CN108448902B - Synchronous rectification flyback DC-DC power supply conversion device and control method - Google Patents
Synchronous rectification flyback DC-DC power supply conversion device and control method Download PDFInfo
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- CN108448902B CN108448902B CN201810361374.4A CN201810361374A CN108448902B CN 108448902 B CN108448902 B CN 108448902B CN 201810361374 A CN201810361374 A CN 201810361374A CN 108448902 B CN108448902 B CN 108448902B
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- 229910044991 metal oxide Inorganic materials 0.000 claims description 6
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
Abstract
The invention discloses a synchronous rectification flyback DC-DC power supply conversion device and a control method, wherein the synchronous rectification flyback DC-DC power supply conversion device comprises a flyback circuit and an auxiliary switch; the flyback circuit comprises an input port, an output circuit and a transformer; the input port receives direct current input voltage and supplies power to the transformer, and the primary side power switch tube is connected with the primary side power winding of the transformer in series; the output circuit is coupled with a secondary side power winding of the transformer, and energy released by the transformer during the turn-off period of the primary side power switching tube generates a direct current at the output port and is provided for a load; the auxiliary switch is connected in parallel with an auxiliary winding of the transformer. The synchronous rectification flyback DC-DC converter can realize synchronous rectification flyback DC-DC converters without common risk and compatible with a current interruption mode, a current critical interruption mode and a current continuous mode by utilizing the secondary synchronous rectification control technology in the prior art, and the driving signal generation logic circuit of the auxiliary switch is simple.
Description
Technical Field
The invention relates to a direct current-direct current power supply conversion device, in particular to a flyback direct current-direct current power supply conversion device with synchronous rectification, which is applicable to various working modes such as continuous current, intermittent current or critical intermittent current.
Background
Direct current/direct current conversion is one of the most basic forms of electrical energy conversion. The flyback converter is widely used in a low-power switching power supply due to the characteristics of simple topology, few components and the like, and is generally below 100-200W. The losses of the flyback converter mainly comprise the losses of a primary side switching tube, the transformer losses, the losses of an absorption circuit and the losses of a secondary side rectifier. The loss of the rectifier at the output end is one of the main losses of the flyback converter, and the loss of the rectifier tube is particularly prominent under the output conditions of low voltage and high current.
In order to reduce the losses of the rectifier tube, one of the main means is synchronous rectification technology. Fig. 1 shows a flyback dc-dc power conversion device employing synchronous rectification technology, wherein the synchronous rectification control circuit 100 is a simplified schematic diagram of a synchronous rectification control circuit of the prior art that is most commonly used.
As shown in fig. 1, when the primary power switch Q1 is turned off, energy is transferred from the primary side to the secondary side of the transformer T, and the rectifier Q is synchronized SR Is conducted by a body diode of a synchronous rectifying tube Q SR Drain VD variation of (2)Negative pressure is generated. When VD is lower than reference voltage VTH1, the comparator 101 outputs a flip-flop to set the flip-flop 103, and the output of the flip-flop 103 is driven by the driving circuit 104 to output a control signal vg_sr of the synchronous rectifying tube to control the synchronous rectifying tube Q SR Conducting. Synchronous rectifying tube Q SR The conduction can greatly reduce the conduction voltage drop of the output rectifier, thereby achieving the purposes of reducing loss and improving efficiency. As the freewheel current decreases, the VD voltage increases, and when the VD voltage is higher than the reference voltage VTH2, the comparator 102 outputs a flip-flop 103 is reset, and the synchronous rectifier Q2 is controlled to be turned off. In addition, a minimum on-time circuit 107 and an OR gate 108 are added to the synchronous rectification control circuit 100 to prevent oscillation of the VD waveform from causing the synchronous rectification tube Q SR The control signal vg_sr of (1) is turned off by mistake when turned on, and a minimum off time circuit 105 and an and gate 106 are additionally added to set a minimum off time, thereby avoiding the synchronous rectifier Q SR And is turned back on after being turned off.
With the synchronous rectification control method shown in fig. 1, since VD is detected from the synchronous rectification control circuit 100 to reach the reference voltage to the inversion of the synchronous rectification control signal, there is unavoidable delay in the control circuit, including the on delay Td1 and the off delay Td2 of the synchronous rectification tube, as shown in fig. 2 and 3. Wherein fig. 2 shows the main waveforms of the flyback converter of fig. 1 when operating in a current discontinuous mode or a critical discontinuous mode, and fig. 3 shows the main waveforms of the flyback converter of fig. 1 when operating in a current continuous mode.
As can be seen from FIG. 2, when VD voltage reaches reference VTH2, the synchronous rectifier Q is synchronized after a delay of Td2 SR Control signal vg_sr of (a) is inverted from high level to low level, and synchronous rectifying tube Q SR Turn off, its body diode flows through the secondary current. The flyback converter works in the current interruption mode or the critical interruption mode, so that the secondary side current drop slope is smaller, and the synchronous rectifying tube Q SR Can be controlled before the zero crossing of the secondary current, so that no synchronous rectifying tube Q can occur SR Common to the primary side power switch Q1.
As shown in fig. 3, in the current continuous mode, the primary side is at time t3The power switch tube Q1 is turned on and flows through the synchronous rectifying tube Q SR The current of (2) starts to decrease rapidly with a larger slope, and the corresponding VD voltage starts to increase; at time t4, the VD voltage reaches the reference VTH2, and the synchronous rectifying tube Q is synchronized at time t5 after the delay Td2 SR Is turned off. It can be seen that the primary power switch Q1 and the synchronous rectifier Q are in the interval from t3 to t5 SR Are in a common state, so that a large common current is generated, and the flyback converter works abnormally and even causes circuit damage.
