Double-transformer flyback converter
By adding voltage divider parallel connection to the flyback converter, the peak voltage and magnetic saturation problems of the Mos tube are solved, and the safety and stability of the Mos tube are improved. It is suitable for high-frequency designs and third-generation power semiconductor devices.
Patent Information
- Application Number
- CN202510483509.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-17
- Publication Date
- 2025-07-29
AI Technical Summary
In gallium nitride (GaN) and silicon carbide (SiC) third-generation power semiconductor flyback converters, the peak and peak value of the instantaneous voltage of the mos tube is too high due to the high switching speed, which increases the risk of the mos tube being broken down, and single-transformer flyback converters have magnetic saturation and mos tube spike voltage problems in high-power applications.
Add a voltage divider to the single-transformer flyback converter to form a dual-transformer flyback converter. The secondary side of the voltage divider is connected in series with the secondary side of the single-transformer, and the primary side is connected in parallel. Through an additional combination of resistors, capacitors and diodes, the two mos tubes are driven using the same driving circuit to ensure the synchronous switch, the flux direction is opposite, and the power is divided equally to reduce the voltage stress of the mos tube.
It effectively solves the magnetic saturation problem of transformers in high-power applications, reduces the voltage stress of the Mos tube, reduces the peak voltage of the Mos tube, improves safety and stability, and reduces cost and design complexity. It is suitable for third-generation power semiconductor devices.
Smart Images
Figure CN120389623A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of electromagnetic compatibility, and particularly relates to a dual-transformer flyback converter. Background Art
[0002] Currently, in the application of the third-generation power semiconductor flyback converter of gallium nitride (GaN) and silicon carbide (SiC), due to the extremely high switching speed of the third-generation power devices, the peak value of the voltage spike caused by the leakage inductance of the transformer becomes extremely high at the moment when the MOS transistor turns off. In practical applications, due to the too high peak value, the probability of the MOS transistor being broken down and causing a safety accident is greatly increased. Therefore, in the design of the flyback converter, reducing the turn-off spike of the MOS transistor is an indispensable design step.
[0003] At the moment when the flyback converter turns off, the drain-source spike voltage of the MOS transistor is caused by the leakage inductance of the transformer. Reducing the voltage spike can be divided into two directions: one is to use an absorption circuit to absorb the leakage inductance energy, another is to reduce the leakage inductance, and the other is to reduce the current change rate.
[0004] The transformer of the single-transformer flyback converter has problems of magnetic saturation of the transformer and the spike voltage of the MOS transistor. When used in high-power applications, the voltage stress of the drain-source of the MOS transistor will be very large, resulting in problems such as the MOS transistor being broken down, causing safety problems in the topology and the inability to achieve the expected function. Summary of the Invention
[0005] Based on this, it is necessary to provide a dual-transformer flyback converter for the above technical problems.
[0006] An embodiment of the present invention provides a dual-transformer flyback converter, including: Adding a voltage-dividing transformer at the single transformer of the single-transformer flyback converter to obtain a dual-transformer flyback converter; wherein, the secondary side of the voltage-dividing transformer is connected in series with the secondary side of the single transformer, and the primary side of the voltage-dividing transformer is connected in parallel with the primary side of the single transformer; the magnetic flux direction of the single transformer is clockwise, and the magnetic flux direction of the voltage-dividing transformer is counterclockwise; The primary side of the voltage-dividing transformer is connected in parallel with a first additional resistor and an additional capacitor, the primary side of the voltage-dividing transformer is connected in series with an additional diode and a second additional resistor, the positive electrode of the additional diode is connected to the primary side of the voltage-dividing transformer, and the negative electrode of the additional diode is connected to the second additional resistor.
