Control circuit of isolated switching converter and control method thereof

Abstract

The invention provides a control circuit of an isolated switching converter and a control method thereof. In the control circuit, before a main switch tube in a primary side circuit is ready to be started, a secondary side controller is preferentially utilized to send an inquiry signal to a primary side controller after a synchronous rectifier tube is turned off, and a time feedback signal is sent to the secondary side controller when the primary side controller confirms that the primary side controller is in a ready state; the secondary side controller confirms that the primary side main switch tube is switched off, and then the primary side controller is used for controlling the main switch tube to be switched on. Namely, according to the control circuit and the control method thereof provided by the invention, when the main switch tube is prepared to be started, the main switch tube is ensured to be started in the turn-off state of the synchronous rectifier tube through information interaction of the primary side and the secondary side, and the risk that the primary side and the secondary side are connected together is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the field of electronic circuits, and particularly to a control circuit and a control method for an isolated switching converter. Background Art

[0002] With the rapid development of large-scale and ultra-large-scale integrated circuits, miniaturized and highly efficient isolated switching converters are widely used in various power supply systems. An isolated switching converter generally includes a primary circuit and a secondary circuit. By controlling the on / off of a power switch in the primary circuit, a constant output of the secondary circuit is achieved. Moreover, during the operation of the isolated switching converter, it is necessary to interlock the driving of the power switch tube in the primary circuit and the synchronous rectifier tube in the secondary circuit to prevent the driving of the primary circuit and the secondary circuit from being common. However, in practical applications, for example, there may be a possibility that the synchronous rectifier tube in the secondary circuit is mis-conducted, resulting in the problem that the primary circuit and the secondary circuit are common.

[0003] Therefore, it is necessary to provide a control circuit and a control method for preventing the primary circuit and the secondary circuit from penetrating through, so as to improve the safety performance and reliability of the isolated switching converter. Summary of the Invention

[0004] The purpose of the present invention is to provide a control circuit for an isolated switching converter to solve the problem that the existing isolated switching converter is prone to the penetration of the primary circuit and the secondary circuit.

[0005] To solve the above technical problems, the present invention provides a control circuit for controlling an isolated switching converter, where the isolated switching converter includes a primary circuit, a secondary circuit, and a transformer coupled between the primary circuit and the secondary circuit; wherein, the control circuit includes: a primary controller having an output terminal electrically connected to the control terminal of the main switch tube in the primary circuit for outputting a control signal of the main switch tube; a primary controller having an output terminal electrically connected to the control terminal of the synchronous rectifier tube in the secondary circuit for outputting a control signal of the synchronous rectifier tube; wherein, after receiving an interrogation signal from the secondary controller, the primary controller sends a feedback signal to the secondary controller, and the secondary controller keeps the synchronous rectifier tube off according to the feedback signal, and the primary controller controls the main switch tube in the primary circuit to turn on after the synchronous rectifier tube is turned off.

[0006] Optionally, the secondary controller is further configured to send a first indication signal to the primary controller after controlling the synchronous rectifier tube to turn off according to the feedback signal to indicate the primary controller to control the main switch tube to turn on.

[0007] Optionally, the secondary side controller is further configured to receive the output voltage of the switching converter, and send the first indication signal when receiving the feedback signal and the output voltage of the switching converter is lower than a preset voltage.

[0008] Optionally, the primary side controller is configured to turn on the main switching transistor at a second predetermined time after sending out the feedback signal, and the second predetermined time is later than the turn-off time of the synchronous rectifier transistor.

[0009] Optionally, the primary side controller is further configured to send a second indication signal when the main switching transistor is turned off, so as to instruct the secondary side controller to control the synchronous rectifier transistor to turn on.

[0010] Optionally, the secondary side controller is further configured to detect the voltage signal of the secondary side winding, and control the synchronous rectifier transistor to turn on when the voltage signal of the secondary side winding drops to a preset value when the main switching transistor is turned off.

[0011] Optionally, the secondary side controller is further configured to detect the secondary side current of the secondary side circuit, and control the synchronous rectifier transistor to turn off when it is detected that the secondary side current drops to a first preset current during the turn-on process of the synchronous rectifier transistor.

[0012] Optionally, the secondary side controller includes a first logic control module, a first sending module, and a first receiving module. Wherein, the first output terminal of the first logic control module is electrically connected to the control terminal of the synchronous rectifier transistor, and is configured to provide a control signal to the synchronous rectifier transistor; the second output terminal of the first logic control module is electrically connected to the first sending module, and is configured to send out the generated signal through the first sending module; and, the first input terminal of the first logic control module is electrically connected to the first receiving module, and is configured to receive a signal from the primary side controller through the first receiving module.

[0013] Optionally, the primary side controller includes a second logic control module, a second receiving module, and a second sending module. Wherein, the input terminal of the second logic control module is connected to the second receiving module, and is configured to receive a signal from the secondary side controller through the second receiving module; the first output terminal of the second logic control module is electrically connected to the control terminal of the main switching transistor, and is configured to provide a control signal to the main switching transistor; and, the second output terminal of the second logic control module is electrically connected to the second sending module, and is configured to send out the generated signal through the second sending module.

[0014] Optionally, the control circuit further includes: at least one isolator, coupled between the primary controller and the secondary controller, for transmitting the signal of the secondary controller to the primary controller through the isolator, and transmitting the signal of the primary controller to the secondary controller through the isolator.

