CN212323999U - Synchronous rectification control circuit and flyback switching power supply - Google Patents
Synchronous rectification control circuit and flyback switching power supply Download PDFInfo
- Publication number
- CN212323999U CN212323999U CN202022184691.9U CN202022184691U CN212323999U CN 212323999 U CN212323999 U CN 212323999U CN 202022184691 U CN202022184691 U CN 202022184691U CN 212323999 U CN212323999 U CN 212323999U
- Authority
- CN
- China
- Prior art keywords
- voltage
- circuit
- product
- volt
- current
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Abstract
The utility model discloses a synchronous rectification control circuit and flyback switching power supply, including volt second integrating circuit, sample hold circuit, comparison circuit and rectifier tube control circuit. Considering that the volt-second product of the voltage at two ends of the secondary winding has a certain rule: the voltage-second product value of the voltage at two ends of the secondary winding excited during normal primary side switching action is maximum, and the voltage-second product value of the voltage at two ends of the secondary winding is gradually reduced during parasitic damped oscillation; therefore, whether the secondary rectifier tube needs to be switched on or not is judged by adopting a method for comparing before and after volt-second product, so that the secondary rectifier tube needs to be switched on, and the rectifier tube is accurately switched on when the voltage of a terminal connected with the rectifier tube on the secondary winding is smaller than the preset starting threshold voltage, thereby avoiding the phenomenon that the secondary rectifier tube is switched on by mistake when parasitic damped oscillation occurs.
Description
Technical Field
The utility model relates to a switching power supply control field especially relates to a synchronous rectification control circuit and flyback switching power supply.
Background
The primary side controlled flyback switching power supply is gradually an important electronic component power supply device due to small volume and high efficiency, and the output end of the primary side controlled flyback switching power supply is generally connected with a rectifier diode in series to provide direct current output voltage. With the development of electronic technology, the output voltage and the output power required by the load electronic component are lower and 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 conventional solution is to use a rectifier tube to simulate a diode for rectification, i.e. so-called synchronous rectification technology, and generally a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is used as the rectifier tube. Synchronous rectification utilizes low resistance when the MOSFET is conducted to reduce loss on a rectifier tube, and a grid control signal needs to be synchronous with the phase of rectified current.
In the prior art, the implementation manner generally adopted by the synchronous rectification control is as follows: referring to fig. 1, a typical synchronous rectification control circuit applied to the secondary side of a primary-side controlled flyback switching power supply is shown. In the primary side controlled flyback switching power supply shown in fig. 1, the switching action of the primary side switch M1 is converted by the transformer, and the voltages at the two ends of the secondary side winding have corresponding responses, so that the switching state of the primary side switch M1 can be known by detecting the change of the voltages at the two ends of the secondary side winding, and further, the synchronous control of the secondary side rectifier tube M2 is realized.
However, when the primary-side-controlled flyback switching power supply operates in DCM (Discontinuous Current Mode), the undesired parasitic element causes damped harmonic oscillation of the voltage across the secondary winding, as shown in fig. 2 a. In fig. 2a, R denotes an equivalent source-drain on-resistance of the rectifying tube M2 when it is turned on, corresponding to the linear rising segment in fig. 2 a; diode indicates that the parasitic body diode of the rectifier M2 is turned on, corresponding to the exponential section at both ends of the linear section in fig. 2 a. Because the synchronous rectification has turn-on delay and turn-off delay, namely front and back exponential sections, the synchronous rectification is conducted by a body diode.
As can be seen from fig. 2a, simply determining the polarity of the voltage across the secondary winding 103 cannot avoid the erroneous control of the rectifier M2, which may cause the reverse current in the secondary loop, resulting in unnecessary energy loss. Therefore, it is necessary to accurately distinguish between the voltage change in the secondary winding and the parasitic ringing that is excited by the normal operation of the primary switch M1.
