KR101528550B1 - 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, and more particularly, to a single stage PFC flyback converter and a single stage PFC flyback converter for LED lighting using LC resonance filters at the output stage to reduce ripple.
An input power supply (100) for outputting an input AC power as a full wave rectified waveform voltage; A transformer magnetization inductor unit 200 receiving the output of the input power unit and generating a current in the magnetization inductance in response to a drive signal of the switch unit; A flyback transformer 300 for transferring the induced current to an output terminal; A switch unit 400 for turning on the switch at a moment when the switch is turned on for a predetermined time and then turned off so that the secondary current of the flyback transformer becomes zero; An output diode having a first end connected to one end of a second winding of the flyback transformer in a reverse direction; a film capacitor connected between one end of the second coil of the output diode and the flyback transformer; and a LC resonant filter, And an output unit 500 connected to the other end of the first stage and the film capacitor to reduce the ripple occurring on the output side.

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 that uses a LC resonance filter at the output stage of a single stage PFC flyback converter to reduce ripple.

Fluorescent lamps have replaced existing incandescent lamps and HID (High Intensity Discharge) lamps with the increasing use of electric lighting technology. However, recently, LED devices have been developed, and as their performance is getting better, new light is coming out. LED lighting is known as eco-friendly lighting because it consumes less power than conventional lighting, has a long life, and is efficient.

Since LED devices are generally driven by direct current, unlike conventional lighting, converters that convert AC to DC are needed. Flyback converters have a smaller number of devices than other converters, it is easy to change the output voltage by changing the winding ratio of the transformer, and since the transformer is electrically insulated from the power source and the load, It is widely used for lighting. A converter of the same type as a flyback converter is commonly referred to as a switching-mode power supply (SMPS).

In general, LED lights are connected to a commercial power source and SMPS is used to convert AC to DC. Power factor is very important for SMPS used in AC. For general-purpose lighting, the power factor must be at least 0.9. Therefore, a power factor correction (PFC) circuit should be included in the SMPS for LEDs. The power factor correction consists of a 2-stage PFC method using a 2-stage converter and a 1-stage PFC method with PFC and constant voltage output characteristics. Generally, 1-stage PFC method is widely used because the power is relatively low in LED lighting. Compared with the 2-stage PFC method, the 1-stage PFC method is easy to implement, simple in control, and has a relatively low cost to implement.

Various capacitors are used in the SMPS. Ceramic capacitors, film capacitors, and electrolytic capacitors are commonly used as the commonly used capacitors. Because of their different characteristics and capacities, the range of application is different. Ceramic capacitors are used for high frequency filters because of their high frequency characteristics. For film capacitors, they are often used for filters at the input stage. Electrolytic capacitors are often used for energy storage because they are cheap, small in size and easy to make large capacity. In LED lighting, they are often used in large capacity in output stage because they use DC output. However, electrolytic capacitors have a very short lifetime compared to LED devices, and they are a fatal factor that hinders long life, which is a big advantage of LED lighting.

According to the prior art, a number of applications have been filed in addition to Korean Patent Laid-Open Publication No. 2010-0133790, a one-stage completed fly-back converter. In the conventional single-stage flyback converter, when the output load is small, the voltage applied to both ends of the DC capacitor becomes large, which causes a high voltage stress of the switching element.

In the single-stage flyback converter in which the input circuit and the output network are electrically insulated from each other at the center of the tap transformer T, the single-stage flyback converter has a single stage structure in which the power factor improving unit and the output voltage control unit are integrated The input network includes an input filtering capacitor Ci and rectifier diodes Dfr1, Dfr2, Dfr3, and Dfr4 for converting the AC power Vi into a DC in sequence, and the rectifier diode Dfr1, Dfr2, Dfr3 and Dfr4 are connected to the primary winding of the transformer through a boost inductor Lb, the positive pole of the DC capacitor Cd is connected to the neutral point of the primary winding of the transformer, One end of a switch capable of on / off switching is connected to the opposite side of the neutral point of the DC capacitor Cd, and the other end of the switch is connected to the negative electrode of the DC capacitor Cd to change the voltage across the DC capacitor Cd Wherein the output circuit is connected to the neutral point of the secondary winding of the transformer corresponding to the primary winding of the transformer and the cathode of the output capacitor Co is connected to the neutral point of the secondary winding of the transformer, And the output terminal of the output diode Do is connected to the anode of the output capacitor Co.

