An 800v high-voltage input dual-tube flyback auxiliary power supply device
The 800V high-voltage input power supply, with its dual-tube flyback topology and precise magnetic circuit design, solves the problem of excessive stress on the switching transistors, achieving efficient, low-cost, and highly reliable power conversion, suitable for new energy vehicles and high-voltage energy storage converters.
Patent Information
- Application Number
- CN202610444820.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-07
- Publication Date
- 2026-07-03
AI Technical Summary
In 800V high-voltage input scenarios, existing technologies require single-tube flyback solutions to withstand extremely high stress on the switching transistors, two-stage conversion solutions to be inefficient, and multi-level solutions to be complex and costly. There is a lack of efficient and low-cost dual-tube flyback designs for high-voltage input.
Employing a dual-tube flyback topology, and through symmetrically wound transformers and precise magnetic circuit design, the voltage stress of the clamping switch is kept at the input voltage level. Combined with synchronous control and multiple protection mechanisms, this achieves efficient and low-cost power conversion.
It achieves precise voltage stress clamping of the switching transistor, selects MOSFETs with appropriate withstand voltage ratings, reduces costs and improves efficiency, and features a miniaturized and highly reliable system suitable for demanding applications such as new energy vehicles and high-voltage energy storage converters.
Smart Images
Figure CN122339259A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of high-voltage power conversion technology, and more specifically, to a dual-tube flyback auxiliary power supply device suitable for 800V high-voltage bus systems, particularly suitable for scenarios in new energy vehicles, high-voltage energy storage converters, and industrial high-voltage drive equipment that require power to be drawn from a high-voltage DC bus to provide a stable low-voltage control power supply. Background Technology
[0002] With the upgrade of new energy vehicle platform voltage from 400V to 800V and the popularization of high-voltage energy storage systems, the design of high-voltage auxiliary power supplies faces new challenges. The auxiliary power supply needs to draw power directly from the 800V high-voltage DC bus to provide stable low-voltage (such as ±12V, 5V) isolated power to MCUs, sensors, driver ICs, etc.
[0003] The existing technologies mainly have the following solutions and shortcomings: (1) Single-transistor flyback scheme: The drain-source voltage that the switching transistor withstands when it is turned off is Vin+VR, where VR is the reflected voltage. Under an input of 800V, the peak stress that the switching transistor actually withstands can easily exceed 1600V. This forces designers to choose high-voltage MOSFETs with voltages of 1700V or higher. Such devices have complex processes, extremely high costs (several times that of ordinary high-voltage transistors), high on-resistance (leading to low efficiency), slow switching speed, and very few available models on the market, resulting in high supply chain risks.
[0004] (2) Two-stage conversion scheme (Buck + flyback): First, step down 800V to 200-400V, and then perform flyback conversion. This scheme adds a front-stage Buck switch and inductor, which not only increases the cost, but also reduces the overall efficiency by 5-10 percentage points due to the energy undergoing two conversions, making it difficult to meet the stringent requirements of high power density and high efficiency.
[0005] (3) Multilevel or cascaded scheme: High voltage is evenly distributed through capacitor voltage division or module series connection. Although this scheme reduces the stress on a single switch, it brings complex voltage equalization control problems and the number of components increases exponentially, resulting in larger PCB size and reduced reliability, which cannot meet the miniaturization and high reliability requirements of automotive and energy storage systems. Although the dual-transistor flyback topology has the theoretical advantage of low voltage stress (clamped to the input voltage), there is currently a lack of refined, low-cost, and highly integrated designs specifically for the high-voltage input scenario. Existing designs often use low-voltage parameters without systematically matching and optimizing transformer distributed parameters, MOSFET selection, EMC filtering, and protection logic. Summary of the Invention
[0006] The purpose of this invention is to provide a dual-tube flyback auxiliary power supply device with 800V high-voltage input. This invention is particularly suitable for high-voltage DC bus systems of 800V and above, such as the 800V platform of new energy vehicles. By utilizing the natural clamping characteristics of the dual-tube flyback topology, the stress of the switching transistor is precisely controlled at the input voltage level, thereby allowing the selection of industrial-grade MOSFETs with a voltage rating that is reasonably matched to the input voltage. Through the overall optimization of the transformer magnetic circuit, winding structure and control and protection logic, a high degree of unity between high efficiency, high reliability, miniaturization and low cost is achieved.
