CN112087148B - Synchronous rectification control circuit and flyback switching power supply - Google Patents
Synchronous rectification control circuit and flyback switching power supply Download PDFInfo
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- CN112087148B CN112087148B CN202011049217.3A CN202011049217A CN112087148B CN 112087148 B CN112087148 B CN 112087148B CN 202011049217 A CN202011049217 A CN 202011049217A CN 112087148 B CN112087148 B CN 112087148B
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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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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
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Abstract
The application discloses a synchronous rectification control circuit and a flyback switching power supply, which comprise a volt-second integrating circuit, a sampling hold circuit, a comparison circuit and a rectifying tube control circuit. Considering that the volt-seconds of the voltages at two ends of the secondary winding accumulate at a certain rule: the voltage of the two ends of the secondary winding excited during normal primary side switch action has the largest volt-second product value, and the voltage of the two ends of the secondary winding gradually decreases during parasitic damping oscillation; therefore, the application adopts a method of comparing the volt-second product with the volt-second product to judge whether the secondary rectifying tube needs to be turned on or not, so as to accurately turn on the rectifying tube when the secondary rectifying tube needs to be turned on and the terminal voltage connected with the rectifying tube on the secondary winding is smaller than the preset starting threshold voltage, thereby avoiding the phenomenon of erroneously turning on the secondary rectifying tube when parasitic damping oscillation occurs.
Description
Technical Field
The invention relates to the field of switching power supply control, in particular to a synchronous rectification control circuit and a flyback switching power supply.
Background
The flyback switching power supply controlled by the primary side gradually becomes an important electronic element power supply device due to small volume and high efficiency, and the output end of the flyback switching power supply is generally connected in series with a rectifier diode to provide direct-current output voltage. With the development of electronic technology, the output voltage required by the load electronic element is lower and the output power is higher, so that the forward conduction voltage drop of the rectifier diode becomes a main factor for limiting the improvement of the efficiency of the switching power supply.
The current common solution is to use a rectifier tube analog diode for rectification, so-called synchronous rectification technology, and MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor, metal-Oxide-semiconductor-field effect transistor) can be generally used as the rectifier tube. Synchronous rectification utilizes the low resistance of MOSFET when it is turned on to reduce the loss on the rectifying tube, and its grid control signal needs to be phase-synchronized with the rectified current.
In the prior art, the synchronous rectification control is generally implemented by the following steps: referring to fig. 1, a synchronous rectification control circuit of a secondary side of a flyback switching power supply is typically applied to primary side control. In the flyback switching power supply controlled by the primary side shown in fig. 1, the switching action of the primary side switch M1 is converted by a transformer, and the voltages at the two ends of the secondary side winding have corresponding responses, so that the change of the voltages at the two ends of the secondary side winding is detected, the switching state of the primary side switch M1 can be known, and the synchronous control of the secondary side rectifying tube M2 is further realized.
However, when the primary-side controlled flyback switching power supply is operated in DCM (Discontinuous Current Mode, current-discontinuous mode), undesirable parasitic elements cause a ringing of the voltage across the secondary winding, as shown in fig. 2 a. In fig. 2a, the equivalent source-drain on-resistance of the R-rectifier tube M2 corresponds to the linear rising section in fig. 2a when it is turned on; the parasitic body diode of diode rectifier tube M2 is turned on, corresponding to the exponential section at both ends of the linear section in fig. 2 a. Because synchronous rectification has on delay and off delay, namely front and back exponential segments, the body diode is conducted at the moment.
As can be seen from fig. 2a, simply determining the polarity of the voltage across the secondary winding 103 does not avoid controlling the rectifier M2 by mistake, which may cause the secondary loop to have a reverse current, resulting in unnecessary energy loss. Therefore, it is necessary to accurately distinguish between the voltage change of the secondary winding caused by the normal operation of the primary switch M1 and the parasitic ringing.
