CN114567182A

CN114567182A - Synchronous rectification control device, chip and switching power supply

Info

Publication number: CN114567182A
Application number: CN202210258769.8A
Authority: CN
Inventors: 蔡林甫; 沈飏; 王梁
Original assignee: Chengdu Lipson Microelectronics Co ltd
Current assignee: Chengdu Lipson Microelectronics Co ltd
Priority date: 2022-03-16
Filing date: 2022-03-16
Publication date: 2022-05-31

Abstract

The application relates to a synchronous rectification control device, a chip and a switching power supply, and belongs to the technical field of electronic circuits. The synchronous rectification control device comprises: the synchronous rectification control circuit is connected with the secondary side rectifying tube; the synchronous rectification control circuit is used for detecting the time when the switching voltage at two ends of the secondary rectifying tube falls from a first preset threshold value to a second preset threshold value; when the time is less than the preset sampling time, controlling the secondary rectifier tube to be conducted; when the switching voltage is detected to be larger than a third preset threshold value, controlling the secondary rectifier tube to be turned off; the first preset threshold is greater than the third preset threshold, and the third preset threshold is greater than the second preset threshold. The switch-on condition of the secondary rectifier tube is accurately controlled by detecting the magnitude of the switch voltage at the two ends of the secondary rectifier tube and presetting the slope in sampling time, so that the error switch-on of the secondary rectifier tube is avoided.

Description

Synchronous rectification control device, chip and switching power supply

Technical Field

The application belongs to the technical field of electronic circuits, and particularly relates to a synchronous rectification control device, a chip and a switching power supply.

Background

At present, there are two types of secondary side rectification schemes for a switching power supply, one is an asynchronous rectification scheme using a diode, and the other is a synchronous rectification scheme using a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The synchronous rectification scheme using the MOSFET transistor has a higher efficiency of power conversion than the non-synchronous rectification scheme using a diode, and thus is widely used.

In the secondary synchronous rectification scheme, the turn-on and turn-off of the secondary rectifier is generally controlled according to the drain-source voltage (Vds) of the secondary rectifier (specifically, MOSFET). However, the control method often causes false triggering due to the drain-source voltage oscillation of the secondary rectifier, and specifically, the inventor of the present application finds in the process of studying the present application that: after the secondary rectifier tube is turned off, the primary inductance of the transformer and the parasitic capacitance of the primary switch tube form LC oscillation, the oscillation is reflected to the secondary side through the transformer, Vds of the secondary rectifier tube oscillates along with the oscillation, the secondary rectifier tube is possibly conducted by mistake, a crossover phenomenon (the primary switch tube and the secondary rectifier tube are conducted simultaneously) is generated, extra chip loss is generated slightly, and the chip is burnt out seriously.

Disclosure of Invention

In view of this, an object of the present application is to provide a synchronous rectification control device, a chip and a switching power supply, so as to solve the problem that the conventional secondary synchronous rectification scheme may cause the secondary rectifier to be turned on erroneously.

The embodiment of the application is realized as follows:

in a first aspect, an embodiment of the present application provides a synchronous rectification control device, including: the synchronous rectification control circuit is connected with the secondary side rectifying tube; the synchronous rectification control circuit is used for detecting the time when the switching voltage at two ends of the secondary rectifying tube falls from a first preset threshold value to a second preset threshold value; when the time is less than the preset sampling time, or the time that the switch voltage is continuously greater than a first preset threshold value is greater than the minimum turn-off time and the time that the switch voltage drops from the first preset threshold value to a second preset threshold value is less than the preset sampling time, controlling the secondary rectifying tube to be conducted; when the switching voltage is detected to be larger than a third preset threshold value, controlling the secondary rectifier tube to be turned off; the first preset threshold is greater than the third preset threshold, and the third preset threshold is greater than the second preset threshold. In the embodiment of the present application, the inventor found in the process of studying the present application that, after the secondary rectifier is turned off, the primary inductance of the transformer and the parasitic capacitance of the primary switching tube form an LC oscillation, the oscillation may cause Vd to oscillate, and as the stored energy is gradually dissipated, the Vd exhibits a damped oscillation, and the amplitude gradually decreases, and in the oscillation phase, the time for Vd to decrease from a first preset threshold (as represented by Vth1) to a second preset threshold (as represented by Vth2) is long, while in the turn-off of the primary switching tube, the time for Vd to decrease from Vth1 to Vth2 is short, that is, the decrease speed of Vd in the turn-off of the primary switching tube is greater than the decrease speed in the oscillation phase, that is, the slope (absolute value) of Vd in the turn-off of the primary switching tube is greater than the slope in the oscillation phase, and therefore, by detecting the magnitude of the switching voltage Vd across the secondary rectifier and the slope in the preset sampling time, the conduction condition of the secondary rectifier tube is accurately controlled, and the false conduction is avoided. In order to further ensure the accuracy of conduction and further avoid mistaken opening, the application also provides a scheme for judging whether the Vd meets two conditions, namely, whether the time of continuously exceeding the first preset threshold value by the Vd exceeds a preset time is judged except that the time of meeting the judgment that the Vd is reduced from the first preset threshold value to the second preset threshold value meets the condition, and the conduction of the secondary rectifier tube is controlled only under the condition that the two conditions are met.

