terminal, a second input terminal, and an output terminal. A first input terminal of the first comparing circuit 211 is coupled to the synchronous rectifier SR for receiving a detection signal Vds representing a voltage difference across the synchronous rectifier SR, and a second input terminal of the first comparing circuit 211 receives a first threshold signal Vth 1. An output terminal of the first comparing circuit 211 is coupled to an input terminal of the time signal generating circuit 212 and a first input terminal of the triggering circuit 213. In the illustrated embodiment, the first input terminal of the first comparing circuit 211 is a non-inverting input terminal, and the second input terminal thereof is an inverting input terminal, and when the detection signal Vds is greater than the first threshold signal Vth1, the first comparing circuit 211 outputs a high level. In one embodiment, the detection signal Vds is obtained by sampling the voltage at the drain terminal D of the synchronous rectifier through a resistance voltage divider circuit, so that the detection signal Vds is proportional to the drain-source voltage of the synchronous rectifier SR. In another embodiment, the detection signal may also be in an inverse variation relationship with the drain-source voltage of the synchronous rectifier SR, and the signals received by the non-inverting input terminal and the inverting input terminal of the first comparing circuit 211 may be exchanged, or the same function may be realized by changing the subsequent logic. The first time signal generation circuit 212 generates the time control signal TC based on at least a comparison of the detection signal Vds and the first threshold signal Vth 1. Two input terminals of the flip-flop circuit 213 respectively receive the output signal V1 provided by the first comparing circuit 211 and the time control signal TC output by the time signal generating circuit 212, and an output terminal of the flip-flop circuit 213 provides the selection control signal SEL. In the illustrated embodiment, the set input terminal of the flip-flop circuit 213 is coupled to the output terminal of the first comparing circuit 211, the reset input terminal of the flip-flop circuit 213 is coupled to the output terminal of the time signal generating circuit, the output terminal of the flip-flop circuit 213 is coupled to the control terminal of the switch K1, and the selection control signal SEL provided by the output terminal of the flip-flop circuit 213 is used for controlling the switch K1 to be turned on or off. In the illustrated embodiment, the conduction time interval of the switch K1 is an allowable time interval for comparing the difference signal across the synchronous rectifier SR with the second threshold, i.e. the detection signal Vds is allowed to be compared with the second threshold signal Vth2 only when the switch K1 is turned on. When the differential voltage signal across the synchronous rectifier SR jumps from being less than the first threshold to being greater than the first threshold, that is, when the output signal of the illustrated first comparator 211 jumps from low to high, the selection control signal SEL goes high, and the control switch K1 is turned on. When the differential pressure signal at the two ends of the synchronous rectifier SR jumps from being greater than the first threshold value to being smaller than the first threshold value, the time signal generating circuit 212 starts timing, and after the preset time, the time control signal TC resets the trigger circuit 213, the selection control signal SEL goes low, and the switch K1 is turned off.
The time signal generating circuit 212 includes a current source 214, a second switch K2, a capacitor C1, and a third comparing circuit 215. A control terminal of the second switch K2 is coupled to the output terminal of the first comparing circuit 211 through the not gate. In another embodiment, when the inputs to first comparator circuit 211 are inverted, the NOT between the output of first comparator circuit 211 and switch K2 may be removed and a NOT added between the output of first comparator circuit 211 and flip-flop 213 accordingly. The switch K2 is coupled to the current source 214, the capacitor C1 is coupled to the switch K2 and the first input terminal of the third comparing circuit 215, the other terminal of the third comparing circuit 215 is coupled to the time threshold signal Vcf, and the output terminal of the third comparing circuit 215 provides the time control signal TC. In the illustrated embodiment, the second switch K2 has a first terminal, a second terminal and a control terminal, wherein the first terminal of the second switch K2 is coupled to the current source 214, the control terminal of the second switch K2 is coupled to the output terminal of the first comparing circuit 211, the second terminal of the second switch K2 is coupled to the first terminal of the capacitor C1 and the first input terminal of the comparing circuit 215, and the other terminal of the capacitor C1 is grounded. When the detection signal Vds is smaller than the first threshold Vth1, the second switch K2 is turned on, the current source 214 charges the capacitor C1, the voltage Vc of the first end of the capacitor C1 increases, and when the voltage Vc of the capacitor end is higher than the time threshold signal Vcf, the output signal of the comparison circuit 215 resets the trigger circuit 213, and the selection control signal SEL is switched to a low level to turn off the switch K1. In the illustrated embodiment, the first input terminal of the comparing circuit 215 is a non-inverting input terminal, the second input terminal of the comparing circuit 215 is an inverting input terminal, and the output terminal of the comparing circuit 215 provides a high level voltage when the voltage Vc across the capacitor C1 is greater than the time threshold signal Vcf. The time signal generating circuit 212 may be further coupled to a threshold configuration component 216 for adjusting the time threshold signal Vcf. The threshold configuration unit 216 may include a resistor or a capacitor disposed outside the chip, and the time threshold signal Vcf may be adjusted by changing the threshold setting resistor or the capacitor, and further the falling slope threshold when the voltage difference between the two ends of the synchronous rectifier drops when the synchronous rectifier starts to flow current is adjusted.