Voltage oscillation on the secondary winding due to parasitic capacitance and leakage inductance is inevitable, and its period and amplitude also vary depending on the application environment. In the case of a low input voltage on the primary side and a high output voltage on the secondary side, the amplitude of the parasitic ringing may reach the value of the voltage across the secondary winding that was excited when the primary switch M1 was turned off, as shown in fig. 2 b. Therefore, it is difficult to avoid the malfunction due to the parasitic ringing by controlling the rectifying tube M2 according to the amplitude of the voltage across the secondary winding.
Therefore, how to provide a solution to the above technical problem is a problem that needs to be solved by those skilled in the art.
SUMMERY OF THE UTILITY MODEL
The utility model aims at providing a synchronous rectification control circuit and flyback switching power supply adopts the method of volt-second long-pending front and back comparison to judge whether vice limit rectifier tube needs to open to need to open at vice limit rectifier tube, and accurate opening rectifier tube when the terminal voltage who is connected with the rectifier tube on the vice limit winding is less than preset starting threshold voltage, thereby the phenomenon of vice limit rectifier tube is opened to the mistake when avoiding appearing parasitic attenuation oscillation.
In order to solve the technical problem, the utility model provides a synchronous rectification control circuit, include:
the voltage-second integration circuit is used for acquiring the voltage-second product of the voltage at the two ends of the secondary winding of the switching power supply;
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 rectifier tube control circuit is used for controlling the rectifier tube to be conducted if the turn-on allowing signal is received and the terminal voltage connected with the rectifier tube on the secondary winding is less than the preset starting threshold voltage.
Preferably, the sample-and-hold circuit further comprises:
and the sub-circuit is used for multiplying the current volt-second product by a coefficient value smaller than 1 when the rectifier tube is conducted, and taking the product result as the current volt-second product value for subsequent sampling and holding.
Preferably, the volt-second integration 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 voltage 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-and-hold circuit and the comparison circuit;
the voltage-to-current circuit is used for converting the voltage at the two current 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 current volt-second product of the voltage at the two ends of the secondary winding.
Preferably, the comparison circuit is a voltage comparator; wherein:
the positive input end of the voltage comparator is connected with the output end of the volt-second integrating circuit, the negative input 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 rectifier tube control circuit;
and 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 problem, the utility model also provides a flyback switching power supply, including transformer, the secondary rectifier tube that contains primary winding and secondary winding and any kind of synchronous rectification control circuit of above-mentioned.
The utility model provides a synchronous rectification control circuit, including volt second integrator circuit, sample hold circuit, comparison circuit and rectifier tube control circuit. The voltage second integration circuit is used for acquiring the voltage second product of the voltage at the two ends of the secondary winding of the switching power supply; the sampling and holding circuit is used for sampling and holding the last voltage-second product obtained by the voltage-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; the rectifier tube control circuit is used for controlling the rectifier tube to be conducted if the rectifier tube control circuit receives the opening permission signal and the terminal voltage connected with the rectifier tube on the secondary winding is smaller than the preset starting threshold voltage. In summary, considering that there is a certain rule for the volt-second product of the voltage across the secondary winding: the voltage-second product value of the voltage at two ends of the secondary winding excited during normal primary side switching action is maximum, and the voltage-second product value of the voltage at two ends of the secondary winding is gradually reduced during parasitic damped oscillation; therefore, whether the secondary rectifier tube needs to be switched on or not is judged by adopting a method for comparing before and after volt-second product, so that the secondary rectifier tube needs to be switched on, and the rectifier tube is accurately switched on when the voltage of a terminal connected with the rectifier tube on the secondary winding is smaller than the preset starting threshold voltage, thereby avoiding the phenomenon that the secondary rectifier tube is switched on by mistake when parasitic damped oscillation occurs.