[0007] Optionally, the primary side of the single transformer is connected in series with a second capacitor, a third resistor, and a second diode; wherein, the positive electrode of the second diode is connected to the primary side of the single transformer, and the negative electrode of the second diode is connected to the third resistor R5; A third ammeter is connected in series between the primary side of the single transformer and the second capacitor. After the second capacitor is connected in series with the fourth ammeter, they are connected in parallel with the second resistor. A fifth ammeter is connected in series between the positive electrode of the second diode and the primary side of the single transformer.
[0008] Optionally, the secondary side of the voltage-dividing transformer and the secondary side of the single transformer are connected in parallel with the first resistor, the first capacitor, and the first voltmeter. The secondary side of the voltage-dividing transformer and the secondary side of the single transformer are connected in series with the first diode, the first ammeter, and the second ammeter.
[0009] Optionally, the single transformer and the voltage-dividing transformer are driven by the same drive circuit. The drive circuit includes: a drive power supply, a comparator, an AC power supply, and an operational amplifier. The drive power supply is connected to the non-inverting input terminal of the comparator, and the phase wire of the AC power supply is connected to the inverting input terminal of the comparator. The output terminal of the comparator is connected to the input terminal of the operational amplifier, and the first output terminal of the operational amplifier is connected to the gate of the additional MOS transistor and the gate of the MOS transistor. The neutral wire of the AC power supply, the second output terminal of the operational amplifier, the source electrode of the MOS transistor, and the source electrode of the additional MOS transistor are all grounded.
[0010] Optionally, a second voltmeter is connected in parallel between the source electrode and the drain electrode of the MOS transistor. A body diode is connected in series between the source electrode and the drain electrode of the MOS transistor. The positive electrode of the body diode is connected to the source electrode of the MOS transistor, and the negative electrode of the body diode is connected to the drain electrode of the MOS transistor.
[0011] Optionally, the drain electrode of the additional MOS transistor is connected to the positive electrode of the additional diode. An additional body diode is connected in series between the source electrode and the drain electrode of the additional MOS transistor. The positive electrode of the additional body diode is connected to the source electrode of the additional MOS transistor, and the negative electrode of the additional body diode is connected to the drain electrode of the additional MOS transistor.
[0012] Optionally, the primary sides of the voltage-dividing transformer and the single transformer are also connected to the positive electrode of the DC power supply, and the negative electrode of the DC power supply is grounded.
[0013] Optionally, the magnetic flux direction of the single transformer is clockwise, and the magnetic flux direction of the voltage-dividing transformer is counterclockwise.
[0014] For the above-mentioned dual-transformer flyback converter provided by the embodiments of the present invention, compared with the prior art, its beneficial effects are as follows: In the present invention, the power required to be transferred by the single-transformer flyback converter is evenly distributed to the single transformer and the voltage-dividing transformer, effectively solving the problem of magnetic saturation of the transformer in high-power application scenarios, thereby reducing the voltage stress between the drain and source electrodes of the MOS transistor and avoiding the situation of excessive voltage stress caused by leakage inductance.
[0015] In addition, adding a voltage-dividing transformer, an additional MOS transistor, an additional diode, an additional capacitor, and two additional resistors to a single-transformer flyback converter, and using a high-voltage withstand MOS transistor for the flyback converter design can reduce the spike voltage of the MOS transistor in the flyback converter without adding a large amount of cost. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 FIG. 6 is a schematic diagram of a dual-transformer flyback converter provided in an embodiment; Figure 2 FIG. 9 is a diagram showing the relationship of MOS transistors of a dual-transformer flyback converter provided in an embodiment; Figure 3 FIG. 12 is a schematic diagram of a transformer magnetic integration scheme of a dual-transformer flyback converter provided in an embodiment; Figure 4 FIG. 15 is a magnetic flux direction diagram of transformer magnetic integration of a dual-transformer flyback converter provided in an embodiment; Figure 5 FIG. 18 is a schematic diagram of transformer magnetic integration of a dual-transformer flyback converter provided in an embodiment; Figure 6 FIG. 21 is a schematic diagram of a single-transformer flyback converter of a dual-transformer flyback converter provided in an embodiment; Figure 7 FIG. 24 is a waveform diagram of the drain-source voltage of the MOS transistor of a single-transformer flyback converter of a dual-transformer flyback converter provided in an embodiment; Figure 8 FIG. 27 is a waveform diagram of the drain-source voltage of the MOS transistor of a dual-transformer flyback converter with the primary side in parallel and the secondary side in series provided in an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0017] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.
