A flyback multi-output converter and a control method thereof

Abstract

The present application relates to the field of switching power supply with multiple output, disclose a flyback type multi-output converter and its control method, converter at least includes: transformer, and the first output circuit and the first switch control circuit which are composed of the first output winding of transformer secondary side, first switch, first output filter capacitor, wherein, the first switch is arranged between the first output winding and the first output filter capacitor, and under the control of the first switch control circuit, the energy of the first output filter capacitor can be flowed back to the first output winding, and finally supplemented to the second output winding. The flyback type multi-output converter and its control method provided by the present application can effectively improve the output voltage precision of the second to the K output circuit, and obviously improve the cross regulation rate of the converter when carrying unbalanced load.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of switching power supply with multiple outputs, in particular to a flyback multi-output converter and a control method thereof. BACKGROUND

[0002] The flyback multi-output converter realizes multiple outputs by increasing the secondary winding of the transformer, and is widely used in industrial and consumer power supply fields due to its low cost and small size.

[0003] The schematic diagram of a conventional flyback multi-output converter is shown in Figure 1 The output voltage of the main path (first output circuit) is sampled and fed back to the primary switch control circuit for closed-loop control, thereby realizing stable output voltage of the main path, while the auxiliary path is open-loop controlled. Therefore, theoretically, the output voltage of the auxiliary path has a constant turns ratio relationship with the output voltage of the main path. However, in practice, due to factors such as transformer leakage inductance and line impedance, the energy stored in the transformer is not reasonably distributed among the branch outputs, especially when the main and auxiliary paths of the converter carry unbalanced loads, which will cause the cross regulation of the auxiliary path to deteriorate, specifically: when the main path of the converter carries heavy load and the auxiliary path carries light load, the auxiliary path voltage will rise; when the main path of the converter carries light load and the auxiliary path carries heavy load, the auxiliary path voltage will drop.

[0004] The existing solutions mainly include: 1. Adding a dummy load to the main path of the converter, which makes the main path maintain sufficient output power even when it carries light load, and the primary controller of the converter will control the primary to transfer more energy to the secondary, so that the auxiliary path will also have additional energy flowing in to maintain the output voltage, thus effectively suppressing the drop of the auxiliary path voltage. However, this solution improves the cross regulation at the expense of the efficiency of the converter, and the problem of the auxiliary path voltage rising when the main path of the converter carries heavy load and the auxiliary path carries light load still exists. 2. Weighted control of the main and auxiliary paths, which samples and feeds back the output voltages of the main and auxiliary paths to the primary controller of the converter, and by setting a reasonable weighting factor, the cross regulation can be improved, but this solution only redistributes the total error among the output circuits, and does not fundamentally eliminate the error, for example: this solution can improve the voltage accuracy of the auxiliary path, but it will worsen the voltage accuracy of the main path. 3. Adding a secondary voltage regulation circuit to the auxiliary path. This solution adds a linear regulation circuit or Buck / Boost circuit to the auxiliary path of the converter to realize secondary regulation of the auxiliary path voltage. Please refer to Chinese patent document CN113676055A, Figure 2The circuit diagram of the multi-output of the patent document. Although this scheme can improve the voltage accuracy of the auxiliary road and the cross regulation rate of the system. However, when the converter is in the extreme working condition of the main road with no load and the auxiliary road with full load, the primary side control circuit makes the primary side of the converter no longer transfer energy to the secondary side. At this time, the voltage of the main road can be maintained because it is with no load. The secondary side will not be supplied with energy, and the auxiliary road will not be able to maintain the output voltage, thereby causing the voltage to drop. In addition, the secondary voltage regulation circuit also increases the power device, which increases the power consumption and cost of the converter. Figure 3 The circuit diagram of the multi-output of the patent document. The scheme only adds one semiconductor switching device to the auxiliary road, and realizes voltage stabilization through an independent loop. Compared with scheme three, this scheme can greatly reduce the material cost and converter loss under the condition of ensuring that the cross regulation rate does not deteriorate. However, this scheme also has the problem of voltage drop of the auxiliary road when the converter is in the extreme working condition of the main road with no load and the auxiliary road with full load.