[0015] Optionally, a first isolator and a second isolator are provided in the control circuit, and both the first isolator and the second isolator are coupled between the primary controller and the secondary controller. The first isolator is used to couple the signal from the secondary controller to the primary controller, and the second isolator is used to couple the signal from the primary controller to the secondary controller.

[0016] The present invention also provides a control method for an isolated switching converter. The isolated switching converter includes a primary circuit, a secondary circuit, and a transformer coupled between the primary circuit and the secondary circuit. The control method includes: sending an interrogation signal from the secondary controller to the primary controller; after receiving the interrogation signal, the primary controller sends a feedback signal to the secondary controller; the secondary controller receives the feedback signal and provides a turn-off signal to the synchronous rectifier tube in the secondary circuit to control the synchronous rectifier tube to remain off; and after the synchronous rectifier tube is turned off, the primary controller provides a turn-on signal to the main switch tube in the primary circuit to control the main switch tube to turn on.

[0017] Optionally, after controlling the synchronous rectifier tube to turn off according to the feedback signal, the secondary controller further sends a first indication signal to the primary controller, and the primary controller controls the main switch tube to turn on according to the first indication signal.

[0018] Optionally, the secondary controller also receives the output voltage of the switching converter, and sends the first indication signal when receiving the feedback signal and the output voltage of the switching converter is lower than a preset voltage.

[0019] Optionally, at a second predetermined time after sending out the feedback signal, the primary controller provides a turn-on signal to the main switch tube to control the main switch tube to turn on, and the second predetermined time is later than the turn-off time of the synchronous rectifier tube.

[0020] Optionally, when the main switch tube is turned off, the primary controller also sends a second indication signal, and the secondary controller provides a turn-on signal to the synchronous rectifier tube according to the second indication signal to control the synchronous rectifier tube to turn on.

[0021] Optionally, the secondary controller detects the voltage signal of the secondary winding, and when the main switch is turned off and the voltage signal of the secondary winding drops to a preset value, provides a turn-on signal to the synchronous rectifier tube to control the synchronous rectifier tube to turn on.

[0022] Optionally, the secondary controller also detects the secondary current of the secondary circuit, and during the turn-on process of the synchronous rectifier tube, when it detects that the secondary current drops to a first preset current, controls the synchronous rectifier tube to turn off.

[0023] Optionally, the method for controlling the isolated switch converter to operate in the discontinuous conduction mode includes: the secondary controller sends the inquiry signal to the primary controller to prepare to enter a new switching cycle; after receiving the inquiry signal, the primary controller sends the feedback signal to the secondary controller; after receiving the feedback signal, the secondary controller keeps the synchronous rectifier tube in the off state, and when it detects that the output voltage of the switch converter drops to a preset voltage, sends a first indication signal to the primary controller; the primary controller receives the first indication signal and controls the main switch to turn on to officially enter the current switching cycle; when the primary current of the primary circuit rises to a second preset current, the primary controller controls the main switch to turn off and sends a second indication signal; after receiving the second indication signal, the secondary controller controls the synchronous rectifier tube to turn on; and after the demagnetization of the secondary circuit is completed, the secondary controller controls the synchronous rectifier tube to turn off and waits to enter the next switching cycle.

[0024] In the control circuit for the isolated switch converter provided by the present invention, before preparing to turn on the main switch in the primary circuit, the secondary controller is preferably used to send an inquiry signal to the primary controller, and when the primary controller confirms the standby state, sends a feedback signal to the secondary controller, so that the secondary controller can control the synchronous rectifier tube to be in the off state according to the feedback signal, and then the primary controller is used to control the main switch to turn on. That is, the control circuit and its control method provided by the present invention, when preparing to turn on the main switch, through the information interaction between the primary side and the secondary side, ensure that the main switch is turned on in the off state of the synchronous rectifier tube, avoiding the problem of mis-conduction of the synchronous rectifier tube when the main switch is turned on, which may cause the penetration of the primary side and the secondary side, and effectively reducing the risk of common conduction between the primary side and the secondary side.

[0025] In addition, based on the control circuit provided by the present invention, in practical applications, a magnetic coupling isolator, a capacitive coupling isolator or a digital isolator, etc. can be selected as the isolator between the primary controller and the secondary controller, so as to use this isolator to realize the bidirectional communication between the primary side and the secondary side, which is beneficial to improving the response speed and reducing the system power consumption. Description of the Drawings

[0026] Figure 1 Schematic diagram of an isolated switch converter coupled with a control circuit in an embodiment of the present invention.

[0027] Figure 2 Schematic diagram of waveforms of key signals of an isolated switch converter coupled with a control circuit in discontinuous conduction mode in an embodiment of the present invention.

[0028] Figure 3 Schematic diagram of waveforms of key signals of an isolated switch converter coupled with a control circuit in continuous conduction mode in an embodiment of the present invention.