[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution: an 800V high-voltage input dual-tube flyback auxiliary power supply device, comprising an input filter module, a dual-tube flyback power conversion module, a control drive module, an output rectification filter module, and a protection module connected in sequence.
[0008] A dual-transistor flyback power converter module, electrically connected to the input filter module, is used to convert filtered high-voltage direct current into isolated low-frequency alternating current; it includes a transformer, a first power switch, a second power switch, and a clamping absorption circuit;
[0009] The primary side of the transformer includes a first primary winding and a second primary winding connected in series. The first power switch is connected in series with the first primary winding, and the second power switch is connected in series with the second primary winding, so that the voltage stress borne by the first power switch and the second power switch in the off state is clamped to the voltage level of the high voltage DC input.
[0010] The control drive module is used to generate two synchronous pulse width modulation signals to drive the first power switch and the second power switch to turn on or off synchronously, respectively.
[0011] The output rectifier and filter module is electrically connected to the secondary winding of the transformer and is used to rectify and filter the converted AC power into a stable low-voltage DC power output.
[0012] The protection module is used to monitor the input voltage, output voltage, or power switch current, and to control the control drive module to stop output when an abnormality is detected.
[0013] By adopting the above technical solution, the high-voltage input dual-transistor flyback auxiliary power supply proposed in this invention achieves precise clamping of the voltage stress on the switching transistors through the dual-transistor flyback topology. In an 800V high-voltage input scenario, this design strictly limits the turn-off voltage stress of the first and second power switches to the input voltage level, avoiding the high-voltage stress problem caused by the superposition of reflected voltages in traditional single-transistor flyback schemes. This characteristic allows the system to select industrial-grade MOSFETs with voltage ratings appropriately matched to the input voltage, such as 900V enhancement-mode devices, ensuring both safety and reducing device costs.
[0014] In terms of transformer design, the first and second primary windings employ symmetrical winding technology, along with precise calculation of the air gap in the magnetic core, effectively suppressing magnetic saturation under high-frequency operation. By optimizing the turns ratio and distributed parameters, efficient energy transfer between the primary and secondary sides is achieved. The secondary winding provides multiple independent outputs (including positive voltage, negative voltage, and standby voltage) to meet the power supply requirements of complex control systems. The two-stage π-type filter structure of the input filter module, combined with the electromagnetic compatibility design of the common-mode inductor, significantly reduces conducted interference, enabling the power supply to meet stringent EMC standards such as CISPR 32.
[0015] The control and drive module achieves electrical isolation through a drive transformer, ensuring safe operation of the high-voltage and low-voltage sides. Its generated synchronous pulse-width modulation signal enables the two power switches to work in precise timing, improving conversion efficiency and simplifying control logic. The protection module's real-time monitoring function covers abnormal conditions such as input overvoltage, output overload, and switch overcurrent, ensuring safe system shutdown under fault conditions through a rapid response mechanism. Experimental data shows that this power supply can achieve a peak efficiency of over 93% at 800V input, with a power density 40% higher than traditional solutions, making it particularly suitable for applications with stringent space and reliability requirements, such as new energy vehicles and high-voltage energy storage converters.
[0016] A further feature of this invention is that the dual-transistor flyback power converter module is the core innovative unit. It includes a transformer (T1), a first power MOSFET (Q1), a second power MOSFET (Q2), and a clamping absorption circuit consisting of two diodes (D1, D2) and a capacitor (Cclamp). The primary winding of the transformer consists of two windings (Np1, Np2) with equal turns connected in series, with their midpoints connected to the input positive and negative buses via D1 and D2. This topology ensures that when Q1 and Q2 are turned off, the drain-source voltage is clamped to the input voltage level, rather than more than twice the input voltage of a conventional single-transistor flyback converter.
[0017] By adopting the above technical solution, this invention effectively solves the problem of excessive stress on the switching transistor in 800V high-voltage input scenarios, avoiding the use of expensive and inefficient 1700V high-voltage MOSFETs. Simultaneously, this design reduces losses caused by distributed parameters and improves power conversion efficiency by optimizing the transformer magnetic circuit and winding structure. Furthermore, the inherent clamping characteristics of the dual-transistor flyback topology simplify protection logic design, reducing system complexity and cost. Compared with existing two-stage conversion or multi-level solutions, this invention achieves smaller size and lower cost while maintaining high efficiency and high reliability, making it ideal for applications with stringent power performance requirements, such as new energy vehicles, high-voltage energy storage converters, and industrial high-voltage drive equipment.
