Load regulation rate control method and open-loop isolation converter

Abstract

The invention discloses a load regulation rate control method and an open-loop isolation converter, the open-loop converter comprises a complementary inverter circuit, a resonance circuit, a transformer and a rectification circuit, in the open-loop isolation converter under complementary driving control, the resonance circuit is additionally arranged in a single winding loop of the transformer, so that the load regulation rate is improved; the resonant frequency of the isolation converter can be close to the working frequency by designing the resonant capacitor of the resonant circuit. Leakage inductance energy is fully utilized through the resonance circuit, negative current in the complementary inverter circuit is eliminated, the problems of poor load regulation rate and low efficiency caused by large leakage inductance due to transformer coupling difference can be simply, conveniently and effectively solved at low cost, and the high-isolation-voltage high-isolation-voltage high-isolation-voltage high-isolation-voltage high-isolation-voltage high-isolation-voltage high-isolation-voltage high-isolation-voltage high-isolation-voltage high-isolation-voltage high-isolation-voltage high-isolation-voltage high-isolation-voltage high-

Description

Technical Field

[0001] The invention relates to a switching power supply technology, and in particular to a load regulation rate control method and an open-loop isolation converter. Background Art

[0002] In the application field of micro-power DC-DC isolation converters, it generally refers to switching power supply products with power levels of 6W and below. Push-pull, half-bridge, full-bridge, etc. are commonly used as primary power topologies. A simple DC-DC open-loop circuit can be formed by combining a transformer with a secondary rectifier circuit to achieve isolation and voltage conversion functions.

[0003] With the continuous development of integrated circuits, the trend of IC productization is becoming more and more prominent. There are already many complementary inverter ICs on the market that integrate push-pull, half-bridge, full-bridge topologies and their control parts, hereinafter referred to as "transformer driver chips", including complementary push-pull ICs, complementary half-bridge ICs, complementary full-bridge ICs, etc. This "transformer driver chip" is specially designed for open-loop isolated converters.

[0004] Open-loop isolated converters are widely used in situations where the input voltage is relatively stable (voltage variation range ±10% Vin) and the output voltage stability is not required to be so high due to their low cost and simple design.

[0005] On the other hand, a significant disadvantage of the open-loop isolated converter is that the output voltage is unregulated and changes with the load. The indicator for measuring the quality of an unregulated power supply is the relative change in output caused by the load, that is, the load regulation rate, which requires that the difference in output voltage between heavy load conditions (load power above 1W) and light load conditions (load power below 0.5W) be small.

[0006] In order to facilitate the understanding of the present invention, in the background technology, the load regulation rate L of the unregulated power supply is first defined as:

[0007]

[0008] V b1 : Nominal input voltage, output voltage measured at 10% rated load;

[0009] V outnom : Nominal input voltage, output voltage measured under rated load.

[0010] In recent years, the reliability standards of various industries have become increasingly higher, including key indicators such as isolation voltage. For example, in industries such as IGBT, medical power supply, and automotive power supply, the isolation voltage must reach 3000VAC / 5000VDC and above. Factors affecting the isolation voltage include the paint film material of the transformer wire, the distance between the primary and secondary sides, and the winding method of the transformer. In high-isolation application scenarios, the distance between the primary and secondary windings needs to be increased, but the leakage flux becomes larger, that is, the leakage inductance of the transformer becomes larger. In order to meet the needs of micro-power high-isolation applications, a transformer design is shown in Figure 1. Its characteristics are that the primary and secondary windings of the transformer are separated, and voltage conversion can be achieved through the primary and secondary turn ratio of the transformer. Through separate winding, the isolation voltage can reach 3000VAC / 5000VDC and above, and the isolation capacitance can be reduced to less than 10pF, but it will bring the following problems:

[0011] 1. Efficiency becomes lower;

[0012] 2. Load regulation rate deteriorates;

[0013] 3. Because the leakage inductance reduces the normalized frequency of the primary side, the circuit works in the ZCS region, and the voltage gain is significantly affected by the change of the quality factor;

[0014] 4. The switch tube of the isolation converter and the leakage inductance produce high-frequency resonance, thereby generating a large negative current, which affects the switch tube;

[0015] 5. Causes the switching tube to produce a large voltage spike.

