KR20110139553A - Power factor correction circuit for lighting and driving method thereof - Google Patents

Abstract

PURPOSE: A power factor correcting circuit for a light and a driving method thereof are provided to feed a signal back which is generated based on the amount of currents, thereby eliminating a need of a current limiting circuit for limiting the currents of an LED. CONSTITUTION: A converter converts first DC power into second DC power. A driving unit provides second DC power to a light source for a light. A control circuit corrects the power factor of the converter. A feedback signal generating unit generates a feedback signal which is provided to the control circuit. The feedback signal generating unit includes a capacitance part for providing the feedback signal. The feedback signal generating unit comprises a current-to-voltage converter and a variable capacity module(140). The capacitance of the variable capacity module is varied according to the amount of output currents of the driving unit.

Description

Power factor correction circuit and driving method for lighting {POWER FACTOR CORRECTION CIRCUIT FOR LIGHTING AND DRIVING METHOD THEREOF}

The present invention relates to a power factor correction circuit and a driving method for lighting, and more particularly, to a power factor correction circuit and a driving method for light emitting diode (LED) lighting.

High brightness LEDs or OLEDs (Organic Electroluminescence) have lower luminous efficiency than fluorescent lamps, but they can be miniaturized, thinned, and extended in life, and above all, mercury-free. As promising.

Both high-brightness LEDs and OLEDs are direct current drive devices, and are devices that emit light by flowing a direct current through these direct current drive devices. Therefore, in order to make a DC drive element emit light using household AC power, a power source for converting AC power to DC power is required. In addition, since both high-brightness LEDs or OLEDs emit light stably by passing a constant current, a circuit for limiting current is required. Moreover, unless the luminous efficiency of these DC drive elements improves dramatically, in order to use these DC drive elements as a lighting apparatus, 50-200W of electric power is needed.

On the other hand, the lighting apparatus with large electric power needs to be equipped with the power factor improvement circuit. Power factor represents the effectiveness of power transfer. In power delivery, the actual delivered power is real power. Power factor is expressed by dividing the effective power by the apparent power represented by the product of the effective values of the voltage and the current of the power. If both voltage and current are sinusoidal, the power factor depends on the phase difference between voltage and current. The smaller the phase difference, the better the power factor is. Thus, in general, power factor correction for improving power factor refers to an operation of reducing a phase difference between voltage and current of power.

The present invention provides an illumination power factor correction circuit for driving efficiently regardless of the magnitude of the LED output current and a driving method therefor.

Technical problems to be achieved in the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

In one aspect of the invention, a converter for converting the first DC power source to the second DC power source; A driving unit providing the second DC power to a light source for illumination; A control circuit for compensating the power factor of the converter; And a feedback signal generator for generating a feedback signal for providing to the control circuit, wherein the feedback signal generator includes a capacitive part for providing the feedback signal, and a capacitance of the capacitive part. Is provided with a power factor correction circuit for illumination that varies depending on the magnitude of the output current of the driver.

Preferably, the feedback signal generator includes a current to voltage converter and a variable capacitance module, and the capacitance of the variable capacitor module varies according to the magnitude of the output current of the driver.

Preferably, the current-voltage converter comprises an optical coupler. In this case, the variable capacitor module may include a first capacitor and a second capacitor connected in parallel, and a switching element may be connected in series to the second capacitor. In addition, the switching element may include a metal-oxide semiconductor field-effect transistor (MOSFET), a junction gate field-effect transistor (JFET) or a bipolar junction transistor (BJT).

Preferably, the converter comprises a buck converter, a boost converter, a forward converter or a flyback converter.

Preferably, the illumination light source includes a light emitting diode (LED) or an organic light emitting device (OLED).

According to embodiments of the present invention, it is possible to efficiently drive the lighting power factor correction circuit regardless of the magnitude of the LED output current. In addition, according to the embodiment of the present invention, it is not necessary to separately form a current limiting circuit for limiting the current of the LED by feeding back a signal according to the magnitude of the current flowing through the LED.

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned above may be clearly understood by those skilled in the art from the following description. will be.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included as part of the detailed description in order to provide a thorough understanding of the present invention, provide an embodiment of the present invention and together with the description, illustrate the technical idea of the present invention.
1 illustrates a schematic block diagram of a circuit for LED lighting.
2 illustrates in more detail a conventional LED lighting circuit.
3 illustrates the structure of the converter control circuit.
4 illustrates a structure of a conventional feedback signal generator.
5 illustrates a structure of a feedback signal generator according to an embodiment of the present invention.
6 and 7 specifically illustrate the structure and operation of a feedback signal generator according to an embodiment of the present invention.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element in between. . Also, when a part is referred to as "including " an element, it does not exclude other elements unless specifically stated otherwise.

