Isolated power converter and control circuit thereof

Abstract

The invention provides an isolated power converter and a control circuit thereof, a secondary side controller receives a first sampling signal representing an output voltage of the isolated power converter to generate a first control signal, and a primary side control module receives a second sampling signal representing a primary side current to generate a second control signal. A second control signal is generated to control the state of a primary side power tube, and a primary side control mode is achieved; the following secondary side control module receives the first control signal to generate a third control signal to control the state of a primary side power tube so as to realize a secondary side control mode; the control right switching module receives a third sampling signal representing the output voltage, and switches from the primary side control mode to the secondary side control mode after the third sampling signal satisfies a predetermined condition. When the isolated power converter is started, the primary side control mode is firstly realized, and the secondary side control mode is switched when the preset condition is met, so that the output voltage overshoot during starting is prevented, and meanwhile, the preset condition is adjusted to adapt to different input and output conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and in particular to an isolated power converter and a control circuit thereof. Background Art

[0002] The current isolated power converter is a multi-controller power converter, which at least includes a primary controller and a primary power tube located on the primary side, a secondary controller located on the secondary side, and a transformer coupled between the primary controller and the secondary controller to provide electrical isolation. The primary controller and the secondary controller are isolated and communicated through a coupler.

[0003] The startup mode of this isolated power converter is: when the power is turned on, the supply voltage of the primary side controller increases, the primary side controller starts to work and controls the state of the primary side power tube, realizing the primary side control mode (Primary Side Regulation, PSR); after the voltage is generated on the winding of the transformer, the secondary side controller is powered, the supply voltage of the secondary side controller increases, the secondary side controller starts to work and controls the state of the primary side power tube, realizing the secondary side control mode (Secondary Side Regulation, SSR).

[0004] In this startup mode, the secondary controller has no power supply when starting the machine, so the primary controller needs to work first. The secondary controller can only get control of the primary power tube after it is powered on, which can easily cause output voltage overshoot when starting the machine. Summary of the invention

[0005] The object of the present invention is to provide an isolated power converter and a control circuit thereof to solve the problem that the output voltage of the existing isolated power converter is prone to overshoot during startup.

[0006] In order to achieve the above object, the present invention provides a control circuit of an isolated power converter, wherein the isolated power converter includes a primary power tube, and the control circuit includes a secondary controller and a primary controller, wherein:

[0007] The secondary-side controller is used to receive a first sampling signal representing the output voltage of the isolated power converter to generate a first control signal;

[0008] The primary side controller comprises:

[0009] A primary side control module, used for receiving a second sampling signal representing the primary side current, so as to generate a second control signal to control the state of the primary side power tube and realize a primary side control mode;

[0010] A follower secondary control module, configured to receive the first control signal to generate a third control signal to control the state of the primary power tube to implement a secondary control mode; and

[0011] The control right switching module is used to receive a third sampling signal representing the output voltage, and switch the primary side control module from the primary side control mode to the secondary side control mode after the third sampling signal meets a predetermined condition, and the predetermined condition is adjustable.

[0012] Optionally, when the value of the third sampling signal is greater than a switching threshold, the third sampling signal satisfies the predetermined condition.

[0013] Optionally, the primary side controller further includes:

[0014] a resistor voltage dividing module, configured to sample the output voltage to generate the third sampling signal; and

[0015] The threshold setting module is used to receive a first reference voltage signal to generate the switching threshold.

[0016] Optionally, the predetermined condition is adjusted by adjusting the resistance value of the voltage-dividing resistor in the resistance-dividing module and adjusting the sampling ratio of the resistance-dividing module.

[0017] Optionally, the predetermined condition is adjusted by adjusting the value of the first reference voltage signal.

[0018] Optionally, the primary side controller further includes:

[0019] a current source; and,

[0020] An adjustment resistor, wherein the first end of the adjustment resistor is connected to the current source and the threshold setting module and provides the first reference voltage signal, and the second end of the adjustment resistor is connected to the primary ground, and the value of the first reference voltage signal is adjusted by the current source, and / or the value of the first reference voltage signal is adjusted by adjusting the resistance value of the adjustment resistor to adjust the predetermined condition.

[0021] Optionally, the primary side control module includes a first drive generation module, and the first drive generation module includes:

[0022] a first comparator, configured to receive and compare the second sampling signal and a primary conduction time control signal to generate a first comparison signal, wherein the primary conduction time control signal is used to control the conduction time of the primary power tube; and

[0023] The first logic circuit is used to receive the first comparison signal and the primary frequency control signal to generate the second control signal, and the primary frequency control signal is used to control the conduction time of the primary power tube.

[0024] Optionally, the primary frequency control signal and the primary on-time control signal are both preset fixed signals.

[0025] Optionally, the primary side control module further includes:

[0026] an operational amplifier, used for receiving the third sampling signal and the second reference voltage signal and performing error amplification to generate a primary-side error amplification signal;

[0027] a frequency control module, configured to receive the primary error amplified signal to generate the primary frequency control signal; and

[0028] The shutdown control module is used to receive the primary side error amplification signal to generate the primary side conduction time control signal.

[0029] Optionally, the switching threshold is less than the value of the second reference voltage signal.