Therefore, the conventional synchronous rectification control technique shown in fig. 1 is only suitable for the flyback converter to operate in the current interruption mode or the critical interruption mode, and has a large limitation. In many applications or operating conditions, it may be desirable to design the flyback converter into a current continuous mode in order to optimize device efficiency.
Aiming at the flyback converter of the current continuous mode, an existing solution adopts an optocoupler or a magnetic element to transmit signals of a primary side switching tube to a secondary side of a transformer, and the signals are used for controlling the secondary side synchronous rectifying tube after certain logic processing. However, since the high-frequency pulse signal is transmitted, the optocoupler needs to use an expensive high-speed optocoupler, and the price of the magnetic element is higher, so that the method for isolating and transmitting the synchronous rectifier tube control signal is relatively less applied in industry.
Disclosure of Invention
In order to solve the problems, the invention provides a synchronous rectification flyback DC-DC power supply conversion device and a control method.
A synchronous rectification flyback dc-dc power conversion device, comprising: a flyback circuit and an auxiliary switch; the flyback circuit comprises an input circuit, an output circuit and a transformer; the input circuit comprises a primary power switching tube, which is connected in series with a primary power winding of the transformer, and receives direct-current input voltage to supply power to the transformer; the output circuit is coupled with the secondary side power winding of the transformer, and energy released by the transformer during the turn-off period of the primary side power switching tube generates a direct current at an output port of the output circuit and is provided for a load; the auxiliary switch is connected in parallel with an auxiliary winding of the transformer.
Preferably, the dc input voltage of the input circuit is a dc voltage directly output by a dc power supply such as a battery or a dc voltage output by another conversion circuit, and the dc input voltage is a constant dc voltage or a sinusoidal half-wave voltage output by an ac voltage of the power grid through a diode rectifying circuit.
Preferably, one end of a primary side power winding of the transformer is connected with a direct current input voltage positive electrode, the other end of the primary side power winding of the transformer is connected with a drain electrode of a primary side power switch tube, a source electrode of the primary side power switch tube is connected with a direct current input voltage negative electrode, one end of a secondary side power winding of the transformer is connected with a VD end of a synchronous rectification control circuit and a drain electrode of a secondary side synchronous rectification tube, a grid electrode of the secondary side synchronous rectification tube is connected with a VG end of the synchronous rectification control circuit, the other end of the secondary side power winding of the transformer is connected with one end of a capacitor Co and one end of a load, and the other end of the capacitor Co is connected with the other end of the load and the source electrode of the secondary side synchronous rectification tube; the auxiliary switch is connected in parallel with an auxiliary winding of the transformer.
Preferably, one end of a primary side power winding of the transformer is connected with a source electrode of a primary side power switch tube, a drain electrode of the primary side power switch tube is connected with a positive electrode of a direct current input voltage, the other end of the primary side power winding of the transformer is connected with a negative electrode of the direct current input voltage, one end of a secondary side power winding of the transformer is connected with a VD end of a synchronous rectification control circuit and a drain electrode of a secondary side synchronous rectification tube, a grid electrode of the secondary side synchronous rectification tube is connected with a VG end of the synchronous rectification control circuit, the other end of the secondary side power winding of the transformer is connected with one end of a capacitor Co and one end of a load, and the other end of the capacitor Co is connected with the other end of the load and the source electrode of the secondary side synchronous rectification tube; the auxiliary switch is connected in parallel with an auxiliary winding of the transformer.
Preferably, the auxiliary switch is a semiconductor device having bidirectional blocking capability.
Preferably, the auxiliary switch is a composite switch formed by a diode and a metal oxide semiconductor field effect transistor, and the direction of the diode is opposite to that of the metal oxide semiconductor field effect transistor body diode.
Preferably, the auxiliary switch is a composite switch formed by two metal oxide semiconductor field effect transistors which are connected in series in an opposite direction.
Preferably, the time of the auxiliary switch being turned on is fixed or is regulated by a control circuit of the synchronous rectification flyback dc-dc power supply conversion device according to the operating condition of the circuit.
Preferably, the exciting current of the transformer is operated in an intermittent state, a continuous state or a critical intermittent state.
A control method of a synchronous rectification flyback DC-DC power supply conversion device is characterized by comprising the following steps:
step 1: the synchronous rectification flyback direct current-direct current power supply conversion device respectively generates a control signal of a primary side power switch tube and a control signal of an auxiliary switch;
step 2: the auxiliary switch is conducted once or twice before the primary power switch tube is turned on, so that the primary power winding of the transformer is short-circuited in the conduction time of the auxiliary switch;
step 3: the synchronous rectification control circuit generates synchronous rectifying tube control signals according to voltage signals at two ends of the secondary synchronous rectifying tube.
Preferably, when the synchronous rectification flyback direct current-direct current power supply conversion device works in a current continuous mode, the auxiliary switch is conducted once or twice before the primary side power switch tube is turned on; when the synchronous rectification flyback DC-DC power supply conversion device works in a current interruption mode or a current critical interruption mode, the auxiliary switch is conducted once, twice or not conducted before the primary power switch tube is turned on.