[0005] Therefore, the above-mentioned existing solutions cannot simultaneously solve the problems of poor cross regulation rate of the multi-output converter with unbalanced load and voltage drop of the auxiliary road when the main road is with no load and the auxiliary road is with heavy load. Therefore, a more perfect solution is needed to meet the needs of high-performance multi-output products. SUMMARY

[0006] The present application aims to overcome at least one of the above-mentioned defects in the prior art, and provides a flyback multi-output converter and a control method thereof to solve the problems of poor cross regulation rate of the flyback multi-output converter with unbalanced load and voltage drop of the auxiliary road when the main road is with no load and the auxiliary road is with heavy load.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0008] A flyback multi-output converter, at least comprising:

[0009] A transformer having a primary side winding, a secondary side first output winding, and a secondary side second output winding;

[0010] A first output circuit having a first switch and a first output filter capacitor, the first end of the first switch being connected to the secondary side first output winding, and the second end of the first switch being connected to the first output filter capacitor;

[0011] A second output circuit having a second switch and a second output filter capacitor, the first end of the second switch being connected to the secondary side second output winding, and the second end of the second switch being connected to the second output filter capacitor;

[0012] The input circuit has a primary side switch connected with the primary side winding;

[0013] The first output circuit further has a first switch control circuit connected with the first switch, the first switch control circuit is used for controlling the first switch so that the energy stored in the secondary side first output winding flows into the first output filter capacitor; the first switch control circuit is further used for controlling the first switch so that the energy stored in the first output filter capacitor flows back to the secondary side first output winding;

[0014] The first switch control circuit comprises a first clock synchronization unit and a volt-second balance logic unit, the first clock synchronization unit is used for detecting the voltage signal of the secondary side first output winding and transmitting the voltage signal of the secondary side first output winding to the volt-second balance logic unit; the volt-second balance logic unit is used for controlling the first switch to turn on according to the voltage signal of the secondary side first output winding and is used for sampling the voltage across the secondary side first output winding during the conduction of the primary side switch and obtaining the volt-second product of the transformer excitation according to the sampled voltage across the secondary side first output winding, the volt-second balance logic unit is further used for controlling the conduction duration of the first switch according to the volt-second product;

[0015] The second output circuit further has a second switch control circuit connected with the second switch, the second switch control circuit is used for controlling the second switch so that the energy flowing back to the secondary side first output winding is supplemented to the secondary side second output winding and is transmitted to the second output filter capacitor through the secondary side second output winding.

[0016] Preferably, sampling the voltage across the secondary side first output winding during the conduction of the primary side switch and obtaining the volt-second product of the transformer excitation according to the sampled voltage across the secondary side first output winding comprises: the volt-second balance logic unit samples the voltage across the secondary side first output winding of positive polarity during the conduction of the primary side switch, converts the voltage across the secondary side first output winding of positive polarity into a first current source representing the voltage across the secondary side first output winding of positive polarity, and obtains the volt-second product by charging a capacitor through the first current source;

[0017] Controlling the conduction duration of the first switch according to the volt-second product comprises: sampling the voltage across the secondary side first output winding of negative polarity and converting the voltage across the secondary side first output winding of negative polarity into a second current source representing the voltage across the secondary side first output winding of negative polarity during the conduction of the first switch, and discharging the capacitor through the second current source to control the conduction duration of the first switch.

[0018] Preferably, the second switch control circuit has a second clock synchronization unit for detecting the voltage signal of the secondary side second output winding to determine the turn-on time of the primary side switch, and an error comparison unit for sampling the output voltage of the second output circuit, comparing and amplifying the sampled output voltage with a preset reference voltage to form an error signal, and comparing the error signal with a preset fixed slope ramp signal to obtain an off signal for controlling the second switch, so as to obtain the turn-on duration of the second switch.

[0019] Preferably, the set voltage across the secondary side second output winding is greater than the output voltage of the second output circuit by a certain value.

[0020] Preferably, the clamping circuit is mainly used to reduce the influence of parasitic parameters to ensure reliable operation of the primary side switch; the primary side switch control circuit can isolate and sample the output voltage of the first output circuit, control the turn-on state of the first switch according to the sampling voltage, so as to realize the stability of the output voltage of the first output circuit.

