A multi-path parallel flyback converter and switching power supply

Abstract

This utility model discloses a multi-parallel flyback converter and a switching power supply, relating to the field of switching power supply technology. Specifically, it includes a transformer, at least two power branches, and a power management controller. The transformer has a magnetic core. At least two power branches are connected in parallel to the DC input terminal. Each power branch includes a primary winding, a power switching element, and a current feedback unit. The primary winding is wound on the magnetic core. The first terminal of the power switching element is electrically connected to the primary winding. One end of the current feedback unit is electrically connected to the second terminal of the corresponding power switching element, and the other end of the current feedback unit is electrically connected to the common reference terminal of the power branch. This application adopts a passive current sharing method, eliminating the need for any additional active current sharing control chip or communication bus between master and slave controllers, significantly reducing material costs and PCB layout area. It also avoids potential failure points caused by introducing complex active control circuits or communication links.

Description

Technical Field

[0001] This utility model relates to the field of switching power supply technology, and in particular to a multi-channel parallel flyback converter and switching power supply. Background Technology

[0002] Flyback converters are widely used in low-to-medium power applications due to their simple structure, low cost, and ease of electrical isolation. However, when the output power increases to the hundred-watt level or above, the traditional single-switch flyback topology experiences high current stress on the switching transistor, leading to a sharp increase in conduction losses; power losses are concentrated in a single device, causing concentrated thermal stress, making heat dissipation design difficult, reducing system reliability; and the leakage inductance of the transformer causes excessively high turn-off voltage spikes.

[0003] To address the aforementioned issues, existing technologies introduce additional control loops to actively regulate the current in each branch. This is primarily achieved by adding dedicated current sharing control chips, employing master-slave controllers, and synchronizing and adjusting the drive signals of each branch in real time via a communication bus. Alternatively, complex current sharing control can be implemented in digital power supplies through software algorithms. The introduction of additional control chips, communication interfaces, and complex control algorithms not only significantly increases the system's material costs, PCB layout area, and design complexity, but also introduces new potential failure points through the added components, thereby reducing the long-term operational reliability of the entire power supply system.

[0004] Therefore, how to provide a multi-parallel flyback converter with a simple structure, high reliability, and high-precision automatic current sharing without introducing complex active control circuits is a technical problem that urgently needs to be solved in this field. Utility Model Content

[0005] The main purpose of this invention is to provide a multi-channel parallel flyback converter and switching power supply, aiming to provide a simple, reliable and high-precision automatic current sharing multi-channel parallel flyback converter.

[0006] To achieve the above objectives, this utility model proposes a multi-parallel flyback converter, including a transformer, at least two power branches, and a power management controller. The transformer has a magnetic core; At least two of the power branches are connected in parallel to the DC input terminal, and each of the power branches includes a primary winding, a power switching element, and a current feedback unit. The primary winding is wound on the magnetic core; The first terminal of the power switching element is electrically connected to the primary winding; One end of the current feedback unit is electrically connected to the second electrode of the corresponding power switching element, and the other end of the current feedback unit is electrically connected to the common reference terminal of the power branch. The output terminal of the power management controller is electrically connected to the control terminals of at least two of the power switching elements, and the input terminal of the power management controller is electrically connected to the common reference terminal of at least two of the current feedback units on the side away from the corresponding power switching element.

[0007] Furthermore, the current feedback unit is a sampling resistor.

[0008] Furthermore, the sampling resistor is a resistor with a positive temperature coefficient.

[0009] Furthermore, at least two of the sampling resistors have equal resistance values.

[0010] Furthermore, at least two of the primary windings are wound together on the magnetic core.

[0011] Furthermore, the power switching element is a MOSFET, with its control terminal being the gate, and its first and second terminals being the drain and source, respectively.

[0012] Furthermore, it also includes at least two absorption circuits, each of which is electrically connected in parallel to both ends of the primary winding.

[0013] Furthermore, the absorption circuit is an RCD clamping circuit.