[0030] Optionally, the secondary side controller includes a secondary side control signal generating module, and the secondary side control signal generating module includes:

[0031] A second comparator is used to receive the first sampling signal and the third reference voltage signal and compare them to generate a second comparison signal, wherein the second comparison signal is used as the first control signal, and the first control signal includes information about the turn-on time of the primary power tube;

[0032] The following secondary side control module comprises:

[0033] a frequency on-time control module, configured to receive the first control signal to generate a secondary side on-time control signal; and

[0034] The second driving generation module is used to receive the first control signal, the secondary side conduction time control signal and the second sampling signal to generate the third control signal.

[0035] Optionally, the secondary side controller includes a secondary side control signal generating module, and the secondary side control signal generating module includes:

[0036] A second comparator, configured to receive and compare the first sampling signal and a third reference voltage signal to generate a second comparison signal;

[0037] A timer, used to start timing from the turn-on moment of the primary power tube and generate a secondary turn-on time control signal after a preset time period;

[0038] a second logic circuit, configured to receive the second comparison signal and the secondary side conduction time control signal to generate the first control signal, wherein the first control signal includes information about the conduction time and the turn-off time of the primary side power tube; and

[0039] The following secondary side control module comprises:

[0040] The second driving generating module is used for receiving the first control signal to generate the third control signal.

[0041] Optionally, the switching threshold is less than the value of the third reference voltage signal.

[0042] Optionally, when the isolated power converter cannot start, or when the isolated power converter starts successfully but the output voltage drops, the switching threshold is increased or the third sampling signal is decreased; when the isolated power converter starts successfully but the output voltage increases unevenly, the switching threshold is decreased or the third sampling signal is increased.

[0043] The present invention also provides an isolated power converter, comprising a control circuit of the isolated power converter, wherein the control circuit is used to control the state of a primary power tube.

[0044] The present invention provides an isolated power converter and a control circuit thereof, wherein a secondary side controller receives a first sampling signal representing an output voltage of the isolated power converter to generate a first control signal, a primary side control module receives a second sampling signal representing a current on the primary side to generate a second control signal to control the state of the primary side power tube, and implement a primary side control mode; a following secondary side control module receives the first control signal to generate a third control signal to control the state of the primary side power tube, and implement a secondary side control mode; a control right switching module receives a third sampling signal representing an output voltage, and switches from the primary side control mode to the secondary side control mode after the third sampling signal meets a predetermined condition. When the isolated power converter in the present invention is started, the primary side control mode is first implemented using the primary side control module, and when the predetermined condition is met, the control right switching module is used to switch from the primary side control mode to the secondary side control mode, and then the following secondary side control module is used to implement the secondary side control mode, so that the output voltage overshoot can be prevented during startup, and the predetermined condition can be configured and adjusted through the control circuit or the circuit parameters of the power converter to adapt to different input and output conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 A circuit diagram of an isolated power converter provided in Embodiment 1 of the present invention;

[0046] Figure 2A specific circuit diagram of a primary side control module provided in Embodiment 1 of the present invention;

[0047] Figure 3 A specific circuit diagram of a first drive generation module provided in Embodiment 1 of the present invention;

[0048] Figure 4 A circuit diagram of a secondary side control signal generating module and a following secondary side control module provided in Embodiment 1 of the present invention;

[0049] Figure 5a A schematic diagram of a circuit for providing a first reference voltage signal provided in Embodiment 1 of the present invention;

[0050] Figure 5b A schematic diagram of another circuit for providing a first reference voltage signal provided in Embodiment 1 of the present invention;

[0051] Figure 5c A schematic diagram of another circuit for providing a first reference voltage signal provided in the first embodiment of the present invention;

[0052] Figure 6 A circuit diagram of a resistor voltage divider module provided in Embodiment 1 of the present invention;

[0053] Figure 7a A schematic diagram of a control method for an isolated power converter provided in Embodiment 1 of the present invention;

[0054] Figure 7b A timing diagram of some signals of an isolated power converter provided in the first embodiment of the present invention;

[0055] Figure 8a A schematic diagram of another situation of the control method of the isolated power converter provided in the first embodiment of the present invention;

[0056] Figure 8b A timing diagram of some signals of an isolated power converter provided in the second embodiment of the present invention;

[0057] Fig. 9 A specific circuit diagram of a primary side control module provided in Embodiment 2 of the present invention;

[0058] Fig.10 is a relationship diagram between the primary side error amplification signal and the primary side frequency control signal, and between the primary side error amplification signal and the primary side conduction time control signal provided by this embodiment;

[0059] Fig.11 is a circuit diagram of a secondary side control signal generating module and a following secondary side control module provided in Embodiment 3 of the present invention;

