KR20220140361A - A circuit for reducing flicker of converter for led lighting - Google Patents

Abstract

A circuit for reducing the flicker of a converter for LED lighting, as a circuit for reducing the flicker of a converter for LED lighting connected to an output terminal of a converter for LED lighting to reduce the flicker of LED lighting, comprises: a second output capacitor which is connected in parallel with an output capacitor of a converter for LED lighting; a first inductor; and a compensation voltage generating element which is connected in series to the first inductor, and which includes auxiliary winding having a predetermined number of windings. The first inductor and the compensation voltage generating element are disposed between the output capacitor and the second output capacitor.

Description

Flicker reduction circuit of converter for LED lighting {A CIRCUIT FOR REDUCING FLICKER OF CONVERTER FOR LED LIGHTING}

The present invention is a flicker reduction circuit of a converter for LED lighting, and more specifically, by winding a very small number of windings around a transformer or inductor, directly connecting it with an inductor for a filter, and inserting it between the output capacitor, a reverse voltage proportional to the input voltage during switching operation It relates to a flicker reduction circuit of a converter for LED lighting that generates an output-side average voltage and current constant.

In general, a converter for LED lighting refers to a device that receives commercial AC power for LED lighting, converts it into rated DC power required for lighting, and supplies it to LED lighting devices.

The voltage or current of an AC power source fluctuates in a sinusoidal (sine wave) shape, and since the sinusoidal phases of voltage and current do not necessarily coincide, the active power varies depending on the phase difference between the voltage and current, and the active power divided by the apparent power The value may be referred to as the power factor.

In such a converter for LED lighting, when the phases of the input voltage and current are matched to increase the power factor of commercial power, a ripple voltage proportional to the input voltage and current is inevitably generated on the output side, which causes flicker (light) in the LED lighting device. flickering) may occur.

In order to reduce the flicker phenomenon, a method of adding a switching constant current circuit or using a constant current device on the output side is being considered (refer to Korean Patent No. 10-1185534), but this increases the cost due to the introduction of an additional circuit and unnecessary power consumption. There is a problem of a decrease in efficiency due to the

In order to solve this problem, by reducing flicker without using a separate switching element or constant current element, the flicker of the converter for LED lighting does not cause a problem of cost increase due to the introduction of an additional circuit and a problem of efficiency decrease due to unnecessary power consumption The need for an abatement circuit is emerging.

The problem to be solved by the present invention is to provide a flicker reduction circuit for a converter for LED lighting that can be applied to various types of LED converters, which minimizes power dissipation and simplifies the circuit while reducing flicker that is inevitably generated in the converter.

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

The flicker reduction circuit of the converter for LED lighting according to an embodiment of the present invention for solving the above problems is connected to the output terminal of the converter for LED lighting as a flicker reduction circuit of the converter for LED lighting for reducing the flicker of the LED lighting, for LED lighting A second output capacitor connected in parallel with the output capacitor of the converter, a first inductor, and a compensation voltage generating element connected in series with the first inductor and including an auxiliary winding having a predetermined number of turns, the first inductor and the compensation voltage generating element is disposed between the output capacitor and the second output capacitor.

According to the present invention, a very small number of windings are wound around the transformer or inductor and directly connected to the filter inductor and inserted between the output capacitors to generate a reverse voltage proportional to the input voltage during the switching operation to keep the average voltage and current on the output side constant. can keep

Accordingly, it is possible to minimize power loss and simplify the circuit while reducing the flicker phenomenon that inevitably occurs in the converter, and the application can be expanded by applying it to various types of LED converters.

In addition, it is composed of a minimum of elements without major changes to the existing circuit, so it is possible to simply reduce the flicker phenomenon without reducing efficiency, and it can be usefully used in the LED lighting market where high quality is required due to a wide range of use.

In addition, it is possible to reduce the harmful effect on the human body by reducing flicker, and it can be utilized when shooting high-performance mobile phone video for UHD TV.

In addition, since it can be implemented in a single stage compared to a converter connected in multiple stages to reduce flicker, the overall size can be reduced by simplifying the components of the converter, efficiency can be increased, and manufacturing cost can be lowered. In addition, by reducing the total number of parts, there is an advantage that the failure probability can also be lowered.