[0014] Furthermore, it also includes the driving resistor; One end of the driving resistor is electrically connected to the output terminal of the power management controller, and the other end of the driving resistor is electrically connected to the control terminals of at least two of the power switching elements.

[0015] This application also discloses a switching power supply, including the aforementioned multi-parallel flyback converter.

[0016] The above technical solution has the following advantages: The current sharing function of this invention relies entirely on its innovative circuit topology, employing a passive current sharing method. It requires no additional active current sharing control chip, a communication bus between master and slave controllers, or complex current sharing algorithms implemented in software. This greatly simplifies the overall system design, significantly reducing material costs and PCB layout area. It also avoids potential failure points caused by introducing complex active control circuits or communication links, fundamentally improving the reliability of the entire power supply system.

[0017] This invention constructs a natural, distributed negative feedback mechanism for each branch by winding multiple primary windings on a single magnetic core and setting an independent current feedback unit for each power branch. The power management controller samples the superimposed signals from these feedback units. Any minute deviation in the current of any branch is converted through its independent feedback unit and applied to the power switching element of that branch, achieving dynamic and natural automatic current balancing. Test results show that this scheme can easily achieve excellent current sharing effects, with peak current differences between branches less than 3% and steady-state operating temperature differences between the corresponding power switches less than 2 degrees Celsius.

[0018] This application evenly distributes the total power loss across N physically separate power switching elements, solving the problem of high heat concentration in single-transistor schemes. This simplifies and simplifies the heat dissipation design, significantly reducing the overall temperature rise. Simultaneously, the total leakage inductance energy of the transformer is also distributed across N independent absorption circuits, significantly reducing the turn-off voltage spike experienced by each switching element. Because the total current is distributed, the current in a single branch decreases, allowing the sampling resistor value used to detect the branch current to be increased by N times compared to the single-transistor scheme. This results in a larger amplitude and stronger noise immunity sampling voltage signal, solving the problem of difficult detection of small resistance signals in traditional high-power flyback converters, and making overcurrent protection and other mechanisms more accurate and reliable.

[0019] This invention introduces a thermal negative feedback mechanism by preferentially employing a sampling resistor with a positive temperature coefficient, which further achieves temperature balance among the power branches and improves the stability and reliability of the system under complex thermal environments. By equipping each primary winding with an independent RCD snubber circuit, leakage inductance energy can be absorbed more efficiently, protecting the power switching components. Attached Figure Description

[0020] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings, wherein: Figure 1 This is a circuit connection schematic diagram of this utility model; Figure 2 This is a schematic diagram of the power management controller of this utility model.

[0021] In the diagram: 100, power management controller; 201, drive resistor; 202, power switching element; 203, current feedback unit; 300, primary winding; 400, absorption circuit. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the following specific embodiments are only used to explain this utility model and do not constitute a limitation on this utility model.

[0023] like Figure 1 As shown, a multi-parallel flyback converter includes a transformer, at least two power branches, and a power management controller 100; the transformer has a magnetic core. At least two power branches are connected in parallel to the DC input terminal. Each power branch includes a primary winding 300, a power switching element 202, and a current feedback unit 203. The primary winding 300 is wound on a magnetic core. The first terminal of the power switching element 202 is electrically connected to the primary winding 300. One end of the current feedback unit 203 is electrically connected to the second terminal of the corresponding power switching element 202, and the other end of the current feedback unit 203 is electrically connected to the common reference terminal of the power branch. The output terminal of the power management controller 100 is electrically connected to the control terminal of at least two power switching elements 202, and the input terminal of the power management controller 100 is electrically connected to the common reference terminal of at least two current feedback units 203 on the side away from the corresponding power switching element 202.

[0024] Specifically, such as Figure 1 As shown, the converter of this application includes a transformer T1, two parallel power branches, and a power management controller 100.

[0025] Transformer T1 has a magnetic core, which can be an EFD40 type ferrite core.

[0026] The two power branches are connected in parallel across the DC input voltage Vin. The first power branch includes a primary winding 300, a power switching element 202, and a current feedback unit 203. The second power branch includes a primary winding 300, a power switching element 202, and a current feedback unit 203.