[0018] In one embodiment, a dual-transformer flyback converter is provided, including: Adding a voltage-dividing transformer to the single transformer of the single-transformer flyback converter to obtain a dual-transformer flyback converter. Among them, the secondary side of the voltage-dividing transformer is connected in series with the secondary side of the single transformer, and the primary side of the voltage-dividing transformer is connected in parallel with the primary side of the single transformer.
[0019] The primary side of the voltage-dividing transformer is connected in parallel with the first additional resistor R3 and the additional capacitor C3. The primary side of the voltage-dividing transformer is connected in series with the additional diode D3 and the second additional resistor R4. The positive electrode of the additional diode D3 is connected to the primary side of the voltage-dividing transformer, and the negative electrode of the additional diode D3 is connected to the second additional resistor R4.
[0020] The primary side of the single transformer is connected in series with the second capacitor C2, the third resistor R5, and the second diode D2. Among them, the positive electrode of the second diode D2 is connected to the primary side of the single transformer, and the negative electrode of the second diode D2 is connected to the third resistor R5. A third ammeter is connected in series between the primary side of the single transformer and the second capacitor C2. After the second capacitor C2 is connected in series with the fourth ammeter, it is connected in parallel with the second resistor R2. A fifth ammeter is connected in series between the positive electrode of the second diode D2 and the primary side of the single transformer.
[0021] The primary sides of the voltage-dividing transformer and the single transformer are also connected to the positive electrode of the DC power supply, and the negative electrode of the DC power supply is grounded.
[0022] The secondary sides of the voltage-dividing transformer and the single transformer are connected in parallel with the first resistor R1, the first capacitor C1, and the first voltmeter V o1 and are connected in series with the first diode D1, the first ammeter, and the second ammeter.
[0023] A second voltmeter V is connected in parallel between the source electrode and the drain electrode of the MOS transistor Q1 o2 . A body diode is connected in series between the source electrode and the drain electrode of the MOS transistor Q1. The positive electrode of the body diode is connected to the source electrode of the MOS transistor Q1, and the negative electrode of the body diode is connected to the drain electrode of the MOS transistor Q1.
[0024] The drain electrode of the additional MOS transistor Q2 is connected to the positive electrode of the additional diode D3. An additional body diode is connected in series between the source electrode and the drain electrode of the additional MOS transistor Q2. The positive electrode of the additional body diode is connected to the source electrode of the additional MOS transistor Q2, and the negative electrode of the additional body diode is connected to the drain electrode of the additional MOS transistor Q2 As Figure 1 shown, in the schematic diagram of the dual-transformer flyback converter with parallel primary sides and series secondary sides provided by the embodiment of the present invention, the driving of the MOS transistors is driven by the same driving circuit to ensure the simultaneous on and off of the two MOS transistors.
[0025] The single transformer and the voltage-dividing transformer are driven by the same driving circuit, which includes: a driving power supply, a comparator, an AC power supply, and an operational amplifier. The driving power supply is connected to the non-inverting input terminal of the comparator, and the phase line of the AC power supply is connected to the inverting input terminal of the comparator; the output terminal of the comparator is connected to the input terminal of the operational amplifier, and the first output terminal of the operational amplifier is connected to the gates of the additional MOS transistor Q2 and the MOS transistor Q1. The neutral line of the AC power supply, the second output terminal of the operational amplifier, the source electrodes of the MOS transistor Q1 and the additional MOS transistor Q2 are all grounded.
