LLC resonant converter suitable for wide output voltage range and small current load
By improving the design of the transformer secondary winding and the position of the diodes in the LLC resonant converter, the problems of loop instability and low current accuracy of the traditional LLC resonant converter under low current load were solved, and a wide output voltage range and high current sampling accuracy were achieved.
Patent Information
- Application Number
- CN202511514060.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-22
- Publication Date
- 2026-02-06
AI Technical Summary
Traditional LLC resonant converters suffer from loop stability issues, narrow output voltage range, and low current accuracy under low current loads.
The LLC converter structure with segmented output is adopted. By changing the design of the transformer secondary winding and the position of the diode, the influence of inter-turn parasitic capacitance is reduced, and a diode is connected in series between the transformer secondary winding and the current transformer to improve the current sampling accuracy.
This achieves improved current detection accuracy under low current loads and expands the output voltage range, thereby enhancing the loop stability and current sampling accuracy of the LLC resonant converter.
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Figure CN121485486A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of lighting electronic circuit, in particular to an LLC resonant converter suitable for wide output voltage range and small current load. BACKGROUND
[0002] LLC resonant converter is widely used in high efficiency power supply design because it can realize zero voltage switching (ZVS) of primary side switch tube and zero current switching (ZCS) of secondary side rectifier tube in full load range. However, the traditional variable frequency control LLC has the following inherent disadvantages when the load is light or the current is small: Loop stability challenge: the transformer winding has parasitic capacitance, when the number of turns of the transformer winding is large, it is impossible to avoid more serious parasitic capacitance, when the frequency is low, the low frequency capacitance is large, which can be ignored. But when the output is small current load, the frequency becomes larger, the capacitance is lower, and the influence on the resonance has to be considered. The distributed capacitance and leakage inductance form a resonance network, which produces vibration, affects the detection accuracy of the loop, and even affects the stability of the loop.
[0003] LLC resonant converter is popular because of its high efficiency, but its gain characteristic (the ratio of output voltage to input voltage) is seriously dependent on the load, and its adjustable gain range is limited, and its output voltage range is relatively narrow, which is an inherent feature.
[0004] Therefore, there is an urgent need for a new LLC topology structure with a wider output voltage range and small current load. SUMMARY
[0005] The problem solved by the present application is how to provide an LLC resonant converter with a wider output voltage range and small current load by changing the output end structure of the traditional LLC converter to reduce the influence of inter-turn parasitic capacitance on the detection circuit, thereby significantly improving the accuracy under small current load.
[0006] To solve the above problems, the application provides an LLC resonant converter suitable for wide output voltage range and small current load, which comprises an LLC half-bridge circuit, a transformer and a current detection circuit, the main winding of the transformer is used as the excitation winding of the LLC half-bridge circuit, the secondary winding of the transformer has four windings with different numbers of turns, which are sequentially a first secondary winding, a second secondary winding, a third secondary winding and a fourth secondary winding, the current detection circuit comprises a first transformer and a second transformer, the first ends of the first secondary winding and the third secondary winding are connected to a high-voltage output end, the first ends of the second secondary winding and the fourth secondary winding are connected to a low-voltage output end through a second diode and a fifth diode respectively, and the second ends are connected to a common negative terminal through the first transformer and the second transformer respectively, so as to form two groups of voltage outputs with different ranges, the second diode and the fifth diode have a rectification function, a first diode is reversely arranged between the second end of the first secondary winding and the first end of the second secondary winding, and a fourth diode is reversely arranged between the second end of the third secondary winding and the first end of the fourth secondary winding, and the first diode and the fourth diode disconnect the two connected secondary winding taps to reduce the turn-to-turn parasitic capacitance parameters of the two secondary windings.
[0007] Further, the application further comprises a third diode and a sixth diode, the third diode is reversely arranged between the second secondary winding and the first transformer, and the sixth diode is reversely arranged between the fourth secondary winding and the second transformer, so as to reduce the influence of the reverse current of the secondary winding of the transformer on the sampling accuracy of the transformer.
[0008] Further, the application further comprises a first capacitor and a second capacitor, the first end of the first capacitor is connected to the high-voltage output end, the second end is connected to the low-voltage output end, the first end of the second capacitor is connected to the second end of the first capacitor, and the second end is connected to the ground.