[0021] Preferably, the secondary side first output winding and the secondary side second output winding are different windings, and the output voltage of the first output circuit and the output voltage of the second output circuit are both isolated outputs.

[0022] The application also provides a control method of a flyback multi-output converter, the flyback multi-output converter comprising a transformer, an input circuit, a first output circuit and a second output circuit, wherein the transformer has a primary side winding, a secondary side first output winding and a secondary side second output winding; the input circuit has a connection with the primary side winding, and the input circuit has a primary side switch; the first output circuit is connected with the secondary side first output winding, and the second output circuit is connected with the secondary side second output winding; the control method comprises the following steps:

[0023] Detecting the voltage signal of the secondary side first output winding and controlling the turn-on of the first switch in the first output circuit according to the voltage signal of the secondary side first output winding;

[0024] Sampling the voltage across the secondary side first output winding during the conduction of the primary side switch, and obtaining the volt-second product of the transformer excitation according to the sampled voltage across the secondary side first output winding;

[0025] Controlling the turn-on duration of the first switch according to the volt-second product.

[0026] Preferably, the voltage across the first secondary-side output winding is sampled during the on period of the primary-side switch, and the volt-second product during the excitation of the transformer is obtained according to the sampled voltage across the first secondary-side output winding, comprising:

[0027] During the on period of the primary-side switch, the voltage across the first secondary-side output winding of positive polarity is sampled to convert the voltage across the first secondary-side output winding into a first current source representing the voltage across the first secondary-side output winding, and the volt-second product is obtained by charging a capacitor with the first current source;

[0028] The on period of the first switch is controlled according to the volt-second product, comprising:

[0029] During the on period of the first switch, the voltage across the first secondary-side output winding of negative polarity is sampled and converted into a second current source representing the voltage across the first secondary-side output winding, and the on period of the first switch is controlled by discharging the capacitor with the second current source.

[0030] Preferably, the control method of the flyback multi-output converter further comprises the following steps:

[0031] The on period of the first switch is controlled so that the energy stored in the first secondary-side output winding flows into the first output filter capacitor, and the energy stored in the first output filter capacitor flows back to the first secondary-side output winding;

[0032] The second switch is controlled to be on for a set time during the on period of the first switch, so that the energy flowing back to the first secondary-side output winding is supplemented to the second secondary-side output winding and transmitted to the second output filter capacitor through the second secondary-side output winding.

[0033] The present application has the following advantages:

[0034] (1) By flowing the energy of the first output circuit (main path) back to the transformer and finally supplementing to the second output circuit (auxiliary path), the voltage of the second output circuit can be maintained stable when the first output circuit of the converter is in no-load and the second output circuit is in full-load, greatly improving the output voltage precision of the second output circuit of the converter.

[0035] (2) By independently controlling the second output circuit in a closed loop, the cross regulation rate of the converter under unbalanced load is greatly improved.

[0036] (3) The first switch control circuit based on the logic control of the voltage-second balance can reliably support the bidirectional flow of the first switch current, thereby reliably supporting the energy backflow process of the first output circuit (main circuit).

[0037] (4) The primary side control circuit, each output circuit and each switch control circuit are independently controlled, so that the number of output circuits can be expanded, each output circuit realizes electrical isolation, and the application is flexible.

[0038] (5) Each output circuit has fewer power devices, and has less energy loss and lower material cost. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a traditional flyback multi-output converter schematic diagram;

[0040] Figure 2 It is a multi-output circuit circuit diagram of an embodiment in the patent document with publication number CN113676055A;

[0041] Figure 3 It is a multi-output circuit circuit diagram of an embodiment in the patent document with publication number CN103178719A;

[0042] Figure 4 It is a typical schematic diagram of the control method and circuit of a multi-output switching converter of the present application;

[0043] Figure 5 It is a typical schematic diagram of the circuit of a multi-output switching converter of the present application;

[0044] Figure 6 It is a working timing diagram of the converter in the embodiment of the present application Figure 5

[0045] Figure 7 It is a logic block diagram of the first switch control circuit of the first output circuit in the embodiment of the present application Figure 5

[0046] Figure 8 It is a logic block diagram of the second switch control circuit of the second output circuit in the embodiment of the present application Figure 5

[0047] Figure 9 It is a simulation waveform diagram under one working condition of the present application

[0048] Figure 10 It is a simulation waveform diagram under another working condition of the present application DETAILED DESCRIPTION ​​​

[0049] The application and its advantages will be understood more fully from the following detailed description, taken in conjunction with the accompanying drawings of certain embodiments. However, the detailed description and the drawings do not limit the scope of the application.

