Control system and method of isolated switching converter

Abstract

The invention belongs to the technical field of integrated circuit driving, and particularly relates to a control system and method of an isolated switching converter. The isolated switching converter is composed of a primary circuit and a secondary circuit which are coupled by a transformer. The primary side circuit comprises a first power tube and a second power tube which are connected in series, and a capacitor connected with the input end of the transformer; and the secondary circuit comprises a synchronous rectifier tube connected with the output end of the transformer. The control system comprises a secondary side control module which controls the on or off of a synchronous rectifier tube according to the voltage of a secondary side winding, and correspondingly outputs a first trigger signal; the isolation module is used for receiving and transmitting the first trigger signal; the primary side control module is used for controlling the first power tube and the second power tube to be switched on or switched off according to the voltage of the primary side circuit and the first trigger signal; and in a working period of the isolated switching converter, the turn-on time of the first power tube is later than the turn-off time of the synchronous rectifier tube, and the turn-off time of the second power tube is later than the turn-off time of the synchronous rectifier tube.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated circuit driving, and in particular relates to a control system and method for an isolated switching converter. Background Art

[0002] As a type of switching power supply, asymmetrical half-bridge (AHB) flyback circuit is usually used in the field of isolated DC-DC conversion. In practical applications, by adjusting the conduction time of the high-voltage side switch tube and the conduction time of the low-voltage side switch tube in the half-bridge structure of the AHB flyback converter, not only can the output voltage be adjusted, but also the low-voltage side switch tube and the high-voltage side switch tube can achieve soft switching function, that is, zero voltage and zero current switching, thereby improving the power conversion efficiency of the AHB flyback circuit. For switching power supplies, using synchronous rectification switch tubes to replace traditional freewheeling diodes is an effective way to improve efficiency.

[0003] At present, the control system of the AHB flyback circuit adopts an optocoupler isolator. Although the structure is simple, due to the high delay of the optocoupler isolator and the fixed circuit structure, it can only control the working state of the primary switch tube according to the secondary voltage signal of the AHB flyback circuit, which can easily cause the primary switch tube to be mis-conducted. Although the probability of this risk can be reduced by optimizing the secondary synchronous rectifier controller, the risk still exists, causing the primary switch tube and the secondary synchronous rectifier tube to be turned on at the same time, causing the system to crash. Summary of the invention

[0004] In view of the shortcomings of the prior art mentioned above, the object of the present invention is to provide a control system and method for an isolated switching converter, which sorts out the conduction sequence of the primary side switch tube and the secondary side switch tube, and only turns on or off after receiving the corresponding trigger signal, thereby effectively preventing the primary side switch tube from being accidentally turned on.

[0005] To achieve the above-mentioned purpose and other related purposes, the present invention provides a control system for an isolated switching converter, wherein the isolated switching converter comprises a primary circuit and a secondary circuit coupled by a transformer; the primary circuit comprises a first power tube and a second power tube connected in series, and a capacitor connected to the input end of the transformer; the secondary circuit comprises a synchronous rectifier connected to the output end of the transformer; the control system comprises: a secondary control module, which controls the switching of the working state of the synchronous rectifier according to the secondary winding voltage of the transformer, and outputs a first trigger signal according to the working state; an isolation module, one end of which is connected to the secondary winding voltage of the transformer; The primary side control module is connected to the isolation module, and is used to receive and transmit the first trigger signal, and isolate the first trigger signal from the primary side circuit; the primary side control module is connected to the other end of the isolation module, and is used to receive the first trigger signal, and control the switching of the working states of the first power tube and the second power tube according to the voltage of the primary side circuit and the first trigger signal; and in several working cycles of the isolated switching converter, within the same working cycle, the turn-on time of the first power tube is later than the turn-off time of the synchronous rectifier tube, and the turn-off time of the second power tube is later than the turn-off time of the synchronous rectifier tube.

[0006] According to a specific embodiment of the present invention, a first control unit controls the first power tube to be turned off according to the voltage of the primary circuit or the conduction time of the first power tube; a second control unit controls the second power tube to be turned off according to the voltage of the primary circuit and the first trigger signal received.

[0007] According to a specific embodiment of the present invention, after controlling the first power tube to shut down, the first control unit also sends the shutdown state of the first power tube to the second control unit through an electrical signal; the second control unit controls the second power tube to turn on according to the received electrical signal of the shutdown state of the first power tube.

[0008] According to a specific embodiment of the present invention, when the voltage of the primary circuit reaches a first primary voltage threshold, the first control unit controls the first power tube to be turned off; or, when the conduction time of the first power tube reaches a preset conduction time, the first control unit controls the first power tube to be turned off.

[0009] According to a specific embodiment of the present invention, after the second control unit receives the first trigger signal and when the voltage of the primary circuit reaches a second primary voltage threshold, the second control unit controls the second power tube to turn off.

[0010] According to a specific embodiment of the present invention, when the secondary control module detects that the secondary winding voltage of the transformer reaches a first secondary voltage threshold, the synchronous rectifier is controlled to be turned off and the first trigger signal is output.

[0011] According to a specific embodiment of the present invention, in a working cycle, when the secondary control module has output a first trigger signal and the output voltage of the isolated switching converter is less than a preset second secondary voltage threshold, the secondary control module outputs a second trigger signal to the isolation module; the isolation module receives and transmits the second trigger signal to the primary control module; and the primary control module controls the conduction of the first power tube according to the received second trigger signal.

