CN109768708B - Zero voltage switching control circuit for flyback power supply circuit - Google Patents
Zero voltage switching control circuit for flyback power supply circuit Download PDFInfo
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- CN109768708B CN109768708B CN201810480345.XA CN201810480345A CN109768708B CN 109768708 B CN109768708 B CN 109768708B CN 201810480345 A CN201810480345 A CN 201810480345A CN 109768708 B CN109768708 B CN 109768708B
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Abstract
The invention provides a zero voltage switching control circuit for a flyback power supply circuit, which is characterized in that a synchronous rectifier transistor is conducted twice in a switching period to generate reverse current on a primary side winding, and a power transistor on the primary side is conducted after the synchronous rectifier transistor is turned off to realize zero voltage switching. The synchronous signal is used for triggering and generating a zero voltage switching pulse and is used for conducting the synchronous rectification transistor to enable the power transistor on the primary side to realize zero voltage switching.
Description
Technical Field
The present invention relates to a control circuit, and more particularly to a zero voltage switching control circuit for a flyback power supply circuit.
Background
Fig. 1 shows a flyback power supply circuit (flyback power supply circuit 1) in the prior art, in which a primary side control circuit 80 controls a power transistor QP to switch a power transformer 10 to generate an output voltage Vo, and a secondary side control circuit 90 generates a synchronous rectification control signal VG to control a synchronous rectification transistor QSR to perform synchronous rectification on the secondary side.
The prior art shown in fig. 1 has the disadvantage that the synchronous rectification transistor QSR cannot be synchronized with the power transistor QP on the primary side in real time and accurately, and the power transistor QP has poor power conversion efficiency without zero-voltage switching.
Compared with the prior art shown in fig. 1, the invention can be accurately synchronized with the power transistor QP on the primary side, and through the same synchronization signal, the power transistor QP can realize zero-voltage switching during switching, thereby effectively improving the power conversion efficiency.
Disclosure of Invention
The present invention is directed to overcome the defects and drawbacks of the prior art, and provides a zero voltage switching control circuit for a flyback power supply circuit, which can precisely synchronize with a primary power transistor QP, and through the same synchronization signal, the power transistor QP can implement zero voltage switching during switching, thereby effectively improving the power conversion efficiency.
To achieve the above object, in one aspect, the present invention provides a zero-voltage switching control circuit for controlling a flyback power supply circuit, the zero-voltage switching control circuit comprising: a primary side control circuit for generating a switching signal and a synchronous rectification synchronous signal, wherein the switching signal is used for controlling a power transistor to switch a power transformer to generate an output voltage; a secondary side control circuit for generating a synchronous rectification control signal to control the conduction and the disconnection of a synchronous rectification transistor, wherein the synchronous rectification control signal comprises a synchronous rectification pulse and a zero-voltage switching pulse, and the synchronous rectification pulse is used for controlling the conduction of the synchronous rectification transistor for a synchronous rectification period; and a pulse transformer for coupling the synchronous rectification synchronous signal from the primary side control circuit to the secondary side control circuit to generate the synchronous rectification control signal; the synchronous rectification control signal triggers and generates the zero-voltage switching pulse according to the synchronous rectification synchronous signal, the zero-voltage switching pulse controls the synchronous rectification transistor to be conducted for a preset zero-voltage switching time period, and when the synchronous rectification transistor is turned off after the zero-voltage switching pulse is finished, the power transistor is triggered to be conducted, so that the power transistor realizes zero-voltage switching.
In a preferred embodiment, when the zero-voltage switching pulse is ended to turn off the synchronous rectification transistor, a predetermined zero-voltage switching delay period is further included before triggering the power transistor to be turned on.
In a preferred embodiment, the zero-voltage switching pulse is used to control the conduction of the synchronous rectification transistor when the power transformer operates in a Discontinuous Conduction (DCM) mode.
In a preferred embodiment, after the power transistor is turned off, the synchronous rectification pulse controls the synchronous rectification transistor to conduct the synchronous rectification time period to perform secondary side synchronous rectification, wherein after the synchronous rectification pulse is ended, when the synchronous rectification synchronous signal is received, the zero-voltage switching pulse is triggered and generated to conduct the synchronous rectification transistor.
