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

Abstract

The application 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. The multi-output flyback converter 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 to the N load branches, the controller detects the load conditions of the N load branches in real time, and 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 transferring energy to the load branch. In this way, the multi-output flyback conversion circuit provides energy to the non-light load branch, reduces the switching frequency of the light load branch, reduces 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 excessively high energy.

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 demand for small size, high efficiency, and high reliability in switching converters is increasing. The flyback converter is a power electronic converter that uses a switching transistor to control the storage and release of energy in a transformer. Due to its simple topology and minimal components, it is widely used in switching power supplies.

[0003] To meet the power supply requirements of different load types, flyback converters require high power efficiency across the entire load range. Related technologies include a primary circuit, a secondary circuit, and a control circuit. In scenarios where the load is no-load or lightly loaded, the flyback converter's output power decreases, necessitating a reduction in the proportion of energy losses to improve the flyback converter's energy conversion efficiency.

[0004] In related art, a control circuit controls the switching frequency of the high-frequency power switch in the primary circuit of the flyback converter by detecting the total load provided by the flyback converter to the load, thereby reducing the switching frequency of the flyback converter and improving the flyback converter's energy conversion efficiency in no-load or light-load scenarios. However, this method of improving energy conversion efficiency by controlling the switching frequency of the high-frequency power switch on the primary side by detecting the total load in 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] The voltage input circuit is electrically connected to a first end of the primary winding, a second end of the primary winding is grounded via the first power switch tube, a first end of the secondary winding is electrically connected to voltage input ends of the voltage output circuits on the N load branches, and a 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 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 configured to sample the output voltages provided to the loads by the voltage output circuits 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 further used to control conduction between the second load branch and the secondary winding, so that all energy output by the multi-output flyback converter is transmitted to the second load branch.

[0011] In some possible designs, the controller is further used to control the conduction between the voltage output circuit on the first load branch and the secondary winding when determining that 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, so that the secondary winding transmits energy to the first load branch.

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

[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 of the nth voltage sampling circuit;

[0015] The nth voltage sampling circuit is configured 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 being configured to receive a reference voltage corresponding to the nth load branch and the nth sampled voltage, and to perform an operation on 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 a load condition of the nth load branch;

[0017] The nth burst mode detection circuit is configured 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 end 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 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; the nth burst mode detection circuit is specifically configured to, when the nth load branch is in a light-load state, 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; and, when the nth load branch exits the light-load state, 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;

[0024] Alternatively, the nth switching circuit is a back-to-back MOS transistor module; the nth burst mode detection circuit is specifically configured to send different nth control signals to the two MOS transistors in the back-to-back MOS transistor module, respectively, to control one MOS transistor in the back-to-back MOS transistor module to be normally on, control the other MOS transistor in the back-to-back MOS transistor module to be turned off when the nth load branch is in a light-load state, thereby disconnecting the nth load branch from the secondary winding; and control the other MOS transistor in the back-to-back MOS transistor module to be turned on when the nth load branch exits the light-load state, thereby connecting the nth load branch 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: an isolation communication circuit and a primary control circuit; the isolation communication circuit is provided between the N load control branches and the primary control circuit, and an output end of the primary control circuit is electrically connected to a 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 by being applied to a controller in the multi-output flyback converter according to any one of the first aspects; the method comprising:

[0030] Real-time detection of output voltages provided to loads by voltage output circuits on N load branches of the multi-output flyback converter, where 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 a time period in which 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 of the N load branches does not reach a system light-load threshold, conduction is controlled between the second load branch and the secondary winding, and all 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] Embodiments of the present application provide a multi-output flyback converter, a control method, a switching power supply, and a chip. The multi-output flyback converter includes a multi-output flyback conversion circuit, N load branches, and a controller. While the multi-output flyback conversion circuit is providing energy to the N load branches, the controller monitors the load conditions of the N load branches in real time. When a load branch is detected to be lightly loaded, the controller disconnects the load branch from the multi-output flyback conversion circuit, halting energy transfer to the load branch. This allows the multi-output flyback conversion circuit to fully supply energy to the load branch in a non-lightly loaded state, reducing the number of switching cycles in the lightly loaded branch and thus reducing switching losses in the lightly loaded branch, thereby improving the overall energy conversion efficiency of the multi-output flyback converter. Furthermore, disconnecting the lightly loaded branch can also prevent the problem of excessive energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0037] Figure 2 A diagram showing a structure of a multi-output flyback converter according to 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 4This is a 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 in FIG.