[0029] Figure 4 Another schematic diagram of waveforms of key signals of an isolated switch converter coupled with a control circuit in continuous conduction mode in an embodiment of the present invention. Detailed implementation manners

[0030] The following further details a control circuit and a control method of an isolated switch converter proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are all in very simplified forms and use non-precise scales, only for conveniently and clearly assisting in explaining the purpose of the embodiments of the present invention. Additionally, it should be noted that the "time", "on-time length", and "on-time" referred to in this specification are all time periods, that is, the length of a period of time; "moment", "when...", and "turn-off moment" are all time points, that is, the moment when a certain event occurs; "valid level" and "high level" indicate that a level that can be detected and judged as valid indicates that a certain component or module performs corresponding actions; "invalid level" and "low level" indicate that a level that can be detected and judged as invalid or a level that cannot be detected indicates that a certain component or module performs corresponding actions; "signal" can represent some specific electrical / magnetic signals, which can be represented by specific waveforms, or can represent some information transmitted in a circuit, which can be represented by specific values.

[0031] Figure 1 Schematic diagram of a circuit of an isolated switch converter coupled with a control circuit in an embodiment of the present invention, as Figure 1 shown, the isolated switch converter includes a primary circuit, a secondary circuit, and a transformer T1 coupled between the primary circuit and the secondary circuit and providing electrical isolation. Among them, the primary circuit and the secondary circuit are electrically isolated and are respectively connected to different ground terminals. The transformer T1 includes a primary winding W1 and a secondary winding W2. The primary circuit is coupled to the primary winding W1 of the transformer T1, and the secondary circuit is coupled to the secondary winding W2 of the transformer T1.

[0032] Continue to refer toFigure 1 As shown, the control circuit includes a primary controller 200 and a secondary controller 100. Among them, the primary controller 200 has an output terminal, and the output terminal of the primary controller 200 is electrically connected to the control terminal of the main switch tube G1 in the primary circuit, and is used to output the control signal PWM of the main switch tube G1 to control the switching state of the main switch tube G1. Also, the secondary controller 100 has an output terminal, and the output terminal of the secondary controller 100 is electrically connected to the control terminal of the synchronous rectifier tube SR in the secondary circuit, and is used to output the control signal of the synchronous rectifier tube SR to control the switching state of the synchronous rectifier tube SR. That is, the primary controller 200 can be used to control the switching state of the main switch tube G1, and the secondary controller 100 can be used to control the switching state of the synchronous rectifier tube SR.

[0033] In one example, the primary circuit may include an input capacitor Cbus and a main switch tube G1. The first end of the input capacitor Cbus is coupled to the primary winding W1 of the transformer T1, and the second end of the input capacitor Cbus is connected to the ground terminal of the primary circuit; also, the main switch tube G1 can be, for example, a power switch tube, the drain of the power switch tube is connected to the primary winding W1 of the transformer T1, the source of the power switch tube is connected to the ground terminal of the primary circuit, and the gate of the power switch tube is connected to the primary controller 200 for receiving the control signal PWM of the main switch tube G1.

[0034] In one example, the secondary circuit may include a synchronous rectifier tube SR and an output capacitor Cout. The first end of the output capacitor Cout is coupled to the secondary winding W2 of the transformer T1 and is connected to the load, and the second end of the output capacitor Cout is connected to the ground terminal of the secondary circuit. The synchronous rectifier tube SR is, for example, a power switch tube, the drain of the power switch tube is connected to the secondary winding W2 of the transformer T1, the source of the power switch tube is connected to the ground terminal of the secondary circuit, and the gate of the power switch tube is connected to the secondary controller 100 for receiving the control signal of the synchronous rectifier tube SR.

[0035] In addition, the secondary controller 100 in this embodiment can also be coupled to the secondary winding W2 of the transformer T1 for obtaining the voltage signal Forward of the secondary winding W2 of the transformer T1. In a specific example, the secondary controller 100 can sense the voltage signal Forward of the secondary winding W2 to reflect the switching state of the main switch tube G1 in the primary circuit. For example, when the voltage signal Forward of the secondary winding W2 drops to a preset value, it means that the main switch tube G1 is in the off state.

[0036] In the control circuit provided in this embodiment, the primary controller 200 and the secondary controller 100 perform information interaction to ensure that the synchronous rectifier SR is in the off state before the main switch tube G1 is turned on; similarly, it can ensure that the synchronous rectifier SR is turned on after the main switch tube G1 is turned off, effectively solving the problem common to the primary and secondary sides.

[0037] Specifically, when preparing to enter a new switching cycle, the primary controller 200 is used to receive the inquiry signal request1_0 sent by the secondary controller 100 and start a self-detection operation to enter a preparatory state (the self-detection operation includes, for example: checking whether the main switch tube G1 in the primary circuit is turned off to ensure that the main switch tube G1 is in the off state; and ensuring that each module in the primary controller 200 is in a preparatory state, etc.). For example Figures 2-4 As shown in, at time t1, the secondary controller 100 sends the inquiry signal request1_0 ( Figures 2-4 the first pulse of the Request1 waveform shown in, and the signals such as request1_1 are similarly postponed) to the primary controller 200.

[0038] In an optional solution, the secondary controller 100 can be used to send the inquiry signal request1_0 at a first predetermined time after the synchronous rectifier SR is turned off in the previous switching cycle to prepare to enter a new switching cycle.

