Multi-output flyback converter, control method, switching power supply and chip

Abstract

The invention provides a multi-output flyback converter, a control method, a switching power supply and a chip, and belongs to the technical field of power electronics, and the multi-output flyback converter provided by the invention comprises a multi-output flyback conversion circuit, N load branches and a controller. In the process that the multi-output flyback conversion circuit provides energy for the N load branches, the controller detects the load conditions of the N load branches in real time, when it is detected that the load branches enter the light load state, the load branches and the multi-output flyback conversion circuit are controlled to be disconnected, and energy transmission to the load branches is stopped. The multi-output flyback conversion circuit supplies all energy to a non-light-load branch, and the switching frequency of the light-load branch is reduced, so that the switching loss of the light-load branch is reduced, and the overall energy conversion efficiency of the multi-output flyback converter is improved; in addition, the problem of over-high energy can be avoided by disconnecting the light load branch.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a multi-output flyback converter, a control method, a switching power supply and a chip. Background Art

[0002] With the rapid development of power electronics technology, the requirements for small size, high efficiency and high reliability of switching converters are getting higher and higher. The flyback converter is a power electronic converter that controls the energy storage and release of the transformer through a switch tube. Due to its simple topology and few components, it is widely used in switching power supplies.

[0003] For the flyback converter, in order to meet the power supply requirements of different types of loads, it is necessary to have a high power supply efficiency within the full load range. In the related art, the flyback converter includes: a primary circuit, a secondary circuit and a control circuit. In the scenario where the load is no-load or light-loaded, since the output power of the flyback converter becomes smaller, it is necessary to reduce the proportion of energy loss, thereby improving the energy conversion efficiency of the flyback converter.

[0004] In the related art, the control circuit controls the switching times of the high-frequency power switch tube on the primary circuit of the flyback converter by detecting the total load provided by the flyback converter to the load, thereby reducing the switching times of the flyback converter and improving the energy conversion efficiency of the flyback converter in no-load or light-load scenarios. However, the method of improving the energy conversion efficiency by controlling the switching times of the high-frequency power switch tube on the primary side by detecting the total load conditions in the related art is not suitable for multi-output flyback converters. Summary of the invention

[0005] The present application provides a multi-output flyback converter, a control method, a switching power supply and a chip to improve the energy conversion efficiency of the multi-output flyback converter in no-load or light-load scenarios.

[0006] In a first aspect, the present application provides a multi-output flyback converter, comprising: a multi-output flyback conversion circuit, N load branches and a controller; N is a positive integer greater than 1; the multi-output flyback conversion circuit comprises: a voltage input circuit, a first power switch tube, and a first transformer including a primary winding and a secondary winding; any of the load branches comprises a voltage output circuit and a load;

[0007] Wherein, the voltage input circuit is electrically connected to the first end of the primary winding, the second end of the primary winding is grounded through the first power switch tube, the first end of the secondary winding is electrically connected to the voltage input ends of the voltage output circuits on the N load branches respectively, the second end of the secondary winding is indirectly grounded, the N first input ends of the controller are electrically connected to the voltage output ends of the N voltage output circuits in a one-to-one correspondence, the N first output ends of the controller are electrically connected to the control signal input ends of the N voltage output circuits, and the second output end of the controller is electrically connected to the control end of the first power switch tube;

[0008] The controller is used to sample the output voltage provided to the load by the voltage output circuit on the N load branches in real time to obtain N sampled voltages;

[0009] When it is determined according to the N sampled voltages that a first load branch among the N load branches is in a light-load state, controlling the first load branch to be disconnected from the secondary winding to stop transmitting energy to the first load branch;

[0010] During the time period when energy transmission to the first load branch is stopped, if a second load branch among the N load branches is in a non-light-load state and the total load condition of the N load branches does not reach the system light-load threshold, the controller is also used to control conduction between the second load branch and the secondary winding, and all the energy output by the multi-output flyback converter is transmitted to the second load branch.

[0011] In some possible designs, the controller is also used to determine that when the first load branch exits the light load state based on the output voltage provided by the voltage output circuit on the first load branch to the load, control the conduction between the voltage output circuit on the first load branch and the secondary winding so that the secondary winding transfers energy to the first load branch.

[0012] In some possible designs, when there are multiple second load branches, the multiple second load branches are turned on complementarily.

[0013] In some possible designs, the controller includes: N load control branches, the nth load control branch corresponds to the nth load branch; n=1, 2, ..., N;

[0014] The nth load control branch comprises: an nth voltage sampling circuit, an nth operational amplifier and an nth burst mode detection circuit electrically connected in sequence; the nth voltage sampling circuit is electrically connected to a voltage output terminal of an nth voltage output circuit on the nth load branch; a first output terminal of the nth burst mode detection circuit is electrically connected to a control signal input terminal on the nth voltage sampling circuit;

[0015] The nth voltage sampling circuit is used to sample the output voltage provided by the nth voltage output circuit to the nth load to obtain an nth sampled voltage, and input the nth sampled voltage to the nth operational amplifier;

[0016] The nth operational amplifier is used to receive the reference voltage corresponding to the nth load branch and the nth sampled voltage, and to operate the reference voltage corresponding to the nth load branch and the nth sampled voltage to output an nth operation result, wherein the nth operation result is used to indicate the load condition of the nth load branch;

[0017] The nth burst mode detection circuit is used to determine whether the nth load branch is in a light-load state or a non-light-load state according to an nth operation result transmitted by the nth operational amplifier;

[0018] When it is determined that the nth load branch is in a light-load state, sending an nth control signal to a control signal input terminal of the nth voltage output circuit, so that the nth voltage output circuit is disconnected from the secondary winding according to the nth control signal;

[0019] When it is determined that the nth load branch is in a non-light-load state, the nth control signal is sent to the control signal input terminal of the nth voltage output circuit, so that the nth voltage output circuit is connected to the secondary winding according to the nth control signal.

[0020] In some possible designs, the nth burst mode detection circuit is specifically used to determine that the nth load branch is in a light load state when the nth operation result is less than a preset voltage threshold corresponding to the nth load branch, and to determine that the nth load branch is in a non-light load state when the nth operation result is greater than or equal to the preset voltage threshold.

[0021] In some possible designs, the nth voltage output circuit includes: an nth switch circuit and an nth output capacitor; the first output terminal of the nth burst mode detection circuit is electrically connected to the control signal input terminal of the nth switch circuit;

[0022] The nth burst mode detection circuit is specifically used to control the nth switch circuit to be turned on or off, so as to realize the conduction or disconnection between the nth load branch and the secondary winding.

[0023] In some possible designs, the nth switch circuit is a first unidirectional switch and a second unidirectional switch connected in series in sequence; the nth burst mode detection circuit is specifically configured to send the same nth control signal to the first unidirectional switch and the second unidirectional switch to disconnect the nth load branch from the secondary winding when the nth load branch is in a light-load state, and to send the same nth control signal to the first unidirectional switch and the second unidirectional switch to connect the nth load branch to the secondary winding when the nth load branch exits the light-load state;

[0024] Alternatively, the nth switch circuit is a back-to-back MOS tube module; the nth burst mode detection circuit is specifically used to send different nth control signals to the two MOS tubes of the back-to-back MOS tube module, respectively, to control one MOS tube in the back-to-back MOS tube module to be normally open, and control the other MOS tube in the back-to-back MOS tube module to be turned off when the nth load branch is in a light-load state, so that the nth load branch is disconnected from the secondary winding, and control the other MOS tube in the back-to-back MOS tube module to be turned on when the nth load branch exits the light-load state, so that the nth load branch is connected to the secondary winding;

[0025] Alternatively, the nth switching circuit is a bidirectional switch; the nth burst mode detection circuit is specifically used to send the nth control signal to the bidirectional switch according to whether the corresponding nth load branch is in a light-load state, so that the bidirectional switch is turned on or off along a first direction, and the first direction is the direction from the secondary winding to the nth load branch.

[0026] In some possible designs, the controller further includes: the controller further includes: an isolation communication circuit and a primary control circuit; the isolation communication circuit is arranged between the N load control branches and the primary control circuit, and the output end of the primary control circuit is electrically connected to the control end of the primary-side power switch tube;

[0027] The operational amplifiers on the N load control branches transmit the generated operation results to the primary control circuit respectively through the isolated communication circuit;

[0028] The primary control circuit is used to control the primary side power switch tube to be turned on or off according to the received N calculation results.

[0029] In a second aspect, the present application provides a multi-output flyback converter control method, characterized in that it is applied to a controller in the multi-output flyback converter according to any one of the first aspects; the method comprises:

[0030] Real-time detection of the output voltage provided to the load by the voltage output circuit on the N load branches of the multi-output flyback converter; N is a positive integer greater than 1;

[0031] When it is detected that a first load branch among the N load branches is in a light-load state, controlling the first load branch to be disconnected from the secondary winding of the transformer in the multi-output flyback converter to stop transmitting energy to the first load branch;

[0032] During the time period when energy transmission to the first load branch is stopped, if a second load branch among the N load branches is in a non-light-load state and the total load condition of the N load branches does not reach the system light-load threshold, the second load branch is controlled to be conductive with the secondary winding, and all the energy output by the multi-output conversion circuit in the multi-output flyback converter is transmitted to the second load branch.