This single-stage flyback converter is characterized in that the LED driver circuit operated at a high temperature has a problem that the life of the electrolytic capacitor is relatively short compared to the lifetime of the LED device. It is also necessary to study the driving circuit which prolongs the lifetime of the LED lighting and has the same lifetime as the lifetime of the LED device by eliminating the electrolytic capacitor that hinders the great advantage of the long life LED lighting.

It is an object of the present invention to provide a single stage PFC flyback converter that reduces the output ripple current by using an LC resonance filter at the output stage of the single stage PFC flyback converter.

An input power supply (100) for outputting an input AC power as a full wave rectified waveform voltage; A transformer magnetization inductor unit 200 receiving the output of the input power unit and generating a current in the magnetization inductance in response to a drive signal of the switch unit; A flyback transformer 300 for transferring the induced current to an output terminal; A switch unit 400 for turning on the switch at a moment when the switch is turned on for a predetermined time and then turned off so that the secondary current of the flyback transformer becomes zero; An output diode connected to one end of the second winding of the flyback transformer; a polyester film capacitor connected to the other end of the first end of the output diode and connected in parallel to the second winding of the flyback transformer; And an output unit 500 connected to the other end of the first stage of the output diode and the film capacitor to reduce a ripple generated on the output side.

Preferably, the LC resonance filter is an LC parallel resonance filter.

Preferably, the LC resonance filter is an LC series resonance filter.

Preferably, the film capacitor is a polyester film capacitor.

According to the present invention, by using a LC resonant filter at a single stage PFC flyback converter and an output stage, replacing an electrolytic capacitor with a film capacitor to meet the long life of the LED illumination and reducing the output current ripple, LED lighting can be realized.

=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 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 in which PFC is performed by operating in a boundary conduction mode with a flyback converter.
7 is a graph showing the ripple characteristic while changing the capacitance of the output capacitor in a steady state.
8 is an equivalent circuit diagram of an actual circuit in consideration of an ideal case and an parasitic resistance component of an LC parallel resonance filter.
Fig. 9 is a graph of a simulation result when an ideal case and a parasitic component are included.
10 is a graph showing an output characteristic comparison when the LC parallel resonance filter is considered in an ideal case and a parasitic component is taken into consideration.
11 is a graph showing an output current waveform when there is no LC parallel resonance filter.
12 is a graph showing an output current waveform when an LC parallel resonance filter is applied.
13 is a graph showing the output current waveform (200 mA / div) when a filter is present.
14 is a graph showing the output current waveform (200 mA / div) when there is no filter.
Figure 15 shows the 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 graph of harmonic analysis of the input current

= 110 [Vrms]).
FIG. 17 shows the 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 graph of harmonic analysis of input current

= 220 [Vrms])
19 is a graph of a result of an LC series resonance analysis simulation according to the second 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 with reference to the accompanying drawings.

1, a single stage PFC flyback converter for LED lighting according to the present invention includes an input power source 100, a transformer magnetization inductor unit 200, a flyback transformer 300, a switch unit 400, (500).

First, the input power source unit 100 is configured to output the input alternating-current power as the full-wave rectified waveform voltage.

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 functions to transfer the current induced in the magnetizing inductance to the output terminal in the transformer magnetization inductor unit.

In addition, the switch unit 400 has a function of conducting the switch for a certain period of time, then turning the switch off, and then conducting the switch again when the secondary current of the flyback transformer unit becomes zero.