1 shows a converter for LED lighting according to the prior art.
2 shows the input voltage and current when the power factor correction circuit operates.
3 shows an output voltage when the power factor correction circuit is operated.
4 illustrates a form in which a flicker reduction circuit according to an embodiment of the present invention is applied to a power factor correction circuit.
5 is a detailed view of a flicker reducing circuit according to an embodiment of the present invention.
6 shows an output waveform of a flicker reducing circuit applied to the power factor correction circuit of FIG. 4 .
7 shows an exemplary single stage converter.
8 illustrates a form in which a flicker reduction circuit according to an embodiment of the present invention is applied to a single-stage converter.
9 shows an output waveform of a flicker reducing circuit applied to the single-stage converter of FIG. 8 .

The present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only these embodiments allow the disclosure of the present invention to be complete, and those of ordinary skill in the art to which the present invention pertains. It is provided to fully inform the person of the scope of the invention.

In this specification, the singular also includes the plural, unless specifically stated otherwise in the phrase. As used herein, "comprises" and/or "comprising" refers to the stated elements, steps, and acts do not exclude the presence or addition of one or more other elements, steps and acts.

Converter for LED lighting with conventional power factor correction circuit

As mentioned above, a converter for LED lighting generally refers to a device that receives commercial AC power for LED lighting, converts it into rated DC power required for lighting, and supplies it to LED lighting equipment.

In such a converter for LED lighting, when the phases of the input voltage and current are matched to increase the power factor of commercial power, a ripple voltage proportional to the input voltage and current is inevitably generated on the output side, which causes flicker (light) in the LED lighting device. flickering) may occur.

1 shows a converter for LED lighting according to the prior art. As shown in FIG. 1 , a conventional conventional converter for LED lighting consists of two stages: a step-up converter part for improving power factor and obtaining a high voltage, and a DC-DC converter part for implementing constant voltage/constant current characteristics required for driving the LED. can be

That is, the converter 10 for LED lighting for generating rated DC power for supplying the LED load 20 includes a rectifier 11 , a filter unit 12 and a power factor correction circuit 13 for converting commercial AC power into DC. ) may be included. On the other hand, in the case of a converter with a small capacity, a single-stage flyback converter may be used.

Such a converter may be configured to match the phases of the input voltage and the current by having the power factor correction circuit 13 to solve the power factor problem, and accordingly, a ripple voltage is inevitably generated on the output side, thereby generating a flicker phenomenon. will do

In the case of the single-stage type, a larger flicker phenomenon may occur compared to the two-stage type. This flicker phenomenon is harmful to the human body and can cause a big problem when shooting high-performance cameras for UHD TVs and mobile phones.

In order to reduce the flicker phenomenon, a method of adding a switching constant current circuit or using a constant current device on the output side is being considered, but this has a problem of cost increase due to introduction of an additional circuit and a problem of efficiency decrease due to unnecessary power consumption.

More specifically described with reference to FIG. 1 , as shown in FIG. 1 , a typical converter for LED lighting 10 may be configured to supply rated DC power to the LED load 20 , and a rectifier 11 , a filter The unit 12 , a power factor correction circuit 13 , and a DC-DC conversion circuit 14 may be included.

The rectifying unit 11 converts the AC of the commercial AC power into DC, and the filter unit 12 repeats the size change to remove the AC component. The power factor correction circuit 13 may increase the power factor by reducing the phase difference between the voltage and the current as much as possible.

In this regard, Fig. 2 shows the input voltage and current during the operation of the power factor correction circuit. More specifically, if the ON time of the switch SW is kept the same, a switching current proportional to the magnitude of the input voltage flows, and the average current may obtain the same phase as the input voltage.

3 shows an output voltage when the power factor correction circuit is operated. As shown in FIG. 3 , in relation to the output voltage Vo of the power factor correction circuit 13 , a change in the current of the power factor correction circuit 13 appears as a ripple voltage.

This ripple voltage may be configured to be applied to the LED load 20 through the DC-DC conversion circuit 14 . Although this can slightly reduce the ripple voltage, it is impossible to completely eliminate it.

On the other hand, when the capacity of the output capacitor (Co) is greatly increased, the ripple may be reduced, but there is a problem in that an excessive capacity capacitor must be used, and the response to the on-off of the power is delayed.

As a result, it is practically impossible to completely eliminate the flicker phenomenon due to the power factor problem in the switched converter, and it may be the best way to minimize the problem by significantly reducing the possible flicker phenomenon.