In another embodiment, the selection control circuit 21 includes a first comparison circuit for controlling the switch K1 to be turned on when the detection signal is greater than the first threshold or after a predetermined delay time greater than the first threshold, and for controlling the switch K1 to be turned off after a predetermined delay time when the detection signal is less than the first threshold.
The switch K1 has a first terminal, a second terminal, and a control terminal, the first terminal of the switch K1 is coupled to the synchronous rectifier SR for receiving the detection signal Vds representing the voltage difference across the synchronous rectifier SR, the second terminal of the switch K2 is coupled to the first input terminal of the second comparing circuit 22, and the control terminal of the switch K1 is coupled to the output terminal of the selection control circuit 21 for receiving the selection control signal SEL. The switch K1 selectively inputs the detection signal Vds to the first input terminal of the second comparison circuit 22 based on the selection control signal SEL.
The second comparing circuit 22 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal of the second comparing circuit 22 is coupled to the second terminal of the switch K1, the second input terminal of the second comparing circuit 22 receives the second threshold signal Vth2, and the output terminal of the second comparing circuit 22 is used for providing a turn-on control signal for controlling the turn-on of the synchronous rectifier SR. In the illustrated embodiment, the first input terminal of the second comparing circuit 22 is an inverting input terminal, the second input terminal of the second comparing circuit 22 is a non-inverting input terminal, and the comparing circuit 22 outputs a high level signal if the detection signal Vds is smaller than the second threshold signal Vth2 in the allowed time interval when the switch K1 allows the detection signal Vds to be input to the second comparing circuit 22.
The control circuit 200 may further include a third switch K3, the third switch K3 being coupled to the first input terminal of the second comparator circuit 22. In the illustrated embodiment, the switch K3 is coupled between the reference ground and the first input of the second comparison circuit 22, wherein the third switch K3 is in the opposite conductive state as the switch K1. The third switch K3 is used to connect the first input of the second comparator circuit 22 to ground or other reference node when the detection signal Vds is disconnected from the first input of the second comparator circuit 22. In one embodiment, the second threshold signal Vth2 at the second input terminal of the comparison circuit 22 is negative. When the switch K3 is turned on, the signal at the output of the comparator circuit 22 is low.
The output of the second comparator circuit 22 provides a conduction control signal for controlling the conduction of the synchronous rectifier. When the selection control signal SEL controls the comparison circuit 22 to be coupled to the synchronous rectifier SR and allows it to receive the detection signal Vds representing the voltage difference between the two ends of the synchronous rectifier SR, if the detection signal Vds is smaller than the second threshold signal Vth2 in the allowable time interval, the comparator 22 outputs a high level, and the trigger circuit 24 outputs a high level for turning on the synchronous rectifier SR.
The shutdown control circuit 23 includes a comparison circuit 23 for comparing the detection signal Vds with a third threshold signal Vth3, and the shutdown control circuit controls the shutdown of the synchronous rectification transistor SR based on the comparison of the detection signal Vds with the third threshold signal Vth 3.
