Single-stage conversion device integrating buck-boost and full-bridge LLC circuit

Abstract

A single-stage conversion device integrating a Buck-Boost circuit and a full-bridge LLC circuit. Said device comprises a Buck-Boost circuit and a full-bridge LLC circuit; and the Buck-Boost circuit comprises two switching transistors Q1 and Q2, the switching transistor Q2 being multiplexed as an upper transistor of the full-bridge LLC circuit. The voltage stress of the switching transistor Q2 of said device is significantly reduced, and the stress of the switching transistor Q1 is equal to an input voltage, and therefore, the type selection of the switching transistors is more facilitated, a 500V MOS transistor which is highly cost-effective can be selected, two power diodes are eliminated in a main loop, and the full-bridge LLC circuit can achieve higher power output, thus achieving a wider application range. Additionally, the working principle of the full-bridge LLC circuit is the same as that of conventional full-bridge LLC circuits, and the switching transistors can achieve zero-voltage switching within a full-load range, thus achieving obvious advantages in thermal design and efficiency, and facilitating product development in practical applications.

Description

A single-stage conversion device integrating buck-boost and full-bridge LLC circuits TECHNICAL FIELD

[0001] The present invention relates to power converters, and in particular to a single-stage conversion device integrating buck-boost and full-bridge LLC circuits. BACKGROUND

[0002] With the rapid development of semiconductor technology, the fourth generation of electric light source LED has been widely promoted and used. Compared with traditional electric light source, LED has many incomparable advantages, such as long service life, high efficiency, low power consumption, high brightness, small size and other advantages, so it is particularly prominent in the application of lighting field. LED lighting system includes LED driving power and LED lamp two parts, and the core is LED driving power. High-efficiency and energy-saving high-power LED driving power becomes an important research direction in the industry.

[0003] High frequency and miniaturization are important indicators of current switching power supply design. If the driving power works in hard switching mode, the increase of switching frequency will generate a lot of switching loss, which reduces the conversion efficiency of the system. Therefore, the soft switching technology aiming at reducing switching loss has also become an important research hotspot in the field of power electronics.

[0004] Resonant converters, including series, parallel, series-parallel resonant converters, etc. are common soft switching converters. Resonant converter can realize zero voltage turn-on of switching tube and zero current turn-off of secondary side rectifier diode in a wide load range through reasonable design, thereby reducing switching tube loss and improving efficiency. AC-DC conversion adopts Buck-Boost topology, and the circuit works in discontinuous mode to automatically realize PFC function. It is a single-switch low-order boost-buck converter circuit, which realizes intermediate DC bus voltage boost-buck, and reduces the stress of LLC switching tube and capacitor in the later stage.

[0005] The current most mainstream technical solution: 1. High power is two-stage, which realizes power factor correction and voltage stabilization by the first stage Boost, and realizes output voltage stabilization (and electrical isolation, etc.) by the second stage DCDC (isolated or non-isolated topology). This scheme is mature in technology, but the system is complex, the cost is high, and the efficiency is low; 2. Small power single-stage PFC flyback, which realizes input power factor correction and output voltage stabilization at the same time by single-stage flyback, mainly applied to small power LED driving power. This scheme is mature in technology, simple in system, low in cost and high in efficiency, but the output has obvious power frequency ripple (which will cause LED lamp flicker), the input voltage range is narrow, and the lack of bus capacitor causes lightning surge problem. SUMMARY

[0006] The present application aims to provide a single-stage conversion device integrating Buck-Boost and full-bridge LLC circuits, which simplifies the circuit, reduces the volume, improves the power density, and lowers the cost.

[0007] To solve the above technical problems, the present application provides a single-stage conversion device integrating Buck-Boost and full-bridge LLC circuits, which comprises a Buck-Boost circuit and a full-bridge LLC circuit; the Buck-Boost circuit comprises two switching tubes Q1 and Q2, and one of the switching tubes Q2 is multiplexed as an upper tube of the full-bridge LLC circuit.

[0008] In a preferred embodiment, the LLC circuit further comprises an upper tube Q3, lower tubes Q4 and Q5.

[0009] In a preferred embodiment, the states of the switching tubes Q1 and Q2 are the same as that of the lower tube Q4, and opposite to that of the upper tube Q3 and the lower tube Q5.