The utility model also provides a flyback switching power supply has the same beneficial effect with above-mentioned 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 are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a circuit diagram of a synchronous rectification control circuit applied to a secondary side of a flyback switching power supply controlled by a primary side in the prior art;
FIG. 2a is a waveform diagram illustrating a first condition of the drain terminal voltage of the secondary rectifier of FIG. 1;
FIG. 2b is a waveform diagram illustrating a second condition of the drain terminal voltage of the secondary rectifier of 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 operation 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 structural diagram of a synchronous rectification control circuit according to an embodiment of the present invention;
fig. 8 is a specific circuit schematic diagram 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 utility model is to provide a synchronous rectification control circuit and flyback switching power supply, whether the method that adopts volt-second long-pending front and back comparison judges vice limit rectifier tube needs to be opened to need to open at vice limit rectifier tube, and accurate opening rectifier tube when the terminal voltage who is connected with the rectifier tube on the vice limit winding is less than preset start threshold voltage, thereby the phenomenon that vice limit rectifier tube was opened to the mistake when avoiding appearing parasitic attenuation oscillation.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, 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 obvious that the described embodiments are some, but not all, embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.
Referring to fig. 3, fig. 3 is a schematic structural diagram of a synchronous rectification control circuit according to an embodiment of the present invention.
The synchronous rectification control circuit includes:
the voltage-second integration circuit 1 is used for acquiring the voltage at the two ends of the secondary winding of the switching power supply at the current voltage-second product;
the sample hold circuit 2 is used for carrying out sample hold on the last voltage-second product obtained by the voltage-second integrating circuit 1;
the comparison circuit 3 is used for generating an opening permission signal if the current volt-second product is larger than the last volt-second product;
and the rectifier tube control circuit 4 is used for controlling the rectifier tube M2 to be conducted if the turn-on permission signal is received and the terminal voltage connected with the rectifier tube M2 on the secondary winding is less than the preset starting threshold voltage.
Specifically, the synchronous rectification control circuit of the present application includes a volt-second integrating circuit 1, a sample-and-hold circuit 2, a comparison circuit 3 and a rectifier tube control circuit 4, and its working principle is:
referring to fig. 4, fig. 4 shows the operating waveforms of VDET (the terminal voltage of the secondary winding connected to the rectifier M2) and DRISR (the driving signal of the secondary rectifier M2) in DCM, where TONP represents the primary side on-time and ton represents the secondary side on-time; TOFF represents the time when the primary side and the secondary side are both turned off, A1, A3, A4 and A5 represent the voltage-second product of the voltages at two ends of the secondary side winding during parasitic damped oscillation; a2 represents the volt-second product of the voltage across the secondary winding that is excited by the normal operation of the primary switch M1. Fig. 4 shows that there is a certain rule for the voltage-second product of the voltages at the two ends of the secondary winding: the voltage-second product value of the voltage at two ends of the secondary winding excited when the normal primary side switch M1 acts is the largest, and the voltage-second product value of the voltage at two ends of the secondary winding during parasitic ringing is gradually reduced, so that the method can be used for distinguishing the voltage-second product of the voltage at two ends of the secondary winding excited when the normal primary side switch M1 acts from the voltage-second product of the voltage at two ends of the secondary winding during parasitic ringing by using a method for comparing the voltage-second products before and after, namely judging whether the secondary side rectifying tube M2 needs to be switched on by using the method for comparing the voltage-second products before and after, and particularly, if the current voltage-second product is larger than the last voltage-second product, indicating that the secondary side rectifying tube M2 needs to be switched on; if the current volt-second product is not larger than the last volt-second product, it indicates that the secondary rectifier 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 < vtho (a preset activation threshold voltage, which may be a value close to 0), the secondary rectifier M2 is turned on. For example, a2> a1, and immediately after VDET < vthcon, the turn-on condition of the secondary rectifier is satisfied, and the secondary rectifier turns on.