Further, the output unit 500 receives the current from the secondary winding of the flyback transformer and outputs it as a constant voltage. At this time, a large-capacity capacitor is required to prevent the output voltage from fluctuating. If the capacity is insufficient, a ripple corresponding to twice the frequency of the input voltage is generated at the output terminal of the output section.

The output unit includes an output diode having a first end connected to one end of the second winding of the flyback transformer, a polyester film capacitor connected to the other end of the first end of the output diode and connected in parallel with the second winding of the flyback transformer, And an LC parallel resonance filter connected to the output diode and the second end of the capacitor is connected.

Here, the capacitor applies a film (polyester) capacitor having a longer lifetime than the electrolytic capacitor. In this case, ripple is generated at the output stage due to a film capacitor having a capacitance smaller than that of the electrolytic capacitor. The LC parallel resonant filter reduces the low frequency ripple generated at the output side.

For reference, a long life film capacitor is used instead of an electrolytic capacitor to solve the lifetime problem of the electrolytic capacitor having a life shorter than the LED. However, when the film capacitor is used, since the capacitance is smaller than that of the electrolytic capacitor, The ripple component of the liquid is generated. It is desirable to minimize the drive or ripple by constant current because it can affect the human optic nerve and cause fatigue when large ripple occurs in LED illumination. A film capacitor is applied instead of an electrolytic capacitor, and a low-frequency ripple generated on the output side is reduced by using an LC resonance filter.

As shown in Fig. 2, according to another embodiment of the present invention, an LC resonance filter is applied as an LC series resonance filter. If we look at the principle of ripple reduction, defining the input voltage vs. resonant current as a transfer function is an admittance to the resonant circuit. At the LC resonant frequency, the gain of the transfer function is theoretically positive infinity. Since the impedance of the resonance frequency component on the resonance circuit side is theoretically negative infinity, the current of the resonance frequency component flows to the LC-resonance circuit, and a current with reduced ripple flows on the output side.

The present invention has the effect of solving the lifetime problem due to the electrolytic capacitor and realizing the long life of the LED illumination.

Hereinafter, the present invention will be described in detail.

In the present invention, a 1-stage PFC flyback converter and an LC parallel resonance filter at the output stage reduce the ripple. By eliminating electrolytic capacitors, the lifetime of the LED lighting driver circuit was extended, and its performance and characteristics were verified through experiments.

First, Table 1 shows the physical characteristics comparison for three kinds of capacitors.

Kinds Life [hours] (Calculated at 85 ℃) Capacitor Capacity Range Electrolytic capacitor <18,000 1uF to 15mF Polyester Film Capacitors > 100,000 10pF to 400uF Ceramic capacitor > 500,000 1pF to 10uF

Among the above three capacitors, electrolytic capacitors are widely used for voltage stabilization and direct current output in LED lighting because they can have larger capacitance at the same size as other capacitors. In addition, the cost per capacitance is the lowest, so it is widely used in industry. However, despite the advantages of electrolytic capacitors, electrolytic capacitors are a major disadvantage in terms of lifetime.

The following equations (1), (2) and (3) represent the expected lifetime formula of electrolytic capacitors, film capacitors, and ceramic capacitors, 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 expected life at the maximum temperature of the rated voltage and the 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 during use.

Equations (1) and (2) represent the lifetime of the electrolytic capacitor and the film capacitor, respectively. When the ambient temperature is lowered by 10 ° C, the lifetime is doubled.

However, in the case of a film capacitor, the longer the voltage is, the longer the voltage applied to the rated voltage is. In selecting a capacitor, a capacitor having a breakdown voltage of about 1.5 times as much as a voltage actually applied is selected and used. Therefore, a film capacitor has a great advantage in life time.

는 3000시간,

는 1.4,

은 105[℃]를 적용하였다.A graph of the temperature-life expectancy of three capacitors through equations (1) through (3) is shown in FIG. here

3000 hours,

1.4,

105 [deg.] C was applied.