[0033] In a third aspect, the present application provides a switching power supply, comprising: a multi-output flyback converter as described in any one of the first aspects.

[0034] In a fourth aspect, the present application provides a chip, comprising: a multi-output flyback converter as described in any one of the first aspects.

[0035] The embodiment of the present application provides a multi-output flyback converter, a control method, a switching power supply and a chip, wherein the multi-output flyback converter includes a multi-output flyback conversion circuit, N load branches and a controller. In the process of the multi-output flyback conversion circuit providing energy to the N load branches, the controller detects the load conditions of the N load branches in real time. When it is detected that a load branch enters a light-load state, the controller controls the load branch to be disconnected from the multi-output flyback conversion circuit and stops transmitting energy to the load branch. In this way, the multi-output flyback conversion circuit provides all the energy to the load branch in a non-light-load state, reduces the number of switching times of the light-load branch, thereby reducing the switching loss of the light-load branch, and improves the overall energy conversion efficiency of the multi-output flyback converter; in addition, disconnecting the light-load branch can also avoid the problem of excessive energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a structural diagram of a flyback converter in the related art shown as an example;

[0037] Figure 2 A scenario structure diagram of a multi-output flyback converter provided in an embodiment of the present application;

[0038] Figure 3 A structural diagram of a multi-output flyback converter provided in another embodiment of the present application;

[0039] Figure 4A structural diagram of a dual-output flyback converter according to an embodiment of the present application;

[0040] Figure 5 For this application Figure 4 The working timing diagram of the dual output flyback converter shown;

[0041] Figure 6 A structural diagram of a dual-output flyback converter according to another embodiment of the present application;

[0042] Figure 7 For this application Figure 6 The working timing diagram of the dual output flyback converter shown;

[0043] Figure 8 A structural diagram of a dual-output flyback converter according to another embodiment of the present application;

[0044] Fig. 9 A flowchart of a multi-output flyback converter control method provided in one embodiment of the present application. DETAILED DESCRIPTION

[0045] In this application, "at least one" means one or more, and "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c alone can represent: a, b, c, a and b, a and c, or a, b, and c, where a, b, and c can be single or multiple. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0046] The directions or positional relationships indicated by terms such as "center", "longitudinal", "lateral", "up", "down", "left", "right", "front", and "back" are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present application and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present application.

[0047] The terms "connected" and "connected" should be understood in a broad sense. For example, the "connected" or "connected" of a circuit structure can refer to not only physical connection, but also electrical connection or signal connection. For example, it can be directly connected, that is, physically connected, or indirectly connected through at least one intermediate element, as long as the circuit is connected, or it can be the internal connection of two elements; signal connection can refer to signal connection through a circuit or through a media medium, such as radio waves. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0048] Figure 1 is a structural diagram of a flyback converter in the related art. Figure 1 As shown, the flyback converter 10 in the related art includes: a first rectifier circuit TB1, a primary side input capacitor C 输入 , transformer T0, primary power switch tube S0, secondary side output capacitor C 输出 and a control circuit 11.

[0049] exist Figure 1 In the flyback converter 10 shown, a primary power switch tube S0 is taken as an N-type metal oxide semiconductor (NMOS, also called NMOS tube) as an example.

[0050] Among them, the first rectifier circuit TB1, the primary side input capacitor C 输入 The primary winding of the transformer T0 and the primary power switch S0 form a primary loop of the flyback converter 10. The input end of the first rectifier circuit TB1 receives an AC signal, and the first output end of the first rectifier circuit TB1 is connected to the primary side input capacitor C 输入 The first end of the first rectifier circuit TB1 is electrically connected to the first end of the primary side input capacitor C 输入 The second end of the primary side input capacitor C is electrically connected to the ground. 输入 The first end of is electrically connected to the first end of the primary winding of the transformer T0, the second end of the primary winding of the transformer T0 is electrically connected to the drain of the primary power switch tube S0, and the source of the primary power switch tube S0 is grounded.

[0051] The secondary winding of transformer T0 and the secondary side output capacitor C 输出 The first end of the secondary winding of the transformer T0 is connected to the secondary side output capacitor C through the blocking diode VD0. 输出 The first end of the secondary winding of the transformer T0 is electrically connected to the secondary side output capacitor C 输出 The second end of the load is connected to the secondary output capacitor C输出 both ends of .

[0052] The input terminal of the control circuit 11 and the secondary side output capacitor C 输出 The first end of the secondary winding of the transformer T0 is electrically connected to the first end of the secondary winding of the transformer T0, so that the control circuit 11 obtains the total load condition by detecting the voltage of the first end of the secondary winding of the transformer T0. And the output end of the control circuit 11 is electrically connected to the gate of the primary power switch tube S0.

[0053] In this application, the load condition refers to the power required by the load. The load condition can be divided into a light load state and a non-light load state.

[0054] The non-light load state refers to the situation where the power required by the load is greater than the preset power threshold. The non-light load state includes the heavy load state and the full load state. The heavy load state refers to the situation where the power required by the load is close to the designed maximum power. The full load state refers to the situation where the power required by the load reaches the designed maximum power.

[0055] The light load state refers to the situation where the power required by the load is less than the preset power threshold. The light load state in this application indicates that the power required by the load is small or no power is required. Among them, the situation where the load does not need power can also be called the no-load state.

[0056] For example, the preset power threshold is 30% of the maximum power.

[0057] For the sake of simplicity in the following description, a load branch in a light-load state is referred to as a light-load branch, and a load branch in a non-light-load state is referred to as a non-light-load branch.

[0058] Figure 1 When the flyback converter shown in the figure is working, when the control circuit 11 detects the secondary side output capacitor C 输出 When the voltage at the first end determines that the current total load condition is not a light load state, the control circuit 11 inputs a driving signal to the gate of the primary power switch tube S0, so that the primary power switch tube S0 is periodically switched, and controls the primary circuit of the flyback converter 10 to periodically transfer energy to the secondary circuit.

[0059] When the control circuit 11 detects the secondary side output capacitance C 输出 When the voltage at the first end of determines that the current total load condition is a light load state, the flyback converter 10 enters the burst mode and intermittently transmits waves to the load, wherein the flyback converter 10 entering the burst mode can also be understood as controlling the primary power switch tube S0 to enter the burst mode. Specifically, the control circuit 11 inputs a driving signal to the gate of the primary power switch tube S0 to change the switching cycle length of the primary power switch tube S0, thereby reducing the number of switches of the flyback converter 10. In this way, the energy provided by the flyback converter 10 to the load is reduced to match the total load condition, thereby improving the energy conversion efficiency of the flyback converter 10.

[0060] However, the method in the related art of improving the energy conversion efficiency of the flyback converter by controlling the switching times of the primary power switch tube S0 on the primary side through the control circuit detecting the total load condition is not applicable to the multi-output flyback converter.

[0061] Specifically, for a multi-output flyback converter, taking two load branches as an example, if one of the load branches is a light-load branch and the other load branch is a non-light-load branch, the total load condition may not reach the system light-load threshold (a pre-set total power threshold), and the multi-output flyback converter will not enter the burst mode to change the number of switching times of the high-frequency power switch tube on the primary side, which results in high energy loss caused by frequent switching actions of the light-load branch, which is not conducive to improving the overall energy conversion efficiency. In addition, if the multi-output flyback converter does not enter the burst mode, the energy transferred to the light-load branch may be greater than the energy required by the light-load branch, thereby triggering the light-load branch to generate overvoltage protection, which is not conducive to the stable and reliable operation of the light-load branch.

[0062] Based on this, the present application provides a multi-output flyback converter, a control method, a switching power supply and a chip, wherein the multi-output flyback converter provided by the present application includes: a multi-output flyback conversion circuit, N load branches and a controller. In the process of the multi-output flyback conversion circuit providing energy to the N load branches, the controller detects the load conditions of the N load branches in real time. When it is detected that a load branch has entered a light-load state, the controller controls the load branch to enter a burst mode, so that the light-load branch is disconnected from the multi-output flyback conversion circuit, that is, energy is stopped from being transferred to the load branch. In this way, since the total load condition does not reach the system light-load threshold, the multi-output flyback conversion circuit provides all the energy to the load branch in a non-light-load state, and the first power switch tube on the primary side of the flyback conversion circuit does not need to enter the burst mode. Disconnecting the light-load branch reduces the number of switching times of the light-load branch on the secondary side, thereby reducing the switching loss caused by the light-load branch, which is beneficial to improving the energy conversion efficiency of the multi-output flyback converter; in addition, the load branch in the light-load state does not absorb energy before exiting the light-load state, which solves the problem of excessive energy in the light-load branch and is beneficial to the stable and reliable operation of the light-load branch.

[0063] Next, the multi-output flyback converter provided in the present application is introduced in detail through some specific embodiments.

[0064] The present application is mainly applied to a multi-output flyback conversion circuit. Figure 2 This is a scenario architecture diagram of a multi-output flyback conversion circuit provided in an embodiment of the present application. Figure 2As shown, the multi-output flyback conversion circuit 20 includes: a voltage input circuit 21 located on the primary side, a first power switch tube S1, and a first transformer T1 including a primary winding Np and a secondary winding Ns. The secondary winding Ns of the first transformer T1 is electrically connected to the first end of the N load branches, and is used to provide energy to the N load branches. Wherein, N is a positive integer greater than 1.