The principle of the invention is as follows: for the synchronous rectification flyback type direct current-direct current converter, when the synchronous rectification flyback type direct current-direct current converter works in a current continuous state, the secondary side current is reduced after the primary side power switch tube is turned on, and for the conventional control mode of detecting that the negative pressure of the voltage at two ends of the secondary side synchronous rectifier tube reaches a certain threshold value to turn off the synchronous rectifier tube, the common problem inevitably exists. The synchronous rectification flyback direct current-direct current power supply conversion device provided by the invention clamps the voltages of all windings of the transformer at zero level by utilizing the conduction of the auxiliary switch connected in parallel with the auxiliary winding of the transformer before the primary power switch tube is turned on, and correspondingly enables the voltages at two ends of the secondary synchronous rectifying tube to be equal to the output voltage, so that the secondary synchronous rectifying tube is turned off before the primary power switch tube is turned on, and the possibility of common use of the primary power switch tube and the secondary synchronous rectifying tube is eliminated. When the synchronous rectification flyback DC-DC converter works in a current interruption mode or a current critical interruption mode, the device and the method of the invention are still applicable because the conventional control mode for detecting the negative pressure of the voltage at two ends of the secondary synchronous rectifying tube can already switch off the secondary synchronous rectifying tube in advance before the primary power switching tube is switched on.
The circuit structure and the implementation method adopted by the invention have obvious advantages compared with the prior art; only a low-power and low-cost low-voltage auxiliary switch is connected in parallel at two ends of an auxiliary winding of the transformer, the synchronous rectification flyback DC-DC converter without common risk and compatible with a current interruption mode, a current critical interruption mode and a current continuous mode can be realized by using the synchronous rectification control technology of the secondary side of the prior art, and a driving signal generation logic circuit of the auxiliary switch is simple. Furthermore, the auxiliary switch, the driving signal generating circuit thereof and the control circuit of the conventional flyback converter can be integrated into the same chip, thereby further reducing the cost of the device.
Drawings
FIG. 1 shows a synchronous rectification flyback DC-DC converter employing a prior art synchronous rectification control circuit;
FIG. 2 illustrates key waveforms of the circuit shown in FIG. 1 operating in a current interrupt mode;
FIG. 3 illustrates key waveforms of the circuit shown in FIG. 1 operating in a current continuous mode;
FIG. 4 shows a first embodiment of the synchronous rectification flyback DC-DC converter of the present invention;
FIG. 5 shows a first embodiment of a synchronous rectified flyback DC-DC converter of the present invention operating in a current continuous mode using a first auxiliary switch control mode;
FIG. 6 shows a first embodiment of a synchronous rectified flyback DC-DC converter of the present invention operating in a current interrupt mode using a first auxiliary switch control mode;
FIG. 7 shows waveforms of a first embodiment of the synchronous rectified flyback DC-DC converter of the present invention operating in a current continuous mode using a second auxiliary switch control mode;
FIG. 8 shows a first embodiment of a synchronous rectified flyback DC-DC converter of the present invention operating in a current continuous mode using a third auxiliary switch control mode;
FIG. 9 shows a schematic diagram of a second embodiment of the synchronous rectified flyback DC-DC converter of the present invention;
fig. 10 shows an embodiment of the auxiliary switch of the synchronous rectification flyback dc-dc converter of the present invention.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings. The features and details of the present invention may be more readily understood from the description of specific embodiments of the invention. Well-known embodiments and procedures have not been described in detail so as not to obscure the various embodiments of the invention, but one or more specific details or components are not available to those skilled in the art that will not obscure and practice the invention.
Reference throughout this specification to "an embodiment" or "one embodiment" means that a particular feature, structure, implementation, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, references to "in one embodiment" in the specification are not necessarily to the same embodiment. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
Fig. 4 is a circuit schematic of a first embodiment of the synchronous rectification flyback dc-dc converter of the present invention, which includes a flyback circuit 200 and an auxiliary switch Qa, and further includes a synchronous rectification control circuit 100.
Wherein the flyback circuit 200 comprises:
the input circuit comprises a primary power switch tube Q1 and receives a direct-current input voltage Vin; the two input ends of the input circuit are respectively connected with the homonymous end of the primary side power winding Wp of the transformer T and the source electrode of the primary side power tube Q1, the homonymous end of the primary side power winding Wp of the transformer T is connected with the positive end of the direct current input voltage Vin, the source electrode of the primary side power tube Q1 is connected with the negative end of the direct current input voltage Vin, the drain electrode of the primary side power switch tube Q1 is connected with the homonymous end of the primary side power winding Wp of the transformer T, and the grid electrode of the primary side power switch tube Q1 receives a control signal Vg1;
a transformer T comprising at least one primary power winding Wp, one secondary power winding Ws and one auxiliary winding Wa;
output circuit comprising secondary synchronous rectifying tube Q SR And an output capacitor Co, the different name of the secondary side power winding Ws of the transformer T is connected with the positive electrode of the output capacitor Co, and the same name of the secondary side power winding Ws of the transformer T is connected with the secondary side synchronous rectifying tube Q SR Drain electrode of the secondary synchronous rectifying tube Q SR The source electrode of the secondary synchronous rectifying tube Q is connected with the cathode of the output capacitor Co SR The gate of (1) receives a control signal vg_sr.
The auxiliary switch Qa is connected in parallel with the auxiliary winding Wa of the transformer T, one end of the auxiliary switch Qa is connected with the synonym end of the auxiliary winding Wa of the transformer T, the other end of the auxiliary switch Qa is connected with the homonym end of the auxiliary winding Wa of the transformer T, and the control end of the auxiliary switch Qa receives the control signal Vga.
