Converter suitable for a wide range of output voltages and control method thereof

Abstract

The application discloses a converter suitable for wide range output voltage and a control method thereof. The converter comprises a PWM half-bridge circuit. The control method comprises the following steps: adjusting a switching frequency to make the PWM half-bridge circuit enter a discontinuous mode; and in each switching cycle, respectively before the first and second power switch tubes are turned on, continuously turning on or twice turning on corresponding synchronous rectifier tubes for a predetermined time to realize zero voltage turn-on of the first and second power switch tubes. The application realizes zero voltage turn-on of primary side power switch tubes, thereby reducing loss.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronic converters, in particular to a converter suitable for wide range output voltage and a control method thereof. BACKGROUND

[0002] At present, there are various types of consumer electronic products on the market, and the required charging voltage range is also relatively wide, for example, the charging voltage of a mobile phone is 5V, the charging voltage of a router is 12V, and the charging voltage of a notebook computer is 20V. In order to facilitate the use of consumers and avoid unnecessary waste, the industry has been committed to promoting adapters with wide range output voltage to meet the one-to-many application requirements.

[0003] At present, the common adapter with wide range output voltage on the market has a rated power of mostly 65W, and the most commonly used topology is Flyback, which has a very wide output voltage regulation capability, and can ensure the output efficiency to meet the energy efficiency requirements through control at light load. However, with the development of client devices, the power level of power supply is getting larger and larger, and there is a demand for high-power, wide-range output power supply on the market, and its power will rise to more than 200W. However, Flyback is not suitable for high-power miniaturization and high power density design due to its inductance energy storage characteristics.

[0004] When the power of the power supply is higher than 75W, a first-stage PFC circuit needs to be added to meet the harmonic requirements, so the input voltage range of the DC-DC stage is very narrow. Similar to the scene of home direct current microgrid and vehicle charging, the input voltage range is small. For such narrow input and wide output applications, the industry has made many attempts, such as using LLC plus Buck two-stage architecture, which can meet the demand of large power wide range output, and due to the high efficiency of LLC, it can realize the design of miniaturization. However, due to the operation of both stages of circuit, the efficiency is low at low voltage output, which cannot meet the energy efficiency requirements, and the circuit structure is complex and the cost is high.

[0005] Therefore, it is necessary to find a converter with wide range output voltage and a control method thereof to improve the average efficiency at low voltage output and solve one or more of the above technical problems. SUMMARY

[0006] Therefore, it is necessary to find a converter with wide range output voltage and a control method thereof to improve the average efficiency at low voltage output and solve one or more of the above technical problems.

[0007] To achieve the above object, the present application provides a control method of a converter with wide range output voltage, the converter comprising a PWM half-bridge circuit, the PWM half-bridge circuit comprising:

[0008] a primary circuit comprising a primary switch bridge arm composed of a first power switch tube and a second power switch tube in series;

[0009] a transformer comprising a primary coil and a secondary coil, the primary coil being coupled with the primary circuit;

[0010] a secondary rectifier circuit comprising at least two synchronous rectifier tubes, an input end of the secondary rectifier circuit being coupled with the secondary coil; and

[0011] an output filter circuit comprising an output inductor and an output capacitor, the output filter circuit being coupled between an output end of the secondary rectifier circuit and a load;

[0012] the control method comprising the following steps:

[0013] adjusting a switching frequency to make the PWM half-bridge circuit enter a discontinuous mode;

[0014] in each switching cycle, before the first power switch tube and the second power switch tube are turned on, respectively, a corresponding synchronous rectifier tube is continuously turned on or turned on twice for a predetermined time to realize zero-voltage turn-on of the first power switch tube and the second power switch tube.

[0015] Further, when the load decreases, the PWM half-bridge circuit enters a BURST mode from the discontinuous mode, each BURST cycle comprising a pulse enable interval and a pulse off interval, in the pulse enable interval, the PWM half-bridge circuit works in the discontinuous mode; in the pulse off interval, all pulse signals are turned off to stop the PWM half-bridge circuit from working.

[0016] The present application also provides a converter with wide range output voltage, the converter comprising a PWM half-bridge circuit and a control unit, the PWM half-bridge circuit comprising:

[0017] a primary circuit comprising a primary switch bridge arm composed of a first power switch tube and a second power switch tube in series;

[0018] a transformer comprising a primary coil and a secondary coil, the primary coil being coupled with the primary circuit;

[0019] a secondary rectifier circuit comprising at least two synchronous rectifier tubes, an input end of the secondary rectifier circuit being coupled with the secondary coil;

[0020] An output filter circuit including an output inductor and an output capacitor is coupled between the output of the secondary-side rectifier circuit and a load.

[0021] The control unit is configured to adjust the switching frequency to make the PWM half-bridge circuit enter the discontinuous mode, and in each switching cycle, before the first power switch and the second power switch are turned on, respectively, the corresponding synchronous rectifier is continuously turned on or turned on twice for a predetermined time to realize zero voltage turn-on of the first power switch and the second power switch.

[0022] The application realizes zero voltage turn-on (ZVS) of the primary power switch by controlling the corresponding synchronous rectifier of the secondary side to be continuously turned on or turned on twice for a predetermined time before the primary power switch of the PWM half-bridge circuit is turned on, thereby reducing the switching loss.

[0023] The above description will be described in detail in the following embodiments, and the technical solutions of the application will be further explained. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to make the above and other purposes, features, advantages and embodiments of the application more obvious and easy to understand, the following is a description of the accompanying drawings:

[0025] Figure 1 The circuit diagram of the prior art PWM half-bridge circuit;

[0026] Figure 2 The working waveform of the PWM half-bridge circuit in the discontinuous mode; Figure 1

[0027] Figure 3 The PWM half-bridge circuit diagram of the converter suitable for wide range output voltage according to the first preferred embodiment of the application;

[0028] Figure 4 The PWM half-bridge circuit diagram of the converter suitable for wide range output voltage according to the second preferred embodiment of the application;

[0029] Figure 5 The PWM half-bridge circuit diagram of the converter suitable for wide range output voltage according to the third preferred embodiment of the application;

[0030] Figure 6 The PWM half-bridge circuit diagram of the converter suitable for wide range output voltage according to the fourth preferred embodiment of the application;

[0031] Figure 7 The working waveform of the PWM half-bridge circuit according to the first preferred embodiment of the application;

[0032] ​Figure 8 The waveform of the PWM half-bridge circuit operating in BURST mode according to the first preferred embodiment of the present invention;

[0033] Figure 9 The waveforms are those of the PWM half-bridge circuit according to the second preferred embodiment of the present invention. Detailed Implementation

[0034] To provide a more detailed and complete description of the invention, reference can be made to the accompanying drawings and the various embodiments described below, in which the same reference numerals represent the same or similar components. Furthermore, well-known components and steps are not described in the embodiments to avoid unnecessarily limiting the invention. Additionally, for the sake of simplicity, some known and conventional structures and elements are illustrated in a simplified schematic manner in the drawings.

[0035] The applicant's research found that, in the applications covered in the background section, the novel topology of the PWM half-bridge circuit can not only utilize the wide-range voltage regulation capability of the PWM half-bridge circuit to achieve voltage switching, but also enable the PWM half-bridge circuit to enter discontinuous mode when the output voltage is low, thereby improving the efficiency of the converter at low voltage output and under light load.

[0036] For existing PWM half-bridge circuits and their operating waveforms, please refer to [link / reference]. Figures 1-2 ,Depend on Figure 2 It is known that when the PWM half-bridge circuit operates in discontinuous mode (DCM), the voltage across the primary-side power switch will oscillate before the primary-side power switch is turned on. If conventional fixed-frequency control is used, the turn-on time of the primary-side power switch is uncontrollable. The primary-side power switch turns on when its voltage reaches its trough, and the turn-on voltage at this time is greater than V. in / 2, resulting in significant losses. If valley control is used, meaning the primary-side power switch turns on when its voltage reaches its valley, the turn-on voltage is less than V. in / 2, the turn-on loss is reduced, but in many applications the output voltage range is usually large, and also because L m Much larger than L o Therefore, when there is a low-voltage output and a high-voltage input, if the load is very small, the switching loss of the primary-side power switch is relatively large, so the effect of valley control is not obvious.