[0041] Figure 6 This is 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 in FIG.

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

[0044] Figure 9 This is a flow chart 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" refers to one or more, and "plurality" refers to 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: the existence of A alone, the existence of A and B at the same time, and the existence of B alone, where A and B can be singular or plural. The character " / " generally indicates that the objects associated 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 or plural items. For example, at least one of a alone, b alone, or c alone can represent: a alone, b alone, c alone, a and b in combination, a and c in combination, b and c in combination, or a, b, and c in combination, where a, b, and c can be single or multiple. In addition, the terms "first" and "second" are used for descriptive purposes only and are not to 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. Therefore, they should not be understood as limiting the present application.

[0047] The terms "connected" and "connect" should be interpreted broadly. For example, "connected" or "connected" in a circuit structure can refer not only to a physical connection, but also to an electrical connection or a signal connection. For example, it can be a direct connection, i.e., a physical connection, or an indirect connection through at least one intermediate component, as long as the circuit is interconnected. It can also refer to internal connectivity between two components. Signal connection can refer not only to signal connection through circuits but also to signal connection through media, such as radio waves. Those skilled in the art will understand the specific meanings of the above terms in this application on a case-by-case basis.

[0048] Figure 1 FIG1 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 S0, secondary side output capacitor C 输出 and a control circuit 11.

[0049] exist Figure 1 In the flyback converter 10 shown, the 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 the primary circuit of the flyback converter 10. The input end of the first rectifier circuit TB1 receives the 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 is electrically connected to the ground, and the load is connected in parallel to the secondary side 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. In this way, 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. 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] A non-light load state refers to a situation where the load power required exceeds the preset power threshold. Non-light load states include heavy load and full load. A heavy load state refers to a situation where the load power required is close to the designed maximum power, and a full load state refers to a situation where the load power required reaches the designed maximum power.

[0055] A light load state refers to a situation where the power required by the load is less than a preset power threshold. In this application, a light load state indicates that the power required by the load is small or no power is required. Among them, the situation where the load does not require power can also be called a 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 works, the control circuit 11 detects the secondary side output capacitor C 输出 When the voltage at the first end of the control circuit 11 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, causing the primary power switch tube S0 to switch periodically, thereby controlling 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 terminal of determines that the current total load condition is light, the flyback converter 10 enters burst mode and intermittently transmits power to the load. Entering burst mode by the flyback converter 10 can also be understood as controlling the primary power switch S0 to enter burst mode. Specifically, the control circuit 11 inputs a drive signal to the gate of the primary power switch S0, changing the duration of the primary power switch S0's switching cycle, thereby reducing the number of switching cycles of the flyback converter 10. This reduces the energy provided to the load by the flyback converter 10 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 S0 on the primary side by detecting the total load condition through a control circuit is not applicable to a multi-output flyback converter.

[0061] Specifically, for a multi-output flyback converter with two load branches, for example, if one load branch is lightly loaded and the other is not lightly loaded, the total load may not reach the system light-load threshold (a pre-set total power threshold). The multi-output flyback converter will not enter burst mode to change the switching frequency of the high-frequency power switch on the primary side. This results in high energy loss due to frequent switching in the light-load branch, which is not conducive to improving overall energy conversion efficiency. Furthermore, if the multi-output flyback converter does not enter burst mode, the energy transferred to the light-load branch may exceed the energy required by the light-load branch, triggering overvoltage protection in the light-load branch, 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. The multi-output flyback converter provided by the present application includes: a multi-output flyback conversion circuit, N load branches, and a controller. During 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, disconnecting the light-load branch from the multi-output flyback conversion circuit, i.e., stopping energy transfer 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 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 a 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 by the present application is introduced in detail through some specific embodiments.

