KR101014644B1 - Led driving circuit - Google Patents

Abstract

PURPOSE: An LED driving circuit is provided to offer excellent efficiency or power factor by using the AC voltage as the driving power. CONSTITUTION: An LED driving circuit comprises a voltage detecting unig(50) and a switching unit(70). The voltage detecting unit outputs the switching control signal of the low level if the high voltage is inputted. The voltage detecting unit outputs the switching control signal of the high level if the low voltage is inputted.

Description

LED driving circuit {LED driving circuit}

The present invention relates to an LED driving circuit, and more particularly to a circuit for driving the LED that is employed in lighting, such as a lighting fixture.

Light emitting diodes (LEDs, hereinafter referred to as "LEDs") have beneficial advantages as light sources in terms of light efficiency and durability compared to power. Therefore, it is actively researching and developing as a light source, such as a backlight of a lighting apparatus or a display apparatus.

Generally, LEDs are driven at low direct currents. Therefore, in order to drive the LED using a commercial voltage (AC 220 volts), a conversion circuit for converting the commercial voltage into a low DC output voltage is required. For example, a circuit in which a switched-mode power supply (SMPS) and a current limiting resistor are combined or a circuit in which a linear power and a current limiting resistor are combined must be included in the LED driving circuit. SMPS and linear power convert AC voltage into DC voltage (DC constant voltage) of constant magnitude, and current limiting resistor lowers the amount of current supplied to the LED.

However, when the LED driving circuit includes such a conversion circuit, there is a problem that the efficiency of the LED driving circuit decreases during the voltage conversion process. In practice, LED drive circuits with conversion circuits incorporating SMPS and resistors have efficiencies in the range of approximately 70% to 75%, and LED drive circuits with conversion circuits incorporating linear power and resistance are approximately 70% to 80%. It has an efficiency within the range.

Accordingly, various types of LED driving circuits that can be driven by an AC voltage without a conversion circuit have been proposed. 1 is an example of an LED driving circuit driving with a conventional AC voltage. The plurality of LEDs L1 to LN connected in series with each other are connected to the output side of the rectifying unit 12. The power rectified by the rectifying unit 12 is applied to the plurality of LEDs L1 to LN through the connector 10 connected to the power supply terminal.

In general, in the LED driving circuit driving with an alternating voltage as shown in FIG. In practice, AC voltage is continuously applied to the LED array, but the LED array operates only when the magnitude of the AC voltage is greater than the value capable of operating all of the LEDs included in the LED array. That is, as illustrated in FIG. 2, the waveform 20 of the applied power is different from the operation waveform 30 in which the plurality of LEDs L1 to LN are actually turned on. In Fig. 2, arrow A means dead zone.

As described above, an AC current having a value smaller than a value capable of operating all of the plurality of LEDs L1 to LN connected in series is not used at all to drive the LED array, thereby reducing the efficiency of the LED driving circuit.

In addition, since the current flows in the circuit only when the magnitude of the AC voltage is greater than the value capable of operating all of the LEDs included in the LED array, the waveform of the current is greatly distorted compared to the waveform of the AC voltage. In this case, the power factor of the LED driving circuit is lowered.

The present invention has been proposed to solve the above-mentioned conventional problems, and an object thereof is to provide an LED driving circuit having superior efficiency or power factor as compared with the related art.

In order to achieve the above object, an LED driving circuit according to a preferred embodiment of the present invention, the voltage detection unit for detecting whether the input AC voltage is a low voltage or a high voltage and outputs a switching control signal corresponding thereto; And a switching unit provided between the plurality of LED modules connected in series to the AC input terminal and configured to sequentially apply AC voltage to the plurality of LED modules based on the switching control signal from the voltage detection unit.

The voltage detector outputs a low level switching control signal when the level of the currently input voltage is high, and outputs a high level switching control signal when the level of the currently input voltage is low.

The voltage detector includes a Zener diode having one end connected to an intermediate node of a plurality of resistors connected in series between both ends of an AC input terminal, and a first end connected to the other end of the Zener diode, and a second end connected to the voltage detector. It includes a switching element.

The switching element is composed of an NPN transistor.

The switching section is composed of an NPN transistor.

An LED driving circuit according to another embodiment of the present invention, the voltage detection unit for detecting whether the input AC voltage is a low voltage or a high voltage and outputs a switching control signal of a series drive or a parallel drive corresponding thereto; A switching unit disposed between a plurality of LED modules connected to an AC input terminal, the switching unit allowing the plurality of LED modules to be driven in parallel or in series according to a switching control signal from a voltage detector; And a path forming helper which assists in forming a corresponding AC voltage application path in parallel driving or series driving by the switching unit.