In a preferred embodiment, the synchronous rectification control signal generates the zero-voltage switching pulse to turn on the synchronous rectification transistor when a drain terminal voltage of the synchronous rectification transistor is less than a low voltage threshold.
In a preferred embodiment, after the zero-voltage switching pulse is ended and the synchronous rectification transistor is turned off, and when the cross voltage of an auxiliary winding of the power transformer is lower than a primary side winding threshold value, the preset zero-voltage switching delay period is started; wherein the auxiliary winding is coupled to the primary side control circuit.
In a preferred embodiment, the pulse width of the synchronous rectification synchronization signal determines the start of the zero-voltage switching pulse.
In a preferred embodiment, the primary side control circuit determines the frequency of the synchronous rectified synchronous signal.
In a preferred embodiment, the pulse width of the synchronous rectified synchronous signal is less than 1 microsecond.
From another perspective, the present invention also provides a zero-voltage switching control circuit for controlling a flyback power supply circuit, the zero-voltage switching control circuit comprising: a primary side control circuit for generating a switching signal for controlling a power transistor to switch a power transformer to generate an output voltage; a secondary side control circuit for generating a synchronous rectification control signal and a PWM synchronous signal, wherein the synchronous rectification control signal controls the on and off of a synchronous rectification transistor, the synchronous rectification control signal has a synchronous rectification pulse and a zero-voltage switching pulse, and the synchronous rectification pulse is used for controlling the synchronous rectification transistor to be conducted for a synchronous rectification period; and a pulse transformer for coupling the PWM synchronization signal from the secondary side control circuit to the primary side control circuit to generate the switching signal; before the PWM synchronous signal sends out a synchronous pulse, the zero-voltage switching pulse controls the synchronous rectification transistor to conduct the zero-voltage switching time interval; when the zero-voltage switching pulse is ended to turn off the synchronous rectification transistor, the PWM synchronous signal is generated to trigger the power transistor to be conducted, so that the power transistor realizes zero-voltage switching.
In a preferred embodiment, the zero-voltage switching pulse is not generated when the flyback power supply circuit is operated under a light load.
In a preferred embodiment, the secondary control circuit starts the predetermined zero-voltage switching delay period when the synchronous rectification transistor is turned off by the end of the zero-voltage switching pulse.
In a preferred embodiment, the secondary side control circuit determines the frequency of the switching signal.
In a preferred embodiment, the pulse width of the PWM synchronization signal is less than 1 microsecond.
The purpose, technical content, features and effects of the invention will be more easily understood through the following detailed description of specific embodiments.
Drawings
FIG. 1 is a schematic diagram of a prior art flyback power supply circuit;
FIGS. 2A-2B are schematic diagrams of an exemplary embodiment of the zero-voltage-switching control circuit of the present invention;
FIG. 3 is a waveform diagram of an embodiment of a zero-voltage switching control circuit according to the present invention;
FIG. 4 is a schematic diagram of an embodiment of the zero-voltage switching control circuit of the present invention;
FIG. 5 is a schematic diagram of another embodiment of the zero-voltage switching control circuit of the present invention;
FIG. 6 shows a schematic waveform diagram corresponding to the embodiment of FIG. 5;
fig. 7A-7B show waveforms corresponding to the embodiment of fig. 5.
Detailed Description
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.
Referring to fig. 2A, there is shown an embodiment of a zero-voltage switching control circuit (zero-voltage switching control circuit 501) according to the present invention, in which the zero-voltage switching control circuit 501 is used to control the flyback power supply circuit 2, and the zero-voltage switching control circuit 501 includes a primary side control circuit 80, a secondary side control circuit 90, and a pulse transformer 20. The primary side control circuit 80 is configured to generate a switching signal Vs, and the switching signal Vs is configured to control the power transistor QP to switch the power transformer 10 to generate the output voltage Vo. The secondary control circuit 90 is configured to generate a synchronous rectification control signal VG to control on and off of a synchronous rectification transistor QSR.