With reference to a possible implementation manner of the embodiment of the first aspect, the synchronous rectification control circuit includes: a master control circuit having a first input terminal, a second input terminal, a third input terminal, a first output terminal, and a second output terminal; the first input end is used for receiving the first preset threshold, the second input end is used for receiving the switching voltage, and the third input end is used for receiving the second preset threshold or the third preset threshold; the main control circuit is used for outputting a level signal for controlling the conduction of the secondary rectifier tube through the first output end when the time for the switch voltage to drop from a first preset threshold value to a second preset threshold value is less than preset sampling time, or the time for the switch voltage to continuously be greater than the first preset threshold value is greater than the minimum turn-off time and the time for the switch voltage to drop from the first preset threshold value to the second preset threshold value is less than preset sampling time; and when the switching voltage is detected to be larger than a third preset threshold value, outputting a level signal for controlling the turn-off of the secondary rectifier tube through the second output end. In the embodiment of the application, the main control circuit with three input ends and two output ends is adopted, so that the on or off of the secondary rectifier tube can be accurately controlled, and the control circuit has the advantages of simple control logic and easiness in implementation.

With reference to one possible implementation manner of the embodiment of the first aspect, the master control circuit includes: the circuit comprises a first comparator, a second comparator, a first timing module and a logic gate; a first input terminal of the first comparator is configured to receive the first preset threshold, and a second input terminal of the first comparator is configured to receive the switching voltage; a first input end of the second comparator is used for receiving the second preset threshold value or the third preset threshold value, and a second input end of the second comparator is used for receiving the switching voltage; the output end of the first comparator is connected with the first timing module, and the first timing module is used for generating a level signal representing time according to the output result of the first comparator; the logic gate is respectively connected with the first timing module and the second comparator, and is used for carrying out logic operation on the level signal of the characterization time and the output signal of the second comparator, and outputting a logic operation result through a first output end of the main control circuit. In this embodiment of the application, the main control circuit with the above structure is adopted, so that when the switching voltage Vd < Vth1 (a first preset threshold), the first timing module starts to generate sampling time (time when a level signal representing time is a high level), in the sampling time, if Vd < Vth2 (a second preset threshold) is detected, that is, the second comparator outputs a high level, the logic gate outputs a level signal for controlling the conduction of the secondary rectifier tube, and the size of the switching voltage Vd and the slope in the preset sampling time are quickly detected by adopting a hardware mode, so that the conduction condition of the secondary rectifier tube is accurately controlled.

With reference to one possible implementation manner of the embodiment of the first aspect, the master control circuit includes:

a first comparator, a first input terminal of which is configured to receive the first preset threshold, and a second input terminal of which is configured to receive the switching voltage;

a second comparator, a first input end of the second comparator is used for receiving the second preset threshold or the third preset threshold, and a second input end of the second comparator is used for receiving the switching voltage;

the output end of the first comparator is connected with the first timing module, and the first timing module is used for generating a level signal representing time according to the output result of the first comparator;

the input end of the second timing module is connected with the first comparator, and the second timing module is used for judging whether the time that the switching voltage is continuously greater than a first preset threshold value is greater than the minimum turn-off time or not;

the logic gate is used for carrying out logic operation on output signals of the first timing module, the second timing module and the second comparator and outputting a logic operation result through a first output end of the main control circuit. The embodiment is different from the last main control circuit, and is applied to the scheme for judging whether Vd meets two conditions. It is understood that the first comparator, the second comparator and the first timing module in this embodiment are the same as the corresponding devices in the foregoing embodiments in structure, function and connection relationship. And will not be described in detail herein.

With reference to one possible implementation manner of the embodiment of the first aspect, the first timing module includes: the circuit comprises an inverter, a capacitor, a switch circuit, a third comparator and a NOR gate; the input end of the phase inverter is connected with the output end of the first comparator; the control end of the switch circuit is connected with the output end of the phase inverter, the input end of the switch circuit is used for being connected with a power supply, and the output end of the switch circuit is grounded through the capacitor; a first input end of the third comparator is connected with an output end of the switch circuit, a second input end of the third comparator is used for receiving a reference signal, and the reference signal is used for adjusting the time of the high level of the level signal representing the time; the first input end of the NOR gate is connected with the output end of the third comparator, the second input end of the NOR gate is connected with the output end of the phase inverter, and the output end of the NOR gate is connected with the logic gate. In the embodiment of the application, the first timing module with the above structure is adopted, so that when the switching voltage Vd is smaller than the first preset threshold, the first timing module starts timing, generates sampling time (time of high level of the level signal representing time), and can adjust the size of the sampling time by adjusting the reference signal, thereby adapting to different scenes.