[0060] 100-isolated power converter; Q-primary power tube; T-isolation transformer; Np-primary winding; Ns-secondary winding; Na-auxiliary winding; SR-secondary synchronous rectifier; Cout-output filter capacitor; AC-AC power supply; Vout-output voltage; 10-secondary controller; 101-secondary control signal generation module; 1011-second comparator; 1012-second logic circuit; 1013-timer; 20-primary controller; 21-primary control module; 2111-first comparator; 2112-first logic circuit; 211-first drive generation module; 212-frequency control module; 213-shutdown control module; 214-operational amplifier; 22-following secondary control module; 222-frequency conduction time control module; 221-second drive generation module; 23-control right switching module; 24-resistance voltage divider module; 25-threshold setting module; 30-coupler; VFB- First sampling signal; Vcs-second sampling signal; Vout_sample-third sampling signal; Vcontrol1-first control signal; Vcontrol2-second control signal; Vcontrol3-third control signal; Cons_fs, PSR_fs-primary frequency control signal; Cons_Vlimit, PSR_Vlimit-primary conduction time control signal; SSR_Vlimit-secondary conduction time control signal; Comp_PSR-primary error amplification signal; Vref1-first reference voltage signal; Vref2-second reference voltage signal; Vref3-third reference voltage signal; transition-switching threshold; R1, R2-voltage divider resistor; R3, R4-adjustment resistor; PGND-primary ground; SGND-secondary ground; IR-current source; VR-voltage source; Vcot_S-secondary conduction time control signal. DETAILED DESCRIPTION

[0061] The specific implementation of the present invention will be described in more detail below in conjunction with the schematic diagram. The advantages and features of the present invention will become clearer based on the following description. It should be noted that the drawings are all in a very simplified form and are not in exact proportions, and are only used to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention.

[0062] Embodiment 1

[0063] This embodiment provides an isolated power converter and a control circuit thereof. Figure 1 FIG. 1 is a circuit diagram of an isolated power converter 100 provided in an embodiment of the present invention. Figure 1As shown, the isolated power converter 100 includes components such as an isolation transformer T, a control circuit, a primary power tube Q, a clamping circuit, a secondary synchronous rectifier tube SR and an output filter capacitor Cout, wherein the isolation transformer T includes a primary winding Np, a secondary winding Ns and an auxiliary winding Na.

[0064] Specifically, the primary winding Np, auxiliary winding Na, primary power tube Q and clamping circuit of the isolation transformer T are all located on the primary side of the isolated power converter 100, and the input end of the primary side is coupled to the external AC power source AC. The secondary winding Ns, secondary synchronous rectifier SR and output filter capacitor Cout of the isolation transformer T are located on the secondary side of the isolated power converter 100, and the output end of the secondary side is coupled to the load to provide an output voltage Vout to power the load.

[0065] The control circuit includes a primary controller 20, a secondary controller 10 and a coupler 30. The primary controller 20 is located on the primary side, and the secondary controller 10 is located on the secondary side. The primary controller 20 and the secondary controller 10 are used to control the energy transfer from the input end to the output end of the isolated power converter 100. The coupler 30 is coupled to the primary controller 20 and the secondary controller 10, and is used to receive the signal sent by the secondary controller 10, and modulate the signal sent by the secondary controller 10 and send it from the secondary side to the primary side.

[0066] It should be understood that the coupler 30 can use any common primary-secondary isolation communication method, such as optical coupling, magnetic coupling or capacitive coupling transmission, or use on-off keying (OOK) technology to modulate and generate pulses to send the signal sent by the secondary controller 10.

[0067] Since the basic topology of the isolated power converter is well known to those skilled in the art, it will not be described in detail here.

[0068] Please continue reading Figure 1 The secondary side controller 10 includes a secondary side control signal generating module 101, which is used to receive a first sampling signal VFB representing the output voltage Vout of the isolated power supply and generate a first control signal Vcontrol1. The first control signal Vcontrol1 can be used to control the state of the primary side power tube Q. The coupler 30 couples the first control signal Vcontrol1 to the primary side controller 20. The specific circuit of the secondary side control signal generating module 101 will be described below.

[0069] In this embodiment, the isolated power converter 100 includes a signal sensor ( Figure 1The signal sensor is used to sense the output voltage Vout of the isolated power converter 100 and generate a first sampling signal VFB. In this embodiment, the signal sensor is located outside the secondary side controller 10 and is composed of discrete components. In other embodiments, the signal sensor can also be integrated with the secondary side controller 10 in a die or chip. Common signal sensors may include a resistor divider, etc., which are well known to those skilled in the art and will not be described in detail.

[0070] Of course, the secondary controller 10 can also control the state of the secondary synchronous rectifier SR. For example, the secondary controller 10 can generate a secondary control signal to control the state of the secondary synchronous rectifier SR according to the voltage signal on the secondary winding Ns and the first sampling signal VFB. Since the scheme of the secondary controller 10 controlling the state of the secondary synchronous rectifier SR is not the focus of the present invention, it will not be described in detail here.

[0071] Furthermore, the primary side controller 20 includes a primary side control module 21, a following secondary side control module 22, a control right switching module 23, a resistor voltage dividing module 24 and a threshold setting module 25.

[0072] The primary side control module 21 is used to implement the primary side control mode (PSR). That is, the primary side control module 21 is used to receive the second sampling signal Vcs representing the primary side current to generate the second control signal Vcontrol2 to control the state of the primary side power tube Q.

[0073] Figure 2 Specific circuit diagram of the primary side control module 21 provided in this embodiment. Figure 2 As shown, the primary control module 21 includes a first drive generation module 211. The first drive generation module 211 is used to receive the second sampling signal Vcs, the primary frequency control signal Cons_fs, and the primary conduction time control signal Cons_Vlimit, and generate a second control signal Vcontrol2 to the primary power tube Q to control the state of the primary power tube Q. Among them, the primary frequency control signal Cons_fs is used to control the conduction moment of the primary power tube Q, and the primary conduction time control signal Cons_Vlimit is used to control the conduction time of the primary power tube Q, that is, to control the turn-off moment of the primary power tube Q.