[0050] A typical schematic diagram of a multi-output switching converter according to an embodiment of the application is shown in FIG. 1, which includes K output circuits, where K is an integer greater than or equal to 2. Hereinafter, a multi-output converter with two output circuits (hereinafter referred to as a converter) will be described as an example. Figure 4

[0051] Referring to FIG. 1, Figure 5 The converter according to the embodiment includes two output circuits, and the signal code set is described as follows:

[0052] V in : input voltage of the converter; V o1 : output voltage of the first output circuit / voltage of the first output filter capacitor; V o2 : output voltage of the second output circuit / voltage of the second output filter capacitor; Ip: primary current; Is1: first switching current; Is2: second switching current; VS1: transformer secondary side first output winding voltage signal (hereinafter referred to as first output winding voltage signal); VS2: transformer secondary side second output winding voltage signal (hereinafter referred to as second output winding voltage signal); S1: first switch; S2: second switch; Q1: primary switch; D2: second rectifier; C in : input capacitor; C o1 : first output filter capacitor; C o2 : second output filter capacitor; R L1 : first output circuit load; R L2 : second output circuit load; N1: transformer secondary side first output winding (hereinafter referred to as first output winding); N2: transformer secondary side second output winding (hereinafter referred to as second output winding).

[0053] The converter according to the embodiment includes an input circuit, a transformer, a first output circuit 10, a second output circuit 20, and a control circuit. The transformer has a primary winding, a first output winding, and a second output winding. The first output circuit 10 includes a first switch S1, a first output filter capacitor C o1 , and a first switch control circuit. The first end of the first switch S1 is connected to the first output winding N1, the second end of the first switch S1 is connected to the first output filter capacitor C o1 , and the control end of the first switch S1 is connected to the first switch control circuit. The second output circuit 20 includes a rectifier D2, a second switch S2, a second output filter capacitor C o2 ​and a second switch control circuit, the first end of the second switch S2 is connected with the second output winding N2, the second end of the second switch S is connected with the second output filter capacitor C o2 is connected with the second switch control circuit; the input circuit comprises a primary side switch Q1, a clamping circuit and a primary side switch control circuit; in the embodiment, the first output circuit is as a main circuit, and the second output circuit is as an auxiliary circuit.

[0054] The converter of the application can work in CCM mode (continuous mode), CRM mode (critical mode) or DCM mode (discontinuous mode), and in the embodiment, the converter works in CRM mode.

[0055] The working timing of the converter of the application is shown in the figure, and in a stable state, one switching cycle has the following working stages: Figure 6

[0056] Stage 1 (t0-t1): the primary side control unit of the converter controls the primary side switch Q1 to be turned on at t0, and the primary side current Ip of the converter linearly rises at a fixed slope V in / Lm, Lm is the excitation inductance of the transformer; the second switch S2 is turned on after a fixed delay at t0; the first output circuit 10 provides energy for the load by the first output filter capacitor C o1 , and the second output circuit provides energy for the load by the second output filter capacitor C o2 .

[0057] Stage 2 (t1-t2): the primary side switch Q1 is turned off at t1, and the first switch S1 is turned on at t1; since the voltage across the second output winding N2 is clamped to a lower value, the voltage across the first output winding N1 is clamped to a value less than the first output voltage, so that the first switch current Is1 starts to decrease from a certain value, and the second switch current Is2 starts to increase from a certain value, and this stage lasts until the first switch current Is1 decreases to zero.