Based on this, the switching principle of the secondary rectifier M2 of the switching power supply is as follows: the volt-second integration circuit 1 detects a potential VDET at one end of the secondary winding of the switching power supply on the one hand, and detects a potential VOUT at the other end of the secondary winding of the switching power supply on the other hand, so as to obtain a voltage (VDET-VOUT) at two ends of the secondary winding, then performs time integration on the voltage (VDET-VOUT) at two ends of the secondary winding, obtains a current volt-second product of the voltage at two ends of the secondary winding, and sends the current volt-second product of the voltage at two ends of the secondary winding to the comparison circuit 3. The sample-and-hold circuit 2 samples and holds the last voltage-second product of the voltages at both ends of the secondary winding obtained by the voltage-second integrating circuit 1, and sends the last voltage-second product of the voltages at both ends of the secondary winding to the comparison circuit 3. The comparison circuit 3 compares the voltage across the secondary winding at the current volt-second product and the voltage-second product at the previous time, and if the voltage across the secondary winding at the current volt-second product is greater than the voltage-second product at the previous time, a turn-on permission signal is generated to the rectifier tube control circuit 4 to inform the rectifier tube control circuit 4 that the secondary rectifier tube M2 meets the preliminary turn-on condition of the voltage-second product. After receiving the turn-on permission signal, the rectifier control circuit 4 determines that the secondary rectifier M2 satisfies the preliminary turn-on condition of volt-second product, and controls the secondary rectifier M2 to be turned on when the terminal voltage VDET connected to the rectifier on the secondary winding is smaller than the preset start threshold voltage vtho under the condition, so that the turn-on accuracy of the secondary rectifier M2 is improved.
It should be noted that, the volt-second integration circuit 1 needs to perform time integration on the voltages at the two ends of the secondary winding again each 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 next obtained volt-second product of the voltages at the two ends of the secondary winding.
The utility model provides a synchronous rectification control circuit, including volt second integrator circuit, sample hold circuit, comparison circuit and rectifier tube control circuit. The voltage second integration circuit is used for acquiring the voltage second product of the voltage at the two ends of the secondary winding of the switching power supply; the sampling and holding circuit is used for sampling and holding the last voltage-second product obtained by the voltage-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; the rectifier tube control circuit is used for controlling the rectifier tube to be conducted if the rectifier tube control circuit receives the opening permission signal and the terminal voltage connected with the rectifier tube on the secondary winding is smaller than the preset starting threshold voltage. In summary, considering that there is a certain rule for the volt-second product of the voltage across the secondary winding: the voltage-second product value of the voltage at two ends of the secondary winding excited during normal primary side switching action is maximum, and the voltage-second product value of the voltage at two ends of the secondary winding is gradually reduced during parasitic damped oscillation; therefore, whether the secondary rectifier tube needs to be switched on or not is judged by adopting a method for comparing before and after volt-second product, so that the secondary rectifier tube needs to be switched on, and the rectifier tube is accurately switched on when the voltage of a terminal connected with the rectifier tube on the secondary winding is smaller than the preset starting threshold voltage, thereby avoiding the phenomenon that the secondary rectifier tube is switched on by mistake when parasitic damped oscillation occurs.
On the basis of the above-described embodiment:
as an alternative embodiment, the sample-and-hold circuit 2 further includes: and the sub-circuit is used for multiplying the current volt-second product by a coefficient value smaller than 1 when the rectifier tube M2 is conducted, and taking the product result as the current volt-second product value for subsequent sampling and holding.