[0039] In addition, the primary controller 200 can control the main switch tube G1 in the primary circuit to turn on after confirming that the synchronous rectifier SR is turned off, thereby entering a new switching cycle. That is, the process of the primary controller 200 controlling the main switch tube G1 in the primary circuit to turn on to enter a new switching cycle can include: after receiving the inquiry signal request1_0, the primary controller 200 starts a self-detection operation, and after the self-detection operation is completed, sends a feedback signal request2_0 to the secondary controller 100 to prompt that the primary controller 200 has entered the preparatory state; the secondary controller 100 keeps the synchronous rectifier SR turned off according to the feedback signal request2_0, and then the primary controller 200 controls the main switch tube G1 in the primary circuit to turn on. For example Figures 2-4 As shown in, at time t2, the primary controller 200 completes the self-detection operation and sends a feedback signal request2_0 to the secondary controller 100 ( Figures 2-4 the first pulse of the Request2 waveform shown in, and the signals such as request2_1 are similarly postponed), and the secondary controller 100 controls the synchronous rectifier SR to still remain in the off state.

[0040] Among them, the primary side controller 200 ensures that the main switch tube G1 can be turned on after the synchronous rectifier tube SR is turned off. For specific examples, please refer to the following.

[0041] In the first example, after the secondary side controller 100 ensures that the synchronous rectifier tube SR remains off, it is also used to send a first indication signal request1_1 to the primary side controller 200 to instruct the primary side controller 200 to turn on the main switch tube G1 in the primary side circuit according to the first indication signal request1_1. That is, in this example, the primary side controller 200 controls the turn-on timing of the main switch tube G1 based on the first indication signal request1_1. When the primary side controller 200 receives the first indication signal request1_1, it means that the synchronous rectifier tube SR has been confirmed to be turned off. At this time, turning on the main switch tube G1 can effectively avoid the problem of common conduction between the primary side and the secondary side. For example Figure 2 and Figure 3 as shown in, at time t3, after the secondary side controller 100 ensures that the synchronous rectifier tube SR remains off, it sends a first indication signal request1_1 to the primary side controller 200, so that the primary side controller 200 controls the main switch tube G1 in the primary side circuit to turn on according to the first indication signal request1_1.

[0042] In this first example, after the secondary side controller 100 ensures that the synchronous rectifier tube SR remains off, it can also be used to judge the timing of sending the first indication signal request1_1 according to the output voltage Vout of the switching converter. Specifically, after receiving the feedback signal request2_0 and turning off the synchronous rectifier tube SR, and when the output voltage Vout of the switching converter is lower than the preset voltage, the secondary side controller 100 sends the first indication signal request1_1 to instruct the primary side controller 200 to turn on the main switch tube G1. For example Figure 2 and Figure 3 as shown in, at time t2, the secondary side controller 100 controls the synchronous rectifier tube SR to remain off according to the feedback signal request2_0 until time t3 when it detects that the output voltage Vout of the switching converter is lower than the preset voltage, and the secondary side controller 100 sends a first indication signal request1_1 to the primary side controller 200.

[0043] That is, when the secondary side controller 100 generates the inquiry signal request1_0, it generates the inquiry signal request1_0 based on the first predetermined time after the synchronous rectifier tube SR is turned off in the previous switching cycle. At this time, after the secondary side controller 100 receives the feedback signal request2_0 and turns off the synchronous rectifier tube SR, it can continue to wait until the output voltage Vout of the switching converter is lower than the preset voltage before sending the first indication signal request1_1.

[0044] In the second example, the primary controller 200 can control the main switching transistor G1 in the primary circuit to turn on at a second predetermined time after sending out the feedback signal request2_0. The second predetermined time mentioned here is later than the turn-off time of the synchronous rectifier SR, so as to ensure that the main switching transistor G1 is turned on after the synchronous rectifier SR is turned off. That is, in this example, the primary controller 200 reserves the time for the secondary controller 100 to control the synchronous rectifier SR to turn off after sending out the feedback signal request2_0, and then controls the main switching transistor G1 to turn on, which can also effectively avoid the problem of common conduction between the primary side and the secondary side. For example Figure 4 As shown in, at time t1, the primary controller 200 sends out the feedback signal request2_0, and controls the main switching transistor G1 to turn on until time t3, while the synchronous rectifier SR is turned off at a time earlier than t3 (i.e., time t2).

[0045] Furthermore, after the main switching transistor G1 is turned on, the primary current Ipri in the primary circuit can gradually increase. In a specific example, after the primary current Ipri increases to a second preset current, the primary controller 200 can control the main switching transistor G1 to turn off. And, after confirming that the main switching transistor G1 is turned off, the secondary controller 100 can control the synchronous rectifier SR in the secondary circuit to turn on. For example Figures 2-4 As shown in, at time t4, the primary current Ipri increases to the second preset current, thereby controlling the main switching transistor G1 to turn off, and controlling the synchronous rectifier SR to turn on at time t5.

[0046] Among them, the way for the secondary controller 100 to ensure that it can control the synchronous rectifier SR to turn on after the main switching transistor G1 is turned off can be specifically referred to the following example.

[0047] In one example, the primary controller 200 is also used to send a second indication signal request2_1 when the main switching transistor G1 is turned off, so as to instruct the secondary controller 100 to control the synchronous rectifier SR to turn on after receiving the second indication signal request2_1. That is, in this example, the secondary controller 100 controls the turn-on timing of the synchronous rectifier SR based on the second indication signal request2_1. When the secondary controller 100 receives the second indication signal request2_1, it means that the main switching transistor G1 has been confirmed to be turned off. At this time, controlling the synchronous rectifier SR to turn on can effectively avoid the problem of common conduction between the primary side and the secondary side. For example Figures 2-4 As shown in, at time t4, the primary current Ipri increases to the second preset current, thereby controlling the main switching transistor G1 to turn off and sending the second indication signal request2_1. The secondary controller 100 can delay until time t5 to control the synchronous rectifier SR to turn on.