[0065] The voltage input circuit 21 , the first power switch tube S1 and the primary winding of the first transformer form a primary loop of the multi-output flyback conversion circuit 20 .

[0066] In some embodiments, the voltage input circuit 21 includes: a second rectifier circuit TB2 and a first input capacitor Cin.

[0067] The second rectifier circuit TB2 may be a bridge circuit formed by connecting four diodes. Figure 2 As shown, the second rectifier circuit TB2 includes: a first diode VD1, a second diode VD2, a third diode VD3, and a fourth diode VD4. The cathode of the first diode VD1 is electrically connected to the anode of the second diode VD2, the cathode of the second diode VD2 is electrically connected to the cathode of the third diode VD3, the anode of the third diode VD3 is electrically connected to the cathode of the fourth diode VD4, and the anode of the fourth diode VD4 is electrically connected to the anode of the first diode VD1.

[0068] Among them, the first connection point a1 located between the first diode VD1 and the second diode VD2 and the second connection point a2 located between the third diode VD3 and the fourth diode VD4 are two input terminals of the second rectifier circuit TB2. The third connection point a3 located between the second diode VD2 and the third diode VD3 and the fourth connection point a4 located between the first diode VD1 and the fourth diode VD4 are two output terminals of the second rectifier circuit TB2.

[0069] The third connection point a3 is electrically connected to the first end of the first input capacitor Cin, and the fourth connection point a4 is electrically connected to the second end of the first input capacitor Cin and is grounded.

[0070] The third connection point a3 is electrically connected to the first end of the primary winding Np of the first transformer T1 as the output end of the voltage input circuit 21, the second end of the primary winding Np of the first transformer T1 is electrically connected to the first end of the first power switch tube S1, and the second end of the first power switch tube S1 is grounded. The control end of the first power switch tube S1 is used to receive the corresponding drive signal.

[0071] The first power switch tube S1 can be an NMOS tube or a PMOS tube. When the first power switch tube S1 is an NMOS tube, the first end is the drain of the NMOS tube, the second end is the source of the NMOS tube, and the control end is the gate of the NMOS tube. When the first power switch tube S1 is a PMOS tube, the first end is the source of the PMOS tube, the second end is the drain of the PMOS tube, and the control end is the gate of the PMOS tube.

[0072] The secondary winding Ns of the first transformer T1 and the N load branches form a secondary loop of the multi-output flyback converter circuit 20. The first end of the secondary winding Ns of the first transformer T1 is electrically connected to the first ends of the N load branches as the output end of the multi-output flyback converter circuit 20, and the second end of the secondary winding Ns of the first transformer T1 is indirectly connected to the second ends of the N load branches and is grounded.

[0073] In some embodiments, a diode is disposed between the second end of the secondary winding Ns of the first transformer T1 and the N load branches, and the unidirectional conduction characteristic of the diode can block the reverse transfer of energy from the secondary winding Ns to the primary winding Np. Specifically, the second end of the secondary winding Ns of the first transformer T1 is electrically connected to the cathode of the fifth diode VD5, and the anode of the fifth diode VD5 is connected to the second ends of the N load branches and grounded.

[0074] The nth load branch includes: an nth voltage output circuit and an nth load Rn. The nth voltage output circuit includes an nth switch circuit SWn and an nth output capacitor Cn; wherein the first end of the nth switch circuit SWn is electrically connected to the first end of the secondary winding Ns, the second end of the nth switch circuit SWn is electrically connected to the first end of the nth output capacitor Cn, the second end of the nth output capacitor Cn is grounded, and the nth load Rn is connected in parallel to both ends of the nth output capacitor Cn. wherein n=1, 2, ..., N. the nth switch circuit SWn is used to control the conduction or disconnection between the nth load branch and the secondary winding Ns of the first transformer T1. the nth output capacitor Cn is used to store the energy transmitted by the secondary winding Ns and release the energy to the nth load Rn.

[0075] The switch circuit on any load branch can be implemented in any of the following ways. Take the nth voltage output circuit as an example:

[0076] In some embodiments, the nth switch circuit SWn is a first unidirectional switch Qn1 and a second unidirectional switch Qn2 connected in series.

[0077] In some other embodiments, the nth switch circuit SWn is a back-to-back MOS tube module, and the back-to-back MOS tube module includes two MOS tubes connected back-to-back in series.

[0078] In some other embodiments, the nth switch circuit SWn is a bidirectional switch.

[0079] Figure 3 This is a structural diagram of a multi-output flyback converter provided in one embodiment of the present application. Figure 3 As shown, the multi-output flyback converter 30 includes Figure 2 The multi-output flyback converter circuit 20, the controller 22 and N load branches 23 are shown.

[0080] The input end of the controller 22 is connected to the output end of the voltage output circuit on the N load branches respectively. The controller 22 samples the output voltages provided by the N voltage output circuits to obtain N sampled voltages. The N first output ends of the controller 22 are electrically connected to the control signal input ends of the N switch circuits in a one-to-one correspondence. The controller 22 sends control signals to the control signal input ends of the N switch circuits respectively. The second output end of the controller 22 is electrically connected to the control end of the first power switch tube S1. Figure 3 In the example, taking the first power switch tube S1 as an NMOS tube, the second output end of the controller 22 is electrically connected to the gate of the first power switch tube S1.

[0081] In some embodiments, the controller 22 includes: N load control circuits 22a, an isolated communication circuit 22b, and a primary control circuit 22c.

[0082] The number of load control circuits is the same as the number of load branches, and the N load control circuits are connected to the N load branches in a one-to-one correspondence. Specifically, the first input terminal of the nth load control circuit is electrically connected to the first terminal of the nth output capacitor Cn on the nth load branch; the first output terminal of the nth load control circuit is electrically connected to the control signal input terminal of the nth switch circuit SWn on the nth load branch.

[0083] The second output ends of the N load control circuits are electrically connected to the first end of the isolated communication circuit 22b respectively. The second end of the isolated communication circuit 22b is electrically connected to the input end of the primary control circuit 22c, and the output end of the primary control circuit 22c is electrically connected to the control end of the first power switch tube S1 as the second output end of the controller 22.

[0084] Each load control circuit is used to sample the output voltage provided by the connected load branch to the load and calculate the load condition of the load branch according to the sampled voltage and the reference voltage, and then perform energy transmission control according to the load condition.

[0085] The energy transmission control performed by the load control circuit in the present application can be understood as burst mode control. The burst mode control for the load branch refers to a working mode of intermittently transmitting waves to the load branch according to the load conditions on the load branch. In the present application, when the load branch enters a light load state, the load branch enters a burst mode, and the first transformer T1 stops transmitting energy to the load branch; when the load branch exits the light load mode, the load branch exits the burst mode, and the first transformer T1 resumes providing energy to the load branch.

[0086] In addition, the N load control circuits transmit the load conditions of the load branches calculated by each of them to the primary control circuit 22c through the isolated communication circuit 22b; the primary control circuit 22c can obtain the load conditions of all load branches, and then control whether the first power switch tube S1 enters the burst mode according to the total load condition, that is, control the switching times of the first power switch tube S1, adjust the output power of the multi-output flyback conversion circuit, and make the power output by the multi-output flyback conversion circuit match the total load condition.

[0087] exist Figure 3 On the basis of the illustrated embodiment, optionally, the nth control circuit includes: an nth voltage sampling circuit, an nth operational amplifier circuit and an nth burst mode detection circuit. The output end of the nth voltage sampling circuit is electrically connected to the voltage output end of the nth voltage output circuit on the nth load branch, that is, the output end of the nth voltage sampling circuit is electrically connected to the first end of the nth output capacitor Cn. The output end of the nth voltage sampling circuit is electrically connected to the first input end of the nth operational amplifier, and the second input end of the nth operational amplifier is used to receive the reference voltage Vrefn corresponding to the nth load branch. The output end of the nth operational amplifier is electrically connected to the input end of the nth burst mode detection circuit, and the output end of the nth burst mode detection circuit is electrically connected to the control signal input end of the nth voltage output circuit, that is, the output end of the nth burst mode detection circuit is electrically connected to the control end of the nth switch circuit SWn. The output end of the nth operational amplifier is also electrically connected to the input end of the isolated communication circuit 22b.

[0088] In the present application, when the multi-output flyback converter 30 is working, when the total power of the N load branches does not reach the system light load threshold, and there are multiple load branches that are in a non-light load state, the multiple non-light load branches meet complementary conduction to prevent energy transfer between the multiple non-light load branches.

[0089] For example, when N load branches are all in a non-light-load state, complementary conduction of the N load branches means that only one load branch is conducted with the secondary winding Ns of the first transformer T1 at the same time, and the other N-1 load branches are disconnected from the secondary winding Ns of the first transformer T1.

[0090] It should be noted that the output voltages provided by the N load branches to the loads may be the same or different.

[0091] Taking N=3 as an example, the output voltages provided to the loads by the three load branches are completely different. Complementary conduction of the three load branches means that when load branch 1 is turned on, load branch 2 and load branch 3 are turned off, when load branch 2 is turned on, load branch 1 and load branch 3 are turned off, and when load branch 3 is turned on, both load branch 1 and load branch 2 are turned off.