Voltage oscillations on the secondary winding caused by parasitic capacitance and leakage inductance are unavoidable and their period and amplitude also vary depending on the application environment. In the case where the primary side is at a low input voltage and the secondary side is at a high output voltage, the amplitude of the parasitic ringing may reach the voltage across the secondary winding that is excited when the primary switch M1 is turned off, as shown in fig. 2 b. Therefore, it is difficult to avoid malfunction due to parasitic ringing by controlling the rectifier M2 according to the magnitude of the voltage across the secondary winding.
Therefore, how to provide a solution to the above technical problem is a problem that a person skilled in the art needs to solve at present.
Disclosure of Invention
The invention aims to provide a synchronous rectification control circuit and a flyback switching power supply, which adopt a method of comparing a volt-second product with a volt-second product to judge whether a secondary rectifying tube needs to be turned on or not so as to accurately turn on the rectifying tube when the secondary rectifying tube needs to be turned on and the terminal voltage connected with the rectifying tube on a secondary winding is smaller than a preset starting threshold voltage, thereby avoiding the phenomenon of erroneously turning on the secondary rectifying tube when parasitic ringing occurs.
In order to solve the above technical problems, the present invention provides a synchronous rectification control circuit, including:
The volt-second integrating circuit is used for obtaining the volt-second product of the voltages at the two ends of the secondary winding of the switching power supply at the current time;
the sampling and holding circuit is used for sampling and holding the last volt-second product acquired by the volt-second integrating circuit;
a comparison circuit, configured to generate an on permission signal if the current volt-second product is greater than the last volt-second product;
And the rectifying tube control circuit is used for controlling the rectifying tube to be conducted if the turn-on permission signal is received and the terminal voltage connected with the rectifying tube on the secondary winding is smaller than a preset starting threshold voltage.
Preferably, the sample-and-hold circuit is further configured to:
When the rectifying tube is conducted, multiplying the current volt-second product by a coefficient value smaller than 1, and taking the product result as the current volt-second product value for subsequent sampling and holding.
Preferably, the volt-second integrating circuit comprises a voltage-to-current circuit and a current integrator; wherein:
The input end of the voltage-to-current circuit is connected with the voltages at two ends of the secondary winding, the output end of the voltage-to-current circuit is connected with the input end of the current integrator, and the output end of the current integrator is respectively connected with the sample hold circuit and the comparison circuit;
The voltage-to-current circuit is used for converting the current voltages at two ends of the secondary winding into current according to a certain proportion; and the current integrator is used for integrating the current to obtain the volt-second product of the voltages at the two ends of the secondary winding.
Preferably, the comparison circuit is embodied as a voltage comparator; wherein:
The input positive end of the voltage comparator is connected with the output end of the volt-second integrating circuit, the input negative end of the voltage comparator is connected with the output end of the sample-hold circuit, and the output end of the voltage comparator is connected with the rectifying tube control circuit;
the voltage comparator is used for generating a high-level signal as an opening permission signal if the current volt-second product is larger than the last volt-second product.
In order to solve the technical problems, the invention also provides a flyback switching power supply which comprises a transformer comprising a primary winding and a secondary winding, a secondary rectifying tube and any synchronous rectifying control circuit.
The application provides a synchronous rectification control circuit which comprises a volt-second integrating circuit, a sampling hold circuit, a comparison circuit and a rectifying tube control circuit. The volt-second integrating circuit is used for obtaining the volt-second product of the voltages at the two ends of the secondary winding of the switching power supply at the current time; the sampling and holding circuit is used for sampling and holding the last volt-second product acquired by the volt-second integrating circuit; the comparison circuit is used for generating an opening permission signal if the current volt-second product is larger than the last volt-second product; and the rectifying tube control circuit is used for controlling the rectifying tube to be conducted if the switching-on permission signal is received and the terminal voltage connected with the rectifying tube on the secondary winding is smaller than the preset starting threshold voltage. In summary, consider that the volt-seconds of the voltages across the secondary winding accumulate at a certain law: the voltage of the two ends of the secondary winding excited during normal primary side switch action has the largest volt-second product value, and the voltage of the two ends of the secondary winding gradually decreases during parasitic damping oscillation; therefore, the application adopts a method of comparing the volt-second product with the volt-second product to judge whether the secondary rectifying tube needs to be turned on or not, so as to accurately turn on the rectifying tube when the secondary rectifying tube needs to be turned on and the terminal voltage connected with the rectifying tube on the secondary winding is smaller than the preset starting threshold voltage, thereby avoiding the phenomenon of erroneously turning on the secondary rectifying tube when parasitic damping oscillation occurs.