[0048] In another example, the secondary side controller 100 can also detect the voltage signal Forward of the secondary side winding W2, and when the voltage signal Forward of the secondary side winding W2 drops to a preset value due to the turn-off of the main switching transistor G1, control the synchronous rectifier SR to turn on. That is, in this example, the secondary side controller 100 independently detects the voltage signal Forward of the secondary side winding W2. When the voltage signal Forward of the secondary side winding W2 drops to the preset value, it means that the main switching transistor G1 has been turned off. At this time, controlling the synchronous rectifier SR to turn on can also effectively avoid the problem common to the primary side and the secondary side.

[0049] In a specific example, after the synchronous rectifier SR is turned on, the secondary side controller 100 can detect the secondary side current Isec of the secondary side circuit in real time, and when the secondary side current Isec drops to a first preset current, provide a turn-off signal to the synchronous rectifier SR to control the synchronous rectifier SR to turn off.

[0050] It should be noted that the control circuit provided by the present disclosure can be applied to a controlled isolated switching converter in continuous conduction mode, and can also be applied to a controlled isolated switching converter in discontinuous conduction mode.

[0051] Continue to refer to the following Figure 1 and elaborate on the specific structure of one of the control circuits in detail.

[0052] As Figure 1 shown, the secondary side controller 100 may specifically include a first logic control module, a first sending module, and a first receiving module.

[0053] Among them, the first output terminal of the first logic control module is electrically connected to the control terminal of the synchronous rectifier SR, and is used to provide a control signal to the synchronous rectifier SR. The second output terminal of the first logic control module is electrically connected to the first sending module, and is used to send the generated signal through the first sending module. For example, the first logic control module can generate an interrogation signal request1_0 and send it out through the first sending module.

[0054] The first input terminal of the first logic control module is electrically connected to the first receiving module, and is used to receive the signal request2 from the primary side controller 200 through the first receiving module. For example, the feedback signal request2_0 from the primary side controller 200 can be received through the first receiving module, so that the first logic control module does not provide an on signal to the synchronous rectifier SR after receiving the feedback signal request2_0, ensuring that the synchronous rectifier SR remains off; and, the second indication signal request2_1 from the primary side controller 200 can also be received through the first receiving module, so that the first logic control module can generate an on signal for the synchronous rectifier SR according to the second indication signal request2_1.

[0055] In an alternative solution, after the first logic control module ensures that the synchronous rectifier tube SR remains off according to the feedback signal request2_0, it can also be used to generate a first indication signal request1_1 and send it to the primary controller 200 through the first sending module to instruct the primary controller 200 to control the main switch tube G1 to turn on.

[0056] In a further solution, the first logic control module further has a second input terminal, and its second input terminal can be electrically connected to the output terminal of the secondary winding W2 of the transformer T1 for obtaining the voltage signal Forward of the secondary winding W2. In a specific example, the first logic control module can be used to generate an enabling signal for the synchronous rectifier tube SR according to the voltage signal Forward. For example, the enabling signal for the synchronous rectifier tube SR can be generated after detecting that the voltage signal Forward drops to a preset value after the main switch tube G1 is turned off. In this embodiment, the first logic control module further has a third input terminal, and its third input terminal is further used to receive the output voltage Vout of the switching converter. In an example, the first logic control module can use the output voltage Vout as the timing for generating the first indication signal request1_1. For example, after receiving the feedback signal request2_0, the first logic control module can also wait until the received output voltage Vout is lower than a preset voltage to generate the first indication signal request1_1.

[0057] Continue to refer to Figure 1 As shown, the primary controller 200 may specifically include a second logic control module, a second receiving module, and a second sending module.

[0058] Among them, the input terminal of the second logic control module is connected to the second receiving module for receiving signals request1 from the secondary controller 100 through the second receiving module. For example, the inquiry signal request1_0, the first indication signal request1_1, etc. from the secondary controller 100 can be received through the second receiving module. The first output terminal of the second logic control module is electrically connected to the control terminal of the main switch tube G1 for providing a control signal PWM to the main switch tube G1. For example, the second logic control module can provide a turn-on signal to the main switch tube G1 after receiving the first indication signal request1_1. The second output terminal of the second logic control module is electrically connected to the second sending module for sending the generated information to the second sending module and sending it out by using the second sending module. For example, the second logic control module can generate a feedback signal request2_0 after completing a self-detection operation and send it out by this second sending module; and the second logic control module can generate a second indication signal request2_1 after turning off the main switch tube G1 and send it out by this second sending module.

[0059] In a specific example, the control circuit further includes an isolator. The isolator is coupled between the primary controller 200 and the secondary controller 100, and is used to isolate the primary controller 200 and the secondary controller 100, and enable the secondary controller 100 and the primary controller 200 to communicate information through the isolator. That is, the signal of the secondary controller 100 can be transmitted to the primary controller 200 through the isolator, and the signal of the primary controller 200 can be transmitted to the secondary controller 100 through the isolator.