[0016] Based on the above problems, the following examples are given:

[0017] like Figure 2 As shown, a circuit for traditional micro-power high-isolation non-regulated voltage application is used. The two switch tubes MN1 and MN2 inside the push-pull IC1 are respectively connected to the primary windings LP1 and LP2 of a transformer T1 with a central shaft head. The secondary winding Ls of the transformer T1, the rectifier circuit DB1 and the output capacitor C2 form a rectifier filter circuit. The two switch tubes MN1 and MN2 are fixed in frequency and alternately turned on. The input and output voltage conversion is achieved by adjusting the transformer turn ratio. In the case of large transformer leakage inductance, the efficiency will be reduced and the load regulation rate will be poor. At the same time, the two switch tubes MN1 and MN2 will produce high-frequency resonance with the leakage inductance, and a large negative current will flow through the two switch tubes MN1 and MN2. At the same time, the two switch tubes MN1 and MN2 will produce a large voltage spike.

[0018] Therefore, in order to solve the low transmission efficiency and poor load regulation caused by large leakage inductance of the transformer in applications, and to eliminate the influence of negative current and large voltage spikes, a technical solution to the above problems needs to be proposed. Summary of the invention

[0019] In view of this, the technical problem to be solved by the present invention is to provide a load regulation rate control method and an open-loop isolation converter, which can fully utilize the leakage inductance energy in the case of large leakage inductance, effectively eliminate negative current and voltage spikes, and improve transmission efficiency and load regulation rate.

[0020] Based on this, the technical solution of the present invention is as follows:

[0021] On the first aspect, a method for controlling a load regulation rate is provided. In an open-loop isolation converter under complementary drive control, a resonant circuit is added to a single winding loop of a transformer T1 and the resonant capacitor of the resonant circuit is designed so that the resonant frequency of the isolation converter can be made close to the operating frequency.

[0022] Secondly, a method for controlling a load regulation rate is provided. In an open-loop isolation converter under complementary drive control and heavy load conditions, a resonant circuit is added to the single winding loop of transformer T1 and the resonant capacitor of the resonant circuit is designed so that the resonant frequency of the isolation converter can be made close to the operating frequency.

[0023] On the third aspect, a method for controlling a load regulation rate is provided. In an open-loop isolation converter under complementary drive control, a resonant circuit is added to a single winding loop of transformer T1, and the resonant capacitor of the resonant circuit is designed to make the resonant frequency of the isolation converter close to the operating frequency, wherein the isolation degree of the isolation converter is above 3000VAC.

[0024] In a fourth aspect, an open-loop isolation converter is provided, comprising a complementary inverter circuit, a transformer T1, a rectifier circuit, and a resonant circuit, wherein the resonant circuit is connected in series to a winding loop of a primary side or a winding loop of a secondary side of the transformer T1, and the winding in the winding loop connected in series with the resonant circuit is a single winding;

[0025] In an open-loop isolated converter under complementary drive control, by adding a resonant circuit in the single winding loop of the transformer T1 and designing the resonant capacitor of the resonant circuit, the resonant frequency of the isolated converter can be made close to the operating frequency.

[0026] Preferably, the complementary inverter circuit is a push-pull circuit F1.

[0027] Preferably, the primary winding Lp of the transformer T1 is a double winding with a central shaft head, and the resonant capacitor is connected in series with the secondary winding Ls of the transformer T1.

[0028] Preferably, the complementary inverter circuit is a complementary bridge circuit.

[0029] Preferably, the primary winding Lp of the transformer T1 is a single winding, and the resonant capacitor is connected in series with the primary winding Lp of the transformer T1.

[0030] Preferably, the rectifier circuit is a half-wave rectifier circuit, a full-wave rectifier circuit, a bridge rectifier circuit, a bridge synchronous rectifier circuit or a voltage doubler rectifier circuit.