With reference to one possible implementation manner of the embodiment of the first aspect, the synchronous rectification control circuit further includes: and the logic circuit is respectively connected with the first output end and the second output end of the main control circuit and is used for generating a control signal for controlling the on/off of the secondary rectifier tube according to the output signal of the first output end and the output signal of the second output end of the main control circuit. In the embodiment of the application, the first output end and the second output end of the main control circuit are connected by using the logic circuit, so that the real-time detection mechanism is buckled in a loop manner, the working stage of the Vd is conveniently and accurately judged, the on-off of the secondary rectifier tube is accurately controlled, and the error on of the secondary rectifier tube is avoided.

With reference to one possible implementation manner of the embodiment of the first aspect, the logic circuit includes: the latch circuit comprises a first latch, a second latch and an inverter; a first input end of the first latch is connected with a first output end of the main control circuit; the first input end of the second latch is connected with the output end of the first latch, and the output end of the second latch is connected with the second input end of the first latch; the input end of the phase inverter is connected with the second output end of the main control circuit, and the output end of the phase inverter is connected with the second input end of the second latch.

In the embodiment of the application, the logic circuit with the structure is adopted, the first output end and the second output end of the main control circuit are connected, the final control signal (VG) is output to control the secondary side rectifying tube after the output signals (S1 and S2) of the first output end and the second output end are subjected to logic operation, and the VG is fed back to the logic circuit, so that the real-time detection mechanism is buckled, the Vd working stage is accurately judged, and the mistaken opening is avoided; in addition, the logic circuit can latch the level signal (for example, when S1 is high level) for turning on the secondary rectifier tube and the level signal (for example, when S2 is low level) for turning off the MOS output by the main control circuit through the latch, so as to realize accurate on-off control of the secondary rectifier tube and avoid misoperation.

With reference to one possible implementation manner of the embodiment of the first aspect, the synchronous rectification control circuit further includes: and the output end of the selector is connected with the third input end of the main control circuit, and the selector is used for selectively outputting the second preset threshold value or the third preset threshold value. In the embodiment of the application, the selector is arranged to rapidly switch the preset threshold value received by the third input end of the main control circuit.

With reference to one possible implementation manner of the embodiment of the first aspect, the synchronous rectification control device further includes: and the sampling circuit is used for sampling the switching voltage at two ends of the secondary rectifier tube and transmitting the switching voltage to the synchronous rectification control circuit. The synchronous rectification control device can obtain the switching voltage at two ends of the secondary rectifying tube by itself without depending on other elements.

In a second aspect, an embodiment of the present application further provides a switching power supply, including: a secondary rectifier and a synchronous rectification control device as provided in the first aspect embodiment and/or in connection with any possible implementation manner of the first aspect embodiment, the synchronous rectification control device being configured to control turning on or off of the secondary rectifier.

In a third aspect, an embodiment of the present application further provides a chip, which is integrated with the synchronous rectification control device provided in the foregoing first aspect and/or in combination with any possible implementation manner of the first aspect.

In a fourth aspect, an embodiment of the present application further provides a synchronous rectification control method, including: detecting the time for the switching voltage at two ends of the secondary rectifier tube to drop from a first preset threshold value to a second preset threshold value; when the time is less than the preset sampling time, generating a control signal for controlling the conduction of the secondary rectifier tube; when the switching voltage is detected to be greater than a third preset threshold value, a control signal for controlling the turn-off of the secondary rectifier tube is generated, wherein the first preset threshold value is greater than the third preset threshold value, and the third preset threshold value is greater than the second preset threshold value.

Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the embodiments of the application. The objectives and other advantages of the application may be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings without creative efforts. The foregoing and other objects, features and advantages of the application will be apparent from the accompanying drawings. Like reference numerals refer to like parts throughout the drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the application.

Fig. 1 illustrates a schematic diagram of a switching power supply provided in an embodiment of the present application.

Fig. 2 is a schematic diagram illustrating a synchronous rectification control device and a secondary rectifier according to an embodiment of the present application.

Fig. 3 shows a schematic diagram of a synchronous rectification control circuit according to an embodiment of the present application.

Fig. 4 shows a schematic diagram of a master control circuit provided in an embodiment of the present application.

Fig. 5 shows a schematic diagram of a first timing module according to an embodiment of the present application.

Fig. 6 shows a schematic diagram of another synchronous rectification control circuit provided in an embodiment of the present application.

Fig. 7 is a schematic diagram illustrating another synchronous rectification control circuit provided in an embodiment of the present application.

Fig. 8 shows a timing diagram of a synchronous rectification control circuit according to an embodiment of the present application.

Fig. 9 shows a schematic diagram of a synchronous rectification control circuit according to another embodiment of the present application.

Detailed Description

The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures. Meanwhile, relational terms such as "first," "second," and the like may be used solely in the description herein 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 the process, method, article, or apparatus that comprises the element.

In the description of the present application, it is also to be noted that, unless otherwise explicitly specified or limited, the terms "connected" and "connected" are to be interpreted broadly, e.g., as meaning either a fixed connection, a detachable connection, or an integral connection; or may be an electrical connection; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present application can be understood in a specific case by those of ordinary skill in the art.

