CN109672341B - Flyback power converter and secondary side control circuit thereof - Google Patents
Flyback power converter and secondary side control circuit thereof Download PDFInfo
- Publication number
- CN109672341B CN109672341B CN201810613592.2A CN201810613592A CN109672341B CN 109672341 B CN109672341 B CN 109672341B CN 201810613592 A CN201810613592 A CN 201810613592A CN 109672341 B CN109672341 B CN 109672341B
- Authority
- CN
- China
- Prior art keywords
- power
- switch
- synchronous rectification
- signal
- level
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Classifications
-
- 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 flyback power converter and a secondary side control circuit thereof. The flyback power converter includes: the synchronous rectification circuit comprises a transformer, a power switch, a switch control unit, a synchronous rectification switch and a secondary side control circuit. The secondary side control circuit at least comprises: a switching signal generating circuit and a first power conversion circuit. The secondary side control circuit is coupled with a secondary side winding of the transformer and the synchronous rectification switch, and the switching signal generating circuit generates a synchronous rectification switching signal according to the first power or the second power so as to control the synchronous rectification switch. The first power is related to the output voltage. The first power conversion circuit generates second power according to the secondary side phase signal.
Description
Technical Field
The present invention relates to a flyback power converter and a secondary control circuit thereof, and more particularly, to a flyback power converter and a secondary control circuit thereof, in which a secondary control circuit of the flyback power converter can generate a synchronous rectification switching signal according to a first power related to an output voltage or a second power related to a secondary phase signal to control a synchronous rectification switch on the secondary side.
Background
Please refer to fig. 1 and fig. 2. Fig. 1 shows a block schematic diagram of a prior art flyback power converter. Fig. 2 is a graph of gate-source voltage versus on-resistance for a prior art power switch. The flyback power converter 100 of the related art includes: a transformer 15, a power switch 17, a switch control unit 13, a feedback circuit 14, a synchronous rectification switch 18 and a secondary side control circuit 12.
In the prior art, the secondary control circuit 12 generates a synchronous rectification switch signal SVG according to a secondary side level detection signal S _ VTR to control the synchronous rectification switch 18. In the prior art, the secondary level detection signal S _ VTR is generated by the secondary phase node D of the synchronous rectification switch 18 and is input to the pin VTR of the secondary control circuit 12 through a voltage dividing resistor.
In the prior art, the prior art has a serious disadvantage because the power S _ VDD related to the output voltage VOUT can be received only through the pin VDD of the secondary control circuit 12. As shown in fig. 2, when the power S _ VDD related to the output voltage VOUT is too low (for example, but not limited to, lower than 5V), the on-resistance of the synchronous rectification switch 18 suddenly and drastically increases, so that the synchronous rectification switch 18 cannot be fully turned on, thereby reducing the efficiency.
The present invention is directed to a flyback power converter and a secondary side control circuit thereof, which can generate a synchronous rectification switching signal according to a first power related to an output voltage or a second power related to a secondary side phase signal to control a synchronous rectification switch on the secondary side. That is, the present invention can adaptively select the first power or the second power according to different conditions to ensure that the generated synchronous rectification switch signal can make the synchronous rectification switch 18 be fully turned on under different conditions.
Disclosure of Invention
From one aspect, the present invention provides a flyback power converter for converting an input voltage into an output voltage at an output terminal of the flyback power converter, the flyback power converter comprising: a transformer; a power switch coupled to the primary winding of the transformer for switching on or off according to an operation signal to control the primary winding of the transformer and further convert the input voltage coupled to the primary winding of the transformer into the output voltage coupled to the secondary winding of the transformer; a switch control unit coupled to the power switch for generating the operation signal according to a feedback signal related to the output voltage; the synchronous rectification switch is coupled between the output end and a ground potential in series with the secondary side winding of the transformer, and is coupled with a secondary side phase node together with the secondary side winding of the transformer, and the synchronous rectification switch is used for conducting or switching off according to a synchronous rectification switch signal so as to carry out synchronous rectification; and a secondary side control circuit coupled to the secondary side winding of the transformer and the synchronous rectifier switch, the secondary side control circuit including: a switch signal generating circuit for generating the synchronous rectification switch signal to control the synchronous rectification switch according to a first power or a second power, wherein the first power is related to the output voltage; and a first power conversion circuit for converting the secondary side phase signal to generate the second power.
From another aspect, the present invention provides a secondary side control circuit of a flyback power converter, the flyback power converter being configured to convert an input voltage into an output voltage at an output terminal of the flyback power converter, wherein the flyback power converter comprises: a transformer; a power switch coupled to the primary winding of the transformer for switching on or off according to an operation signal to control the primary winding of the transformer and further convert the input voltage coupled to the primary winding of the transformer into the output voltage coupled to the secondary winding of the transformer; a switch control unit coupled to the power switch for generating the operation signal according to a feedback signal related to the output voltage; the synchronous rectification switch is coupled between the output end and a ground potential in series with the secondary side winding of the transformer, the synchronous rectification switch and the secondary side winding of the transformer are coupled to a secondary side phase node together, the synchronous rectification switch is used for being switched on or switched off according to a synchronous rectification switch signal so as to carry out synchronous rectification, and the secondary side control circuit is coupled with the secondary side winding of the transformer and the synchronous rectification switch; the secondary side control circuit includes: a switch signal generating circuit for generating the synchronous rectification switch signal to control the synchronous rectification switch according to a first power or a second power, wherein the first power is related to the output voltage; and a first power conversion circuit for converting the secondary side phase signal to generate the second power.