Flicker reduction circuit applied to multi-stage (two-stage) converter

A flicker reducing circuit according to an embodiment of the present invention relates to a flicker reducing circuit for solving the above-described problems.

According to an embodiment of the present invention, without using a separate switching element or constant current element, a very small number of windings are wound around the switching transformer (or inductor) and directly connected to the filter inductor and inserted between the output capacitors. By generating a reverse voltage proportional to the voltage, the average voltage and current of the output side can be kept constant. Accordingly, it is possible to reduce the flicker phenomenon while hardly generating power loss.

More specifically, the flicker reduction circuit 400 according to an embodiment of the present invention may be a circuit for reducing flicker of an LED load (illumination) by being coupled to an output terminal of a converter for LED lighting.

That is, the flicker reducing circuit 400 according to an embodiment of the present invention may be applied to a multi-stage converter including a rectifying unit 401 , a filter unit 402 , and a power factor correction circuit 403 .

For example, it may be implemented by adding a flicker reducing circuit to the boosting circuit for power factor correction.

To this end, the flicker reduction circuit 400 according to an embodiment of the present invention includes a first inductor 410 , a compensation voltage generating element 420 , a second output capacitor 430 , and an RC snubber circuit 440 . may include

The first inductor 410 may be an inductor for a filter, and the inductor for a filter may keep a constant average current by passing a DC component and suppressing an AC component having large fluctuations.

The compensation voltage generator 420 is a device that generates a reverse voltage proportional to the input voltage of the converter according to the switching operation of the converter to maintain the fluctuations of the output voltage and the output current of the flicker reducing circuit below a predetermined threshold value. .

The compensation voltage generating element 420 may be inserted into either the switching inductor Lm or the switching transformer. 5 illustrates an example in which the compensation voltage generating element 420 is added to the switching inductor Lm.

The compensation voltage generating element 420 is connected in series to the filter inductor Lo, and may include an auxiliary winding in which a predetermined number of turns is wound.

The number of turns of the auxiliary winding may be determined according to the magnitude of the output voltage and the ripple voltage of the converter. In FIG. 5 , the number of windings of the auxiliary winding inserted into the switching inductor Lm may be adjusted according to the magnitude of the output voltage and the magnitude of the ripple voltage.

Here, the predetermined number of turns of the auxiliary winding may be 0.5 to 2 turns (Turn) or less, but is not limited thereto.

The second output capacitor 430 is a capacitor connected in parallel with the output capacitor 4031 of the converter for LED lighting.

As described above, the filter inductor (Lo) and the compensation voltage generating element 420 are connected in series, and the filter inductor (Lo) and the compensation voltage generating element 420 connected in series are the output capacitor 4031 and the first It may be disposed between the two output capacitors 430 .

Meanwhile, the output capacitor 4031 may be configured to have more than twice the capacity of the second output capacitor 430 .

The RC snubber circuit 440 is a circuit that prevents a voltage greater than a predetermined threshold value from being induced in the filter inductor Lo from the compensation voltage generating element 420 .

More specifically, since the voltage of the auxiliary winding is repeatedly changed to a negative voltage and a positive voltage according to the on-off of the switching element, a high voltage may be induced in the filter inductor Lo. In consideration of this point, the RC snubber circuit 440 connected in parallel to the auxiliary winding may be configured to mitigate this.

The RC snubber circuit 440 may be connected in parallel to the compensation voltage generating element 420 and may include a resistor 441 and a capacitor 443 connected in series.

Under the configuration described above, the operation of the flicker reducing circuit will be described with reference to FIGS. 4 to 6 .

6 shows an output waveform of a flicker reducing circuit applied to the power factor correction circuit of FIG. 4 . In this regard, referring to FIG. 4 , when the switch element SW is turned on, a current Ilm flows in the switching inductor Lm and a voltage Vlm equal to Vin is applied.

Accordingly, a voltage of Vlm/N is applied to the auxiliary winding 420 composed of a coupling inductor. Here, N may represent a turns ratio between the switching inductor Lm and the auxiliary winding 420 . When the input voltage Vin is high, Vlm is also high, and Vlm/N of the auxiliary winding also becomes high in reverse voltage on the output side. It may correspond to a portion shown below Vco1 in a direction opposite to Vs in FIG. 6 .