The invention also provides a flyback switching power supply, which has the same beneficial effects as the synchronous rectification control circuit.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required in the prior art and the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a circuit diagram of synchronous rectification control of a secondary side of a flyback switching power supply for primary side control according to the prior art;
FIG. 2a is a waveform diagram of the secondary side rectifier of FIG. 1 under a first condition of drain voltage;
FIG. 2b is a waveform diagram showing the second condition of the drain voltage of the secondary side rectifier in FIG. 1;
Fig. 3 is a schematic structural diagram of a synchronous rectification control circuit according to an embodiment of the present invention;
FIG. 4 is a diagram illustrating waveforms of VDET and DRISR in DCM according to an embodiment of the present invention;
FIG. 5 is a diagram illustrating waveforms of VDET and DRISR in QR mode according to an embodiment of the present invention;
FIG. 6 is a waveform diagram of each key node of the synchronous rectification control circuit shown in FIG. 3 according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a specific structure of a synchronous rectification control circuit according to an embodiment of the present invention;
Fig. 8 is a schematic diagram of a specific circuit of a synchronous rectification control circuit according to an embodiment of the present invention;
fig. 9 is a waveform diagram of each key node of the synchronous rectification control circuit shown in fig. 8 according to an embodiment of the present invention.
Detailed Description
The core of the invention is to provide a synchronous rectification control circuit and a flyback switching power supply, which adopts a method of comparing the volt-second product with the volt-second product to judge whether the secondary rectifying tube needs to be turned on or not, so as to accurately turn on the rectifying tube when the secondary rectifying tube needs to be turned on and the terminal voltage connected with the rectifying tube on the secondary winding is smaller than the preset starting threshold voltage, thereby avoiding the phenomenon of erroneously turning on the secondary rectifying tube when parasitic ringing occurs.
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 3, fig. 3 is a schematic structural diagram of a synchronous rectification control circuit according to an embodiment of the invention.
The synchronous rectification control circuit includes:
The volt-second integrating circuit 1 is used for obtaining the volt-second product of the voltages at the two ends of the secondary winding of the switching power supply at the current time;
a sample-hold circuit 2 for sample-holding the last volt-second product obtained by the volt-second integrating circuit 1;
A comparison circuit 3 for generating an on permission signal if the current volt-second product is larger than the last volt-second product;
And the rectifying tube control circuit 4 is used for controlling the rectifying tube M2 to be conducted if the switching-on permission signal is received and the terminal voltage connected with the rectifying tube M2 on the secondary winding is smaller than the preset starting threshold voltage.
Specifically, the synchronous rectification control circuit of the application comprises a volt-second integrating circuit 1, a sampling hold circuit 2, a comparison circuit 3 and a rectifying tube control circuit 4, and the working principle is as follows:
referring to fig. 4, fig. 4 shows waveforms of operations of VDET (terminal voltage connected to the rectifying tube M2 on the secondary winding) and DRISR (driving signal of the secondary rectifying tube M2) in DCM mode, wherein TONP represents primary on-time, and TONS represents secondary on-time; TOFF represents the time when both primary and secondary are turned off, and A1, A3, A4, A5 represent the volt-second product of the voltages across the secondary winding during parasitic ringing; a2 represents the volt-second product of the voltages across the secondary winding that are excited when the normal primary switch M1 is operated. From the analysis of fig. 4, it can be seen that the volt-second product of the voltages across the secondary winding has a certain rule: the voltage of the two ends of the secondary winding which is excited during the normal primary switch M1 acts is the largest in volt-second product value, and the voltage of the two ends of the secondary winding is gradually reduced during parasitic damping oscillation, so that the application can utilize the rule, and a method of comparing the volt-second product before and after is adopted to distinguish the voltage of the two ends of the secondary winding which is excited during the normal primary switch M1 acts from the voltage of the two ends of the secondary winding, namely, a method of comparing the volt-second product before and after is adopted to judge whether the secondary rectifying tube M2 needs to be opened or not, and particularly if the volt-second product at this time is larger than the volt-second product at last time, the fact that the secondary rectifying tube M2 needs to be opened is shown; if the current volt-second product is not larger than the last volt-second product, the secondary rectifying tube M2 does not need to be turned on. As can be seen from the analysis of fig. 4, when the secondary rectifier M2 needs to be turned on and VDET < VthON (the preset start-up threshold voltage, which can be set to a value close to 0), the secondary rectifier M2 is turned on. For example, A2> A1, and immediately following VDET < VthON, the on condition of the secondary rectifier is satisfied and the secondary rectifier is on.