In a preferred embodiment, the switching signal generating circuit includes: a power selection circuit for comparing a level of the first power with a first reference power threshold to select and convert the first power or the second power to generate a third power; and a driving circuit, which generates the synchronous rectification switch signal by using the third power as a power supply; wherein the power selection circuit selects and converts the first power to generate the third power when the level of the first power is greater than the first reference power threshold; when the level of the first power is lower than the first reference power threshold, the power selection circuit selects and converts the second power to generate the third power for generating the synchronous rectification switch signal in at least one period.
In a preferred embodiment, the first reference power threshold is a level of the second power.
In a preferred embodiment, the power selection circuit further compares the synchronous rectification switch signal with a second reference power threshold to select and convert the first power or the second power when the level of the first power is less than the first reference power threshold or when the level of the first power is less than the second power threshold; when the synchronous rectification switch signal is smaller than the second reference power threshold value, the power selection circuit selects and converts the first power to generate the third power; when the synchronous rectification switch signal is greater than the second reference power threshold value, the power selection circuit selects and converts the second power to generate the third power.
In a preferred embodiment, the level of the first power is determined according to a waveform of the secondary side phase signal.
In a preferred embodiment, the first power conversion circuit includes a linear regulator or a switching power supply.
In a preferred embodiment, the power selection circuit includes: a comparison circuit for comparing the level of the first power with the first reference power threshold to output a first switch control signal and a second switch control signal; a first switch coupled to the first power and turned on or off according to the first switch control signal; and a second switch, coupled to the second power, and turned on or off according to the second switch control signal; when the level of the first power is greater than the first reference power threshold, the first switch control signal controls the first switch to be turned on, and the second switch control signal controls the second switch to be turned off, so that the power selection circuit selects and converts the first power to generate the third power; when the level of the first power is lower than the first reference power threshold, the first switch control signal controls the first switch to be turned off, and the second switch control signal controls the second switch to be turned on, so that the power selection circuit selects and converts the second power to generate the third power.
In a preferred embodiment, the comparison circuit further compares the synchronous rectification switch signal with a second reference power threshold to select and convert the first power or the second power when the level of the first power is less than the first reference power threshold or when the level of the first power is less than the second power threshold; when the synchronous rectification switch signal is smaller than the second reference power threshold value, the first switch control signal controls the first switch to be switched on, and the second switch control signal controls the second switch to be switched off, so that the power selection circuit selects and converts the first power to generate the third power; when the synchronous rectification switch signal is greater than the second reference power threshold, the first switch control signal controls the first switch to be disconnected, and the second switch control signal controls the second switch to be connected, so that the power selection circuit selects and converts the second power to generate the third power.
In a preferred embodiment, the first switch conducts the first power as the third power, or the second switch conducts the second power as the third power.
In a preferred embodiment, the power selection circuit further includes: the second power conversion circuit is used for converting the first power or the second power to generate the third power.
In a preferred embodiment, the second power conversion circuit includes a linear regulator or a switching power supply.
In a preferred embodiment, a current output terminal of the synchronous rectification switch is coupled to the secondary side phase node, and a current input terminal of the synchronous rectification switch is coupled to the ground potential.
Drawings
FIG. 1 shows a schematic diagram of a prior art flyback power converter;
FIG. 2 is a graph of gate-source voltage versus on-resistance for a prior art power switch;
fig. 3 is a schematic diagram of a flyback power converter according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a secondary side control circuit according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a secondary side control circuit according to an embodiment of the present invention;
fig. 6A is a schematic diagram of a power conversion circuit of the secondary side control circuit according to an embodiment of the present invention;
fig. 6B is a schematic diagram of another embodiment of the power conversion circuit of the secondary side control circuit of the present invention;
FIG. 7A is a schematic diagram of a power selection circuit of the secondary control circuit according to an embodiment of the present invention;
FIG. 7B is a schematic diagram of another embodiment of the power selection circuit of the secondary side control circuit of the present invention;
FIG. 8 is a schematic diagram of a power selection circuit of a secondary side control circuit according to still another embodiment of the present invention;
fig. 9A is a schematic diagram of a power selection circuit of a secondary side control circuit according to another embodiment of the present invention;
FIG. 9B is a schematic diagram of a power selection circuit of the secondary side control circuit according to a further embodiment of the present invention;
FIG. 10A is a schematic diagram of a power conversion circuit according to an embodiment of the invention;
FIG. 10B illustrates a schematic diagram of another embodiment of a power conversion circuit of the present invention;
FIG. 10C illustrates a schematic diagram of a power conversion circuit according to another embodiment of the invention;
11A-11B, compare FIG. 7A, show waveform diagrams for different signals;
12A-12B, compare FIG. 7B, show waveform diagrams for different signals;
fig. 13, compare fig. 8, shows waveforms of different signals.
Detailed Description
The foregoing and other technical and scientific aspects, features and advantages of the present invention will be apparent from the following detailed description of a preferred embodiment, which is to be read in connection with the accompanying drawings. The drawings in the present disclosure are schematic and are intended to show the coupling relationship between circuits and the relationship between signal waveforms, and the circuits, signal waveforms and frequencies are not drawn to scale.