When the switch element SW is turned off, a current flows to Co1 through the diode by the magnetization energy of the switching inductor Lm, and at this time, the relationship of Vin + Vlm = Vco1 is established. Since the capacitance of the capacitor Co1 is very large, the voltage fluctuation of Vco1 is small. When the input voltage Vin is low, Vlm is high, and when Vin is high, Vlm is low. The voltage on the auxiliary winding is Vlm/N, which is the forward voltage on the output side. It may correspond to a portion shown above Vco1 in the forward direction of Vs in FIG. 6 .

The waveform of each voltage when the switch element repeats on-off for a certain period may be a voltage in which Vco1 includes a ripple having a frequency of, for example, 120 Hz, as shown in FIG. 6, and an inductor for a filter ( Lo) and the auxiliary winding, the voltage Vs increases as a reverse voltage when the ripple voltage of Vco1 is high, and increases in the forward direction when Vco1 is low. It can appear as a flat voltage.

In other words, the compensation voltage generating element 420 generates a reverse voltage proportional to the input voltage of the converter according to the switching operation of the converter to maintain the fluctuations of the output voltage and output current of the flicker reducing circuit below a predetermined threshold value. It can be configured to

Such a principle can be easily applied to various types of switching-type converters. The flicker reduction circuit according to the present invention, as described above, the power factor correction circuit and the DC-can be applied not only to the two-stage converter consisting of the DC converter, but also to the insulated flyback converter operating in a single stage.

Hereinafter, a case in which the flicker reduction circuit according to the present invention is applied to an insulated flyback converter operating in a single stage will be described.

Flicker reduction circuit applied to single stage converter

7 shows an exemplary single-stage converter, and FIG. 8 illustrates a form in which a flicker reducing circuit according to an embodiment of the present invention is applied to a single-stage converter. Hereinafter, a flicker reducing circuit according to an embodiment of the present invention will be described in more detail with reference to FIGS. 7 to 8 .

As shown in FIG. 8 , the flicker reduction circuit 800 according to an embodiment of the present invention may be applied to a single stage converter (flyback) circuit as shown in FIG. 7 . For example, it can be implemented by adding a flicker reducing circuit to a single stage converter (flyback) circuit.

More specifically, the flicker reduction circuit 800 according to an embodiment of the present invention may be a circuit for reducing flicker of an LED load (illumination) by being coupled to an output terminal of a converter for LED lighting.

Similar to the flicker reduction circuit applied to the above-described multi-stage converter, the second output capacitor (Co2) connected in parallel with the output capacitor (Co1) of the converter, the first inductor and the first inductor are connected in series to a predetermined number of times. The auxiliary winding may include a wound compensation voltage generating element.

Here, the first inductor Lo and the compensation voltage generating element may be disposed between the output capacitor Co1 and the second output capacitor Co2.

Meanwhile, the compensation voltage generating element may be an auxiliary winding inserted into any one of a switching inductor or a switching transformer. In FIG. 8 , a form in which a compensation voltage generating element is used in a switching transformer is exemplified. Also, according to one aspect, the first inductor may be an inductor Lo for a filter.

That is, according to one aspect of the present invention, an auxiliary winding with a small number of turns, for example between 0.5 and 2 Turn, is added to the switching transformer, and this is directly connected to the inductor Lo for a filter, the output capacitor Co1 and the second A compensation voltage generating element and an inductor Lo for a filter may be inserted between the output capacitor Co2.

Here, the number of windings of the auxiliary winding wound around the switching transformer may be determined according to the magnitudes of the output voltage and the ripple voltage of the converter. In FIG. 8 , the number of turns of the auxiliary winding applied to the switching transformer may be adjusted according to the magnitude of the output voltage and the magnitude of the ripple voltage. Meanwhile, the output capacitor Co1 may be configured to have twice the capacity of the second output capacitor Co2 or more.

9 shows an output waveform of a flicker reducing circuit applied to the single-stage converter of FIG. 8 .

In this regard, when the switch element SW is turned on, a current Ilm flows to the primary side of the switching transformer and a voltage Vlm equal to Vin is applied. Therefore, a voltage of Vlm/N is applied to the auxiliary winding. Here, N may represent a turns ratio between the primary side of the switching transformer and the auxiliary winding. When the input voltage Vin is high, Vlm is also high, and Vlm/N of the auxiliary winding also becomes high in reverse voltage on the output side. It may correspond to a portion shown below Vco1 in the reverse direction of Vs in FIG. 9 .