After the power transistor QP Is turned on and then turned off again, and when the primary winding W1 Is demagnetized, and the synchronous rectification transistor QSR Is turned on, the power transformer 10 induces a circulating current Is (as shown in fig. 2A) in the secondary winding W2, the circulating current Is transfers energy from the output capacitor CO to the secondary winding W2, and when the synchronous rectification transistor QSR Is turned off again, the power transformer 10 induces a circulating current Ip (as shown in fig. 2B) in the primary winding W1, according to the present invention, the circulating current Ip of the primary winding W1 may discharge the parasitic capacitor CP of the power transistor QP to substantially 0V and charge the parasitic capacitor back to the input capacitor CI, and when the power transistor QP Is then turned on, the power transistor QP may realize Zero Voltage Switching (ZVS-Zero Voltage Switching).
The aforementioned "zero voltage switching" means that before the transistor is turned on, a parasitic capacitor of the transistor is discharged to 0V by a discharge current, and charges the charge back to the device without energy loss, so that when the transistor is turned on, the drain-source voltage of the transistor is already reduced to 0V, and the parasitic capacitor is not discharged by the on-resistance of the transistor, thereby improving the power conversion efficiency.
Further, it should be noted that: since the parasitic effect of the circuit components or the matching between the components is not necessarily ideal, although the parasitic capacitance CP is discharged to 0V, it may not be discharged to 0V exactly, but only close to 0V, that is, according to the present invention, it is acceptable that there is a certain degree of error between the voltage of the discharged parasitic capacitance CP and 0V due to the non-ideality of the circuit, that is, the aforementioned discharge to "substantially" is 0V, and the other points mentioned "substantially" are the same.
Referring to fig. 3, fig. 3 is a waveform diagram of a zero voltage switching control circuit according to an embodiment of the invention. According to the present invention, the synchronous rectification control signal VG may have a synchronous rectification pulse PSR for controlling the synchronous rectification transistor QSR to conduct a synchronous rectification period T _ SR, and a zero-voltage switching pulse PZV, wherein the synchronous rectification period T _ SR Is substantially synchronous with the conduction time of the circulating current Is, such that the power conversion efficiency can be improved; on the other hand, the zero-voltage switching pulse PZV can be used for the zero-voltage switching of the power transistor QP.
The pulse transformer 20 is used for transmitting a synchronous signal between the primary-side control circuit 80 and the secondary-side control circuit 90 in an isolated (non-direct electrical contact) transmission manner to synchronize the switching signal Vs and the synchronous rectification control signal VG. Specifically, the pulse transformer 20 is used for synchronizing the synchronous rectification pulse PSR and the zero-voltage switching pulse PZV by the synchronous signal, and simultaneously, it can achieve the synchronous rectification on the secondary side and the zero-voltage switching of the power transistor QP, and its implementation details will be described later.
Referring to fig. 4, there is shown an embodiment of the zero voltage switching control circuit (zero voltage switching control circuit 502) of the present invention, in which the pulse transformer 20 is used to couple the synchronous rectification synchronous signal SR _ sync from the primary-side control circuit 100 to transmit to the secondary-side control circuit 200 to generate the synchronous rectification control signal VG; referring to fig. 3, in detail, the synchronous rectification control signal VG generates the zero-voltage switching pulse PZV according to the synchronous rectification synchronous signal SR _ sync, the zero-voltage switching pulse PZV controls the synchronous rectification transistor QSR to conduct for a predetermined zero-voltage switching period T _ ZVS (e.g., T1-T2), and when the synchronous rectification transistor QSR is turned off (e.g., T2) after the zero-voltage switching pulse PZV ends, the power transistor QP is triggered to conduct (e.g., T3-T4), as mentioned above, the predetermined zero-voltage switching period T _ ZVS may discharge the parasitic capacitor CP of the power transistor QP to substantially 0, so that the zero-voltage switching may be achieved when the power transistor QP is conducted (e.g., T3-T4).
Referring to fig. 4 and fig. 3, in an embodiment, when the zero-voltage switching pulse PZV ends and turns off the synchronous rectification transistor QSR, a predetermined zero-voltage switching delay period Td (e.g., t2-t3) is further included before triggering the power transistor QP to turn on. In one embodiment, the predetermined zero switching delay period Td ensures that the power transistor QP does not turn on simultaneously with the synchronous rectification transistor QSR, and in one embodiment, the predetermined zero switching delay period Td ensures more accurate zero voltage switching of the power transistor QP.