Please refer to fig. 3. Fig. 3 is a schematic diagram of a flyback power converter according to an embodiment of the present invention.
In the present embodiment, the flyback power converter 200 may be, for example, but not limited to, an isolated type AC-DC converter (isolated type AC-DC converter). In the isolated ac-dc converter embodiment, the flyback power converter 200 can convert an input voltage VIN into an output voltage VOUT at an output terminal OUT of the flyback power converter 200. The flyback power converter 200 includes: a transformer 15, a power switch 17, a switch control unit 13, a synchronous rectification switch 18 and a secondary side control circuit 12.
In addition, the flyback power converter 200 may further optionally include a feedback circuit 14. The isolated ac-dc converter is a circuit familiar to those skilled in the art, and therefore, other circuit details except for those related to the present application are omitted for the sake of brevity.
The transformer 15 includes a primary winding W1, a secondary winding W2, and a tertiary winding W3. The primary winding W1 is disposed on the primary side 15a of the transformer circuit 15 for receiving the input voltage VIN. The secondary winding W2 is located on the secondary side 15b of the transformer circuit 15 for generating the output voltage VOUT at an output terminal OUT. In one embodiment, the input voltage VIN can be generated by an ac power source Vac via a rectifier circuit 11.
The power switch 17 is coupled to the primary winding W1 of the transformer 15 and is turned on or off according to an operation signal SW to control a current flowing through the primary winding W1, so as to convert the input voltage VIN into the output voltage VOUT by the induction of the secondary winding W2.
The switch control unit 13 is coupled to the power switch 17 for generating an operation signal SW (outputting the operation signal SW from an operation signal terminal GATE thereof) to control the power switch 17 to be turned on or off. In one embodiment, the switch control unit 13 generates the operation signal SW according to the feedback signal COMP. The feedback signal COMP is generated, for example, but not limited to, through a feedback path on the primary side or the secondary side. In one embodiment, the third winding W3 is disposed on the primary side 15a of the transformer circuit 15 for generating information related to the input voltage VIN and/or the output voltage VOUT as the primary-side feedback information according to the input voltage VIN, and in one embodiment, the third winding W3 may further provide power for the switch control unit 13.
The synchronous rectification switch 18 and the secondary winding W2 of the transformer 15 are coupled in series between the output terminal OUT and a ground potential GND, and the synchronous rectification switch 18 and the secondary winding W2 of the transformer 15 are coupled together at a secondary phase node D. In the present embodiment, the synchronous rectification switch 18 is configured to be turned on or off according to a synchronous rectification switch signal Pvg for synchronous rectification. In one embodiment, a current output terminal of the synchronous rectification switch 18 is coupled to the secondary-side phase node D, and a current input terminal of the synchronous rectification switch 18 is coupled to the ground potential GND.
In the present embodiment, the power switch 17 and the synchronous rectification switch 18 may be, for example, but not limited to, NMOS transistor switches. Of course, in other embodiments, the power switch 17 and the synchronous rectification switch 18 may also be PMOS transistor switches. In the following description of the embodiments, the high level is turned on and the low level is turned off as an example. It is clear that the meaning of high and low levels can be interchanged and that the circuit can be changed accordingly.
In one embodiment, the synchronous rectification switch 18 may have a diode M1, a current inflow end of which is coupled to the ground potential GND, and a current outflow end of which is coupled to the secondary winding W2 of the transformer 15. The diode M1 may be a separate diode connected in parallel, and may be a conventional diode or a zener diode, or a parasitic diode of the synchronous rectification switch 18 itself.
In the present embodiment, the secondary-side control circuit 12 is coupled to the secondary winding W2 of the transformer 15 and the synchronous rectification switch 18.
The secondary control circuit 12 of the present invention is capable of generating the synchronous rectification switch signal Pvg to control the synchronous rectification switch 18 according to a first power S _ VDD or a second power S _ VCC. In this embodiment, the first power S _ VDD is related to the output voltage VOUT, and the second power S _ VCC is related to a secondary-side phase signal PHS 2. In one embodiment, as shown in fig. 3, the first power S _ VDD is directly electrically connected to the output voltage VOUT.
Referring to fig. 4, an embodiment of the secondary side control circuit 12 of the present invention is shown. As shown in fig. 4, the secondary control circuit 12 of the present invention includes a switching signal generating circuit 120 and a power converting circuit 122. The switch signal generating circuit 120 is configured to generate a synchronous rectification switch signal Pvg to control the synchronous rectification switch 18 according to the first power S _ VDD or the second power S _ VCC, wherein the first power S _ VDD is related to the output voltage VOUT. The power conversion circuit 122 generates the second power S _ VCC based on the secondary-side phase signal PHS 2. In one embodiment, the power conversion circuit 122 may be, for example but not limited to, a linear regulator (as shown in fig. 6A) or a switching power supply (as shown in fig. 6B), and is configured to convert the secondary-side phase signal PHS2 to generate the second power S _ VCC. The second power S _ VCC is not limited to a level higher or lower than the secondary-side phase signal PHS 2. In an embodiment, the second power S _ VCC may be a fixed voltage or a variable voltage.