In the present specification, the illumination includes all DC lighting elements such as LED lighting, OLED lighting, organic EL lighting, and the like, and uses LED lighting representatively for convenience of description.

1 illustrates a schematic block diagram of a circuit for LED lighting.

Referring to FIG. 1, the LED lighting circuit includes a rectifier circuit 110, a converter 120, an LED driver 130, a feedback signal generator 140, and a control circuit 150.

The rectifier circuit 110 converts household alternating current (AC) into direct current (DC) using a diode. The rectifier circuit 110 is implemented in various ways according to the use, and includes a half-wave rectifier circuit, full-wave rectifier circuit, bridge full-wave rectifier circuit, half-wave double-voltage rectifier circuit, full-wave double-voltage rectifier circuit, and the like. .

The converter 120 converts the DC power output from the rectifier circuit 120 into a DC power suitable for driving the LED. Circuits for small capacity DC / DC converters of about 200 W or less include, but are not limited to, buck converters, boost converters, forward converters, flyback converters, and the like.

Buck converters use switching elements that switch at regular intervals (on / off repetition), so that the input power is disconnected from the circuit while the switch is 'on' while the input power is connected to the circuit and 'off'. The buck converter periodically outputs a low voltage DC voltage by smoothing (averaging) a pulse-shaped voltage through the LC (inductor and capacitor) filter that the input power is connected and disconnected. This type of converter is called a voltage-fed converter. The longer the switch is 'on' within the switching cycle, the wider the pulse voltage is, and the higher the output voltage is. On the other hand, the shorter the time the switch is 'on', the lower the output voltage. If the 'on' time / switching period is the rate D, the output voltage is V _OUT = D * V _IN .

In boost converters, when the switch is 'on' the input power is connected across the inductor to charge the current, and when the switch is 'off' the charged current is delivered to the load filter. Unlike a buck converter, a boost converter is called a current-fed method because the current repeatedly flows in and out of the filter on the load side. The current at the output stage is smaller than the current at the input stage, and the output voltage is higher than the input voltage in the relationship of input current * input voltage = output current * output voltage. The output voltage is V _OUT = V _IN / (1-D).

The forward converter, like a buck converter, is a voltage source type converter, and is electrically isolated between input and output by using a high frequency transformer between an input terminal and an output terminal. Since it is a voltage source converter that cuts and averages a voltage like a buck converter, the output voltage is basically smaller than the input voltage, but the output voltage is increased by the turns ratio of the transformer inserted in the middle. The output voltage is V _OUT = N * D * V _IN , where N is the winding ratio of the secondary winding / 1 primary winding.

The flyback converter is an isolated form of the (buck) boost converter. The flyback converter uses the magnetizing inductance component of the transformer as a boost inductor.When the switch is 'on', the magnetizing inductance of the transformer is charged.When the switch is 'off', the current in the magnetizing inductance is passed to the transformer secondary side and the output voltage is V. _OUT = N * D * V _IN / (1-D)

The LED driver 130 supplies the DC power output from the converter 120 to the illumination light source. Illumination light sources include, but are not limited to, direct current light sources and include LED devices, OLED devices, and organic EL devices.

The feedback signal generator 140 generates a feedback signal for informing the control circuit 150 of information on the DC power output from the converter 120 to compensate for the power factor. The feedback signal is generated in the form of voltage or current and provided to the control circuit 150. The feedback signal generator 140 will be described in more detail with reference to the accompanying drawings.

The control circuit 150 controls the converter 120 based on the voltage or current signal received from the feedback signal generator 140. Through this, the power factor of the converter 120 is compensated. The control circuit 150 is also illustrated in more detail with reference to the drawings later.

2 illustrates in more detail a conventional LED lighting circuit.

Referring to FIG. 2, the LED lighting circuit includes a rectifier circuit 110, a converter 120, an LED driver 130, a feedback signal generator 140, and a control circuit 150. In this example, the converter 120 exemplifies a flyback converter. The flyback converter 120 includes a switching element Q1, a transformer T1, a diode D1, and a capacitor C1. The LED driver 130 supplies DC power output from the flyback converter 120 to the LEDs. The LED driver 130 may include an output filter for stabilizing / adjusting power supplied to the LED. The feedback signal generator 140 includes a resistor R1 and a differential amplifier.