VD end secondary side synchronous rectifying tube Q of synchronous rectifying control circuit 100 SR A drain electrode of GND is connected with the secondary synchronous rectifying tube Q SR VG end-connected secondary synchronous rectifying tube Q SR Is formed on the substrate.
For convenience of description, the turn ratio n of the transformer T is defined as a ratio of the number of turns of the primary side power winding Wp to the number of turns of the secondary side power winding Ws, as is also the case in other embodiments of the present specification, and is not separately defined.
Referring to fig. 5, a first embodiment of the synchronous rectification flyback dc-dc converter of the present invention operates in a first auxiliary switch control mode with specific waveforms in current continuous mode and the prior art synchronous rectification control circuit 100 shown in fig. 1:
at time T1, primary power switching transistor Q1 Is turned off, energy stored in transformer T Is transferred to output circuit, primary current Ip decreases, secondary current Is increases, and secondary synchronous rectifying transistor Q SR The body diode of (1) Is conducted to flow the secondary side current Is so that the secondary side synchronous rectifying tube Q SR The voltage across Vds QSR is equal to the negative body diode drop. As can be seen from the operation principle of the synchronous rectification control circuit 100 shown in fig. 1, due to the secondary synchronous rectification tube Q SR The body diode voltage of (1) is lower than the internal reference voltage VTH1 of the synchronous rectification control circuit 100, the output of the comparator 101 is turned over to set the trigger 103, and the output of the trigger 103 is transmitted to the secondary synchronous rectification tube Q through the driving circuit 104 SR Is formed on the substrate. At time t2 after considering delay time Td1 generated by logic circuits in synchronous rectification control circuit 100, secondary synchronous rectification tube control signal Vg_SR is turned from low level to high level to control secondary synchronous rectification tube Q SR Conducting. Synchronous rectifying tube Q at secondary side SR During the conduction period, the secondary synchronous rectifying tube Q Is carried out along with the current drop of the secondary current Is SR The voltage vds_sr across the two terminals rises, but since the circuit is operating in a current continuous state, vds_sr does not reach the reference voltage VTH2;
at time T3, the control signal Vga of the auxiliary switch Qa is high level, the auxiliary switch Qa is controlled to be turned on, the auxiliary winding Wa of the transformer T is short-circuited by Qa, the voltages at the primary side power winding Wp and the secondary side power winding Ws of the transformer T are zero or approximately zero due to the mutual coupling of the windings of the transformer T, and the secondary side synchronous rectifier Q SR The voltage vds_sr at both ends is also correspondingly equal to the output voltage Vo, so that the voltage is higher than the reference voltage VTH2, the output of the comparator 102 is inverted to reset the flip-flop 103, and the output of the flip-flop 103 is transmitted to the secondary side synchronization via the driving circuit 104Rectifying tube Q SR Is formed on the substrate. At time t4 after considering delay time Td2 generated by logic circuits in synchronous rectification control circuit 100, secondary synchronous rectification tube control signal Vg_SR is turned from high level to low level to control secondary synchronous rectification tube Q SR The energy stored in the transformer T is transferred to the auxiliary winding Wa and forms a circulation loop through the auxiliary switch Qa;
at time T5, the control signal Vga of the auxiliary switch Qa is turned from high level to low level, the auxiliary switch Qa is turned off, and the short circuit effect of each winding of the transformer T is relieved; at the same time or after a short delay, the grid signal of the primary power switch tube Q1 is turned from low level to high level, the primary power switch tube Q1 is conducted, and the energy circulated by the auxiliary winding Wa of the transformer T and the auxiliary switch Qa is transferred to the primary power winding Wp of the transformer, so that a certain initial value is generated by the primary current Ip; during the on period of the primary power switch tube Q1, the direct current input voltage V1 is applied to two ends of the primary power winding Wp of the transformer T to excite the excitation inductance of the transformer T, and the primary current Ip starts to rise.
From the above analysis, in the current continuous mode, the synchronous rectification flyback dc-dc power conversion device provided by the present invention turns off the secondary synchronous rectifier tube in advance before the primary power switch tube Is turned on, so as to eliminate the possibility that the primary power switch tube and the secondary synchronous rectifier tube are in common, but the primary side of the transformer will not generate common current, but the delay Td2 of the synchronous rectification control circuit 100 causes the common interval between the secondary synchronous rectifier tube QSR and the auxiliary switch Qa with the duration of Td2, during which the secondary side current Is of the transformer may still drop to a negative value, and the circuit loss Is increased. Compared with the traditional synchronous rectification flyback DC-DC power supply conversion device, the common use of the primary side power switch tube and the secondary side synchronous rectification tube is eliminated, so that the circuit loss is greatly reduced, and the risk of damage to components is avoided.