In the case where the output voltage VOUT is variable or low, as mentioned above, the synchronous rectification switch 18 is driven by the first power S _ VDD related to the output voltage VOUT, which may cause the on-resistance of the synchronous rectification switch 18 to be high, resulting in high conduction energy loss, because the secondary-side phase signal PHS2 has a high voltage in some time period, the flyback power converter of the present invention can convert the secondary-side phase signal PHS2 to generate the second power S _ VCC, and adaptively select the first power S _ VDD or the second power S _ VCC according to different conditions as the power for driving the synchronous rectification switch 18, so as to ensure that the generated synchronous rectification switch signal Pvg can make the synchronous rectification switch 18 fully conductive under different conditions, thereby having low conduction energy loss and improving the conversion efficiency. The term "fully on" refers to the fact that the on-resistance of the synchronous rectifier switch 18 can be made lower than an on-resistance threshold (in the on state) under the control of the synchronous rectifier switch signal Pvg, as follows. In one aspect, the first power S _ VDD or the second power S _ VCC is used to provide power for the switching signal generating circuit 120, so that the synchronous rectification switching signal Pvg can reach a better level under different conditions to ensure that the synchronous rectification switch 18 has a lower on-resistance. In one embodiment, the second power S _ VCC may be higher than a predetermined voltage level to ensure that the on-resistance of the synchronous rectification switch 18 is lower than the on-resistance threshold. The characteristics and details of how the first power S _ VDD or the second power S _ VCC can be adaptively selected according to different situations will be described in detail later.
Please refer to fig. 5 and compare fig. 7A with fig. 11A-11B. Fig. 5 shows an embodiment of the secondary side control circuit of the present invention. Fig. 7A shows an embodiment of the power selection circuit 121 of the secondary side control circuit of the present invention. Fig. 11A to 11B, and fig. 7A are diagrams showing waveforms of different signals.
As shown in fig. 5, in an embodiment, the switching signal generating circuit 120 includes a power selecting circuit 121 and a driving circuit 123. The power selection circuit 121 may be used to select and convert the first power S _ VDD or the second power S _ VCC to generate the third power P1. The driving circuit 123 generates a synchronous rectification switching signal Pvg by using the third power P1 as a power source. The power selection circuit 121 may generate the third power P1 by determining whether to select the first power S _ VDD or the second power S _ VCC in various ways. In one embodiment, the determination may be made according to a comparison between the level of the first power S _ VDD and the first reference power threshold Vref1, in another embodiment, the comparison between the level of the first power S _ VDD and the level of the second power S _ VCC, in yet another embodiment, the determination may be made according to the secondary-side phase signal PHS2, and in yet another embodiment, the determination may be made according to the synchronous rectification switch signal Pvg, which will be described in detail later.
As shown in fig. 7A, in one embodiment, the power selection circuit 121 includes: a comparison circuit 1211, a first switch SW1 and a second switch SW 2. The comparison circuit 1211 is used for comparing the level of the first power S _ VDD with the first reference power threshold Vref1 to output a first switch control signal S1 and a second switch control signal S2. In this embodiment, the first switch SW1 is coupled to the first power S _ VDD, and the first switch SW1 is turned on or off according to the first switch control signal S1. The second switch SW2 is coupled to the second power S _ VCC and is turned on or off according to the second switch control signal S2.
Referring to fig. 7A and fig. 11A, when the level of the first power S _ VDD is greater than the first reference power threshold Vref1, the first switch control signal S1 controls the first switch SW1 to be turned on, and the second switch control signal S2 controls the second switch SW2 to be turned off, so that the power selection circuit 121 selects and converts the first power S _ VDD to generate the third power P1 (for example, but not limited to, as shown in fig. 11A, the first power S _ VDD is turned on as the third power P1).
Referring to fig. 7A and 11B, when the level of the first power S _ VDD is less than the first reference power threshold Vref1, the first switch control signal S1 controls the first switch SW1 to be open and the second switch control signal S2 controls the second switch SW2 to be closed, so that the power selection circuit 121 selects and converts the second power S _ VCC to generate the third power P1 (for example, but not limited to, as shown in fig. 11B, the first power S _ VCC is turned on as the third power P1).
Please refer to fig. 5 and compare fig. 7B with fig. 12A-12B. Fig. 7B shows another embodiment of the power selection circuit 121 of the secondary side control circuit of the present invention. Fig. 12A to 12B, and fig. 7B are diagrams showing waveforms of different signals.
In one embodiment, the first reference power threshold Vref1 may be, for example and without limitation, a level of the second power S _ VCC. In other words, in the present embodiment, the power selection circuit 121 may be configured to compare the level of the first power S _ VDD with the level of the second power S _ VCC to select and convert the first power S _ VDD or the second power S _ VCC to generate the third power P1.
Referring to fig. 7B and 12A, when the level of the first power S _ VDD is greater than the level of the second power S _ VCC, the first switch control signal S1 controls the first switch SW1 to be turned on, and the second switch control signal S2 controls the second switch SW2 to be turned off, so that the power selection circuit 121 selects and converts the first power S _ VDD to generate the third power P1 (for example, but not limited to, as shown in fig. 12A, the first power S _ VDD is turned on to serve as the third power P1).
Referring to fig. 7B and 12B, when the level of the first power S _ VDD is lower than the level of the second power S _ VCC, the first switch control signal S1 controls the first switch SW1 to be open and the second switch control signal S2 controls the second switch SW2 to be open, so that the power selection circuit 121 selects and converts the second power S _ VCC to generate the third power P1 (for example, but not limited to, as shown in fig. 12B, the first power S _ VCC is turned on as the third power P1).
