TW201332274A - LLC resonant type converter operated at near constant frequency - Google Patents

Abstract

LLC resonant type converter operated at near constant frequency comprises a switch circuit having a power source connected to several power switches, wherein the power switch is used for controlling input voltages and input currents of the power source; a control chip having several control pins, wherein two control pins are for controlling turn-on or turn-off of the power switch; a resonant circuit composed of cascading a resonant capacitor and a linear side magnetizing inductor through a variable resonant inductor, and the resonant circuit is connected to the switch circuit; a transformer composed of a wire frame and at least two magnetic iron cores, which characterized in that an end of the magnetic iron core can be casted to form a specific surface, and when two magnetic iron cores are connected, an air gap generated there between, and the magnetic iron cores saturated by the air gap to further change resonant inductance, and the transformer connected to the resonant circuit to receive the output of the resonant circuit; and a rectification circuit having secondary side diodes connected to the transformer to receive and rectify the output voltage and output current of the transformer, both connected to an output capacitor and a load.

Description

Near-fixed-frequency LLC resonant converter

The present invention relates to a near-frequency operated LLC resonant converter, and more particularly to a near-frequency operated LLC resonant converter.

In recent years, with the rapid development of semiconductor technology and technology, the current electronic products are developing towards light, thin, short and precise. Therefore, it is imperative to improve the efficiency of converters. Therefore, countries around the world have set light and air-saving aspects for electronic products in terms of environmental protection and energy saving. The regulation of energy consumption, so how to reduce the energy consumption of electronic products is an important issue for the current major improvement.

Generally, the early power supply adopts a hard switching mode, which causes a serious switching loss (Switching Loss) when the power switch is switched. As the switching power supply technology matures, the switching frequency is gradually increased, resulting in overall efficiency. The situation of lowering and temperature rise occurs, and Soft Switching technology is derived in order to effectively solve the shortcomings of high frequency switching.

In 1988, CQ Lee and R. Liu proposed the LLC Series Resonant Converter (LLC-SRC). Because the LLC resonant converter has the advantage of soft switching, its conversion efficiency is high, hence its name, but it is controlled by frequency conversion. The relationship makes EMI filter design difficult and light load efficiency become the main disadvantage; therefore, the present invention develops a fixed frequency control and light load low loss LLC resonant power converter.

It can be seen that there are still many shortcomings in the above-mentioned household items, which is not a good designer and needs to be improved.

In view of the above shortcomings derived from the above-mentioned LLC fixed-frequency converters, the inventors of the present invention have improved and innovated, and after years of painstaking research, finally successfully developed the LLC resonance of the near-fixed operation of this piece. Converter.

It is an object of the present invention to provide a near-frequency-operated LLC resonant converter in which a specific shape air gap is generated between a plurality of magnetic cores, and the magnetic core is partially saturated by the air gap. Further, the variable resonant inductor value is changed to greatly reduce the change in the switching frequency of the power switch.

A second object of the present invention is to provide an LLC resonant converter with near-frequency operation, thereby effectively improving the working efficiency of light load and extremely light load.

The LLC resonant converter capable of achieving the near-frequency operation of the above invention includes: a switching circuit having a power supply connected to a plurality of power switches for controlling an input voltage and an input current of the power source; a control chip having a plurality of control pins, wherein two control pins are used to control the opening or closing of the power switch; a resonant circuit is composed of a variable resonant inductor connected in series with a resonant capacitor and a primary side electromagnetic inductor And the resonant circuit is connected to the switch circuit; a transformer is composed of a wire frame and a magnetic core of at least two or more pieces, wherein the magnetic core end can be cast to form a specific surface, when two pieces of magnetic iron When the core is connected, an air gap is generated between the core, and the magnetic core is partially saturated by the air gap, thereby changing the variable resonant inductance value, and the transformer is connected to the resonant circuit to receive the output of the resonant circuit; a rectifier circuit having a secondary side diode connected to the transformer for receiving and rectifying an output voltage and an output current of the transformer To an output capacitor and a load.

Referring to FIG. 1 , the LLC resonant converter of the near-frequency operation provided by the present invention mainly includes: a switch circuit 1 having a power supply connected to a plurality of power switches Q ₁ , Q ₂ , and the power switch Q ₁ Q ₂ is used to control the input voltage V _in and the input current I _{in of} the power supply; a control chip 5 has a plurality of control pins, wherein the two control pins are used to control the power switches Q ₁ , Q ₂ Turning on or off; a resonant circuit 2 is composed of a variable resonant inductor L _r connected in series with a resonant capacitor C _r and a primary side magnetizing inductance L _m , and the resonant circuit 2 is connected to the switching circuit 1; a transformer 3 The bobbin is composed of at least two or more magnetic cores 31, wherein the end of the magnetic core 31 can be cast to form a specific surface 32. When the two magnetic cores 31 are connected, An air gap is generated, the magnetic core is partially saturated by the air gap, thereby changing the variable resonant inductance value, and the transformer 3 is connected to the resonant circuit 2 to receive the output of the resonant circuit 2; 4 circuit, a secondary-side diode D ₁ D ₂ is connected to the transformer 3, and configured to receive the rectified output voltage and output current of the transformer 3, the output lines connected to a capacitor C _o and a load R _L.