[0058] Stage 3 (t2-t3): the first switch current Is1 decreases to zero at t2, and then the first switch current Is1 starts to increase negatively, while the second switch current Is2 continues to increase, which means that the first output circuit 10 starts to supplement the energy of the second output circuit 20, so that the energy source of the second output circuit 20 is composed of the excitation energy storage of the transformer and the energy of the first output circuit 10, and this stage lasts until the second switch S2 is turned off.

[0059] Stage 4 (t3-t4): the second switch S2 is turned off at t3, so that the second output filter capacitor C o2 no longer absorbs the excitation energy storage of the transformer and the energy of the first output circuit 10, and only the second output filter capacitor C o2 ​Load R to the second output circuit L2 Power is supplied. At the same time, the first output winding N1 is no longer clamped, and the first output circuit 10 begins to demagnetize the transformer independently. Therefore, the first switching current Is1 changes from negative to positive in this stage, and then begins to decrease in the positive direction. When the current Is1 drops to zero at time t4, it means the end of the transformer demagnetization stage. The first switch controller controls the first switch S1 to turn off, and one working cycle of the converter also ends.

[0060] This invention specifically improves the first output circuit and its control. The first switch control circuit controls the opening and closing of the first switch S1, ensuring the forward flow of the first switch current Is1, and enabling the first output winding N1 to function as the first output filter capacitor C. o1 In addition to transmitting energy, it also ensures that the first switching current Is1 flows in the negative direction, thus realizing the first output filter capacitor C. o1 To provide energy to the second output circuit 20, that is, by controlling the first switch S1, the energy stored in the first output winding N1 flows into the first output filter capacitor C. o1 And cause the first output filter capacitor C to be stored in the first output filter capacitor C o1 The energy is reversed to the first output winding N1, so that the auxiliary output voltage can maintain high accuracy under extreme conditions when the main output is lightly loaded and the auxiliary output is fully loaded.

[0061] In this embodiment, the first output winding N1 and the second output winding N2 are different windings, and the output voltages of the first output circuit and the second output circuit are both isolated outputs. The set voltage across the second output winding N2 is greater than a certain value of the output voltage of the second output circuit, thereby enabling the energy of the first output circuit to be fed back to the second output circuit.

[0062] like Figure 7 The following is an embodiment of the present invention. Figure 5 The schematic diagram of the first switch control circuit of the first output circuit 10 of the intermediate frequency converter is shown. The first switch control circuit has a first clock synchronization unit 101 and a volt-second balance logic unit 102. The first clock synchronization unit is used to detect the voltage signal of the first output winding and transmit the voltage signal of the first output winding to the volt-second balance logic unit. The volt-second balance logic unit is used to control the first switch to turn on according to the voltage signal of the first output winding, and to sample the voltage across the first output winding on the secondary side during the primary side switch conduction period, and to obtain the volt-second product of the transformer during the primary side switch conduction time according to the sampled voltage across the first output winding on the secondary side. The volt-second balance logic unit is also used to control the conduction time of the first switch according to the volt-second product.

[0063] Specifically, the first clock synchronization unit 101 has a comparator COM1, a comparator COM2; the volt-second balance logic unit 102 includes a flip-flop FF1, a flip-flop FF2, a flip-flop FF3, a comparator COM3, a subtractor OP1, a subtractor OP2, a switch K1, a switch K2, a first current source I1, a second current source I2, a capacitor C1. Please refer to Figure 6 When the primary side switch Q1 is turned on at t0, the first output winding voltage VS1 quickly rises to be higher than the reference voltage V ref2 set inside the comparator COM1 of the first clock synchronization unit 101, the comparator COM2 outputs a high level, and enables the flip-flop FF2 to output a high level to control the switch K1 of the volt-second balance logic unit 102 to be turned on, so that the first current source I1 charges the capacitor C1, and the voltage VT1 of the capacitor C1 is a signal representing the volt-second product when the transformer is excited. The first current source I1 is a voltage-controlled current source. Specifically, the embodiment realizes the conversion of the sampled positive polarity first output winding voltage (VS11-V O1 ) into the first current source I1 representing the voltage through the subtractor OP1 and the first current source I1. ref1 When the primary side switch Q1 is turned off at t1, the first output winding voltage VS1 is less than the reference voltage V Q1,on set inside the comparator COM1 of the first clock synchronization unit 101, the comparator COM1 outputs a high level, and enables the flip-flop FF2 of the volt-second balance logic unit 102 to be reset, thereby turning off the switch K1 and ending the charging of the capacitor C1. At this time, the voltage of the capacitor C1 can be represented as where t Q1,on is the excitation time (the on time of the primary side switch Q1), and C represents the capacitance of the capacitor C1. At the same time, the comparator COM1 enables the flip-flop FF1 of the volt-second balance logic unit 102 to output a high level to control the first switch S1 to be turned on. At the same time, the comparator COM1 enables the flip-flop FF3 to output a high level to control the switch K2 to be turned on, so that the second current source I2 discharges the capacitor C1. The second current source I2 is a voltage-controlled current source. Specifically, the embodiment realizes the conversion of the sampled negative polarity first output winding voltage (VS11-V O1 ) into the second current source I2 representing the voltage through the adder OP2 and the first current source I2.