As described above, according to the present invention, when the first power S _ VDD is low (e.g., lower than the first reference power threshold Vref1, or lower than the second power S _ VCC), the second power S _ VCC may be selected to generate the third power P1 and further generate the synchronous rectification switch signal Pvg, so that the synchronous rectification switch 18 can be fully turned on. On the other hand, when the first power S _ VDD is higher (for example, higher than the first reference power threshold Vref1 or higher than the second power S _ VCC), since the on resistance of the synchronous rectification switch 18 has reached above the minimum threshold or is a lower resistance, the first power S _ VDD is selected to generate the third power P1 and further generate the synchronous rectification switch signal Pvg, and since the first power S _ VDD is generated by the secondary winding, the conversion efficiency is high, and thus, the overall energy loss during the operation of the synchronous rectification switch 18 can be further saved.
It is noted that in the embodiments of fig. 11A, 11B, 12A and 12B, the level of the first power S _ VDD can be determined according to, for example, but not limited to, the waveform of the secondary-side phase signal PHS 2. As shown in fig. 11A, 11B, 12A and 12B, for example but not limited to, during the time period t1-t2, since the secondary-side current Is 0 and the transformer 15 Is demagnetized, the level of the secondary-side phase signal PHS2 Is equal to the output voltage VOUT, in other words, the level of the first power S _ VDD during the time period t1-t2, which can be determined according to the waveform of the secondary-side phase signal PHS 2.
Referring to fig. 9A-9B, two other embodiments of the power selection circuit of the present invention are shown, in which a comparison circuit 1211 is used for comparing the waveform of the secondary-side phase signal PHS2 with the first reference power threshold Vref1 or the level of the second power S _ VCC to output a first switch control signal S1 and a second switch control signal S2.
Please refer to fig. 8 and fig. 13. Fig. 8 shows still another embodiment of the power selection circuit 121 of the secondary side control circuit of the present invention. Fig. 13, compare fig. 8, shows waveforms of different signals.
As shown in fig. 8, in the present embodiment, the power selection circuit 121 may be configured to compare the level of the first power S _ VDD with the first reference power threshold Vref1 (or the level of the second power S _ VCC). When the level of the first power S _ VDD is less than the first reference power threshold Vref1 (or the level of the second power S _ VCC), the power selection circuit 121 may be further configured to compare the synchronous rectification switch signal Pvg with a second reference power threshold Vref2 to output a first switch control signal S1 and a second switch control signal S2, thereby selecting and converting the first power S _ VDD or the second power S _ VCC.
Referring to fig. 13, on the premise that the level of the first power S _ VDD is smaller than the first reference power threshold Vref1 (or the level of the second power S _ VCC), when the synchronous rectification switch signal Pvg is smaller than the second reference power threshold Vref2 (e.g., t2-t3), the first switch control signal S1 controls the first switch SW1 to be turned on, and the second switch control signal S2 controls the second switch SW2 to be turned off, so that the power selection circuit 121 selects and converts the first power S _ VDD to generate the third power P1, which may be turned on as the third power P1 in a time period t2-t3 as shown in fig. 13. On the other hand, also on the premise that the level of the first power S _ VDD is smaller than the first reference power threshold Vref1 (or the level of the second power S _ VCC), when the synchronous rectification switch signal Pvg is greater than the second reference power threshold Vref2 (e.g., t1-t2 or t3-t4), the first switch control signal S1 controls the first switch SW1 to be open, and the second switch control signal S2 controls the second switch SW2 to be open, so that the power selection circuit 121 selects and converts the second power S _ VCC to generate the third power P1, in one embodiment, as shown in fig. 13, the second power S _ VCC is turned on as the third power P1 in the time period t1-t2 or t3-t4, and in this embodiment, the high level of the synchronous rectification switch signal Pvg can reach the level of the second power S _ VCC.
In a preferred embodiment, the second reference power threshold Vref2 is smaller than the first power S _ VDD, and in this embodiment, since the first power S _ VDD can still supply the voltage level required by the synchronous rectification switch signal Pvg when the synchronous rectification switch signal Pvg is smaller than the second reference power threshold Vref2 (e.g., t2-t3 in fig. 13), the power selection circuit 121 selects and converts the first power S _ VDD to generate the third power P1 during this period, which has a higher conversion efficiency.
In the embodiments of fig. 8 and 13, the switching power loss Psw can be calculated as follows:
Psw＝VDrain x Is+S_VDD*IVDD＝[S_VDD+VIN/(Np/Ns)]*[Cg*(S_VCC-Vref2)*Fsw]+S_VDD*[Cg*(Vref2–0V)*Fsw]
VDrain Is the drain voltage of the synchronous rectification switch 18, Is the current (i.e. the secondary side current) of the synchronous rectification switch 18, IVDD Is the current of the first power, Np/Ns Is the ratio of the number of turns of the primary winding to the secondary winding, Cg Is the parasitic capacitance of the synchronous rectification switch 18, and Fsw Is the operating frequency of the synchronous rectification switch 18.
As can be seen from the above equations, in the embodiments of fig. 8 and 13, in addition to the comparison between the first power S _ VDD and the first reference power threshold Vref1 or the second power S _ VCC, the synchronous rectification switch signal Pvg is added to the comparison between the second reference power threshold Vref2 to adaptively select and convert the first power S _ VDD or the second power S _ VCC to generate the third power P1, so that the switching power loss Psw can be further reduced.