[0031] Preferably, the resonant circuit comprises a resonant inductor Lr and a resonant capacitor Cr which are equivalent to the leakage inductance of the transformer.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention introduces a resonant circuit by adding a resonant capacitor in an open-loop isolation converter, and utilizes the leakage inductance and the resonant capacitor to participate in the resonance, which can effectively solve the problem that the leakage inductance energy cannot be transmitted to the secondary side, thereby maintaining a larger output voltage under heavy output load conditions, optimizing the load regulation rate, and improving the efficiency, which is very advantageous for products with higher isolation voltages; adopting the circuit of the present invention can enable the switch tube in the complementary inverter circuit to achieve zero voltage turn-on and zero current turn-off, and in the case of large leakage inductance, fully utilize the leakage inductance energy, eliminate negative current and voltage spikes, and improve transmission efficiency.

[0033] The working principle of the present invention is briefly analyzed as follows:

[0034] The complementary inverter circuit is a voltage square wave generator. Under the action of a driving signal with a duty cycle D close to 0.5, a square wave voltage with a fixed operating frequency fs, an amplitude close to the input voltage Uin, and a duty cycle close to 0.5 is obtained at both ends of the primary winding Lp of the transformer.

[0035] The transformer T1 is connected in series with the resonant circuit, which is equivalent to an LLC circuit. The AC voltage is then rectified into a stable DC voltage through the rectifier circuit DB1.

[0036] The beneficial effects of the present invention are as follows: in an open-loop isolated converter under complementary drive control, a resonant circuit is added to a single winding loop of a transformer and a resonant capacitor of the resonant circuit is designed so that the resonant frequency of the isolated converter approaches the operating frequency. In the case of large leakage inductance, the leakage inductance energy is fully utilized, negative current and voltage spikes are eliminated, transmission efficiency is improved, and load regulation is especially improved, thereby solving the problem that under heavy output load, traditional circuits will cause low output voltage, poor load regulation and poor efficiency; and the switch tube in the complementary inverter circuit is turned on with zero voltage and turned off with zero current. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1a - Figure 1b It is an equivalent schematic diagram and winding schematic diagram of an existing high isolation transformer;

[0038] Figure 2 This is the schematic diagram of the traditional push-pull circuit;

[0039] Figure 3is a principle block diagram of the open-loop isolation converter described in the first embodiment;

[0040] Figure 4 is a circuit schematic diagram of the open-loop isolation converter described in the first embodiment;

[0041] Figure 5 is an equivalent circuit diagram of the open-loop isolation converter described in the first embodiment;

[0042] Figure 6 is a circuit schematic diagram of the open-loop isolation converter described in the second embodiment;

[0043] Figure 7 Schematic diagram of the voltage gain |M| changing with normalized frequency. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solution and characteristics of the present invention clearer, the working principle of the present invention will be described in detail below in conjunction with the drawings. The specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0045] Any feature disclosed in this specification (including any abstract and drawings), unless otherwise stated, may be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0046] The meaning of electrical connection includes not only direct connection but also indirect electrical connection (that is, other components can be electrically connected between two electrically connected objects) and inductive coupling and other methods.

[0047] First embodiment

[0048] Figure 3 is a principle block diagram of the open-loop isolation converter described in the first embodiment, and Figure 2 The difference between the existing technology is that a new resonant circuit is added to form LLC resonance, which can enable the switch tube in the complementary inverter circuit to achieve zero voltage turn-on and zero current turn-off. In the case of large leakage inductance, the leakage inductance energy can be fully utilized to eliminate negative current and voltage spikes, thereby improving transmission efficiency and load regulation.

[0049] In this embodiment, a method for controlling a load regulation rate is provided. In an open-loop isolation converter under complementary drive control, a resonant circuit is added to a single winding loop of a transformer and the resonant capacitor of the resonant circuit is designed so that the resonant frequency of the isolation converter can be made close to the operating frequency.

[0050] In another embodiment, a method for controlling a load regulation rate is provided. In an open-loop isolation converter under complementary drive control and heavy load conditions, a resonant circuit is added to a single winding loop of a transformer and the resonant capacitor of the resonant circuit is designed so that the resonant frequency of the isolation converter can be made close to the operating frequency.

[0051] Specifically, the heavy-load operating condition described in this embodiment is a condition where the load power is 1W or above.