A set input terminal of the trigger circuit 24 is coupled to an output terminal of the second comparator circuit 22, i.e., an output terminal of the on-state control circuit, a reset input terminal of the trigger circuit 24 is coupled to an output terminal of the off-state control circuit 23, and an output terminal of the trigger circuit 24 provides a synchronous control signal Gate for controlling the on-state or off-state of the synchronous rectifier SR. It should be noted that "on" and "off" herein refer to synchronous on and synchronous off of the synchronous rectifier SR, respectively, and when the synchronous rectifier SR is synchronously off, the body diode of the synchronous rectifier SR can pass a current. In the illustrated embodiment, the output terminal of the trigger circuit 24 is coupled to the driving circuit 25 for amplifying the synchronous control signal Gate to a voltage suitable for driving, and the control terminal of the synchronous rectifier SR is coupled to the output terminal of the driving circuit 25. The control circuit 200 may further include other circuits such as a conduction signal waveform control circuit, etc., which are not described herein.
The switches K1, K2, K2 may be any suitable devices, such as Junction Field Effect Transistors (JFETs), transistors (BJTs), Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), etc.
In the embodiment shown in fig. 2, the first threshold signal Vth1 is greater than the second threshold signal Vth 2. The third threshold signal Vth3 is less than Vth1 and greater than Vth 2. In one embodiment, the first threshold signal Vth1 is a positive voltage, such as 3V (volts), the second threshold signal is a negative voltage, such as-300 mV, and the third threshold signal is a voltage signal approaching a zero value. In another embodiment, the detection signal is a signal having an inverse relationship with the drain-source voltage of the synchronous rectifier, the detection signal decreases when the drain-source voltage increases, and the magnitude relationship among the first threshold signal, the second threshold signal, and the third threshold signal may be reversed.
Fig. 3 shows a conduction control circuit for controlling conduction of the synchronous rectifier SR according to an embodiment of the invention. In this embodiment, the non-inverting input terminal of the first comparing circuit 31 is coupled to the detecting signal Vds, the inverting input terminal is coupled to the first threshold signal Vth1, the current source 311 of the time signal generating circuit is coupled to the first terminal of the second switch K2, the first terminal of the capacitor C1 and the first input terminal of the comparing circuit 32, and the second terminal of the capacitor C1 and the second terminal of the switch K2 are grounded. When the detection signal Vds jumps from being smaller than the first threshold signal Vth1 to being larger than the first threshold signal Vth1, the trigger circuit 312 is set, the selection control signal SEL controls the first switch K1 to be turned on, the switch K2 is turned on, the non-inverting input terminal of the comparison circuit 32 is grounded, and the comparison circuit 32 outputs a low level. When the detection signal Vds jumps from being greater than the first threshold signal Vth1 to being smaller than the first threshold signal Vth1, the switch K2 is turned off, the current source 311 starts to charge the capacitor C1, after a preset time represented by the time threshold signal Vcf elapses, the capacitor voltage exceeds the time threshold signal Vcf, the comparison circuit 32 outputs a high level, the selection control signal SEL goes low, and the switch K1 is turned off. A delay circuit may be further included between the output terminal of the first comparison circuit 31 and the set input terminal of the trigger circuit 312. The trigger circuit 312 may further include an edge detection circuit before the input end thereof for generating a pulse signal at a rising edge or a falling edge thereof based on the output signal of the comparison circuit for stable triggering.
Fig. 4 shows a schematic diagram of a flyback voltage converter according to an embodiment of the present invention, which includes a primary switch Qp, a transformer T, a secondary synchronous rectifier SR, and a control circuit 400. The primary switch Qp is coupled to the primary winding of the transformer T, the secondary synchronous rectifier SR is coupled to the secondary winding of the transformer T, and the control circuit 300 is coupled to the control terminal of the secondary synchronous rectifier SR for controlling the on/off of the synchronous rectifier SR. Control circuit 400 may include various circuit embodiments combining control circuit 100 as shown in fig. 1, control circuit 200 as shown in fig. 2, a conduction control circuit as shown in fig. 3, and various features. In other embodiments, the control circuit may be applied to other circuit topologies, such as a Buck circuit (Buck) or a Buck-boost circuit (Buck-boost).