[0037] On the basis of the research, according to a preferred embodiment of the present application, a control method suitable for a transformer with a wide range of output voltages is provided, which controls the corresponding synchronous rectifier to be continuously or twice conducted for a period of time before the primary side power switch tube is turned on, so as to generate a discharge current in the output inductor, and after the corresponding synchronous rectifier is turned off, a reverse current is induced in the primary side circuit by the discharge current, the reverse current is used to participate in the resonance process of the output inductor, the excitation inductor of the transformer and the parasitic capacitor of the PWM half-bridge circuit, and the power switch tube is turned on when the voltage across the corresponding primary side power switch tube resonates to zero, so as to realize zero voltage switching (ZVS) of the primary side power switch tube, thereby reducing the switching loss.

[0038] Specifically, the transformer includes a PWM half-bridge circuit and a control unit, wherein the control unit can be coupled with the PWM half-bridge circuit through wired or wireless means. Advantageously, by using the topology architecture of the PWM half-bridge circuit, on the one hand, the voltage switching function can be realized by using the wide range voltage regulation capability of the PWM half-bridge circuit, and on the other hand, the PWM half-bridge circuit is controlled to work in the discontinuous mode at low voltage output, thereby improving the efficiency at low voltage output.

[0039] Referring again to Figure 3 The PWM half-bridge circuit includes a primary side circuit, a transformer, a secondary side rectifier circuit and an output filter circuit. The primary side circuit includes a primary side switching bridge arm composed of a first power switch tube S1 and a second power switch tube S2 in series. The transformer includes a primary side coil and a secondary side coil, and the primary side coil is coupled with the output end of the primary side circuit. The secondary side rectifier circuit includes at least two synchronous rectifier tubes SR1 and SR2, and the input end of the secondary side rectifier circuit is coupled with the secondary side coil. The output filter circuit includes an output inductor L o and an output capacitor C o The output filter circuit is coupled between the output end of the secondary side rectifier circuit and a load.

[0040] It can be understood that the output inductor L o and the transformer can be integrated together, i.e. integrated in the same magnetic element, to reduce the total volume of the magnetic elements in the circuit and improve the power density of the transformer. Of course, they can also be discrete, and the present application is not limited in this way.

[0041] Further, the control method includes the following steps: by adjusting the switching frequency f sw to make the PWM half-bridge circuit enter the discontinuous mode, for example, by reducing the switching frequency f swThe PWM half-bridge circuit enters the discontinuous mode; and in each switching cycle, the corresponding synchronous rectifier is continuously or twice continuously turned on for a predetermined time before the first power switch S1 and the second power switch S2 are turned on, so as to realize zero voltage turn-on of the first power switch S1 and the second power switch S2, thereby achieving the purpose of reducing switching loss.

[0042] It can be understood that the parasitic capacitance of the PWM half-bridge circuit can be equivalent to the parasitic capacitance of the synchronous rectifier, the first power switch S1, the second power switch S2 and the transformer, and can be equivalent to the parasitic capacitance of the midpoint of the primary side switching bridge arm to the ground. The midpoint of the primary side switching bridge arm is the connection node of the first power switch S1 and the second power switch S2.

[0043] Preferably, referring to Figure 3 , the primary side circuit further comprises a capacitor bridge arm composed of a first capacitor and a second capacitor in series, one end of the primary side coil of the transformer is coupled to the midpoint of the capacitor bridge arm, wherein the midpoint of the capacitor bridge arm is the connection node of the first capacitor and the second capacitor, and the other end of the primary side coil is coupled to the midpoint of the primary side switching bridge arm. The PWM half-bridge circuit of the present application is not limited to the structure in Figure 3 . For example, referring to Figure 4 and Figure 5 , the primary side circuit can further comprise a capacitor connected to the positive input terminal or the negative input terminal of the primary side circuit, that is, one end of the capacitor is coupled to the positive input terminal or the negative input terminal of the primary side circuit, and the other end of the capacitor is coupled to one end of the primary side coil of the transformer, and the other end of the primary side coil is coupled to the midpoint of the primary side switching bridge arm. It can be understood that the capacitor can also be connected in series at other positions in the primary side circuit, for example, in series between the other end of the primary side coil and the midpoint of the primary side switching bridge arm.

[0044] Preferably, as shown in Figure 3 , the first power switch S1 is connected to the negative input terminal of the primary side circuit, and the second power switch S2 is connected to the positive input terminal of the primary side circuit. The midpoint voltage of the primary side switching bridge arm is detected, the first power switch S1 is turned on when the midpoint voltage of the primary side switching bridge arm is less than a first preset voltage, and the second power switch S2 is turned on when the midpoint voltage of the primary side switching bridge arm is greater than a second preset voltage. The first preset voltage can be a value close to zero, and the second preset voltage can be a value close to V in . Therefore, zero voltage turn-on of the first power switch S1 and the second power switch S2 can be realized, and the switching loss is greatly reduced.

[0045] Preferably, the secondary side rectifier circuit can be a full-wave rectifier circuit or a full-bridge rectifier circuit. As Figures 3-5As shown, when the secondary coil adopts a center-tapped structure, that is, the secondary coil of the transformer includes a first terminal, a second terminal, and a common terminal. The secondary rectifier circuit includes a first synchronous rectifier diode SR1 and a second synchronous rectifier diode SR2. One end of the first synchronous rectifier diode SR1 and one end of the second synchronous rectifier diode SR2 are respectively connected to the first terminal and the second terminal of the secondary coil. The other end of the first synchronous rectifier diode SR1 and the other end of the second synchronous rectifier diode SR2 are simultaneously connected to the output capacitor C. o One end is connected to the output inductor L. o The two ends are respectively connected to the common terminal of the secondary coil and the output capacitor C. o The other end is connected.

[0046] like Figure 6 As shown, when the secondary rectifier circuit adopts a full-bridge structure, the secondary coil of the transformer includes a first terminal and a second terminal. The secondary rectifier circuit includes first to fourth synchronous rectifier diodes SR1-SR4. The first synchronous rectifier diode SR1 and the second synchronous rectifier diode SR2 are connected in series to form the first bridge arm of the secondary side, and the third synchronous rectifier diode SR3 and the fourth synchronous rectifier diode SR4 are connected in series to form the second bridge arm of the secondary side. The first terminal and the second terminal of the secondary coil are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm of the secondary side. The output capacitor C... o Through the output inductor L o It is connected in parallel to both ends of the first and second arms of the secondary side.

[0047] According to another preferred embodiment of the present invention, during the switching state transition interval of the first power switch S1 and the second power switch S2, that is, during the dead time when the two power switches are alternately turned on, the current flowing through the first synchronous rectifier SR1 and the current flowing through the second synchronous rectifier SR2 are detected, and the corresponding synchronous rectifier is controlled to be turned off or kept on according to the current on the synchronous rectifier. In one embodiment, such as Figure 7 As shown, during the dead time from the first power switch S1 being turned off to the second power switch S2 being turned on, the current on the first synchronous rectifier SR1 decreases linearly. When the current drops to 0, the first synchronous rectifier SR1 remains on, and the second synchronous rectifier SR2 remains on. During the dead time from the second power switch S2 being turned off to the first power switch S1 being turned on, the current on the second synchronous rectifier SR2 decreases linearly. When the current drops to 0, the second synchronous rectifier SR2 remains on, and the first synchronous rectifier SR1 remains on.