Referring to fig. 4 and fig. 3, in an embodiment of the zero-voltage switching control circuit of the present invention, the zero-voltage switching pulse PZV controls the turn-on of the synchronous rectification transistor QSR when the power transformer 10 operates in a Discontinuous Conduction (DCM) mode.
Referring to fig. 3, in an embodiment, after the power transistor QP is turned off (e.g., T4), the synchronous rectification pulse PSR controls the synchronous rectification transistor QSR to turn on the synchronous rectification period T _ SR (e.g., T5-T6) to perform secondary-side synchronous rectification, wherein after the synchronous rectification pulse PSR is ended (e.g., T6), when the synchronous rectification synchronous signal SR _ sync is received (e.g., T7 or T0), the zero-voltage switching pulse PZV (e.g., T8 or T1) is triggered to turn on the synchronous rectification transistor QSR.
Referring to fig. 4 and fig. 3, in an embodiment, when the drain terminal voltage VTR of the synchronous rectification transistor QSR is less than a low voltage threshold VT2 (e.g., t0 or t7), the synchronous rectification control signal VG generates the zero-voltage switching pulse PZV to turn on the synchronous rectification transistor QSR, so that the synchronous rectification transistor QSR can also realize zero-voltage switching, thereby further improving the power conversion efficiency. In one embodiment, this condition may be omitted, i.e., the zero-voltage switching pulse PZV may be generated according to other conditions without determining the low voltage threshold VT 2.
Referring to fig. 4 and fig. 3, in an embodiment, after the zero-voltage switching pulse PZV is ended to turn off the synchronous rectification transistor QSR, and when the cross-voltage VM of the auxiliary winding WA of the power transformer 10 is lower than the primary winding threshold VT1 (e.g., t 2'), a predetermined zero-voltage switching delay period Td is initiated to ensure more accurate zero-voltage switching of the power transistor QP; as shown in fig. 4, the auxiliary winding WA is coupled to the primary-side control circuit 80 to obtain the voltage VM across the auxiliary winding WA or the related signal. In one embodiment, the condition on the primary winding threshold VT1 may also be omitted.
In one embodiment, the pulse width of the synchronous rectified sync signal SR _ sync determines the start of the zero voltage switching pulse PZV. From an aspect, the zero voltage switching pulse PZV can be triggered by the negative edge of the synchronous rectified sync signal SR _ sync as shown in fig. 3, but in other embodiments, it is not limited thereto, and the zero voltage switching pulse PZV can be triggered by the positive edge of the synchronous rectified sync signal SR _ sync.
Referring to fig. 4, in an embodiment, the frequency Fs of the synchronous rectified sync signal SR _ sync is determined by the primary side control circuit 100, and in an embodiment, the primary side control circuit 100 may include an oscillator 110 for generating the synchronous rectified sync signal SR _ sync and determining the frequency Fs thereof. In one implementation, the frequency Fs may be a fixed value (e.g., the flyback power supply circuit 4 is operating at a fixed frequency), or may be an adjustable value, or may be a variable value (e.g., the flyback power supply circuit 4 is operating at a non-fixed frequency).
In a preferred embodiment, the pulse width T _ sync of the synchronous rectified synchronous signal SR _ sync may occupy only a small portion of its period, and in one embodiment, the pulse width T _ sync of the synchronous rectified synchronous signal SR _ sync is less than 1 microsecond.
Referring to fig. 5 and fig. 6, fig. 5 shows an embodiment of a zero voltage switching control circuit (zero voltage switching control circuit 503) according to the present invention, and fig. 6 shows a waveform diagram corresponding to the embodiment of fig. 5.
In fig. 5, the zero-voltage switching control circuit 503 is similar to the zero-voltage switching control circuit 502, except that in the zero-voltage switching control circuit 503, the pulse transformer 20 is coupled with the PWM synchronization signal PWM _ SYNC from the secondary-side control circuit 400 to transmit to the primary-side control circuit 300 to generate the switching signal Vs, and controls the power transistor QP to switch the power transformer 10 to generate the output voltage Vo.