[0052] In another embodiment, a load regulation rate control method is provided. In an open-loop isolation converter under complementary drive control, a resonant circuit is added to a single winding loop of a transformer and the resonant capacitor of the resonant circuit is designed so that the resonant frequency of the isolation converter can be made close to the operating frequency, wherein the isolation degree of the isolation converter is above 3000VAC.

[0053] In another embodiment, Figure 3 As shown, an open-loop isolation converter is provided, comprising a complementary inverter circuit, a transformer T1, a rectifier circuit, and a resonant circuit, wherein the resonant circuit is connected in series to a winding loop of the primary side or a winding loop of the secondary side of the transformer T1, and the winding in the winding loop connected in series with the resonant circuit is a single winding;

[0054] In an open-loop isolated converter under complementary drive control, a resonant circuit is added to a single winding loop of a transformer and the resonant capacitor of the resonant circuit is designed so that the resonant frequency of the isolated converter can be made close to the operating frequency.

[0055] Specifically, the resonant circuit and the windings in the winding loop connected thereto form an LLC resonant circuit; the Vin port and the GND port of the complementary inverter circuit are used to connect to the input, the VD1 port and the VD2 port are respectively connected to the primary winding Lp of the transformer T1, the pin 1 of the resonant circuit is connected to one end of the secondary winding Ls of the transformer T1, the pin 2 of the resonant circuit is connected to the AC1 pin of the rectifier circuit, the AC2 pin of the rectifier circuit is connected to the other end of the secondary winding Ls of the transformer T1, and the Vout port and the 0V port of the rectifier circuit are used to connect to the output.

[0056] In the specific implementation process of this embodiment, the open-loop isolation converter described in this embodiment is a micro-power open-loop isolation converter.

[0057] As a specific implementation of the open-loop converter described in this embodiment, in this embodiment, the complementary inverter circuit is a push-pull circuit F1, such as Figure 4 , which is a schematic diagram of the open-loop isolation converter circuit described in this embodiment.

[0058] Specifically, the open-loop isolated converter circuit of this embodiment includes an input capacitor C1, a push-pull circuit F1, a transformer T1, a resonant capacitor Cr, a resonant inductor Lr equivalent to the secondary leakage inductance of the transformer, a secondary rectifier circuit DB1 and an output capacitor C2, wherein the resonant capacitor Cr and the resonant inductor Lr equivalent to the secondary leakage inductance of the transformer T form the resonant circuit, the push-pull circuit F1 is a complementary push-pull IC, the VSS terminal of the complementary push-pull IC is electrically connected to the input ground GND, the VD1 terminal of the complementary push-pull IC is electrically connected to one end of the primary winding Lp1 of the transformer T1, and the other end of the primary winding Lp2 of the transformer T1 is electrically connected to the VD2 terminal of the complementary push-pull IC; the central axis heads of the primary windings Lp1 and Lp2 are connected to the input Vin, and the resonant capacitor Cr is connected in series between the resonant inductor Lr equivalent to the secondary leakage inductance and the rectifier circuit DB1.

[0059] Specifically, in this embodiment, when the primary winding of the transformer T includes multiple windings, the resonant circuit is not added to the primary side, but is selected to be added to the secondary side having only a single winding.

[0060] Specifically, the open-loop isolation converter circuit of this embodiment further includes an input capacitor C1 , one end of the input capacitor C1 is electrically connected to the input voltage Vin, and the other end of the input capacitor C1 is electrically connected to the input ground GND.

[0061] Specifically, the push-pull circuit F1 is a complementary push-pull IC, including two NMOS transistors MN1 and MN2, which transmit complementary drive signals CLK1 and CLK2 to the NMOS transistors MN1 and MN2 respectively, thereby driving the NMOS transistors MN1 and MN2 respectively. Specifically, two complementary square wave voltages U A with U B , U A with U B It is a square wave voltage with a fixed frequency f, a duty cycle slightly less than 0.5, and an amplitude equal to the input voltage.

[0062] Specifically, the transformer T1 described in this embodiment has a primary winding including two windings LP1 and LP2 with the same turn ratio, and a secondary winding of a single winding LS, which mainly functions as voltage transformation, isolation, and energy transmission.

[0063] In one embodiment, the rectifier circuit DB1 is a bridge rectifier circuit, which may be a full-bridge rectifier circuit or a half-bridge rectifier circuit.