Further, referring to fig. 5, fig. 5 shows the operating waveforms of VDET and DRISR in the QR (valley bottom on) mode, where the primary side of each period is turned on at the valley bottom, and correspondingly, the voltage-second product of the secondary side VDET above VCC of each period is equal, that is, a1 is a2 is A3, and if only the method of comparing the voltage-second product before and after the voltage-second product of the above embodiment is adopted to determine whether the secondary side rectifier tube M2 needs to be turned on, the secondary side rectifier tube M2 cannot be turned on normally, so the present application further improves the sample-and-hold circuit 2: when the secondary rectifier M2 is turned on, the current volt-second product obtained by the volt-second integrator 1 is multiplied by a coefficient K smaller than 1 (e.g., 0.8), so as to compare the current volt-second product multiplied by the coefficient K smaller than 1 with the next volt-second product. For example, taking fig. 5 as an example, when the secondary rectifier tube in the first period is turned on, the volt-second product in this period is K × a1, and the second period volt-second product is compared with a2 and K × a1 to obtain a2> K × a1, and when VDET < vtho, the secondary rectifier tube is turned on in the second period, and similarly, the second period volt-second product is K × a2, K a2 is compared with the next third period volt-second product A3, and so on, so that the improvement can ensure that the secondary rectifier tube can be turned on accurately when the system operates in the DCM and QR modes.
Based on this, referring to fig. 6, fig. 6 shows the operating waveforms of VDET, DRISR, V + (voltage value converted by the current volt-second product), V- (voltage value converted by the previous volt-second product), and OUT (output signal of the comparison circuit 3) in the DCM mode, and the circuit operating timing is as follows: in the TONP stage, VDET is located above VCC, and (VDET-VCC) is converted into current to charge the internal capacitor until the TONP stage is finished, then the voltage V + obtained by the current integrator increases linearly from 0V, and at this time V-is the last volt-second product and is relatively small. In the TONP stage, when V + is greater than V-, OUT jumps, which indicates that the current volt-second product is greater than the last one, and the preliminary turn-on condition of the secondary rectifier is satisfied, and when VDET < Vthon, the secondary rectifier is turned on, and then the ton stage is entered, and the highest voltage that V + is accumulated in the TONP stage is multiplied by a coefficient K (K <1), so as to prepare for comparison of the next volt-second product. During the TONS phase, the voltage of V +, V-is maintained. In the TOFF stage, the VDET excites ring and is positioned above VCC, the VDET-VCC is converted into current to charge an internal capacitor until the VDET is less than VCC, the voltage V + obtained by a current integrator is linearly increased from 0V, the V-obtains K times of the highest voltage obtained by the TONP stage through a sampling and holding circuit, the voltage of the V + terminal and the voltage of the V-terminal are compared by a comparison circuit, the voltage of the V + terminal is always less than the voltage of the V-terminal due to the fact that the voltage of the ring in seconds is smaller than that of the ring in the TOFF stage, and the OUT is low, which indicates that the voltage-second product of the ring excited in the TOFF stage is less than that of the TONP stage, and does not meet the initial starting condition of the secondary side. The subsequent VDET excited ring has smaller and smaller volt-second products, and the preliminary starting condition of the secondary rectifier tube is not met through comparison of the previous and subsequent volt-second products.
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 integration circuit 1 includes 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 voltage 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 sampling 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 currents according to a certain proportion; the current integrator 12 is configured to integrate the current to obtain a current volt-second product of the voltage across the secondary winding.
Specifically, the volt-second integration circuit 1 of the present application includes a voltage-to-current circuit 11 and a current integrator 12, and its operating principle is as follows:
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, and 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 current volt-second product of the voltages at the two ends of the secondary winding.
As an alternative embodiment, the comparison circuit 3 is embodied as a voltage comparator D; wherein:
the positive input end of the voltage comparator D is connected with the output end of the volt-second integrating circuit 1, the negative input end of the voltage comparator D is connected with the output end of the sample-and-hold circuit 2, and the output end of the voltage comparator D is connected with the rectifier tube control circuit 4;
the voltage comparator D is configured to generate a high-level signal as an on-enable signal if the present voltage-second product is greater than the last voltage-second product.
Specifically, the comparison circuit 3 of the present application may select the voltage comparator D, the positive input terminal of the voltage comparator D inputs the voltage at the two ends of the secondary winding at the current voltage-second product, the negative input terminal of the voltage comparator D inputs the voltage at the two ends of the secondary winding at the last voltage-second product, and if the voltage at the two ends of the secondary winding at the current voltage-second product is greater than the voltage-second product at the last voltage-second product, 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.