Referring to fig. 5 and fig. 6, in the present embodiment, the synchronous rectification control signal VG also has a synchronous rectification pulse PSR and a zero-voltage switching pulse PZV. Before the PWM synchronization signal PWM _ SYNC is sent out the synchronization pulse PPS, the zero-voltage switching pulse PZV controls the synchronous rectification transistor QSR to turn on the zero-voltage switching period T _ ZVS (e.g. T1-T2 in fig. 6), when the zero-voltage switching pulse PZV is ended and the synchronous rectification transistor QSR is turned off (e.g. T2 in fig. 6), the PWM synchronization signal PWM _ SYNC is generated to trigger the power transistor QP to turn on (e.g. T4-T5 in fig. 6, through the switching signal Vs), similar to the aforementioned operation principle, after the synchronous rectification transistor QSR is turned on the zero-voltage switching period T _ ZVS, the primary winding W1 induces the circulating current Ip, and discharges the parasitic capacitance CP of the power transistor QP to substantially 0, and when the PWM synchronization signal PWM _ SYNC is generated to trigger the power transistor QP to turn on, the power transistor QP can realize zero-voltage switching.
Referring to fig. 6, in an embodiment, when the zero-voltage switching pulse PZV ends and turns off the synchronous rectification transistor QSR, the power transistor QP is triggered to turn on after a predetermined zero-voltage switching delay period Td (e.g., t2-t4 of fig. 6) before the power transistor QP is triggered to turn on. In one embodiment, the predetermined zero switching delay period Td ensures that the power transistor QP does not turn on simultaneously with the synchronous rectification transistor QSR, and in one embodiment, the predetermined zero switching delay period Td ensures more accurate zero voltage switching of the power transistor QP.
Referring to fig. 6, in an embodiment, the zero-voltage switching control circuit 503 controls the turn-on synchronous rectification transistor QSR to turn on with the zero-voltage switching pulse PZV when the power transformer 10 operates in a Discontinuous Conduction (DCM) mode.
Referring to fig. 6, in an embodiment, when the drain voltage of the synchronous rectification transistor QSR is lower than a low voltage threshold VT2 (e.g., T0 of fig. 6), the zero-voltage switching pulse PZV controls the synchronous rectification transistor QSR to turn on for the predetermined zero-voltage switching period T _ ZVS.
In one embodiment, when the zero-voltage switching pulse PZV ends to turn off the synchronous rectification transistor QSR, the secondary-side control circuit 400 may start the preset zero-voltage switching delay period Td. In one aspect, the manner of triggering the switching signal by the PWM synchronization signal PWM _ SYNC is not limited to triggering by the positive edge of the synchronization pulse PPS (as shown in fig. 6 at t2), and the switching signal Vs turns on the power transistor QP after the zero-voltage switching delay period Td (as shown in fig. 6 at t 4). In one embodiment, the zero-voltage switching delay period Td may also be triggered from the negative edge of the synchronization pulse PPS (i.e., Td may be as shown in t3-t4 of fig. 6). In another embodiment, the PWM synchronization signal PWM _ SYNC may trigger the switching signal, and the secondary control circuit 400 may trigger the switching signal Vs by a positive edge (e.g. t4 in fig. 7A) or a negative edge (e.g. t4 in fig. 7B) of the synchronization pulse PPS after the zero-voltage switching delay period Td elapses when the zero-voltage switching pulse PZV ends and the synchronous rectification transistor QSR is turned off, so as to turn on the power transistor QP.
Referring to fig. 5, in an embodiment, the frequency Fs' of the switching signal Vs is determined by the secondary control circuit 400. In one embodiment, the secondary control circuit 400 may include an oscillator 410 for generating the PWM synchronization signal PWM _ SYNC and determining the frequency Fs'. In one implementation, the frequency Fs' may be a fixed value (e.g., the flyback power supply circuit 5 is operating at a fixed frequency), or may be an adjustable value, or may be a variable value (e.g., the flyback power supply circuit 5 is operating at a non-fixed frequency).