[0012] According to a specific embodiment of the present invention, the isolation unit adopts a magnetic coupling isolator, a capacitive isolator or a digital isolator.

[0013] A control method for an isolated switching converter, the isolated switching converter comprising a primary circuit and a secondary circuit coupled by a transformer; the primary circuit comprising a first power tube and a second power tube connected in series, and a capacitor connected to the input end of the transformer; the secondary circuit comprising a synchronous rectifier connected to the output end of the transformer; the control method comprising: a secondary control module controlling the switching of the working state of the synchronous rectifier according to the secondary winding voltage of the transformer, and sending a first trigger signal to the primary control module during switching; the primary control module controlling the switching of the working states of the first power tube and the second power tube according to the first trigger signal and the voltage of the primary circuit; wherein, in several working cycles of the isolated switching converter, the turn-on time of the first power tube is later than the turn-off time of the synchronous rectifier, and the turn-off time of the second power tube is later than the turn-off time of the synchronous rectifier.

[0014] According to a specific embodiment of the present invention, the secondary control module controls the switching of the working state of the synchronous rectifier according to the secondary winding voltage of the transformer, and sends the first trigger signal to the primary control module during switching, the step comprising: when the secondary winding voltage of the transformer reaches the first secondary voltage threshold, the secondary control module controls the synchronous rectifier to turn off, and outputs the first trigger signal.

[0015] According to a specific embodiment of the present invention, the control method also includes: after the first trigger signal is sent, the secondary side control module sends a second trigger signal according to the output voltage of the isolated switching converter; the first control unit receives the second trigger signal and controls the first power tube to be turned on according to the second trigger signal.

[0016] According to a specific embodiment of the present invention, the steps of the primary control module controlling the switching of the working states of the first power tube and the second power tube according to the first trigger signal and the voltage of the primary circuit include: the first control unit of the primary control module controls the first power tube to shut down according to the voltage of the primary circuit, and outputs the shutdown state of the first power tube through an electrical signal; the second control unit of the primary control module receives the electrical signal of the shutdown state of the first power tube, and controls the conduction of the second power tube according to the electrical signal of the shutdown state of the first power tube; the second control unit receives the first trigger signal, and controls the shutdown of the second power tube according to the voltage of the primary circuit and the first trigger signal.

[0017] According to a specific embodiment of the present invention, the primary control module receives the first trigger signal and the second trigger signal, and controls the switching of the working states of the first power tube and the second power tube according to the voltage of the primary circuit, the first trigger signal and the second trigger signal, so that the second power tube is turned off after receiving the first trigger signal, and the step of turning on the first power tube after receiving the second trigger signal includes: when the voltage of the primary circuit reaches the first primary voltage threshold, the first control unit controls the first power tube to turn off; or, when the conduction time of the first power tube reaches a preset conduction time, the first control unit controls the first power tube to turn off.

[0018] According to a specific embodiment of the present invention, the second control unit receives the first trigger signal, and according to the voltage of the primary circuit and the first trigger signal, the step of controlling the second power tube to shut down includes: after the second control unit receives the first trigger signal, and when the voltage of the primary circuit reaches a second primary voltage threshold, the second control unit controls the second power tube to shut down.

[0019] The present invention is to avoid the problem that the primary power tube and the secondary synchronous rectifier tube may be common due to the high delay and inflexible circuit structure of the traditional isolated switch converter control system using optical coupling. Based on a high-speed, flexibly configurable isolation device, such as a magnetic coupling isolator or a digital isolator or a capacitor isolator, a new control system and a corresponding control method are provided. The on or off of the primary power tube is controlled by the working state of the secondary synchronous rectifier tube and the output voltage of the isolated switch converter, so that the first power tube is turned on after the synchronous rectifier tube is turned off, and the second power tube is turned off after the synchronous rectifier tube is turned off. The on and off sequence of the primary power tube and the secondary synchronous rectifier tube is sorted out, effectively preventing the occurrence of false on phenomenon, greatly improving the reliability of the isolated switch converter, and correspondingly extending its service life. At the same time, based on the delay setting between each power tube, the zero voltage conduction of the power tube is achieved, and the working efficiency of the isolated switch converter is correspondingly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A circuit topology diagram of a specific embodiment of a control system of an isolated switching converter provided by the present invention;

[0021] Figure 2 A circuit topology diagram of another specific embodiment of a control system of an isolated switching converter provided by the present invention;

[0022] Figure 3 A timing diagram of multiple parameters of a control system of an isolated switching converter provided by the present invention within a working cycle;

[0023] Figure 4 A schematic flow chart of a control method for an isolated switching converter provided by the present invention. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0025] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present invention in a schematic manner, and thus the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0026] Example 1

[0027] See also Figure 1-2 As shown, a control system of an isolated switching converter includes: an isolated switching converter 100 and a control system 200 thereof. The isolated switching converter 100 may adopt an AHB flyback circuit, specifically including a primary circuit 110 and a secondary circuit 130 coupled by a transformer 120, and the primary circuit 110 includes a first power tube Q1 and a second power tube Q2 connected in series, which are used to adjust the working mode of the primary circuit 110 to achieve conversion and regulation of the input voltage; and a capacitor C1 connected to the primary winding of the transformer 120, which is used as a storage capacitor; the secondary circuit 130 includes a synchronous rectifier tube SR connected to the secondary winding of the transformer 120 to achieve a high-efficiency rectification function.