[0064] This application is mainly used in multi-output flyback conversion circuits. Figure 2 This is a diagram of the architecture of a multi-output flyback converter circuit according to an embodiment of the present application. Figure 2As shown, the multi-output flyback converter circuit 20 includes a voltage input circuit 21 on the primary side, a first power switch 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 ends of N load branches for providing energy to the N load branches. N is a positive integer greater than 1.

[0065] The voltage input circuit 21 , the first power switch 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] A first connection point a1 between the first diode VD1 and the second diode VD2 and a second connection point a2 between the third diode VD3 and the fourth diode VD4 serve as two input terminals of the second rectifier circuit TB2. A third connection point a3 between the second diode VD2 and the third diode VD3 and a fourth connection point a4 between the first diode VD1 and the fourth diode VD4 serve as 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, serving as the output terminal of the voltage input circuit 21, is electrically connected to a first terminal of the primary winding Np of the first transformer T1. A second terminal of the primary winding Np of the first transformer T1 is electrically connected to a first terminal of the first power switch S1. The second terminal of the first power switch S1 is grounded. The control terminal of the first power switch S1 is configured to receive a corresponding drive signal.

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

[0072] The secondary winding Ns of the first transformer T1 and the N load branches form the secondary circuit of the multi-output flyback converter circuit 20. The first end of the secondary winding Ns of the first transformer T1, serving as the output end of the multi-output flyback converter circuit 20, is electrically connected to the first ends of the N load branches. 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. The diode's unidirectional conduction characteristic can block reverse energy transfer 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 a fifth diode VD5, and the anode of the fifth diode VD5 is connected to the second ends of the N load branches and to ground.

[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. A first end of the nth switch circuit SWn is electrically connected to a first end of the secondary winding Ns, a second end of the nth switch circuit SWn is electrically connected to a first end of the nth output capacitor Cn, a second end of the nth output capacitor Cn is grounded, and the nth load Rn is connected in parallel across the nth output capacitor Cn. Where 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 energy transferred from the secondary winding Ns and release 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 transistor module, which includes two MOS transistors 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 by an 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 voltage 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 22 a , an isolated communication circuit 22 b , and a primary control circuit 22 c .

[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; and 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 terminals of the N load control circuits are electrically connected to the first terminal of the isolated communication circuit 22b. The second terminal of the isolated communication circuit 22b is electrically connected to the input terminal of the primary control circuit 22c. The output terminal of the primary control circuit 22c serves as the second output terminal of the controller 22 and is electrically connected to the control terminal of the first power switch S1.

[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 based on 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 this application can be understood as burst mode control. Burst mode control for a load branch refers to an operating mode in which intermittent power is transmitted to the load branch based on the load conditions on the load branch. In this application, when the load branch enters a light-load state, the load branch enters burst mode, and the first transformer T1 stops transmitting energy to the load branch; when the load branch exits light-load mode, the load branch exits burst mode, and the first transformer T1 resumes supplying 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, controls the switching times of the first power switch tube S1, adjusts the output power of the multi-output flyback conversion circuit, and makes the output power of the multi-output flyback conversion circuit match the total load condition.

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

[0088] In the present application, when the multi-output flyback converter 30 is operating, 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 all N load branches are in a non-light-load state, complementary conduction of the N load branches means that at the same time only one load branch is conductively connected to the secondary winding Ns of the first transformer T1, 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 to the load by the N load branches may be the same or different.