[0074] Figure 3 Detailed circuit diagram of the first drive generation module 211 provided in this embodiment. Figure 3As shown, the first drive generation module 211 includes a first comparator 2111 and a first logic circuit 2112. The first comparator 2111 is used to receive and compare the primary conduction time control signal Cons_Vlimit and the second sampling signal Vcs, and output a first comparison signal indicating the magnitude relationship between the primary conduction time control signal Cons_Vlimit and the second sampling signal Vcs. The first logic circuit 2112 is used to receive the first comparison signal and the primary frequency control signal Cons_fs to generate a second control signal Vcontrol2.

[0075] Specifically, the first logic circuit 2112 is an RS trigger, the non-inverting input terminal of the first comparator 2111 is used to receive the second sampling signal Vcs, the inverting input terminal is used to receive the primary conduction time control signal Cons_Vlimit, the output terminal outputs the first comparison signal to the reset terminal R of the RS trigger, the set terminal S of the RS trigger is used to receive the primary frequency control signal Cons_fs, and the output terminal of the RS trigger outputs the second control signal Vcontrol2, the second control signal Vcontrol2 includes the information of the turn-on time and the turn-off time of the primary power tube Q, so as to control the state of the primary power tube Q and realize the primary control mode.

[0076] Exemplarily, when the second sampling signal Vcs is higher than the primary conduction time control signal Cons_Vlimit, the output terminal of the first comparator 2111 outputs a high level to the reset terminal R of the RS trigger, and the output terminal of the RS trigger outputs a low level, thereby turning off the primary power tube Q.

[0077] In this embodiment, the primary on-time control signal Cons_Vlimit and the primary frequency control signal Cons_fs are preset fixed signals and will not change.

[0078] It should be understood that the second sampling signal Vcs may be obtained in any manner in the prior art, such as providing a sampling resistor on the primary side and sampling the voltage across the sampling resistor to obtain the second sampling signal Vcs.

[0079] The following secondary control module 22 is used to implement a secondary control mode (SSR), that is, the following secondary control module 22 can receive the first control signal Vcontrol1 provided by the coupler 30 and generate a third control signal Vcontrol3 to control the state of the primary power tube Q.

[0080] Figure 4 The circuit diagram of the secondary control signal generating module 101 and the following secondary control module 22 provided in this embodiment. Figure 4As shown, taking the control method based on the output voltage ripple as an example, in this embodiment, the secondary side control signal generating module 101 includes a second comparator 1011, and the second comparator 1011 is used to receive the first sampling signal VFB and the third reference voltage signal Vref3 and compare them to generate a second comparison signal indicating the magnitude relationship between the first sampling signal VFB and the third reference voltage signal Vref3. At this time, the second comparison signal is used as the first control signal Vcontrol1. At this time, the first control signal Vcontrol1 only contains the information of the turn-on time of the primary power tube Q. The coupler 30 receives the first control signal Vcontrol1 and sends the first control signal Vcontrol1 from the secondary side to the follower secondary side control module 22 of the primary side.

[0081] Further, the follower secondary control module 22 includes a frequency on-time control module 222 and a second drive generation module 221. The frequency on-time control module 222 receives the first control signal Vcontrol1 forwarded by the coupler 30, and generates a secondary on-time control signal SSR_Vlimit, which is used to control the on-time of the primary power tube Q, that is, the secondary on-time control signal SSR_Vlimit is used to control the turn-off moment of the primary power tube Q. The second drive generation module 221 receives the first control signal Vcontrol1, the secondary on-time control signal SSR_Vlimit and the second sampling signal Vcs sent by the coupler 30, and generates a third control signal Vcontrol3 to the primary power tube Q to control the state of the primary power tube Q.

[0082] In this embodiment, although the first control signal Vcontrol1 only includes information about the turn-on time of the primary power tube Q, the secondary control module 22 follows the frequency turn-on time control module 222 to obtain the secondary turn-on time control signal SSR_Vlimit, so that the third control signal Vcontrol3 finally output to the primary power tube Q can control the state of the primary power tube Q.

[0083] Since the specific circuit of the second driving generation module 221 can be referred to Figure 3 The specific circuit of the first driving generation module 211 is not described in detail here.

[0084] Please continue reading Figure 1 The threshold setting module 25 is used to receive the first reference voltage signal Vref1 to generate a switching threshold transition.

[0085] It is worth noting that, in this embodiment, the switching threshold transition needs to be smaller than the value of the third reference voltage signal Vref3 to increase the startup success probability of the isolated power converter.

[0086] Figure 5a A schematic diagram of a circuit for providing a first reference voltage signal Vref1 provided in this embodiment. Figure 5a As shown, the primary side controller 20 also includes an adjustment resistor R3, a first end of the adjustment resistor R3 is connected to the threshold setting module 25, a second end of the adjustment resistor R3 is connected to the primary side ground PGND, and the first end of the adjustment resistor R3 is used to provide a first reference voltage signal Vref1, that is, the voltage signal on the first end of the adjustment resistor R3 is the first reference voltage signal Vref1.

[0087] In this embodiment, the adjustment resistor R3 may be an adjustable resistor. The first reference voltage signal Vref1 may be adjusted by adjusting the resistance of the adjustment resistor R3 , thereby adjusting the magnitude of the switching threshold value transition.