[0018] A further feature of the present invention is that the transformer (T1) preferably uses an EE-type ferrite core and has a precisely calculated air gap. The primary windings Np1 and Np2 are wound with two wires in parallel or symmetrically, with a strictly consistent number of turns to ensure balanced voltage division in series and avoid overvoltage breakdown of any MOSFET.
[0019] By adopting the above technical solutions, the air gap design of the transformer core effectively prevents magnetic saturation, maintaining stable permeability even under high-voltage input and transient load changes. The symmetrical winding process of the primary winding not only reduces leakage inductance but also significantly reduces the impact of high-frequency switching noise on EMC performance. In addition, the flat structure of the EE-type core facilitates heat dissipation design, and combined with optimized air gap calculations, the transformer's temperature rise under full load is controlled below 25°C, significantly improving the long-term reliability of the power supply.
[0020] A further feature of the present invention is that the drain-source breakdown voltage of the power switch is preferably 1.1 to 1.3 times the rated voltage of the high-voltage DC input.
[0021] By adopting the above technical solutions, the voltage rating design of power switching transistors avoids both the risk of breakdown due to insufficient safety margin and the cost waste caused by excessive redundancy. For example, in an 800V input scenario, a MOSFET with a voltage rating of 900V is selected. This precise matching strategy significantly reduces switching losses and heat dissipation requirements while ensuring reliability, providing crucial support for high power density designs. This range ensures sufficient safety margin while avoiding the selection of devices with excessively high on-resistance and cost due to an overemphasis on ultra-high voltage rating.
[0022] A further feature of the present invention is that the control drive module preferably employs a drive transformer isolation scheme. The signal generated by the PWM controller drives the low-side switch (Q2) directly through the drive transformer, and drives the high-side switch (Q1) through the isolation winding, ensuring strict synchronization of the switching actions of the two transistors.
[0023] By adopting the above technical solution, the drive transformer isolation scheme not only achieves electrical isolation between the primary and secondary sides, but also eliminates the delay and accuracy loss caused by traditional optocoupler isolation. Through precise design of the drive transformer's turns ratio and core parameters, the drive signals of the high- and low-side switching transistors can be ensured to remain highly synchronized across the entire temperature range, avoiding the risks of transformer magnetization and transistor shoot-through caused by switching timing deviations. Furthermore, this scheme simplifies PCB layout, reduces interference coupling paths between the high-voltage and low-voltage sides, and significantly improves the system's EMC performance.
[0024] A further feature of this invention is that the protection module integrates overcurrent and overvoltage protection. Overcurrent protection is achieved by sampling the source current of Q2 and sensing the voltage of the resistor (Rs); overvoltage protection is achieved by sampling the output voltage through optocoupler isolation and feeding it back to the PWM controller.
[0025] By adopting the above technical solution, the protection module constructs a dual safety defense by monitoring the power switch current and output voltage in real time. When the source current of Q2 exceeds a preset threshold, the protection circuit immediately triggers the PWM controller to shut down the drive signal, preventing the MOSFET from being damaged by overcurrent. Simultaneously, the optocoupler-isolated sampling circuit accurately captures abnormal fluctuations in the output voltage and quickly cuts off the power output when the voltage exceeds the safe range. This dual protection mechanism not only effectively prevents component damage but also avoids the transmission of high-voltage side faults to the low-voltage control circuit through electrical isolation design, significantly improving the system's reliability under complex operating conditions. Furthermore, the protection module's response time is less than 500ns, far faster than the blowing speed of traditional fuses, providing more reliable protection for sensitive loads.
[0026] The beneficial effects of this invention are:
[0027] 1. Precise voltage stress clamping: Compared with the existing technology, the present invention strictly clamps the maximum voltage stress of the switching transistor to the input voltage (800V), avoiding the extreme stress of more than 1600V in the single-transistor solution, making it possible to use a mature industrial-grade MOSFET with a voltage rating of 900V, reducing costs by more than 70%, and greatly improving supply chain stability.
[0028] 2. High-efficiency single-stage conversion: Compared with the two-stage conversion scheme, the present invention completes the conversion from high voltage to low voltage through only a single-stage DC / DC conversion, without additional step-down stage losses, and the full-load efficiency is significantly improved.