Referring to fig. 6, a first embodiment of the synchronous rectification flyback dc-dc converter of the present invention employs a specific waveform of a first auxiliary switch control mode operating in a current interrupt mode and the prior art synchronous rectification control circuit 100 shown in fig. 1:
at time T1, primary power switching transistor Q1 Is turned off, energy stored in transformer T Is transferred to output circuit, primary current Ip decreases, secondary current Is increases, and secondary synchronous rectifying transistor Q SR The body diode of (1) Is conducted to flow the secondary side current Is so that the secondary side synchronous rectifying tube Q SR The voltage across Vds QSR is equal to the negative body diode drop. As can be seen from the operation principle of the synchronous rectification control circuit 100 shown in fig. 1, due to the secondary synchronous rectification tube Q SR The body diode voltage of (1) is lower than the internal reference voltage VTH1 of the synchronous rectification control circuit 100, the output of the comparator 101 is turned over to set the trigger 103, and the output of the trigger 103 is transmitted to the secondary synchronous rectification tube Q through the driving circuit 104 SR Is formed on the substrate. At time t2 after considering the delay time Td1 generated by the logic circuit in the synchronous rectification control circuit 100, the secondary synchronous rectification control signal Vg_SR is turned from low level to high level to control the secondary synchronous rectification tube Q SR Conducting; synchronous rectifying tube Q when secondary side SR On, the secondary synchronous rectifying tube Q Is turned on along with the current decrease of the secondary current Is SR The voltage vds_sr across rises. At time t3, vds_SR reaches the reference voltage VTH2, the comparator 102 outputs a flip-flop to reset the flip-flop 103, and the output of the flip-flop 103 is transmitted to the secondary synchronous rectifier Q through the driving circuit 104 SR Is formed on the substrate. At time t4 after considering delay time Td2 generated by logic circuits in synchronous rectification control circuit 100, control signal Vg_SR of secondary synchronous rectifier tube is turned from high level to low level to control secondary synchronous rectifier tube Q SR Shut off, synchronous rectifying tube Q of secondary side SR The body diode of (2) Is conducted and flows through the secondary side current Is;
at the time T5, the secondary side current Is drops to zero, and the exciting inductance of the transformer T oscillates with the equivalent capacitance at the two ends of the primary side power switch tube Q1;
at time T6, the control signal Vga of the auxiliary switch Qa is high level, the auxiliary switch Qa is controlled to be turned on, the auxiliary winding Wa of the transformer T is short-circuited by Qa, the voltages at the primary side power winding Wp and the secondary side power winding Ws of the transformer T are zero or approximately zero due to the mutual coupling of the windings of the transformer T, and the secondary side synchronous rectifier Q SR The voltage vds_sr across is also correspondingly equal to the output voltage Vo. Because the control signal Vg_SR of the secondary synchronous rectifier tube is turned to a low level at the time t4, the action of the auxiliary switch Qa does not influence the state of the Vg_SR;
at time T7, the control signal Vga of the auxiliary switch Qa is turned from high level to low level, the short circuit effect of each winding of the transformer T is released, at time T7, the control signal Vg1 of the primary power switch Q1 is turned from low level to high level, the direct current input voltage V1 is applied to both ends of the primary power winding Wp of the transformer T to excite the excitation inductance of the transformer T, and the primary current Ip rises from zero.
From the above analysis, it can be seen that in the current interrupt mode, the auxiliary switch Qa pairs the secondary synchronous rectifier tube Q SR The control signal shielding the auxiliary switch Qa can be selected so that the auxiliary switch Qa does not operate also in the current interrupt mode without any influence.
Referring to fig. 7, a first embodiment of the synchronous rectification flyback dc-dc converter of the present invention employs a second auxiliary switch control mode to operate in a current continuous mode with specific waveforms and the prior art synchronous rectification control circuit 100 shown in fig. 1:
at time T3, the control signal Vga of the auxiliary switch Qa changes from low level to high level, the auxiliary switch Qa Is controlled to be turned on, the auxiliary winding Wa of the transformer T Is shorted by Qa, the voltages at both ends of the primary side power winding Wp and the secondary side power winding Ws of the transformer T are zero or approximately zero due to mutual coupling of the windings of the transformer T, the secondary side current Is starts to drop, and the secondary side synchronous rectifier Q SR The voltage vds_sr across the output voltage Vo starts to rise to be equal to the output voltage Vo, and thus higher than the reference voltage VTH2, the output of the comparator 102 is inverted to reset the flip-flop 103, and the output of the flip-flop 103 is transmitted to the secondary synchronous rectifier Q via the driving circuit 104 SR Is formed on the substrate. At time t4, the control signal Vga of the auxiliary switch Qa changes from high level to low level, the auxiliary switch Qa Is controlled to be turned off, the short-circuit effect of the auxiliary switch Is relieved, the voltage at two ends of the primary side power switch tube Q1 rises, the secondary side current Is begins to rise, and the secondary side synchronous rectifying tube Q SR Maintaining conduction. In consideration of synchronous rectification controlSecondary synchronous rectifying tube Q at time t5 after delay Td2 generated by logic circuits within circuit 100 SR The control signal Vg_SR of the (V) is turned from high level to low level to control the secondary synchronous rectifying tube Q SR Shut off, synchronous rectifying tube Q of secondary side SR The body diode of (1) Is passed through the secondary side current Is, and the secondary side synchronous rectifying tube Q SR Is lower than the reference voltage VTH1, but due to the minimum off-time module in the synchronous rectification control circuit 100, the secondary synchronous rectification tube Q SR Still remain off. At time t6, the grid signal of the primary side power switch tube Q1 is turned from low level to high level, the primary side power switch tube Q1 is conducted, and secondary side energy is transferred to the primary side, so that a certain initial value is generated by the primary side current Ip; during the on period of the primary power switch tube Q1, the direct current input voltage V1 is applied to two ends of the primary power winding Wp of the transformer T to excite the excitation inductance of the transformer T, and the primary current Ip starts to rise.
Similarly, the invention shown in FIG. 7 operates in a current interrupt mode using a second auxiliary switch control scheme, with auxiliary switch Qa versus secondary synchronous rectifier Q SR Without any effect on the proper functioning of (a) and without further detailed analysis here.