[0026] At the same time, when calculating the relevant parameters of the absorption circuit, the split transformers should be used for calculation, and the power transmitted by a single transformer is approximately half of the output power. Specifically, the two transformers each provide half of the output voltage, and the two are connected in series to obtain the output voltage.
[0027] As Figure 2 shown, the MOS transistors of the schematic diagram of the dual-transformer flyback converter with parallel primary sides and series secondary sides provided by the embodiments of the present invention are driven by a single driving circuit to ensure that the two MOS transistors are turned on and off simultaneously.
[0028] As Figure 3 shown, the specific steps of the magnetic integration of the dual-transformer flyback converter with parallel primary sides and series secondary sides provided by the embodiments of the present invention are as follows: The first step: After removing the skeleton of the EE-shaped magnetic core, grind the same length of air gaps on both side columns of the magnetic core to ensure that the excitation inductance values of the two transformers are the same; The second step: Wind the copper wire on the secondary side in two sections for winding two windings. The primary side and the secondary side are wound on both ends of the magnetic core with air gaps by the sandwich winding method respectively;
[0029] The third step: After installing the skeleton, wind the winding on the pins.
[0030] As Figure 4 shown, the magnetic fluxes of the magnetic cores on both sides of the transformer of the dual-transformer flyback converter with parallel primary sides and series secondary sides provided by the embodiments of the present invention need to be ensured to be in opposite directions, that is, the magnetic flux direction of a single transformer is clockwise, and the magnetic flux direction of the voltage-dividing transformer is counterclockwise. The reverse magnetic flux is used to ensure that the two transformers form a low magnetic flux loop in the middle column and the two side columns and the magnetic flux in the middle column of the magnetic core is in the same direction;
[0031] As Figure 5 shown, the schematic diagram of the transformer of the dual-transformer flyback converter with parallel primary sides and series secondary sides provided by the embodiments of the present invention is as shown in the figure, which is convenient for calculating the magnetic flux of the entire EE-shaped magnetic core. Ensure that the magnetic core will not saturate and the heat of the magnetic core can be calculated.
[0032] As Figure 6As shown, the schematic diagram of a single - transformer flyback converter is as shown, which is used to compare the differences with the dual - transformer flyback converter with parallel primary and series secondary provided in the embodiments of the present invention.
[0033] As Figure 7 , 8 shown, by comparing the MOS - tube peak voltage of the dual - transformer flyback converter with parallel primary and series secondary provided in the embodiments of the invention and the single - transformer flyback converter, it can be obtained that the energy in a single transformer is significantly reduced, and the MOS - tube voltage spike caused by leakage inductance is significantly reduced.
[0034] As Figure 1 , Figure 5 , Figure 7 , Figure 8 shown, the principle of the single - transformer flyback converter and the dual - transformer flyback converter with parallel primary and series secondary provided in the embodiments of the invention is not overly complex. Regarding the problem of MOS - tube spikes caused by leakage inductance, the dual - transformer flyback converter with parallel primary and series secondary provided in the embodiments of the invention can significantly reduce the MOS - tube spikes caused by leakage inductance.
[0035] The present invention achieves a certain reduction effect of MOS - tube spikes caused by leakage inductance through the method of power sharing by dual transformers. This invention patent helps to ensure the safety and stability of MOS - tubes at a lower cost and lower price. And, in the actual product design, dividing the absorption circuit into two also helps to reduce the heat generation of the absorption - circuit resistance, improving its stability to a certain extent. At the same time, the dual - transformer flyback converter with parallel primary and series secondary provided in the embodiments of the invention only makes local modifications on the basis of the parameter design of the single - transformer flyback converter, and the relevant parameters of output and input can continue to be used, reducing the complexity of the design for designers compared with other methods. Then, the dual - transformer flyback converter with parallel primary and series secondary provided in the embodiments of the invention integrates two transformers into one magnetic core through magnetic integration, and its volume size is not much different from that of the single - transformer flyback converter of a single transformer, and it will not have a negative impact on the miniaturization of the PCB. Finally, the dual - transformer flyback converter with parallel primary and series secondary provided in the embodiments of the invention only requires the purchase of four more components in terms of cost, which is beneficial for cost control.