In view of the problem that the conventional secondary synchronous rectification scheme may cause the secondary rectifier, such as a MOSFET (as denoted by P1), to be turned on erroneously, in a first aspect, embodiments of the present application provide a synchronous rectification control apparatus, which accurately controls the turn-on condition of the secondary rectifier by detecting the magnitude of a switching voltage (as denoted by Vd) across the secondary rectifier and a slope within a preset sampling time, so as to avoid the erroneous turn-on condition. The slope is described in this application as an absolute value.

The inventor of the present application finds out in the process of studying the present application that: after the secondary side rectifying tube is turned off, the primary side inductance of the transformer (as represented by T) and the parasitic capacitance of the primary side switching tube (as represented by P2) form LC oscillation, the oscillation can cause Vd to oscillate, and as the stored energy is gradually dissipated, the oscillation is damped, the amplitude is gradually reduced, in the oscillation phase, the time for Vd to drop from a first preset threshold (as represented by Vth1) to a second preset threshold (as represented by Vth2) is long, and when the primary side switching tube is turned off, the time for Vd to drop from Vth1 to Vth2 is short, namely the dropping speed of Vd when the primary side switching tube is turned off is greater than that in the oscillation phase, namely the slope of Vd when the primary side switching tube is turned off is greater than that in the oscillation phase. Therefore, by distinguishing the time when Vd drops from Vth1 to Vth2 (which is equivalent to distinguishing the slope of Vd), it can be determined when the secondary rectifier should be turned on (for example, the primary switch is turned off, and the secondary rectifier should be turned on immediately), so that the condition that the secondary rectifier is turned on by mistake due to Vd oscillation can be avoided. It should be noted that the discovery process of the above-mentioned problems and the solutions proposed by the embodiments of the present invention to the above-mentioned problems should be the contributions of the inventors to the present invention in the process of the present invention.

For ease of understanding, the following description is made in conjunction with a switching power supply provided in an embodiment of the present application, and the switching power supply includes a synchronous rectification control device for controlling on or off of a secondary rectifier. In one embodiment, a schematic diagram of a switching power supply is shown in fig. 1. The switching power supply comprises a synchronous rectification control device, a transformer T, a primary side switching tube P2, a secondary side rectifying tube P1 and an energy storage capacitor C0. The resistor R0 shown in fig. 1 is a load supplied by the switching power supply. The synchronous rectification control device is used for controlling the on-off of the secondary rectifier tube. Normally, the primary side switching tube P2 and the secondary side rectifying tube P1 cannot be turned on simultaneously, and when the primary side switching tube P2 is turned on, the secondary side rectifying tube P1 is in an off state. When the secondary rectifier P1 is turned off, the time for Vd to drop from Vth1 to Vth2 is long, and when P2 is turned off, the time for Vd to drop from Vth1 to Vth2 is short. Therefore, in the first aspect, in this embodiment of the present application, the time when the switching voltage across the secondary rectifier tube drops from the first preset threshold to the second preset threshold is detected, and when the time is less than the preset sampling time, the secondary rectifier tube is controlled to be turned on, so that the secondary rectifier tube is prevented from being turned on by mistake.

The synchronous rectification control device provided in the embodiment of the present application will be described with reference to fig. 2. The synchronous rectification control device comprises a synchronous rectification control circuit and a sampling circuit, wherein the sampling circuit is connected with the synchronous rectification control circuit. It should be noted that the synchronous rectification control device may not include a sampling circuit, but directly receives the switching voltage sampled by the external sampling device at two ends of the secondary rectifier tube.

The sampling circuit is used for sampling the switching voltage Vd at two ends of the secondary rectifier tube and transmitting the switching voltage to the synchronous rectification control circuit. Optionally, the switching voltage Vd in this application refers to a drain-source voltage, and when the source is grounded, the collected voltage at the drain end is the switching voltage. Since one end (source) of the secondary rectifier shown in fig. 1 is grounded, the switching voltage Vd across the secondary rectifier is equal to the voltage at the point H (i.e., the drain), and therefore the sampling circuit may be used to collect the voltage at the point H in fig. 1. The sampling circuit may be a voltage sampling circuit that is common today.

The synchronous rectification control circuit is connected with the secondary rectifier tube and used for accurately controlling the conduction condition of the secondary rectifier tube according to the magnitude of switching voltage (shown as Vd) at two ends of the secondary rectifier tube and the slope in preset sampling time. Specifically, the synchronous rectification control circuit is configured to detect a time when the switching voltage across the secondary rectifier tube drops from a first preset threshold to a second preset threshold, control the secondary rectifier tube to be turned on when the time is less than a preset sampling time, and control the secondary rectifier tube to be turned off when the switching voltage is detected to be greater than a third preset threshold (e.g., as represented by Vth 3).

The first preset threshold is greater than a third preset threshold, and the third preset threshold is greater than the second preset threshold, that is, Vth1> Vth3> Vth 2. Optionally, the voltage of Vth1 is greater than the turn-on threshold of the secondary rectifier (e.g., Vth1 may be selected to be 2V or other), Vth3 may be any voltage in the range of-10 mV to 10mV, such as 0V, and Vth2 may be a voltage less than-100 mV.