[0048] In another embodiment, such as Figure 9As shown, during the dead time from the first power switch S1 being turned off to the second power switch S2 being turned on, when the current on the first synchronous rectifier SR1 drops to 0, the first synchronous rectifier SR1 is turned off, while the second synchronous rectifier SR2 remains on. The voltage across the first synchronous rectifier SR1 is further determined; for example, if the first synchronous rectifier SR1 is a MOSFET, its drain-source voltage V is determined. DS_SR1 Whether the instantaneous value reaches the bottom of the waveform depends on the drain-source voltage V of the first synchronous rectifier SR1. DS_SR1 At the m-th valley, the first synchronous rectifier diode SR1 is turned on again to enable the output inductor L o The magnetizing inductance L of the transformer m The parasitic capacitance of the PWM half-bridge circuit resonates. During the dead time between the turn-off of the second power switch S2 and the turn-on of the first power switch S1, when the current on the second synchronous rectifier SR2 drops to 0, the second synchronous rectifier SR2 is turned off, while the first synchronous rectifier SR1 remains on. The voltage across the second synchronous rectifier SR2 is further determined; for example, if the second synchronous rectifier SR2 is a MOSFET, its drain-source voltage V is determined. DS_SR2 Whether the instantaneous value reaches the bottom of the waveform depends on the drain-source voltage V of the second synchronous rectifier SR2. DS_SR2 At the m-th valley, the second synchronous rectifier SR2 is turned on again to make the output inductor L o The magnetizing inductance L of the transformer m The circuit resonates with the parasitic capacitance of the PWM half-bridge circuit. By adjusting the duration of this resonance, the switching frequency can be further reduced, thereby reducing switching losses. Here, m is an integer greater than or equal to 1. It can be understood that the value of m is related to the load size and the switching frequency; a decrease in load leads to an increase in the value of m, and vice versa.

[0049] Preferably, when the load decreases further, the PWM half-bridge circuit will switch from the discontinuous mode to the BURST mode. Each BURST cycle includes a pulse enable interval (Burst ON) and a pulse disable interval (Burst OFF). During the pulse enable interval, the PWM half-bridge circuit operates in the aforementioned discontinuous mode. During the pulse disable interval, all pulse signals are turned off, that is, the drive signals of the primary circuit and the secondary rectifier circuit are turned off, so that the PWM half-bridge circuit stops working.

[0050] Preferably, in each pulse enable interval, the first switching cycle is processed to enable the magnetizing inductor L. m current i Lm and the output inductor L o current i LoThe predetermined trajectory is accessed, and the last switching cycle is processed to make the magnetizing inductor L... m current i Lm The pulse signal that turns off the primary circuit when it is zero.

[0051] See Figure 7 and Figure 9 ZVS control can be divided into two operating modes based on the relationship between the driving of the synchronous rectifier and the power switch: complementary and non-complementary. The complementary operating mode corresponds to the synchronous rectifier being continuously turned on during the switching interval, while the non-complementary operating mode corresponds to the synchronous rectifier being turned on twice during the switching interval. The following section will combine... Figures 7-9 The examples further illustrate the complementary and non-complementary ZVS control methods, as well as the complementary ZVS control method operating in BURST mode. It should be noted that due to the transformer leakage inductance L... k Much smaller than the magnetizing inductance L m Therefore, the following process ignores the leakage inductance L. k The impact.

[0052] First, there is the complementary working model, such as Figure 7 As shown, it illustrates Figure 3 The waveform of the PWM half-bridge circuit shown is shown.

[0053] [t0-t1] phase:

[0054] At time t0, the first power switch S1 is turned off, and the voltage V across S1 is... ds_S1 From 0V to V in / 2(where V) in (Input voltage); Primary current i p From peak current i p_pk It becomes 0A; the magnetizing inductance L m current i Lm Maintain peak current i Lm_pk Unchanged; the voltage V across the second synchronous rectifier diode SR2 remains unchanged. ds_SR2 By V in When the turns ratio of the transformer's primary and secondary sides (n) becomes 0, SR2 turns on. At this time, the first synchronous rectifier diode SR1 is in the conducting state, and the output inductor L... o Current i on Lo The current i on the first synchronous rectifier diode SR1 SR1 The current i on the second synchronous rectifier tube SR2 SR2 The linear decrease continues until time t1, when i SR1 Reduced to 0, i SR2 and i Lo Reduced to n*i Lm_pk .

[0055] [t1-t2] stage:

[0056] At time t1, the current i SR1 on the first synchronous rectifier SR1 drops to 0, the current i SR2 on the second synchronous rectifier SR2 and the current i Lo on the output inductor drop to n*i Lm_pk , the first synchronous rectifier SR1 is controlled to be continuously turned on, and the current i Lo on the output inductor continues to linearly decrease to generate a discharge current, until time t2, the first synchronous rectifier SR1 is turned off. The time t1-t2 can be calculated by a control chip.

[0057] [t2-t3] stage:

[0058] At time t2, the first synchronous rectifier SR1 is turned off, at this time, the second synchronous rectifier SR2 is still in a turned-on state, and a reverse current is generated by the primary side circuit, which is used to discharge the parasitic capacitor between the second power switch S2 to be turned on and the parasitic capacitor between the transformer excitation inductor L m , the output inductor L o and the PWM half-bridge circuit, at time t3, the voltage borne by the first power switch S1 is greater than or equal to a second preset voltage, for example, reaches V in , at this time, the second power switch S2 is turned on, so that the zero-voltage turn-on of S2 can be realized.

[0059] [t3-t4] stage:

[0060] At time t3, the second power switch S2 is turned on, the primary side current i p and the current i Lm of the transformer excitation inductor linearly decrease, and the current i Lo of the output inductor linearly increases, until time t4, the primary side current i p reaches a negative peak current -i p_pk .

[0061] [t4-t5] stage:

[0062] At time t4, the second power switch S2 is turned off, the voltage V ds_S1 borne by the first power switch S1 changes from V in to V in / 2; the primary side current i p changes from the negative peak current -i p_pk to 0A; the current i Lm of the excitation inductor remains the negative peak current -i Lm_pk unchanged; the voltage V ds_SR1 borne by the first synchronous rectifier SR1 changes from Vin n becomes 0, the first synchronous rectifier SR1 is turned on, at this time the second synchronous rectifier SR2 is in a continuous conduction state, the current i Lo on the first synchronous rectifier SR1 i SR1 and the current i SR2 on the second synchronous rectifier SR2 linearly decreases until the time t5, i SR2 drops to 0, i SR1 and i Lo drop to n*i Lm_pk . [t5-t6] phase:

[0063] At the time t5, the current i SR2 on the second synchronous rectifier SR2 drops to 0, the current i SR1 on the first synchronous rectifier SR1 and the current i Lo on the output inductor drop to n*i Lm_pk , the second synchronous rectifier SR2 is controlled to continue to be turned on, the current i Lo on the output inductor continues to linearly decrease to generate a discharge current, until the time t6, the second synchronous rectifier SR2 is turned off. The time t5-t6 can be calculated by a control chip.

[0064] [t6-t7] phase:

[0065] At the time t6, the second synchronous rectifier SR2 is turned off, at this time the first synchronous rectifier SR1 is still in a conduction state, the discharge current of the previous stage promotes the primary side circuit to generate a reverse current, the reverse current is used to discharge the parasitic capacitance between the first power switch S1 and the second power switch S2, specifically, the reverse current participates in the resonance between the transformer excitation inductor L m , the output inductor L o and the parasitic capacitance of the PWM half-bridge circuit, at the time t7, the voltage V ds_S1 suffered by the first power switch S1 is less than or equal to a first preset voltage, for example, 0V, at this time the first power switch S1 is turned on, so that the zero voltage turn-on of the first power switch S1 can be realized.

[0066] [t7-t8] phase:

[0067] At the time t7, the first power switch S1 is turned on, the current i p on the primary side, the current i Lm of the transformer excitation inductor and the current i Lo of the output inductor linearly increase, until the time t8, the primary current i p reaches a peak current i p_pk , the first power switch S1 is turned off, and the process is repeated thereafter.

[0068] It should be noted that the ZVS control method in the complementary mode of the PWM half-bridge circuit has a limitation condition: the circuit must work in the non-strict discontinuous mode, i.e., the critical conduction mode, in the entire input voltage range and the entire load range. However, if the PWM half-bridge circuit works in the critical conduction mode, the light load efficiency of low-voltage output is seriously affected, and the reason is as follows: when the PWM half-bridge circuit works in the critical conduction mode, the switching frequency is inversely proportional to the load, and the lighter the load, the higher the switching frequency. Therefore, the switching frequency of the low-voltage output light load case will be very high, and the switching loss caused thereby seriously affects the efficiency. In order to solve the above problem, the present application provides a complementary ZVS control method in the BURST mode.