[0060] In one example, the control circuit may be provided with only one isolator, and the primary controller 200 and the secondary controller 100 both communicate information through the same isolator. In another example, for example Figure 1 As shown, the control circuit may be provided with a first isolator and a second isolator. The first isolator is used to couple the signal request1 from the secondary controller 100 to the primary controller 200, and the second isolator is used to couple the signal request2 from the primary controller 200 to the secondary controller 100. It should be recognized that in other examples, only one isolator may also be provided, and this isolator can be multiplexed in different time periods to achieve the signal transmission from the secondary controller 100 to the primary controller 200 and the signal transmission from the primary controller 200 to the secondary controller 100. Among them, the first isolator and the second isolator are, for example, magnetic isolation isolators, capacitive isolation isolators, or digital isolation isolators, etc.

[0061] Based on the control circuit described above, the control method of the isolated switching converter provided by the present invention will be further described in detail below by listing three examples.

[0062] <Example 1>

[0063] In this example, taking the operation of the isolated switching converter in the discontinuous conduction mode (DCM) as an example, the process of entering a complete switching cycle is explained.

[0064] Specifically, it can be combined with Figure 1 on the basis of Figure 2 the key signal waveform diagram shown. It should be noted that Figure 2 Request1 in is used to represent the signal from the secondary controller 100, Figure 2 and Request2 in is used to represent the signal from the primary controller 200.

[0065] At time t1, the secondary side controller 100 can send an interrogation signal request1_0 to the primary side controller 200 through the first isolator to prepare to enter a new switching cycle. As described above, the secondary side controller 100 can send the interrogation signal request1_0 according to a first predetermined time after the synchronous rectifier SR is turned off in the previous switching cycle. Also, after receiving the interrogation signal request1_0, the primary side controller 200 performs a self-detection operation to enter a preparatory state.

[0066] At time t2, the primary side controller 200 completes the self-detection operation and is in a preparatory state. At this time, it can send a feedback signal request2_0 to the secondary side controller 100 through the second isolator; after receiving the feedback signal request2_0, the secondary side controller 100 checks whether the synchronous rectifier SR is turned off and ensures that the synchronous rectifier SR is in the off state. In this embodiment, after receiving the feedback signal request2_0, the secondary side controller 100 still maintains the off state of the synchronous rectifier SR.

[0067] At time t3, when the secondary side controller 100 ensures that the synchronous rectifier SR is in the off state and detects that the output voltage Vout of the switching converter drops to a preset voltage at time t3, it sends a first indication signal request1_1 to the primary side controller 200 through the first isolator to instruct the primary side controller 200 to control the main switch tube G1 to turn on.

[0068] At time t4, as the main switch tube G1 turns on, the primary side current Ipir of the primary side circuit gradually increases, and when the primary side current Ipir increases to a second preset current, the primary side controller 200 controls the main switch tube G1 to turn off and sends a second indication signal request2_1 through the second isolator.

[0069] At time t5, after receiving the second indication signal request2_1 indicating that the main switch tube G1 has been turned off, the secondary side controller 100 controls the synchronous rectifier SR to turn on.

[0070] At time t6, as the main switch tube G1 turns off and the synchronous rectifier SR turns on, the secondary side current Isec in the secondary side circuit gradually decreases. After the demagnetization of the secondary side circuit is completed, the secondary side controller 100 controls the synchronous rectifier SR to turn off.

[0071] In this way, one switching cycle is completed. Also, after a first predetermined time when the synchronous rectifier SR is turned off, the secondary side controller 100 can continue to send the interrogation signal request1_0 to the primary side controller 200 to prepare to enter the next switching cycle.

[0072] <Example 2>

[0073] In this example, taking the operation of an isolated switch converter in continuous conduction mode (CCM) as an example, the process of entering a complete switching cycle is explained and illustrated.

[0074] Specifically, it can be based on Figure 1 and combined with Figure 3 the key signal waveform diagram shown. It should be noted that Figure 3 Request1 in Figure 3 is used to represent the signal from the secondary controller 100, and

[0075] Request2 in

[0076] is used to represent the signal from the primary controller 200.

[0077] At time t1, the secondary controller 100 can send an interrogation signal request1_0 to the primary controller 200 through the first isolator to prepare to enter a new switching cycle. Also, after receiving the interrogation signal request1_0, the primary controller 200 performs a self-detection operation to enter a preparatory state.

[0078] At time t2, the primary controller 200 completes the self-detection operation and is in a preparatory state. At this time, it can send a feedback signal request2_0 to the secondary controller 100 through the second isolator, and the secondary controller 100 keeps the synchronous rectifier SR in the off state according to the feedback signal request2_0.

[0079] At time t3, after keeping the synchronous rectifier SR in the off state, the secondary controller 100 sends a first indication signal request1_1 to the primary controller 200 through the first isolator to instruct the primary controller 200 to control the main switch tube G1 to turn on.

[0080] At time t4, as the main switch tube G1 turns on, the primary current Ipir of the primary circuit gradually increases, and when the primary current Ipir rises to the second preset current, the primary controller 200 controls the main switch tube G1 to turn off and sends a second indication signal request2_1 through the second isolator.