In one embodiment, the functional logic of the synchronous rectification control circuit may be implemented by software, and in this case, the synchronous rectification control circuit includes a processor, the processor is configured to detect a time when a switching voltage across the secondary rectifier tube drops from a first preset threshold to a second preset threshold, and control the secondary rectifier tube to be turned on when the time is less than a preset sampling time; and controlling the secondary rectifier tube to be switched off when the switching voltage is detected to be larger than a third preset threshold value.

The processor may be an integrated circuit chip having signal processing capabilities. The Processor may be a general-purpose Processor, including a Central Processing Unit (CPU), a Network Processor (NP), and the like; but also Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) or other Programmable logic devices, discrete Gate or transistor logic devices, discrete hardware components. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.

In another embodiment, as shown in fig. 3, the synchronous rectification control circuit includes a main control circuit having a first input terminal, a second input terminal, a third input terminal, a first output terminal, and a second output terminal. The first input terminal is used for receiving a first preset threshold value (Vth1), the second input terminal is used for receiving a switching voltage (Vd), and the third input terminal is used for receiving a second preset threshold value (Vth2) or a third preset threshold value (Vth 3).

The main control circuit is configured to detect a time when the switching voltage drops from a first preset threshold to a second preset threshold, and output a level signal for controlling the conduction of the secondary rectifier tube through the first output terminal when the time is less than a preset sampling time (the output signal of the first output terminal is a high level at this time as represented by S1); and when the switching voltage is detected to be larger than the third preset threshold value, outputting a level signal for controlling the secondary rectifier tube to be turned off through the second output end (the output signal of the second output end is low level at this time as represented by S2).

The functional logic of the main control circuit may be implemented in a software manner, in this case, the main control circuit may include a processor, and in addition, the functional logic of the main control circuit may also be implemented in a hardware manner, in this case, optionally, as shown in fig. 4, the main control circuit includes: a first comparator (e.g., represented by COM 1), a second comparator (e.g., represented by COM 2), a first timing block (i.e., the timing block in fig. 4, 6-7), and a logic gate (which may be an and gate).

When detecting that the switching voltage is smaller than a first preset threshold value, the main control circuit generates a level signal (for example, represented by Sample _ time) representing time, and if detecting that the switching voltage is smaller than a second preset threshold value within an effective level (for example, high level) of the level signal representing time, the main control circuit outputs a level signal for controlling the conduction of the secondary rectifier tube. And when the switching voltage is detected to be larger than a third preset threshold value, outputting a level signal for controlling the turn-off of the secondary rectifier tube.

The first input terminal of the first comparator is used for receiving a first preset threshold value, the second input terminal of the first comparator is used for receiving a switching voltage, and the switching voltage is used for comparing the Vth1 and Vd, for example, when Vth1> Vd, a high level is output, and when Vth1< Vd, a low level is output.

The first input terminal of the second comparator is used for receiving a second preset threshold or a third preset threshold, and the second input terminal of the second comparator is used for receiving a switching voltage for comparing the magnitude of Vth2 (or Vth3) and Vd. When the input of the first input terminal of the second comparator is Vth2, the second comparator compares the magnitude of Vth2 and Vd at this time, for example, when Vth2> Vd, a high level is output, and when Vth2< Vd, a low level is output. When the input of the first input terminal of the second comparator is Vth3, the second comparator compares the magnitude of Vth3 and Vd at this time, for example, when Vth3> Vd, a high level is output, and when Vth3< Vd, a low level is output.

The output end of the first comparator is connected with a first timing module, and the first timing module is used for generating a level signal representing time, such as a Sample _ time signal, according to the output result of the first comparator.

The logic gate is connected to the first timing module and the second comparator, respectively, and is configured to perform a logic operation on the level signal (or the output signal of the first timing module) representing time and the output signal (e.g., COM2_ OUT) of the second comparator, for example, perform an and operation, and output a logic operation result, that is, output the S1 signal. It should be noted that, in part of this application, the output signal of the second comparator is represented by S2, that is, S2 and COM2_ OUT represent the same signal.

In the second aspect, in order to further ensure that the error conduction is avoided, optionally, in some embodiments of the present application, the synchronous rectification control device needs to satisfy two conditions to control the conduction of the secondary rectifier, that is, compared with the embodiment of the first aspect, the difference of this embodiment is that the secondary rectifier is not only conducted when the time for the switching voltage to drop from the first preset threshold to the second preset threshold is less than the preset sampling time.

Specifically, when the time that the switching voltage Vd is continuously greater than the first preset threshold is greater than a preset time (also called a minimum off time) and the time that the switching voltage drops from the first preset threshold to the second preset threshold is less than a preset sampling time, the secondary rectifier tube is controlled to be turned on. That is, compared to the embodiment of the first aspect, the difference between the main control circuit and the main control circuit in this embodiment is that the main control circuit outputs the level signal for controlling the turn-on of the secondary rectifier tube through the first output end when the time that the switching voltage is continuously greater than the first preset threshold is greater than the minimum turn-off time and the time that the switching voltage is decreased from the first preset threshold to the second preset threshold is less than the preset sampling time.