[0028] Therefore, this also poses a challenge to the turn-on and turn-off time of the synchronous rectifier SR. If the turn-off is delayed, it may cause the synchronous rectifier SR of the secondary circuit 130 and the power tube of the primary circuit 110 to be common, that is, the primary power tube and the synchronous rectifier are turned on at the same time, which will cause reliability and stability problems of the isolated switching converter 100; if the turn-off is premature, the synchronous rectification function is turned off when the freewheeling current is large, which reduces the working efficiency of the isolated switching converter 100.

[0029] To avoid this situation, the control system 200 in this embodiment strictly controls the on-off sequence of the first power tube Q1, the second power tube Q2 and the synchronous rectifier tube SR, which greatly reduces the possibility of the power tube being mistakenly turned on, and effectively improves the reliability and working efficiency of the isolated switching converter 100.

[0030] In this embodiment, the control system 200 includes: a secondary side control module 210, which is used to control the switching of the working state of the synchronous rectifier SR according to the secondary winding voltage of the transformer 120, that is, the conduction and shutdown of the synchronous rectifier SR, and output a corresponding first trigger signal according to the conduction or shutdown of the synchronous rectifier SR.

[0031] Specifically, for example, when the synchronous rectifier SR is turned off, the secondary control module 210 outputs the first trigger signal, and when the synchronous rectifier SR is turned on, the secondary control module 210 does not output the first trigger signal. Through the transmission of electrical signals, the on-off state of the synchronous rectifier SR is fed back to the primary control module 230, so as to prompt the primary control module 230 to control the first power tube Q1 and the second power tube Q2 to turn on or off accordingly.

[0032] It should be noted that the implementation method of the above-mentioned first trigger signal is only a preferred embodiment to make the technology of the present invention easy to understand. Without departing from the spirit of the present invention, the modifications and embellishments made to the embodiments of the present invention by those skilled in the art still fall within the scope of the invention application patent of the present invention.

[0033] The isolation module 220 is connected to the secondary control module 210 at one end and to the primary control module 230 at the other end, and is used to receive and transmit the first trigger signal and isolate the first trigger signal from the primary circuit 110 .

[0034] In this embodiment, in order to avoid the phenomenon that the power tube of the primary circuit 110 and the synchronous rectifier tube SR of the secondary circuit 130 are common, an isolation device with a faster transmission rate is selected to improve the real-time performance of the first trigger signal. Optionally, a magnetic coupling isolator, a capacitive isolator or a digital isolator is selected to speed up the transmission of the electrical signal.

[0035] The primary control module 230 is used to receive the first trigger signal transmitted by the isolation module 220, and control the working states of the first power tube Q1 and the second power tube Q2 to switch according to the first trigger signal and the voltage of the primary circuit 110, that is, the turn-on time and turn-off time of the first power tube Q1 and the second power tube Q2.

[0036] In order to ensure the on-off sequence of the first power tube Q1, the second power tube Q2 and the synchronous rectifier tube SR and avoid the power tubes from being turned on by mistake, in any one of the several working cycles of the isolation converter 100, the turn-on time of the first power tube Q1 is later than the turn-off time of the synchronous rectifier tube SR, and the turn-off time of the second power tube Q2 is later than the turn-off time of the synchronous rectifier tube SR.

[0037] It should be noted that the working cycle of the above-mentioned isolated switching converter 100, that is, the cycle period when the isolated switching converter 100 tends to a steady state, and the conduction and shutdown of the first power tube Q1, the second power tube Q2 and the synchronous rectifier tube SR are performed according to the above-mentioned settings to avoid the first power tube Q1 and / or the second power tube Q2 from being mistakenly turned on.

[0038] In a specific embodiment, if Figure 1 As shown, the primary control module 230 includes: a first control unit 231, which controls the first power tube Q1 to turn off according to the voltage of the primary circuit 110, and outputs the off state of the first power tube Q1 through an electrical signal. A second control unit 232, which controls the second power tube Q2 to turn on according to the off state of the first power tube Q1.

[0039] Specifically, in application, the output end of the first control unit 231 is connected to the control end of the first power tube Q1, and the duty cycle of the first power tube Q1 is adjusted through the PWM signal, that is, the first power tube Q1 is controlled to be turned on and off. One input end of the first control unit 231 is also connected to one end of the isolation module 220, and the other input end of the first control unit 231 is used to obtain the voltage of the primary circuit of the isolated switching converter 100. In a preferred embodiment of the present invention, the other input end of the first control unit 231 can be directly connected to the primary circuit 110 of the isolated switching converter 100 to collect the voltage of the primary circuit 110. It should be noted that the present invention does not limit the method for obtaining the voltage of the primary circuit 110, as long as the obtained voltage of the primary circuit 110 is connected to the other input end of the first control unit 231, it is within the protection scope of the present invention.

[0040] When the voltage on the primary circuit 110 reaches the first primary voltage threshold, the first control unit 231 controls the first power tube Q1 to be turned off.

[0041] Similarly, the output end of the second control unit 232 is connected to the control end of the second power tube Q2, and the input end is connected to one end of the isolation module 220 to receive the first trigger signal; the other input end is used to obtain the voltage of the primary circuit of the isolated switching converter 100. In addition, another input end of the second control unit 232 is connected to the output port of the first control unit 231 for outputting the electrical signal of the off state of the first power tube Q1.

[0042] Furthermore, the first control unit 231 and the second control unit 232 can be connected to each other for communication, and transmit the on / off status of the power tubes to each other, so as to better stagger the on-time of the first power tube Q1 and the second power tube Q2.