In FIG. 2, the AC power source AC is full-wave rectified by, for example, a diode bridge 110 composed of four diodes. The full wave rectifying output is connected to one end of the switching element Q1 via the primary winding of the transformer T1. The flyback converter controller 150 may be configured as a control IC (Integrated Chip), and by controlling the switching time of the switching element Q1 to control the phase of the AC power supply (V _AC ) and the power current (I _AC ) flowing therethrough. Improve power factor The switching element Q1 is controlled on / off by the flyback converter controller 150 and regulates the primary current of the transformer T1. Although the switching element Q1 illustrates a metal-oxide semiconductor field-effect transistor (MOSFET) element, the present invention is not limited thereto. Junction gate field-effect transistors (JFETs), depletion metal-oxide semiconductor field-effect transistors (MOSFETs), and bipolar junction transistors (BJTs) may be used instead of MOSFET devices.

The transformer T1 transfers energy due to the intermittent primary current to the secondary side and generates a voltage in the secondary winding according to the ratio of the primary winding and the secondary winding. The secondary voltage of the transformer T1 is rectified by a direct current having low ripple through the diode D1 and the capacitor C1, and is supplied to the LED through the LED driver 130. LED is a light emitting diode which becomes a light source of an illuminating device, and uses single or multiple in series / parallel connection. A resistor R1 is formed in the feedback line of the LED driver 130, and the resistor R1 detects a current I _LED flowing through the _LED . The current flowing through the resistor R1 in the feedback signal generator 140 is converted into a voltage by current-voltage conversion and then provided to the flyback converter controller 150 through an amplifier.

3 illustrates the structure of a converter control circuit.

Referring to FIG. 3, the control circuit 150 includes a comparator 152, an SR flip-flop 153, and an oscillator 154.

The comparator 152 includes a non-inverting terminal (+) to which the feedback signal V _FB is input and an inverting terminal (−) to which the reference signal V _REF is input. The comparator 152 is a reference signal (V _REF) is a feedback signal (V _FB) is less than if the duty control signal of high level: generate (Duty Control Signal DCS), and the reference signal (V _REF) is a feedback signal (V _FB), If it is, the low level duty control signal DCS is generated. In the case of FIG. 2, the feedback signal V _FB is a voltage signal converted from the LED output current and changes linearly with the increase or decrease of the LED output current. The feedback signal V _FB may be directly input to the comparator 152 as shown, but may be multiplied with another signal through a multiplier and then input to the comparator 152.

The oscillator 154 generates a clock signal CLK that rises and falls by a predetermined reference number during one period for the operation of the flyback converter 130. The period of the clock signal CLK coincides with the switching period of the switching element Q1. The SR flip-flop 153 includes a set stage S to which the clock signal CLK of a predetermined period is input, a reset stage R to which the duty control signal DCS is input, and an output stage Q. The SR flip-flop 153 generates a gate signal VG by performing a logic operation on two signals input to the set stage S and the reset stage R, and outputs the gate signal VG to the gate of the switching element Q1 through the output stage Q. . Specifically, the SR flip-flop 153 generates a high level gate signal VG when the input signal of the set terminal S is at a high level, and a low level gate signal when the input signal of the reset terminal R is at a high level. Create (VG). The SR flip-flop 153 maintains the current gate signal VG when a low level signal is input to both the set terminal S and the reset terminal R. FIG.

For example, when the feedback signal V _FB increases from the reference signal V _REF due to the increase in the LED output current, the comparator outputs a high level duty control signal. The SR flip-flop 153 which receives the high level duty control signal through the reset terminal R generates the low level gate signal VG. Thus, the duty of the switching element 151 is reduced to reduce the output voltage. On the other hand, when the feedback signal V _FB decreases from the reference signal V _REF due to the reduction of the LED output current, the comparator outputs a low level duty control signal. The SR flip-flop 153 generates a high level gate signal VG according to the clock signal CLK input to the set terminal S. Thus, the duty of the switching element 151 increases to increase the output voltage.

As an example of the structure of the control circuit described with reference to FIG. 3, a control circuit having various structures may be used for power factor correction of the converter.

4 illustrates a structure of a conventional feedback signal generator. This example shows an example of a feedback signal generator using an optical coupler.