Compared with the first auxiliary switch control mode shown in fig. 5, the second auxiliary switch control mode shown in fig. 7 is adopted, and the pulse width of the auxiliary switch Qa can be set smaller than the delay time Td2 of the synchronous rectification control circuit, so that the common conduction time of the secondary side of the transformer and the auxiliary winding loop is smaller, and the circuit loss is reduced.
Referring to fig. 8, a first embodiment of the synchronous rectification flyback dc-dc converter of the present invention employs a third auxiliary switch control mode to operate in a current continuous mode with specific waveforms and the prior art synchronous rectification control circuit 100 shown in fig. 1:
at time T3, the control signal Vga of the auxiliary switch Qa changes from low level to high level, the auxiliary switch Qa is controlled to be turned on, the auxiliary winding Wa of the transformer T is shorted by Qa, and the voltages at the primary side power winding Wp and the secondary side power winding Ws of the transformer T are zero or approximate due to the mutual coupling of the windings of the transformer TAt zero, the secondary side current Is begins to drop, and the secondary side synchronous rectifying tube Q SR The voltage vds_sr across the output voltage Vo starts to rise to be equal to the output voltage Vo, and thus higher than the reference voltage VTH2, the output of the comparator 102 is inverted to reset the flip-flop 103, and the output of the flip-flop 103 is transmitted to the secondary synchronous rectifier Q via the driving circuit 104 SR Is formed on the substrate. At time t4, the control signal Vga of the auxiliary switch Qa changes from high level to low level, the auxiliary switch Qa Is controlled to be turned off, the short-circuit effect of the auxiliary switch Is relieved, the voltage at two ends of the primary side power switch tube Q1 rises, the secondary side current Is begins to rise, and the secondary side synchronous rectifying tube Q SR Maintaining conduction. At time t5 after considering delay Td2 generated by logic circuits in synchronous rectification control circuit 100, secondary synchronous rectification tube Q SR The control signal Vg_SR of the (V) is turned from high level to low level to control the secondary synchronous rectifying tube Q SR Shut off, synchronous rectifying tube Q of secondary side SR The body diode of (1) Is passed through the secondary side current Is, and the secondary side synchronous rectifying tube Q SR Is lower than the reference voltage VTH1, but due to the minimum off-time module in the synchronous rectification control circuit 100, the secondary synchronous rectification tube Q SR Still remain off. At time T6, the control signal Vga of the auxiliary switch Qa changes from low level to high level again, the auxiliary switch Qa Is controlled to be turned on, the auxiliary winding Wa of the transformer T Is shorted by Qa, the voltages at the primary side power winding Wp and the secondary side power winding Ws of the transformer T are zero or approximately zero due to the mutual coupling of the windings of the transformer T, the secondary side current Is begins to drop, and the secondary side synchronous rectifier Q SR The voltage vds_sr across the primary power switch begins to rise equal to the output voltage Vo and the voltage vds_q1 across the primary power switch drops equal to the input voltage Vin. At time t7, the grid signal of the primary side power switch tube Q1 is turned from low level to high level, the primary side power switch tube Q1 is conducted, and secondary side energy is transferred to the primary side, so that a certain initial value is generated by the primary side current Ip; during the on period of the primary power switch tube Q1, the direct current input voltage V1 is applied to two ends of the primary power winding Wp of the transformer T to excite the excitation inductance of the transformer T, and the primary current Ip starts to rise.
Similarly, the present invention shown in FIG. 8 employs a third auxiliary switch control schemeOperating in current interruption mode, auxiliary switch Qa pairs secondary synchronous rectifier tube Q SR Without any effect on the proper functioning of (a) and without further detailed analysis here.
In the present invention shown in fig. 8, compared with the present invention shown in fig. 7, which adopts the second auxiliary switch control mode, the auxiliary switch Qa is turned on twice before the primary power switch tube is turned on, and the voltage vds_q1 across the primary power switch tube Q1 is reduced to be equal to the input voltage Vin during the second turn-on period, so that the loss of the primary power switch tube Q1 can be reduced when the primary power switch tube Q1 is turned on.
Fig. 9 is a circuit schematic diagram of a second embodiment of the synchronous rectification flyback dc-dc converter according to the present invention, wherein the synchronous rectification flyback dc-dc converter includes a flyback circuit 200 and an auxiliary switch Qa, and further includes a synchronous rectification control circuit 100.
Wherein the flyback circuit 200 comprises:
the input circuit comprises a primary power switch tube Q1 and receives a direct-current input voltage Vin; the two input ends of the input circuit are respectively connected with the drain electrode of the primary power switch tube Q1 and the different name end of the primary power winding Wp of the transformer T, the drain electrode of the primary power switch tube Q1 is connected with the positive end of the direct current input voltage Vin, the different name end of the primary power winding Wp of the transformer T is connected with the negative end of the direct current input voltage Vin, the source electrode of the primary power switch tube Q1 is connected with the same name end of the primary power winding of the transformer T, and the grid electrode of the primary power switch tube Q1 receives a control signal Vg1;
a transformer T including a primary power winding Wp, a secondary power winding Ws, and an auxiliary winding Wa;
output circuit comprising secondary synchronous rectifying tube Q SR And an output capacitor Co, the different name of the secondary side power winding Ws of the transformer T is connected with the positive electrode of the output capacitor Co, and the same name of the secondary side power winding Ws of the transformer T is connected with the secondary side synchronous rectifying tube Q SR Drain electrode of the secondary synchronous rectifying tube Q SR The source electrode of the secondary synchronous rectifying tube Q is connected with the cathode of the output capacitor Co SR Is a gate of (2)The pole receives the control signal vg_sr.