[0009] Further, the LLC half-bridge circuit comprises a controller, a first MOS tube, a second MOS tube, a resonant inductor and a resonant capacitor, the gates of the first MOS tube and the second MOS tube are connected to the output end of the controller respectively, the drain of the first MOS tube is connected to a positive power supply, the source is connected to the first end of the resonant inductor, the drain of the second MOS tube is connected to the source of the first MOS tube, and the drain is connected to the ground, and the second end of the resonant inductor is connected to the ground through the main winding of the transformer and the resonant capacitor in sequence.
[0010] Further, the current sampling output ends of the first transformer and the second transformer are connected to the controller respectively.
[0011] Compared with the prior art, the application has the following beneficial effects: 1. By adopting a segmented output strategy and designing multiple secondary windings with different turns ratios from the main winding, the output voltage range is improved. At the same time, by changing the position of the secondary diodes of the LLC transformer and the structure of the output winding, the influence of the transformer parasitic capacitance parameters on the detection current is reduced, thereby improving the current sampling accuracy of the circuit under low current load.
[0012] 2. By connecting a diode in series between the secondary winding of the transformer and the current transformer, the impact of the reverse current of the transformer winding on the current sampling accuracy of the current transformer is reduced, thereby further improving the detection accuracy of the output current. Attached Figure Description
[0013] Figure 1 This is a schematic diagram of the overall structure of a conventional LLC resonant converter according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the circuit principle of a conventional LLC resonant converter according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the circuit principle of the wide output voltage range LLC resonant converter according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the circuit principle of an LLC resonant converter suitable for a wide output voltage range and low current load according to an embodiment of the present invention. Detailed Implementation
[0014] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0015] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0016] In the description of this specification, references to terms such as "embodiment," "one embodiment," and "one implementation" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or implementation is included in at least one embodiment or illustrative implementation of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or implementation. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or implementations.
[0017] like Figure 4As shown, the present invention provides an LLC resonant converter suitable for a wide output voltage range and low current load, which can achieve a wide output voltage range and good low current load regulation and current accuracy.
[0018] Generally, medium-to-high power constant current dimming LED drivers use LLC half-bridge circuits. LLC circuits can achieve zero-voltage switching (ZVS) or zero-current switching (ZCS), which greatly reduces the switching losses of switching devices, thereby improving overall efficiency. The traditional LLC circuit topology is as follows: Figure 1 As shown, the circuit includes the primary and secondary sides of the LLC circuit, a current detection circuit, and a control IC. The primary side of the LLC circuit typically uses a half-bridge or full-bridge circuit connected to the main winding of the transformer. The control IC controls the half-bridge or full-bridge circuit via a PWM signal, adjusting the voltage and current output of the transformer's secondary winding. In the secondary side of the LLC circuit, the transformer's secondary winding outputs the current to the load after filtering and rectification. The current detection circuit collects the current output of the secondary side of the LLC circuit to the load and feeds it back to the control IC, forming a closed-loop circuit. For detailed circuit principles, please refer to [reference needed]. Figure 2 ,exist Figure 2 In the circuit, the primary side of the LLC circuit adopts a half-bridge LLC structure, including switching transistors S1 and S2, resonant networks Cr, Lr, and Lm, and transformer T1A. The secondary side consists of the output terminal composed of diodes D1 and D2 and output capacitor C0, while L2A and L2B are the sampling terminals of the current sampling transformer.
[0019] However, the traditional LLC circuit structure described above suffers from a narrow output voltage range and low current accuracy under low current loads. To address the narrow output voltage range issue, a further solution is proposed: like Figure 3 As shown, the power stage is a half-bridge LLC structure, including switching transistors S1 and S2, resonant networks Cr, Lr, and Lm, and transformer T1A. The secondary side employs a dual-output design (high-voltage side and low-voltage side), with different turns ratios between the secondary windings and the primary windings. This design allows for segmented load handling, increasing the output voltage range of the load. Figure 3 In this circuit, when outputting from one end, the high-voltage output terminal consists of diodes D1 and D4 connected in series with output capacitors C0 and C1, while the low-voltage output terminal consists of diodes D2 and D5 and output capacitor C1. Because the turns ratios of the primary and secondary windings at both ends are different, the output voltage range at each end can be different, significantly increasing the output voltage range. However, the problem of low accuracy at low currents still exists.