[0091] Taking N=3 as an example, the three load branches provide completely different output voltages to the loads. 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; 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. 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; 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 as an example. 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 it into a DC input signal using the second rectifier circuit, and then transmits it to the primary winding Np of the first transformer T1 via the input capacitor Cin. When the primary control circuit 22c turns on the first power switch S1, the primary winding Np of the first transformer T1 transfers energy to the secondary winding Ns, which in turn transfers energy to the load branches that are in the conducting state among the N load branches.

[0096] During the above process, the nth voltage sampling circuit in the nth load control circuit samples the voltage Von at the first terminal of the nth output capacitor Cn in real time to generate the nth sampled voltage Vosn. The nth sampled voltage Vosn is then transmitted to the nth operational amplifier. The nth operational amplifier performs an operation on the nth sampled voltage Vosn and the reference voltage Vrefn corresponding to the nth load branch to obtain the nth operation result Vcompn. The nth operation result Vcompn reflects the current load condition of the nth load branch. The nth operational amplifier transmits the nth operation result Vcompn to the nth burst mode detection circuit. 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 has entered a light load state and needs to enter burst mode. The nth burst mode detection circuit then transmits the nth control signal to the nth switch circuit SWn on the nth load branch to activate the nth switch circuit SWn. 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 has exited 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, turning on the nth switch circuit SWn. The nth load branch is then connected to 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 determination of the nth burst mode detection circuit, if the nth load branch enters burst mode, after the nth load branch stops generating power, 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, causing the nth operational result Vcompn output by the nth operational amplifier to be greater than or equal to the preset voltage threshold Vcompn-th, the nth load branch will turn back on, exiting burst mode. The secondary winding Ns of the first transformer T1 will resume generating power to the nth load branch. In other words, the multi-output flyback converter circuit replenishes energy to the nth output capacitor Cn, causing the output voltage Von at the first terminal of the nth output capacitor Cn to recover.

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

[0100] Figure 3 The illustrated multi-output flyback converter controls the first transformer to transfer energy to the load based on the load's actual power demand. By disconnecting the lightly loaded branch, the number of switching cycles in the lightly loaded branch is reduced, thereby reducing switching losses in the lightly loaded branch and improving the energy conversion efficiency of the multi-output flyback converter. Furthermore, when the load branch is lightly loaded, stopping the transmission of power to the lightly loaded branch also prevents excessive energy in the lightly loaded 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, 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] This application does not limit the specific implementation of the operational amplifier, which is only an example.

[0103] Next, we will use a multi-output flyback converter connected to two load branches and implementing different forms of switch components on the load branches as examples. The two load branches are a first load branch and a second load branch; accordingly, the load control circuit includes a first load control circuit and a 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 consists of 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 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 shown is the same, 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] In the secondary circuit, the first load branch includes a first switching circuit SW1 comprising 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 and second unidirectional switches Q11 and Q12 are respectively electrically connected to the first output end of the first burst mode detection circuit in the first load control circuit. The first burst mode detection circuit sends the same control signal D11 to control the first and second unidirectional switches Q11 and Q12.

[0108] The second load branch includes a second switch circuit SW2 comprising 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 and second unidirectional switches Q21 and Q22 are respectively electrically connected to the output ends of the second burst mode detection circuit in the second load control circuit. The second burst mode detection circuit sends the same control signal D22 to control the first and second unidirectional switches Q21 and 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 has entered a light-load state, the first load control circuit sends the same first control signal D11 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 first load control circuit sends the same first control signal D11 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 has entered a light-load state, the second load control circuit sends the same second control signal D22 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 second load control circuit sends the same second control signal D22 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 neither the first load branch nor the second load branch is a light-load branch, the first load branch and the second load branch meet the complementary conduction condition.

[0113] Next, take the example 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. Figure 5 The signal timing diagram shown below details the operation of the dual-output flyback converter:

[0114] in, Figure 5 The signal timing diagram shown specifically illustrates 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 when performing 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. 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, indicating that the second load branch has entered a light-load state and needs to enter burst mode. Therefore, 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, controlling the second switch circuit SW2 to turn off. 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 then provides all its energy to the first load branch.