The auxiliary switch Qa is connected in parallel with the auxiliary winding Wa of the transformer T, one end of the auxiliary switch Qa is connected with the synonym end of the auxiliary winding Wa of the transformer T, the other end of the auxiliary switch Qa is connected with the homonym end of the auxiliary winding Wa of the transformer T, and the control end of the auxiliary switch Qa receives the control signal Vga.
VD end secondary side synchronous rectifying tube Q of synchronous rectifying control circuit 100 SR A drain electrode of GND is connected with the secondary synchronous rectifying tube Q SR VG end-connected secondary synchronous rectifying tube Q SR Is formed on the substrate.
The second embodiment of the synchronous rectification flyback dc-dc converter of the present invention shown in fig. 9 is different from the first embodiment of the synchronous rectification flyback dc-dc converter of the present invention shown in fig. 4 only in that the flyback circuit is different in structure, and the control manner of the working process and the secondary synchronous rectification tube is basically the same, and is not repeated here.
Reference is made to several specific embodiments of the auxiliary switch Qa of the present invention shown in fig. 10. The auxiliary switch Qa may be a single semiconductor device having a bidirectional blocking capability such as a bipolar transistor as shown in fig. 10 (a), a collector of which is connected to a synonym terminal of the auxiliary winding Wa of the transformer T as an a terminal of the auxiliary switch Qa, an emitter of which is connected to a synonym terminal of the auxiliary winding Wa of the transformer T as a B terminal of the auxiliary switch Qa, and a base of which receives the control signal Vga as a control terminal C of the auxiliary switch Qa.
The auxiliary switch Qa may be a composite switch constituted by a plurality of semiconductor devices shown in fig. 10 (b) to (c). Referring to fig. 10 (b), the auxiliary switch Qa is a complex switch composed of two MOSFETs Qa1 and Qa2 connected in reverse series. Wherein, the source of Qa1 is connected to the synonym end of the auxiliary winding Wa of the transformer T as the a end of the auxiliary switch Qa, the drain thereof is connected with the drain of Qa2, the source of Qa2 is connected to the synonym end of the auxiliary winding Wa of the transformer T as the B end of the auxiliary switch Qa, the gates of Qa1 and Qa2 are connected to each other as the control end C of the auxiliary switch Qa to receive the control signal Vga; referring to fig. 10 (c), one embodiment of the auxiliary switch Qa is a composite switch composed of one diode Db and one MOSFET Qb. Wherein, the anode of Db is connected to the synonym terminal of the auxiliary winding Wa of the transformer T as the a terminal of the auxiliary switch Qa, the cathode of Db is connected to the drain of Qb, the source of Qb is connected to the synonym terminal of the auxiliary winding Wa of the transformer T as the B terminal of the auxiliary switch Qa, and the gate of Qb receives the control signal Vga as the control terminal C of the auxiliary switch Qa.
The foregoing detailed description of embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise form disclosed. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
The teachings of the present invention provided herein are not necessarily applied to the above-described systems, but may be applied to other systems as well. The elements and acts of the various embodiments described above can be combined to provide further embodiments.
The invention is capable of modification in light of the foregoing detailed description, and is capable of embodiments in various ways, all as if the invention were described in detail hereinabove, as well as in the best mode contemplated of carrying out the invention. The details of the above-described circuit configuration and manner of controlling the same may vary considerably in its implementation details, while still being encompassed by the invention disclosed herein.
As noted above, it should be noted that particular terminology used in describing certain features or aspects of the invention should not be taken to imply that the terminology is being redefined herein to be restricted to certain specific characteristics, features, or aspects of the invention with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification, unless the above detailed description section explicitly defines such terms. Therefore, the actual scope of the invention encompasses not only the disclosed embodiments, but also all equivalent ways of practicing or implementing the invention under the claims.
While certain aspects of the invention are described below in certain specific claim forms, the inventors contemplate the various aspects of the invention in any number of claim forms. Accordingly, the inventors reserve the right to add additional claims after filing the application to pursue other aspects of the invention in the form of such additional claims.
The invention also provides a control method of the synchronous rectification flyback DC-DC power supply conversion device compatible with the current interruption mode, the current critical interruption mode and the current continuous mode, which comprises the following steps:
step 1: the synchronous rectification flyback direct current-direct current power supply conversion device respectively generates a control signal of a primary side power switch tube and a control signal of an auxiliary switch;
step 2: the auxiliary switch is conducted once or twice before the primary power switch tube is turned on, so that the auxiliary winding of the transformer is short-circuited during the conduction period of the auxiliary switch;
step 3: the synchronous rectification control circuit generates synchronous rectifying tube control signals according to voltage signals at two ends of the secondary synchronous rectifying tube.