[0036] Use the simulation software based on PSIM to simulate the flyback circuit of two transformers with parallel primary and series secondary. The specific steps are as follows:
[0037] Step 1: Determine the following parameters of the traditional single-transformer flyback circuit: input voltage Vin, output voltage V0, load resistance R, secondary support capacitor C, MOSFET switching frequency f, MOSFET duty cycle D, a series of parasitic parameters of the MOSFET, primary inductance L of the transformer, magnetizing inductance Lm of the transformer, leakage inductance LK of the transformer, number of turns NS of the primary side of the transformer, number of turns NP of the secondary side of the transformer, turns ratio n of the transformer, resistance RSN of the snubber circuit, capacitance CSN of the snubber circuit.
[0038] Step 2: Simulate the traditional single-transformer flyback to verify the correctness of the design parameters and optimize them.
[0039] Step 3: Connect a voltage probe between the two ends of the MOSFET, i.e., between the drain and source, to determine the MOSFET peak voltage value.
[0040] Step 4: Split the single transformer into two transformers with parallel primary sides and series secondary sides, and redesign the parameters of the primary inductance L of the transformer, magnetizing inductance Lm of the transformer, leakage inductance LK of the transformer, number of turns NS of the primary side of the transformer, number of turns NP of the secondary side of the transformer, turns ratio n of the transformer, resistance RSN of the snubber circuit, and capacitance CSN of the snubber circuit according to the primary peak current IP.
[0041] Step 5: Simulate the dual-transformer flyback to verify the correctness of the design parameters and optimize them.
[0042] Step 6: Connect voltage probes between the two ends of the two MOSFETs, i.e., between the drain and source, respectively, to determine the peak voltage values of the two MOSFETs.
[0043] Step 7: Compare the results of Step 3 and Step 6 and draw a conclusion.
[0044] The advantages and positive effects of the technical solution to be protected by the present invention are as follows: First, after being transformed through experiments, the technical solution of the present invention can directly reduce the MOSFET peak problem of the flyback converter. This enables the flyback converter under the same parameters to exhibit higher performance and safety.
[0045] Second, considering the technical solution as a whole or from the perspective of the product, the present invention can solve the key problems in the product design of the flyback converter at a lower cost, effectively reducing the product production and R & D costs.
[0046] Third, as the creative auxiliary evidence of the claims of the present invention, it is also reflected in the following two important aspects: (1) The expected benefits and commercial value after the transformation of the technical solution of the present invention are: This invention patent can design the flyback converter frequency to a higher frequency by reducing the peak voltage, thereby making the entire circuit design more compact. At the same time, the reduction of voltage stress enables the flyback converter to adapt to more third-generation power semiconductor devices. Generally speaking, MOS transistors with lower breakdown voltage have smaller on-resistance and parasitic capacitance. Using MOS transistors with smaller parasitic parameters can improve the overall performance of the flyback converter and have better performance in some fields.
[0047] (2) Does the technical solution of the present invention overcome the technical prejudice? The dual-transformer flyback converter with parallel primary and series secondary overcomes the traditional flyback technology prejudice problem. The technical problems of the single-transformer flyback converter are mainly due to the fact that the flyback converter cannot be used in relatively high-power applications. The main reasons are: the magnetic saturation problem of the transformer and the MOS transistor peak voltage problem. In relatively high-power applications, the voltage stress across the drain-source of the MOS transistor will be very large, which may very likely cause the MOS transistor to be broken down, resulting in safety problems in the topology and the inability to achieve the expected functions. The dual-transformer flyback converter with parallel primary and series secondary distributes the power required by the single-transformer flyback converter to two transformers through the dual transformers, effectively solving the magnetic saturation problem of the transformer; and reducing the peak current in the primary side reduces the problem of excessive voltage stress caused by leakage inductance. The dual-transformer flyback converter with parallel primary and series secondary provides a new method different from the existing methods for reducing voltage spikes: reducing the leakage inductance and reducing the voltage stress between the drain-source of the MOS transistor by reducing the current change rate.