Based on this, the principle of turning on the secondary rectifying tube M2 of the switching power supply is: the volt-second integrating circuit 1 detects the potential VDET at one end of the secondary winding of the switching power supply on the one hand, and detects the potential VOUT at the other end of the secondary winding of the switching power supply on the other hand, so as to obtain the voltage (VDET-VOUT) at both ends of the secondary winding, then integrates the voltage (VDET-VOUT) at both ends of the secondary winding for time, obtains the volt-second product of the voltage at both ends of the secondary winding at this time, and sends the volt-second product of the voltage at both ends of the secondary winding at this time to the comparing circuit 3. The sample-hold circuit 2 samples and holds the last volt-second product of the voltages at the two ends of the secondary winding obtained by the volt-second integrating circuit 1, and sends the last volt-second product of the voltages at the two ends of the secondary winding to the comparing circuit 3. The comparison circuit 3 compares the current volt-second product of the voltages at the two ends of the secondary winding with the last volt-second product, and if the current volt-second product of the voltages at the two ends of the secondary winding is larger than the last volt-second product, an opening permission signal is generated to the rectifying tube control circuit 4 so as to inform the rectifying tube control circuit 4 that the secondary rectifying tube M2 meets the initial opening condition of the volt-second product. After receiving the turn-on permission signal, the rectifier tube control circuit 4 determines that the secondary rectifier tube M2 meets the preliminary turn-on condition of the volt-second product, and in this case, when the terminal voltage VDET connected with the rectifier tube on the secondary winding is smaller than the preset start threshold voltage VthON, the secondary rectifier tube M2 is controlled to be turned on, so that the turn-on accuracy of the secondary rectifier tube M2 is improved.
The volt-second integrating circuit 1 needs to integrate the voltages at the two ends of the secondary winding again every time the potential VDET of the secondary winding has a positive voltage, so as to avoid the influence of the last integrated value on the volt-second product of the voltages at the two ends of the secondary winding acquired next time.
The application provides a synchronous rectification control circuit which comprises a volt-second integrating circuit, a sampling hold circuit, a comparison circuit and a rectifying tube control circuit. The volt-second integrating circuit is used for obtaining the volt-second product of the voltages at the two ends of the secondary winding of the switching power supply at the current time; the sampling and holding circuit is used for sampling and holding the last volt-second product acquired by the volt-second integrating circuit; the comparison circuit is used for generating an opening permission signal if the current volt-second product is larger than the last volt-second product; and the rectifying tube control circuit is used for controlling the rectifying tube to be conducted if the switching-on permission signal is received and the terminal voltage connected with the rectifying tube on the secondary winding is smaller than the preset starting threshold voltage. In summary, consider that the volt-seconds of the voltages across the secondary winding accumulate at a certain law: the voltage of the two ends of the secondary winding excited during normal primary side switch action has the largest volt-second product value, and the voltage of the two ends of the secondary winding gradually decreases during parasitic damping oscillation; therefore, the application adopts a method of comparing the volt-second product with the volt-second product to judge whether the secondary rectifying tube needs to be turned on or not, so as to accurately turn on the rectifying tube when the secondary rectifying tube needs to be turned on and the terminal voltage connected with the rectifying tube on the secondary winding is smaller than the preset starting threshold voltage, thereby avoiding the phenomenon of erroneously turning on the secondary rectifying tube when parasitic damping oscillation occurs.