[0092] Taking N=3 as an example, the output voltages provided to the loads by the three load branches are partially the same. Specifically, the output voltages of load branch 1 and load branch 2 are the same, and the output voltage of load branch 3 is different from the output voltages of load branch 1 and load branch 2. The complementary conduction of the three load branches means that when load branch 1 is turned on, load branch 2 and load branch 3 are turned off, when load branch 2 is turned on, load branch 1 and load branch 3 are turned off, and when load branch 3 is turned on, both load branch 1 and load branch 2 are turned off.

[0093] The complementary conduction of the N load branches can be achieved by the N load control circuits sending control signals for turning on the switch circuits on the N load branches at different times within one cycle.

[0094] Take the case where the output voltages of N load branches are completely different. Figure 3 The operation process of the multi-output flyback converter 30 shown is as follows:

[0095] The voltage input circuit in the primary loop receives an AC input signal, converts the AC input signal into a DC input signal using the second rectifier circuit, and then transmits it to the primary winding Np of the first transformer T1 through the input capacitor Cin. When the primary control circuit 22c controls the first power switch tube S1 to be turned on, the primary winding Np of the first transformer T1 transfers energy to the secondary winding Ns, and the secondary winding Ns transfers energy to the load branch in the on state among the N load branches.

[0096] In the above process, the nth voltage sampling circuit on the nth load control circuit will collect the voltage Von of the first end of the nth output capacitor Cn in real time to generate the nth sampling voltage Vosn, and transmit the nth sampling voltage Vosn to the nth operational amplifier, and the nth operational amplifier will operate the nth sampling voltage Vosn and the reference voltage Vrefn corresponding to the nth load branch to obtain the nth operation result Vcompn, and the nth operation result Vcompn can reflect the current load condition of the nth load branch. The nth operational amplifier sends the nth operation result Vcompn to the nth burst mode detection circuit, and the nth burst mode detection circuit then compares the nth operation result Vcompn with the preset voltage threshold Vcompn-th corresponding to the nth load branch; if the nth operation result Vcompn is less than the preset voltage threshold Vcompn-th, it is determined that the nth load branch enters the light load state, and the nth load branch needs to enter the burst mode, and the nth burst mode detection circuit sends the nth control signal to the nth switch circuit SWn on the nth load branch, so that the nth switch The circuit SWn is turned off, and the nth load branch is disconnected from the secondary winding Ns of the first transformer T1; if the nth operation result Vcompn is greater than or equal to the preset voltage threshold Vcompn-th, it is determined that the nth load branch exits the light load state, and the nth load branch needs to exit the burst mode. The nth burst mode detection circuit sends an nth control signal to the nth switch circuit SWn on the nth load branch, so that the nth switch circuit SWn is turned on, and the nth load branch is turned on from the secondary winding Ns of the first transformer T1, so that the secondary winding Ns can transfer energy to the nth load.

[0097] In the present application, the secondary winding Ns of the first transformer T1 transmitting energy to the load branch can also be understood as the secondary winding Ns of the first transformer T1 emitting waves to the load branch, which have the same meaning.

[0098] Based on the judgment of the nth burst mode detection circuit, if the nth load branch enters the burst mode, after the nth load branch stops emitting waves, the nth output capacitor Cn on the nth load branch will continue to discharge to maintain the output voltage level. After a period of time, the output voltage Von on the nth load branch will decrease. When the output voltage Von on the nth load branch decreases, so that the nth operation result Vcompn output by the nth operational amplifier is greater than or equal to the preset voltage threshold Vcompn-th, the nth load branch will be turned on again, exiting the burst mode, and the secondary winding Ns of the first transformer T1 will resume emitting waves to the nth load branch, that is, the multi-output flyback conversion circuit replenishes energy to the nth output capacitor Cn, so that the output voltage Von at the first end of the nth output capacitor Cn rises.

[0099] When the output voltage Von provided by the nth load branch to the nth load Rn rises, the nth burst mode detection circuit determines that the nth load branch needs to re-enter the burst mode, and sends the nth control signal to the nth switch circuit SWn on the nth load branch again, so that the nth load branch is disconnected from the secondary winding Ns of the first transformer T1. This cycle continues.

[0100] Figure 3 The multi-output flyback converter shown can control the first transformer to transfer energy to the load according to the actual power demand of the load, and by disconnecting the light-load branch, the number of switching times of the light-load branch is reduced, thereby reducing the switching loss of the light-load branch and improving the energy conversion efficiency of the multi-output flyback converter. At the same time, when the load branch is in a light-load state, stopping the wave transmission to the light-load branch can also avoid excessive energy in the light-load branch.

[0101] exist Figure 3 Based on the illustrated embodiment, the nth operational amplifier can obtain the nth operation result in the following manner but is not limited to: the nth operational amplifier calculates the voltage difference between the nth sampling voltage Vosn and the reference voltage Vrefn, and then calculates the product of the voltage difference and the coefficient kn corresponding to the nth load branch, and uses the calculated product as the nth operation result Vcompn.

[0102] The present application does not limit the specific implementation of the operational amplifier, which is only an example.

[0103] Next, a multi-output flyback converter is connected to two load branches and is implemented in different forms in combination with the switch components on the load branches. The two load branches are the first load branch and the second load branch; accordingly, the load control circuit includes the first load control circuit and the second load control circuit, wherein the first load control circuit corresponds to the first load branch, and the second load control circuit corresponds to the second load branch.

[0104] Case 1: The switch assembly is two unidirectional switches connected in series

[0105] The unidirectional switch may be a transistor, such as an NMOS transistor, a PMOS transistor, etc., or may also be a gallium nitride device.

[0106] See also Figure 4 As shown, the primary circuit of the dual-output flyback converter is Figure 2 The primary circuit structure is the same as shown, please refer to Figure 2 In addition, in the secondary circuit, the second end of the secondary winding Ns of the first transformer T1 is electrically connected to the cathode of the fifth diode VD5, and the anode of the fifth diode VD5 is connected to the second ends of the two load branches and grounded.

[0107] On the secondary loop, the first load branch includes: a first switch circuit SW1 including a first unidirectional switch Q11 and a second unidirectional switch Q12, a first output capacitor C1 and a first load R1. The first end of the first unidirectional switch Q11 is electrically connected to the first end of the secondary winding Ns of the first transformer T1, the second end of the first unidirectional switch Q12 is electrically connected to the first end of the second unidirectional switch Q12, the second end of the second unidirectional switch Q12 is electrically connected to the first end of the first output capacitor C1, and the second end of the first output capacitor C1 is grounded; the first end of the first load R1 is electrically connected to the first end of the first output capacitor C1, and the second end of the first load R1 is grounded. The control signal input ends of the first unidirectional switch Q11 and the second unidirectional switch Q12 are electrically connected to the first output end of the first burst mode detection circuit on the first load control circuit, respectively. The first burst mode detection circuit sends the same control signal D11 to control the first unidirectional switch Q11 and the second unidirectional switch Q12.

[0108] The second load branch includes: a second switch circuit SW2 including a first unidirectional switch Q21 and a second unidirectional switch Q22, a second output capacitor C2 and a second load R2. The first end of the first unidirectional switch Q21 is electrically connected to the first end of the secondary winding Ns of the first transformer T1, the second end of the first unidirectional switch Q22 is electrically connected to the first end of the second unidirectional switch Q22, the second end of the second unidirectional switch Q22 is electrically connected to the first end of the second output capacitor C2, and the second end of the second output capacitor C2 is grounded; the first end of the second load R2 is electrically connected to the first end of the second output capacitor C2, and the second end of the second load R2 is grounded. The control signal input ends of the first unidirectional switch Q21 and the second unidirectional switch Q12 are electrically connected to the output ends of the second burst mode detection circuit on the second load control circuit, respectively. The second burst mode detection circuit sends the same control signal D22 to control the first unidirectional switch Q21 and the second unidirectional switch Q22.

[0109] Figure 4 The operation of the dual output flyback converter shown is as follows:

[0110] The first load control circuit determines the load condition of the first load branch. When it is determined that the first load branch enters a light-load state, the same first control signal D11 is sent to the first unidirectional switch Q11 and the second unidirectional switch Q12 to turn off the switch circuit SW1 formed by the first unidirectional switch Q11 and the second unidirectional switch Q12. When the first load branch exits the light-load state, the same first control signal D11 is sent to the first unidirectional switch Q11 and the second unidirectional switch Q12 to turn on the switch circuit SW1 formed by the first unidirectional switch Q11 and the second unidirectional switch Q12 again.

[0111] The second load control circuit determines the load condition of the second load branch. When it is determined that the second load branch enters a light load state, the same second control signal D22 is sent to the first unidirectional switch Q21 and the second unidirectional switch Q22 to turn off the switch circuit SW2 formed by the first unidirectional switch Q21 and the second unidirectional switch Q22. When the second load branch exits the light load state, the same second control signal D22 is sent to the first unidirectional switch Q21 and the second unidirectional switch Q22 to turn on the switch circuit SW2 formed by the first unidirectional switch Q21 and the second unidirectional switch Q22 again.