[0064] In one embodiment, the rectifier circuit DB1 is a bridge synchronous rectifier circuit, which may be a full-bridge synchronous rectifier circuit or a half-bridge synchronous rectifier circuit.

[0065] In one embodiment, the rectifier circuit DB1 is a voltage doubling rectifier circuit.

[0066] The working principle of this embodiment is:

[0067] The push-pull circuit F1 is a complementary push-pull IC, including NMOS transistor MN1 and NMOS transistor MN2. By giving complementary drive signals CLK1 and CLK2, the NMOS transistors drive MN1 and NMOS transistor MN2 respectively. Its main function is to convert the input voltage into a square wave voltage with a duty cycle slightly less than 0.5.

[0068] The magnetic flux of the primary winding Lp of the transformer T1 cannot be fully coupled to the secondary side, which will produce a large leakage inductance. The leakage inductance energy cannot be transferred to the secondary side, which will cause the output voltage to become low under heavy load conditions. The impact brought about is poor load regulation and poor efficiency under heavy load conditions. This embodiment adds a resonant capacitor Cr to introduce a resonant circuit, and uses the leakage inductance of the secondary winding Ls and the resonant capacitor Cr to participate in the resonance, which can effectively solve the problem that the leakage inductance energy cannot be transferred to the secondary side, and then the output voltage maintains a large value under heavy load conditions, the load regulation rate becomes better, and the efficiency is improved.

[0069] Moreover, this embodiment works in ZVS region 1, and the switch tube is turned on at zero voltage, which is more efficient.

[0070] This embodiment can be simplified to an LLC resonant circuit, such as Figure 5 As shown, for the convenience of explanation, the voltage at the input end of the resonant circuit is called U A1 , the resonant circuit output voltage is called Up. The ratio of the resonant circuit output voltage to the input voltage is called the voltage gain M:

[0071]

[0072] The resonant frequency of a resonant circuit is called f R ; Control circuit frequency fsw and resonant frequency f R The ratio of is called the normalized frequency X:

[0073]

[0074] Series resonant frequency:

[0075]

[0076]

[0077] Among them, f R is the series resonant frequency formed by the resonant inductor Lr, f P is the resonant inductance Lr and the excitation inductance L p The series resonance frequency formed by the joint participation; series resonance frequency f R The ratio of the resonant inductance Lr to the primary load RA is called the quality factor Q:

[0078]

[0079] By designing the values ​​of Cr and Lr so that the normalized frequency X approaches 1, the influence of leakage inductance on the load regulation rate can be resolved, thereby optimizing the load regulation rate.

[0080] Moreover, this embodiment works in ZVS region 1 (the control circuit frequency fsw is at f R With f p The switch tube is turned on at zero voltage, which is more efficient.

[0081] The test data of products using this technical solution compared with traditional push-pull circuits are as follows:

[0082] index Before improvement After Improvement Load 2W, output voltage 4.5V 4.85V Load 0.2W, output voltage 5.25V 5.26V Load 2W, efficiency 83％ 89％ Load 2W, load regulation rate 16.7％ 8.5％

[0083] It can be seen from the above test data that when the load is 2W (heavy load) and the circuit parameters are the same, compared with the traditional push-pull circuit, the technical solution described in this embodiment can increase the output voltage from 4.5V to 4.85V, the transmission efficiency is increased from 83% to 89%, and the load regulation rate is reduced from 16.7% to 8.5%, which solves the problem that the traditional push-pull circuit will cause low output voltage, poor load regulation rate and poor efficiency under heavy load conditions.

[0084] Second embodiment

[0085] Figure 6 The diagram shows the circuit principle diagram of the open-loop isolation converter of the second embodiment of the present invention. Different from the first embodiment, in this embodiment, the complementary inverter circuit is a complementary bridge circuit; the complementary bridge circuit can be a full-bridge circuit or a half-bridge circuit; in the specific implementation process, the complementary bridge circuit is a full-bridge circuit F2, and the full-bridge circuit F2 is a complementary full-bridge IC, the VSS end of the full-bridge IC is electrically connected to the input ground GND, the drive VD1 of the full-bridge IC is electrically connected to one end of the resonant capacitor Cr, the other end of the resonant capacitor Cr is electrically connected to one end of the resonant inductance Lr equivalent to the primary leakage inductance of the transformer T1, and one end of the primary winding Lp of the transformer T1 is electrically connected to the VD2 end of the full-bridge IC. The secondary winding Ls of the transformer T1 is connected to the AC1 end and the AC2 end of the rectifier circuit DB1.