[0069] Specifically, as shown in Figure 8 , during the Burst ON, the first and last switching periods need to be processed to make the current i Lm of the excitation inductor and the current i Lo of the output inductor quickly access the predetermined trajectory, and make the current i Lm of the excitation inductor zero, and then turn off the drive signal of the primary power switch tube, and when the current i Lo of the output inductor decreases to 0, enter the Burst OFF state, thereby avoiding loss and oscillation, wherein the predetermined trajectory of the current i Lm of the excitation inductor and the current i Lo of the output inductor is the trajectory of the current i Lm of the excitation inductor and the current i Lo of the output inductor in the aforementioned discontinuous mode. For the remaining switching periods during the Burst ON, the frequency and conduction time can be kept constant, and the present application is not limited thereto.

[0070] The working waveforms of Figure 8 will be combined below to describe the control stages in detail.

[0071] [t0-t1] stage:

[0072] At t0, enter the Burst ON interval, the first power switch tube S1 is turned on, the voltage V ds_S1 suffered by S1 changes from V in / 2 to 0, the voltage V ds_SR1 suffered by the first synchronous rectifier SR1 changes from V o to 0, the first synchronous rectifier SR1 is turned on, the voltage V ds_SR2 suffered by the second synchronous rectifier SR2 changes from V o to V in / n, the primary current i p , the current i Lmand the current i of the output inductor Lo Linearly rises from zero until the moment t1, the current i of the excitation inductor Lm Reaches the peak value, since the current of the excitation inductor cannot be detected, so this time can be calculated by the control chip.

[0073] [t1-t8] stage:

[0074] At the moment t1, the current i of the excitation inductor Lm and the current i of the output inductor Lo After entering the predetermined trajectory, turn off the first power switch S1, and the working process of the time t1-t8 is the same as that of t0-t7 in Figure 7 , which will not be described here. The switching frequency and conduction time remain constant during this period until the moment t8 enters the last switching cycle of the current Burst ON state.

[0075] [t8-t9] stage:

[0076] At the moment t8, the first power switch S1 is turned on, the primary current i p , the current i of the excitation inductor Lm and the current i of the output inductor Lo Linearly rises until the moment t9, the current i of the excitation inductor Lm Reaches 0, the first power switch S1 is turned off, and t8-t9 can also be calculated.

[0077] [t9-t10] stage:

[0078] At the moment t9, the first power switch S1 is turned off, and the voltage V in / 2 borne by S1 changes from 0 to V ds_SR2 / 2, the voltage V in borne by the second synchronous rectifier SR2 changes from V p / n to 0, and the second synchronous rectifier SR2 is turned on. At this time, the first synchronous rectifier SR1 is in the on state, the primary current i Lm and the current i of the excitation inductor Lo Remain unchanged at 0, and the current i of the output inductor Lo Linearly decreases until the moment t10, the current i of the output inductor Lo Decreases to 0.

[0079] [t10-t11] stage:

[0080] At the moment t10, the current i of the output inductor o, enters the Burst OFF state, until the time t11 re-enters the Burst ON state, after which the previous process is repeated.

[0081] It can be understood that the first and last switching periods in the Burst ON process do not necessarily correspond to the first power switch S1, and can also be the second power switch S2, and the working mode is the same.

[0082] Further, for the frequency of Burst ON / OFF and the number of switching periods in the Burst ON process, there are two control modes: 1. The number of switching periods in the Burst ON process is fixed, and the frequency of Burst ON / OFF is adjusted according to the size of the load. The larger the load, the higher the frequency; the smaller the load, the lower the frequency; 2. Keep the frequency of Burst ON / OFF relatively fixed, adjust the number of switching periods in the Burst ON process according to the size of the load. The larger the load, the more the number; the smaller the load, the less the number.

[0083] Second, the non-complementary working mode, as shown in Figure 9 , wherein the working waveform of the PWM half-bridge circuit shown in Figure 3 in another embodiment is shown.

[0084] [t0-t1] stage:

[0085] At time t0, the first power switch S1 is turned off, and the voltage V ds_S1 applied to S1 changes from 0V to V in / 2; the primary current i p changes from the peak current i p_pk to 0A; the current i m of the excitation inductor L Lm remains the peak current i Lm_pk unchanged; the voltage V ds_SR2 applied to the synchronous rectifier SR2 changes from V in / n to 0, and SR2 is turned on. At this time, the synchronous rectifier SR1 is in the on state, the current i o on the output inductor L Lo , the current i SR1 on the first synchronous rectifier SR1, and the current i SR2 on the second synchronous rectifier SR2 linearly decrease until time t1, i SR1 drops to 0, i SR2 and i Lo drop to n*i Lm_pk .

[0086] [t1-t2] stage:

[0087] At time t1, the current i on the first synchronous rectifier diode SR1 is SR1 The current i on the second synchronous rectifier diode SR2 drops to 0. SR2 and the current i on the output inductor Lo Reduced to n*i Lm_pk At this time, the first synchronous rectifier diode SR1 is turned off, while the second synchronous rectifier diode SR2 remains on, and the output inductor L... o Transformer magnetizing inductance L m The parasitic capacitance of the PWM half-bridge circuit causes oscillation; the voltage V across the first power switch S1 ds_S1 by As the equilibrium point, The amplitude is oscillated; the voltage V that the first synchronous rectifier diode SR1 withstands is... ds_SR1 by As the equilibrium point, The amplitude is oscillated; the current i of the output inductor is... Lo Taking a linearly decreasing current as the equilibrium point, it oscillates with another specific amplitude; and the oscillation periods of all three are the same, equal to... (Where CEQ is the parasitic capacitance of the PWM half-bridge circuit). Until time t2, the voltage V across the first synchronous rectifier diode SR1... ds_SR1 The oscillation reaches the m-th trough. Understandably, the duration of t1-t2 can be chosen to occur at the m-th trough. The value of m is related to the load and switching frequency; the lower the switching frequency or the smaller the load, the larger the value of m. When the load decreases, the frequency is rapidly reduced by increasing the number of troughs m, thereby reducing switching losses and improving light-load efficiency.

[0088] [t2-t3] phase:

[0089] At time t2, the first synchronous rectifier diode SR1 is turned on again, and the current i in the output inductor... Lo The discharge current decreases linearly until time t3, at which point the first synchronous rectifier diode SR1 turns off. The time interval t2-t3 can be calculated by the control chip.

[0090] [t3-t4] phase:

[0091] At time t3, the first synchronous rectifier diode SR1 is turned off, while the second synchronous rectifier diode SR2 remains on. A reverse current is generated in the primary circuit. This reverse current discharges the parasitic capacitance across the second power switch diode S2, which is about to be turned on. Specifically, this reverse current participates in the transformer magnetizing inductance L. m Output inductor L o The resonance between the parasitic capacitance of the PWM half-bridge circuit and the voltage V across the first power switch S1 at time t4. ds_S1greater than or equal to a second preset voltage, for example, V in At this time, the second power switch S2 is turned on, so that the zero-voltage turn-on of S2 can be realized.

[0092] [t4-t5] phase:

[0093] At t4, the second power switch S2 is turned on, and the primary current i p and the current i Lm of the transformer excitation inductance linearly decreases, and the current i Lo of the output inductance linearly increases until t5, the primary current i p reaches the negative peak current -i p_pk .

[0094] [t5-t6] phase:

[0095] At t5, the second power switch S2 is turned off, and the voltage V ds_S1 suffered by the first power switch S1 changes from V in to V in / 2; the primary current i p changes from the negative peak current -i p_pk to 0A; the current i Lm of the excitation inductance remains the negative peak current -i Lm_pk unchanged; the voltage suffered by the first synchronous rectifier SR1 changes from V in / n to 0, and SR1 is turned on. At this time, the second synchronous rectifier SR2 is in the on state, the current i Lo on the output inductance, the current i SR1 on the first synchronous rectifier SR1, and the current i SR2 on the second synchronous rectifier SR2 linearly decrease until t6, i SR2 drops to 0, i SR1 and i Lo drop to n*i Lm_pk .