[0081] At time t7 , the secondary-side controller 100 sends an inquiry signal request1_0 to prepare for entering the next switching cycle. After receiving the inquiry signal request1_0 , the primary-side controller 200 performs a self-detection operation.

[0082] At time t8, the primary controller 200 completes the self-detection operation and is in a standby state, and sends a feedback signal request2_0 to the secondary controller 100. The secondary controller 100 receives the feedback signal request2_0 and turns off the synchronous rectifier SR. In this way, the current switching cycle ends and then enters the next switching cycle.

[0083] <Example 3>

[0084] The difference from Example 1 and Example 2 is that the main switch tube G1 in this example is turned on at the second predetermined time after the primary side controller 200 sends the feedback signal request2_0; while the main switch tube G1 in Example 1 and Example 2 is turned on based on the first indication signal request1_1 sent by the secondary side controller 100.

[0085] Specific can be found in Figure 1 Based on the combination Figure 4 The key signal waveform diagram shown in the figure. It should be noted that Figure 4 The continuous conduction mode (CCM) is still used as an example for explanation, and Request1 is used to represent a signal from the secondary side controller 100. Figure 4 Request2 in FIG. 1 is used to represent a signal from the primary side controller 200 .

[0086] At time t1 and time t2, Figure 3 The example shown is similar, that is, the secondary controller 100 sends an inquiry signal request1_0 to the primary controller 200 through the first isolator to prepare for entering a new switching cycle. And, after receiving the inquiry signal request1_0, the primary controller 200 performs a self-detection operation to enter a preparatory state, and sends a feedback signal request2_0 to the secondary controller 100 through the second isolator. The secondary controller 100 keeps the synchronous rectifier SR in the off state according to the feedback signal request2_0.

[0087] At time t3, the primary controller 200 delays until the second predetermined time after sending the feedback signal request2_0, and controls the main switch tube G1 to turn on. It should be appreciated that the second predetermined time after sending the feedback signal request2_0 is later than the turn-off time of the synchronous rectifier tube SR. Figure 4 As shown, the synchronous rectifier tube SR is turned off at time t2, and the main switch tube G1 is turned on at time t3.

[0088] At time t4 and time t5, similar to Figure 3 the example shown, that is, as the primary current Ipir of the primary-side circuit gradually increases, and when the primary current Ipir increases to the second preset current, the primary controller 200 controls the main switch tube G1 to turn off and sends a second indication signal request2_1 through the second isolator. Then, after receiving the second indication signal request2_1, the secondary controller 100 controls the synchronous rectifier tube SR to conduct.

[0089] From time t4 to time t8 afterwards, similar to Figure 3 the example shown, which will not be elaborated here.

[0090] It should be noted that the various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. The system disclosed in the embodiment corresponds to the method disclosed in the embodiment, and the relevant parts can be referred to each other. Although the present invention has been disclosed above with preferred embodiments, the above embodiments are not intended to limit the present invention. For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible changes and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or it can be modified into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of protection of the technical solution of the present invention.

[0091] It should also be understood that unless specifically stated or indicated otherwise, the terms "first", "second", "third", etc. in the specification are only used to distinguish the various components, elements, steps, etc. in the specification, rather than to represent the logical relationship or sequential relationship, etc. between the various components, elements, steps. In addition, it should be recognized that the singular forms "a" and "an" used herein and in the appended claims include plural referents unless the context clearly dictates otherwise. For example, a reference to "a step" or "a device" means a reference to one or more steps or devices and may include secondary steps and secondary devices. All conjunctions used should be understood in the broadest sense.

Claims

1. A control circuit for controlling an isolated switching converter, the isolated switching converter including a primary circuit, a secondary circuit, and a transformer coupled between the primary circuit and the secondary circuit. Characterized in that, The control circuit includes: A primary controller having an output terminal electrically connected to the control terminal of the main switch tube in the primary circuit for outputting a control signal of the main switch tube; A secondary controller having an output terminal electrically connected to the control terminal of the synchronous rectifier tube in the secondary circuit for outputting a control signal of the synchronous rectifier tube; Wherein, the secondary controller is used to send an interrogation signal at a first predetermined time after the synchronous rectifier tube is turned off in the previous switching cycle. After receiving the interrogation signal, the primary controller detects the state of the main switch tube and sends a feedback signal to the secondary controller when it confirms that the main switch tube is turned off; the secondary controller keeps the synchronous rectifier tube in the off state according to the feedback signal, and then the primary controller controls the main switch tube in the primary circuit to turn on.

2. The control circuit according to claim 1, Characterized in that, The secondary controller is further used to send a first indication signal to the primary controller after keeping the synchronous rectifier tube off according to the feedback signal to indicate the primary controller to control the main switch tube to turn on.

3. The control circuit according to claim 2, Characterized in that, The secondary controller is further used to receive the output voltage of the switching converter and send the first indication signal when it receives the feedback signal and the output voltage of the switching converter is lower than a preset voltage.

4. The control circuit according to claim 1, Characterized in that, The primary controller is used to control the main switch tube to turn on at a second predetermined time after sending out the feedback signal, and the second predetermined time is later than the turn-off time of the synchronous rectifier tube.

5. The control circuit according to claim 1, Characterized in that, The primary controller is further used to send a second indication signal when the main switch tube is turned off to indicate the secondary controller to control the synchronous rectifier tube to turn on.