[0088] Figure 5b FIG. 1 is a schematic diagram of another circuit for providing a first reference voltage signal Vref1 provided in this embodiment. Figure 5b As shown, the primary side controller 20 also includes an adjustment resistor R4 and a current source IR, the first end of the adjustment resistor R4 is connected to the current source IR and the threshold setting module 25, the second end of the adjustment resistor R4 is connected to the primary ground PGND, and the node between the first end of the adjustment resistor R4 and the current source IR is used to provide a first reference voltage signal Vref1, that is, the voltage signal on the node between the first end of the adjustment resistor R4 and the current source IR is the first reference voltage signal Vref1.

[0089] In this embodiment, the first reference voltage signal Vref1 can be adjusted by the current source IR, thereby adjusting the magnitude of the switching threshold transition.

[0090] In some embodiments, the adjustment resistor R4 may also be an adjustable resistor. Thus, in addition to adjusting the magnitude of the switching threshold transition by the current source IR, the magnitude of the switching threshold transition may also be adjusted by adjusting the resistance value of the adjustment resistor R4.

[0091] Figure 5c A schematic diagram of another circuit for providing a first reference voltage signal Vref1 provided in this embodiment. Figure 5c As shown, the primary side controller 20 further includes a voltage source VR, which is connected to the threshold setting module 25, thereby directly providing the threshold setting module 25 with a first reference voltage signal Vref1, that is, the signal output by the voltage source VR is the first reference voltage signal Vref1.

[0092] In this embodiment, the first reference voltage signal Vref1 can be adjusted by the voltage source VR, thereby adjusting the magnitude of the switching threshold transition.

[0093] Figure 6 A circuit diagram of the resistor voltage divider module 24 provided in this embodiment. As shown in FIG5 , the resistor voltage divider module 24 includes a voltage divider resistor R1 and a voltage divider resistor R2 connected in series. Specifically, a first end of the voltage divider resistor R1 is connected to a first end of an auxiliary winding Na, a second end of the voltage divider resistor R1 is connected to a first end of the voltage divider resistor R2, a second end of the voltage divider resistor R2 is connected to a second end of the auxiliary winding Na and to a primary ground PGND, and a node between the second end of the voltage divider resistor R1 and the first end of the voltage divider resistor R2 provides a third sampling signal Vout_sample representing the output voltage Vout.

[0094] In this embodiment, the voltage divider resistor R1 and / or the voltage divider resistor R2 may be an adjustable resistor. By adjusting the resistance of the voltage divider resistor R1 and / or the voltage divider resistor R2, the sampling ratio of the resistor voltage divider module 24 may be adjusted, thereby adjusting the size of the third sampling signal Vout_sample.

[0095] In some embodiments, the voltage-dividing resistors R1 and R2 may also be fixed-value resistors, and a voltage adjustment module may be connected to the output end of the resistor voltage-dividing module 24 to adjust the magnitude of the third sampling signal Vout_sample. In this case, the voltage adjustment module may be similar to Figure 5a to Figure 5c The structure in .

[0096] For further information, please refer to Figure 1 The control right switching module 23 is used to receive the third sampling signal Vout_sample, and switch the primary side controller 10 from the primary side control mode to the secondary side control mode after the third sampling signal Vout_sample meets a predetermined condition.

[0097] Specifically, in this embodiment, when the value of the third sampling signal Vout_sample is greater than the switching threshold transition, it can be determined that the third sampling signal Vout_sample meets the predetermined condition. Since the size of the third sampling signal Vout_sample and / or the size of the switching threshold transition in this embodiment can be adjusted, it is equivalent to adjusting the predetermined condition (the condition for switching between the primary side control mode and the secondary side control mode). The technical effect of adjusting the predetermined condition will be described below.

[0098] Figure 7a A schematic diagram of a control method for an isolated power converter provided in this embodiment. Figure 7bThe timing diagram of some signals of the isolated power converter provided in this embodiment. Figure 1 , Figure 7a and Figure 7b As shown, first, the isolated power converter 100 is started, the AC power source AC is applied to the isolated power converter 100, and the primary controller 20 is powered on first and starts working. The primary control module 21 obtains the second sampling signal Vcs representing the primary current to generate a second control signal Vcontrol2 to control the state of the primary power tube Q, thereby realizing the primary control mode. At this time, the output voltage Vout gradually increases.

[0099] The control right switching module 23 receives the third sampling signal Vout_sample representing the output voltage Vout in real time, and determines whether the third sampling signal Vout_sample satisfies a predetermined condition (whether the third sampling signal Vout_sample is greater than a switching threshold transition).

[0100] Further, the secondary side controller 10 is powered on and starts to work. The secondary side controller 10 obtains the first sampling signal VFB representing the output voltage Vout and generates a first control signal Vcontrol1. The coupler 30 sends the first control signal Vcontrol1 from the secondary side to the primary side.

[0101] At time t1 , the control right switching module 23 determines that the third sampling signal Vout_sample satisfies a predetermined condition (the third sampling signal Vout_sample is greater than the switching threshold transition), so the control right switching module 23 switches the primary side controller 10 from the primary side control mode to the secondary side control mode.