[0027] The primary windings 300 of the two power branches are wound together on the magnetic core of transformer T1. Specifically, one end of the two primary windings 300 is connected to the positive terminal of the DC input voltage Vin, and the other end is connected to the first terminal of the corresponding power switching element 202.

[0028] The power switching element 202 is preferably a MOSFET, and the first terminal of the power switching element 202, i.e. the drain, is electrically connected to the other end of the primary winding 300.

[0029] The current feedback unit 203 can employ a sampling resistor. One end of the sampling resistor is electrically connected to the second terminal of the power switching element 202, which is the source of the MOSFET. The other end of the sampling resistor is connected to the common reference terminal of the power branch, preferably power ground GND.

[0030] Similarly, the drain of the power switching element 202 is electrically connected to the primary winding 300, one end of the current feedback unit 203 is electrically connected to the source of the power switching element 202, and the other end is also connected to the power ground GND.

[0031] like Figure 1 and Figure 2 As shown, the power management controller 100, for example, can be a controller of model OB2365. Its drive output terminal can be the Gate pin of this controller model. The output terminal of the power management controller 100 is connected to the control terminal, i.e., the gate, of the two power switching elements 202 to provide a synchronous drive signal. The current sampling input terminal of the power management controller 100 is preferably the CS pin, which is used to connect to the common reference terminal on the side of the two current feedback units 203 away from the corresponding power switching element 202, that is, the common connection point at the ground terminal. The CS pin of the power management controller 100 samples the superimposed voltage signal generated by the total current flowing through the two current feedback units 203.

[0032] The power switching element 202 of the first power branch uses a MOSFET Q1, the sampling resistor of the current feedback unit 203 is selected as Rs1, and the primary winding 300 is selected as LP1; correspondingly, the power switching element 202 of the second power branch uses a MOSFET Q2, the sampling resistor of the current feedback unit 203 is selected as Rs2, and the primary winding 300 is selected as LP2.

[0033] During operation, the Gate pin of the power management controller 100 outputs a high-level drive signal, causing both power switching elements 202 to conduct simultaneously. Input current flows through the power branches Lp1-Q1-Rs1 and Lp2-Q2-Rs2, respectively, and energy is stored in the core of transformer T1. The power management controller 100 continuously monitors the total voltage across the two current feedback units 203 via the CS pin. When this total voltage reaches an internally set threshold, the Gate pin of the power management controller 100 outputs a low level, causing both power switching elements 202 to turn off simultaneously, and the transformer transfers the stored energy to the secondary side.

[0034] The core of this embodiment lies in the current sharing mechanism. Since the two primary windings 300 are wound in parallel on the same magnetic core, their electrical parameters such as inductance, leakage inductance, and DC resistance are highly consistent, making it easier to achieve the effect of current sharing. The two current feedback units 203 are set independently. Ideally, the current flowing through the two branches is equal. However, in reality, due to slight differences in parameters such as the turn-on voltage of Q1 and Q2, the current in one power branch may be slightly greater than the current in the other power branch. At this time, the voltage drop generated on Rs1 will be slightly greater than the voltage drop generated on Rs2. For the power management controller 100, it samples the sum of the two voltage drops to determine the total turn-off time. However, for the power switching element 202Q1 itself, its effective gate-source drive voltage is actually the Gate pin voltage minus its source voltage. Since the voltage value of Rs1 is relatively large, it is equivalent to weakening the drive of the power switching element 202, thereby naturally suppressing the current growth trend of this power branch. Conversely, for the other power branch, its current is lower, resulting in a lower voltage across Rs2. This leads to a relatively stronger voltage across its power switching element 202Q2, promoting an increase in the current of that power branch. Based on these actions, a dynamic, distributed natural feedback regulation process is formed, allowing the currents of the two branches to quickly reach equilibrium, ultimately achieving a natural current sharing effect.

