KR20120054517A - Method and device for driving light-emitting diode - Google Patents

Abstract

PURPOSE: A driving method and apparatus of a light emitting diode are provided to reduce power loss by being established so that maximum light emitting diode modules emit light in the fixed voltage level. CONSTITUTION: A voltage source provides an AC voltage. A rectifier circuit(40) changes the AC voltage from the voltage source into a pulse DC voltage source. A current source circuit(30) is combined between the rectifier circuit and plurality of light emitting diode modules. The current source circuit provides a loop current corresponding to different current level of a positive portion of the voltage source. Two or more modules(11-15) comprise a plurality of light emitting diodes which are connected. A current guide control circuit is combined between the adjacent light emitting diode modules.

Description

METHOD AND DEVICE FOR DRIVING LIGHT-EMITTING DIODE}

The present invention relates to a driving method, and more particularly, to a method and apparatus for driving a light emitting diode (LED) with improved power factor and power utilization efficiency and reduced electromagnetic interference.

As natural energy resources are depleted, new alternative energy sources are proposed but cannot be an immediate answer to the needs of all mankind. Therefore, conservation of natural resources has become a very important issue. Thus, many electronic devices or equipment have been improved to reduce power consumption. For example, assuming that a tungsten lamp of the prior art consumes 100 units of power, only 5 units of power are converted to light and the remainder of the power is converted to heat. Therefore, the conversion efficiency of the tungsten lamp of the prior art is far from satisfying. In addition, a heat sink or cooler system may be required to dissipate heat generated from conventional tungsten lamps, which will consume additional power. Prior art lamp equipment has long had the disadvantage of low power utilization efficiency. As technology development and innovation in the semiconductor industry progress rapidly in recent years, light emitting diodes (LEDs) continue to be popular due to their long life and low power consumption, and are increasingly used in the lighting field.

As mentioned above, LEDs have the advantage of long life, low power consumption and low heat loss. All of these advantages facilitate the development of LED lighting equipment. LEDs are typically powered by a DC power supply. Therefore, when the LED is connected to an AC power source as a main power source, an LED drive circuit is provided that converts the input AC power into a pulsed DC power source so that the LED can receive DC power and emit light.

As shown in FIG. 4A, the conventional LED driving circuit 100 is connected to at least one LED 101 and is capable of receiving AC power V _AC . The LED driving circuit 100 basically includes a bridge rectifier 110 and a capacitor (C). Bridge rectifier 110 is used to rectify AC power V _AC to pulse DC power, and capacitor C drives LED 101 to stabilize the voltage of pulse DC power to emit light. As shown in FIG. 4B, a phase current circuit is further provided to maintain the current at a constant level to stabilize the brightness and chromaticity of the light emitted from the LED. Inductive reactance elements such as capacitors or inductors, if present in the circuit, will cause the voltage and current to be out of phase by the phase difference [theta], as shown in FIG. 4C. Considering the formula PF (power factor) = V (voltage) × I (current) × cosθ, since the voltage and current are out of phase in this case, the presence of the phase difference θ causes a decrease in power factor, which in turn causes power loss. Causes an increase.

Taiwan Patent No. I220047 “LED Driving Circuit” discloses an LED driving circuit as shown in FIG. 5, which is a multi-current guide control circuit composed of a power supply 51 and one or more common-ground current control units 521. 52, and a voltage detection circuit 53 for detecting a voltage level of the supplied electric power. The power source 51 is connected in series to one or more LED sets 54 each consisting of one or more LEDs. The current control unit 521 of the current guide control circuit 52 is sequentially connected to the N-electrode (negative electrode) of each LED set 54. The voltage level of the positive portion of the power supply is detected by the voltage detection circuit 53. Next, one of the current guide control circuits 52 is selectively placed in a conductive state according to the voltage level, thereby driving the appropriate number of LED sets 54 to emit light. The voltage of the positive portion of the power supplied by such a circuit design drives the LED set directly, so that the maximum number of LED sets are driven to emit light according to the voltage level without coupling to the filtered capacitors, effectively utilizing power. And increase the power factor and reduce the power loss.

However, the driving circuit described above has the following disadvantages.

1. A voltage detection circuit is needed to detect the voltage level of the positive portion of the supplied power, which complicates the circuit structure.

2. A selected one of the current guide control circuits is placed in a conductive state in an environment where the voltage detection circuit detects the input voltage level (the remaining current guide control circuits remain electrically isolated), so that a certain number of LED sets To release. If the voltage detection circuit malfunctions, no set of LEDs can be driven to emit light.