Based on the above embodiments:
as an alternative embodiment, the sample-and-hold circuit 2 is also arranged to:
When the rectifying tube M2 is conducted, the current volt-second product is multiplied by a coefficient value smaller than 1, and the product result is used as the current volt-second product value for subsequent sampling and holding.
Further, referring to fig. 5, fig. 5 shows the working waveforms of VDET and DRISR in the QR (valley opening) mode, where the primary side of each period is turned on in the valley, and correspondingly, the volt-second product of the secondary side VDET above VCC of each period is equal, that is, a1=a2=a3, if only the method of comparing the volt-second product of the above embodiment is used to determine whether the secondary side rectifying tube M2 needs to be turned on, the secondary side rectifying tube M2 cannot be turned on normally, so the application further improves the sample-hold circuit 2: when the secondary rectifying tube M2 is turned on, the current volt-second product obtained by the volt-second integrating circuit 1 is multiplied by a coefficient K smaller than 1 (for example, 0.8), so that the volt-second product multiplied by the coefficient K smaller than 1 is compared with the next volt-second product. For example, taking fig. 5 as an example, the secondary rectifying tube is turned on in the first period, the volt-second product of the period is k×a1, the volt-second product of the second period is compared with k×a1 by A2 to obtain A2> k×a1, and when VDET < VthON, the secondary rectifying tube is turned on in the second period, and similarly, the volt-second product of the second period is compared with k×a2, k×a2 and the following third period volt-second product A3, and so on, so that the system can be ensured to be accurately turned on in DCM and QR modes by the improvement.
Based on this, referring to fig. 6, fig. 6 shows the operation waveforms of VDET, DRISR, V + (the voltage value of the current volt-second product conversion), V- (the voltage value of the last volt-second product conversion) and OUT (the output signal of the comparison circuit 3) in the DCM mode, and the circuit operation sequence is as follows: in stage TONP, VDET is located above VCC, (VDET-VCC) is converted into current to charge the internal capacitor until the end of stage TONP, the voltage V+ obtained by the current integrator increases linearly from 0V, and V-is the last volt-second product and is smaller. Then in TONP stage, when V+ is larger than V-, OUT jumps up, which shows that the current volt-second product is larger than the last volt-second product, the preliminary opening condition of the secondary rectifying tube is satisfied, and when VDET is smaller than Vthon, the secondary rectifying tube is opened, and then the TONS stage is entered, the highest voltage of the V+ product in TONP stage is multiplied by a coefficient K (K < 1), and preparation is made for the comparison of the next volt-second product. In the TONS phase, the voltage of V+, V-is maintained. In the TOFF stage, VDET excites ring and is positioned above VCC, the (VDET-VCC) is converted into current to charge an internal capacitor until VDET is smaller than VCC, the voltage V+ obtained by a current integrator is linearly increased from 0V, the voltage V+ is K times of the highest voltage obtained by the TONP stage through a sample hold circuit, the voltage V+ terminal is compared with the voltage V-terminal through a comparison circuit, and as the volt-second product of ring is smaller, the voltage V+ terminal is always smaller than the voltage V-terminal, OUT is low, so that the volt-second product of ring excited in the TOFF stage is smaller than the volt-second product in the TONP stage, and the preliminary starting condition of the secondary rectifying tube is not met. The volt-second product of the subsequent VDET exciting ring is smaller and smaller, and the preliminary opening condition of the secondary rectifying tube is not met through comparison of the front volt-second product and the back volt-second product.
Referring to fig. 7, fig. 7 is a schematic diagram of a specific structure of a synchronous rectification control circuit according to an embodiment of the present invention.