[0035] As another embodiment of this application, applicable to higher power applications, the converter also includes a transformer T1, three power branches, and a power management controller 100. The transformer T1 uses a larger magnetic core, such as PQ50. The three power branches have similar structures to the embodiments described above. The first, second, and third power branches each include a primary winding 300, a power switching element 202, and a current feedback unit 203. The primary winding 300, power switching element 202, and current feedback unit 203 of the first power branch are named LP1, Q1, and Rs1, respectively; the primary winding 300, power switching element 202, and current feedback unit 203 of the second power branch are named Lp2, Q2, and Rs2, respectively; and the primary winding 300, power switching element 202, and current feedback unit 203 of the third power branch are named Lp3, Q3, and Rs3, respectively.

[0036] Lp1, Lp2, and Lp3 are wound in parallel on the same magnetic core to ensure high parameter consistency. Their common end is connected to the DC input terminal, i.e., the DC input positive terminal Vin. Q1, Q2, and Q3 are selected as appropriate MOSFETs, and the drain of each MOSFET is connected to the other end of the corresponding Lp1, Lp2, or Lp3. One end of the three independent Rs1, Rs2, and Rs3 is connected to the source of Q1, Q2, and Q3 respectively, and the other end is connected to the common reference terminal, i.e., power ground GND.

[0037] The Gate drive output of the power management controller 100 is connected to the gates of Q1, Q2, and Q3 simultaneously. The CS pin current sampling input of the power management controller 100 is connected to the common ground point of Rs1, Rs2, and Rs3.

[0038] Its working principle and current sharing mechanism are exactly the same as those in the above embodiment, except that the current and power loss are distributed among the three power branches. Each power branch has an independent negative feedback mechanism. When the current in any branch deviates, the power switching element 202 of that power branch will be adjusted by the voltage change generated by its corresponding current feedback unit 203, thereby achieving high-precision automatic current sharing among the three power branches.

[0039] The aforementioned power branches may also include multiple branches. For example, the fourth power branch includes Lp4, Q4, and Rs4, and so on. The Nth power branch includes LpN, QN, and RsN. The specific connection method is similar to that in the above embodiment, and will not be repeated here.

[0040] The current feedback unit 203 is a sampling resistor; that is, the specific implementation of the current feedback unit 203Rs1, Rs2, and Rs3 is a sampling resistor. A sampling resistor is a passive device with stable resistance, capable of linearly converting the flowing current into a voltage signal. It has a simple structure and low cost. In a dual-channel parallel converter, two surface-mount resistors can be selected as Rs1 and Rs2. After converting the current signal into a voltage signal, it is convenient for sampling and comparison by the CS pin of the power management controller 100.

[0041] The sampling resistors are positive temperature coefficient (PTC) resistors. To further improve the thermal balance and reliability of the system, the sampling resistors Rs1, Rs2, etc., can preferably be resistors with a positive temperature coefficient. A PTC resistor's resistance increases with its temperature. In a multi-parallel system, if the first power branch experiences a higher temperature for its power switching element 202 than other power branches due to layout, uneven heat dissipation, or individual component differences, the temperature of the sampling resistor Rs1 in that power branch will also rise. Because Rs1 has a PTC characteristic, its resistance will increase accordingly. According to the aforementioned negative feedback principle, a larger Rs1 resistance will generate a larger voltage drop under the same current, thereby weakening the on-state voltage of the power switching element 202 in that power branch and further suppressing current growth in that power branch. For power branches with higher sampling resistor temperatures, the current is suppressed more, thus reducing heat generation in that power branch and promoting temperature equilibrium among the parallel power branches, greatly improving the system's reliable operation.

[0042] At least two sampling resistors must have equal resistance values. In the above embodiments, to ensure the symmetry of each parallel branch, the nominal resistance values ​​of the selected N independent sampling resistors, such as Rs1, Rs2, ..., RsN, should be equal. For example, in a dual-path parallel design, Rs1 and Rs2 are both 0.33Ω resistors. In a triple-path parallel design, Rs1, Rs2, and Rs3 are all 0.22Ω resistors. Selecting sampling resistors with equal resistance values ​​ensures that the current feedback gain of each branch is the same, allowing the negative feedback mechanisms of each power branch to operate on the same reference, thereby achieving optimal current sharing accuracy.