Referring to FIG. 4, the feedback signal generator 140 includes an optical coupler (OC) OC1 and a capacitor C2. The optical coupler OC1 includes a light emitting diode and a transistor. The light emitting diode is connected to the output terminal of the converter 130 or the LED driver 130 and senses the LED output current and transmits a signal to a corresponding transistor. The transistor of the optical coupler OC1 operates according to the intensity of light transmitted from the light emitting diode. Both ends of the capacitor C2 are connected to the collector and emitter of the transistor, and the flyback converter controller 150 is connected to the collector of the transistor. According to the intensity of the light emitting diode, a feedback voltage V _FB appears in the collector of the transistor, and a ripple occurs in the feedback voltage V _FB applied to the capacitor C2 according to the state and time constant of the LED output current. That is, the ripple of the feedback voltage V _FB occurs according to the change of the LED output current, and the flyback converter controller 140 senses such a change in the feedback voltage V _FB to improve the power factor of the converter 120. For convenience of understanding and description, the connection between the feedback signal generator 140 and a voltage source or a current source required for driving the transistor is not shown.

In the conventional circuit configuration as shown in FIG. 4, the capacitor C2 is largely determined according to the case where the LED output current is large. However, when such a circuit configuration is used, when the LED output current is small, the ripple of the feedback signal V _FB is canceled to cause a problem in that the power factor compensation is lowered. In other words, the power factor drops when the output current is small.

Accordingly, the present invention is to provide a power factor correction circuit for lighting, a power supply circuit for lighting, and a driving method thereof having improved power factor correction regardless of the magnitude of the LED output current. To this end, the present inventors provide a power factor correction for lighting in which the capacitance of the capacitance part used to provide the feedback signal V _FB in the feedback signal generator varies according to the LED output current or a corresponding value. Provides a circuit and a power supply circuit for lighting.

Hereinafter, an embodiment of the present invention will be specifically described with reference to FIGS. 5 to 7. In the following drawings, a flyback converter controller is shown as an example of a control circuit. However, this is an example for explanation, and the control circuit herein is not limited to that for a specific converter.

5 illustrates a structure of a feedback signal generator according to an embodiment of the present invention.

Referring to FIG. 5, the feedback signal generator 140 includes an optical coupler OC1 and a variable capacitance module. The optical coupler OC1 includes a light emitting diode and a transistor. Although the figure shows a BJT as a transistor of an optical coupler, it can be used instead of the MOSFET and JFET as an example. The collector voltage V _FB of the BJT connected to the flyback converter controller 140 changes according to the change of the LED output current sensed by the optical coupler OC1. The optical coupler OC1 in this embodiment exemplarily shows a means for providing the LED output current as a voltage, and may be replaced without limitation by any module / element / means for performing this function. The optical coupler OC1 can be generalized to a current to voltage conveter.

The variable capacitance module is connected in parallel with a current-voltage converter (eg an optical coupler). That is, both ends of the variable capacitance module are connected to the collector and emitter of the BJT constituting the optical coupler OC1. The capacitance of the variable capacity module varies according to the LED output current / voltage or the intensity of a signal associated therewith, for example, has a first capacitance value when the LED output current (or its associated signal value) is less than the reference value. When the LED output current (or a signal value related thereto) is larger than the reference value, the LED output current may have a second capacitance value. In this case, the first capacitance value is smaller than the second capacitance value. The variable capacity module may have three or more capacitance values, in which case a plurality of reference values may be used. Although not limited thereto, the variable capacitance module may be configured by a combination of a switching element and a capacitor. As the switching element, a transistor such as a MOSFET, a JFET, a BJT, or the like can be used.

That is, when the LED output current is large, the capacitance of the variable capacitance module has a first capacitance value, and when the LED output current is small, the capacitance of the variable capacitance module has a second capacitance value smaller than the first capacitance value. As such, the capacitance value of the capacitive module connected to the current-voltage converter is changed according to the intensity of the LED output current, thereby solving the problem of power factor correction performance declining by canceling the ripple when the LED output current is small.

6 and 7 specifically illustrate the structure and operation of a feedback signal generator according to an embodiment of the present invention.

6 and 7, the feedback signal generator 140 includes an optical coupler OC1 and a variable capacitor module. The optical coupler OC1 includes a light emitting diode and a transistor. Although the figure shows a BJT as a transistor of an optical coupler, it can be used instead of the MOSFET and JFET as an example. In addition, the variable capacity module includes a plurality of capacitors C2 and C3 connected in parallel, and the capacitor C3 is connected in series with BJT Q2 as a switching element. Specifically, the collector of BJT (Q2) is connected to one end of capacitor C3, and the base of BJT (Q2) provides a voltage signal (e.g., V _FB ) associated with the LED output current through resistor Rb. Is connected to. The figure illustrates that the base of the BJT Q2 is connected to the collector of the BJT included in the optical coupler OC1 through the resistor Rb. However, the point where the base of the BJT Q2 is connected is not limited thereto, and may be connected to various points providing a voltage signal related to the LED output current. In addition, although the figure shows the BJT as a switching element for the capacitor C3, it can be used instead of the MOSFET and JFET as an example.