[0043] When the second control unit 232 receives the electrical signal indicating the first power tube Q1 is in the off state, the second power tube Q2 is controlled to be turned on after the dead time is delayed. In addition, the second control unit 232 controls the second power tube Q2 to be turned off only after receiving the first trigger signal and when the voltage collected on the primary circuit 110 reaches the second primary voltage threshold.

[0044] It should be noted that the power tube of the primary circuit 110 is turned on and off not limited to switching according to the voltage of the primary circuit 110, for example, it can also be based on the on-time of the power tube, including when the on-time of the first power tube Q1 reaches a preset value, the first control unit 231 controls the first power tube to turn off Q1. Those skilled in the art, without departing from the spirit of the present invention, still fall within the scope of the invention application of the present invention. It should also be added that the second power tube Q2 is turned off only after receiving the first trigger signal.

[0045] In a specific embodiment, when the secondary winding voltage reaches the first secondary voltage threshold, the secondary control module 210 controls the synchronous rectifier SR to turn off and sends a first trigger signal to the isolation module 220. In addition, the secondary control module 210 is also used to send a second trigger signal according to the output voltage of the isolated switching converter 100. In one working cycle, the second trigger signal is only allowed to be sent after the first trigger signal is sent.

[0046] Specifically, in application, when the output voltage of the isolated switching converter 100 is less than the second secondary voltage threshold, in order to continue to maintain the normal working voltage output by the isolated switching converter 100, the first power tube Q1 needs to be turned on again to enter the next working cycle. Therefore, the secondary control module 210 sends a second trigger signal, and transmits it to the first control unit 231 through the isolation module 220, and the first control unit 231 controls the first power tube Q1 to be turned on only after receiving the second trigger signal, and enters the next working cycle, forming a cycle, and maintaining the stability of the output voltage of the isolated switching converter 100.

[0047] Therefore, in this embodiment, the isolation module 220 can be connected in parallel with two magnetic coupling isolators, capacitive isolators or digital isolators, and corresponding to the first trigger signal and the second trigger signal, respectively connected to the first control unit 231 and the second control unit 232, so that the first trigger signal is only transmitted to the second control unit 232, and the second trigger signal is only transmitted to the first control unit 231, thereby avoiding mutual interference between the two signals, and the primary control module 230 misidentifying the signal, resulting in the wrong opening of the power tube. Setting different transmission lines for the first trigger signal and the second trigger signal effectively improves the reliability of the control system.

[0048] In addition, the control system 200 may include one or more detection units, which are respectively used to detect the voltage on the primary circuit 110 and transmit it to the primary control module 230, and to detect the secondary winding voltage on the secondary circuit 130 and the output voltage of the isolated switching converter 100 and transmit them to the secondary control module 210. Correspondingly, the detection unit can also be set in the circuit of the isolated switching converter 100, and connected to the primary control module 230 and the secondary control module 210 in the control system 200. There are no specific restrictions and it can be flexibly set according to needs.

[0049] In a specific embodiment, if Figure 1As shown, the isolated switching converter 100 adopts an AHB flyback circuit, specifically including: a first power tube Q1, a second power tube Q2, a capacitor C1, a first inductor L1, a second inductor L2, a detection resistor Rcs, an ideal transformer N:1, a synchronous rectifier SR and a capacitor C2. Among them, the first power tube Q1, the second power tube Q2, the capacitor C1, and the detection resistor Rcs constitute a primary circuit 110, the first inductor L1, the second inductor L2, and the ideal transformer N:1 constitute a transformer 120, and the synchronous rectifier SR and the capacitor C2 constitute a secondary circuit 130.

[0050] In the primary circuit 110: the source of the first power tube Q1 is connected to the drain of the second power tube Q2, the drain of the first power tube Q1 can be used to access the input voltage, or connected to the positive electrode of the power supply, and the source of the second power tube Q2 is grounded. The gate of the first power tube Q1 and the gate of the second power tube Q2 are respectively used to connect to the output ends of the first control unit 231 and the second control unit 232. One end of the capacitor C1 is connected to the series connection point SW of the first power tube Q1 and the second power tube Q2, and one end of the detection resistor Rcs is connected to the source of the second power tube Q2.

[0051] In the transformer 120: one end of the first inductor L1 is connected to the other end of the capacitor C1, and the other end is respectively connected to one end of the second inductor L2 and one end of the primary winding of the ideal transformer N:1. The other end of the second inductor L2 is respectively connected to the other end of the primary winding of the ideal transformer N:1 and the other end of the detection resistor Rcs.

[0052] In the secondary circuit 130 , the capacitor C2 is connected in parallel to the secondary winding of the ideal transformer N:1, and the drain of the synchronous rectifier SR is connected to one end of the secondary winding of the ideal transformer N:1, and the other end is connected to one end of the capacitor C2 .

[0053] Among them, the inductance L1 and the inductance L2 in the transformer 120 can be separately set elements or parasitic elements of the transformer in actual applications. Using the inductance L1, the inductance L2 and the ideal transformer N:1 to represent a non-ideal real transformer in the circuit is a conventional method that can be understood by technical personnel in this field.