As shown in FIG. 1 , the circuit structure of the LLC resonant converter for near-frequency operation is composed of a variable resonant inductor L _r , a resonant capacitor C _r and a primary side magnetizing inductance L _m , which is a series resonant tank. The frequency operated LLC resonant converter is operated by two power switches Q ₁ , Q _{2 with a} duty cycle of approximately 50%, the regulated switching output voltage is used to adjust the stable output voltage, and the power switch Q _{1 is} made by the resonant circuit 2 Q ₂ reaches zero voltage switching.

2 is a circuit diagram of an equivalent transfer function of the LLC resonant converter of the near-frequency operation, which can be seen from two points a and b, and can be obtained through derivation:

Through the above formula, the voltage gain graph of FIG. 3 can be drawn, and it can be seen that the curve has two resonant frequencies, and the first resonant frequency f _{r is} determined by the variable resonant inductor L _r and the resonant capacitor C _r ; The two resonant frequencies f _m are determined by the primary side magnetizing inductance L _m and the variable resonant inductor L _r and the resonant capacitor C _r . The two resonant frequencies can be defined as:

It can be seen from Fig. 3 that when the working interval is on the right half of the first resonance frequency f _r , similar to the series resonant converter, if the working interval is on the left half of f _r , it is similar to the parallel resonant converter when the converter operates For heavy load, the characteristic is the same as that of the series resonant converter, the light load is the same as the parallel resonant converter; the voltage gain graph can be divided into three intervals; the f _r resonant frequency point is the right half plane, and the zero voltage is switched (Region) 1), between the first resonant frequency point f _r and the second resonant frequency point f _m , this interval can also reach zero voltage switching (Region 2), then the third interval (Region 3) is the second resonant frequency point f _m left half plane, this interval can achieve zero current switching; therefore, the present invention proposes a near-fixed-rate LLC resonant converter that performs only minimal changes from light load to heavy-duty switching frequency f _s and greatly improves light load Figure 4 is the characteristic curve of the traditional LLC resonant converter. If the working curve K=5, it can be known that the light load works at the red curve of Q=0.1, while at the full load, Q is 0.5, so Know that the working range is from A to E, the frequency variation range It is Δf _s (generally up to tens of kHz).

In the near-frequency LLC resonant converter, assuming that the K value changes by 5, for different loads R _L respectively take different inductances, and draw the working curve of the near-fixed-frequency resonant converter as shown in Figure 5. From this curve, it can be known that the curve forms an interlaced operating point due to different inductances. The switching frequency of the interlaced point can be adjusted by different resonant frequencies and different powers. Therefore, the corresponding inductance under different loads R _L is lightly loaded to At the full load, the working point is fixed at point A, and the frequency change is almost unchanged, thereby achieving the effect of near-fixed frequency.

The present invention relates to a near-frequency-rate LLC resonant converter which utilizes a saturation characteristic of a magnetic material to change the variable resonant inductance value, and the magnetic core 31 changes the variable resonant inductance value due to partial saturation; The schematic diagram of the magnetic core 31 is shown in Figure 6-1. The structure of the magnetic core 31 can be used to know that the end of the core is a specific surface. Therefore, when the near-frequency LLC resonant converter operates at light load, the magnetic The iron core 31 is completely unsaturated, so the variable resonant inductance value is the largest; when the working frequency of the near-fixed LLC resonant converter increases, the magnetic core 31 of the smaller air gap begins to saturate, and the variable resonant inductance value gradually changes. Small; near-frequency LLC resonant converter works at full load, the magnetic core 31 has the largest area to reach saturation, and the variable resonant inductor value is the minimum value, so as to achieve the purpose of near-fixed frequency control.