[0020] To address the issue of low accuracy with low current, the final solution is as follows: like Figure 4 As shown, Figure 3Diode D1 is moved to the middle of the transformer secondary windings 14-15 and 16-17, disconnecting the two windings in the middle and dividing them into two windings with fewer turns. Fewer turns result in smaller inter-turn capacitance, thus reducing the overall inter-turn parasitic parameters of the windings. Diode D4 is moved to the middle of the transformer secondary windings 13-14 and 11-12, disconnecting the taps of the two windings and dividing them into two windings with fewer turns, further reducing the inter-turn parasitic parameters of the two windings. Adding diodes D3 and D6 in series between the current transformer and the transformer windings reduces the impact of the reverse current of the transformer windings on the current sampling accuracy of the current transformer. These methods improve the current sampling accuracy of the circuit under low-current loads.
[0021] In the diagram above, transformer T1A secondary windings 14-15, 16-17, 13-14, and 11-12 are the first, second, third, and fourth secondary windings, respectively; L2B and L2A are the first and second current transformers, respectively; diodes D1-D6 are the first to sixth diodes, respectively; capacitors C0 and C1 are the first and second capacitors, respectively; Cr is the resonant capacitor; Lr is the resonant inductor; and switching transistors S1 and S2 are the first and second MOSFETs, respectively.
[0022] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.
Claims
1. An LLC resonant converter suitable for a wide output voltage range and low current load, characterized in that, include: The LLC half-bridge circuit comprises a transformer and a current detection circuit. The main winding of the transformer serves as the excitation winding of the LLC half-bridge circuit. The secondary winding of the transformer has four windings with different numbers of turns, namely, the first secondary winding, the second secondary winding, the third secondary winding, and the fourth secondary winding. The current detection circuit includes a first current transformer and a second current transformer. The first ends of the first and third secondary windings are connected to the high-voltage output terminal. The first ends of the second and fourth secondary windings are connected to the low-voltage output terminal via a second diode and a fifth diode, respectively. The second ends are connected to the common negative terminal via the first and second current transformers, respectively, to form two sets of voltage outputs with different ranges. The second and fifth diodes function as rectifiers. The first diode is reverse-biased and positioned between the second end of the first secondary winding and the first end of the second secondary winding. The fourth diode is reverse-biased and positioned between the second end of the third secondary winding and the first end of the fourth secondary winding. The first and fourth diodes are used to disconnect the taps of the two connected secondary windings to reduce the inter-turn parasitic capacitance parameters of the two secondary windings.
2. The LLC resonant converter suitable for wide output voltage range and low current load according to claim 1, characterized in that, It also includes a third diode and a sixth diode. The third diode is reverse-coupled between the second secondary winding and the first current transformer, and the sixth diode is reverse-coupled between the fourth secondary winding and the second current transformer, so as to reduce the impact of the reverse current of the secondary winding of the transformer on the sampling accuracy of the current transformer.
3. The LLC resonant converter suitable for wide output voltage range and low current load according to claim 2, characterized in that, It also includes a first capacitor and a second capacitor. The first terminal of the first capacitor is connected to the high voltage output terminal, and the second terminal is connected to the low voltage output terminal. The first terminal of the second capacitor is connected to the second terminal of the first capacitor, and the second terminal is grounded.
4. The LLC resonant converter suitable for wide output voltage range and low current load according to claim 3, characterized in that, The LLC half-bridge circuit includes a controller, a first MOSFET, a second MOSFET, a resonant inductor, and a resonant capacitor. The gates of the first MOSFET and the second MOSFET are respectively connected to the output terminal of the controller. The drain of the first MOSFET is connected to the positive power supply, and the source is connected to the first terminal of the resonant inductor. The drain of the second MOSFET is connected to the source of the first MOSFET, and the drain is grounded. The second terminal of the resonant inductor is grounded in sequence through the main winding of the transformer and the resonant capacitor.
5. The LLC resonant converter suitable for wide output voltage range and low current load according to claim 4, characterized in that, The current sampling output terminals of the first and second current transformers are respectively connected to the controller.