[0029] 3. Miniaturization and high power density: Compared with cascaded or multi-module solutions, this invention only requires a single transformer and two switching transistors. The circuit topology is simple, the number of components is small, significantly saving PCB area and facilitating system miniaturization and integration.
[0030] 4. High reliability design: By using the symmetrical winding process of the transformer and the precise design of the air gap of the magnetic core, the problem of bias saturation under large duty cycles of traditional dual-tube flyback transformers is solved; combined with multiple hardware-level protection circuits, the device is ensured to operate stably for a long time under harsh conditions of 800V high voltage. Attached Figure Description
[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0032] Figure 1 This is a circuit diagram of the dual-transistor flyback power converter module in an embodiment of the present invention.
[0033] Figure 2 This is a circuit schematic diagram in an embodiment of the present invention. Detailed Implementation
[0034] The technical solution of the present invention will now be clearly and completely described with reference to specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0035] Example 1: As Figure 1 As shown, this embodiment provides an 800V high-voltage input dual-tube flyback auxiliary power supply device, which includes: an input filtering module, a dual-tube flyback power conversion module, a control drive module, an output rectification and filtering module, and a protection module.
[0036] Input filtering module: Used to suppress common-mode / differential-mode interference from the power grid or upstream bus and prevent noise generated by this device from polluting the bus. In this embodiment, the input filtering module 100 adopts a two-stage π-type filter. It includes a first-stage X capacitor Cx1 (0.022μF / 1000V), a common-mode inductor L1 (2mH), and Y capacitors Cy1-Cy4, as well as a second-stage X capacitor Cx2 (0.01μF / 1000V). This design can effectively suppress high-frequency switching noise and meet the CISPR 25 Class 3 standard.
[0037] Dual-tube flyback power converter module 200: includes transformer T1, power switching transistors Q1 and Q2, and clamping snubber circuit (D1, D2, Cclamp).
[0038] Transformer T1 Design: Transformer T1 uses an EE28 magnetic core (PC40 material). Primary side: The first primary winding Np1 (pins 1-3) and the second primary winding Np2 (pins 5-4) both have 33 turns, connected at pin 2. Secondary side: Includes +12V winding Ns1 (8 turns), -12V winding Ns2 (8 turns), and +7V winding Ns3 (3 turns). To prevent core saturation, an air gap lg = 1mm is maintained, controlling the primary inductance Lp at 1.2mH ± 5%, and the maximum magnetic flux density Bmax = 0.25T.
[0039] Power switch selection: Both Q1 and Q2 are FQPF6N90C (900V / 6A / 2.3Ω). The 900V withstand voltage provides a 12.5% voltage margin (relative to 800V input), and while ensuring safety, the on-resistance is reduced by approximately 60% compared to 1700V devices.
[0040] Clamping snubber circuit: When Q1 and Q2 are turned off, the voltage spike generated by the transformer leakage inductance charges the Cclamp through D1 and D2. Since D1 and D2 clamp the source of Q1 and the drain of Q2 to the input bus respectively, the Vds voltage of Q1 and Q2 is limited to Vin (800V) + a very small clamping capacitor voltage. This circuit eliminates the need for a high-power resistor in the RCD snubber, further reducing losses.
[0041] Control Drive Module: This embodiment preferably adopts an isolated drive scheme. The PWM controller U1 (such as the UC2845 series) outputs a PWM signal to the primary side of the drive transformer T2. The two secondary windings of T2 are connected to the gates of Q1 and Q2 respectively via gate resistors Rg1 and Rg2. This scheme eliminates the need for a high-side bootstrap circuit and provides negative voltage shutdown, enhancing anti-interference capabilities.
[0042] Output rectification and filtering module: Secondary windings Ns1, Ns2, and Ns3 output high-frequency square waves respectively. Ns1 is rectified by fast recovery diode D3 and filtered by LC (L2, Cout1) to output +12V; Ns2 is rectified by diode D4 and filtered to output -12V; Ns3 is rectified by diode D5 and filtered to output +7V. The feedback signal is taken from the +12V output, isolated by an optocoupler, and fed back to the FB pin of U1.
[0043] Protection Module: Integrated into the internal or external circuitry of U1. Overcurrent Protection: The voltage across the sampling resistor Rs (0.1Ω) is fed to the CS pin of U1; the output is shut off when the voltage exceeds 1V. Overvoltage Protection: A Zener diode clamp is set at the +12V output terminal, and the output voltage is monitored through the auxiliary winding or sampling circuit; the PWM output is locked in case of an abnormality.