[0122] Because the second output capacitor C2 stores a certain amount of energy, it can continue to supply power to the second load R2. The output voltage Vo2 provided by the second output capacitor C2 gradually decreases over time, and the difference between the second output voltage Vo2 and the reference voltage Vref2 increases, correspondingly increasing the second computation result Vcomp2.

[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 has exited 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 sequence of the driving signal DRV and the first control signal D11, the second load branch needs to remain off during the time period t1 to t2. That is, the second control signal D22 is a low-level signal during the time period t1 to t2. Based on this, the output voltage Vo2 will further decrease during the time period t1 to t2.

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

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

[0127] This process is repeated continuously, thereby achieving control over the output voltage Vo2 on the second load branch.

[0128] During the above process, the first load branch is not lightly loaded, 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 the first control signal D11 and the drive signal DRV are complementary to each other during the time period t1 to t2.

[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 article. For the sake of brevity, it will not be repeated here.

[0130] In addition, when both the first load branch and the second load branch are in a light-load state, the primary control circuit 22c can determine that the total load condition has reached the system light-load threshold based on the first calculation result Vcomp1 transmitted by the first load control circuit and the second calculation 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 transistor module includes: a first NMOS transistor and a second NMOS transistor, the drain of the first NMOS transistor is electrically connected to the drain of the second NMOS transistor, the source of the first NMOS transistor serves as the first end of the back-to-back MOS transistor module and is electrically connected to the first end of the secondary winding Ns of the first transformer T1, the source of the second NMOS transistor serves as the second end of the back-to-back MOS transistor assembly and is electrically connected to the first end of the output capacitor, and the gate of the first NMOS transistor and the gate of the second NMOS transistor serve as two control signal input ends of the back-to-back MOS transistor assembly and are electrically connected to the two first output ends of the burst mode detection circuit on the load control circuit.

[0134] When the exemplary back-to-back MOS transistor module is operating, the burst mode detection circuit sends different control signals to the two MOS transistors. One NMOS transistor is turned on or off based on the received control signal, while the other NMOS transistor remains normally open based on another received control signal. For example, the first NMOS transistor is turned on or off based on the received control signal, while the second NMOS transistor remains normally open based on the received control signal. In another example, the second NMOS transistor is turned on or off based on the received control signal, while the first NMOS transistor remains normally open based on the 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 serves as the first end of the back-to-back MOS tube module and is electrically connected to the first end of the secondary winding Ns of the first transformer T1, the drain of the second PMOS tube serves as the second end of the back-to-back MOS tube assembly and is electrically connected to the first end of the output capacitor, and the gate of the first PMOS tube and the gate of the second PMOS tube serve as the control signal input end of the back-to-back MOS tube assembly and are electrically connected to the output end of the burst mode detection circuit on the load control circuit.

[0136] When the exemplary back-to-back MOS transistor module is operating, the burst mode detection circuit sends different control signals to the two MOS transistors. One MOS transistor is turned on or off based on the received control signal, while the other MOS transistor remains normally open based on the received control signal. For example, the first PMOS transistor is turned on or off based on the received control signal, while the second PMOS transistor remains normally open based on another received control signal. In another example, the second PMOS transistor is turned on or off based on the received control signal, while the first PMOS transistor remains normally open based on the other 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 shown is the same, 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 transistor assembly in which the switch circuit is a first NMOS transistor and a second NMOS transistor connected back-to-back in series as an example.

[0139] In the secondary circuit, the first load branch includes a first switching circuit SW1 comprising 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, serving as the first end of the first switching circuit SW1, is electrically connected to the first end of the secondary winding Ns of the first transformer T1. The source of the second NMOS transistor M12, serving as the second end of the first switching circuit SW1, is electrically connected to the first end of the first output capacitor C1. The gates of the first NMOS transistor M11 and the second NMOS transistor M12, serving as the two control signal inputs of the first switching circuit SW1, are electrically connected in a one-to-one correspondence to the two first outputs of the first burst mode detection circuit on the first load control circuit. 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 to ground.