[0096] [t6-t7] phase:

[0097] At t6, the current i SR2 on the second synchronous rectifier SR2 drops to 0, the current i SR1 on the first synchronous rectifier SR1, and the current i Lo on the output inductance drop to n*i Lm_pk . At this time, the second synchronous rectifier SR2 is turned off, and the first synchronous rectifier SR1 remains in the on state. The output inductance L o and the transformer excitation inductance L m oscillate with the parasitic capacitance; the voltage V ds_S1 suffered by the first power switch S1 changes from V is balanced point, oscillate with amplitude; the voltage V ds_SR2 with is balanced point, oscillate with amplitude; the current i Lo with linearly descending current as balanced point, oscillate with another certain amplitude, and the oscillation periods of the three are equal to Until the moment t7, the voltage V ds_SR2 oscillate to the mth valley. Similarly, when the load decreases, the frequency can be quickly reduced by increasing the valley number m in the period t6-t7, thereby reducing the switching loss and improving the light load efficiency.

[0098] [t7-t8] stage:

[0099] At the moment t7, the second synchronous rectifier SR2 is turned on again, and the current i Lo linearly descends to generate a discharge current, until the moment t8, the second synchronous rectifier SR2 is turned off. The time t7-t8 can also be calculated by the control chip.

[0100] [t8-t9] stage:

[0101] At the moment t8, the second synchronous rectifier SR2 is turned off, and at this moment, the first synchronous rectifier SR1 is still in the on state, and the primary side circuit generates a reverse current, which is used to discharge the parasitic capacitor between the first power switch S1 to be turned on. Specifically, the reverse current participates in the resonance between the transformer excitation inductance L m , the output inductance L o and the parasitic capacitor of the PWM half-bridge circuit, and at the moment t9, the voltage V ds_S1 suffered by the first power switch S1 is less than or equal to the first preset voltage, for example, 0V, at this moment, the first power switch S1 is turned on, thereby realizing the zero-voltage turn-on of S1.

[0102] [t9-t10] stage:

[0103] At the moment t9, the first power switch S1 is turned on, and the primary current i p , the transformer excitation current i Lm and the output inductance current i Lo linearly rise, until the moment t10, the primary current i p reaches the peak current i p_pk , the first power switch S1 is turned off, and thereafter the previous process is repeated.

[0104] According to another preferred embodiment of the present application, the ZVS control in the complementary and non-complementary modes described above can also be applied to Figure 6 The PWM half-bridge circuit shown in Fig. 1 is a half-bridge circuit with full-bridge rectifier, in which the first synchronous rectifier SR1 and the third synchronous rectifier SR3 work synchronously, and the second synchronous rectifier SR2 and the fourth synchronous rectifier SR4 work synchronously:

[0105] In the complementary mode, the first power switch S1 is turned off, the first synchronous rectifier SR1 and the third synchronous rectifier SR3 are controlled to be turned on, the current i SR1 on the first synchronous rectifier SR1 linearly decreases, the current i SR2 on the second synchronous rectifier SR2 linearly decreases, the current i SR3 on the third synchronous rectifier SR3 linearly decreases, and the current i SR4 on the fourth synchronous rectifier SR4 linearly decreases, until i SR2 and i SR4 drop to 0, the second synchronous rectifier SR2 and the fourth synchronous rectifier SR4 are controlled to be continuously turned on for a preset time, so as to realize the zero-voltage turn-on of the second power switch S2; similarly, the second power switch S2 is turned off, the second synchronous rectifier SR2 and the fourth synchronous rectifier SR4 are controlled to be turned on, the current i SR1 on the first synchronous rectifier SR1 linearly decreases, the current i SR2 on the second synchronous rectifier SR2 linearly decreases, the current i SR3 on the third synchronous rectifier SR3 linearly decreases, and the current i SR4 on the fourth synchronous rectifier SR4 linearly decreases, until i SR1 and i SR3 drop to 0, the first synchronous rectifier SR1 and the third synchronous rectifier SR3 are controlled to be continuously turned on for a preset time, so as to realize the zero-voltage turn-on of the first power switch S1.

[0106] In the non-complementary mode, the first power switch S1 is turned off, the first synchronous rectifier SR1 and the third synchronous rectifier SR3 are controlled to be turned on, the current i SR1 on the first synchronous rectifier SR1 linearly decreases, the current i SR2 on the second synchronous rectifier SR2 linearly decreases, the current i SR3 on the third synchronous rectifier SR3 linearly decreases, and the current i SR4 on the fourth synchronous rectifier SR4 linearly decreases, until i SR2 and i SR4 drop to 0, the second synchronous rectifier SR2 and the fourth synchronous rectifier SR4 are turned off, the output inductor L o and the transformer excitation inductor L m oscillate with the parasitic capacitance of the PWM half-bridge circuit, and when the voltage V ds_SR2the voltage V across the fourth synchronous rectifier SR4 ds_SR4 When the oscillation reaches the mth valley, the second synchronous rectifier SR2 and the fourth synchronous rectifier SR4 are controlled to be turned on twice for a preset time to realize the zero-voltage turn-on of the second power switch S2. SR1 the current i across the second synchronous rectifier SR2 SR2 the current i across the third synchronous rectifier SR3 SR3 and the current i across the fourth synchronous rectifier SR4 SR4 linearly decreases until i SR1 and i SR3 reach 0, the first synchronous rectifier SR1 and the third synchronous rectifier SR3 are turned off, and the output inductor L o and the transformer excitation inductor L m oscillate with the parasitic capacitance of the PWM half-bridge circuit, and the voltage V across the first synchronous rectifier SR1 ds_SR1 and the voltage V across the third synchronous rectifier SR3 ds_SR3 When the oscillation reaches the mth valley, the first synchronous rectifier SR1 and the third synchronous rectifier SR3 are controlled to be turned on twice for a preset time to realize the zero-voltage turn-on of the first power switch S1.

[0107] According to another preferred embodiment of the present application, the present application further provides a converter suitable for a wide range of output voltages. The converter comprises a PWM half-bridge circuit. The PWM half-bridge circuit comprises a primary circuit comprising a primary switching bridge arm composed of a first power switch S1 and a second power switch S2 connected in series; a transformer comprising a primary coil and a secondary coil, the primary coil being coupled to an output terminal of the primary circuit; a secondary rectifier circuit comprising at least two synchronous rectifiers, an input terminal of the secondary rectifier circuit being coupled to the secondary coil; an output filter circuit comprising an output inductor and an output capacitor, the output filter circuit being coupled between an output terminal of the secondary rectifier circuit and a load; and a control unit for adjusting the switching frequency (e.g. reducing the switching frequency) to make the PWM half-bridge circuit enter the discontinuous mode, and in each switching cycle, before the first power switch S1 and the second power switch S2 are turned on, respectively, the corresponding synchronous rectifier is continuously turned on or turned on twice for a predetermined time to realize the zero-voltage turn-on of the first power switch S1 and the second power switch S2.

[0108] Preferably, the secondary winding of the transformer is a center-tapped structure, comprising a first end, a second end and a common end, the secondary rectifier circuit comprises a first synchronous rectifier SR1 and a second synchronous rectifier SR2, one end of the first synchronous rectifier SR1 and one end of the second synchronous rectifier SR2 are connected to the first end and the second end of the secondary winding respectively, the other end of the first synchronous rectifier SR1 and the other end of the second synchronous rectifier SR2 are connected to one end of the output capacitor simultaneously, the other ends of the output inductor are connected to the common end of the secondary winding and the other end of the output capacitor respectively.

[0109] According to another preferred embodiment of the present application, the converter further comprises a current detection unit for detecting the current on the first synchronous rectifier SR1 and the current on the second synchronous rectifier SR2. The control unit is further configured to receive the detection result of the current detection unit, and when the current on the first synchronous rectifier SR1 drops to 0 during the dead time from the turn-off of the first power switch S1 to the turn-on of the second power switch S2, the first synchronous rectifier SR1 is kept on for a predetermined time; when the current on the second synchronous rectifier SR2 drops to 0 during the dead time from the turn-off of the second power switch S2 to the turn-on of the first power switch S1, the second synchronous rectifier SR2 is kept on for a predetermined time.