[0044] Working principle:
[0045] When Q1 and Q2 are both on, the input voltage Vin (800V) is applied across the series-connected Np1+Np2 transformer, energizing the transformer and causing the primary current to rise linearly. When Q1 and Q2 are both off, since the inductor current cannot change abruptly, the voltages at the same terminals are reversed, and D1 and D2 are forward-biased, feeding the leakage inductance energy back to the input and clamping the drain-source voltages of Q1 and Q2 at Vin+VD (diode voltage drop). The secondary diodes then conduct, releasing the energizing energy to the load. By adjusting the PWM duty cycle, the output voltage can be stabilized.
Claims
1. An 800V high voltage input dual tube flyback auxiliary power supply powered device, characterized in that: include: The input filtering module is used to connect to the high-voltage DC input and perform electromagnetic compatibility filtering; The dual-tube flyback power converter module is electrically connected to the input filter module and is used to convert the filtered high-voltage DC power into isolated low-frequency AC power. It includes a transformer, a first power switch, a second power switch, and a clamping snubber circuit; The primary side of the transformer includes a first primary winding and a second primary winding connected in series. The first power switch is connected in series with the first primary winding, and the second power switch is connected in series with the second primary winding, so that the voltage stress borne by the first power switch and the second power switch in the off state is clamped to the voltage level of the high voltage DC input. The control drive module is used to generate two synchronous pulse width modulation signals to drive the first power switch and the second power switch to turn on or off synchronously, respectively. The output rectifier and filter module is electrically connected to the secondary winding of the transformer and is used to rectify and filter the converted AC power into a stable low-voltage DC power output. The protection module is used to monitor the input voltage, output voltage, or power switch current, and to control the control drive module to stop output when an abnormality is detected.
2. The 800V high-voltage input dual-tube flyback auxiliary power supply power supply device according to claim 1, characterized in that: The clamping absorption circuit includes a first diode, a second diode, and an absorption capacitor; the cathode of the first diode is connected to the drain of the first power switch, and the anode is connected to the connection point of the first primary winding and the second primary winding; the anode of the second diode is connected to the source of the second power switch, and the cathode is connected to the connection point of the first primary winding and the second primary winding; the absorption capacitor is connected in parallel between the cathode of the first diode and the anode of the second diode.
3. The dual-tube flyback auxiliary power supply device with 800V high-voltage input according to claim 2, characterized in that: The first primary winding and the second primary winding have the same number of turns and are manufactured using a symmetrical winding process.
4. The dual-tube flyback auxiliary power supply device with 800V high-voltage input according to claim 3, characterized in that: The drain-source breakdown voltage of the first power switch and the second power switch is 1.1-1.3 times the rated voltage of the high voltage DC input.
5. The dual-tube flyback auxiliary power supply device with 800V high-voltage input according to claim 4, characterized in that: The high-voltage DC input is an 800V platform, and both the first and second power switching transistors are enhancement-type MOSFETs with a withstand voltage between 850V and 950V.
6. The dual-tube flyback auxiliary power supply device with 800V high-voltage input according to claim 1, characterized in that: The secondary winding of the transformer includes at least three independent windings for providing positive voltage output, negative voltage output, and low voltage standby output.
7. The dual-tube flyback auxiliary power supply device with 800V high-voltage input according to claim 6, characterized in that: The input filtering module adopts a two-stage π-type filtering structure; The two-stage π-type filter structure includes at least a first X capacitor and a second X capacitor connected in series, and a common-mode inductor disposed between the two stages.
8. The dual-tube flyback auxiliary power supply device with 800V high-voltage input according to claim 1, characterized in that: The control drive module includes: a PWM controller for generating the pulse width modulation signal; and a drive transformer, the primary winding of which is connected to the PWM controller, the first secondary winding of which is connected to the gate of the first power switch, and the second secondary winding of which is connected to the gate of the second power switch, so as to achieve electrical isolation between the primary and secondary sides and synchronous drive between the high-side and low-side switches.
9. The dual-tube flyback auxiliary power supply device with 800V high-voltage input according to claim 3, characterized in that: The transformer core has an air gap, and the length of the air gap is calculated and determined based on the preset maximum magnetic flux density and the inductance of the primary winding.