As an alternative embodiment, the volt-second integrating circuit 1 comprises a voltage-to-current circuit 11 and a current integrator 12; wherein:
the input end of the voltage-to-current circuit 11 is connected with the voltages at the two ends of the secondary winding, the output end of the voltage-to-current circuit 11 is connected with the input end of the current integrator 12, and the output end of the current integrator 12 is respectively connected with the sample hold circuit 2 and the comparison circuit 3;
the voltage-to-current circuit 11 is used for converting the current voltages at two ends of the secondary winding into current according to a certain proportion; the current integrator 12 is used for integrating the current to obtain the volt-second product of the voltages at the two ends of the secondary winding.
Specifically, the volt-second integrating circuit 1 of the present application includes a voltage-to-current circuit 11 and a current integrator 12, and its working principle is:
The voltage-to-current circuit 11 converts the current voltages at the two ends of the secondary winding into currents according to a certain proportion, the currents flow into the current integrator 12, and the current integrator 12 integrates the flowing currents to obtain a current integral value, namely the voltage at the two ends of the secondary winding is accumulated in the current volt seconds.
As an alternative embodiment, the comparison circuit 3 is embodied as a voltage comparator D; wherein:
The input positive end of the voltage comparator D is connected with the output end of the volt-second integrating circuit 1, the input negative end of the voltage comparator D is connected with the output end of the sample-hold circuit 2, and the output end of the voltage comparator D is connected with the rectifying tube control circuit 4;
The voltage comparator D is configured to generate a high-level signal as an on permission signal if the current volt-second product is greater than the last volt-second product.
Specifically, the comparison circuit 3 of the present application may select a voltage comparator D, wherein the input positive end of the voltage comparator D inputs the voltage at the two ends of the secondary winding as the current volt-second product, the input negative end of the voltage comparator D inputs the last volt-second product of the voltage at the two ends of the secondary winding, and if the voltage at the two ends of the secondary winding as the current volt-second product is greater than the last volt-second product thereof, the voltage comparator D generates a high-level signal (i.e. the turn-on permission signal mentioned in the above embodiment) to the rectifier control circuit 4.
In addition, referring to fig. 8, fig. 8 shows a specific circuit structure of the current integrator 12 and the sample-and-hold circuit 2, which includes switches SW1, SW2, SW3, SW4, SW5, SW6, SW7, SW8, SW9, SW10 (ten switches are all turned on at a high level and turned off at a low level), capacitors C1, C2, C3, C4, and C5, and the working principle thereof will be described with reference to fig. 9:
When VDET is larger than VCC by a certain value, demag is high level, clear outputs a fixed pulse signal at each Demag rising edge, and the fixed pulse signal is used for resetting the charge of the corresponding capacitor. Demag1 jumps once on each rising edge of Demag for comparing the last volt-second product sampled in with the current real-time volt-second product. Demag1_n is the reverse level of Demag 1. Select only outputs a fixed pulse signal when the secondary rectifying tube is turned on, and the fixed pulse signal is used for comparing the current volt-second product value multiplied by K (K < 1) with the next volt-second product.
The circuit operates in the following sequence: in the TONP stage, VDET is located above VCC, demag is high level, clear signals are sent out by clear signals, charges on the capacitors C1, C2, C4 and C5 are cleared, the switches SW1, SW2 and SW5 are closed, (VDET-VCC) is converted into current to charge the capacitors C1 and C2 until the TONP stage is finished, and the V-end of the voltage comparator D is connected with the capacitor C3 through the switch SW5, and the value of the V-end is the last volt-second product value and is smaller. In TONP process, when the voltage of the V+ end of the voltage comparator D is larger than the voltage of the V-end, TONPDET hops high, which shows that the current volt-second product is larger than the last volt-second product, the preliminary starting condition of the secondary rectifying tube is met, when VDET is smaller than Vthon, the secondary rectifying tube is formally started, at the moment, the TONS stage is entered, a fixed pulse signal is output by a Select, and thus charges on the capacitors C1 and C2 are transferred to the capacitor C5, and the V+ voltage can drop to the original K times by setting the capacitors C1, C2 and C5 to a certain proportion. In the TONS phase, the voltage of V+, V-is maintained. In the TOFF stage, VDET excites ring and is positioned above VCC, demag is high level, demag1 is low level, at the moment, switches SW1, SW3 and SW4 are closed, clear signals are sent out by clear, charges on capacitors C1, C3, C4 and C5 are cleared, the information of the last V+ end is sampled and held by the V-end, the (VDET-VCC) is converted into current to charge the capacitors C1 and C3 until Demag is low, at the moment, the V+ end voltage rises from zero, the larger the volt-second product is, the higher the V+ end is, the voltage of the V+ end is sampled to the voltage of the V+ end when the Demag1 is low, the voltage is K times of the highest voltage obtained in the TONS stage, the V+ end voltage is compared with the V-end voltage in real time, and the voltage of the V+ end is always smaller than the V-end voltage, TONPDET is low because the volt-second product of ring is always smaller than the V-end voltage, and the second product of the excited ring in the FF stage is smaller than the volt-second product of TONP, and the initial opening condition is not met. The volt-second product of the subsequent VDET exciting ring is smaller and smaller, and the preliminary opening condition of the secondary rectifying tube is not met through comparison of the front volt-second product and the back volt-second product.