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 turned on at high level and turned off at low level), capacitors C1, C2, C3, C4, and C5, and the operation principle thereof will be described with reference to fig. 9:
when VDET is larger than VCC by a certain value, Demag is high level, and clear outputs a fixed pulse signal at each rising edge of Demag for clearing the charge of the corresponding capacitor. Demag1 jumps once on each rising edge of Demag for comparing the last voltage-second product sample with the current real-time voltage-second product. Demag1_ N is the inverse of Demag 1. And the Select outputs a fixed pulse signal only when the secondary rectifier tube is opened, 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 has the following working sequence: in the TONP stage, VDET is located above VCC, Demag is high, clear signals are output, charges on the capacitors C1, C2, C4 and C5 are cleared, the switches SW1, SW2 and SW5 are closed, VDET-VCC is converted into currents to charge the capacitors C1 and C2 until the TONP stage is finished, the V-terminal of the voltage comparator D is connected with the capacitor C3 through the switch SW5, and the value of the voltage comparator D is the last volt-second product value and is small. In the process of the TONP, when the voltage of a V + end of a voltage comparator D is larger than the voltage of a V-end, the TONPDT jumps high, the voltage-second product of the current time is larger than the voltage-second product of the last time, the primary starting condition of a secondary side rectifying tube is met, when VDET is smaller than Vthon, the secondary side rectifying tube is formally started, at the moment, a TONS stage is entered, a fixed pulse signal is generated by Select, therefore, charges on capacitors C1 and C2 are transferred to a capacitor C5, and the voltage of the V + end falls to the original K times by setting certain proportions of capacitors C1, C2 and C5. During 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, switches SW1, SW3 and SW4 are closed, clear signals are generated to clear charges on capacitors C1, C3, C4 and C5, V-terminal samples the information of the last V + terminal and keeps the information, (VDET-VCC) is converted into current to charge capacitors C1 and C3 until Demag is low, V + terminal voltage rises from zero at the moment, the larger the Vos-second product is, the higher the V + terminal rises, the V-terminal voltage is sampled at the moment that Demag1 is low to the voltage of V + terminal at the moment that TONS is sampled, the voltage is K times of the highest voltage obtained in the TONP stage, the V + terminal voltage is compared with the V-terminal voltage in real time, because the Vos-second product of ring is smaller, the V + terminal voltage is always smaller than the V-terminal voltage, the TONP output is low, which indicates that TONPFF output of TOS in the TOF stage is smaller than TOK times of TOK second product of exciting of TOK second, the preliminary opening condition of the secondary side rectifier tube is not met. The subsequent VDET excited ring has smaller and smaller volt-second products, and the preliminary starting condition of the secondary rectifier tube is not met through comparison of the previous and subsequent volt-second products.
The application also provides a flyback switching power supply which comprises a transformer comprising a primary winding and a secondary winding, a secondary rectifier tube and any one of the synchronous rectification control circuits.
For the introduction of the flyback switching power supply provided in the present application, reference is made to the above-mentioned embodiment of the synchronous rectification control circuit, and details are not repeated herein.
It is further noted that, in the present 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. Also, 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 an … …" does not exclude the presence of other identical 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 voltage-second integration circuit is used for acquiring the voltage-second product of the voltage at the two ends of the secondary winding of the switching power supply;
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 rectifier tube control circuit is used for controlling the rectifier tube to be conducted if the turn-on allowing signal is received and the terminal voltage connected with the rectifier tube on the secondary winding is less than the preset starting threshold voltage.
2. The synchronous rectification control circuit of claim 1, wherein the sample and hold circuit further comprises:
and the sub-circuit is used for multiplying the current volt-second product by a coefficient value smaller than 1 when the rectifier tube is conducted, 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 the volt-second integration 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 voltage 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-and-hold circuit and the comparison circuit;
the voltage-to-current circuit is used for converting the voltage at the two current 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 current volt-second product of the voltage at the two ends of the secondary winding.