The minimum off time may be set according to specific needs, and may be 500ns, for example. That is, not only the above requirement for the Vd changing speed is satisfied, but also Vd is maintained above a preset value (e.g., a first preset threshold) for a certain time (the time is greater than the minimum turn-off time), so that the secondary rectifier tube can be turned on. For example, it may be determined first whether Vd continues to be greater than a first preset threshold for a time greater than a minimum off-time, and a signal representing the determination result is output (if the high level representation is yes); and then judging whether the time for Vd to fall from the first preset threshold to the second preset threshold is less than the preset sampling time, and outputting a signal representing the judgment result. And only under the condition that the two judgment results are yes, the secondary rectifier tube is controlled to be conducted. Optionally, when Vd continues to be greater than the first preset threshold for a time greater than the minimum off-time, the next determination (whether the determination is less than the preset sampling time) is performed.

As shown in fig. 9, in this embodiment, the main control circuit is different from the main control circuit of the first aspect (for example, fig. 4), and further includes: and a second timing module. The second timing module is used for judging whether the time that the switch voltage is continuously greater than a first preset threshold value is greater than the minimum turn-off time or not; and outputs a level (e.g., high level) representing the determination result to the aforementioned logic gate. The logic gate is used for carrying out logic operation (such as logical AND) on output signals of the first timing module, the second timing module and the second comparator, and outputting a logic operation result through a first output end of the main control circuit. In the present embodiment, the first comparator, the second comparator, and the first timing module are the same as the corresponding devices in the foregoing embodiments in structure, function, connection relationship, and the like. And will not be described in detail herein.

Specifically, an input end of the second timing module is connected to an output end of the first comparator, and an output end of the second timing module is connected to an input end of the logic gate. That is, compared to the previous embodiment of the first aspect, the logic gate (e.g., logical and) in this embodiment has a third input terminal for receiving the output of the second timing module in addition to the two input terminals connected to the first timing module and the second comparator in the previous embodiment. The logic gate performs logic operation on the three inputs and outputs a logic operation result.

Optionally, the second timing module further includes a reset module, which resets an output of the second timing module according to the switching voltage. For example, when the first comparator determines that the switching voltage is greater than the first threshold voltage, the first comparator is inverted, the inverted signal (such as a rising edge) triggers a pulse signal to be given, and the second timing module resets the output (such as outputting a low level) according to the pulse signal.

It should be noted that, in fig. 9, the output end of the second latch is further connected to an inverter, and the output end is connected to the secondary rectifier via the inverter. In practice, it may not be required. Whether to set the inverter is determined according to the type of the secondary rectifier (such as P tube and N tube).

Optionally, in this application, the first timing module is configured to generate a level signal representing time according to an output result of the first comparator. Optionally, as shown in fig. 5, the first timing module includes: an inverter, a capacitor (as represented by C1), a switching circuit (including a P3 switching tube and an N1 switching tube), a third comparator (as represented by COM 3), and a NOR gate. The input end of the phase inverter is connected with the output end of the first comparator, the control end of the switch circuit is connected with the output end of the phase inverter, the input end of the switch circuit is used for being connected with a power supply (which can be a constant current source), the output end of the switch circuit is grounded through a capacitor, the output end of the switch circuit is further connected with the first input end of the third comparator, the second input end of the third comparator is used for receiving a reference signal (such as Vref), the first input end of the NOR gate is connected with the output end of the third comparator, the second input end of the NOR gate is connected with the output end of the phase inverter, and the output end of the NOR gate is connected with the logic gate. Wherein the reference signal is used to adjust the time of the high level of the level signal representing the time.

Explaining the principle of the first timing module, when Vd > Vth1, a point a outputs a high level, the N1 switching tube is turned on, a point B outputs a low level, if VB < Vref, VC is a low level, and the nor gate outputs a low level, that is, the Sample _ time signal (the level signal representing time) is a low level; when Vd is less than Vth1, a point A outputs a low level, a P3 switching tube is conducted to charge a capacitor C1, the voltage of a point B gradually rises, if VB is less than Vref, VC is a low level, a NOR gate outputs a high level, namely a Sample _ time signal is pulled to be a high level; when Vd < Vth1, point A is low, and if VB > Vref, VC is high, and the Sample _ time signal is low. Where VB is the voltage at point B and VC is the voltage at point C.

The time when the level signal representing the time (e.g., the Sample _ time signal) is at the high level is the preset sampling time, the time at the high level of the Sample _ time can be adjusted by the capacity of the capacitor C1, the magnitude of the reference signal Vref, and the magnitude of the charging current, and the time at the high level of the Sample _ time can be adjusted by adjusting the magnitude of the reference signal Vref under the condition that the capacity of the capacitor C1 and the magnitude of the charging current are fixed.

In an alternative embodiment, the synchronous rectification control circuit of the present application may further include a selector and/or a logic circuit in addition to the main control circuit, as shown in fig. 6 (fig. 6 to 8 are examples of judging only one of the foregoing conditions, and the following selector and/or logic circuit is also applicable to the case where the scheme is to judge two conditions).