When the switch element SW is turned off, a current flows to Co1 through the diode by the magnetization energy of the switching transformer, and in the case of a one-to-one turns ratio transformer - Vlm = Vco1 is established. Since the capacitance of the capacitor Co1 is very large, the voltage fluctuation of Vco1 is small, so Vlm is maintained the same as Vco1 regardless of the input voltage Vin. The voltage on the auxiliary winding is Vlm/N, which is the forward voltage on the output side. It may correspond to a portion shown above Vco1 in the forward direction of Vs in FIG. 9 .

As shown in FIG. 9, the waveform of each voltage when the switch element repeats on-off for a certain period may be a voltage in which Vco1 includes a ripple, and the voltage Vs between the filter inductor (Lo) and the auxiliary winding When the ripple voltage of Vco1 is high, it becomes a reverse voltage, and when Vco1 is low, it increases in the forward direction.

Meanwhile, as shown in FIG. 8 , the flicker reduction circuit 800 according to an embodiment of the present invention may further include an RC snubber circuit connected in parallel to the compensation voltage generating element. The RC snubber circuit may include a resistor R and a capacitor C connected in series.

Here, the RC snubber circuit may be configured to prevent a voltage higher than a predetermined threshold value from being induced in the first inductor from the compensation voltage generating element. More specifically, since the voltage of the auxiliary winding varies from a negative voltage to a positive voltage according to the switching period, a high voltage may be induced in the filter inductor (Lo). can

In the above, for convenience of description, a form in which the flicker reducing circuit according to an aspect of the present invention is applied to a multi-stage converter or a single-stage converter having a power factor correction circuit has been exemplarily described.

However, the flicker reduction circuit according to the present invention may operate by being coupled to at least one of a non-insulated step-up type, step-down type, and step-up type converter. In addition, it can be applied to all LED lighting converters of various switching methods.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, those of ordinary skill in the art to which the present invention pertains can realize that the present invention can be embodied in other specific forms without changing its technical spirit or essential features. you will be able to understand Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

10: converter for LED lighting 11, 401: rectifier
12, 402: filter unit 13, 403: power factor correction circuit
14: DC-DC conversion circuit 20: LED load
400, 800: flicker reducing circuit 410: first inductor
420: compensation voltage generating element 430: second output capacitor
440: RC snubber circuit 441: resistance
443: capacitor 4031: output capacitor

Claims (9)

A flicker reduction circuit of a converter for LED lighting for reducing flicker of LED lighting by being connected to an output terminal of a converter for LED lighting,
a second output capacitor connected in parallel with the output capacitor of the converter for LED lighting;
a first inductor; and
and a compensation voltage generating element connected in series to the first inductor and including an auxiliary winding having a predetermined number of turns,
The first inductor and the compensation voltage generating element is a flicker reduction circuit of a converter for LED lighting that is disposed between the output capacitor and the second output capacitor. The method of claim 1,
The first inductor is
A flicker reduction circuit of a converter for LED lighting that is an inductor for a filter. The method of claim 1,
The number of windings is
The flicker reduction circuit of the converter for LED lighting is determined according to the magnitude of the output voltage and ripple voltage of the converter for LED lighting. The method of claim 1,
The output capacitor is
The flicker reduction circuit of the converter for LED lighting, which will have more than twice the capacity compared to the second output capacitor. The method of claim 1,
Further comprising an RC snubber circuit connected in parallel to the compensation voltage generating element,
The RC snubber circuit is a flicker reduction circuit of a converter for LED lighting that is configured to prevent a voltage higher than a threshold value from being induced in the first inductor from the compensation voltage generating element. The method of claim 1,
The compensation voltage generating element is
By generating a reverse voltage proportional to the input voltage of the converter for LED lighting in accordance with the switching operation of the converter for LED lighting, the flicker reduction circuit of the converter for LED lighting is to keep the average voltage and average current on the output side constant. The method of claim 1,
The converter for LED lighting is a two-stage converter including a power factor correction circuit and a DC-DC conversion circuit,
The auxiliary winding is added to the switching inductor, the flicker reduction circuit of the converter for LED lighting. The method of claim 1,
The converter for LED lighting is a single-stage converter,
The auxiliary winding is added to the switching transformer, the flicker reduction circuit of the converter for LED lighting. The method of claim 1,
The converter for LED lighting,
A flicker reduction circuit of a converter for LED lighting that is any one of a non-insulated step-up type, step-down type, and step-up type converter.

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