The voltage detector outputs a switching control signal for serial driving when the level of the currently input voltage is high voltage, and outputs a switching control signal for parallel driving when the level of the currently input voltage is low voltage.

The voltage detector includes a Zener diode having one end connected to an intermediate node of a plurality of resistors connected in series between both ends of an AC input terminal, a first end connected to the other end of the Zener diode, and a second end and a third end connected to an AC input end. A first switching element connected to both ends of the second switching element, and a second switching element connected to the first switching element and performing a switching operation opposite to the first switching element.

The voltage detecting unit turns off the first switching element and turns on the second switching element when the input AC voltage is a low voltage.

The voltage detecting unit turns on the first switching element and turns off the second switching element when the input AC voltage is a high voltage.

The first switching element and the second switching element are composed of NPN transistors.

The switching unit includes the same number of switching units as the number of LED modules.

The path forming help consists of a diode installed between the plurality of LED modules.

According to the present invention having such a configuration, when the input AC voltage is a low voltage, only a predetermined LED module of the plurality of LED modules is applied with an AC voltage, and when the input AC voltage becomes a high voltage, the AC voltage is also applied to all the LED modules. Since almost all of the AC voltage input to the plurality of installed LED modules can be appropriately used as driving power according to the situation, the efficiency or power factor is significantly improved compared with the related art.

On the other hand, when the input AC voltage is a low voltage, a plurality of LED modules are driven in parallel, and when the input AC voltage becomes a high voltage, the plurality of LED modules are driven in series. Since almost all of the AC voltage input to the plurality of installed LED modules can be appropriately used as driving power according to the situation, the efficiency or power factor is significantly improved compared with the related art.

As such, the efficiency is improved as compared with the related art, and thus, an additional effect of increasing the amount of light is particularly obtained at a driving power such as an AC LED.

When applied to direct current, full volts can be used and rated output is also possible at half volts.

In addition, since the component is a basic element, a high voltage can be used. Dimmer devices for general lighting (using Triac) are available.

Hereinafter, an LED driving circuit according to an embodiment of the present invention will be described with reference to the accompanying drawings. Prior to the detailed description of the present invention, the terms or words used in the specification and claims described below should not be construed as being limited to the ordinary or dictionary meanings. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only one of the most preferred embodiments of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

(First embodiment)

3 is a circuit diagram of the LED driving circuit according to the first embodiment of the present invention, Figures 4 and 5 are views for explaining the operation of the circuit of FIG.

The LED driving circuit of the first embodiment includes a voltage detector 50, a plurality of LED modules 60 and 62, and a switching unit 70.

The voltage detector 50 detects the level of the voltage input through the rectifier (not shown). The voltage detector 50 includes voltage divider resistors R1 and R2, a zener diode ZD, and a transistor Q1. The voltage detector 50 compares the voltage divided by the voltage dividing resistors R1 and R2 with a Zener voltage (preset) of the Zener diode ZD and detects a level of a voltage currently input. One end of the zener diode ZD is connected to the intermediate node of the voltage divider R1 and R2 connected in series with each other, and the other end of the zener diode ZD is connected to the base (control terminal; first end) of the transistor Q1. do. The collector of the transistor Q1 is connected to one end of an AC input terminal (not shown) via the resistor R3. The emitter of transistor Q1 is connected to the other end of an AC input terminal (not shown). Of course, one end of the resistor R1 is connected to one end of an AC input terminal (not shown) and the other end of the resistor R1 is connected to the other end of an AC input terminal (not shown). .

The voltage detector 50 turns on the transistor Q1 when the level of the currently input voltage is high, and turns off the transistor Q1 when the level of the currently input voltage is low. Accordingly, the voltage detector 50 outputs a low level switching control signal informing of the high voltage being input. The voltage detector 50 outputs a switching control signal of a high level indicating when the level of the current input voltage is low.

The LED module 60 has a plurality of LEDs D1 to D3 connected in series with each other and is connected to one end of an AC input terminal (not shown). The LED module 62 has a plurality of LEDs D4 to D6 connected in series with each other, and is connected in series to the LED module 60.

The switching unit 70 is turned on / off according to the switching control signal from the voltage detecting unit 50 to selectively apply power to the LED modules 60 and 62. The switching unit 70 has a base (control stage; first stage) connected to the collector of the transistor Q1, a collector connected between the LED modules 60 and 62, and an emitter connected to the other end of the AC input terminal (not shown). (I.e., the portion where the emitter of transistor Q1 is connected). For example, transistor Q2 is an NPN transistor similar to transistor Q1.

The switching unit 70 is turned on when the switching control signal from the voltage detecting unit 50 is at a high level. That is, when the input AC voltage is a low voltage, power from an AC input terminal (not shown) is applied only to the LED module 60 as illustrated in FIG. 4. As shown in FIG. 4, an operation of applying AC power to only the LED module 60 is referred to as "A" operation.