The light emitting diode of the optical coupler is connected to the output terminal of the converter 130 or the LED driver 130 and senses the LED output current and transmits a signal to a corresponding transistor. The transistor of the optical coupler OC1 operates according to the intensity of light transmitted from the light emitting diode. According to the intensity of the light emitting diode, a feedback voltage V _FB appears in the collector of the transistor, and a ripple occurs in the feedback voltage V _FB according to the state of the LED output current and the capacitance value of the variable capacitance module. The flyback converter controller 140 senses this change in the feedback voltage V _FB to improve the power factor of the converter 120.

The magnitude of the feedback voltage V _FB appearing on the collector of the BJT included in the optical coupler OC1 depends on the LED output current. If the LED output current is large, the feedback voltage (V _FB ) appearing on the collector of the BJT included in the optical coupler (OC1) is also large.If the LED output current is small, the feedback voltage appears on the collector of the BJT included in the optical coupler (OC1). (V _FB ) also appears small.

BJT Q2 is conducting when feedback voltage V _FB is greater than base-emitter threshold voltage VQ2 _BE (eg, 0.7V) of BJT Q2. The resistor Rb generates a current input to the base of the BJT Q2 and has a high resistance value to prevent current loss. In this case, since the current flowing through the resistor Rb is very small, the base of the BJT Q2 and one end of the capacitor C2 can be treated as short-circuited. Therefore, when the LED output current is large and the BJT Q2 is conducted, the capacitor C2 and the capacitor C3 are shown in parallel connection form as shown in FIG. 7A. In this case, since the total capacitance connected to the optical coupler OC1 is C2 + C3, the time constant increases, so that the ripple change of the feedback voltage V _FB is insensitive to the change of the LED output current.

On the other hand, when the feedback voltage V _FB is smaller than the base-emitter threshold voltage VQ2 _BE (eg, 0.7 V) of the BJT Q2, the BJT Q2 is not conductive. Therefore, when the LED output current is small so that the BJT (Q2) does not conduct, only the capacitor C2 looks like FIG. 7B. In this case, since the total capacitance connected to the optical coupler OC1 is C2, the time constant decreases so that the change in the ripple of the feedback voltage V _FB is sensitive to the change in the LED output current.

Therefore, according to the embodiment of the present invention, it is possible to provide a circuit for improving the power factor correction function regardless of the magnitude of the LED output current.

Industrial Applicability The present invention can be applied to a power supply unit of a lighting device using LED or OLED as a light source. For example, the present invention can be applied to general home lighting devices or store lightings instead of reading lights, guide lights, decorative lights or fluorescent lights.

While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims. . It is therefore to be understood that the modified embodiments are included in the technical scope of the present invention if they basically include elements of the claims of the present invention.

110: rectifier circuit 120: converter
130: LED driver 140: feedback signal generator
150: control circuit

Claims (7)

A converter for converting the first DC power into the second DC power;
A driving unit providing the second DC power to a light source for illumination;
A control circuit for compensating the power factor of the converter; And
A feedback signal generator for generating a feedback signal for providing to the control circuit,
The feedback signal generator includes a capacitive part for providing the feedback signal, and the capacitance of the capacitive part is variable according to the magnitude of the output current of the driver. The method of claim 1,
The feedback signal generator includes a current-to-voltage converter and a variable capacitance module, and the capacitance of the variable capacitor module varies according to the magnitude of the output current of the driver. . The method of claim 2,
The current-voltage converter comprises an optical coupler. The method of claim 2,
The variable capacitance module includes a first capacitor and a second capacitor connected in parallel, and the second capacitor has a power factor correction circuit for lighting connected in series. The method of claim 4, wherein
The switching device includes a metal-oxide semiconductor field-effect transistor (MOSFET), a junction gate field-effect transistor (JFET) or a bipolar junction transistor (BJT). The method of claim 1,
And said converter comprises a buck converter, a boost converter, a forward converter or a flyback converter. The method of claim 1,
The illumination light source is a power factor correction circuit for illumination comprising a light emitting diode (LED) or an organic light emitting device (OLED).

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