[0140] Figure 6 In the illustrated embodiment, 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 comprising 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 serves as the first end of the second switch circuit SW2 and is electrically connected to the first end of the secondary winding Ns of the first transformer T1. The source of the second NMOS transistor M22 serves as the second end of the second switch circuit SW2 and is electrically connected to the first end of the second output capacitor C2. The gates of the first NMOS transistor M21 and the second NMOS transistor M22 serve as the two control signal inputs of the second switch circuit SW2 and are electrically connected in a one-to-one correspondence with the two first outputs of the second burst mode detection circuit. 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 electrically connected to the second end of the second output capacitor C2 and to ground.

[0142] Figure 6 In the illustrated embodiment, the second control signal includes a control signal D21 and a control signal D22. 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 has entered a light-load state, it controls the first NMOS transistor M11 on the first load branch to be turned off. When the first load branch exits the light-load state, it controls the first NMOS transistor M11 on the first load branch to be turned on again. During 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. If it determines that the second load branch has entered a light-load state, it controls the second NMOS transistor M22 on the second load branch to be turned off. When the second load branch exits the light-load state, it controls the second NMOS transistor M22 on the second load branch to be turned back on. During this process, the first NMOS transistor M21 on the second load branch remains normally 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 control signals D12 and D21 are always at a high level, the on and off of the two load branches are mainly determined by control signals D11 and D22. When both the first load branch and the second load branch are in a non-light-load state, control signals D11 and D22 need to be complementary to each other to ensure that the first load branch and the second load branch are complementary to each other.

[0147] Next, take the example that 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, 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 illustrates 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 and D12 output by the first burst mode detection circuit, and the control signals D21 and 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, and the vertical axis represents the output voltage Vo2. The dotted line in the coordinate system represents the reference voltage Vref2 received by the second operational amplifier in the second load control circuit. 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 control signals D12 / D21, the horizontal axis represents time t, and the vertical axis represents the level of control signals 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 control signals D12 / D21 are always high.

[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 in operation, 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, causing the second NMOS transistor M12 to remain normally on; and 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, causing the first NMOS transistor M21 to remain normally on.

[0157] At time t0, the output voltage Vo2 is less than or equal to the reference voltage Vref2. 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 thus determines that the second load branch has entered a light-load state. In other words, the second load branch needs to enter burst mode. Therefore, the second burst mode detection circuit sends a low-level control signal D22 to the second NMOS transistor M22 of the second switch circuit SW2, turning off the second switch circuit SW2. 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 then provides all its energy to the first load branch.

[0158] Because the second output capacitor C2 on the second load branch has stored a certain amount of energy, it can continue to supply power to the second load R2. The output voltage Vo2 provided by the second output capacitor C2 gradually decreases over time, and the difference between the output voltage Vo2 and the reference voltage Vref2 increases. Accordingly, the second computation result Vcomp2 increases.

[0159] At time t1, the second computation result Vcomp2 equals the preset voltage threshold Vcomp-th2, and the second burst mode detection circuit determines that the second load branch has exited the light-load state, i.e., the burst mode. Because the first and second load branches exhibit complementary conduction, the second switch circuit SW2 can only be switched on after the dual-output flyback converter completes its current cycle on-time. The dual-output flyback converter completing its current cycle on-time can also be understood as the first power switch S1 completing its current cycle on-time.

[0160] Combine Figure 7 Regarding the timing of drive signal DRV and control signals D11 and D22, the primary-side first power switch M1 and first switch circuit SW1 must be fully conductive between t1 and t2. Therefore, the second load branch must remain off during this time. This means that control signal D22 is at a low level during this time. During this time, the second output capacitor C2 cannot be replenished, and therefore the output voltage Vo2 further decreases.

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

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

[0164] This process is repeated continuously, thereby achieving control over the output voltage Vo2 on the second load branch.