[0010] In a preferred embodiment, the Buck-Boost circuit further comprises alternating current (AC) input rectifier diodes D1, D2, D3 and D4; the AC input rectifier diodes D1, D2, D3 and D4 rectify the AC input to pulsating direct current (DC).

[0011] In a preferred embodiment, the AC input ends of the AC input rectifier diodes D1, D2, D3 and D4 are connected to an AC power supply, and the DC output ends are connected to a high-frequency transformer T1 through the Buck-Boost circuit and the LLC circuit.

[0012] In a preferred embodiment, the Buck-Boost circuit further comprises a freewheeling diode D5, and the full-bridge LLC circuit further comprises rectifier diodes D6 and D7, which are used to rectify the high-frequency AC voltage of the secondary winding of the high-frequency transformer T1 to DC.

[0013] In a preferred embodiment, the non-identical name ends of the secondary winding of the high-frequency transformer T1 are respectively connected to the anodes of the diodes D6 and D7, the cathodes of the diodes D6 and D7 are connected to each other and grounded through an electrolytic capacitor C2, and the cathodes of the diodes D6 and D7 are further connected to the identical name ends of the secondary winding through a load R1.

[0014] In a preferred embodiment, the identical name ends of the primary winding Np and the secondary windings Ns1 and Ns2 of the high-frequency transformer T1 are in the same direction.

[0015] In a preferred embodiment, one end of the primary winding of the high-frequency transformer T1 is connected to a resonance loop composed of an inductor Lr and a capacitor Cr connected in series.

[0016] In a preferred embodiment, the resonance frequency of the resonance loop is Lm is the magnetizing inductance.

[0017] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0018] The present application provides a single-stage conversion device integrating Buck-Boost and full-bridge LLC circuits, the voltage stress of MOS tube Q2 can be significantly reduced, the stress of the added MOS tube Q1 is equal to the input voltage, so the selection of MOS tube is more favorable, a 500V MOS tube with high cost performance can be selected, two power diodes are saved in the main circuit, and the full-bridge LLC can realize greater power output, so the application range can be more extensive. At the same time, the working principle of the LLC circuit part is exactly the same as that of the conventional LLC circuit, Q2-Q5 can realize ZVS in the full load range, and there will be obvious advantages in thermal design and efficiency, which is more convenient for product development in practical application. BRIEF DESCRIPTION OF DRAWINGS

[0019] Fig. 1 is a circuit diagram of the preferred embodiment of the present application;

[0020] Fig. 2 is a timing diagram of the preferred embodiment of the present application;

[0021] Figs. 3-10 are equivalent circuit diagrams of the preferred embodiment of the present application in various modes. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application; obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0023] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom end" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0024] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "provided with", "sleeved / connected", "connected" and the like should be understood in a broad sense, for example, "connected" can be wall-mounted connection, can also be detachable connection, or integral connection, can be mechanical connection, can also be electrical connection, can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication of two elements, and those skilled in the art can understand the specific meaning of the above terms in the present application according to the specific circumstances.

[0025] Referring to FIG. 1, the present example provides a single-stage conversion device integrating Buck-Boost and full-bridge LLC circuits, including a Buck-Boost circuit and a full-bridge LLC circuit; the Buck-Boost circuit includes two switching tubes Q1 and Q2, and one of the switching tubes Q2 is multiplexed as the upper tube of the full-bridge LLC circuit. Q1-Q5 are power MOS tubes, wherein Q1 and Q2 are the switching tubes of the Buck-Boost, Q2 and Q3 are the upper tubes of the full-bridge LLC circuit, and Q4 and Q5 are the lower tubes of the full-bridge LLC circuit. In control, Q1-Q6 adopt PWM\PFM\phase shift control, Q1, Q2 and Q4 are simultaneously turned on and turned off, and Q3\Q5 and Q1\Q2\Q4 are driven complementarily. D1-D4 are AC input rectifier diodes for rectifying AC input to pulsating DC. D6 and D7 are power diodes, wherein D5 is the freewheeling diode of the Buck-Boost circuit, and D6 and D7 are used to rectify the high-frequency AC voltage of the secondary winding of T1 to DC. L1 and Lr are high-frequency inductors, C1 and C2 are electrolytic capacitors, and Cr is a high-frequency capacitor. T1 is a high-frequency transformer, and the same-named ends of the primary winding Np and the secondary windings Ns1 and Ns2 are in the same direction.