[0110] According to another preferred embodiment of the present application, the converter further comprises a current detection unit for detecting the current on the first synchronous rectifier SR1 and the current on the second synchronous rectifier SR2. The control unit is further configured to receive the detection result of the current detection unit, and when the current on the first synchronous rectifier SR1 drops to 0 during the dead time from the turn-off of the first power switch S1 to the turn-on of the second power switch S2, the first synchronous rectifier SR1 is turned off and the second synchronous rectifier SR2 is kept on; when the current on the second synchronous rectifier SR2 drops to 0 during the dead time from the turn-off of the second power switch S2 to the turn-on of the first power switch S1, the second synchronous rectifier SR2 is turned off and the first synchronous rectifier SR1 is kept on.

[0111] Further, the converter further comprises a secondary voltage detection unit for detecting the voltage across the first synchronous rectifier SR1 and the second synchronous rectifier SR2, for example, whether the instantaneous value of the drain-source voltage of a MOSFET reaches the valley value of the waveform, when the voltage across the first synchronous rectifier SR1 oscillates to the mth valley, the control unit controls the second synchronous rectification of the first synchronous rectifier SR1; when the voltage across the second synchronous rectifier SR2 oscillates to the mth valley, the control unit controls the second synchronous rectification of the second synchronous rectifier SR2, wherein m is an integer greater than or equal to 1.

[0112] According to another preferred embodiment of the present application, the secondary winding of the transformer comprises a first end and a second end, the secondary rectifier circuit comprises first to fourth synchronous rectifier tubes SR1-SR4, the first synchronous rectifier tube SR1 and the second synchronous rectifier tube SR2 are connected in series to form a first secondary bridge arm, the third synchronous rectifier tube SR3 and the fourth synchronous rectifier tube SR4 are connected in series to form a second secondary bridge arm, the first end and the second end of the secondary winding are connected to the midpoints of the first secondary bridge arm and the second secondary bridge arm respectively, and the output capacitor C o The output inductor L o is connected in parallel to the two ends of the first secondary bridge arm and the second secondary bridge arm.

[0113] Preferably, corresponding to the complementary mode, the converter further comprises a current detection unit for detecting the currents on the first synchronous rectifier tube SR1, the second synchronous rectifier tube SR2, the third synchronous rectifier tube SR3 and the fourth synchronous rectifier tube SR4. The control unit is further configured to receive the detection results of the current detection unit, and control the first synchronous rectifier tube SR1 and the third synchronous rectifier tube SR3 to work synchronously, and control the second synchronous rectifier tube SR2 and the fourth synchronous rectifier tube SR4 to work synchronously; and during the dead time from the turn-off of the first power switch tube S1 to the turn-on of the second power switch tube S2, control the first synchronous rectifier tube SR1 and the third synchronous rectifier tube SR3 to be turned on, and when the currents on the second synchronous rectifier tube SR2 and the fourth synchronous rectifier tube SR4 drop to 0, continue to turn on the second synchronous rectifier tube SR2 and the fourth synchronous rectifier tube SR4 for a predetermined time; during the dead time from the turn-off of the second power switch tube S2 to the turn-on of the first power switch tube S1, control the second synchronous rectifier tube SR2 and the fourth synchronous rectifier tube SR4 to be turned on, and when the currents on the first synchronous rectifier tube SR1 and the third synchronous rectifier tube SR3 drop to 0, continue to turn on the first synchronous rectifier tube SR1 and the third synchronous rectifier tube SR3 for a predetermined time.

[0114] Preferably, corresponding to the non-complementary mode, the converter further includes a current detection unit for detecting the current on the first synchronous rectifier SR1, the second synchronous rectifier SR2, the third synchronous rectifier SR3, and the fourth synchronous rectifier SR4. The control unit is further configured to receive the detection result from the current detection unit and control the first synchronous rectifier SR1 and the third synchronous rectifier SR3 to operate synchronously, control the second synchronous rectifier SR2 and the fourth synchronous rectifier SR4 to operate synchronously; and, during the dead time from the first power switch S1 being turned off to the second power switch S2 being turned on, control the first synchronous rectifier SR1 and the third synchronous rectifier SR3 to conduct; and when the current on the second synchronous rectifier SR2 and the fourth synchronous rectifier SR4 drops to 0, turn off the second synchronous rectifier SR2 and the fourth synchronous rectifier SR4. At this time, the output inductor L... o and the excitation inductance L of the transformer m The parasitic capacitance of the PWM half-bridge circuit creates oscillation, when the voltage V across the second synchronous rectifier SR2... ds_SR2 The voltage V across the fourth synchronous rectifier diode SR4 ds_SR4 When the oscillation reaches the m-th trough, the second synchronous rectifier SR2 and the fourth synchronous rectifier SR4 are turned on again and continue to conduct for the preset time to achieve zero-voltage turn-on of the second power switch S2. During the dead time between the turn-off of the second power switch S2 and the turn-on of the first power switch S1, the second synchronous rectifier SR2 and the fourth synchronous rectifier SR4 are turned on. When the current on the first synchronous rectifier SR1 and the third synchronous rectifier SR3 drops to 0, the first synchronous rectifier SR1 and the third synchronous rectifier SR3 are turned off. At this time, the output inductor L... o and the excitation inductance L of the transformer m The parasitic capacitance of the PWM half-bridge circuit creates oscillation, when the voltage V across the first synchronous rectifier SR1... ds_SR1 The voltage V across the third synchronous rectifier diode SR3 ds_SR3 When the oscillation reaches the m-th trough, the first synchronous rectifier SR1 and the third synchronous rectifier SR3 are turned on again and continue to conduct for the preset time to achieve zero-voltage turn-on of the first power switch S1. Here, m is an integer greater than or equal to 1.

[0115] Preferably, when the load is further reduced, the control unit controls the PWM half-bridge circuit to enter the BURST mode from the discontinuous mode. Each BURST cycle includes a pulse enable interval and a pulse disable interval. In the pulse enable interval, the PWM half-bridge circuit operates in the discontinuous mode; in the pulse disable interval, all pulse signals are turned off, causing the PWM half-bridge circuit to stop working.

[0116] Further, in each of the pulse enable intervals, the first switch period is processed to make the current of the excitation inductor and the current of the output inductor access a predetermined trajectory, and the last switch period is processed to make the current of the excitation inductor be zero and then the pulse signal of the primary side circuit is closed.

[0117] It can be understood that the predetermined trajectory is the trajectory of the current of the excitation inductor and the current of the output inductor in the discontinuous mode.

[0118] Preferably, the transformer further comprises a primary side voltage detection unit configured to detect the midpoint voltage of the primary side switching bridge arm and output the detection result to the control unit. The first power switch S1 is connected to the negative input end of the primary side circuit, and the second power switch S2 is connected to the positive input end of the primary side circuit; when the midpoint voltage of the primary side switching bridge arm is less than or equal to a first preset voltage, the control unit turns on the first power switch S1, and when the midpoint voltage of the primary side switching bridge arm is greater than or equal to a second preset voltage, the control unit turns on the second power switch S2. The first preset voltage can be a value close to zero or equal to zero, and the second preset voltage can be a value close to the input voltage or equal to the input voltage.

[0119] The application controls the corresponding synchronous rectifier to be continuously or twice conducted for a period of time before the primary side power switch is turned on, so as to generate a discharge current in the output inductor, and generate a reverse current in the primary side circuit after the corresponding synchronous rectifier is turned off, and the reverse current participates in the resonance of the output inductor, the excitation inductor of the transformer and the parasitic capacitor of the PWM half-bridge circuit, so as to realize the zero voltage turn-on of the primary side power switch, thereby reducing the loss.

[0120] Although the application has been disclosed as above with embodiments, it is not intended to limit the application, and any person skilled in the art can make various modifications and decorations without departing from the spirit and scope of the application, and the protection scope of the application should be defined by the appended claims.