[0048] The above-described embodiments merely represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.
Claims
1. A dual-transformer flyback converter, characterized in that, Including: Adding a voltage-dividing transformer at the single transformer of a single-transformer flyback converter to obtain a dual-transformer flyback converter; wherein, the secondary side of the voltage-dividing transformer is connected in series with the secondary side of the single transformer, and the primary side of the voltage-dividing transformer is connected in parallel with the primary side of the single transformer; the magnetic flux direction of the single transformer is clockwise, and the magnetic flux direction of the voltage-dividing transformer is counterclockwise. The primary side of the voltage-dividing transformer is connected in parallel with a first additional resistor and an additional capacitor, and the primary side of the voltage-dividing transformer is connected in series with an additional diode and a second additional resistor. The positive electrode of the additional diode is connected to the primary side of the voltage-dividing transformer, and the negative electrode of the additional diode is connected to the second additional resistor.
2. The flyback converter with dual transformers according to claim 1, wherein The primary side of the single transformer is connected in series with a second capacitor, a third resistor, and a second diode; wherein, the positive electrode of the second diode is connected to the primary side of the single transformer, and the negative electrode of the second diode is connected to the third resistor R5. A third ammeter is connected in series between the primary side of the single transformer and the second capacitor. After the second capacitor is connected in series with a fourth ammeter, it is connected in parallel with a second resistor. A fifth ammeter is connected in series between the positive electrode of the second diode and the primary side of the single transformer.
3. A dual-transformer flyback converter as claimed in claim 1, wherein, The secondary side of the voltage-dividing transformer and the secondary side of the single transformer are connected in parallel with a first resistor, a first capacitor, and a first voltmeter, and the secondary side of the voltage-dividing transformer and the secondary side of the single transformer are connected in series with a first diode, a first ammeter, and a second ammeter.
4. A dual-transformer flyback converter as claimed in claim 1, wherein, The single transformer and the voltage-dividing transformer are driven by the same driving circuit; the driving circuit includes: a driving power supply, a comparator, an AC power supply, and an operational amplifier. The driving power supply is connected to the non-inverting input terminal of the comparator, and the phase wire of the AC power supply is connected to the inverting input terminal of the comparator; the output terminal of the comparator is connected to the input terminal of the operational amplifier, and the first output terminal of the operational amplifier is connected to the gate of the additional MOS transistor and the gate of the MOS transistor. The neutral wire of the AC power supply, the second output terminal of the operational amplifier, the source electrode of the MOS transistor, and the source electrode of the additional MOS transistor are all grounded.
5. A dual-transformer flyback converter according to claim 4, wherein, A second voltmeter is connected in parallel between the source electrode and the drain electrode of the MOS transistor. A body diode is connected in series between the source electrode and the drain electrode of the MOS transistor; the positive electrode of the body diode is connected to the source electrode of the MOS transistor, and the negative electrode of the body diode is connected to the drain electrode of the MOS transistor.
6. The flyback converter with dual transformers according to claim 4, wherein, The drain electrode of the additional MOS transistor is connected to the positive electrode of the additional diode, and an additional body diode is connected in series between the source electrode and the drain electrode of the additional MOS transistor; the positive electrode of the additional body diode is connected to the source electrode of the additional MOS transistor, and the negative electrode of the additional body diode is connected to the drain electrode of the additional MOS transistor.
7. A dual-transformer flyback converter as claimed in claim 1, wherein, The primary sides of the voltage-dividing transformer and the single transformer are also connected to the positive electrode of a DC power supply, and the negative electrode of the DC power supply is grounded.