In an embodiment, the power selection circuit 121 may further include a power conversion circuit (e.g., the power conversion circuit 1212 in the embodiments of fig. 7A, 7B, 8, 9A, and 9B). The power conversion circuit 1212 is configured to convert the first power S _ VDD or the second power S _ VCC to generate a third power P1. In one embodiment, the power conversion circuit 1212 may be, for example, but not limited to, a linear regulator, as shown in fig. 10A. In another embodiment, the power conversion circuit 1212 may be, for example, but not limited to, a switching power supply, as shown in fig. 10B.
In one embodiment, the first switch SW1 may directly turn on the first power S _ VDD as the third power P1, or the second switch SW2 may directly turn on the second power S _ VCC as the third power P1. In other words, the power conversion circuit 1212 in the previous figures may be a short circuit, as shown in fig. 10C. It should be noted that, in the waveforms of fig. 11A, 11B, 12A, 12B and 13, the first power S _ VDD or the second power S _ VCC is directly used as the waveform of the third power P1 to illustrate the operation strategy of the present invention, however, according to the spirit of the present invention, the third power P1 may be lower or higher than the first power S _ VDD or the second power S _ VCC in the embodiment where the power conversion circuit 1212 is a linear regulator or a switching power supply. In embodiments with a linear regulator or a switching power supply, the third power P1 can be maintained or regulated at a predetermined power level, so as to avoid the first power S _ VDD from being too high, which results in higher switching power loss.
In summary, the flyback power converter of the present invention can adaptively select the first power S _ VDD or the second power S _ VCC according to different conditions, so as to ensure that the generated synchronous rectification switch signal Pvg can make the synchronous rectification switch 18 fully conduct under different conditions, and obtain the best balance between the conduction loss and the switching loss.
The present invention has been described with respect to the preferred embodiments, but the above description is only for the purpose of making the content of the present invention easy to understand for those skilled in the art, and is not intended to limit the scope of the present invention. Equivalent variations will occur to those skilled in the art, within the same spirit of the invention. For example, circuit components, such as switches or resistors, may be inserted between the directly connected circuit components shown without affecting the primary function of the circuit. All of which can be analogized to the teachings of the present invention. In addition, the embodiments described are not limited to be used alone, and may also be used in combination, for example, but not limited to, the two embodiments are used together, or a local circuit of one embodiment is used to replace a corresponding circuit of the other embodiment. Accordingly, the scope of the present invention should be determined to encompass all such equivalent variations as described above. Furthermore, it is not necessary for any embodiment of the invention to achieve all of the objects or advantages, and thus, any one of the claims should not be limited thereby.
Claims (21)
1. A flyback power converter for converting an input voltage to an output voltage at an output terminal of the flyback power converter, the flyback power converter comprising:
a transformer;
a power switch coupled to the primary winding of the transformer for switching on or off according to an operation signal to control the primary winding of the transformer and further convert the input voltage coupled to the primary winding of the transformer into the output voltage coupled to the secondary winding of the transformer;
a switch control unit coupled to the power switch for generating the operation signal according to a feedback signal related to the output voltage;
the synchronous rectification switch is coupled between the output end and a ground potential in series with the secondary side winding of the transformer, and is coupled with a secondary side phase node together with the secondary side winding of the transformer, and the synchronous rectification switch is used for conducting or switching off according to a synchronous rectification switch signal so as to carry out synchronous rectification; and
a secondary side control circuit coupled to the secondary side winding of the transformer and the synchronous rectifier switch, the secondary side control circuit comprising:
a switch signal generating circuit for generating the synchronous rectification switch signal to control the synchronous rectification switch according to a first power or a second power, wherein the first power is related to the output voltage; and
a first power conversion circuit for converting the secondary side phase signal to generate the second power;
wherein the switching signal generating circuit includes:
a power selection circuit for comparing a level of the first power with a first reference power threshold to select and convert the first power or the second power to generate a third power; and
a driving circuit, which generates the synchronous rectification switch signal by using the third power as a power supply;
wherein the power selection circuit selects and converts the first power to generate the third power when the level of the first power is greater than the first reference power threshold;
when the level of the first power is lower than the first reference power threshold, the power selection circuit selects and converts the second power to generate the third power for generating the synchronous rectification switch signal in at least one period.
2. The flyback power converter of claim 1, wherein the first reference power threshold is a level of the second power.
3. The flyback power converter of claim 1 or 2, wherein the power selection circuit further selects and converts the first power or the second power by comparing the synchronous rectification switch signal with a second reference power threshold when the level of the first power is less than the first reference power threshold or when the level of the first power is less than the level of the second power;
when the synchronous rectification switch signal is smaller than the second reference power threshold value, the power selection circuit selects and converts the first power to generate the third power;
when the synchronous rectification switch signal is greater than the second reference power threshold value, the power selection circuit selects and converts the second power to generate the third power.
4. The flyback power converter of claim 1 or 2, wherein the level of the first power is determined according to a waveform of the secondary-side phase signal.
5. The flyback power converter of claim 1, wherein the first power conversion circuit comprises a linear regulator or a switching power supply.