Claims

1. A control method for a converter applicable to a wide range of output voltages, characterized in that, The converter includes a PWM half-bridge circuit, the PWM half-bridge circuit comprising: The primary-side circuit includes a primary-side switching bridge arm composed of a first power switch and a second power switch connected in series. A transformer includes a primary winding and a secondary winding, wherein the primary winding is coupled to the primary circuit; A secondary-side rectifier circuit includes at least two synchronous rectifier diodes, the input terminal of which is coupled to the secondary-side coil; and An output filter circuit, including an output inductor and an output capacitor, is coupled between the output terminal of the secondary rectifier circuit and a load. The control method includes: The PWM half-bridge circuit is brought into discontinuous mode by adjusting the switching frequency. In each switching cycle, before the first power switch and the second power switch are turned on, the corresponding synchronous rectifier is continuously or twice turned on for a predetermined time to achieve zero-voltage turn-on of the first power switch and the second power switch.

2. The control method according to claim 1, characterized in that, The secondary winding of the transformer has a center-tapped structure, including a first terminal, a second terminal, and a common terminal. The secondary rectifier circuit includes a first synchronous rectifier and a second synchronous rectifier. One end of the first synchronous rectifier and one end of the second synchronous rectifier are respectively connected to the first terminal and the second terminal of the secondary winding. The other ends of the first synchronous rectifier and the other ends of the second synchronous rectifier are simultaneously connected to one end of the output capacitor. The two ends of the output inductor are respectively connected to the common terminal of the secondary winding and the other end of the output capacitor.

3. The control method according to claim 2, characterized in that, Also includes: Control the first power switch and the second synchronous rectifier to work in a complementary manner; During the dead time from the first power switch being turned off to the second power switch being turned on, when the current on the first synchronous rectifier tube drops to 0, the first synchronous rectifier tube is continuously turned on for the predetermined time. During the dead time from when the second power switch is turned off to when the first power switch is turned on, the second synchronous rectifier is kept on for the predetermined time when the current on the second synchronous rectifier drops to 0.

4. The control method according to claim 2, characterized in that, Also includes: Control the first power switch and the second synchronous rectifier to operate in a non-complementary manner; During the dead time between the first power switch being turned off and the second power switch being turned on, when the current on the first synchronous rectifier drops to 0, the first synchronous rectifier is turned off, while the second synchronous rectifier remains in the on state. During the dead time between the second power switch being turned off and the first power switch being turned on, when the current on the second synchronous rectifier drops to 0, the second synchronous rectifier is turned off, while the first synchronous rectifier remains in the on state.

5. The control method according to claim 4, characterized in that, Also includes: During the dead time from the first power switch being turned off to the second power switch being turned on, it is further determined whether the voltage across the first synchronous rectifier has reached its lowest point. When the voltage across the first synchronous rectifier reaches its lowest point, the first synchronous rectifier is turned on again for the predetermined time. During the dead time from the second power switch being turned off to the first power switch being turned on, it is further determined whether the voltage across the second synchronous rectifier has reached its lowest point. When the voltage across the second synchronous rectifier reaches its lowest point, the second synchronous rectifier is turned on again for the predetermined time.

6. The control method as described in claim 5, characterized in that, When the voltage across the first synchronous rectifier reaches the m-th valley, the first synchronous rectifier is turned on again for the predetermined time; when the voltage across the second synchronous rectifier reaches the m-th valley, the second synchronous rectifier is turned on again for the predetermined time, where m is an integer greater than or equal to 1.

7. The control method according to claim 1, characterized in that, The secondary winding of the transformer includes a first end and a second end. The secondary rectifier circuit includes a first to a fourth synchronous rectifier tube. The first and second synchronous rectifier tubes are connected in series to form the first bridge arm of the secondary winding. The third and fourth synchronous rectifier tubes are connected in series to form the second bridge arm of the secondary winding. The first and second ends of the secondary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm of the secondary winding. The output capacitor is connected in parallel to the two ends of the first and second bridge arms of the secondary winding through the output inductor.

8. The control method according to claim 7, characterized in that, Also includes: The first synchronous rectifier tube and the third synchronous rectifier tube are controlled to work synchronously, and the second synchronous rectifier tube and the fourth synchronous rectifier tube are controlled to work synchronously. and During the dead time from the first power switch being turned off to the second power switch being turned on, the first synchronous rectifier and the third synchronous rectifier are controlled to be turned on. When the current on the second synchronous rectifier and the fourth synchronous rectifier drops to 0, the second synchronous rectifier and the fourth synchronous rectifier are continuously turned on for the predetermined time. During the dead time from the second power switch being turned off to the first power switch being turned on, the second synchronous rectifier and the fourth synchronous rectifier are controlled to be turned on. When the current on the first synchronous rectifier and the third synchronous rectifier drops to 0, the first synchronous rectifier and the third synchronous rectifier are continuously turned on for the predetermined time.

9. The control method according to claim 7, characterized in that, Also includes: The first synchronous rectifier tube and the third synchronous rectifier tube are controlled to work synchronously, and the second synchronous rectifier tube and the fourth synchronous rectifier tube are controlled to work synchronously. and During the dead time from the first power switch being turned off to the second power switch being turned on, the first synchronous rectifier and the third synchronous rectifier are controlled to be turned on. When the current on the second synchronous rectifier and the fourth synchronous rectifier drops to 0, the second synchronous rectifier and the fourth synchronous rectifier are turned off. During the dead time between the second power switch being turned off and the first power switch being turned on, the second synchronous rectifier and the fourth synchronous rectifier are controlled to be turned on. When the current on the first synchronous rectifier and the third synchronous rectifier drops to 0, the first synchronous rectifier and the third synchronous rectifier are turned off.

10. The control method according to claim 9, characterized in that, Also includes: During the dead time from the first power switch being turned off to the second power switch being turned on, it is further determined whether the voltage across the second synchronous rectifier and the fourth synchronous rectifier has reached its lowest point. When the voltage across the second synchronous rectifier and the fourth synchronous rectifier reaches its lowest point, the second synchronous rectifier and the fourth synchronous rectifier are turned on again for the predetermined time. During the dead time from the second power switch being turned off to the first power switch being turned on, it is further determined whether the voltage across the first synchronous rectifier and the third synchronous rectifier has reached its lowest point. When the voltage across the first synchronous rectifier and the third synchronous rectifier reaches its lowest point, the first synchronous rectifier and the third synchronous rectifier are turned on again for the predetermined time.

11. The control method according to claim 1, characterized in that, Also includes: When the load decreases further, the PWM half-bridge circuit is controlled to enter the BURST mode from the discontinuous mode. Each BURST cycle includes a pulse enable interval and a pulse disable interval. During the pulse enable interval, the PWM half-bridge circuit operates in the discontinuous mode. During the pulse shutdown interval, all pulse signals are turned off, causing the PWM half-bridge circuit to stop working.

12. The control method according to claim 11, characterized in that, In each of the pulse enable intervals, the first switching cycle is processed to connect the current of the magnetizing inductor and the current of the output inductor to a predetermined trajectory; the last switching cycle is processed to turn off the pulse signal of the primary circuit after the current of the magnetizing inductor is zero.

13. The control method according to claim 12, characterized in that, The predetermined trajectory is the trajectory of the current in the magnetizing inductor and the current in the output inductor in the discontinuous mode.

14. The control method according to claim 1, characterized in that, The first power switch is connected to the negative input terminal of the primary circuit, and the second power switch is connected to the positive input terminal of the primary circuit. When the midpoint voltage of the primary switch arm is less than or equal to a first preset voltage, the first power switch is turned on; when the midpoint voltage of the primary switch arm is greater than or equal to a second preset voltage, the second power switch is turned on.

15. The control method according to claim 1, characterized in that, The primary-side circuit also includes a capacitor bridge arm formed by a first capacitor and a second capacitor connected in series. One end of the primary-side coil is coupled to the midpoint of the capacitor bridge arm, and the other end of the primary-side coil is coupled to the midpoint of the primary-side switch bridge arm.

16. The control method according to claim 1, characterized in that, The primary-side circuit also includes a capacitor, one end of which is coupled to the positive or negative input terminal of the primary-side circuit, and the other end of which is coupled to one end of the primary-side coil. The other end of the primary-side coil is coupled to the midpoint of the primary-side switch bridge arm.