[0086] Specifically, the full-bridge circuit F2 is a complementary full-bridge IC, including NMOS tube MN1, NMOS tube MN2, PMOS tube MP1 and PMOS tube MP2. The drive signal CLK1 is transmitted to the PMOS tube MP1 and the NMOS tube MN2, and the drive signal CLK2 is transmitted to the PMOS tube MP2 and the NMOS tube MN1, so that the drive signal CLK1 and the drive signal CLK2 are complementary.

[0087] Specifically, in the full-bridge circuit F2 described in this embodiment, a square wave voltage U is generated at both ends of VD1 and VD2. A , U A It is a square wave voltage with a fixed frequency f, a duty cycle slightly less than 0.5, and an amplitude of the input voltage.

[0088] Specifically, the primary winding Lp of the transformer T1 described in this embodiment is a single winding, and its main functions are voltage transformation, isolation, and energy transmission.

[0089] Specifically, in the rectifier circuit DB1 described in this embodiment, the rectifier circuit DB1 unit is a half-wave rectifier circuit.

[0090] Specifically, in the rectifier circuit DB1 described in this embodiment, the rectifier circuit DB1 unit is a full-wave rectifier circuit, and the secondary winding of the transformer T1 is a double winding.

[0091] Specifically, in the rectifier circuit DB1 described in this embodiment, the rectifier circuit DB1 unit is a bridge rectifier circuit.

[0092] Specifically, in the rectifier circuit DB1 described in this embodiment, the rectifier circuit DB1 unit is a bridge-type synchronous rectifier circuit.

[0093] Specifically, in the rectifier circuit DB1 described in this embodiment, the rectifier circuit DB1 unit is a voltage doubling rectifier circuit.

[0094] The working principle of this embodiment is basically the same as that of the first embodiment, except that the full-bridge circuit F1 is a complementary full-bridge inverter, and the primary winding Lp of the transformer T1 is a single winding.

[0095] The magnetic flux of the primary winding of the transformer cannot be fully coupled to the secondary side, which will produce a large leakage inductance. The leakage inductance energy cannot be transferred to the secondary side, which will cause the output voltage to become low when the output is overloaded. The impact is that the load regulation rate is poor, and the efficiency is also poor under heavy load conditions. This embodiment adds a resonant capacitor Cr to introduce a resonant circuit, and uses the leakage inductance of the primary winding Lp and the resonant capacitor to participate in the resonance, which can effectively solve the problem that the leakage inductance energy cannot be transferred to the secondary side, and then the output voltage maintains a large value under heavy load conditions, the load regulation rate is improved, and the efficiency is improved.

[0096] like Figure 7 As shown, Figure 7 Figure 1 is a schematic diagram of the voltage gain |M| changing with the normalized frequency. When the normalized frequency is low and the circuit works in the ZCS region, the voltage gain M is seriously affected by the quality factor Q. The load change causes the quality factor to change, resulting in a huge change in the voltage gain of the resonant circuit. A1The voltage is determined by the input voltage Vin, and the output voltage Up of the resonant circuit changes greatly after the voltage gain, and the final output voltage changes proportionally, so the load regulation rate is poor, that is, the output load Io decreases → the output load Ro increases → the primary load RA increases → the quality factor Q decreases → the voltage gain increases → the output voltage increases; Among them, the ZCS area described in this embodiment refers to Figure 7 The ZCS area is marked in Figure 7 The ZVS region 1 and ZVS region 2 are marked in

[0097] The traditional full-bridge circuit works in the ZCS region due to the low normalized frequency. In the case of large leakage inductance, soft switching cannot be achieved, the loop current is large, the MOS tube turn-on loss is too high, and the efficiency is low.