[0054] It should be noted that the above Figure 1 The AHB flyback circuit shown is only a specific embodiment of the present invention, and its circuit variations also fall within the protection scope of the present application. Figure 4The isolated switching converter shown also includes: a first power tube Q1, a second power tube Q2, a capacitor C1, a first inductor L1, a second inductor L2, a detection resistor Rcs, an ideal transformer N:1, a synchronous rectifier SR and a capacitor C2. The first power tube Q1, the second power tube Q2, the capacitor C1 and the detection resistor Rcs form a primary circuit 110, the first inductor L1, the second inductor L2 and the ideal transformer N:1 form a transformer 120, and the synchronous rectifier SR and the capacitor C2 form a secondary circuit 130.

[0055] In the primary circuit 110: the source of the first power tube Q1 is connected to the drain of the second power tube Q2, the drain of the first power tube Q1 can be used to access the input voltage, or connected to the positive electrode of the power supply, and the source of the second power tube Q2 is grounded. The gate of the first power tube Q1 and the gate of the second power tube Q2 are respectively used to connect to the output ends of the first control unit 231 and the second control unit 232. One end of the capacitor C1 is connected to the drain of the first power tube Q1.

[0056] In the transformer 120: one end of the first inductor L1 is connected to the other end of the capacitor C1, and the other end is respectively connected to one end of the second inductor L2 and one end of the primary winding of the ideal transformer N:1. The other end of the second inductor L2 and the other end of the primary winding of the ideal transformer N:1 are connected to the series connection point SW of the first power tube Q1 and the second power tube Q2.

[0057] The secondary circuit 130 is consistent with the above, that is, the capacitor C2 is connected in parallel to the secondary winding of the ideal transformer N:1, and the drain of the synchronous rectifier SR is connected to one end of the secondary winding of the ideal transformer N:1, and the other end is connected to one end of the capacitor C2.

[0058] Therefore, circuits with the same or similar working principles as the isolated switching converter in this embodiment are applicable to the control system 200 and fall within the protection scope of this application.

[0059] It should be noted that the detection unit can be connected in parallel to the detection voltage Rcs in the primary circuit 110, for example, to collect the voltage of the primary circuit 110, which reflects the current of the primary circuit 110, and is respectively connected to an input end of the first control unit 231 and the second control unit 232. The detection unit can also be connected in parallel to the two ends of the secondary winding of the ideal transformer N:1 and the two ends of the capacitor C2, for collecting the secondary winding voltage and the output voltage of the isolated switching converter 100, and connected to the input end of the secondary control module. The above detection unit is only a preferred embodiment in this implementation, which can be adjusted according to the actual application scenario without too much restriction.

[0060] Specifically, in order to strictly manage the on-off sequence between the first power tube Q1, the second power tube Q2 and the synchronous rectifier tube SR to avoid common failures that may cause the system to crash, the control system 200 in this embodiment uses a magnetic coupling isolator / capacitor isolator / digital isolator to timely feed back the on-off state of the synchronous rectifier tube SR to the primary control module 230, and adjusts the duty cycle of the first power tube Q1 and the second power tube Q2 through a PWM signal to maintain the normal operation of the isolated switching converter 100.

[0061] In addition, the isolated switching converter 100 operates at a fixed operating frequency to repeat the process of excitation and demagnetization in each working cycle, and the output end of the isolated switching converter 100 provides a stable output voltage Vout to the connected load, and the output voltage Vout corresponds to the operating voltage of the connected load, and the capacitor C2 is used to stabilize the output voltage Vout of the isolated switching converter 100.

[0062] Specifically, Figure 3 2 is a timing diagram of the working cycle of the isolated switching converter 100 under the control of the control system 200. In the figure, PWMH is the control signal of the first power tube Q1, PWML is the control signal of the second power tube Q2, SW represents the voltage at the serial connection point of the first power tube Q1 and the second power tube Q2, and the black line segment IL1 and the gray line segment IL2 represent the current changes on the first inductor L1 and the second inductor L2 respectively.

[0063] At time t0, the first power tube Q1 is controlled to be turned on, and the second power tube Q2 is turned off, so that the isolated switching converter 100 starts to work. During the period from time t0 to time t1, the first power tube Q1 is kept in the turned-on state, and the second power tube Q2 is kept in the turned-off state. During this period, the input voltage Vbus charges the primary winding of the ideal transformer N:1 through the capacitor C1, and begins to excite. The current IL1 of the first inductor L1 continues to increase, indicating that the current of the primary winding of the ideal transformer N:1 continues to increase. During this period, the voltage across the parasitic capacitor between the drain and source of the first power tube Q1 is close to 0V.

[0064] At time t1, when the voltage of the primary circuit 110, i.e., the voltage across the detection resistor Rcs, reaches the first primary voltage threshold, i.e., the maximum voltage, it indicates that the current of the primary winding of the ideal transformer N:1 also reaches the maximum value. At this time, the first control unit 231 controls the first power tube Q1 to turn off, and sends the off state of the first power tube Q1 to the second control unit 232 through an electrical signal.

[0065] Among them, when the first power tube Q1 is turned off and before the second power tube Q2 is turned on, it will enter the freewheeling mode, that is, the body diode of the second power tube Q2 and the body diode of the synchronous rectifier tube SR start to freewheel, and a sudden drop in the secondary winding voltage is detected, and then the secondary control module 210 controls the synchronous rectifier tube SR to switch to the on state.

[0066] In other embodiments, the first power tube Q1 can also be turned off by a time control unit in the first control unit 231 (not shown). For example, a preset on-time of the first power tube Q1 is set, and the time control unit starts timing after the first power tube Q1 is turned on, and controls the first power tube Q1 to be turned off after the on-time has passed. Alternatively, the on-time of the first power tube Q1 can be an adaptively changing value, and the time control unit starts timing after the first power tube Q1 is turned on, and controls the first power tube Q1 to be turned off after the on-time has passed.