In a preferred embodiment, the pulse width T _ SYNC of the PWM synchronization signal PWM _ SYNC may occupy only a small portion of its period, and in one embodiment, the pulse width T _ SYNC of the PWM synchronization signal PWM _ SYNC is less than 1 microsecond.
In addition, in an embodiment, when the flyback power supply circuit of the present invention is operated under a light load, the zero-voltage switching pulse PZV is not generated, in other words, the zero-voltage switching control circuit of the present invention can adjust whether the zero-voltage switching pulse PZV is generated according to the load condition, and when the load current is a light load or an extremely light load, the zero-voltage switching control circuit (the zero-voltage switching control circuit 501, 502, or 503) of the present invention is adjusted to not generate the zero-voltage switching pulse PZV, so that the power conversion efficiency can be further improved.
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. The embodiments described are not limited to single use, but may be used in combination, for example, two or more embodiments may be combined, and some components in one embodiment may be substituted for corresponding components in another embodiment. Further, equivalent variations and combinations are contemplated by those skilled in the art within the spirit of the present invention, and the term "processing or computing or generating an output result based on a signal" is not limited to the signal itself, and includes, if necessary, performing voltage-to-current conversion, current-to-voltage conversion, and/or scaling on the signal, and then processing or computing the converted signal to generate an output result. It is understood that equivalent variations and combinations, not necessarily all illustrated, will occur to those of skill in the art, which combinations are not necessarily intended to be limiting. Accordingly, the scope of the present invention should be determined to encompass all such equivalent variations as described above.
Claims (9)
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| Application Number | Priority Date | Filing Date | Title |
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| US16/134,906 US10566893B2 (en) | 2017-11-10 | 2018-09-18 | ZVS control circuit for use in a flyback power converter |
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| US201762584714P | 2017-11-10 | 2017-11-10 | |
| US62/584,714 | 2017-11-10 |
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Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
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| TWI707527B (en) * | 2019-10-15 | 2020-10-11 | 立錡科技股份有限公司 | Flyback powr converter and secondary side controller circuit and control method thereof |
| TWI721802B (en) * | 2019-10-24 | 2021-03-11 | 立錡科技股份有限公司 | Switching controller circuit and method for controlling flyback powr converter |
| CN110798075B (en) * | 2019-11-08 | 2021-04-02 | 矽力杰半导体技术(杭州)有限公司 | Control circuit and switching converter using same |
| CN111293892B (en) * | 2020-03-24 | 2021-05-11 | 福州瑞芯微电子股份有限公司 | Control circuit, control method, chip and flyback converter |
| CN115378266A (en) | 2021-05-19 | 2022-11-22 | 台达电子企业管理（上海）有限公司 | Converter suitable for wide-range output voltage and control method thereof |
| TWI798702B (en) * | 2021-05-20 | 2023-04-11 | 芯巧科技股份有限公司 | Synchronous Rectification Controller |
| CN118214249A (en) * | 2022-12-15 | 2024-06-18 | 华为技术有限公司 | Switching power supply circuit, switching power supply, electronic equipment and power supply system |
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| CN1478318A (en) * | 2000-11-11 | 2004-02-25 | ������������ʽ���� | Power converter |
| CN106130349A (en) * | 2015-05-06 | 2016-11-16 | 立锜科技股份有限公司 | Flyback power supply and controller and driver thereof |
| CN106612074A (en) * | 2015-10-26 | 2017-05-03 | 万国半导体(开曼)股份有限公司 | Power supply device |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US7907426B2 (en) * | 2008-08-11 | 2011-03-15 | Fsp Technology Inc. | Flyback circuit providing synchronized control |
| US9444357B1 (en) * | 2015-04-09 | 2016-09-13 | Power Integrations, Inc. | Active reduced voltage switching using secondary switch |
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|---|---|---|---|---|
| CN1478318A (en) * | 2000-11-11 | 2004-02-25 | ������������ʽ���� | Power converter |
| CN106130349A (en) * | 2015-05-06 | 2016-11-16 | 立锜科技股份有限公司 | Flyback power supply and controller and driver thereof |
| CN106612074A (en) * | 2015-10-26 | 2017-05-03 | 万国半导体(开曼)股份有限公司 | Power supply device |
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