As shown in FIG. 3, it can be seen that the film capacitor is the most potent capacitor to replace the electrolytic capacitor. However, since the capacitance is lower than that of the electrolytic capacitor, there is a disadvantage that the output characteristic may be changed.

In the case of a single-stage PFC flyback converter (single-stage AC-DC converter), even though there is a large ripple component at the output, it can be a better solution than the 2-stage in terms of cost and energy density .

A single-stage AC-DC converter refers to a converter that directly converts an alternating current into a direct current, and 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 in the inductor.

In the case of a flyback converter, the inductor is divided by the magnetizing current, that is, the magnetic flux, because it has two windings or multiple windings and the winding ratio is different, and is divided into continuous conduction mode (CCM), discontinuous conduction mode (DCM), and boundary conduction mode . Boundary conduction mode is a way to turn the switch back on after the switch is turned off for a period of time and then the secondary current is zero.

As a result, there is no need to sense input current and input voltage, simplifying the circuit and eliminating the need for a complicated controller. 5 schematically shows a single-stage PFC flyback converter.

6 shows waveforms in which PFC is performed by operating in a boundary conduction mode with a flyback converter. The input voltage of the flyback converter is 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. 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 obtained by connecting the peak value of the switch current,

Is the instantaneous value of the diode current,

Is a value obtained by connecting the peak value of the diode current,

Represents the average value of the input current (equal to 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.To design the converter, the magnetizing inductance of the flyback transformer must be obtained. To obtain the magnetizing inductance, the time at which the switch conducts when the converter operates

The longest of

. Table 2 summarizes the parameters required to derive the formula.

On the other hand, the magnetization inductance can be obtained by the following equation (4).

The magnetization inductance value obtained from Equation (4) is the boundary value between the continuous conduction mode and the discontinuous conduction mode. In practice, since the power is supplied to the peripheral circuit using the loss and the auxiliary winding, the value is larger than the calculated value.

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

An LC parallel resonance circuit for reducing the output ripple current is as follows.

In a single-stage PFC flyback converter, the smaller the output-side capacitance of the capacitor, the ripple component will be 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 greater the ripple component. This is because the input voltage of the flyback converter is not a DC voltage but a voltage of 60 [Hz] is applied by full-wave rectification and the input voltage is lower than the output voltage. In particular, when the input voltage drops to zero, the energy that flows from the input side during this period is small, and as the capacitance of the output side capacitor becomes small, the ripple component becomes large.

In a single-stage PFC flyback converter, replacing electrolytic capacitors with film capacitors will benefit life, but the 120-Hz ripple component on the output side can not be avoided due to the relatively low capacitance of the capacitor.

The LC parallel resonant filter 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.Fig. 8 shows an ideal case (a) of an LC parallel resonance filter and an equivalent circuit (b) of an actual circuit considering a parasitic resistance component. In general, passive components such as resistors, inductors, and capacitors have parasitic components. In particular, the equivalent series resistance of capacitors (Equivalent Series Resistor,

), The resistance component of the inductor (

) Has the greatest effect on this circuit. This parasitic resistance component changes the characteristics of the filter.

Equation (6) represents an ideal transfer function, and Equation (7) represents a transfer function including a parasitic component. And Equation (8) represents the resonance frequency of the LC parallel resonance circuit.

,

를 나타낸다.here,

,

.

Fig. 9 shows the ideal case and the bode plot when the parasitic component is included.

The LC parallel resonance filter is also referred to as a bandstop filter since the resonance frequency does not appear on the output side. In an ideal case, the gain of the LC parallel resonant filter at the resonant frequency has a negative infinity. However, considering the resistance component of the inductor and the equivalent series resistance component of the capacitor, since the gain has a finite value, the response speed of the filter is slowed down, performance is degraded, and additional power loss occurs.