[0112] It should be noted that Figure 4 In the illustrated embodiment, when the first load branch and the second load branch are not light-load branches, the first load branch and the second load branch meet complementary conduction.

[0113] Next, take the case where the first load branch is in a non-light load state, the second load branch enters a light load state, and the total load condition does not reach the system light load threshold as an example, and combine Figure 5 The signal timing diagram shown in the figure details the operation of the dual output flyback converter:

[0114] in, Figure 5 The signal timing diagram shown specifically shows the temporal changes of the output voltage Vo2 provided by the second load branch, the second operation result Vcomp2 output by the second operational amplifier, the drive signal DRV of the first power switch tube S1, the first control signal D11 output by the first burst mode detection circuit to the first load branch, and the second control signal D22 output by the second burst mode detection circuit to the second load branch.

[0115] For the output voltage Vo2 provided by the second load branch, the horizontal axis of the coordinate system represents time t, the vertical axis represents the output voltage Vo2, and the dotted line in the coordinate system represents the reference voltage Vref2 received by the second operational amplifier. The reference voltage Vref2 is the reference voltage corresponding to the second load branch.

[0116] For the second operation result Vcomp2, the horizontal axis of the coordinate system represents time t, and the vertical axis represents the second operation result Vcomp2. The dotted line in the coordinate system is the preset voltage threshold Vcomp-th2 used by the second burst mode detection circuit to perform burst mode judgment. The size of the preset voltage threshold Vcomp-th2 is related to the load size on the second load branch.

[0117] For the driving signal DRV, the horizontal axis in the coordinate system represents time t, and the vertical axis represents the level value of the driving signal DRV.

[0118] Regarding the first control signal D11 , the horizontal axis in the coordinate system represents time t, and the vertical axis represents the level value of the first control signal D11 .

[0119] Regarding the second control signal D22 , the horizontal axis in the coordinate system represents time t, and the vertical axis represents the level value of the second control signal D22 .

[0120] Please combine Figure 4 and Figure 5 As shown:

[0121] At time t0, the output voltage Vo2 is less than or equal to the reference voltage Vref2, and the second burst mode detection circuit determines that the second operation result Vcomp2 output by the second operational amplifier is less than the preset voltage threshold Vcomp-th2, and determines that the second load branch enters the light load state, and the second load branch needs to enter the burst mode, thus, the second burst mode detection circuit sends a low-level second control signal D22 to the two unidirectional switches of the second switch circuit SW2, controls the second switch circuit SW2 to turn off, and the secondary winding Ns of the first transformer T1 stops transferring energy to the second load branch. The secondary winding Ns of the first transformer T1 provides all the energy to the first load branch.

[0122] Since the second output capacitor C2 stores a certain amount of energy, the second output capacitor C2 can continue to supply power to the second load R2. The output voltage Vo2 provided by the second output capacitor C2 will gradually decrease over time, and the difference between the second output voltage Vo2 and the reference voltage Vref2 will continue to increase, and the second operation result Vcomp2 will increase accordingly.

[0123] At time t1, the second operation result Vcomp2 is equal to the preset voltage threshold Vcomp-th2, and the second burst mode detection circuit determines that the second load branch exits the light load state, that is, the second load branch needs to exit the burst mode. Since the first load branch and the second load branch meet the complementary conduction, the second switch circuit SW2 on the second load branch can only be switched to conduction after the dual-output flyback converter completes the current cycle conduction time. Figure 5 In the timing of the driving signal DRV and the first control signal D11, the second load branch needs to be turned off during the time period from t1 to t2, that is, the second control signal D22 is a low level signal during the time period from t1 to t2. Based on this, during the time period from t1 to t2, the output voltage Vo2 will further decrease.

[0124] At time t2, the dual-output flyback converter completes the conduction time of the current cycle, and the second burst mode detection circuit sends a high-level second control signal D22 to the switch component SW2 on the second load branch, so that the second load branch and the secondary winding Ns of the first transformer T1 are turned on, and the second output capacitor C2 on the second load branch is charged. The output voltage Vo2 provided by the second output capacitor C2 increases, and the difference between the output voltage Vo2 and the reference voltage Vref2 will gradually decrease, and accordingly the calculation result Vcomp2 will gradually decrease.

[0125] During the entire operation of the dual-output flyback converter, the second burst mode detection circuit monitors the load condition of the second load branch in real time.

[0126] At time t3, the second burst mode detection circuit detects again that the second operation result Vcomp2 is less than the preset voltage threshold Vcomp-th2, and the second load branch enters the light load state and the burst mode again. The second burst mode detection circuit sends a low-level second control signal D22 to the second switch circuit SW2 to control the second switch circuit SW2 to turn off. After time t3, the output voltage Vo2 will continue to decrease until the second load branch exits the light load state and the burst mode and turns on again.

[0127] In this way, the process is repeated continuously, thereby achieving control of the output voltage Vo2 on the second load branch.

[0128] In the above process, the first load branch is a non-light load branch, and the first burst mode detection circuit sends the first control signal to the switch circuit SW1 according to the pre-designed switching cycle. Combining the timing of the first control signal D11 and the timing of the drive signal DRV, it can be seen that in the time period from t1 to t2, the first control signal D11 and the drive signal DRV meet complementary conduction.

[0129] When the total load condition does not reach the system light load threshold, if it is detected that the first load branch is a light load branch and the second load branch is a non-light load branch, the control method for the first load branch is similar to the control method for the second load branch. Please refer to the detailed description in the previous text. For the sake of brevity, it will not be repeated here.

[0130] In addition, when the first load branch and the second load branch are both in a light load state, the primary control circuit 22c can determine that the total load condition reaches the system light load threshold based on the first operation result Vcomp1 transmitted by the first load control circuit and the second operation result Vcomp2 transmitted by the second load control circuit, and will change it by controlling the first power switch tube S1 to enter the burst mode (i.e., enter the intermittent wave state).

[0131] Case 2: The switch component is a back-to-back MOS tube module

[0132] The back-to-back MOS tube module is a switching circuit formed by two MOS tubes of the same type connected back-to-back in series.

[0133] Exemplarily, the back-to-back MOS tube module includes: a first NMOS tube and a second NMOS tube, the drain of the first NMOS tube is electrically connected to the drain of the second NMOS tube, the source of the first NMOS tube is electrically connected to the first end of the secondary winding Ns of the first transformer T1 as the first end of the back-to-back MOS tube module, the source of the second NMOS tube is electrically connected to the first end of the output capacitor as the second end of the back-to-back MOS tube assembly, and the gate of the first NMOS tube and the gate of the second NMOS tube are electrically connected to the two first output ends of the burst mode detection circuit on the load control circuit as the two control signal input ends of the back-to-back MOS tube assembly.

[0134] When the example back-to-back MOS tube module is working, the burst mode detection circuit sends different control signals to the two MOS tubes, wherein one NMOS tube is turned on or off based on the received control signal, and the other NMOS tube is kept normally open based on another received control signal. For example, the first NMOS tube is turned on or off based on the received control signal, and the second NMOS tube is kept normally open based on another received control signal. For another example, the second NMOS tube is turned on or off based on the received control signal, and the first NMOS tube is kept normally open based on another received control signal.

[0135] Exemplarily, the back-to-back MOS tube module includes: a first PMOS tube and a second PMOS tube, the source of the first PMOS tube is electrically connected to the source of the second PMOS tube, the drain of the first PMOS tube is electrically connected to the first end of the secondary winding Ns of the first transformer T1 as the first end of the back-to-back MOS tube module, the drain of the second PMOS tube is electrically connected to the first end of the output capacitor as the second end of the back-to-back MOS tube assembly, and the gate of the first PMOS tube and the gate of the second PMOS tube are electrically connected to the output end of the burst mode detection circuit on the load control circuit as the control signal input end of the back-to-back MOS tube assembly.

[0136] When the example back-to-back MOS tube module is working, the burst mode detection circuit sends different control signals to the two MOS tubes respectively, wherein one MOS tube is turned on or off based on the received control signal, and the other MOS tube remains normally open based on the received control signal. For example, the first PMOS tube is turned on or off based on the received control signal, and the second PMOS tube remains normally open based on another received control signal. For another example, the second PMOS tube is turned on or off based on the received control signal, and the first PMOS tube remains normally open based on another received control signal.

[0137] See also Figure 6 As shown, the primary circuit of the dual-output flyback converter is Figure 2 The primary circuit structure is the same as shown, please refer to Figure 2 In addition, in the secondary circuit, the second end of the secondary winding Ns of the first transformer T1 is electrically connected to the cathode of the fifth diode VD5, and the anode of the fifth diode VD5 is connected to the second ends of the two load branches and grounded.

[0138] Take a back-to-back MOS tube assembly in which the switch circuit is a first NMOS tube and a second NMOS tube connected in series back to back as an example.