[0165] In the above process, the first load branch is not lightly loaded, and the first burst mode detection circuit sends control signals D11 and D12 to the switch circuit SW1 according to a pre-designed switching cycle. Combining the timing of the first control signals D11 and D12 with the timing of the drive signal DRV, it can be seen that during the time period from t1 to t2, the first control signal D11 and the drive signal DRV meet complementary conduction conditions.

[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 article. For the sake of brevity, it will not be repeated here.

[0167] Furthermore, when both the first load branch and the second load branch are in a light-load state, the primary control circuit 22 c can determine that the total load condition has reached the system light-load threshold based on the first calculation result Vcomp1 transmitted by the first load control circuit and the second calculation result Vcomp2 transmitted by the second load control circuit, and control the first power switch S1 to enter the burst mode (i.e., enter the intermittent power state).

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

[0169] A bidirectional switch is a switch capable of bidirectional conduction. When the bidirectional switch is on, current can flow in both directions. In this application, when the bidirectional switch is on, current can flow 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 off, the body diode within the bidirectional switch is in a reverse series state, blocking current from flowing 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 shown is the same, 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] In the secondary circuit, 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, serving as the first end of the first switch circuit SW1, is electrically connected to the first end of the secondary winding Ns of the first transformer T1. The second end of the first bidirectional switch Q1, serving as the second end of the first switch circuit SW1, is electrically connected to the first end of the first output capacitor C1. The third end of the first bidirectional switch Q1, serving as the control signal input end of the first switch circuit SW1, is electrically connected to the output end of the first burst mode detection circuit in the first load control circuit. 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, serving as the first end of the second switch circuit SW2, is electrically connected to the first end of the secondary winding Ns of the first transformer T1. The second end of the second bidirectional switch Q2, serving as the second end of the second switch circuit SW2, is electrically connected to the first end of the second output capacitor C2. The third end of the second bidirectional switch Q2, serving as the control signal input end of the second switch circuit SW2, is electrically connected to the output end of the second burst mode detection circuit in the second load control circuit. 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 turn 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 turn 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 separately 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 controlled to enter the burst mode alone; 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) Both the first load branch and the second load branch are in a light-load state. Based on the total load reaching the system light-load threshold, the first power switch S1 on the primary side is controlled to enter the burst mode.

[0182] In this application, the light-load branch enters burst mode, that is, the light-load branch is disconnected from the secondary winding, and no switching action is required. This can reduce the number of switching operations of the light-load branch, thereby reducing the switching losses 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 load demand due to unreasonable energy distribution in the multi-output flyback converter, which is conducive to improving the reliable and stable operation of the light-load branch.

[0183] Figure 9 This is a flow chart of a multi-output flyback converter control method provided in one 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 Figure 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, which correspond to N load branches one by one. Each load control circuit includes: a voltage sampling circuit, an operational amplifier, and a burst mode detection circuit.

[0187] The output voltages of the connected voltage output circuits are sampled by 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 a 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 energy transmission 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 the N load branches, a load branch in a lightly loaded state is referred to as a first load branch, and the number of first load branches may be one or more. When there are multiple first load branches, the output voltages provided to the load by the voltage output circuits on the multiple first load branches may be equal or unequal, and this application does not impose any restrictions thereon. Similarly, a branch in a non-lightly loaded state among the N load branches is referred to as a second load branch, and the number of second load branches may be one or more. When there are multiple second load branches, the output voltages provided by the voltage output circuits on the multiple second load branches may be equal or unequal, and this application does not impose any restrictions thereon.

[0190] For any load control circuit, the load control circuit uses an operational amplifier to calculate the sampled voltage and the reference voltage corresponding to the load branch to obtain an operation result. The burst mode detection circuit then compares the operation result with a preset voltage threshold to determine whether the corresponding load branch has entered a light-load state. In some embodiments, if the voltage comparison result is greater than or equal to the preset voltage threshold, the load branch is determined to have exited the light-load state; if the voltage comparison result is less than the preset voltage threshold, the load branch is determined to be 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 stopping the secondary winding from 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-lightly loaded branch (i.e., 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 based on the actual power demand of the load, thereby reducing energy loss caused by the lightly loaded branch and improving the energy conversion efficiency of the multi-output flyback converter. At the same time, it can prevent the lightly loaded branch from being overly high in energy.