The near-fixed-frequency LLC resonant converter proposed by the present invention has the same resonant element design as the conventional LLC resonant-type converter, except that the variable resonant inductor L _r of the present invention is variable and utilizes a variable resonant inductor. L _r replaces the original resonant inductor, and has the disadvantage of wide frequency variation range and low light load efficiency; the magnetic core 31 of the transformer 3 of the present invention adopts the EI type as the embodiment, but is not used to limit the technology of the present invention, and others are EE core, EI core, RM core, E core, PQ core, EC core, ETD core, or other shapes of at least two or more magnetic cores 31 The method for changing the variable resonant inductance value by using the saturation characteristic of the magnetic material may also be included in the present invention (as shown in FIG. 6-2 to FIG. 6-10), and a preferred embodiment of the present invention is designed as follows Description: Its main component control chip system selects ST company's L6599, power switch Q ₁ and Q ₂ selects IRF840, variable resonant inductor is 130μH, resonant capacitor is 16.4 n F, primary side magnetizing inductance is 650 μH, transformer EER-40 ( PC40, TDK), magnetic core 31 selects EI-30 (PC40, TDK), The end of the magnetic core 31 is cast to form a specific surface, the air gap angle θ=1° between the specific surface and the other magnetic core, the secondary side diode MBR20H100CT, and the output capacitance is 4400 μF, which is measured through the above components. The experimental data is as follows; as shown in Fig. 7, is the voltage and current of the power switches Q ₁ and Q ₂ and the waveform of the driving signal, wherein the ratio of the variable resonant inductor L _r to the primary side magnetizing inductance L _m is K=5, The measurement waveform shows that the switching frequency of the switch is about f _s =99.3 kHz, and the power switches Q ₁ and Q ₂ achieve zero voltage switching, which confirms that there is no switching loss of the power switches Q ₁ and Q ₂ (as shown in FIG. 8 ).

Figure 9 shows the voltage and current waveforms of the variable resonant inductor L _r , the resonant capacitor C _r , and the secondary diodes D ₁ and D ₂ at full load; Figure 10 to Figure 14 are full load (240W) to light load (24W). The measured V _GS2 , i _Lr , V _Cr and f _s .

From the waveform measured from full load to light load, it can be known that the power switches Q ₁ , Q ₂ and V _GS2 are almost identical. Therefore, it can be known that the method of the present invention is feasible, and the frequency operation is close to the fixed frequency. From the variable resonant inductor L _r and the current i _{Lr , it} can be seen that the full load to the light carrier shape is almost the same. Therefore, it can be found that the characteristic curve of any load R _L is almost operated at the same frequency point, and FIG. 15 is K=5. At the same time, the measurement data of the near-frequency LLC resonant converter, it can be seen that the invention can greatly improve the light load efficiency, so it can meet the 80 PLUS certification mechanism managed by ECOS in the United States, such as 80 PLUS silver medal (> 85~88%), 80 PLUS Gold (>87~89%) and 80 PLUS Platinum (>89~92%), Figures 16~17 are the efficiency and frequency of traditional LLC and near-frequency LLC resonant converters Compare the graphs.

The LLC resonant converter of the near-frequency operation provided by the present invention has the following advantages when compared with the foregoing cited documents and other conventional techniques:

1. An LLC resonant converter operating near a fixed frequency, using a variable frequency resonant tank, so that the resonant frequency of the resonant tank can be changed with the change of the load R _L without any other components, the design cost and The traditional LLC resonant converter is the same, and the purpose of working near the fixed frequency.

Second, in addition to retaining the high conversion efficiency characteristics of the original traditional LLC resonant converter, its light load conversion efficiency has also been greatly improved.

The detailed description of the preferred embodiments of the present invention is intended to be limited to the scope of the invention, and is not intended to limit the scope of the invention. The patent scope of this case.

In summary, this case is not only innovative in terms of space type, but also can enhance the above-mentioned multiple functions compared with the customary items. It should fully meet the statutory invention patent requirements of novelty and progressiveness, and apply for it according to law. This invention patent application, in order to invent invention, to the sense of virtue.

1. . . Switch circuit

Q ₁ , Q ₂ . . . Power switch

V _in . . . Input voltage

I _in . . . Input Current

2. . . Resonant circuit

L _r . . . Variable resonant inductor

C _r . . . Resonant capacitor

L _m . . . Primary side magnetizing inductance

3. . . transformer

31. . . Magnetic core

32. . . Specific face

θ. . . Air gap angle

4. . . Rectifier circuit

D ₁ , D ₂ . . . Secondary side diode

C _o . . . Output capacitor

R _L . . . load

5. . . Control chip

1 is a circuit diagram of an LLC resonant converter of near-frequency operation of the present invention;

2 is a circuit diagram of an equivalent transfer function of the LLC resonant converter of the near-frequency operation;

3 is a voltage gain function graph of an LLC resonant converter;

Figure 4 is a working graph of a conventional LLC resonant converter;

Figure 5 is a working graph of an LLC resonant converter operating near a fixed frequency;

Figure 6-1 is an embodiment of a magnetic core of the LLC resonant converter of the near-frequency operation;