The output end of the selector is connected with the third input end of the main control circuit, and the selector is used for selectively outputting a second preset threshold value or a third preset threshold value. For example, when the selection signal of the selector is low level "0", Vth2 is output, and when the selection signal is high level "1", Vth3 is output.

The logic circuit is used for generating a control signal (as represented by VG) for controlling the secondary side rectifying tube to be switched on or switched off according to an output signal (as S1) of the first output terminal of the main control circuit and an output signal (as S2) of the second output terminal of the main control circuit.

The control signal is a level signal, and for example, when the control signal is a high level signal, VG is 1, and when the control signal is a low level signal, VG is 0. The "0", "1" level of the selector may be provided by VG, which is 0, the selector output Vth 2; VG is 1, and the selector outputs Vth 3. When VG is 0, the selector outputs Vth2, and at this time, the second comparator compares the magnitudes of Vth2 and Vd. When VG is 1, the selector outputs Vth3, and at this time, the second comparator compares the magnitudes of Vth3 and Vd.

In this application, the synchronous rectification control circuit that this application provided's simple structure controls the output of selector through the output signal (VG) that utilizes logic circuit to form the loop, make real-time detection mechanism ring looks knot, so that the working phase of accurate judgement Vd, thereby the switching on or turn-off of accurate control secondary side rectifier tube, can further avoid the misconnection of secondary side rectifier tube.

Alternatively, as shown in fig. 7. The logic circuit includes a first latch (as represented by U1), a second latch (as represented by U2), and an inverter. The first input end (such as the S end) of the first latch is connected with the first output end of the main control circuit, the first input end (such as the S end) of the second latch is connected with the output end (such as the Q end) of the first latch, the output end (such as the Q end) of the second latch is connected with the second input end (such as the R end) of the first latch, the input end of the phase inverter is connected with the second output end of the main control circuit, and the output end of the phase inverter is connected with the second input end (such as the R end) of the second latch. Optionally, the first latch and the second latch may be selected as SR latches. Wherein S is a set terminal, and R is a reset terminal. The SR latch may alternatively be an SR latch consisting of two nor gates, or an SR latch consisting of two nand gates.

To better understand the principle of the synchronous rectification control circuit shown in fig. 7, it will be described below with reference to the sequential circuit diagram shown in fig. 8.

At the initial time, VG is 0, the secondary rectifier is turned off, the selector outputs Vth2, when Vd < Vth1, the first timing block starts generating a sampling time (time when the Sample _ time signal is at high level), and when Vd < Vth2 is detected within the sampling time, COM2 outputs high level, and the and gate outputs high level. At this time, it is known that the time for Vd to drop from Vth1 to Vth2 is shorter than the sampling time, which means that the primary side switching tube is in an off state, the secondary side rectifying tube should be immediately turned on, the high level of the and gate output is connected to the input terminal (S) of the first latch, VG is made 1, and the secondary side rectifying tube is turned on. When VG is 1, the selector outputs Vth 3. At this time Vd < Vth3, COM2 outputs high, and VG is still high by the second latch. When Vd > Vth3, COM2 outputs low, the second latch is reset (high reset), VG is 0, the secondary rectifier is turned off, and the selector outputs Vth 2. At this time Vd > Vth2, COM2 outputs low level, VG is 0, the secondary rectifier is kept closed, and then the next cycle of detection is performed.

That is, VG is 0, the selector outputs Vth2, and if Vd < Vth2, S1 is 1, S2 is 1, reset end R of U2 is 0, and output VG is 1 during the sampling time; VG is 1, the selector outputs Vth3, and if Vd < Vth3, S1 is 1, S2 is 1, reset terminal R of U2 is 0, and output VG is 1; VG is 1, the selector outputs Vth3, and if Vd > Vth3, S2 is 0, the reset terminal R of U2 is 1, and the output VG is 0; VG is 0, the selector outputs Vth2, and if Vd > Vth2, S2 is 0, the reset terminal R of U2 is 1, and the output VG is 0.

Based on the same inventive concept, the embodiment of the present application further provides a chip, and the chip is integrated with the synchronous rectification control device. The chip integrated with the synchronous rectification control device can be applied to a switching power supply and is used for controlling the on/off of a secondary rectifier tube in the switching power supply. The chip provided in the embodiment of the present application has the same implementation principle and technical effect as those of the foregoing embodiment of the synchronous rectification control device, and for the sake of brief description, no part of the embodiment of the chip is mentioned, and reference may be made to the corresponding contents in the foregoing embodiment of the synchronous rectification control device.

Based on the same inventive concept, the embodiment of the present application further provides a synchronous rectification control method, which is applied to the synchronous rectification control device, and the method includes:

s1: and detecting the time when the switching voltage at the two ends of the secondary rectifier tube falls from a first preset threshold value to a second preset threshold value.

S2: and when the time is less than the preset sampling time, generating a control signal for controlling the conduction of the secondary rectifier tube.

S3: and when detecting that the switching voltage is greater than a third preset threshold value, generating a control signal for controlling the secondary rectifier tube to be switched off.