[0102] Afterwards, the follower secondary control module 22 receives the first control signal Vcontrol1 and generates a third control signal Vcontrol3 to control the state of the primary power tube Q, thereby realizing the secondary control mode.

[0103] It can be seen that when the isolated power converter 100 in this embodiment is started, the primary-side controller 20 is first in the primary-side control mode and then in the secondary-side control mode, thereby preventing the output voltage Vout from overshooting during startup.

[0104] Figure 8a A schematic diagram of another situation of the control method of the isolated power converter provided in this embodiment, Figure 8b The timing diagram of some signals of the isolated power converter provided in this embodiment. Figure 1 , Figure 8a and Figure 8bAs shown, first, the isolated power converter 100 is started, the AC power source AC is applied to the isolated power converter 100, and the primary controller 20 is powered on first and starts working. The primary control module 21 obtains the second sampling signal Vcs representing the primary current to generate a second control signal Vcontrol2 to control the state of the primary power tube Q, thereby realizing the primary control mode. At this time, the output voltage Vout gradually increases.

[0105] The control right switching module 23 receives the third sampling signal Vout_sample representing the output voltage Vout in real time, and determines whether the third sampling signal Vout_sample satisfies a predetermined condition (whether it is greater than a switching threshold transition).

[0106] At time t1, the control right switching module 23 determines that the third sampling signal Vout_sample meets the predetermined condition (greater than the switching threshold transition), so the control right switching module 23 switches the primary side controller 10 from the primary side control mode to the secondary side control mode. At this time, the primary side controller 10 is in a state of waiting for the first control signal Vcontrol1, and the output voltage Vout begins to drop.

[0107] After time t1, the secondary controller 10 is powered on and starts to work. The secondary controller 10 starts to obtain the first sampling signal VFB representing the output voltage Vout and generates the first control signal Vcontrol1. The coupler 30 sends the first control signal Vcontrol1 from the secondary side to the primary side.

[0108] Afterwards, the follower secondary control module 22 receives the first control signal Vcontrol1 and generates a third control signal Vcontrol3 at time t2 to control the state of the primary power tube, thereby realizing the secondary control mode.

[0109] When the isolated power converter 100 of this embodiment is started, the primary side controller 20 is first in the primary side control mode and then in the secondary side control mode, so that the output voltage Vout can be prevented from overshooting during startup. Figure 7b and Figure 8b It can be seen that when the primary-side controller 10 has switched from the primary-side control mode to the secondary-side control mode but the secondary-side controller 10 has not yet issued the first control signal Vcontrol1 , the output voltage Vout will show a downward trend.

[0110] Based on this, in this embodiment, the predetermined condition is adjustable, which is equivalent to being able to Figure 8bThe switching point between the primary side control mode and the secondary side control mode is moved to the left or right so that when the isolated power converter 100 is started, the output voltage Vout can rise smoothly, avoiding the problem of the output voltage Vout dropping, improving the reliability and safety of the system, and adjusting the application scenarios of the isolated power converter 100 so that the isolated power converter 100 can adapt to different input and output conditions.

[0111] Specifically, on the basis that the switching threshold value transition is less than the value of the third reference voltage signal Vref3, if the isolated power converter 100 cannot be started, or the isolated power converter 100 is successfully started but the output voltage Vout drops, the switching threshold value transition can be increased or the third sampling signal Vout_sample can be decreased; when the isolated power converter 100 is successfully started but the output voltage Vout does not increase smoothly, the switching threshold value transition can be decreased or the third sampling signal Vout_sample can be increased.

[0112] Embodiment 2

[0113] Fig. 9 Specific circuit diagram of the primary side control module 21 provided in this embodiment. Fig. 9 As shown, the difference from the first embodiment is that, in this embodiment, the primary control module 21 further includes an operational amplifier 214, a frequency control module 212 and a shutdown control module 213. The operational amplifier 214 is used to receive the third sampling signal Vout_sample representing the output voltage Vout and the second reference voltage signal Vref2 and perform error amplification to generate a primary error amplified signal Comp_PSR. The frequency control module 212 receives the primary error amplified signal Comp_PSR and generates a primary frequency control signal PSR_fs, which is used to control the turn-on time of the primary power tube Q. The shutdown control module 213 receives the primary error amplified signal Comp_PSR and generates a primary turn-on time control signal PSR_Vlimit, which is used to control the turn-on time of the primary power tube Q, that is, to control the turn-off time of the primary power tube Q.

[0114] Specifically, the inverting input terminal of the operational amplifier 214 is used to receive the third sampling signal Vout_sample, and the non-inverting input terminal is used to receive the second reference voltage signal Vref2. The output terminal of the operational amplifier 214 outputs the primary error amplification signal Comp_PSR to the input terminal of the frequency control module 212 and the input terminal of the shutdown control module 213. The output terminal of the frequency control module 212 outputs the primary frequency control signal PSR_fs to an input terminal of the first drive generation module 211 to control the frequency of the primary power tube Q, that is, to control the conduction time of the primary power tube Q. The output terminal of the shutdown control module 213 outputs the primary conduction time control signal PSR_Vlimit to the other input terminal of the first drive generation module 211 to control the conduction time of the primary power tube Q, that is, to control the shutdown time of the primary power tube Q. The output terminal of the first drive generation module 211 outputs the second control signal Vcontrol2 to control the state of the primary power tube Q, thereby realizing the primary control mode.