6. The flyback power converter of claim 1 or 2, wherein the power selection circuit comprises:
a comparison circuit for comparing the level of the first power with the first reference power threshold to output a first switch control signal and a second switch control signal;
a first switch coupled to the first power and turned on or off according to the first switch control signal; and
a second switch coupled to the second power and turned on or off according to the second switch control signal;
when the level of the first power is greater than the first reference power threshold, the first switch control signal controls the first switch to be turned on, and the second switch control signal controls the second switch to be turned off, so that the power selection circuit selects and converts the first power to generate the third power;
when the level of the first power is lower than the first reference power threshold, the first switch control signal controls the first switch to be turned off, and the second switch control signal controls the second switch to be turned on, so that the power selection circuit selects and converts the second power to generate the third power.
7. The flyback power converter of claim 6, wherein the comparison circuit further compares the synchronous rectification switch signal with a second reference power threshold to select and convert the first power or the second power when the level of the first power is less than the first reference power threshold or when the level of the first power is less than the second power threshold;
when the synchronous rectification switch signal is smaller than the second reference power threshold value, the first switch control signal controls the first switch to be switched on, and the second switch control signal controls the second switch to be switched off, so that the power selection circuit selects and converts the first power to generate the third power;
when the synchronous rectification switch signal is greater than the second reference power threshold, the first switch control signal controls the first switch to be disconnected, and the second switch control signal controls the second switch to be connected, so that the power selection circuit selects and converts the second power to generate the third power.
8. The flyback power converter of claim 6, wherein the first switch turns on the first power as the third power or the second switch turns on the second power as the third power.
9. The flyback power converter of claim 6, wherein the power selection circuit further comprises:
the second power conversion circuit is used for converting the first power or the second power to generate the third power.
10. The flyback power converter of claim 9, wherein the second power conversion circuit comprises a linear regulator or a switching power supply.
11. The flyback power converter of claim 1, wherein a current output of the synchronous rectifier switch is coupled to the secondary-side phase node, and a current input of the synchronous rectifier switch is coupled to the ground potential.
12. A secondary side control circuit of a flyback power converter, the flyback power converter is used to convert an input voltage into an output voltage at an output terminal of the flyback power converter, wherein the flyback power converter comprises: a transformer; a power switch coupled to the primary winding of the transformer for switching on or off according to an operation signal to control the primary winding of the transformer and further convert the input voltage coupled to the primary winding of the transformer into the output voltage coupled to the secondary winding of the transformer; a switch control unit coupled to the power switch for generating the operation signal according to a feedback signal related to the output voltage; the synchronous rectification switch is coupled between the output end and a ground potential in series with the secondary side winding of the transformer, the synchronous rectification switch and the secondary side winding of the transformer are coupled to a secondary side phase node together, the synchronous rectification switch is used for being switched on or switched off according to a synchronous rectification switch signal so as to carry out synchronous rectification, and the secondary side control circuit is coupled with the secondary side winding of the transformer and the synchronous rectification switch; the secondary side control circuit includes:
a switch signal generating circuit for generating the synchronous rectification switch signal to control the synchronous rectification switch according to a first power or a second power, wherein the first power is related to the output voltage; and
a first power conversion circuit for converting the secondary side phase signal to generate the second power;
wherein the switching signal generating circuit includes:
a power selection circuit for comparing a level of the first power with a first reference power threshold to select and convert the first power or the second power to generate a third power; and
a driving circuit, which generates the synchronous rectification switch signal by using the third power as a power supply;
wherein the power selection circuit selects and converts the first power to generate the third power when the level of the first power is greater than the first reference power threshold;
when the level of the first power is lower than the first reference power threshold, the power selection circuit selects and converts the second power to generate the third power for generating the synchronous rectification switch signal in at least one period.
13. The secondary control circuit of the flyback power converter as in claim 12, wherein the first reference power threshold is a level of the second power.
14. The secondary-side control circuit of the flyback power converter as claimed in claim 12 or 13, wherein the power selection circuit further compares the synchronous rectification switch signal with a second reference power threshold to select and convert the first power or the second power when the level of the first power is less than the first reference power threshold or when the level of the first power is less than the level of the second power;
when the synchronous rectification switch signal is smaller than the second reference power threshold value, the power selection circuit selects and converts the first power to generate the third power;
when the synchronous rectification switch signal is greater than the second reference power threshold value, the power selection circuit selects and converts the second power to generate the third power.
15. The secondary-side control circuit of the flyback power converter as in claim 12 or 13, wherein the level of the first power is determined according to a waveform of the secondary-side phase signal.
16. The secondary control circuit of the flyback power converter as in claim 12, wherein the first power conversion circuit comprises a linear regulator or a switching power supply.
17. The secondary side control circuit of the flyback power converter as claimed in claim 12 or 13, wherein the power selection circuit comprises:
a comparison circuit for comparing the level of the first power with the first reference power threshold to output a first switch control signal and a second switch control signal;
a first switch coupled to the first power and turned on or off according to the first switch control signal; and
a second switch coupled to the second power and turned on or off according to the second switch control signal;
when the level of the first power is greater than the first reference power threshold, the first switch control signal controls the first switch to be turned on, and the second switch control signal controls the second switch to be turned off, so that the power selection circuit selects and converts the first power to generate the third power;
when the level of the first power is lower than the first reference power threshold, the first switch control signal controls the first switch to be turned off, and the second switch control signal controls the second switch to be turned on, so that the power selection circuit selects and converts the second power to generate the third power.