[0026] In the present embodiment, the Buck-Boost circuit works in discontinuous mode. Within the positive and negative cycles of the AC power supply operating frequency, the working state of the circuit is symmetrical, and here the positive half cycle is taken as an example for illustration, and the negative half cycle is not described one by one. FIG. 2 is the corresponding key waveform, and FIGS. 3-10 are the eight mode equivalent diagrams of the positive half cycle.

[0027] Mode 1 [t0-t1]: Before t0, the current iL of the inductor L1 has dropped to 0, and at the same time, since the body diodes of Q2 and Q4 are turned on, at t0, Q2 and Q4 are zero-voltage turned on, Q1 is zero-current turned on, and u in The MOS tubes Q1 and Q2 charge the Buck-Boost inductor L1, and the current i L The slope u in / L1 increases linearly. At the same time, the DC bus capacitor C1 provides energy for the LLC circuit through the MOS tubes Q2 and Q4. In this stage, the resonant inductor L r , the resonant capacitor Cr participate in resonance, the resonance frequency is The secondary diode D7 is on, charging the output capacitor C2 and powering the output load R1, and also clamping the primary winding of the transformer, so the magnetizing inductance of the transformer T1 does not participate in resonance. The magnetizing current i Lm with the slope nV o / L m linearly increases.

[0028] Mode 2 [t1~t2]: At t1, the resonance current is equal to the magnetizing current, at this time the secondary diode D7 current drops to zero and turns off, the primary winding of the transformer is no longer clamped by the output voltage, the magnetizing inductance participates in resonance, the resonance frequency is The MOS tubes Q1, Q2, Q4 are still on, the current i L continues to linearly increase.

[0029] Mode 3 [t2~t3]: At t2, the MOS tubes Q1, Q2, Q4 are off, entering the dead time. The inductor L1 begins to discharge, its current i L charges the DC bus capacitor C1 through the power diode D5, the current i L linearly decreases. The magnetizing inductance Lm, the resonance inductance Lr, and the resonance capacitor Cr form a series resonance circuit, with a resonance frequency resonates, the resonance current charges the junction capacitors of the MOS tubes Q2, Q4, and the junction capacitors of the MOS tubes Q3, Q5 discharge, until the voltage across the junction capacitors of the MOS tubes Q3, Q5 drops to 0. At this stage, the resonance current is still equal to the magnetizing current, and the secondary diode continues to be off.

[0030] Mode 4 [t3~t4]: At t3, the resonance current flows entirely through the body diodes of the MOS tubes Q3, Q5, and the MOS tubes Q3, Q5 meet the zero-voltage switching condition. At this stage, the resonance inductance Lr and the resonance capacitor Cr resonate at a resonance frequency resonates, the resonance current is greater than the magnetizing current, and the secondary diode D6 is on. The voltage across the primary winding of the transformer is clamped at -nVo, and the magnetizing current increases linearly with the slope nV o / L m linearly increases. At this stage, the current i L continues to decrease.

[0031] Mode 5 [t4~t5]: At t4, the current iL of the inductor L1 in the Buck-Boost circuit drops to zero. The MOS tubes Q3, Q5 continue to be on, and the resonance inductance Lr and the resonance capacitor Cr continue to resonate at a resonance frequency resonates, the resonance current is greater than the magnetizing current, and the secondary diode D6 is on.

[0032] Mode 6 [t5~t6]: at t5, the current in Lr is equal to the current in Lm, the secondary rectifier diode D6 is off with zero current, the output voltage is no longer clamped to the transformer, Lm becomes a free resonant inductor, participates in the resonance, the excitation inductor Lm, the resonant inductor Lr and the resonant capacitor Cr form a series resonant circuit, and the resonant frequency Resonance, because the excitation inductor Lm is large, the resonance period is large, and the resonant current is consistent with the excitation current in this stage, which is approximately constant.