[0139] On the secondary loop, the first load branch includes: a first switch circuit SW1 including a first NMOS transistor M11 and a second NMOS transistor M12, a first output capacitor C1 and a first load R1. The drain of the first NMOS transistor M11 is electrically connected to the drain of the second NMOS transistor M12, the source of the first NMOS transistor M11 is electrically connected to the first end of the secondary winding Ns of the first transformer T1 as the first end of the first switch circuit SW1, the source of the second NMOS transistor M12 is electrically connected to the first end of the first output capacitor C1 as the second end of the first switch circuit SW1, the gate of the first NMOS transistor M11 and the gate of the second NMOS transistor M12 are electrically connected to the first end of the first output capacitor C1 as the two control signal input ends of the first switch circuit SW1, and the gate of the first NMOS transistor M11 and the gate of the second NMOS transistor M12 are electrically connected to the two first output ends of the first burst mode detection circuit on the first load control circuit in a one-to-one correspondence. The first end of the first load R1 is electrically connected to the first end of the first output capacitor C1, and the second end of the first load R1 is electrically connected to the second end of the first output capacitor C1 and grounded.

[0140] Figure 6 In the embodiment shown, the first control signal includes a control signal D11 and a control signal D12. The first burst mode detection circuit sends the control signal D11 to the first NMOS transistor M11 on the first load branch, and sends the first control signal D12 to the second NMOS transistor M12 on the first load branch.

[0141] The second load branch includes: a second switch circuit SW2 including a first NMOS transistor M21 and a second NMOS transistor M22, a second output capacitor C2 and a second load R2. The drain of the first NMOS transistor M21 is electrically connected to the drain of the second NMOS transistor M22, the source of the first NMOS transistor M21 is electrically connected to the first end of the secondary winding Ns of the first transformer T1 as the first end of the second switch circuit SW2, the source of the second NMOS transistor M22 is electrically connected to the first end of the second output capacitor C2 as the second end of the second switch circuit SW2, the gate of the first NMOS transistor M21 and the gate of the second NMOS transistor M22 are electrically connected to the first end of the second output capacitor C2 as the two control signal input ends of the second switch circuit SW2, and the first end of the second load R2 is electrically connected to the first end of the second output capacitor C2 and grounded.

[0142] Figure 6 In the illustrated embodiment, the second control signal includes a control signal D21 and a control signal D22, wherein the second burst mode detection circuit sends the control signal D21 to the first NMOS transistor M21 on the second load branch and sends the control signal D22 to the second NMOS transistor M22 on the second load branch.

[0143] Figure 6 The operation of the dual output flyback converter shown is as follows:

[0144] The first load control circuit determines the load condition of the first load branch. When it is determined that the first load branch enters a light load state, the first NMOS transistor M11 on the first load branch is controlled to be turned off; when the first load branch exits the light load state, the first NMOS transistor M11 on the first load branch is controlled to be turned on again. In this process, the second NMOS transistor M12 on the first load branch remains in a normally on state.

[0145] The second load control circuit determines the load condition of the second load branch. When it is determined that the second load branch enters the light load state, the second NMOS transistor M22 on the second load branch is controlled to be turned off; when the second load branch exits the light load state, the second NMOS transistor M22 on the second load branch is controlled to be turned on again. In this process, the first NMOS transistor M21 on the second load branch remains normally turned on.

[0146] It should be noted that Figure 6 In the illustrated embodiment, when the first load branch and the second load branch are both in a non-light load state, complementary conduction needs to be satisfied. Figure 6During operation of the dual-output flyback converter shown, since the control signals D12 and D21 are always at a high level, the turn-on and turn-off of the two load branches are mainly determined by the control signals D11 and D22. When the first load branch and the second load branch are both in a non-light-load state, the control signals D11 and D22 need to be complementary to each other so as to satisfy the complementary conduction of the first load branch and the second load branch.

[0147] Next, take the case where the first load branch is in a non-light load state, the second load branch enters a light load state, and the total load condition does not reach the system light load threshold as an example, and combine Figure 7 The signal timing diagram shown in detail Figure 6 The working process of the dual output flyback converter shown in the figure is:

[0148] in, Figure 7 The signal timing diagram shown specifically shows the temporal changes of the output voltage Vo2 provided by the second load branch, the second operation result Vcomp2 output by the second operational amplifier, the drive signal DRV of the first power switch tube S1, the control signals D11, D12 output by the first burst mode detection circuit, and the control signals D21, D22 output by the second burst mode detection circuit.

[0149] For the output voltage Vo2 provided by the second load branch, the horizontal axis of the coordinate system represents time t, the vertical axis represents the output voltage Vo2, and the dotted line in the coordinate system is the reference voltage Vref2 received by the second operational amplifier on the second load control circuit. The reference voltage Vref2 is the reference voltage corresponding to the second load branch.

[0150] For the calculation result Vcomp2, the horizontal axis of the coordinate system represents time t, the vertical axis represents the calculation result Vcomp2, and the dotted line in the coordinate system is the preset voltage threshold Vcomp-th2 used by the second burst mode detection circuit to determine the burst mode.

[0151] For the driving signal DRV, the horizontal axis in the coordinate system represents time t, and the vertical axis represents the level value of the driving signal DRV.

[0152] For the control signal D11 , the horizontal axis in the coordinate system represents time t, and the vertical axis represents the level value of the control signal D11 .

[0153] For the control signal D22 , the horizontal axis in the coordinate system represents time t, and the vertical axis represents the level value of the control signal D22 .

[0154] For the control signal D12 / D21, the horizontal axis in the coordinate system represents time t, and the vertical axis represents the level value of the control signal D12 / D21. The second NMOS transistor M12 in the first switch circuit SW1 and the first NMOS transistor M21 in the second switch circuit SW2 are normally open, so the control signal D12 / D21 is always a high level signal.

[0155] Please combine Figure 6 and Figure 7 As shown:

[0156] First, see Figure 7 The timing diagram of the control signal D12 and the control signal D21 shown in FIG. Figure 6 When the dual-output flyback converter shown is working, the first burst mode detection circuit sends a high-level control signal D12 to the second NMOS transistor M12 in the first switch circuit SW1, so that the second NMOS transistor M12 remains normally on; the second burst mode detection circuit sends a high-level control signal D21 to the first NMOS transistor M21 in the second switch circuit SW2, so that the first NMOS transistor M21 remains normally on.

[0157] At time t0, the output voltage Vo2 is less than or equal to the reference voltage Vref2, and the second burst mode detection circuit determines that the second operation result Vcomp2 output by the second operational amplifier is less than the preset voltage threshold Vcomp-th2, and determines that the second load branch enters the light load state, that is, the second load branch needs to enter the burst mode, thus, the second burst mode detection circuit sends a low-level control signal D22 to the second NMOS tube M22 of the second switch circuit SW2, controls the second switch circuit SW2 to turn off, and the secondary winding Ns of the first transformer T1 stops transferring energy to the second load branch. The secondary winding Ns of the first transformer T1 provides all the energy to the first load branch.

[0158] Since the second output capacitor C2 on the second load branch stores a certain amount of energy, the second output capacitor C2 can continue to supply power to the second load R2. The output voltage Vo2 provided by the second output capacitor C2 will gradually decrease over time, and the difference between the output voltage Vo2 and the reference voltage Vref2 will continue to increase, and accordingly the second operation result Vcomp2 will continue to increase.

[0159] At time t1, the second operation result Vcomp2 is equal to the preset voltage threshold Vcomp-th2, and the second burst mode detection circuit determines that the second load branch exits the light load state, that is, exits the burst mode. Since the first load branch and the second load branch meet complementary conduction, the second switch circuit SW2 can only be switched to conduction after the dual-output flyback converter completes the current cycle conduction time. Among them, the dual-output flyback converter completes the current cycle conduction time can also be understood as the first power switch tube S1 completes the current cycle conduction time.

[0160] Combination Figure 7 In the timing of the driving signal DRV and the control signals D11 and D22, the first power switch tube M1 and the first switch circuit SW1 on the primary side need to complete their respective conduction within the time period from t1 to t2. Therefore, the second load branch needs to remain off within the time period from t1 to t2, that is, the control signal D22 is at a low level within the time period from t1 to t2. During the time period from t1 to t2, the second output capacitor C2 has no energy replenishment, so the output voltage Vo2 will further decrease.

[0161] At time t2, the dual-output flyback converter completes the current cycle conduction time, and the second burst mode detection circuit sends a high-level control signal D22 to the second NMOS tube M22 on the second load branch. The second NMOS tube M22 is turned on, so that the second load branch is connected to the secondary winding Ns of the first transformer T1, and the output capacitor C2 on the second load branch is charged. The output voltage Vo2 provided by the second output capacitor C2 gradually increases, and the difference between the output voltage Vo2 and the reference voltage Vref2 will gradually decrease, and accordingly the second operation result Vcomp2 will gradually decrease.

[0162] During the entire operation of the dual-output flyback converter, the second burst mode detection circuit monitors the load condition of the second load branch in real time.

[0163] At time t3, the second burst mode detection circuit detects again that the second operation result Vcomp2 is less than the preset voltage threshold Vcomp-th2, and the second load branch enters the light load state and the burst mode again. The second burst mode detection circuit sends a low-level control signal D22 to the second NMOS transistor M22 on the second load branch, and the second NMOS transistor M22 is turned off, so that the second switch circuit SW2 is turned off. After time t3, the output voltage Vo2 will continue to decrease until the second load branch exits the light load state and the burst mode and is turned on again.

[0164] In this way, the process is repeated continuously, thereby achieving control of the output voltage Vo2 on the second load branch.