6-2 is a second embodiment of the EI-type magnetic iron core of the LLC resonant converter of the near-frequency operation;

6-3 is a third embodiment of the EI-type magnetic iron core of the LLC resonant converter of the near-frequency operation;

6-4 is a fourth embodiment of the EI type magnetic iron core of the LLC converter of the near-frequency operation;

6-5 is a fifth embodiment of the EI type magnetic iron core of the LLC converter of the near-frequency operation;

6-6 is a sixth embodiment of the EI type magnetic iron core of the LLC converter of the near-frequency operation;

6-7 is a seventh embodiment of the EI-type magnetic iron core of the LLC resonant converter of the near-frequency operation;

6-8 is a view showing an eighth embodiment of the EI type magnetic iron core of the LLC converter of the near-frequency operation;

6-9 is another embodiment of the CC type magnetic core of the LLC resonant converter of the near-frequency operation;

6-10 are views showing another embodiment of the EE type magnetic iron core of the LLC converter of the near-frequency operation;

7 is a power switch voltage and current waveform when the LLC converter of the near-frequency operation is fully loaded;

8 is a diagram showing a zero-voltage switching of a power switch when the LLC resonant converter of the near-frequency operation is fully loaded;

9 is a voltage and current waveform of a variable resonant inductor current, a resonant capacitor voltage, and secondary diodes D ₁ and D ₂ when the LLC resonant converter of the near-frequency operation is fully loaded;

10 is a waveform of V _GS2 , i _Lr , V _{cr ,} and f _s when the output power of the LLC resonant converter of the near-frequency operation is 240 W and 216 W;

11 is a waveform of V _GS2 , i _Lr , V _{cr ,} and f _s when the output power of the LLC resonant converter of the near-frequency operation is 192 W and 168 W;

12 is a waveform of V _GS2 , i _Lr , V _{cr ,} and f _s when the output power of the LLC resonant converter of the near-frequency operation is 144 W and 120 W;

FIG. 13 is a waveform of V _GS2 , i _Lr , V _{cr ,} and f _s when the output power of the LLC resonant converter of the near-frequency operation is 96 W and 72 W;

14 is a waveform of the output power of the near-frequency-operated LLC resonant converter of 48 W, 24 W, V _GS2 , i _Lr , V _{cr ,} and f _s ;

Figure 15 is a measurement data table of the LLC resonant converter of the near-frequency operation;

Figure 16 is a comparison diagram of the efficiency of the near-frequency operated LLC resonant converter and the conventional LLC resonant converter;

FIG. 17 is a comparison diagram of switching frequencies of the LLC resonant converter of the near-frequency operation and the conventional LLC resonant converter.

1. . . Switch circuit

Q ₁ , Q ₂ . . . Power switch

V _in . . . Input voltage

I _in . . . Input Current

2. . . Resonant circuit

L _r . . . Variable resonant inductor

C _r . . . Resonant capacitor

L _m . . . Primary side magnetizing inductance

3. . . transformer

31. . . Magnetic core

32. . . Specific face

θ. . . Air gap angle

4. . . Rectifier circuit

5. . . Control chip

D ₁ , D ₂ . . . Secondary side diode

C _o . . . Output capacitor

R _L . . . load

Claims (4)

A near-frequency-operated LLC resonant converter comprising: a switching circuit having a power supply coupled to a plurality of power switches for controlling an input voltage and an input current of the power supply; a control chip having a plurality of Control pins, wherein two control pins are used to control the opening or closing of the power switch; a resonant circuit is composed of a variable resonant inductor connected in series with a resonant capacitor and a primary side electromagnetic inductor, and the resonant circuit is connected To a switching circuit; a transformer consisting of a wire frame and a magnetic core of at least two or more pieces, characterized in that the magnetic core end can be cast to form a specific surface, and when the two magnetic cores are connected, the magnetic iron An air gap is generated between the cores, and the magnetic core is partially saturated by the small area of the air gap. When the maximum saturation region is reached, the variable resonant inductor value is a minimum value, thereby changing the variable resonant inductance value. And the transformer is connected to the resonant circuit to receive an output of the resonant circuit; a rectifier circuit having a secondary side diode connected to the transformer, And to receive the rectified output voltage and output current of the transformer, which is connected to an output line, and a capacitive load. The LLC resonant converter of the near-frequency operation as described in claim 1 , wherein the specific surface can be connected to a slope from a point to a point. The near-frequency-operated LLC resonant converter of claim 1 , wherein the specific face can be a geometric plane. The LLC resonant converter of the near-frequency operation as described in claim 1 , wherein the magnetic core can be an EE core, an EI core, an RM core, an E core, or a PQ. Type iron core, EC type iron core, ETD type iron core or other shape of iron core.