6. The control circuit according to claim 1, Characterized in that, The secondary controller is further used to detect the voltage signal of the secondary winding of the transformer and control the synchronous rectifier tube to turn on when the voltage signal of the secondary winding drops to a preset value when the main switch tube is turned off.

7. The control circuit according to claim 1, Characterized in that, The secondary controller is further used to detect the secondary current of the secondary circuit and control the synchronous rectifier tube to turn off when the detected secondary current drops to a first preset current during the turn-on process of the synchronous rectifier tube.

8. The control circuit according to claim 1, Characterized in that, The secondary controller includes a first logic control module, a first sending module, and a first receiving module; wherein, The first output terminal of the first logic control module is electrically connected to the control terminal of the synchronous rectifier tube for providing a control signal to the synchronous rectifier tube. The second output terminal of the first logic control module is electrically connected to the first sending module, and is used to send the generated signal to the primary controller through the first sending module; and, The first input terminal of the first logic control module is electrically connected to the first receiving module, and is used to receive the signal from the primary controller through the first receiving module.

9. The control circuit according to claim 1, characterized in that the primary controller includes a second logic control module, a second receiving module and a second sending module; wherein, the input terminal of the second logic control module is connected to the second receiving module, and is used to receive the signal from the secondary controller through the second receiving module; the first output terminal of the second logic control module is electrically connected to the control terminal of the main switch tube, and is used to provide a control signal to the main switch tube; and, the second output terminal of the second logic control module is electrically connected to the second sending module, and is used to send the generated signal to the secondary controller through the second sending module.

10. The control circuit according to claim 1, characterized in that the control circuit further includes: an isolator, coupled between the primary controller and the secondary controller, and is used to enable the signals of the secondary controller and the primary controller to be transmitted to each other through the isolator.

11. The control circuit according to claim 1, characterized in that a first isolator and a second isolator are provided in the control circuit, the first isolator and the second isolator are both coupled between the primary controller and the secondary controller, the first isolator is used to couple the signal from the secondary controller to the primary controller, and the second isolator is used to couple the signal from the primary controller to the secondary controller.

12. A control method for an isolated switching converter, the isolated switching converter includes a primary circuit, a secondary circuit and a transformer coupled between the primary circuit and the secondary circuit, characterized in that the control method includes: at a first predetermined time after the synchronous rectifier tube is turned off in the previous switching cycle, the secondary controller sends an interrogation signal; after the primary controller receives the interrogation signal, it detects the state of the main switch tube, and sends a feedback signal to the secondary controller when the main switch tube is turned off; the secondary controller receives the feedback signal and keeps the synchronous rectifier tube turned off; and, the primary controller provides a turn-on signal to the main switch tube in the primary circuit to control the main switch tube to turn on.

13. The control method according to claim 12, characterized in that after the secondary controller keeps the synchronous rectifier tube turned off according to the feedback signal, it further sends a first indication signal to the primary controller, and the primary controller controls the main switch tube to turn on according to the first indication signal.

14. The control method according to claim 13, characterized in that the secondary controller further receives the output voltage of the switching converter, and sends the first indication signal when it receives the feedback signal and the output voltage of the switching converter is lower than a preset voltage.

15. The control method according to claim 12, wherein, after a second predetermined time after the primary controller sends out the feedback signal, the primary controller provides a turn-on signal to the main switch tube to control the main switch tube to turn on, and the second predetermined time is later than the turn-off time of the synchronous rectifier tube.

16. The control method according to claim 12, wherein, when the main switch tube is turned off, the primary controller also sends a second indication signal, and the secondary controller provides a turn-on signal to the synchronous rectifier tube according to the second indication signal to control the synchronous rectifier tube to turn on.

17. The control method according to claim 12, wherein, the secondary controller detects the voltage signal of the secondary winding of the transformer, and when the voltage signal of the secondary winding drops to a preset value when the main switch tube is turned off, the secondary controller provides a turn-on signal to the synchronous rectifier tube to control the synchronous rectifier tube to turn on.

18. The control method according to claim 12, wherein, the secondary controller also detects the secondary current of the secondary circuit, and during the turn-on process of the synchronous rectifier tube, when it detects that the secondary current drops to a first preset current, the secondary controller controls the synchronous rectifier tube to turn off.

19. The control method according to claim 12, wherein, the control method for the isolated switch converter includes: at a first predetermined time after the synchronous rectifier tube is turned off in the previous switching cycle, the secondary controller sends the inquiry signal to the primary controller to prepare to enter a new switching cycle; after receiving the inquiry signal, the primary controller sends the feedback signal to the secondary controller; after receiving the feedback signal, the secondary controller keeps the synchronous rectifier tube in the off state, and when it detects that the output voltage of the switch converter drops to a preset voltage, the secondary controller sends a first indication signal to the primary controller; after receiving the first indication signal, the primary controller controls the main switch tube to turn on to officially enter the current switching cycle; when the primary current in the primary circuit rises to a second preset current, the primary controller controls the main switch tube to turn off and sends a second indication signal; after receiving the second indication signal, the secondary controller controls the synchronous rectifier tube to turn on; and, after the demagnetization of the secondary circuit is completed, the secondary controller controls the synchronous rectifier tube to turn off and waits to enter the next switching cycle.

20. An isolated switch converter, wherein, it includes the control circuit according to any one of claims 1-11.

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