17. A converter suitable for a wide range of output voltages, characterized in that, The converter includes a PWM half-bridge circuit and a control unit, wherein the PWM half-bridge circuit includes: The primary-side circuit includes a primary-side switching bridge arm composed of a first power switch and a second power switch connected in series. A transformer includes a primary winding and a secondary winding, wherein the primary winding is coupled to the primary circuit; The secondary-side rectifier circuit includes at least two synchronous rectifier diodes, and the input terminal of the secondary-side rectifier circuit is coupled to the secondary-side coil. An output filter circuit, including an output inductor and an output capacitor, is coupled between the output terminal of the secondary rectifier circuit and a load. The control unit is used to adjust the switching frequency to put the PWM half-bridge circuit into discontinuous mode, and in each switching cycle, before the first power switch and the second power switch are turned on, to continuously or twice turn on the corresponding synchronous rectifier for a predetermined time, so as to achieve zero-voltage turn-on of the first power switch and the second power switch.

18. The converter according to claim 17, characterized in that, The secondary winding of the transformer has a center-tapped structure, including a first terminal, a second terminal, and a common terminal. The secondary rectifier circuit includes a first synchronous rectifier and a second synchronous rectifier. One end of the first synchronous rectifier and one end of the second synchronous rectifier are respectively connected to the first terminal and the second terminal of the secondary winding. The other ends of the first synchronous rectifier and the other ends of the second synchronous rectifier are simultaneously connected to one end of the output capacitor. The two ends of the output inductor are respectively connected to the common terminal of the secondary winding and the other end of the output capacitor.

19. The converter according to claim 18, characterized in that, It also includes a current detection unit for detecting the current on the first synchronous rectifier and the current on the second synchronous rectifier; The control unit is further configured to receive the detection result of the current detection unit, and during the dead time from the first power switch being turned off to the second power switch being turned on, when the current on the first synchronous rectifier tube drops to 0, continue to conduct the first synchronous rectifier tube for the predetermined time. During the dead time from when the second power switch is turned off to when the first power switch is turned on, the second synchronous rectifier is kept on for the predetermined time when the current on the second synchronous rectifier drops to 0.

20. The converter according to claim 18, characterized in that, It also includes a current detection unit for detecting the current on the first synchronous rectifier and the current on the second synchronous rectifier; The control unit is further configured to receive the detection result of the current detection unit, and during the dead time from the first power switch being turned off to the second power switch being turned on, when the current on the first synchronous rectifier drops to 0, turn off the first synchronous rectifier and continue to conduct the second synchronous rectifier; during the dead time from the second power switch being turned off to the first power switch being turned on, when the current on the second synchronous rectifier drops to 0, turn off the second synchronous rectifier and continue to conduct the first synchronous rectifier.

21. The converter according to claim 20, characterized in that, It also includes a secondary voltage detection unit for detecting the voltage across the first synchronous rectifier and the second synchronous rectifier; When the voltage across the first synchronous rectifier reaches the m-th valley, the control unit controls the first synchronous rectifier to conduct for the second time; when the voltage across the second synchronous rectifier reaches the m-th valley, the control unit controls the second synchronous rectifier to conduct for the second time, where m is an integer greater than or equal to 1.

22. The converter according to claim 17, characterized in that, The secondary winding of the transformer includes a first end and a second end. The secondary rectifier circuit includes a first to a fourth synchronous rectifier tube. The first and second synchronous rectifier tubes are connected in series to form the first bridge arm of the secondary winding. The third and fourth synchronous rectifier tubes are connected in series to form the second bridge arm of the secondary winding. The first and second ends of the secondary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm of the secondary winding. The output capacitor is connected in parallel to the two ends of the first and second bridge arms of the secondary winding through the output inductor.

23. The converter according to claim 22, characterized in that, The control unit is further configured to control the first synchronous rectifier tube and the third synchronous rectifier tube to operate synchronously, and to control the second synchronous rectifier tube and the fourth synchronous rectifier tube to operate synchronously; and, During the dead time from the first power switch being turned off to the second power switch being turned on, the first synchronous rectifier and the third synchronous rectifier are controlled to be turned on. When the current on the second synchronous rectifier and the fourth synchronous rectifier drops to 0, the second synchronous rectifier and the fourth synchronous rectifier are continuously turned on for the predetermined time. During the dead time from the second power switch being turned off to the first power switch being turned on, the second synchronous rectifier and the fourth synchronous rectifier are controlled to be turned on. When the current on the first synchronous rectifier and the third synchronous rectifier drops to 0, the first synchronous rectifier and the third synchronous rectifier are continuously turned on for the predetermined time.

24. The converter according to claim 22, characterized in that, The control unit is further configured to control the first synchronous rectifier tube and the third synchronous rectifier tube to operate synchronously, and to control the second synchronous rectifier tube and the fourth synchronous rectifier tube to operate synchronously; and, During the dead time from the first power switch being turned off to the second power switch being turned on, the first synchronous rectifier and the third synchronous rectifier are controlled to be turned on. When the current on the second synchronous rectifier and the fourth synchronous rectifier drops to 0, the second synchronous rectifier and the fourth synchronous rectifier are turned off. During the dead time between the second power switch being turned off and the first power switch being turned on, the second synchronous rectifier and the fourth synchronous rectifier are controlled to be turned on. When the current on the first synchronous rectifier and the third synchronous rectifier drops to 0, the first synchronous rectifier and the third synchronous rectifier are turned off.

25. The converter according to claim 24, characterized in that, The control unit is further configured to, during the dead time from the first power switch being turned off to the second power switch being turned on, further determine whether the voltage across the second synchronous rectifier and the fourth synchronous rectifier has reached its lowest point, and when the voltage across the second synchronous rectifier and the fourth synchronous rectifier reaches its lowest point, re-enable the second synchronous rectifier and the fourth synchronous rectifier for the predetermined time. During the dead time from the second power switch being turned off to the first power switch being turned on, it is further determined whether the voltage across the first synchronous rectifier and the third synchronous rectifier has reached its lowest point. When the voltage across the first synchronous rectifier and the third synchronous rectifier reaches its lowest point, the first synchronous rectifier and the third synchronous rectifier are turned on again for the predetermined time.

26. The converter according to claim 17, characterized in that, When the load is further reduced, the control unit is used to control the PWM half-bridge circuit to enter the BURST mode from the discontinuous mode. Each BURST cycle includes a pulse enable interval and a pulse disable interval. During the pulse enable interval, the PWM half-bridge circuit operates in the discontinuous mode. During the pulse shutdown interval, all pulse signals are turned off, causing the PWM half-bridge circuit to stop working.

27. The converter according to claim 26, characterized in that, Within each pulse enable interval, the control unit processes the first switching cycle to connect the current of the magnetizing inductor and the current of the output inductor to a predetermined trajectory; and processes the last switching cycle to turn off the pulse signal of the primary circuit after the current of the magnetizing inductor is zero.

28. The converter according to claim 27, characterized in that, The predetermined trajectory is the trajectory of the current in the magnetizing inductor and the current in the output inductor in the discontinuous mode.

29. The converter according to claim 17, characterized in that, It also includes a primary-side voltage detection unit for detecting the midpoint voltage of the primary-side switching bridge arm; The first power switch is connected to the negative input terminal of the primary circuit, and the second power switch is connected to the positive input terminal of the primary circuit. The control unit is further configured to receive the detection result of the primary-side voltage detection unit, and when the midpoint voltage of the primary-side switching bridge arm is less than or equal to a first preset voltage, turn on the first power switch, and when the midpoint voltage of the primary-side switching bridge arm is greater than or equal to a second preset voltage, turn on the second power switch.

30. The converter according to claim 17, characterized in that, The primary-side circuit also includes a capacitor bridge arm formed by a first capacitor and a second capacitor connected in series. One end of the primary-side coil is coupled to the midpoint of the capacitor bridge arm, and the other end of the primary-side coil is coupled to the midpoint of the primary-side switch bridge arm.

31. The converter according to claim 17, characterized in that, The primary-side circuit also includes a capacitor, one end of which is coupled to the positive or negative input terminal of the primary-side circuit, and the other end of which is coupled to one end of the primary-side coil. The other end of the primary-side coil is coupled to the midpoint of the primary-side switch bridge arm.

32. The converter according to claim 17, characterized in that, The output inductor is integrated with the transformer.

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