[0064] It should be noted that the volt-second balance control unit 102 utilizes the characteristic that the transformer excitation inductance Lm has volt-second balance when the transformer is in steady state, and the volt-second balance characteristic refers to that the volt-second product of the excitation winding during excitation in a cycle is equal to the volt-second product during demagnetization, i.e.

[0065] V in ·t Q1,on = V off ·t S1,on ,

[0066] In the formula, t Q1,on is the excitation time (the conduction time of the primary side switch Q1), t S1,on is the demagnetization time (the conduction time of the first switch S1), V in is the voltage across the primary side winding during excitation, and V off is the voltage across the primary side winding during demagnetization. Because the voltages of the windings of the transformer have a certain turns ratio relationship, the volt-second balance principle can be represented by the voltage across the first output winding N1, which is

[0067] (VS11-V o1 )·t Q1,on = (V o1 -VS12)·t S1,on

[0068] In the formula, VS11-V o1 is the voltage across the first output winding N1 during excitation (positive polarity), and V o1 -VS12 is the voltage across the first output winding N1 during demagnetization (the conduction period of the first switch S1) (negative polarity). Multiplying the two ends of the equation by the corresponding coefficient, we have:

[0069] k×(VS11-V o1 )·t Q1，on =k×(V o1 -VS12)·t S1,on

[0070] After converting the proportional winding voltage into current, the current source representing the voltage can be obtained, which is

[0071] I1·t Q1,on =I2·t S1,on

[0072] Therefore, volt-second balance of the transformer excitation inductance Lm can be achieved by controlling the ampere-second balance of the capacitor C1.

[0073] The second switch control circuit controls the opening and closing of the second switch S2, thereby effectively controlling the energy transmitted from the transformer to the second output circuit. During the opening of the first switch S1, the second switch control circuit controls the second switch S2 to conduct for a set time; that is, the first switch S1 and the second switch S2 have a common on-time. This allows the energy flowing back to the first output winding N1 to replenish the second output winding N2, and then transmitted through the second output winding N2 to the second output filter capacitor C. o2 This ensures that the auxiliary output voltage maintains high accuracy even under extreme conditions where the main output is fully loaded and the auxiliary output is lightly loaded.

[0074] Specifically, the second switch control circuit has a second clock synchronization unit 201 and an error comparison unit 202, such as Figure 8 The following is an embodiment of the present invention. Figure 5 The schematic diagram of the second switch control circuit of the second output circuit 20 of the intermediate frequency converter shows that the second clock synchronization unit 201 includes: comparator COM1, comparator COM2, and delay unit U1; the error comparison unit 202 includes: trigger FF1, comparator COM3, error amplifier EA1, and ramp signal U2. Please refer to... Figure 6 When the primary-side switch Q1 is turned on at time t0, the voltage VS2 of the second output winding quickly rises and exceeds the reference voltage V of comparator COM2. ref1 Subsequently, after a fixed delay, the comparator COM1 of the second clock synchronization unit 201 outputs a high level, which enables the trigger FF1 to output a high level to control the second switch S2 to turn on during the primary-side switch conduction period. When the primary-side switch Q1 turns off at time t1, the second output winding voltage VS2 quickly flips low and falls below the reference voltage V of the comparator COM2. ref2 Subsequently, comparator COM2 outputs a high level to enable ramp signal U2, thereby synchronously switching the frequency of ramp signal U1 with the frequency of primary-side switch Q1. Ramp signal U1 is a sawtooth wave with an initial voltage value of zero and a fixed voltage rise slope. Error comparator EA1 samples the output voltage of the second output circuit and compares the sampled output voltage with a preset reference voltage V. ref2 The error voltage is compared and amplified. When the voltage of the ramp signal U2 rises to the error voltage output by the error comparator EA1, the comparator COM3 outputs a high level to reset the trigger FF1, thereby controlling the second switch S2 to turn off.