Fig. 5 shows a waveform diagram according to an embodiment of the invention. The description may be made with respect to signals in the circuit shown in fig. 2. The signals from top to bottom are the drain-source voltage of the synchronous rectifier SR or the detection signal Vds thereof, the output signal V1 of the first comparison circuit, the charging voltage Vc of the capacitor C1, the selection control signal SEL, the on control signal Con, and the synchronous control signal Gate, respectively. When the primary side switch Qp of the flyback voltage conversion circuit is turned on, the drain-source voltage rises, at time t1, the drain-source voltage Vds is greater than the first threshold Vth1, the signal V1 jumps from a low level to a high level, at this time, the trigger circuit 213 is set, and the selection control signal SEL jumps from a low level to a high level. From time t1, the switch K1 is turned on, and the drain-source voltage detection signal Vds is input to the inverting input terminal of the second comparison circuit 22. When the primary side switch Qp turns off, the drain-source voltage Vds drops. At time t2, the drain-source voltage Vds is less than the first threshold Vth1, the signal V1 transitions low, the current source 214 begins to charge the capacitor C1, and the voltage Vc begins to rise. At time t3, the drain-source voltage Vds drops to be less than the second threshold Vth2, the output signal Con of the second comparator circuit 22 transitions to a high level, the flip-flop circuit 24 is set, the synchronous control signal Gate changes to a high level, and the synchronous rectifier SR is turned on. At time t4, the voltage Vc rises above the threshold signal Vcf, the comparator circuit 215 outputs a high level, the flip-flop circuit 213 is reset, the selection control signal SEL changes to a low level, the switch K1 is turned off, the switch K3 is turned on, the voltage at the inverting input terminal of the comparator circuit 22 is higher than the second threshold Vth2, and the output signal Con of the comparator circuit 22 transitions to a low level. During the period when the signal SEL is at the high level, the drain-source signal Vds is allowed to be compared with the second threshold Vth2, and this period is an allowed time interval a. In this interval, when the drain-source voltage Vds is smaller than the second threshold Vth2, the synchronous rectifier SR is triggered to be turned on. If the drain-source voltage Vds is not smaller than the second threshold Vth2 in the allowable time interval, the synchronous rectifier SR remains in the original state.
When the follow current of the synchronous rectifier SR is finished, the drain-source voltage Vds rises. At time t5, the drain-source voltage Vds is greater than the third threshold Vth3, the off control signal Coff jumps to a high level, the flip-flop circuit 24 is reset, and the synchronous rectifier SR is turned off. In the Discontinuous Control Mode (DCM), when the synchronous rectifier SR is turned off, the drain-source voltage Vds will oscillate, and the drain-source voltage Vds may rise again to the first threshold Vth1, see time t6, or fall to the second threshold Vth2, see time t7, and the capacitor voltage Vc is charged again and is higher than the threshold Vcf at time t 8. Between time t6 and t8, switch K1 is turned on again, forming an allowed time interval B. Since the falling slope of the oscillating signal is small, until the time t9, the drain-source voltage Vds is smaller than the second threshold Vth2, or the drain-source voltage Vds starts to rise without falling to the second threshold Vth2, so that the drain-source voltage Vds is smaller than the second threshold Vth2 within the allowable time interval B, and the conduction of the synchronous rectifier SR is not triggered.
Fig. 6 is a flowchart illustrating a method for controlling the conduction of a synchronous rectifier according to an embodiment of the invention. The control method includes comparing a difference signal Vds across the synchronous rectifier to a first threshold Vth1 at step 601. In one embodiment, the difference signal is the drain-source voltage Vds of the field effect transistor. The difference signal may be obtained by coupling a sampling circuit to the drain of the field effect transistor, and the sampling circuit may include a resistance voltage divider circuit. The control method comprises determining an allowed time interval during which the difference signal Vds is allowed to be compared with the second threshold Vth2 based at least on the comparison of the difference signal Vds with the first threshold Vth1 in step 602. In one embodiment, the method of determining the allowed time interval includes setting a start point of the allowed time interval in step 6021 when the difference signal Vds jumps from being less than the first threshold Vth1 to being greater than the first threshold Vth 1; when the difference signal Vds jumps from being greater than the first threshold Vth1 to being less than the first threshold Vth1, counting is started in step 6022 and a preset time elapses, and after a preset delay time elapses, the end of the permitted time interval is set in step 6023. In one embodiment, the method for setting the preset time comprises the following steps: when the difference signal Vds jumps from being larger than a first threshold Vth1 to being smaller than a first threshold Vth1, the capacitor is charged by adopting a constant current source; comparing the capacitor voltage to a time threshold; when the capacitor voltage is greater than the time threshold, the end of the allowed time interval is determined. In another embodiment, the starting point of the allowed time interval is any time point in the time interval when the difference signal Vds is greater than the first threshold Vth1, such as when the difference signal Vds jumps from being less than the first threshold Vth1 to being greater than the first threshold Vth1, a preset delay is elapsed, and the starting point of the allowed time interval is set. The difference signal Vds is input to the comparison circuit only in the allowable time interval for comparison with the second threshold Vth 2. Preferably, by providing a switch between the difference signal and the comparison circuit, the switch is turned on only during the permitted time interval for permitting the difference signal Vds to be compared with the second threshold Vth 2.