[0165] In the above process, the first load branch is a non-light load branch, and the first burst mode detection circuit sends control signals D11 and D12 to the switch circuit SW1 according to the pre-designed switching cycle. Combining the timing of the first control signals D11 and D12 and the timing of the drive signal DRV, it can be seen that in the time period from t1 to t2, the first control signal D11 and the drive signal DRV meet complementary conduction.

[0166] When the total load condition does not reach the system light load threshold, if it is detected that the first load branch is a light load branch and the second load branch is a non-light load branch, the control method for the first load branch is similar to the control method for the second load branch. Please refer to the detailed description in the previous text. For the sake of brevity, it will not be repeated here.

[0167] In addition, when the first load branch and the second load branch are both in a light load state, the primary control circuit 22c can determine that the total load condition reaches the system light load threshold based on the first operation result Vcomp1 transmitted by the first load control circuit and the second operation result Vcomp2 transmitted by the second load control circuit, and will control the first power switch tube S1 to enter the burst mode (that is, enter the intermittent wave state).

[0168] Case 3: The switch component is a bidirectional switch

[0169] A bidirectional switch is a switch that can conduct in both directions. When the bidirectional switch is turned on, the current can flow in both directions. In the present application, when the bidirectional switch is turned on, the current can flow in the direction from the secondary winding to the load branch, and energy can be transferred from the secondary winding of the first transformer to the load; when the bidirectional switch is turned off, the body diode in the bidirectional switch is in a reverse series state, which can block the current from flowing in the direction from the load branch to the secondary winding.

[0170] Figure 8 This is a structural diagram of a dual-output flyback converter provided in one embodiment of the present application. Figure 8 As shown, the primary circuit of the dual-output flyback converter is Figure 2 The primary circuit structure is the same as shown, please refer to Figure 2 In addition, in the secondary circuit, the second end of the secondary winding Ns of the first transformer T1 is electrically connected to the cathode of the fifth diode VD5, and the anode of the fifth diode VD5 is connected to the second ends of the two load branches and grounded.

[0171] On the secondary loop, the first load branch includes a first bidirectional switch Q1, a first output capacitor C1 and a first load R1. The first end of the first bidirectional switch Q1 is electrically connected to the first end of the secondary winding Ns of the first transformer T1 as the first end of the first switch circuit SW1, the second end of the first bidirectional switch Q1 is electrically connected to the first end of the first output capacitor C1 as the second end of the first switch circuit SW1, and the third end of the first bidirectional switch Q1 is electrically connected to the output end of the first burst mode detection circuit on the first load control circuit as the control signal input end of the first switch circuit SW1. The second end of the first output capacitor C1 is grounded. The first end of the first load R1 is electrically connected to the first end of the first output capacitor C1, and the second end of the first load R1 is grounded. The first burst mode detection circuit sends a control signal D11 to the first bidirectional switch Q1.

[0172] The second load branch includes a second bidirectional switch Q2, a second output capacitor C2 and a second load R2. The first end of the second bidirectional switch Q2 is electrically connected to the first end of the secondary winding Ns of the first transformer T1 as the first end of the second switch circuit SW2, the second end of the second bidirectional switch Q2 is electrically connected to the first end of the second output capacitor C2 as the second end of the second switch circuit SW2, and the third end of the second bidirectional switch Q2 is electrically connected to the output end of the second burst mode detection circuit on the second load control circuit as the control signal input end of the second switch circuit SW2. The second end of the second output capacitor C2 is grounded. The first end of the second load R2 is electrically connected to the first end of the second output capacitor C2, and the second end of the second load R2 is grounded. The second burst mode detection circuit sends a control signal D22 to the second bidirectional switch Q2.

[0173] Figure 8 The operation of the dual output flyback converter shown is as follows:

[0174] The first load control circuit determines the load condition of the first load branch. When it is determined that the first load branch enters a light load state, the first bidirectional switch Q1 is controlled to conduct along the direction from the first load branch to the secondary winding; when the first load branch exits the light load state, the first bidirectional switch Q1 is controlled to be turned off.

[0175] The second load control circuit determines the load condition of the second load branch. When it is determined that the second load branch enters a light load state, the second bidirectional switch Q2 is controlled to conduct along the direction from the second load branch to the secondary winding; when the second load branch exits the light load state, the second bidirectional switch Q2 is controlled to be turned off.

[0176] Figure 8 The working process of the dual output flyback converter shown in Figure 5 The dual-output flyback converter shown in the figure has a similar working process. Figure 5For the sake of brevity, the detailed description is not repeated here.

[0177] In summary, the above Figure 5 , Figure 7 as well as Figure 8 The dual-output flyback converter shown can detect the load condition of each load branch respectively and determine whether the load branch needs to enter the burst mode. The primary control circuit 22c can control whether the first power switch tube needs to enter the burst mode.

[0178] Specifically, the following controls can be achieved:

[0179] (1) When the first load branch is in a light-load state and the total load condition does not reach the system light-load threshold, the first load branch is independently controlled to enter the burst mode; at this time, all the energy is provided to the second load branch.

[0180] (2) When the second load branch is in a light-load state and the total load condition does not reach the system light-load threshold, the second load branch is independently controlled to enter the burst mode; at this time, all the energy is provided to the first load branch.

[0181] (3) The first load branch and the second load branch are both in a light load state. Based on the total load reaching the system light load threshold, the first power switch tube S1 on the primary side is controlled to enter the burst mode.

[0182] In the present application, the light-load branch enters the burst mode, that is, the light-load branch is disconnected from the secondary winding, and there is no need to perform a switching action, which can reduce the number of switching times of the light-load branch, thereby reducing the switching loss caused by the light-load branch and improving the energy conversion efficiency of the multi-output flyback converter. At the same time, it can avoid the phenomenon of excessive load energy caused by the light-load branch absorbing energy exceeding the actual demand of the load due to unreasonable energy distribution of the multi-output flyback converter, which is conducive to improving the reliable and stable operation of the light-load branch.

[0183] Fig. 9 This is a flow chart of a multi-output flyback converter control method provided in an embodiment of the present application. The method of this embodiment is applied to a controller in a multi-output flyback converter. The structure of the multi-output flyback converter and the connection relationship between the controller and the multi-output flyback conversion circuit and N load branches in the multi-output flyback converter can be found in the previous text. Figure 3 A detailed description of the illustrated embodiment.

[0184] See also Fig. 9 As shown, the method of this embodiment includes:

[0185] S901 , sampling output voltages provided to loads by voltage output circuits on N load branches respectively to obtain N sampled voltages.

[0186] Combined with the previous article Figure 3 As shown, the controller includes N load control circuits, and the N load control circuits correspond to the N load branches one by one. Any load control circuit includes: a voltage sampling circuit, an operational amplifier, and a burst mode detection circuit.

[0187] The output voltages of the voltage output circuits connected to each other are sampled by using the voltage sampling circuit on the load control circuit, so that the sampled voltages corresponding to the N load branches can be obtained.

[0188] S902. When it is detected that the first load branch among the N load branches is in a light-load state, the first load branch is controlled to be disconnected from the secondary winding of the first transformer in the multi-output flyback converter to stop transmitting energy to the first load branch; during the time period of stopping transmitting energy to the first load branch, if a second load branch among the N load branches is in a non-light-load state, the second load branch is controlled to be connected to the secondary winding, and all the energy output by the multi-output flyback conversion circuit is transmitted to the second load branch.

[0189] Among them, the load branch in the light-load state among the N load branches is called the first load branch, and the number of the first load branches can be one or more; when the number of the first load branches is multiple, the output voltages provided to the load by the voltage output circuits on the multiple first load branches can be equal or unequal, and this application does not limit this. Similarly, the branch in the non-light-load state among the N load branches is called the second load branch, and the number of the second load branches can be one or more; when the number of the second load branches is multiple, the output voltages provided by the voltage output circuits on the multiple second load branches can be equal or unequal, and this application does not limit this.

[0190] For any load control circuit, the load control circuit uses an operational amplifier to calculate the sampling voltage and the reference voltage corresponding to the load branch to obtain an operation result, and then uses a burst mode detection circuit to compare the operation result with the preset voltage threshold to determine whether the corresponding load branch enters a light load state. In some embodiments, if the voltage comparison result is greater than or equal to the preset voltage threshold, it is determined that the load branch exits the light load state; if the voltage comparison result is less than the preset voltage threshold, it is determined that the load branch is in a light load state.

[0191] When the total load of N load branches does not reach the system light load threshold:

[0192] When the burst mode detection circuit on any load control circuit determines that the load branch is in a light-load state (i.e., the load branch is the first load branch), a control signal is sent to the switch circuit in the voltage output circuit on the first load branch to control the switch circuit to disconnect, so that the first load branch is disconnected from the secondary winding of the first transformer, thereby the secondary winding stops transmitting energy to the first load branch.

[0193] When the burst mode detection circuit on any load control circuit determines that the load branch is a non-light-load branch (that is, the load branch is the second load branch), a control signal is sent to the switch circuit in the voltage output circuit on the second load branch to control the switch circuit to be turned on, so that the second load branch is connected to the secondary winding of the first transformer, and the secondary winding can provide all the energy to the second load branch.

[0194] It should be noted that the total load condition of N load branches in the present application represents the sum of the powers required by the N load branches.