[0043] At least two primary windings 300 are wound together on the magnetic core. In the embodiment described above, which uses only two primary windings 300, Lp1 and Lp2 are fabricated using a common parallel winding method. Specifically, two insulated enameled wires can be wound together and simultaneously wound with a specified number of turns on the frame of the transformer core. After winding, the starting ends of the two wires are used as the input terminals of Lp1 and Lp2, and are connected together to the DC input terminal Vin; the ends of the two wires are used as the output terminals of Lp1 and Lp2, and are respectively connected to the drain of the power switching unit. By using a parallel winding process, the number of turns, length, and DC resistance of Lp1 and Lp2 are guaranteed to be completely consistent to the greatest extent. In particular, since the two wires are closely adjacent at every position on the magnetic core, the magnetic field environment they experience is almost identical, which makes their mutual inductance coupling very tight, and their self-inductance and leakage inductance are also highly consistent. In addition to this embodiment, three primary windings 300, four primary windings 300, etc., can also be used, all of which can use the parallel winding process of this embodiment.

[0044] The power switching element 202 is a MOSFET, with its gate as the control terminal and its first and second terminals as the drain and source, respectively. In the above embodiment, the selected power switching elements 202Q1, Q2, ..., QN are all N-channel enhancement-mode metal-oxide-semiconductor field-effect transistors. The MOSFET's gate is the control terminal, used to receive drive signals from the power management controller 100. The first terminal of the power switching element 202 is the drain, used to connect to one end of the primary winding 300, serving as the inflow terminal of the main current. The second terminal of the power switching element 202 is the source, used to connect to one end of the current feedback unit 203, serving as the outflow terminal of the main current. In a 150W design, a MOSFET of model IPA60R360P7 can be selected as the power switching unit.

[0045] This application also includes at least two snubber circuits 400, each of which is connected in parallel across the primary winding 300. In the above embodiment, to suppress voltage spikes generated when the power switching element 202 is turned off, each power branch is equipped with an independent snubber circuit 400. Specifically, one snubber circuit 400 is connected in parallel across the primary winding 300, i.e., between the DC input terminal of this application and the drain of the corresponding power switching element 202, and the connection method of the snubber circuit 400 of the other power branch is similar. Each power branch has its own independent snubber circuit 400. The advantage of this is that each snubber circuit 400 only needs to handle the leakage inductance energy of its own branch, resulting in lower power consumption. At the same time, the snubber circuit path is shorter, which can more effectively clamp voltage spikes and protect the corresponding power switching element 202.

[0046] Furthermore, the absorption circuit 400 is an RCD clamping circuit. In the above embodiment, the absorption circuit 400 can specifically take the form of an RCD clamping circuit, which consists of a resistor R, a capacitor C, and a diode D. For example, for the first power branch, its corresponding RCD clamping circuit consists of a resistor R1, a capacitor C1, and a diode D1. The anode of diode D1 is connected to the drain of Q1, and the cathode of diode D1 is connected to the common junction of resistor R1 and capacitor C1. The other ends of capacitor C1 and resistor R1 are electrically connected to the DC input terminal. When the power switch element 202 is turned off, the high voltage spike generated across Lp1 will charge C1 through D1, transferring the leakage inductance energy to C1, and then slowly dissipating it through R1, thereby clamping the drain voltage of Q1 to a safe level. For Lp2, an RCD clamping circuit consisting of R2, C2, and D2 with the same parameters as the former is also connected in parallel.

[0047] This application also includes a drive resistor 201, one end of which is electrically connected to the output terminal of the power management controller 100, and the other end of which is electrically connected to the control terminals of at least two power switching elements 202. In the above embodiment, to optimize the driving method of the power switching elements 202, a drive resistor 201 can be added between the Gate output pin of the power management controller 100 and the gates of Q1 and Q2. For example, one end of the drive resistor 201 is connected to the Gate pin of the power management controller 100, and the other end is connected to the common connection point of the gates of Q1 and Q2. The function of the drive resistor 201 is to limit the charging and discharging current of the gate, which can slow down the switching speed of the switching transistor, thereby helping to suppress ringing and electromagnetic interference generated during the switching process.