In one embodiment, the preset time is adjustable by the external configuration element, i.e. by adjusting a parameter of the external configuration element to adjust the time threshold signal. The control method includes determining whether the difference signal Vds is smaller than a second threshold Vth2 in the allowed time interval in step 603, and if the difference signal Vds is smaller than the second threshold Vth2, controlling the synchronous rectification tube to be turned on, wherein the second threshold Vth2 is smaller than the first threshold.
Those skilled in the art should understand that the logic controls of "high" and "low", "set" and "reset", "and" or "," in-phase "and" reverse "in the above logic controls can be interchanged or changed, and the subsequent logic controls can be adjusted to achieve the same functions or purposes as those of the above embodiments.
The description and applications of the invention herein are illustrative and are not intended to limit the scope of the invention to the embodiments described above. The descriptions related to the effects or advantages in the specification may not be reflected in practical experimental examples due to uncertainty of specific condition parameters or influence of other factors, and the descriptions related to the effects or advantages are not used for limiting the scope of the invention. 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 (14)
1. A control circuit for controlling a synchronous rectifier, comprising:
the selection control circuit comprises a first comparison circuit, and generates a selection control signal at least based on the comparison between a detection signal representing the pressure difference between two ends of the synchronous rectifier tube and a first threshold signal;
a second comparator circuit having a first input terminal, a second input terminal and an output terminal, wherein the second input terminal is coupled to a second threshold signal; and
a switch selectively inputting the detection signal to the first input terminal of the second comparison circuit based on the selection control signal;
the output end of the second comparison circuit provides a conduction control signal for controlling the conduction of the synchronous rectifier tube.
2. The control circuit of claim 1, wherein selecting the control circuit further comprises:
a time signal generating circuit that generates a time control signal based on at least a comparison of the detection signal with a first threshold signal; and
and the input ends of the trigger circuits respectively receive the output signal and the time control signal provided by the first comparison circuit, and the output ends of the trigger circuits provide the selection control signal.
3. The control circuit as claimed in claim 2, wherein the selection control signal controls the switch to be turned on when the output signal of the first comparison circuit jumps from the first state to the second state, the time signal generation circuit starts to count time when the output signal of the first comparison circuit jumps from the second state to the first state, and the time control signal controls the switch to be turned off after a preset time elapses.
4. The control circuit of claim 2, wherein the time signal generating circuit comprises:
a current source;
a control end of the second switch is coupled with an output end of the first comparison circuit;
when the detection signal is smaller than the first threshold value, the second switch controls the current source to charge the capacitor, and the voltage of the capacitor end is increased; and
a first input terminal of the third comparison circuit is coupled to the capacitor terminal, the other terminal of the third comparison circuit receives the time threshold signal, and an output terminal of the third comparison circuit provides the time control signal.
5. The control circuit of claim 2, wherein the time signal generating circuit is coupled to the threshold configuration component for adjusting the time threshold signal.
6. The control circuit of claim 1, further comprising:
the turn-off control circuit provides a turn-off control signal based on the comparison of the detection signal and the third threshold signal and is used for controlling the turn-off of the synchronous rectifier tube; and
and the second trigger circuit controls the on and off of the synchronous rectifier tube based on the on control signal and the off control signal.