[0067] Furthermore, the time control unit can also adjust the conduction time of the first power tube Q1 according to the switching frequency of the first power tube Q1. For example, when the switching frequency is high, the conduction time is adjusted to be longer, and when the switching frequency is low, the conduction time is adjusted to be shorter, thereby limiting the overall switching frequency change to a smaller range and reducing ripple.

[0068] It should be supplemented that when the preset time length is used to control the first power tube Q1 to be turned off, an overcurrent protection unit needs to be used in conjunction with the isolated switching converter 100 to achieve reliable control of the switching converter.

[0069] During the period from time t1 to time t2, the first power tube Q1 and the second power tube Q2 are both kept in the disconnected state, and the charging loop of the input voltage Vbus to the primary circuit 110 is disconnected. Since the current in the inductor cannot change suddenly, the current of the first inductor L1 and the second inductor L2, and the parasitic capacitance of the second power tube Q2 charge the parasitic capacitance of the first power tube Q1, so that the voltage at the node SW gradually decreases until the body diode of the second power tube Q2 is turned on. Therefore, at time t2, the voltage of the node SW drops to near 0V. That is, after the second control unit 232 delays the dead time, at time t2, it controls the second power tube Q2 to turn on with zero voltage.

[0070] During the period from time t2 to time t3, the capacitor C1 resonates with the first inductor L1, and the current IL1 of the first inductor L1 decreases to 0 A and then increases negatively. At the same time, the ideal transformer N:1 begins to demagnetize through the secondary winding, and the excitation current IL2 of the primary winding decreases linearly.

[0071] At time t3, the current IL1 of the first inductor L1 resonates to be the same as the current IL2 of the second inductor L2, that is, the current of the primary winding of the ideal transformer N:1 drops to 0. At this time, the demagnetization of the ideal transformer N:1 is completed, and the voltage of the secondary winding drops to 0, that is, the secondary winding voltage reaches the first secondary voltage threshold, and the first secondary voltage threshold can be set to a low value close to 0. At this time, the secondary control module 210 controls the synchronous rectifier SR to switch to the off state and outputs the first trigger signal.

[0072] During the period from time t3 to time t4 , the capacitor C1 is discharged, and the current IL1 of the first inductor L1 continues to decrease.

[0073] At time t4, since the second control unit 232 has received the first trigger signal, and the voltage of the primary circuit 110, i.e., the voltage across the detection resistor Rcs, reaches the second primary voltage threshold, the second control unit 232 controls the second power tube Q2 to disconnect, and the discharge loop of the capacitor C1 to the primary winding of the ideal transformer N:1 is disconnected.

[0074] When the output voltage Vout of the isolated switching converter 100 is less than the second secondary voltage threshold, i.e., at time t5, and the first trigger signal has been output at time t3, the secondary control module outputs the second trigger signal to the primary control module. When the first control unit 231 receives the second trigger signal, after a delay of a period of time, i.e., at time t6, the first power tube Q1 is controlled to be turned on and enter the next working cycle to continue to transfer energy from the primary side of the isolated switching converter 100 to the secondary side, so as to keep the isolated switching converter 100 continuously outputting the voltage Vout to the load.

[0075] Among them, in this embodiment, request1 in the figure represents the second trigger signal, which represents a signal prompting the first power tube Q1 to turn on, for example, it can be triggered when the output voltage Vout of the isolated switching converter 100 is less than a preset value. The second trigger signal can also be derived from other electrical signals in the control loop, which can be adjusted according to the actual application. Request2 in the figure is the first trigger signal, which represents a signal prompting the second power tube Q2 to turn off, for example, it can be based on the control signal or drive signal of the synchronous rectifier SR, or other signals related thereto. Without departing from the spirit of the present invention, modifications and embellishments made to the embodiments of the present invention by those skilled in the art still fall within the scope of the invention application of the present invention.

[0076] In this embodiment, the first power tube Q1 is turned on only after receiving the second trigger signal, and the second power tube Q2 is turned off only after receiving the first trigger signal, thereby effectively avoiding the phenomenon of the primary circuit power tube being mistakenly turned on, and greatly improving the reliability and working efficiency of the isolated switching converter 100.

[0077] Example 2

[0078] See also Figure 4 As shown, this embodiment also provides a control method for an isolated switching converter, wherein the isolated switching converter includes a primary circuit and a secondary circuit coupled by a transformer; the primary circuit includes a first power tube and a second power tube connected in series, and a capacitor connected to the input end of the transformer; the secondary circuit includes a synchronous rectifier connected to the output end of the transformer; the control method includes:

[0079] In step S10, the secondary control module controls the switching of the working state of the synchronous rectifier according to the secondary winding voltage of the transformer, and sends a first trigger signal to the primary control module during the switching.

[0080] Step S20: The primary control module controls the switching of the working states of the first power tube and the second power tube according to the first trigger signal and the voltage of the primary circuit.

[0081] Among them, in several working cycles of the isolated switching converter, the turn-on time of the first power tube is later than the turn-off time of the synchronous rectifier tube, and the turn-off time of the second power tube is later than the turn-off time of the synchronous rectifier tube.

[0082] In a specific embodiment, the method further comprises:

[0083] Step S30: After the first trigger signal is sent, the secondary-side control module sends a second trigger signal according to the output voltage of the isolated switching converter.