[0098] In this embodiment, the resonant capacitor Cr is added. R The normalized frequency X increases by designing the values ​​of Cr and Lr, so that the normalized frequency X approaches 1, and the circuit works in ZVS area 1 (the control circuit frequency fsw is at f R With f p As shown in the above argument, the voltage gain M is significantly less affected by the quality factor Q, the output voltage variation is reduced, the load regulation rate is significantly improved, the switch tube is turned on at zero voltage, and the efficiency is high.

[0099] The test data of the product using this technical solution compared with the traditional full-bridge circuit are as follows:

[0100] index Before improvement After Improvement Load 1W, output voltage 11.35V 12.06V Load 0.1W, output voltage 12.7V 12.75V Load 1W, efficiency 83.6％ 87.8％ Load 1W, load regulation rate 11.89％ 5.7％

[0101] It can be seen from the above test data that when the load is 1W (heavy load) and the circuit parameters are the same, compared with the traditional full-bridge circuit, the technical solution described in this embodiment is adopted. The output voltage is increased from 11.35V to 12.06V, the transmission efficiency is increased from 83.6% to 87.8%, and the load regulation rate is reduced from 11.89% to 5.7%, which solves the problem that under heavy load conditions, the traditional full-bridge circuit will cause low output voltage, poor load regulation rate and poor efficiency.

[0102] The above are only preferred embodiments of the present invention. It should be pointed out that the above preferred embodiments should not be regarded as limiting the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention. Improvements and modifications to the transformer structure should also be regarded as the protection scope of the present invention. The embodiments will not be repeated here. The protection scope of the present invention shall be based on the scope defined by the claims.

Claims

1. A method for controlling a load regulation rate, characterized in that: In an open-loop isolated converter under complementary drive control, by adding a resonant circuit in the single winding loop of the transformer T1 and designing the resonant capacitor of the resonant circuit, the resonant frequency of the isolated converter can be made close to the operating frequency.

2. A method for controlling a load regulation rate, characterized in that: In an open-loop isolation converter under complementary drive control and heavy load conditions, by adding a resonant circuit in the single winding loop of transformer T1 and designing the resonant capacitor of the resonant circuit, the resonant frequency of the isolation converter can be made close to the operating frequency.

3. A method for controlling a load regulation rate, characterized in that: In an open-loop isolation converter under complementary drive control, by adding a resonant circuit in the single winding loop of transformer T1 and designing the resonant capacitor of the resonant circuit, the resonant frequency of the isolation converter can be made close to the operating frequency, wherein the isolation degree of the isolation converter is above 3000VAC.

4. An open-loop isolation converter, comprising a complementary inverter circuit, a transformer T1, and a rectifier circuit, characterized in that: It also includes a resonant circuit, the resonant circuit is connected in series to the winding loop of the primary side or the winding loop of the secondary side of the transformer T1, and the winding in the winding loop connected in series with the resonant circuit is a single winding; In an open-loop isolated converter under complementary drive control, by adding a resonant circuit in the single winding loop of the transformer T1 and designing the resonant capacitor of the resonant circuit, the resonant frequency of the isolated converter can be made close to the operating frequency.

5. The open-loop isolation converter according to claim 4, characterized in that: The complementary inverter circuit is a push-pull circuit F1.

6. The open-loop isolation converter according to claim 4, characterized in that: The complementary inverter circuit is a complementary bridge circuit.

7. The open-loop isolation converter according to claim 5, characterized in that: The primary winding Lp of the transformer T1 is a double winding with a central shaft head, and the resonant capacitor is connected in series with the secondary winding Ls of the transformer T1.

8. The open-loop isolation converter according to claim 6, characterized in that: The primary winding Lp of the transformer T1 is a single winding, and the resonant capacitor is connected in series with the primary winding Lp of the transformer T1.

9. The open-loop isolation converter according to claim 4, characterized in that: The rectifier circuit is a half-wave rectifier circuit, a full-wave rectifier circuit, a bridge rectifier circuit, a bridge synchronous rectifier circuit or a voltage doubler rectifier circuit.

10. The open-loop isolation converter according to any one of claims 4 to 9, characterized in that: The resonant circuit includes a resonant inductor Lr and a resonant capacitor Cr which are equivalent to the leakage inductance of the transformer.

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