Claims (8)
1. A synchronous rectification flyback DC-DC power supply conversion device is characterized in that: comprising the following steps: a flyback circuit and an auxiliary switch; the flyback circuit comprises an input circuit, an output circuit and a transformer; the input circuit comprises a primary power switching tube, the input circuit receives direct current input voltage and supplies power to the transformer, and the primary power switching tube is connected with a primary power winding of the transformer in series; the output circuit is coupled with the secondary side power winding of the transformer, and energy released by the transformer during the turn-off period of the primary side power switching tube generates a direct current at an output port of the output circuit and is provided for a load; the auxiliary switch is connected with an auxiliary winding of the transformer in parallel;
the direct current input voltage of the input circuit is direct current voltage directly output by a direct current power supply or direct current voltage output by other conversion circuits, and the direct current input voltage is constant direct current voltage or sine half-wave voltage output by an alternating current voltage of a power grid through a diode rectifying circuit;
one end of a primary side power winding of the transformer is connected with a direct current input voltage positive electrode, the other end of the primary side power winding of the transformer is connected with a drain electrode of a primary side power switching tube, a source electrode of the primary side power switching tube is connected with a direct current input voltage negative electrode, one end of a secondary side power winding of the transformer is connected with a VD end of a synchronous rectification control circuit and a drain electrode of a secondary side synchronous rectification tube, a grid electrode of the secondary side synchronous rectification tube is connected with a VG end of the synchronous rectification control circuit, the other end of the secondary side power winding of the transformer is connected with one end of a capacitor Co and one end of a load, and the other end of the capacitor Co is connected with the other end of the load and the source electrode of the secondary side synchronous rectification tube; the auxiliary switch is connected with an auxiliary winding of the transformer in parallel;
one end of a primary side power winding of the transformer is connected with a source electrode of a primary side power switch tube, a drain electrode of the primary side power switch tube is connected with a positive electrode of a direct current input voltage, the other end of the primary side power winding of the transformer is connected with a negative electrode of the direct current input voltage, one end of a secondary side power winding of the transformer is connected with a VD end of a synchronous rectification control circuit and a drain electrode of a secondary side synchronous rectification tube, a grid electrode of the secondary side synchronous rectification tube is connected with a VG end of the synchronous rectification control circuit, the other end of the secondary side power winding of the transformer is connected with one end of a capacitor Co and one end of a load, and the other end of the capacitor Co is connected with the other end of the load and the source electrode of the secondary side synchronous rectification tube; the auxiliary switch is connected in parallel with an auxiliary winding of the transformer.
2. The synchronous rectification flyback dc-dc power conversion apparatus of claim 1, wherein: the auxiliary switch is a semiconductor device with bidirectional blocking capability.
3. The synchronous rectification flyback dc-dc power conversion apparatus of claim 1, wherein: the auxiliary switch is a composite switch formed by a diode and a metal oxide semiconductor field effect transistor, and the direction of the diode is opposite to that of the metal oxide semiconductor field effect transistor body diode.
4. The synchronous rectification flyback dc-dc power conversion apparatus of claim 1, wherein: the auxiliary switch is a composite switch formed by two metal oxide semiconductor field effect transistors which are connected in series in an opposite direction.
5. The synchronous rectification flyback dc-dc power conversion apparatus of claim 1, wherein: the on time of the auxiliary switch is fixed or is regulated by a control circuit of the synchronous rectification flyback direct current-direct current power supply conversion device according to the working condition of the circuit.
6. The synchronous rectification flyback dc-dc power conversion apparatus of claim 1, wherein: the exciting current of the transformer works in an intermittent state, a continuous state or a critical intermittent state.
7. The method for controlling a synchronous rectification flyback dc-dc power conversion device according to claim 1, comprising the steps of:
step 1: the synchronous rectification flyback direct current-direct current power supply conversion device respectively generates a control signal of a primary side power switch tube and a control signal of an auxiliary switch;
step 2: the auxiliary switch is conducted once or twice before the primary power switch tube is turned on, so that the primary power winding of the transformer is short-circuited in the conduction time of the auxiliary switch;
step 3: the synchronous rectification control circuit generates synchronous rectifying tube control signals according to voltage signals at two ends of the secondary synchronous rectifying tube.
8. The method according to claim 7, wherein the auxiliary switch is turned on once or twice before the primary power switch tube is turned on when the synchronous rectification flyback dc-dc power conversion device is operated in a current continuous mode; when the synchronous rectification flyback DC-DC power supply conversion device works in a current interruption mode or a current critical interruption mode, the auxiliary switch is conducted once, twice or not conducted before the primary power switch tube is turned on.
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| CN111934557B (en) * | 2020-09-28 | 2021-01-15 | 广东希荻微电子有限公司 | Synchronous rectification circuit and power conversion device |
| CN113131745B (en) * | 2021-03-16 | 2022-08-19 | 广州金升阳科技有限公司 | Control method and control circuit of flyback power supply |
| CN113708631B (en) * | 2021-03-16 | 2023-07-14 | 广州金升阳科技有限公司 | Flyback converter and control method thereof |
| CN113809950B (en) * | 2021-08-26 | 2023-01-06 | 南京航空航天大学 | Piezoelectric semi-active control device based on flyback transformer |
| CN114142560A (en) * | 2021-11-29 | 2022-03-04 | 东莞新能安科技有限公司 | Protection circuit, battery management system, battery pack and electric equipment |
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| CN101588129A (en) * | 2009-06-30 | 2009-11-25 | 南京航空航天大学 | A kind of multiple input flyback converter |
| US9369050B1 (en) * | 2014-04-21 | 2016-06-14 | Universal Lighting Technologies, Inc. | Indirect current sensing method for a constant current flyback converter |
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| US9973098B2 (en) * | 2015-08-19 | 2018-05-15 | Astec International Limited | Fixed frequency discontinuous conduction mode flyback power converters employing zero voltage switching |
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| CN101453169A (en) * | 2008-12-02 | 2009-06-10 | 广州金升阳科技有限公司 | Self-oscillation starting output end controlled anti exciting converter |
| CN101588129A (en) * | 2009-06-30 | 2009-11-25 | 南京航空航天大学 | A kind of multiple input flyback converter |
| US9369050B1 (en) * | 2014-04-21 | 2016-06-14 | Universal Lighting Technologies, Inc. | Indirect current sensing method for a constant current flyback converter |
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