[0075] It should be noted that the purpose of the second switch control circuit controlling the second switch S2 to turn on during the conduction of the primary switch Q1 is to enable the second switch S2 to turn on with zero current, thereby reducing the turn-on loss.

[0076] The control method and circuit provided by the embodiment are simulated by using SIMetrix-SIMPLIS Elements software. Simulation parameters are as follows:

[0077] The working frequency of the primary switch Q1 is 65 kHz, the input DC voltage is 375 V, the number of turns of the primary winding of the transformer is 43, the number of turns of the first output winding is 4, the number of turns of the second output winding is 10, the excitation inductance Lm of the transformer is 550 uH, the leakage inductance Lr of the primary side of the transformer is 7 uH, the first output filter capacitor C o1 : 1000 uF, the second output filter capacitor C o2 : 1000 uF, the rated output of the first output circuit is 5 V / 6 A, and the rated output of the second output circuit is 12 V / 2 A.

[0078] Figure 9 The simulation waveforms of the converter in the working condition that the first output circuit load R L1 : 8.33 Ω (10% load) and the second output circuit load R L2 : 6 Ω (100% load) are shown.

[0079] Figure 10 The simulation waveforms of the converter in the working condition that the first output circuit load R L1 : 8.33 Ω (10% load) and the first output circuit load R L2 : 60 Ω (10% load) are shown.

[0080] The present application is not limited to the above-mentioned specific embodiments. According to the above content, other various equivalent modifications, replacements or changes can be made according to the common technical knowledge and conventional means in the art without departing from the above-mentioned basic technical idea of the present application, and all fall within the protection scope of the present application.

Claims

1. A flyback multi-output converter, characterized in that, At least comprising: a transformer having a primary side winding, a secondary side first output winding, a secondary side second output winding; a first output circuit having a first switch, a first output filter capacitor, a first end of the first switch being connected with the secondary side first output winding, a second end of the first switch being connected with the first output filter capacitor; a second output circuit having a second switch, a second output filter capacitor, a first end of the second switch being connected with the secondary side second output winding, a second end of the second switch being connected with the second output filter capacitor; an input circuit having a primary switch connected with the primary side winding; the first output circuit further has a first switch control circuit connected with the first switch, the first switch control circuit being used for controlling the first switch, so that the energy stored in the secondary side first output winding flows into the first output filter capacitor, and the energy stored in the first output filter capacitor flows back to the secondary side first output winding; the first switch control circuit comprises a first clock synchronization unit and a volt-second balance logic unit, the first clock synchronization unit is used for detecting a voltage signal of the secondary side first output winding and transmitting the voltage signal of the secondary side first output winding to the volt-second balance logic unit; the volt-second balance logic unit is used for: controlling the first switch to turn on according to the voltage signal of the secondary side first output winding; during the conduction of the primary switch, sampling a voltage across the secondary side first output winding, and obtaining a volt-second product when the transformer is excited according to the sampled voltage across the secondary side first output winding; controlling the conduction duration of the first switch according to the volt-second product; the second output circuit further has a second switch control circuit connected with the second switch, the second switch control circuit being used for controlling the second switch, so that the energy flowing back to the secondary side first output winding is supplemented to the secondary side second output winding, and is transmitted to the second output filter capacitor through the secondary side second output winding.