[0033] Mode 7 [t6~t7]: at t6, MOS tubes Q3 and Q5 are off. Enter the dead time, and the excitation inductor Lm, the resonant inductor Lr and the resonant capacitor Cr resonate at the resonant frequency Resonance, in this stage, the resonant current is still equal to the excitation current, and the secondary rectifier diode is off. The resonant current is the discharge of the junction capacitance of MOS tubes Q2 and Q4, and the charging of the junction capacitance of MOS tubes Q3 and Q5, until the voltage across the junction capacitance of MOS tubes Q2 and Q4 drops to 0.

[0034] The above is only a preferred specific embodiment of the present application, but the design concept of the present application is not limited thereto, and any person skilled in the art can make non-essential changes to the present application within the technical scope disclosed by the present application, which is an act of infringing the protection scope of the present application. Industrial applicability

[0035] The present application provides a single-stage conversion device integrating Buck-Boost and full-bridge LLC circuits, the voltage stress of MOS tube Q2 can be significantly reduced, the stress of added MOS tube Q1 is equal to the input voltage, so the selection of MOS tube is more favorable, and a 500V MOS tube with high cost performance can be selected, two power diodes are saved in the main circuit, and the full-bridge LLC can realize larger power output, and the application range can be more widely. At the same time, the working principle of the LLC circuit part is exactly the same as that of the conventional LLC circuit, Q2~Q5 can realize ZVS in the full load range, and there is obvious advantage in thermal design and efficiency, which is more convenient for product development in practical application.

[0036] .

Claims

1. A single-stage converter integrating Buck-Boost and full-bridge LLC circuits, characterized in that: It includes a Buck-Boost circuit and a full-bridge LLC circuit; the Buck-Boost circuit includes two switching transistors Q1 and Q2, and one of the switching transistors Q2 is multiplexed as the upper transistor of the full-bridge LLC circuit.

2. The single-stage converter integrating Buck-Boost and full-bridge LLC circuits according to claim 1, characterized in that: The LLC circuit also includes upper transistor Q3 and lower transistors Q4 and Q5.

3. A single-stage converter integrating Buck-Boost and full-bridge LLC circuits according to claim 2, characterized in that: Switches Q1 and Q2 have the same state as the lower switch Q4, and the opposite state to the upper switch Q3 and the lower switch Q5.

4. A single-stage converter integrating Buck-Boost and full-bridge LLC circuits according to claim 3, characterized in that: The Buck-Boost circuit also includes AC input rectifier diodes D1, D2, D3, and D4; the AC input rectifier diodes D1, D2, D3, and D4 rectify the AC input into pulsating DC.

5. A single-stage converter integrating Buck-Boost and full-bridge LLC circuits according to claim 4, characterized in that: The AC input terminals of the AC input rectifier diodes D1, D2, D3, and D4 are connected to the AC power supply, and the DC output terminals are connected to the high-frequency transformer T1 through the Buck-Boost circuit and the LLC circuit.

6. A single-stage converter integrating Buck-Boost and full-bridge LLC circuits according to claim 4, characterized in that: The Buck-Boost circuit also includes a freewheeling diode D5, and the full-bridge LLC circuit also includes rectifier diodes D6 and D7. The rectifier diodes D6 and D7 are used to rectify the high-frequency AC voltage of the secondary winding of the high-frequency transformer T1 into DC voltage.

7. A single-stage converter integrating Buck-Boost and full-bridge LLC circuits according to claim 6, characterized in that: The opposite terminals of the secondary winding of the high-frequency transformer T1 are connected to the anodes of diodes D6 and D7, respectively. The cathodes of diodes D6 and D7 are connected to each other and grounded through electrolytic capacitor C2. The cathodes of diodes D6 and D7 are also connected to the same terminals of the secondary winding through load R1.

8. A single-stage converter integrating Buck-Boost and full-bridge LLC circuits according to claim 7, characterized in that: The primary winding Np of the high-frequency transformer T1 is in the same direction as the corresponding terminals of the secondary windings Ns1 and Ns2.

9. A single-stage converter integrating Buck-Boost and full-bridge LLC circuits according to claim 6, characterized in that: One end of the primary winding of the high-frequency transformer T1 is connected to a resonant circuit consisting of an inductor Lr and a capacitor Cr connected in series.

10. A single-stage converter integrating Buck-Boost and full-bridge LLC circuits according to claim 8, characterized in that: The resonant frequency of the resonant circuit is Lm is the magnetizing inductance.

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