The switching unit 70 is turned off when the switching control signal from the voltage detection unit 50 is at a low level. That is, when the input AC voltage is a high voltage, power from the AC input terminal (not shown) is applied to the LED modules 60 and 62 as illustrated in FIG. 5. As shown in FIG. 5, an operation of applying AC power to all the LED modules 60 and 62 is referred to as "B" operation.

That is, since the switching unit 70 is turned on / off according to the switching control signal of the voltage detection unit 50, the AC voltage input to the LED modules 60 and 62 is selectively performed.

6 is a waveform diagram comparing the operation waveform of the circuit of the first embodiment of the present invention with the existing operation waveform.

In the conventional case, since the current flows in the circuit only when the magnitude of the input AC voltage (see waveform 72) is greater than the value capable of operating all the LEDs included in the connected LED modules 60 and 62, the dead zone This was largely formed.

However, according to the first embodiment of the present invention, when the input AC voltage is a low voltage, an AC voltage is first applied only to the LED module 60 ("A" operation section), and when the input AC voltage becomes a high voltage, the LED module AC voltage is also applied to the 62 (operation section "B"). In the case of the first embodiment of the present invention, the dead zone is formed smaller than before. In FIG. 6, reference numeral 74 denotes an existing operation waveform, and reference numeral 76 denotes an operation waveform of the first embodiment of the present invention.

In other words, according to the first embodiment of the present invention, since most of the AC voltage input to the installed LED modules 60 and 62 can be used as the driving power source, efficiency or power factor is significantly improved compared with the conventional art.

(Second embodiment)

7 is a circuit diagram of the LED driving circuit according to the second embodiment of the present invention, Figures 8 and 9 are views for explaining the operation of the circuit of FIG.

The LED driving circuit of the second embodiment includes the voltage detector 120, the plurality of LED modules 130 and 140, the switching units 150 and 160, and the path forming helper D7. Reference numeral 110 in FIG. 7 is a connector connected to an AC input terminal.

The voltage detector 120 detects the level of the voltage input through the rectifier 110. The voltage detector 120 includes voltage dividing resistors R11 and R12, a zener diode ZD, and switching elements Q1 and Q2 (NPN type transistors). The voltage detector 120 compares the voltage divided by the voltage dividing resistors R11 and R12 with a Zener voltage (preset) of the Zener diode ZD to detect a level of a voltage currently input. One end of the Zener diode ZD is connected to an intermediate node of the divided resistors R11 and R12 connected in series with each other, and the other end of the Zener diode ZD is connected to a base (control stage; first stage of the first switching element Q1). ) Is connected. The collector of the first switching element Q1 is connected to one end of an AC input terminal (not shown) via the resistor R13. The emitter of the first switching element Q1 is connected to the other end of an AC input terminal (not shown). The base of the second switching element Q2 is connected between the resistor R13 and the collector of the first switching element Q1 via a resistance. The collector of the second switching element Q2 is connected to one end of the AC input terminal via a resistance, and the emitter of the second switching element Q2 is connected to the other end of the AC input terminal.

The voltage detector 120 turns on the first switching element Q1 and turns off the second switching element Q2 when the level of the current input voltage is a high voltage. The voltage detector 120 turns off the first switching element Q1 and turns on the second switching element Q2 when the level of the current input voltage is low.

The LED module 130 includes a plurality of LEDs D1 to D3 connected in series to each other and is connected to one end of an AC input terminal (not shown). The LED module 140 includes a plurality of LEDs D4 to D6 connected in series to each other and is connected to the other end of an AC input terminal (not shown).

The switching unit includes a first switching unit 150 and a second switching unit 160. Of course, the number of switching units may be increased according to the number of LED modules.

The first switching unit 150 and the second switching unit 160 are turned on by a switching control signal indicating parallel driving from the voltage detecting unit 120. The first switching unit 150 and the second switching unit 160 are turned off by a switching control signal indicating series driving from the voltage detection unit 120.

The first switching unit 150 includes an NMOSFET Q3 having a gate connected to the collector of the second switching element Q2 and a drain and a source connected between the LED modules 130 and 140. The second switching unit 160 includes an NMOSFET Q4 having a gate connected between the collector of the first switching element Q1 and the base of the second switching element Q2 and a drain and a source connected between the LED modules 130 and 140. It consists of

The path forming helper assists in the formation of a corresponding AC voltage application path in parallel driving or series driving by the switching unit. Preferably, the path forming help is comprised of diode D7. One end of the diode D7 is connected between the LED module 130 and the second switching unit 160, and the other end of the diode D7 is connected between the first switching unit 150 and the LED module 140.