[0195] In this embodiment, the multi-output flyback converter can control the first transformer to transfer energy to the load according to the actual power demand of the load, thereby reducing the energy loss caused by the light-load branch and improving the energy conversion efficiency of the multi-output flyback converter. At the same time, it can avoid excessive energy in the light-load branch.

[0196] exist Fig. 9 Based on the embodiment shown, after S902, the method further includes:

[0197] S903. When it is determined, based on the sampled voltage of the first load branch, that the first load branch exits the light-load state, the voltage output circuit on the first load branch is controlled to be conductive with the secondary winding of the first transformer, so that the secondary winding transmits energy to the first load branch.

[0198] The load control circuit corresponding to the first load branch performs energy transmission control on the first load branch. Specifically, the voltage sampling circuit on the load control branch samples the output voltage provided to the load by the voltage output circuit on the first load branch in real time, and uses an operational amplifier to calculate the sampled voltage and the reference voltage corresponding to the first load branch to obtain a voltage comparison result. When the burst mode detection circuit determines that the voltage comparison result is greater than or equal to the preset voltage threshold corresponding to the first load branch, it is determined that the first load branch exits the light load state, and the first load branch is controlled to be turned on with the secondary winding of the first transformer, so as to replenish energy to the first load branch through the secondary winding.

[0199] It should be noted that in Fig. 9 The contents not disclosed in detail in the method embodiment shown in the figure can be referred to in the previous text. Figures 2 to 8 For the sake of brevity, the detailed description of the illustrated embodiment will not be repeated here.

[0200] This embodiment can transfer energy to the load within a suitable time according to the actual power demand of the load branch, thereby avoiding energy overcharging and improving the energy conversion efficiency of the entire system.

[0201] An embodiment of the present application also provides a controller, which is used to execute the operations performed by the controller in any of the aforementioned embodiments.

[0202] An embodiment of the present application also provides a chip, including: a multi-output flyback converter as shown in any of the above embodiments.

[0203] An embodiment of the present application also provides a switching power supply, including: a multi-output flyback converter as shown in any of the above embodiments.

[0204] Finally, it should be noted that the above embodiments are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A multi-output flyback converter, characterized in that: include: A multi-output flyback conversion circuit, N load branches and a controller; N is a positive integer greater than 1; The multi-output flyback conversion circuit comprises: a voltage input circuit, a first power switch tube, and a first transformer including a primary winding and a secondary winding; any of the load branches comprises a voltage output circuit and a load; Wherein, the voltage input circuit is electrically connected to the first end of the primary winding, the second end of the primary winding is grounded through the first power switch tube, the first end of the secondary winding is electrically connected to the voltage input ends of the voltage output circuits on the N load branches respectively, the second end of the secondary winding is indirectly grounded, the N first input ends of the controller are electrically connected to the voltage output ends of the N voltage output circuits in a one-to-one correspondence, the N first output ends of the controller are electrically connected to the control signal input ends of the N voltage output circuits, and the second output end of the controller is electrically connected to the control end of the first power switch tube; The controller is used to sample the output voltage provided to the load by the voltage output circuit on the N load branches in real time to obtain N sampled voltages; When it is determined according to the N sampled voltages that a first load branch among the N load branches is in a light-load state, controlling the first load branch to be disconnected from the secondary winding to stop transmitting energy to the first load branch; During the time period when energy transmission to the first load branch is stopped, if a second load branch among the N load branches is in a non-light-load state and the total load condition of the N load branches does not reach the system light-load threshold, the controller is also used to control conduction between the second load branch and the secondary winding, and all the energy output by the multi-output flyback converter is transmitted to the second load branch.

2. The multi-output flyback converter according to claim 1, characterized in that: The controller is also used to determine that when the first load branch exits the light load state based on the output voltage provided by the voltage output circuit on the first load branch to the load, control the conduction between the voltage output circuit on the first load branch and the secondary winding so that the secondary winding transmits energy to the first load branch.

3. The multi-output flyback converter according to claim 1, characterized in that: When there are multiple second load branches, the multiple second load branches are complementarily turned on.

4. The multi-output flyback converter according to claim 1, characterized in that: The controller comprises: N load control branches, the nth load control branch corresponds to the nth load branch; n=1, 2, ..., N; The nth load control branch comprises: an nth voltage sampling circuit, an nth operational amplifier and an nth burst mode detection circuit electrically connected in sequence; the nth voltage sampling circuit is electrically connected to a voltage output terminal of an nth voltage output circuit on the nth load branch; a first output terminal of the nth burst mode detection circuit is electrically connected to a control signal input terminal on the nth voltage sampling circuit; The nth voltage sampling circuit is used to sample the output voltage provided by the nth voltage output circuit to the nth load to obtain an nth sampled voltage, and input the nth sampled voltage to the nth operational amplifier; The nth operational amplifier is used to receive the reference voltage corresponding to the nth load branch and the nth sampled voltage, and to operate the reference voltage corresponding to the nth load branch and the nth sampled voltage to output an nth operation result, wherein the nth operation result is used to indicate the load condition of the nth load branch; The nth burst mode detection circuit is used to determine whether the nth load branch is in a light-load state or a non-light-load state according to an nth operation result transmitted by the nth operational amplifier; When it is determined that the nth load branch is in a light-load state, sending an nth control signal to a control signal input terminal of the nth voltage output circuit, so that the nth voltage output circuit is disconnected from the secondary winding according to the nth control signal; When it is determined that the nth load branch is in a non-light-load state, the nth control signal is sent to the control signal input terminal of the nth voltage output circuit, so that the nth voltage output circuit is connected to the secondary winding according to the nth control signal.

5. The multi-output flyback converter according to claim 4, characterized in that: The nth burst mode detection circuit is specifically used to determine that the nth load branch is in a light load state when the nth operation result is less than a preset voltage threshold corresponding to the nth load branch, and to determine that the nth load branch is in a non-light load state when the nth operation result is greater than or equal to the preset voltage threshold.

6. The multi-output flyback converter according to claim 4, characterized in that: The nth voltage output circuit comprises: an nth switch circuit and an nth output capacitor; the first output terminal of the nth burst mode detection circuit is electrically connected to the control signal input terminal of the nth switch circuit; The nth burst mode detection circuit is specifically used to control the nth switch circuit to be turned on or off, so as to realize the conduction or disconnection between the nth load branch and the secondary winding.

7. The multi-output flyback converter according to claim 6, characterized in that: The nth switch circuit is a first unidirectional switch and a second unidirectional switch connected in series in sequence; the nth burst mode detection circuit is specifically used to send the same nth control signal to the first unidirectional switch and the second unidirectional switch to disconnect the nth load branch from the secondary winding when the nth load branch is in a light-load state, and to send the same nth control signal to the first unidirectional switch and the second unidirectional switch to connect the nth load branch to the secondary winding when the nth load branch exits the light-load state; Alternatively, the nth switch circuit is a back-to-back MOS tube module; the nth burst mode detection circuit is specifically used to send different nth control signals to the two MOS tubes of the back-to-back MOS tube module, respectively, to control one MOS tube in the back-to-back MOS tube module to be normally open, and control the other MOS tube in the back-to-back MOS tube module to be turned off when the nth load branch is in a light-load state, so that the nth load branch is disconnected from the secondary winding, and control the other MOS tube in the back-to-back MOS tube module to be turned on when the nth load branch exits the light-load state, so that the nth load branch is connected to the secondary winding; Alternatively, the nth switching circuit is a bidirectional switch; the nth burst mode detection circuit is specifically used to send the nth control signal to the bidirectional switch according to whether the corresponding nth load branch is in a light-load state, so that the bidirectional switch is turned on or off along a first direction, and the first direction is the direction from the secondary winding to the nth load branch.

8. The multi-output flyback converter according to claim 4, characterized in that: The controller further comprises: an isolation communication circuit and a primary control circuit; the isolation communication circuit is arranged between the N load control branches and the primary control circuit, and the output end of the primary control circuit is electrically connected to the control end of the primary-side power switch tube; The operational amplifiers on the N load control branches transmit the generated operation results to the primary control circuit respectively through the isolated communication circuit; The primary control circuit is used to control the primary side power switch tube to be turned on or off according to the received N calculation results.

9. A multi-output flyback converter control method, characterized in that: A controller applied to a multi-output flyback converter according to any one of claims 1 to 8; the method comprising: Sampling the output voltage provided to the load by the voltage output circuit on the N load branches of the multi-output flyback converter in real time to obtain N sampled voltages; N is a positive integer greater than 1; When it is determined according to the N sampled voltages that a first load branch among the N load branches is in a light-load state, controlling the first load branch to be disconnected from a secondary winding of a first transformer in the multi-output flyback converter to stop transmitting energy to the first load branch; During the time period when energy transmission to the first load branch is stopped, if a second load branch among the N load branches is in a non-light-load state and the total load condition of the N load branches does not reach the system light-load threshold, the second load branch is controlled to be conductive with the secondary winding, and all the energy output by the multi-output conversion circuit in the multi-output flyback converter is transmitted to the second load branch.

10. A switching power supply, characterized in that: include: A multi-output flyback converter as claimed in any one of claims 1 to 8.

11. A chip, characterized in that: include: A multi-output flyback converter as claimed in any one of claims 1 to 8.

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