7. The control circuit of claim 1, further comprising a third switch coupled to the first input of the second comparison circuit, the third switch configured to ground the first input of the second comparison circuit when the detection signal is disconnected from the first input of the second comparison circuit.
8. A control circuit for controlling conduction of a synchronous rectifier, comprising:
the first input end of the first comparison circuit receives a detection signal representing the voltage difference between two ends of the synchronous rectifier tube, and the second input end of the first comparison circuit receives a first threshold signal;
the switch is provided with a first end, a second end and a control end, wherein the first end of the switch receives the detection signal, the control end of the switch is coupled with a selection control signal, and the selection control signal is generated at least based on an output end signal of the first comparison circuit; and
and the second comparison circuit is provided with a first input end, a second input end and an output end, wherein the first input end of the second comparison circuit is coupled with the second end of the switch, the second input end of the second comparison circuit receives a second threshold signal, and the output end of the second comparison circuit is used for providing a conduction control signal for controlling the conduction of the synchronous rectifier tube.
9. The control circuit of claim 8, further comprising:
a current source;
the second switch is coupled with the current source;
the capacitor is coupled with the second switch;
a third comparison circuit, a first input terminal of which is coupled to (a first terminal of) the capacitor, and the other terminal of which receives the time threshold signal; and
a first input terminal of the trigger circuit is coupled to the output terminal of the first comparing circuit, a second input terminal of the trigger circuit is coupled to the output terminal of the third comparing circuit, and an output terminal of the trigger circuit is coupled to the control terminal of the switch.
10. A flyback voltage converter circuit comprising a primary switch coupled to a primary winding of a transformer, a secondary synchronous rectifier coupled to a secondary winding of the transformer, and a control circuit according to any of claims 1-9 coupled to a control terminal of the secondary synchronous rectifier.
11. A control method for controlling the conduction of a synchronous rectifier tube comprises the following steps:
comparing the difference signal at two ends of the synchronous rectifier tube with a first threshold value;
determining an allowed time interval for which the comparison of the difference signal with the second threshold value is allowed, based at least on a result of the comparison of the difference signal with the first threshold value;
and in the allowed time interval, if the difference signal is smaller than a second threshold value, controlling the synchronous rectifier tube to be conducted, wherein the first threshold value is larger than the second threshold value.
12. The control method of claim 11, wherein the method of determining the allowable time interval comprises:
determining a starting point of an allowable time interval at any time of the time interval when the difference signal is greater than the first threshold value;
when the difference signal jumps from being larger than the first threshold value to being smaller than the first threshold value, determining the end point of the allowable time interval after the preset time;
and if the difference signal is smaller than the second threshold value in the allowed time interval, controlling the synchronous rectifier tube to be conducted.
13. The control method of claim 12, further comprising adjusting the preset time by an external configuration element.
14. The control method according to claim 12, further comprising:
when the difference signal jumps from being larger than a first threshold value to being smaller than the first threshold value, the capacitor is charged by adopting a current source;
comparing the capacitor voltage to an adjustable time threshold;
when the difference signal jumps from being smaller than a first threshold value to being larger than the first threshold value, determining the starting point of the allowable time interval; and when the capacitor voltage is larger than the adjustable time threshold, determining the end point of the allowable time interval.
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| CN202010647360.6A CN111669033A (en) | 2020-07-07 | 2020-07-07 | Synchronous rectifier tube control circuit, flyback voltage conversion circuit and control method |
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| CN202010647360.6A CN111669033A (en) | 2020-07-07 | 2020-07-07 | Synchronous rectifier tube control circuit, flyback voltage conversion circuit and control method |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117155136A (en) * | 2023-10-27 | 2023-12-01 | 茂睿芯（深圳）科技有限公司 | Synchronous rectification control circuit and method for inhibiting ringing false turn-on of rectifier tube |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117155136A (en) * | 2023-10-27 | 2023-12-01 | 茂睿芯（深圳）科技有限公司 | Synchronous rectification control circuit and method for inhibiting ringing false turn-on of rectifier tube |
| CN117155136B (en) * | 2023-10-27 | 2024-01-26 | 茂睿芯（深圳）科技有限公司 | Synchronous rectification control circuit and method for inhibiting ringing false turn-on of rectifier tube |
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