[0084] In step S31, the first control unit receives the second trigger signal and controls the first power tube to be turned on according to the second trigger signal.

[0085] Specifically, the specific process of step S10 is as follows:

[0086] Step S11, when the secondary winding voltage of the transformer reaches a first secondary voltage threshold, the secondary control module controls the synchronous rectifier to turn off and outputs the first trigger signal.

[0087] The specific process of step S20 is as follows:

[0088] Step S21: The first control unit of the primary control module controls the first power tube to be turned off according to the voltage of the primary circuit, and outputs the turn-off state of the first power tube through an electrical signal.

[0089] Among them, in step S211, when the voltage of the primary circuit reaches the first primary voltage threshold, the first control unit controls the first power tube to be turned off; or, when the conduction time of the first power tube reaches a preset conduction time, the first control unit controls the first power tube to be turned off.

[0090] Step S22: The second control unit of the primary-side control module receives the electrical signal indicating that the first power tube is in an off state, and controls the second power tube to be turned on according to the electrical signal indicating that the first power tube is in an off state.

[0091] Step S23, the second control unit receives the first trigger signal, and controls the second power tube to be turned off according to the voltage of the primary circuit and the first trigger signal;

[0092] In step S231, after the second control unit receives the first trigger signal and when the voltage of the primary circuit reaches a second primary voltage threshold, the second control unit controls the second power tube to turn off.

[0093] In summary, the present invention is to avoid the problem that the primary power tube and the secondary synchronous rectifier tube may be common due to the high delay and inflexible circuit structure of the traditional isolated switch converter control system using optocouplers. Based on a high-speed, flexibly configurable isolation device, such as a magnetic coupling isolator or a digital isolator or a capacitor isolator, a new control system and a corresponding control method are provided. The on or off of the primary power tube is controlled by the working state of the secondary synchronous rectifier tube and the output voltage of the isolated switch converter, so that the first power tube is turned on after the synchronous rectifier tube is turned off, and the second power tube is turned off after the synchronous rectifier tube is turned off. The on and off sequence of the primary power tube and the secondary synchronous rectifier tube is sorted out, effectively preventing the occurrence of false on phenomenon, greatly improving the reliability of the isolated switch converter, and correspondingly extending its service life. At the same time, based on the delay setting between each power tube, the zero voltage conduction of the power tube is achieved, and the working efficiency of the isolated switch converter is correspondingly improved.

[0094] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

[0095] References throughout this specification to "one embodiment," "an embodiment," or "a specific embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, and not necessarily in all embodiments. Thus, various appearances of the phrases "in one embodiment," "in an embodiment," or "in a specific embodiment" in different places throughout this specification do not necessarily refer to the same embodiment. In addition, the particular features, structures, or characteristics of any specific embodiment of the invention may be combined with one or more other embodiments in any suitable manner. It should be understood that other variations and modifications of the embodiments of the invention described and illustrated herein may be possible in light of the teachings herein and are to be considered part of the spirit and scope of the invention.

[0096] In addition, unless otherwise explicitly indicated, any marking arrows in the drawings should be regarded as exemplary only and not limiting. In addition, unless otherwise indicated, the term "or" used herein is generally intended to mean "and / or". In the case where the term is not clear because it is anticipated that the ability to separate or combine is provided, the combination of components or steps will also be regarded as indicated.

[0097] As used in the description herein and throughout the claims that follow, "a", "an", and "the" include plural references unless otherwise indicated. Likewise, as used in the description herein and throughout the claims that follow, the meaning of "in" includes "in" and "on" unless otherwise indicated.

[0098] The above description of the illustrated embodiments of the present invention (including the contents described in the Abstract) is not intended to be an exhaustive list or to limit the present invention to the precise form disclosed herein. Although specific embodiments of the present invention and examples of the present invention are described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the present invention as will be recognized and appreciated by those skilled in the art. As noted, these modifications may be made to the present invention in accordance with the above description of the embodiments described in the present invention, and these modifications will be within the spirit and scope of the present invention.

[0099] Systems and methods have been generally described herein as details that aid in understanding the present invention. In addition, various specific details have been given to provide an overall understanding of embodiments of the present invention. However, those skilled in the relevant art will recognize that embodiments of the present invention may be practiced without one or more of the specific details, or may be practiced using other devices, systems, accessories, methods, components, materials, parts, etc. In other cases, well-known structures, materials, and / or operations are not specifically shown or described in detail to avoid confusion with various aspects of embodiments of the present invention.

[0100] Thus, although the invention has been described herein with reference to specific embodiments thereof, freedom of modification, various changes and substitutions are also within the foregoing disclosure, and it should be understood that in some cases, some features of the invention will be employed without the corresponding use of other features without departing from the scope and spirit of the proposed invention. Thus, many modifications may be made to adapt a particular environment or material to the essential scope and spirit of the invention. The invention is not intended to be limited to the specific terms used in the claims below and / or the specific embodiments disclosed as the best mode contemplated for carrying out the invention, but the invention will include any and all embodiments and equivalents falling within the scope of the appended claims. Thus, the scope of the invention will be determined solely by the appended claims.