4. The synchronous rectification control circuit of claim 1, wherein the comparison circuit is embodied as a voltage comparator; wherein:
the positive input end of the voltage comparator is connected with the output end of the volt-second integrating circuit, the negative input 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 rectifier tube control circuit;
and 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 including a primary winding and a secondary winding, a secondary rectifier, and a synchronous rectification control circuit as claimed in any one of claims 1 to 4.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202022184691.9U CN212323999U (en) | 2020-09-29 | 2020-09-29 | Synchronous rectification control circuit and flyback switching power supply |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202022184691.9U CN212323999U (en) | 2020-09-29 | 2020-09-29 | Synchronous rectification control circuit and flyback switching power supply |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN212323999U true CN212323999U (en) | 2021-01-08 |
Family
ID=74016463
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202022184691.9U Active CN212323999U (en) | 2020-09-29 | 2020-09-29 | Synchronous rectification control circuit and flyback switching power supply |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN212323999U (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115065221A (en) * | 2022-08-16 | 2022-09-16 | 成都利普芯微电子有限公司 | Synchronous rectification dynamic accelerating circuit, control circuit and switching power supply |
-
2020
- 2020-09-29 CN CN202022184691.9U patent/CN212323999U/en active Active
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115065221A (en) * | 2022-08-16 | 2022-09-16 | 成都利普芯微电子有限公司 | Synchronous rectification dynamic accelerating circuit, control circuit and switching power supply |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US11081964B2 (en) | Output-side controller with switching request at relaxation ring extremum | |
| US9350252B2 (en) | Systems and methods for protecting power conversion systems based on at least feedback signals | |
| US8085558B2 (en) | Resonant converter | |
| JP5693877B2 (en) | Controller for power supply, power supply, and method of controlling power supply | |
| US7426120B2 (en) | Switching control circuit having a valley voltage detector to achieve soft switching for a resonant power converter | |
| US7495934B2 (en) | Adaptive synchronous rectification control circuit and method thereof | |
| KR101468719B1 (en) | Power converter and driving method thereof | |
| US7701735B2 (en) | Converter and driving method thereof | |
| US8711581B2 (en) | Synchronous rectifier network unit circuit and method | |
| CN111865095A (en) | Synchronous rectification control circuit and flyback switching power supply | |
| TW201018062A (en) | Control circuit having off-time modulation to operate power converter at quasi-resonance and in continuous current mode | |
| US20240063724A1 (en) | Systems and methods for synchronous rectification of power supply systems | |
| KR101542645B1 (en) | On time sampling prevention | |
| CN107834857B (en) | Power supply control device and insulated switching power supply device | |
| CN111934557B (en) | Synchronous rectification circuit and power conversion device | |
| CN112087148A (en) | Synchronous rectification control circuit and flyback switching power supply | |
| CN112803722B (en) | Isolated switch converter and controller and control method thereof | |
| US20210111634A1 (en) | Flyback powr converter and secondary side controller circuit and control method thereof | |
| KR102143254B1 (en) | Pwm controlling apparatus for flyback converter | |
| CN212323999U (en) | Synchronous rectification control circuit and flyback switching power supply | |
| US9401634B2 (en) | Saturation prevention in an energy transfer element of a power converter | |
| US10972013B2 (en) | Switching power supply device with current limiting operation by feedback current | |
| US20230283165A1 (en) | Switch-mode power converters with control of turning off transistors for zero-voltage switching | |
| CN212323998U (en) | Synchronous rectification control circuit and flyback switching power supply | |
| Chakraborty et al. | An improved asymmetric half-bridge converter with zero DC offset of magnetizing current |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| GR01 | Patent grant | ||
| GR01 | Patent grant |