18. The secondary control circuit of the flyback power converter as in claim 17, wherein the comparing circuit further compares the synchronous rectification switch signal with a second reference power threshold to select and convert the first power or the second power when the level of the first power is less than the first reference power threshold or when the level of the first power is less than the level of the second power;
when the synchronous rectification switch signal is smaller than the second reference power threshold value, the first switch control signal controls the first switch to be switched on, and the second switch control signal controls the second switch to be switched off, so that the power selection circuit selects and converts the first power to generate the third power;
when the synchronous rectification switch signal is greater than the second reference power threshold, the first switch control signal controls the first switch to be disconnected, and the second switch control signal controls the second switch to be connected, so that the power selection circuit selects and converts the second power to generate the third power.
19. The secondary-side control circuit of the flyback power converter as in claim 17, wherein the first switch conducts the first power as the third power or the second switch conducts the second power as the third power.
20. The secondary-side control circuit of the flyback power converter of claim 17, wherein the power selection circuit further comprises:
the second power conversion circuit is used for converting the first power or the second power to generate the third power.
21. The secondary control circuit of the flyback power converter as in claim 20, wherein the second power conversion circuit comprises a linear regulator or a switching power supply.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US16/132,367 US10461652B2 (en) | 2017-10-17 | 2018-09-15 | Flyback power converter and secondary side control circuit thereof |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US201762573646P | 2017-10-17 | 2017-10-17 | |
| US62/573,646 | 2017-10-17 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN109672341A CN109672341A (en) | 2019-04-23 |
| CN109672341B true CN109672341B (en) | 2020-06-30 |
Family
ID=66142705
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201810613592.2A Active CN109672341B (en) | 2017-10-17 | 2018-06-14 | Flyback power converter and secondary side control circuit thereof |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN109672341B (en) |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105680694A (en) * | 2014-04-01 | 2016-06-15 | 英飞凌科技奥地利有限公司 | System and method for a switched-mode power supply |
| CN106169870A (en) * | 2015-05-21 | 2016-11-30 | 立锜科技股份有限公司 | There is power supply changeover device and the control method thereof of synchronization control function |
| CN106849666A (en) * | 2015-11-30 | 2017-06-13 | 台湾快捷国际股份有限公司 | The control circuit of the secondary side control of the power converter with synchronous rectifier |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TWI389432B (en) * | 2009-11-10 | 2013-03-11 | Analog Integrations Corp | Flyback converter system capable of preventing two side switchs from being turned on simutaneously |
-
2018
- 2018-06-14 CN CN201810613592.2A patent/CN109672341B/en active Active
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105680694A (en) * | 2014-04-01 | 2016-06-15 | 英飞凌科技奥地利有限公司 | System and method for a switched-mode power supply |
| CN106169870A (en) * | 2015-05-21 | 2016-11-30 | 立锜科技股份有限公司 | There is power supply changeover device and the control method thereof of synchronization control function |
| CN106849666A (en) * | 2015-11-30 | 2017-06-13 | 台湾快捷国际股份有限公司 | The control circuit of the secondary side control of the power converter with synchronous rectifier |
Also Published As
| Publication number | Publication date |
|---|---|
| CN109672341A (en) | 2019-04-23 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US9520868B2 (en) | Power transistor driving circuits and methods for switching mode power supplies | |
| US9812856B2 (en) | Modulation mode control circuit, switch control circuit including the modulation mode control circuit and power supply device including the switch control circuit | |
| US8526202B2 (en) | System and method for synchronous rectifier | |
| US8724346B2 (en) | DC/DC converter, and power supply and electronic device using the same | |
| US10644607B2 (en) | Auxiliary power supply apparatus and method for isolated power converters | |
| KR101274213B1 (en) | Switching mode power supply and the driving method thereof | |
| KR101921793B1 (en) | Tapped winding flyback converter for multiple output voltages | |
| KR20080088006A (en) | Switching mode power supply and the driving method thereof | |
| US6246594B1 (en) | Switching power supply having low loss characteristics | |
| US10784789B1 (en) | Switched mode power supply with multi-mode operation and method therefor | |
| US10461652B2 (en) | Flyback power converter and secondary side control circuit thereof | |
| US7012821B1 (en) | Flyback converter with synchronous rectifier | |
| US7209372B2 (en) | Flyback converter with synchronous rectifier | |
| EP2442435A2 (en) | AD-DC converter | |
| US9178435B2 (en) | Switching power supply | |
| US10355612B2 (en) | Flyback power converter circuit and secondary side controller circuit thereof | |
| CN109672341B (en) | Flyback power converter and secondary side control circuit thereof | |
| JP4543021B2 (en) | POWER SUPPLY DEVICE, ITS CONTROL CIRCUIT, AND CONTROL METHOD | |
| JP2005073403A (en) | Rush current suppressing circuit | |
| CN112953241A (en) | Power converter | |
| CN112994447B (en) | Low-delay-time power conversion circuit and driving circuit therein | |
| JP2020061820A (en) | Drive device, insulation-type dc/dc converter, ac/dc converter, power supply adaptor, and electrical apparatus | |
| JP2020205470A (en) | Pulse transformer device for isolated communications, insulated dc/dc converter, ac/dc converter, power adapter, and electric device | |
| JP6049532B2 (en) | Soft start control circuit, semiconductor integrated circuit, and isolated switching power supply | |
| US20240039389A1 (en) | Isolated switching converter with soft switching and control method thereof |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |