KR20140028903A - Single-stage power factor correction flyback converter for led lighting - Google Patents

Abstract

The present invention relates to a single-stage PFC flyback converter for LED lighting, in particular, to a single-stage PFC flyback converter for LED lighting capable of reducing a ripple in a single-stage PFC flyback converter and an output stage using an LC resonance filter. The single-stage PFC flyback converter for LED lighting comprises an input power unit (100) for outputting an input alternating current power to a voltage of a full-wave rectified waveform; a transformer magnetization inductor unit (200) for receiving the output of the input power unit, responding to a driving signal of a switch unit and inducing a current to magnetization inductance; a flyback transformer unit (300) for transmitting the induced current to an output stage; the switch unit (400) for turning a switch on during a certain time and then turning the switch off to turn the switch on when a secondary current of the flyback transformer unit becomes 0; and an output unit (500) which is connected to an output diode having a first end reversely connected to one end of a second winding of the flyback transformer unit, to a film capacitor connected between the output diode and one end of the second winding of the flyback transformer unit, and to an LC resonance filter connected to the other end of the first end of the output diode and the film capacitor so that a ripple generated in an output side can be reduced.

Description

Single-Stage Power Factor Correction Flyback Converter for LED Lighting

The present invention relates to a single stage PFC flyback converter for LED lighting, and more particularly, to a single stage PFC flyback converter for LED lighting to reduce ripple by using an LC resonant filter at the output stage of the single stage PFC flyback converter.

As electric lighting technology increases, fluorescent lamps have replaced conventional incandescent lamps and high intensity discharge (HID) lamps. Recently, however, as LED devices have been developed and their performances have improved, new lighting has emerged. LED lighting is known as environmentally friendly lighting because it consumes less power, has a longer life, and has higher efficiency than conventional lighting.

Since LED devices are generally driven by direct current, there is a need for a converter that converts alternating current into direct current, unlike conventional lighting. Flyback converter has fewer elements than other converters, it is easy to change the output voltage by changing the winding ratio of transformer, and the LED is less than 100 [W] because the power and load are electrically isolated by the transformer. It is used a lot in lighting. Converters such as flyback converters are commonly referred to as Switching-Mode Power Supply (SMPS).

Typically, LED lighting is connected to a commercial power source, and SMPS is used to convert alternating current into direct current. Power factor is very important for SMPS used in AC. In general lighting the power factor must be at least 0.9. Therefore, SMPS for LEDs must include a power factor correction (PFC) circuit. Power factor correction includes two stage PFC method using two stage converter and one stage PFC method with its own PFC and constant voltage output. In general, 1-stage PFC method is widely used because of the relatively low power in LED lighting. Compared to the 2-stage PFC method, the 1-stage PFC method is easy to implement a circuit, is simple to control, and has a relatively low cost to implement.

Various capacitors are used in SMPS, and ceramic capacitors, film capacitors, and electrolytic capacitors are commonly used. Because the characteristics and capacities are different, the range of application is different. Ceramic capacitors are often used for high frequency filters because of their high frequency characteristics, and film capacitors are often used for input filters. In the case of electrolytic capacitors, the price is low, it is small and easy to make a large capacity, and is used for energy storage.In the case of LED lighting, since it uses DC output, it is often used in large capacity at the output stage. However, because electrolytic capacitors have a much smaller lifespan than LED devices, they are critical to counteract the long lifespan of LED lighting.

According to the prior art, a number of applications have been filed in addition to Korean Patent Publication No. 2010-0133790, "Single-semi quasi-resonant flyback converter." In the conventional single-stage flyback converter, when the output load is small, the voltage applied to both ends of the DC capacitor increases, so that the voltage stress of the switching element is high.

Single-stage quasi-resonant flyback converter technology has a single-stage structure integrating the power factor improving unit and the output voltage control unit. In the input network, rectifier diodes Dfr1, Dfr2, Dfr3, and Dfr4, which convert an input filtering capacitor Ci and the AC power source Vi into DC, are sequentially connected to the AC power source Vi. The output side of Dfr1, Dfr2, Dfr3, Dfr4) is connected to the transformer primary winding through a boost inductor Lb, the anode of the DC capacitor Cd is connected to the neutral point of the transformer primary winding, and the transformer primary winding One end of the switch capable of on / off switching is connected to the opposite side of the neutral point, and the other end of the switch is connected to the cathode of the DC capacitor Cd to change the voltage at both ends applied to the DC capacitor Cd. The output network has a structure for feeding back to the primary winding of the transformer, and the output network has an output diode (Do) at the neutral point of the transformer secondary winding corresponding to the transformer primary winding and the cathode of the output capacitor (Co) at the neutral point of the transformer secondary winding. Is connected, the output terminal of the output diode (Do) is characterized in that configured to be connected to the anode of the output capacitor (Co).

The single stage flyback converter has a problem in that the life of the electrolytic capacitor is relatively smaller than that of the LED device due to the characteristics of the LED driving circuit operating at a high temperature. And by eliminating the electrolytic capacitor that interferes with the big advantage of the LED light of long life, it is necessary to study the driving circuit having the same life as the life of the LED device to extend the life of the LED lighting.

An object of the present invention is to provide a single stage PFC flyback converter for reducing output ripple current by using an LC resonant filter at an output stage of a single stage PFC flyback converter.

The present invention provides an input power supply unit 100 for outputting an input AC power as a voltage of a full wave rectified waveform; A transformer magnetizing inductor unit 200 receiving the output of the input power supply unit and inducing a current to the magnetizing inductance in response to a driving signal of the switch unit; A flyback transformer 300 for transferring the induced current to an output terminal; A switch unit 400 which turns the switch on after the switch is turned on for a predetermined time and turns off the moment when the secondary current of the flyback transformer becomes 0; And an output diode having a first end connected to an end of the second winding of the flyback transformer in a reverse direction, a film capacitor connected between the output diode and the second winding of the flyback transformer, and an LC resonance filter. And an output unit 500 connected to the other end of the first stage and the film capacitor to reduce ripple generated on the output side.

Preferably, the LC resonant filter is characterized in that the LC parallel resonant filter.

Also preferably, the LC resonant filter is an LC series resonant filter.

And preferably the film capacitor is characterized in that the polyester film capacitor.

According to the present invention as described above, by using an LC resonant filter for the single stage PFC flyback converter and the output stage, replacing the electrolytic capacitor with a film capacitor to meet the long life of the LED lighting, and to reduce the output side current ripple, LED lighting can be implemented.

=110[Vrms], CH 1 : 입력 전압

(100V/div), CH3 : 입력 전류

(500mA/div), CH4 : 출력 전류

(500mA/div) )을 나타낸 그래프.
도 16은 입력 전류의 고조파 분석 그래프(

=110[Vrms]).
도 17은 제안한 회로의 실험 파형(

=220[Vrms], CH 1 : 입력 전압

(100V/div), CH3 : 입력 전류

(500mA/div), CH4 : 출력 전류

(500mA/div) )을 나타낸 그래프.
도 18은 입력 전류의 고조파 분석 그래프(

=220[Vrms])
도 19는 본 발명의 제2 실시예에 따른 LC 직렬 공진분석 시뮬레이션 결과 그래프.1 is a circuit diagram of a single stage PFC flyback converter for LED lighting according to a first embodiment of the present invention.
2 is a circuit diagram of a single stage PFC flyback converter for LED lighting according to a second embodiment of the present invention.
3 is a graph showing temperature-life expectancy characteristics of three types of capacitors.
4 is a schematic circuit diagram of a single-stage AC-DC converter.
5 is a schematic circuit diagram of a single stage PFC flyback converter.
6 is a graph showing a waveform for performing PFC by operating in a boundary conduction mode with a flyback converter.
7 is a graph showing the ripple characteristics while changing the capacity of the output capacitor in a steady state.
8 is an equivalent circuit diagram of an actual circuit considering an ideal case of an LC parallel resonance filter and a parasitic resistance component.
9 is a graph of simulation results in the ideal case and in the case of including parasitic components.
10 is a graph illustrating output characteristics when considering an ideal case of an LC parallel resonance filter and a parasitic component.
11 is a graph showing the output current waveform when there is no LC parallel resonant filter.
12 is a graph showing an output current waveform when an LC parallel resonance filter is applied.
Fig. 13 is a graph showing an output current waveform (200 mA / div) with a filter.
Fig. 14 is a graph showing an output current waveform (200 mA / div) when there is no filter.
15 is an experimental waveform of the proposed circuit (

= 110 [Vrms], CH 1: input voltage

(100V / div), CH3: Input Current

(500mA / div), CH4: Output Current

(500 mA / div)).
16 is a harmonic analysis graph of input current (

= 110 [Vrms]).
17 shows an experimental waveform of the proposed circuit (

= 220 [Vrms], CH 1: input voltage

(100V / div), CH3: Input Current

(500mA / div), CH4: Output Current

(500 mA / div)).
18 is a harmonic analysis graph of input current (

= 220 [Vrms])
19 is a graph showing the results of an LC series resonance analysis simulation according to a second exemplary embodiment of the present invention.

Hereinafter, a single stage PFC flyback converter for LED lighting according to the present invention will be described in detail based on the accompanying drawings.

As shown in FIG. 1, the single stage PFC flyback converter for LED lighting according to the present invention includes an input power supply unit 100, a transformer magnetization inductor unit 200, a flyback transformer unit 300, a switch unit 400, and an output unit. It is configured to include a portion 500.

First, the input power supply unit 100 is configured to output the input AC power as the voltage of the wave rectified.

In addition, the transformer magnetization inductor unit 200 functions to induce a current in the magnetization inductance in response to the drive signal of the switch unit.

In addition, the flyback transformer 300 serves to transfer the current induced in the magnetization inductance in the transformer magnetization inductor to the output terminal.

In addition, the switch unit 400 conducts the switch for a predetermined time, and then turns off the switch and then conducts the switch again as soon as the secondary current of the flyback transformer becomes zero.

In addition, the output unit 500 receives a current from the secondary winding of the flyback transformer unit and outputs a constant voltage. In order to keep the output voltage from shaking, a large capacitor is needed. If the capacity is insufficient, a ripple corresponding to twice the frequency of the input voltage occurs at the output of the output.

The output unit includes an output diode having a first end connected in a reverse direction to one end of a second winding of the flyback transformer, a capacitor connected between the output diode and one end of the second winding of the flyback transformer, and a first portion of the output diode and the capacitor. It is characterized in that the LC parallel resonant filter connected to the second stage.

Here, the capacitor applies a film (polyester) capacitor, which has a longer life than the electrolytic capacitor. In this case, a film capacitor having a smaller capacity than that of an electrolytic capacitor causes ripple at the output stage. An LC parallel resonance filter is used to reduce low frequency ripple generated at the output side.

For reference, using a long-life film capacitor instead of an electrolytic capacitor solves the lifetime problem for electrolytic capacitors that have a shorter lifespan than LEDs, but using film capacitors has 120 [Hz] Ripple component of occurs. When a large ripple occurs in the LED light, it is desirable to minimize the ripple or drive with a constant current because it can affect the optic nerve of the person to feel fatigue. The film capacitor is applied instead of the electrolytic capacitor, and the low frequency ripple generated on the output side is reduced by using the LC resonance filter.

As shown in FIG. 2, according to another embodiment of the present invention, an LC resonant filter is applied as an LC series resonant filter. The principle of ripple reduction is to look at the input voltage versus resonant current as a transfer function, which is an admittance to the resonant circuit. The gain of the transfer function at the LC resonant frequency is theoretically positive infinity. Since the impedance of the resonant circuit component is theoretically negative infinity, the current of the resonant frequency component flows to the LC-resonant circuit, and the current of which the ripple is reduced flows to the output side.

The present invention has the effect of solving the life problem due to the electrolytic capacitor, and to implement a long life of the LED lighting.

Hereinafter, a detailed description of the present invention.

In the present invention, a circuit having a ripple reduction using a 1-stage PFC flyback converter and an LC parallel resonant filter at the output stage is proposed. The elimination of electrolytic capacitors prolonged the life of the LED lighting driving circuit and proved its performance and characteristics through experiments.

First, Table 1 shows physical property comparisons for three types of capacitors.

Kinds Lifetime [hours] (calculated at 85 ℃) Capacitor Capacity Range Electrolytic capacitor <18,000 1 uF to 15 mF Polyester film capacitors > 100,000 10 pF to 400 uF Ceramic capacitor > 500,000 1 pF to 10 uF

Of the above three capacitors, electrolytic capacitors are widely used for voltage stabilization and direct current output in LED lighting because they have a large capacitance at the same size as other capacitors. In addition, the price per capacitance is the least used in the industry. However, electrolytic capacitors, despite their many advantages, are a major drawback in LED lighting in terms of lifetime.

Equations 1, 2, and 3 represent the life expectancy of the electrolytic capacitor, the film capacitor, and the ceramic capacitor, respectively.

는 정격 전압과 허용 온도의 최대온도에서의 기대수명이고,

는 커패시터의 정격전압/실제 커패시터에 인가된 전압이며,

는 허용 온도의 최대 온도이고,

는 사용시 주변 온도를 나타낸다.here,

Is the life expectancy at the maximum temperature of rated voltage and allowable temperature,

Is the rated voltage of the capacitor / voltage applied to the actual capacitor,

Is the maximum temperature of the allowable temperature,

Indicates the ambient temperature in use.

Equations 1 and 2 represent the lifespan of the electrolytic capacitor and the film capacitor, respectively, and have a characteristic that the life is doubled when the ambient temperature drops to 10 ° C.

However, in the case of a film capacitor, the greater the voltage applied to the rated voltage, the longer the life span. When selecting a capacitor, a capacitor having a voltage withstand voltage of about 1.5 times of the actual applied voltage is selected and used. Thus, a film capacitor has a great advantage in life.

는 3000시간,

는 1.4,

은 105[℃]를 적용하였다.Through Equations 1 to 3, a graph of temperature-expected life of three capacitors is shown in FIG. 3. here

Is 3000 hours,

Is 1.4,

105 [° C.] was applied.

As shown in Figure 3, it can be seen that the film capacitor is the most potent capacitor that can replace the electrolytic capacitor. However, there is a disadvantage that the output characteristics can be changed because of the lower capacitance than the electrolytic capacitor.

Single-stage PFC flyback converters are a better solution than 2-stage in terms of cost and energy density, despite the presence of large ripples in the output. .

Single-stage AC-DC converter means a converter that directly converts AC into direct current, a schematic diagram is shown in FIG.

When correcting the power factor, it is classified into three methods based on the continuous-discontinuity of the current flowing through the inductor.

In the case of a flyback converter, since the inductor is two windings or multiple windings and the turns ratio is different, it is divided by magnetization current, that is, magnetic flux, and divided into continuous conduction mode (CCM), discontinuous conduction mode (DCM), and boundary conduction mode (BCM). Can be. Boundary conduction mode is a method of conducting a switch for a certain period of time and then turning the switch back on as soon as the secondary current becomes zero.

As a result, there is no need to sense input current and input voltage, which simplifies the circuit and eliminates the need for complicated controllers. 5 shows a simplified illustration of a single-stage PFC flyback converter.

Figure 6 shows a waveform of performing a PFC by operating in a boundary conduction mode with a flyback converter. The input voltage of the flyback converter is applied with the voltage of the waveform where the input AC power is full-wave rectified. If the switching frequency is very fast compared to the frequency of the input voltage, the input voltage appears to be fixed in one cycle of switching, so the peak value of the current changes every switching cycle, and the switching time is constant so that the shape of the input current is determined by the applied voltage. The power factor is corrected by following the shape.

는 스위치 전류의 순시치,

는 스위치 전류의 피크치를 연결한 값,

는 다이오드 전류의 순시치,

는 다이오드 전류의 피크치를 연결한 값,

는 입력 전류의 평균값(스위치 전류의 평균값과 동일)을 나타낸다. 그리고

와

는 각각의 이른 그래프에서의 최대값을 나타낸다.6

Is the instantaneous value of the switch current,

Is the value of the peak of the switch current,

Is the instantaneous value of the diode current,

Is the peak of diode current,

Denotes the average value of the input current (same as the average value of the switch current). And

Wow

Represents the maximum value in each early graph.

중에서 가장 긴

를 정의해야한다. 이외에도 수식을 유도함에 있어 필요한 파라메터를 표 2에 정리하였다.In order to design the converter, the magnetizing inductance of the flyback transformer must be found, and to obtain the magnetizing inductance, the time the switch conducts when the converter is operating.

The longest of the

Should be defined. In addition, the necessary parameters for deriving the equations are summarized in Table 2.

On the other hand, the magnetization inductance can be obtained as shown in Equation 4 below.

The magnetization inductance value obtained in Equation 4 is the boundary between the continuous conduction mode and the discontinuous conduction mode, and a value larger than the calculated value is used because the loss and the auxiliary winding are used to supply the peripheral circuit.

The turnover ratio of a flyback transformer can be calculated as follows, considering the forward voltage drop of the diode.

The LC parallel resonant circuit to reduce the output ripple current is as follows.

In a single-stage PFC flyback converter, the output capacitor's small capacity produces a ripple component that is twice the input frequency. 7 is a graph showing the ripple characteristic while changing the capacity of the output capacitor in the steady state.

The smaller the capacitor, the larger the ripple component. This is because the input voltage of the flyback converter is applied by full-wave rectification of a voltage of 60 [Hz] instead of a DC voltage, so that a section in which the input voltage is lower than the output voltage occurs. In particular, the input voltage drops to zero. During this period, the energy from the input side is so small that the smaller the capacity of the output capacitor, the larger the ripple component.

The replacement of film capacitors without the use of electrolytic capacitors in single-stage PFC flyback converters is beneficial in terms of lifetime, but the relatively low capacitor capacity inevitably avoids 120 [Hz] ripple on the output side.

LC parallel resonant filters can be used to reduce the ripple component on the output side.

), 인덕터의 저항 성분(

)이 회로에 가장 큰 영향을 미친다. 이러한 기생 저항 성분은 필터의 특성을 변화시킨다.8 shows an ideal case (a) of an LC parallel resonance filter and an equivalent circuit (b) of an actual circuit in consideration of parasitic resistance components. In general, passive devices such as resistors, inductors, and capacitors have parasitic components. In particular, the equivalent series resistance of the capacitor (Equivalent Series Resistor,

), The resistance component of the inductor (

) Has the greatest effect on the circuit. This parasitic resistance component changes the filter's properties.

Equation 6 shows the transfer function in the ideal case, and Equation 7 shows the transfer function in the case of including the parasitic component. Equation 8 shows the resonance frequency of the LC parallel resonance circuit.

,

를 나타낸다.here,

,

Indicates.

9 shows Bodeplot in the ideal case and in the case of including parasitic components.

LC parallel resonant filters are also called bandstop filters because the resonant frequency does not appear on the output side. Ideally, the gain of the LC parallel resonant filter at resonant frequency has a negative infinity. However, considering the resistance component of the inductor and the equivalent series resistance component of the capacitor, the gain has a finite value, resulting in a slow filter response, poor performance, and additional power loss.

Fig. 10 shows a comparison of output characteristics in consideration of the ideal case of the LC parallel resonance filter and the parasitic component. In both cases, the average current is almost the same, but compared to the ideal case, the parasitic component has a larger ripple and distortion occurs at the beginning of the 120 [Hz] cycle. In the case of a film capacitor, the equivalent series resistance is significantly lower than other capacitors, and the resistance component of the inductor is generally larger than the equivalent series resistance of the capacitor, so the resistance component of the inductor has a greater influence on the performance of the LC parallel resonant filter.

The simulation results are as follows. First, in the circuit diagram of a single stage PFC flyback converter according to an embodiment of the present invention, a large capacity electrolytic capacitor of an output stage is replaced with a small capacity polyester film capacitor in an existing converter, and an LC parallel resonance filter is applied.

Table 3 shows the system parameters obtained from equations (4) and (5).

The output capacitor was selected as 78 [uF] in consideration of the physical size and price, and the inductance value of the LC parallel resonant filter was determined from Equation (8), considering that the frequency of the input voltage was 60 [Hz]. Since the capacitance varies for each frequency band, the capacitance measured from the LCR meter is used.

FIG. 11 is a waveform when only a small film capacitor 78 [uF] is applied to the output terminal without an LC parallel resonant filter. Due to the small capacity of the capacitors, large current ripples occurred. The average current is 1.2 [A] and the peak-to-peak current is 732 [mA].

12 is a waveform when an LC parallel resonant filter in which parasitic resistance components are considered in an output terminal is applied. The average current is 1.18 [A] and the peak-to-peak current is 181 [mA].

Simulation results showed that the current ripple decreased by 75 [%] from 732 [mA] to 181 [mA].

To verify the proposed circuit, we fabricated a 60 [W] single-stage PFC flyback converter and an LC parallel resonant filter. The waveforms with and without the LC parallel resonant filter are shown in FIGS. 13 and 14, respectively.

By applying an LC parallel resonant filter, the peak-to-peak ripple current was reduced from 790 [mA] to 205 [mA]. Reducing the ripple component allows the LED device to operate at higher average currents, allowing efficient use of the LED device.

)이 110[Vrms]일 때의 입력 전압, 입력 전류, 출력 전류의 실험 파형이고, 그림 16은 입력 전류를 IEC61000-3-2의 Class C와 비교한 그래프이다. 역률은 0.982로 측정되었고, 고조파 성분은 IEC 규격을 모두 만족하였다.15 shows an input voltage (

) Is the experimental waveform of input voltage, input current and output current when 110 [Vrms], and Figure 16 is a graph comparing input current with Class C of IEC61000-3-2. The power factor was measured as 0.982, and the harmonic content satisfies all IEC standards.

)이 220[Vrms]일 때의 입력 전압, 입력 전류, 출력 전류의 실험 파형이고, 도 18은 입력 전류를 IEC61000-3-2의 Class C와 비교한 그래프이다. 역률은 0.986으로 측정되었고, 고조파 성분은 IEC 규격을 모두 만족하였다. 두 경우 모두 IEC61000-3-2의 Class C 기준을 만족하였다.17 shows the input voltage (

) Is an experimental waveform of input voltage, input current, and output current when 220 [Vrms], and FIG. 18 is a graph comparing the input current with Class C of IEC61000-3-2. The power factor was measured as 0.986, and the harmonic content satisfies all IEC standards. In both cases, the Class C standard of IEC61000-3-2 was met.

The present invention proposed a single-stage PFC flyback converter for LED lighting without an electrolytic capacitor, and verified its validity through simulation and experiment. The flyback converter operated in boundary conduction mode for PFC, power factor above 0.95, and harmonics met all Class C standards of IEC61000-3-2. The LC parallel resonant filter was used to reduce the current ripple of 120 [Hz] components from 790 [mA] to 205 [mA] by about 74 [%].

The proposed converter does not include an electrolytic capacitor, which has the advantage of matching the long life of LED lighting. In addition, the output current ripple is greatly reduced, enabling high quality LED lighting.

Meanwhile, referring to the LC series resonance analysis according to another embodiment, referring to the Bodeplot of FIG. 19 using the following transfer function, the gain of the transfer function at the LC resonance frequency is theoretically positive infinity and the current of the resonance frequency component is Since the impedance on the resonant circuit is theoretically negative infinity, all of them have characteristics that flow into the LC resonant circuit. Ripple-reduced current flows on the output side.

를 나타낸다.here,

Indicates.

On the output side, the component of the resonance frequency (Equation 11) is the largest.

100: input power supply 200: transformer magnetization inductor
300: flyback transformer 400: switch unit
500: Output section

Claims (4)

An input power supply unit 100 for outputting an input AC power as a voltage of a full wave rectified waveform;
A transformer magnetizing inductor unit 200 receiving the output of the input power supply unit and inducing a current to the magnetizing inductance in response to a driving signal of the switch unit;
A flyback transformer 300 for transferring the induced current to an output terminal;
A switch unit 400 which turns the switch on after the switch is turned on for a predetermined time and turns off the moment when the secondary current of the flyback transformer becomes 0; And
An output diode having a first end connected in a reverse direction to one end of a second winding of the flyback transformer part, a film capacitor connected between the output diode and one end of the second winding of the flyback transformer part, and an LC resonant filter is provided in the first diode of the output diode; Single stage PFC flyback converter for LED lighting, comprising: an output unit (500) connected to the other end of the stage and connected to the film capacitor to reduce the ripple generated on the output side. The method of claim 1,
And said LC resonant filter is an LC parallel resonant filter. The method of claim 1,
And said LC resonant filter is an LC series resonant filter. The method of claim 1,
The film capacitor is a single stage PFC flyback converter for LED lighting, characterized in that the polyester film capacitor.

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