[0048] In applications with higher requirements for drive performance and system stability, an independent gate drive resistor 201 scheme can be adopted. That is, after output from the Gate pin of the power management controller 100, the signal paths are separated, with an independent drive resistor 201 connected in series with the gate of each power switching element 202. For example, an independent drive resistor 201 is connected in series before the gate of Q1, and another independent drive resistor 201 is connected in series before the gate of Q2. Compared to the scheme in the above embodiments that uses a single drive resistor 201, this approach can better suppress gate oscillations caused by different parasitic inductances between the various power switching elements 202, further improving drive stability and reliability, and is also more beneficial for improving EMI performance.

[0049] A switching power supply includes the aforementioned multi-parallel flyback converter. This embodiment provides a switching power supply adapter, such as a 150W switching power supply adapter, whose core power conversion section utilizes the aforementioned multi-parallel flyback converter. In addition to the core converter circuit, the switching power supply also includes an input EMI filter and a rectifier filter circuit for converting AC mains power into high-voltage DC power to supply the flyback converter. On the secondary side of the flyback converter, a secondary rectifier diode, a filter capacitor, and a voltage feedback circuit are also included to convert the high-frequency pulse voltage output from the transformer into a stable DC output voltage. The output voltage signal is then fed back to the power management controller 100 on the primary side via isolation devices such as optocouplers, forming a closed-loop control to achieve a stable output voltage. Because the entire switching power supply system employs the multi-parallel current sharing technology of this application, its core power stage section features high efficiency, low temperature rise, and high reliability.

[0050] The above description is only a preferred embodiment of the present utility model and does not limit the patent scope of the present utility model. All equivalent structural transformations made under the inventive concept of the present utility model using the contents of the present utility model specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present utility model.

Claims

1. A multi-path parallel flyback converter, characterized in that, Includes a transformer, at least two power branches, and a power management controller; The transformer has a magnetic core; At least two of the power branches are connected in parallel to the DC input terminal, and each of the power branches includes a primary winding, a power switching element, and a current feedback unit. The primary winding is wound on the magnetic core; The first terminal of the power switching element is electrically connected to the primary winding; One end of the current feedback unit is electrically connected to the second electrode of the corresponding power switching element, and the other end of the current feedback unit is electrically connected to the common reference terminal of the power branch. The output terminal of the power management controller is electrically connected to the control terminals of at least two of the power switching elements, and the input terminal of the power management controller is electrically connected to the common reference terminal of at least two of the current feedback units on the side away from the corresponding power switching element.

2. The multi-channel parallel flyback converter as described in claim 1, characterized in that, The current feedback unit is a sampling resistor.

3. The multi-pass parallel flyback converter of claim 2, wherein, The sampling resistor is a resistor with a positive temperature coefficient.

4. The multi-pass parallel flyback converter of claim 3, wherein, At least two of the sampling resistors have the same resistance value.

5. The multi-parallel flyback converter of claim 1, wherein, At least two of the primary windings are wound together on the magnetic core.

6. The multi-pass parallel flyback converter of claim 1, wherein, The power switching element is a MOSFET, with its control terminal being the gate, and its first and second terminals being the drain and source, respectively.

7. The multi-pass parallel flyback converter of claim 1, wherein, It also includes at least two absorption circuits, each of which is electrically connected in parallel to both ends of the primary winding.

8. The multi-parallel flyback converter of claim 7, wherein, The absorption circuit is an RCD clamping circuit.

9. The multi-pass parallel flyback converter of claim 1, wherein, It also includes the drive resistor; One end of the driving resistor is electrically connected to the output terminal of the power management controller, and the other end of the driving resistor is electrically connected to the control terminals of at least two of the power switching elements.

10. A switching power supply, characterized by comprising: Includes the multi-parallel flyback converter as described in any one of claims 1 to 9.

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