2. The flyback multi-output converter of claim 1, wherein, sampling a voltage across the secondary side first output winding during the conduction of the primary switch, and obtaining a volt-second product when the transformer is excited according to the sampled voltage across the secondary side first output winding, comprises: during the conduction of the primary switch, sampling the voltage across the secondary side first output winding in a positive polarity, converting the voltage across the secondary side first output winding into a first current source representing the voltage across the secondary side first output winding, and charging a capacitor in the volt-second balance logic unit through the first current source to obtain the volt-second product; controlling the conduction duration of the first switch according to the volt-second product, comprises: during the conduction of the first switch, sampling the voltage across the secondary side first output winding in a negative polarity, converting the voltage across the secondary side first output winding in the negative polarity into a second current source representing the voltage across the secondary side first output winding, and discharging the capacitor in the volt-second balance logic unit through the second current source to control the conduction duration of the first switch.

3. The flyback multi-output converter of claim 1, wherein, The second switch control circuit has a second clock synchronization unit and an error comparison unit, the second clock synchronization unit is used for detecting a voltage signal of the secondary side second output winding to determine a turn-on time of the primary side switch; the error comparison unit is used for sampling an output voltage of the second output circuit, comparing and amplifying the sampled output voltage with a preset reference voltage to form an error signal, and comparing the error signal with a preset slope signal with a fixed slope to obtain an off signal for controlling the second switch, so as to obtain a conduction duration of the second switch.

4. The flyback multi-output converter of claim 1, wherein, The set voltage between the secondary side second output winding is greater than the output voltage of the second output circuit by a certain value.

5. The flyback multi-output converter of claim 1, wherein, The input circuit further has a primary side switch control circuit, which is used for isolating sampling the output voltage of the first output circuit, and controlling the conduction state of the first switch according to the sampling voltage, so as to realize the stability of the output voltage of the first output circuit.

6. The flyback multi-output converter of claim 1, wherein, The secondary side first output winding and the secondary side second output winding are different windings, and the output voltage of the first output circuit and the output voltage of the second output circuit are both isolated outputs.

7. A control method of a flyback multi-output converter, the flyback multi-output converter comprising a transformer, an input circuit, a first output circuit, and a second output circuit, wherein, The transformer has a primary side winding, a secondary side first output winding and a secondary side second output winding; the input circuit has a primary side switch connected with the primary side winding, the first output circuit is connected with the secondary side first output winding, and the second output circuit is connected with the secondary side second output winding; the control method comprises the following steps: Detecting a voltage signal of the secondary side first output winding, and controlling a first switch in the first output circuit to turn on according to the voltage signal of the secondary side first output winding, so that the energy stored in the secondary side first output winding flows into a first output filter capacitor in the first output circuit, and the energy stored in the first output filter capacitor flows back to the secondary side first output winding; During the conduction of the primary side switch, sampling a voltage between the secondary side first output winding, and obtaining a volt-second product at the excitation of the transformer according to the sampled voltage between the secondary side first output winding; Controlling a conduction duration of the first switch according to the volt-second product; Controlling a second switch in the second output circuit to conduct for a set time during the turn-on of the first switch, so that the energy flowing back to the secondary side first output winding is supplemented to the secondary side second output winding, and is transmitted to a second output filter capacitor in the second output circuit through the secondary side second output winding.

8. The control method of the flyback multi-output converter according to claim 7, wherein Sampling a voltage between the secondary side first output winding during the conduction of the primary side switch, and obtaining a volt-second product at the excitation of the transformer according to the sampled voltage between the secondary side first output winding, comprises: During the primary-side switch turn-on period, sampling the positive polarity of the secondary-side first output winding voltage converts the secondary-side first output winding voltage into a first current source representing the secondary-side first output winding voltage, and charges a capacitor in a voltage-second balance logic unit by the first current source to obtain the voltage-second product; According to the voltage-second product, the conduction duration of the first switch is controlled, including: During the first switch turn-on period, sampling the negative polarity of the secondary-side first output winding voltage converts the negative polarity of the secondary-side first output winding voltage into a second current source representing the secondary-side first output winding voltage, and discharges the capacitor in the voltage-second balance logic unit by the second current source to control the conduction duration of the first switch.

Images