When the voltage detector 120 determines that the level of the voltage currently input is a low voltage, the first switching device Q1 is turned off and the second switching device Q2 is turned on. Accordingly, the first switching unit 150 and the second switching unit 160 are both turned on. Thus, as shown in FIG. 8, the LED modules 130 and 140 are driven in parallel.

In contrast, when the voltage detector 120 determines that the level of the voltage currently input is the high voltage, the first switching device Q1 is turned on and the second switching device Q2 is turned off. Accordingly, both the first switching unit 150 and the second switching unit 160 of the switching unit are turned off. Thus, as shown in FIG. 9, the LED modules 130 and 140 are driven in series.

According to the second embodiment of the present invention, when the input AC voltage is a low voltage, the plurality of LED modules 130 and 140 are driven in parallel, and when the input AC voltage becomes a high voltage, the plurality of LED modules 130 and 140 are ) Is driven in series. Since almost all of the AC voltage inputted to the installed LED modules 130 and 140 can be used as a driving power source, efficiency or power factor is significantly improved compared with the related art.

On the other hand, the second embodiment of the present invention can also be driven by DC voltage. For example, when a low voltage of about 12V is applied, the plurality of LED modules 130 and 140 are driven in parallel, and when a high voltage of about 24V is applied, the plurality of LED modules 130 and 140 are driven. Driven in series. That is, when the circuit of the second embodiment is applied to the DC power supply, the DC 12V operates normally in parallel driving, and the DC 24V operates normally in series driving.

The present invention is not limited only to the above-described embodiments, but may be modified and modified without departing from the scope of the present invention, and the technical spirit to which such modifications and variations are applied should also be regarded as belonging to the following claims. .

1 is an example of an LED driving circuit driving with a conventional AC voltage.

2 is an input waveform and an operating waveform for the circuit of FIG.

3 is a circuit diagram of the LED driving circuit according to the first embodiment of the present invention.

4 and 5 are diagrams for describing an operation of the circuit of FIG. 3.

6 is a waveform diagram comparing the operation waveform of the circuit of the first embodiment of the present invention with the existing operation waveform.

7 is a circuit diagram of the LED driving circuit according to the second embodiment of the present invention.

8 and 9 are diagrams for describing an operation of the circuit of FIG. 7.

Claims (13)

A voltage detector for detecting whether an input AC voltage is a low voltage or a high voltage and outputting a switching control signal corresponding thereto; And And a switching unit provided between the plurality of LED modules connected to the AC input terminal in series, and sequentially applying AC voltage to the plurality of LED modules based on the switching control signal from the voltage detection unit. LED drive circuit. The method according to claim 1, And the voltage detector outputs a low level switching control signal when the current input voltage is high voltage, and outputs a high level switching control signal when the current input voltage is low voltage. The method according to claim 1, The voltage detector includes a Zener diode having one end connected to an intermediate node of a plurality of resistors connected in series between both ends of an AC input terminal, and a first end connected to the other end of the Zener diode, and a second end connected to the voltage detector. An LED drive circuit comprising a connected switching element. The method of claim 3, The switching device is an LED driving circuit, characterized in that consisting of NPN transistor. The method according to claim 1, The switching unit LED driving circuit, characterized in that consisting of NPN transistor. A voltage detector for detecting whether an input AC voltage is a low voltage or a high voltage and outputting a switching control signal of a series driving or a parallel driving corresponding thereto; A switching unit disposed between a plurality of LED modules connected to an AC input terminal and configured to cause the plurality of LED modules to be driven in parallel or in series according to a switching control signal from the voltage detector; And And a path forming helper for forming an AC voltage application path corresponding to the parallel driving or the series driving by the switching unit. The method according to claim 6, The voltage detector outputs a switching control signal for serial driving when the current input voltage is high voltage, and outputs a switching control signal for parallel driving when the current input voltage is low voltage. LED driving circuit. The method according to claim 6, The voltage detector includes a Zener diode having one end connected to an intermediate node of a plurality of resistors connected in series between both ends of the AC input terminal, a first end connected to the other end of the Zener diode, and a second end and a third end connected to each other. And a second switching element connected to both ends of the AC input terminal, and a second switching element connected to the first switching element and performing a switching operation opposite to that of the first switching element. The method according to claim 8, And the voltage detector is configured to turn off the first switching element and turn on the second switching element when the input AC voltage is a low voltage. The method according to claim 8, And the voltage detector is configured to turn on the first switching element and turn off the second switching element when the input AC voltage is a high voltage. The method according to claim 8, And said first switching element and said second switching element comprise NPN transistors. The method according to claim 6, And the switching unit includes the same number of switching units as the number of LED modules. The method according to claim 6, And the path forming helper is composed of a diode provided between the plurality of LED modules.

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