The application also provides a flyback switching power supply, which comprises a transformer comprising a primary winding and a secondary winding, a secondary rectifying tube and any synchronous rectifying control circuit.
The description of the flyback switching power supply provided by the application refers to the embodiment of the synchronous rectification control circuit, and the application is not repeated here.
It should also be noted that in this specification, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (5)
1. A synchronous rectification control circuit, comprising:
The volt-second integrating circuit is used for obtaining the volt-second product of the voltages at the two ends of the secondary winding of the switching power supply at the current time;
the sampling and holding circuit is used for sampling and holding the last volt-second product acquired by the volt-second integrating circuit;
a comparison circuit, configured to generate an on permission signal if the current volt-second product is greater than the last volt-second product;
And the rectifying tube control circuit is used for controlling the rectifying tube to be conducted if the turn-on permission signal is received and the terminal voltage connected with the rectifying tube on the secondary winding is smaller than a preset starting threshold voltage.
2. The synchronous rectification control circuit of claim 1, wherein said sample-and-hold circuit is further configured to:
When the rectifying tube is conducted, multiplying the current volt-second product by a coefficient value smaller than 1, and taking the product result as the current volt-second product value for subsequent sampling and holding.
3. The synchronous rectification control circuit of claim 1, wherein said volt-second integrating circuit comprises a voltage-to-current circuit and a current integrator; wherein:
The input end of the voltage-to-current circuit is connected with the voltages at two ends of the secondary winding, the output end of the voltage-to-current circuit is connected with the input end of the current integrator, and the output end of the current integrator is respectively connected with the sample hold circuit and the comparison circuit;
The voltage-to-current circuit is used for converting the current voltages at two ends of the secondary winding into current according to a certain proportion; and the current integrator is used for integrating the current to obtain the volt-second product of the voltages at the two ends of the secondary winding.
4. The synchronous rectification control circuit of claim 1, wherein said comparison circuit is embodied as a voltage comparator; wherein:
The input positive end of the voltage comparator is connected with the output end of the volt-second integrating circuit, the input negative end of the voltage comparator is connected with the output end of the sample-hold circuit, and the output end of the voltage comparator is connected with the rectifying tube control circuit;
the voltage comparator is used for generating a high-level signal as an opening permission signal if the current volt-second product is larger than the last volt-second product.
5. A flyback switching power supply comprising a transformer comprising a primary winding and a secondary winding, a secondary rectifier and a synchronous rectification control circuit according to any one of claims 1 to 4.
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| CN115065221B (en) * | 2022-08-16 | 2022-11-04 | 成都利普芯微电子有限公司 | Synchronous rectification dynamic accelerating circuit, control circuit and switching power supply |
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| CN106452086B (en) * | 2016-10-31 | 2019-01-04 | 陕西亚成微电子股份有限公司 | A kind of synchronous commutating control circuit |
| CN208971392U (en) * | 2017-12-15 | 2019-06-11 | 杰华特微电子（杭州）有限公司 | Inverse-excitation type switch power-supply |
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