Claims

1. A control system for an isolated switching converter, characterized in that: The isolated switching converter comprises a primary circuit and a secondary circuit coupled by a transformer; the primary circuit comprises a first power tube and a second power tube connected in series, and a capacitor connected to the input end of the transformer; the secondary circuit comprises a synchronous rectifier connected to the output end of the transformer; the control system comprises: A secondary control module controls the switching of the working state of the synchronous rectifier according to the secondary winding voltage of the transformer, and outputs a first trigger signal according to the working state; an isolation module, one end of which is connected to the secondary control module, and is used to receive and transmit the first trigger signal and isolate the first trigger signal from the primary circuit; A primary control module is connected to the other end of the isolation module, and is used to receive the first trigger signal, and control the switching of the working states of the first power tube and the second power tube according to the voltage of the primary circuit and the first trigger signal; and in several working cycles of the isolated switching converter, within the same working cycle, the turn-on time of the first power tube is later than the turn-off time of the synchronous rectifier tube, and the turn-off time of the second power tube is later than the turn-off time of the synchronous rectifier tube.

2. The control system of the isolated switching converter according to claim 1, characterized in that: The primary side control module comprises: A first control unit, controlling the first power tube to be turned off according to the voltage of the primary circuit or the conduction time of the first power tube; The second control unit controls the second power tube to be turned off according to the voltage of the primary circuit and the received first trigger signal.

3. The control system of the isolated switching converter according to claim 1, characterized in that: After controlling the first power tube to be turned off, the first control unit also sends the turn-off state of the first power tube to the second control unit through an electrical signal; The second control unit controls the second power tube to be turned on according to the received electrical signal indicating the off state of the first power tube.

4. The control system of the isolated switching converter according to claim 2, characterized in that: When the voltage of the primary circuit reaches a first primary voltage threshold, the first control unit controls the first power tube to be turned off; or, When the conduction time of the first power tube reaches a preset conduction time, the first control unit controls the first power tube to be turned off.

5. The control system of the isolated switching converter according to claim 2, characterized in that: After the second control unit receives the first trigger signal and when the voltage of the primary circuit reaches a second primary voltage threshold, the second control unit controls the second power tube to turn off.

6. The control system of the isolated switching converter according to claim 1, characterized in that: When the secondary control module detects that the secondary winding voltage of the transformer reaches a first secondary voltage threshold, it controls the synchronous rectifier to be turned off and outputs the first trigger signal.

7. The control system of the isolated switching converter according to claim 1, characterized in that: In one of the working cycles, When the secondary-side control module has output the first trigger signal and the output voltage of the isolated switching converter is less than a preset second secondary-side voltage threshold, the secondary-side control module outputs a second trigger signal to the isolation module; The isolation module receives and transmits the second trigger signal to the primary control module; The primary side control module controls the first power tube to be turned on according to the received second trigger signal.

8. The control system of the isolated switching converter according to claim 1, characterized in that: The isolation module adopts a magnetic coupling isolator, a capacitive isolator or a digital isolator.

9. A control method for an isolated switching converter, characterized in that: The isolated switching converter comprises a primary circuit and a secondary circuit coupled by a transformer; the primary circuit comprises a first power tube and a second power tube connected in series, and a capacitor connected to the input end of the transformer; the secondary circuit comprises a synchronous rectifier connected to the output end of the transformer; the control method comprises: The secondary side control module controls the switching of the working state of the synchronous rectifier according to the secondary side winding voltage of the transformer, and sends a first trigger signal to the primary side control module during the switching; The primary side control module controls the switching of the working states of the first power tube and the second power tube according to the first trigger signal and the voltage of the primary side circuit; Among them, in several working cycles of the isolated switching converter, the turn-on time of the first power tube is later than the turn-off time of the synchronous rectifier tube, and the turn-off time of the second power tube is later than the turn-off time of the synchronous rectifier tube.

10. The control method of the isolated switching converter according to claim 9, characterized in that: The steps of the secondary control module controlling the switching of the working state of the synchronous rectifier according to the secondary winding voltage of the transformer and sending the first trigger signal to the primary control module during the switching include: When the secondary winding voltage of the transformer reaches a first secondary voltage threshold, the secondary control module controls the synchronous rectifier to turn off and outputs the first trigger signal.

11. The control method of the isolated switching converter according to claim 9, characterized in that: The control method further comprises: After the first trigger signal is sent, the secondary side control module sends a second trigger signal according to the output voltage of the isolated switching converter; The first control unit receives the second trigger signal, and controls the first power tube to be turned on according to the second trigger signal.

12. The control method of the isolated switching converter according to claim 9, characterized in that: The step of the primary control module controlling the switching of the working states of the first power tube and the second power tube according to the first trigger signal and the voltage of the primary circuit comprises: The first control unit of the primary control module controls the first power tube to be turned off according to the voltage of the primary circuit, and outputs the turn-off state of the first power tube through an electrical signal; The second control unit of the primary side control module receives the electrical signal of the first power tube being in an off state, and controls the second power tube to be turned on according to the electrical signal of the first power tube being in an off state.

13. The control method of the isolated switching converter according to claim 12, characterized in that: The first control unit of the primary control module controls the first power tube to turn off according to the voltage of the primary circuit, and outputs the shutdown state of the first power tube through an electrical signal, including: When the voltage of the primary circuit reaches a first primary voltage threshold, the first control unit controls the first power tube to be turned off; or, When the conduction time of the first power tube reaches a preset conduction time, the first control unit controls the first power tube to be turned off.

14. The control method of the isolated switching converter according to claim 12, characterized in that: The second control unit receives the first trigger signal, and controls the second power tube to shut down according to the voltage of the primary circuit and the first trigger signal, comprising: After the second control unit receives the first trigger signal and when the voltage of the primary circuit reaches a second primary voltage threshold, the second control unit controls the second power tube to turn off.

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