Fig. 10 shows the comparison of the output characteristics when the ideal case of the LC parallel resonance filter and the parasitic component are taken into consideration. In both cases, the average current value is almost the same, but the ripple is larger when considering the parasitic component than in the ideal case, and the distortion is generated at the first part of the 120 [Hz] cycle. In the case of a film capacitor, the resistance component of the inductor has a greater influence on the performance of the LC parallel resonant filter because the equivalent series resistance is significantly lower than other capacitors and the resistance of the inductor is generally larger than the equivalent series resistance of the capacitor.

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 at the output stage is replaced with a small capacity polyester film capacitor and an LC parallel resonance filter is applied to a conventional converter.

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

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

11 is a waveform when only a small-capacity film capacitor (78 [uF]) is applied without an LC parallel resonance filter at the output end. A large current ripple occurred due to the small capacity of the capacitor. The average current is 1.2 [A] and the peak-to-peak current is 732 [mA].

12 is a waveform when an LC parallel resonance filter in which a parasitic resistance component is considered at the output stage is applied. The average current is 1.18 [A] and the peak-to-peak current is 181 [mA].

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

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

Applying an LC parallel resonant filter reduces the peak-to-peak ripple current from 790 [mA] to 205 [mA]. As the ripple component decreases, the LED device can operate at a higher average current, so that the LED device can be used efficiently.

)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 is a graph showing the relationship between the input voltage

) Is the input voltage, input current, and output current at 110 [Vrms], and Figure 16 is a graph comparing the input current with Class C of IEC61000-3-2. The power factor was measured as 0.982, and the harmonic components satisfied 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 is a graph showing the relationship between the input voltage

) Is 220 [Vrms], and FIG. 18 is a graph comparing input current with Class C of IEC61000-3-2. The power factor was measured as 0.986, and the harmonic components satisfied all IEC standards. Both cases satisfied the Class C criteria of IEC61000-3-2.

The present invention proposes a single-stage PFC flyback converter for LED lighting without electrolytic capacitors and verifies its validity through simulation and experiments. Flyback converter operated in boundary conduction mode for PFC, power factor is over 0.95, and harmonics meets all of Class C criteria of IEC61000-3-2. Using the LC parallel resonant filter, the current ripple of 120 [Hz] component, which is caused by changing the capacity of a large capacity electrolytic capacitor by a small amount of film capacitor, was reduced by about 74% from 790 [mA] to 205 [mA].

The proposed converter does not include an electrolytic capacitor, which has the advantage of meeting the long life of LED lighting. It is also possible to implement high quality LED lighting by greatly reducing output side current ripple.

19, the gain of the transfer function at the LC resonance frequency is theoretically positive infinity, and the current of the resonance frequency component is expressed by the following equation Since the impedance of the resonance circuit is theoretically negative infinity, it has a characteristic that it flows all the way to the LC resonance circuit. A current with reduced ripple flows on the output side.

를 나타낸다.here,

.

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

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

Claims (4)

An input power unit for outputting an input alternating-current power as a full-wave rectified waveform voltage;
A transformer magnetization inductor unit receiving the output of the input power unit and generating a current in the magnetizing inductance in response to a drive signal of the switch unit;
A flyback transformer for transmitting the induced current to an output terminal;
A switch unit for turning on a switch at a moment when the second winding current of the flyback transformer is zero after turning on the switch for a predetermined time and then turning off the switch; And
An output diode connected to the other end of the first stage of the output diode and receiving a current from the second winding of the flyback transformer and outputting a constant voltage, the flyback transformer being connected to one end of a second winding of the flyback transformer; And an LC resonance filter connected to the other end of the first stage of the output diode and the polyester film capacitor to reduce low frequency ripple generated on the output side of the output diode, &Lt; / RTI &gt;
Wherein the LC resonance filter is an LC parallel resonance filter. delete The method according to claim 1,
Wherein the LC resonance filter is an LC series resonance filter. delete

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