The first preset threshold is greater than the third preset threshold, and the third preset threshold is greater than the second preset threshold.

The implementation principle and the generated technical effect of the synchronous rectification control method provided by the embodiment of the present application are the same as those of the synchronous rectification control device embodiment, and for the sake of brief description, no part of the method embodiment is mentioned, and reference may be made to the corresponding contents in the synchronous rectification control device embodiment.

It should be noted that, in this specification, each embodiment is described in a progressive manner, and each embodiment focuses on differences from other embodiments, and portions that are the same as and similar to each other in each embodiment may be referred to.

The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A synchronous rectification control device, comprising:

the synchronous rectification control circuit is connected with the secondary side rectifying tube;

the synchronous rectification control circuit is used for detecting the time when the switching voltage at two ends of the secondary rectifying tube falls from a first preset threshold value to a second preset threshold value;

when the time is less than the preset sampling time, or the time that the switch voltage is continuously greater than a first preset threshold value is greater than the minimum turn-off time and the time that the switch voltage drops from the first preset threshold value to a second preset threshold value is less than the preset sampling time, controlling the secondary rectifying tube to be conducted; when the switching voltage is detected to be larger than a third preset threshold value, controlling the secondary rectifier tube to be turned off;

2. The synchronous rectification control device of claim 1, wherein the synchronous rectification control circuit comprises:

a master control circuit having a first input terminal, a second input terminal, a third input terminal, a first output terminal, and a second output terminal;

the first input end is used for receiving the first preset threshold, the second input end is used for receiving the switching voltage, and the third input end is used for receiving the second preset threshold or the third preset threshold;

the main control circuit is used for outputting a level signal for controlling the conduction of the secondary rectifier tube through the first output end when the time for the switch voltage to drop from a first preset threshold value to a second preset threshold value is less than preset sampling time, or the time for the switch voltage to continuously be greater than the first preset threshold value is greater than the minimum turn-off time and the time for the switch voltage to drop from the first preset threshold value to the second preset threshold value is less than preset sampling time; and when the switching voltage is detected to be larger than a third preset threshold value, outputting a level signal for controlling the turn-off of the secondary rectifier tube through the second output end.

3. The synchronous rectification control device of claim 2, wherein the master circuit comprises:

and the logic gate is respectively connected with the first timing module and the second comparator, and is used for carrying out logic operation on the level signal of the representation time and the output signal of the second comparator and outputting a logic operation result through a first output end of the main control circuit.

4. The synchronous rectification control device of claim 2, wherein the master circuit comprises:

the input end of the second timing module is connected with the output end of the first comparator, and the second timing module is used for judging whether the time that the switching voltage is continuously greater than a first preset threshold value is greater than the minimum turn-off time or not;

and the logic gate is used for carrying out logic operation on the output signals of the first timing module, the second timing module and the second comparator and outputting a logic operation result through the first output end of the main control circuit.

5. The synchronous rectification control device of any one of claims 3-4, wherein the first timing module comprises:

the input end of the inverter is connected with the output end of the first comparator;

the control end of the switch circuit is connected with the output end of the phase inverter, the input end of the switch circuit is used for being connected with a power supply, and the output end of the switch circuit is grounded through the capacitor;

a third comparator, a first input terminal of the third comparator is connected with the output terminal of the switch circuit, a second input terminal of the third comparator is used for receiving a reference signal, and the reference signal is used for adjusting the time of the high level of the level signal representing the time;

and a first input end of the NOR gate is connected with the output end of the third comparator, a second input end of the NOR gate is connected with the output end of the phase inverter, and an output end of the NOR gate is connected with the logic gate.

6. The synchronous rectification control device of any one of claims 2 to 5, wherein the synchronous rectification control circuit further comprises:

and the logic circuit is respectively connected with the first output end and the second output end of the main control circuit and is used for generating a control signal for controlling the on/off of the secondary rectifier tube according to the output signal of the first output end and the output signal of the second output end of the main control circuit.

7. The synchronous rectification control device of claim 6, wherein the logic circuit comprises:

a first input end of the first latch is connected with a first output end of the main control circuit;

a first input end of the second latch is connected with an output end of the first latch, an output end of the second latch is connected with a second input end of the first latch, and an output end of the second latch is also connected with the secondary rectifier tube;

and the input end of the phase inverter is connected with the second output end of the main control circuit, and the output end of the phase inverter is connected with the second input end of the second latch.

8. The synchronous rectification control device of any one of claims 2 to 7, wherein the synchronous rectification control circuit further comprises:

and the output end of the selector is connected with the third input end of the main control circuit, and the selector is used for selectively outputting the second preset threshold value or the third preset threshold value.

9. The synchronous rectification control device of claim 8, further comprising:

and the sampling circuit is used for sampling the switching voltage at two ends of the secondary rectifier tube and transmitting the switching voltage to the synchronous rectification control circuit.

10. A switching power supply, comprising: a secondary rectifier and a synchronous rectification control apparatus as claimed in any one of claims 1 to 9.

11. A chip incorporating a synchronous rectification control device as claimed in any one of claims 1 to 9.