[0115] In this embodiment, the primary on-time control signal PSR_Vlimit and the primary frequency control signal PSR_fs are adaptive signals, which will change with the value of the output voltage Vout.

[0116] Fig.10 : is a relationship diagram between the primary error amplified signal Comp_PSR and the primary frequency control signal PSR_fs, and the primary error amplified signal Comp_PSR and the primary conduction time control signal PSR_Vlimit provided by this embodiment. Fig.10 As shown, the primary error amplified signal Comp_PSR is positively correlated with the primary frequency control signal PSR_fs, and increases with the increase of the primary error amplified signal Comp_PSR. The primary conduction time control signal PSR_Vlimit is constant and does not change with the change of the primary error amplified signal Comp_PSR. Of course, in other embodiments, the primary error amplified signal Comp_PSR and the primary frequency control signal PSR_fs, and the primary error amplified signal Comp_PSR and the primary conduction time control signal PSR_Vlimit can also have other relationships, and the present invention is not limited to this.

[0117] It is worth noting that, in this embodiment, the switching threshold transition needs to be smaller than the value of the second reference voltage signal Vref2 and the value of the third reference voltage signal Vref3 , so as to increase the startup success probability of the isolated power converter.

[0118] Embodiment 3

[0119] Fig.11 1 is a circuit diagram of the secondary control signal generating module 101 and the following secondary control module 22 provided in this embodiment. Fig.11 As shown, the difference from the first embodiment is that in this embodiment, the first control signal Vcontrol1 includes information about the turn-on time and turn-off time of the primary power tube Q.

[0120] Taking the control method based on output voltage ripple as an example, in this embodiment, the secondary side control signal generating module 101 includes a second comparator 1011, a second logic circuit 1012 and a timer 1013. The second comparator 1011 is used to receive the first sampling signal VFB and the third reference voltage signal Vref3 and compare them to generate a second comparison signal.

[0121] Specifically, the third reference voltage signal Vref3 is input to the in-phase output terminal of the second comparator 1011, the first sampling signal VFB is input to the inverting input terminal, and the second comparison signal is output to the output terminal. The timer 1013 starts timing from the turn-on moment of the primary power tube Q, and outputs the secondary turn-on time control signal Vcot_S after a preset time length to control the turn-on time of the primary power tube Q. The second logic circuit 1012 is used to receive the second comparison signal and the secondary turn-on time control signal Vcot_S to generate a first control signal Vcontrol1. At this time, the first control signal Vcontrol1 can include the information of the turn-on moment and the turn-off moment of the primary power tube Q. The coupler 30 receives the first control signal Vcontrol1 and forwards the first control signal Vcontrol1 to the follower secondary control module 22.

[0122] In this embodiment, the second logic circuit 1012 is an RS trigger, the reset terminal R of the RS trigger receives the second comparison signal, and the output terminal outputs the first control signal Vcontrol1. The timer 1013 receives the first control signal Vcontrol1, outputs the secondary side conduction time control signal Vcot_S, and transmits it to the reset terminal R of the trigger.

[0123] The following secondary control module 22 includes a second driving generation module 221 . The second driving generation module 221 receives the first control signal Vcontrol1 and generates a third control signal Vcontrol3 .

[0124] In this embodiment, since the first control signal Vcontrol1 includes information about the turn-on time and turn-off time of the primary power tube Q, only the second drive generation module 221 needs to be set in the follower secondary control module 22, so that the third control signal Vcontrol3 finally output to the primary power tube Q can control the state of the primary power tube Q.

[0125] In summary, in the isolated power converter and its control circuit provided by the embodiment of the present invention, the secondary controller receives the first sampling signal representing the output voltage of the isolated power converter to generate the first control signal, the primary control module receives the second sampling signal representing the current on the primary side to generate the second control signal to control the state of the primary power tube to realize the primary control mode; the following secondary control module receives the first control signal to generate the third control signal to control the state of the primary power tube to realize the secondary control mode; the control right switching module receives the third sampling signal representing the output voltage, and switches from the primary control mode to the secondary control mode after the third sampling signal meets the predetermined condition. When the isolated power converter in the present invention is started, the primary control mode is first realized by the primary control module, and when the predetermined condition is met, the control right switching module is used to switch from the primary control mode to the secondary control mode, and then the following secondary control module is used to realize the secondary control mode, so as to prevent the output voltage from overshooting when starting, and the predetermined condition can be configured and adjusted through the control circuit or the circuit parameters of the power converter to adapt to different input and output conditions.

[0126] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0127] It should also be noted that, although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

[0128] It should also be understood that, unless otherwise specified or indicated, the terms "first", "second", "third", etc. in the specification are merely used to distinguish between the various components, elements, steps, etc. in the specification, and are not used to indicate the logical relationship or sequential relationship between the various components, elements, steps, etc.

[0129] It should also be recognized that the terms described herein are only used to describe specific embodiments and are not intended to limit the scope of the invention. It should be noted that the singular forms "a" and "an" used herein and in the appended claims include plural references unless the context clearly indicates the opposite. 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. And, the word "or" should be understood to have the definition of a logical "or", rather than a logical "exclusive or" definition, unless the context clearly indicates the opposite. In addition, the implementation of the method and / or device in the embodiment of the present invention may include performing the selected task manually, automatically, or in combination.