[0196] exist Figure 9 Based on the embodiment shown, after S902, the following steps are further included:

[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, conduction is controlled between the voltage output circuit on the first load branch and 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 controls energy transmission to the first load branch. Specifically, a 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 a voltage comparison result between the sampled voltage and a reference voltage corresponding to the first load branch. When the burst mode detection circuit determines that the voltage comparison result is greater than or equal to a preset voltage threshold corresponding to the first load branch, the first load branch is determined to have exited the light-load state, and conduction is controlled between the first load branch and the secondary winding of the first transformer to replenish energy to the first load branch via the secondary winding.

[0199] It should be noted that in Figure 9 The details not disclosed in the embodiment of the method shown 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 deliver 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 further provides a controller, which is used to execute the operations executed by the controller in any of the aforementioned embodiments.

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

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

[0204] Finally, it should be noted that the above embodiments are merely specific implementations of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A multi-output flyback converter, characterized in that: include: Multi-output flyback converter circuit, N load branches and controller; N is a positive integer greater than 1; The multi-output flyback conversion circuit includes: 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 includes a voltage output circuit and a load; The voltage input circuit is electrically connected to the first end of the primary winding, the second end of the primary winding is grounded via 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, and 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 configured to sample the output voltages provided to the loads by the voltage output circuits 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 further used to control conduction between the second load branch and the secondary winding, so that all 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, wherein: The controller is further configured to control conduction between the voltage output circuit on the first load branch and the secondary winding when determining that the first load branch exits the light load state based on the output voltage provided to the load by the voltage output circuit on the first load branch, so that the secondary winding transmits energy to the first load branch.

3. The multi-output flyback converter according to claim 1, wherein: 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, wherein: The controller includes: 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 of the nth voltage sampling circuit; The nth voltage sampling circuit is configured 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 being configured to receive a reference voltage corresponding to the nth load branch and the nth sampled voltage, and to perform an operation on 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 a load condition of the nth load branch; The nth burst mode detection circuit is configured 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 end 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 conduction or disconnection between the nth load branch and the secondary winding.

7. The multi-output flyback converter according to claim 6, wherein: The nth switch circuit comprises a first unidirectional switch and a second unidirectional switch connected in series. The nth burst mode detection circuit is 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. Alternatively, the nth switching circuit is a back-to-back MOS transistor module; the nth burst mode detection circuit is specifically configured to send different nth control signals to the two MOS transistors in the back-to-back MOS transistor module, respectively, to control one MOS transistor in the back-to-back MOS transistor module to be normally on, control the other MOS transistor in the back-to-back MOS transistor module to be turned off when the nth load branch is in a light-load state, thereby disconnecting the nth load branch from the secondary winding; and control the other MOS transistor in the back-to-back MOS transistor module to be turned on when the nth load branch exits the light-load state, thereby connecting the nth load branch to the secondary winding. Alternatively, the nth switching circuit is a bidirectional switch; the nth burst mode detection circuit is specifically configured 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, where 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, wherein: The controller further includes: an isolation communication circuit and a primary control circuit; the isolation communication circuit is provided 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 first 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 first 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: In real time, the output voltage provided to the load by the voltage output circuit on the N load branches of the multi-output flyback converter is sampled to obtain N sampled voltages, where N is a positive integer greater than 1; When it is determined, based on 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 of the first transformer in the multi-output flyback converter to stop transmitting energy to the first load branch; During a time period in which 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 of the N load branches does not reach a system light-load threshold, conduction is controlled between the second load branch and the secondary winding, and all 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: The multi-output flyback converter according to any one of claims 1 to 8.

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

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