Claims

1. A control circuit of an isolated power converter, the isolated power converter comprising a primary power tube, characterized in that: The control circuit includes a secondary side controller and a primary side controller, wherein: The secondary-side controller is used to receive a first sampling signal representing the output voltage of the isolated power converter to generate a first control signal; The primary side controller comprises: A primary side control module, used for receiving a second sampling signal representing the primary side current, so as to generate a second control signal to control the state of the primary side power tube and realize a primary side control mode; A follower secondary control module, configured to receive the first control signal to generate a third control signal to control the state of the primary power tube to implement a secondary control mode; and The control right switching module is used to receive a third sampling signal representing the output voltage, and switch the primary side control module from the primary side control mode to the secondary side control mode after the third sampling signal meets a predetermined condition, and the predetermined condition is adjustable.

2. The control circuit of the isolated power converter according to claim 1, characterized in that: When the value of the third sampling signal is greater than a switching threshold, the third sampling signal satisfies the predetermined condition.

3. The control circuit of the isolated power converter as claimed in claim 2, characterized in that: The primary side controller also includes: a resistor voltage dividing module, configured to sample the output voltage to generate the third sampling signal; and The threshold setting module is used to receive a first reference voltage signal to generate the switching threshold.

4. The control circuit of the isolated power converter as claimed in claim 3, characterized in that: The predetermined condition is adjusted by adjusting the resistance value of the voltage-dividing resistor in the resistance-dividing module and adjusting the sampling ratio of the resistance-dividing module.

5. The control circuit of the isolated power converter as claimed in claim 3, characterized in that: The predetermined condition is adjusted by adjusting the value of the first reference voltage signal.

6. The control circuit of the isolated power converter as claimed in claim 5, characterized in that: The primary side controller also includes: a current source; and, An adjustment resistor, wherein the first end of the adjustment resistor is connected to the current source and the threshold setting module and provides the first reference voltage signal, and the second end of the adjustment resistor is connected to the primary ground, and the value of the first reference voltage signal is adjusted by the current source, and / or the value of the first reference voltage signal is adjusted by adjusting the resistance value of the adjustment resistor to adjust the predetermined condition.

7. The control circuit of the isolated power converter according to claim 1, wherein: The primary side control module includes a first drive generation module, and the first drive generation module includes: a first comparator, configured to receive and compare the second sampling signal and a primary conduction time control signal to generate a first comparison signal, wherein the primary conduction time control signal is used to control the conduction time of the primary power tube; and The first logic circuit is used to receive the first comparison signal and the primary frequency control signal to generate the second control signal, and the primary frequency control signal is used to control the conduction time of the primary power tube.

8. The control circuit of the isolated power converter as claimed in claim 7, characterized in that: The primary frequency control signal and the primary conduction time control signal are both preset fixed signals.

9. The control circuit of the isolated power converter according to claim 7, wherein: The primary side control module also includes: an operational amplifier, used for receiving the third sampling signal and the second reference voltage signal and performing error amplification to generate a primary-side error amplification signal; a frequency control module, configured to receive the primary error amplified signal to generate the primary frequency control signal; and The shutdown control module is used to receive the primary side error amplification signal to generate the primary side conduction time control signal.

10. The control circuit of the isolated power converter as claimed in claim 9, characterized in that: The switching threshold is smaller than a value of the second reference voltage signal.

11. The control circuit of the isolated power converter according to claim 1, wherein: The secondary side controller includes a secondary side control signal generating module, and the secondary side control signal generating module includes: A second comparator is used to receive the first sampling signal and the third reference voltage signal and compare them to generate a second comparison signal, wherein the second comparison signal is used as the first control signal, and the first control signal includes information about the turn-on time of the primary power tube; The following secondary side control module comprises: a frequency on-time control module, configured to receive the first control signal to generate a secondary side on-time control signal; and The second driving generation module is used to receive the first control signal, the secondary side conduction time control signal and the second sampling signal to generate the third control signal.

12. The control circuit of the isolated power converter according to claim 1, wherein: The secondary side controller includes a secondary side control signal generating module, and the secondary side control signal generating module includes: A second comparator, configured to receive and compare the first sampling signal and a third reference voltage signal to generate a second comparison signal; A timer, used to start timing from the turn-on moment of the primary power tube and generate a secondary turn-on time control signal after a preset time period; a second logic circuit, configured to receive the second comparison signal and the secondary side conduction time control signal to generate the first control signal, wherein the first control signal includes information about the conduction time and the turn-off time of the primary side power tube; and The following secondary side control module comprises: The second driving generating module is used for receiving the first control signal to generate the third control signal.

13. The control circuit of the isolated power converter according to claim 11 or 12, characterized in that: The switching threshold is smaller than a value of the third reference voltage signal.

14. The control circuit of the isolated power converter according to any one of claims 3 to 12, characterized in that: When the isolated power converter fails to start, or when the isolated power converter starts successfully but the output voltage drops, the switching threshold is increased or the third sampling signal is decreased; when the isolated power converter starts successfully but the output voltage increases unevenly, the switching threshold is decreased or the third sampling signal is increased.

15. An isolated power converter, characterized in that: The invention comprises a control circuit of an isolated power converter as claimed in any one of claims 1 to 14, wherein the control circuit is used to control the state of a primary power tube.

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