Accordingly, it is an object of the present invention to provide a driving method, and in particular, a method for directly driving a light emitting diode (LED) by AC main power without changing frequency, to improve power factor and to reduce power loss and electromagnetic interference, and To provide a device.

In order to achieve this object, the driving method according to the present invention uses a plurality of current guide control circuits for driving a plurality of LED modules, each of which is connected in parallel to constitute at least two switch circuits. At least two transistors. Each current guide control circuit is adapted to allow or prevent current from flowing immediately downstream of the LED module in response to a predetermined voltage level of the positive portion of the voltage source. Each current guide control circuit responds to a different voltage level.

As a result, the maximum number of LED modules are driven to emit light at a given voltage level, thereby achieving the purpose of utilizing power efficiently and reducing power loss.

The above and other objects, features and effects of the present invention will become more apparent with reference to the following description of the preferred embodiments in conjunction with the accompanying drawings.
1 shows schematically a drive device according to the invention;
2 is a partially enlarged view of a drive device according to the present invention;
3A illustrates the phases of a pulsed DC voltage source and a pulsed DC current source in accordance with the present invention.
Fig. 3B is a diagram showing the ON / OFF state of each LED module in half of the waveform period of supplied AC power.
4A is a schematic diagram showing a drive device of the prior art;
FIG. 4B shows the current flow by using a prior art drive with a filter circuit. FIG.
4C shows that current advances the voltage.
5 is a schematic view showing a driving circuit disclosed in Taiwan Patent No. I220047.

The present invention provides a method for driving a light emitting diode. The method includes using a plurality of current guide control circuits for driving a plurality of LED modules, each current guide control circuit comprising at least two transistors connected to constitute at least two switch circuits, each current guide The control circuits differ from each other by the response to the different current levels of the voltage source, so that each LED module under their control is selectively driven to emit light at different voltage levels. In a practical experiment, the present invention further provides a drive device as shown in FIG. 1, which includes the following components:

(1) Voltage source (Vs)

The voltage source includes a rectifier circuit 40 (e.g., bridge rectifier) so that the alternating current (AC) power received from the voltage source is converted to a pulsed direct current (DC) voltage source as shown in FIG. 3A.

(2) current guide control circuit

At least two LED modules are included in the present invention. According to the embodiment shown in FIG. 1, five LED modules 11, 12, 13, 14, 15 are included in the device, each of which has a single or a plurality of LEDs L connected in series or in parallel, or both. It includes a combination of. Preferably, the quantity of LEDs mounted in each LED module gradually increases and decreases from the LED module 11 to the LED module 15.

At least one current guide control circuit is coupled between two adjacent LED modules. According to the embodiment shown in FIG. 1, four current guide control circuits 21, 22, 23, 24 are included in the device, each of the first and second transistors 251, 252, the first through the fourth. Resistors 253, 254, 259, 250, first and second input terminals 255, 256 and first and second output terminals 257, 258.

The first and second transistors 251 and 252 have a first terminal, a second terminal and a control terminal, respectively. According to this embodiment, the first and second transistors 251 and 252 are NPN-type bipolar junction transistors (BJTs), and the first terminal, the second terminal and the control terminal are each emitter E. , Collector C and base B.

Referring to FIG. 2, the first input terminal 255 is connected in parallel to one positive electrode of the LED modules 12, 13, 14, and 15, and includes one LED module upstream of the one LED module ( 11, 12, 13, 14) in series with the other negative electrode. The second input terminal 256 is connected to the voltage source Vs to receive the rectified power. The first input terminal 255 is connected to the emitter E at the first terminal of the first transistor 251. The base B at the control terminal is connected to one end of the first resistor 253, and the collector C at the other end of the first resistor 253 and the first terminal of the second transistor 252 connects a common line. The second output terminal 256 is mounted to the second output terminal 256 through the third resistor 259. The base B at the control terminal of the second transistor 252 is connected to one end of the second resistor 254, the other end of the second resistor 254 and an emi at the second terminal of the first transistor 251. The emitter E is connected to a first output terminal 257 which is connected to the negative electrode of the LED module under control via a common line. The emitter E at the second terminal of the second transistor 252 is connected to a second output terminal connected to the other positive electrode of the LED modules 13, 14, 15 downstream of the one LED module ( 258). The fourth resistor 250 is coupled between the base B at the control terminal of the second transistor 252 and the emitter E at the second terminal.

(3) current source circuit

The current source circuit 30 is coupled between the rectifier circuit 40 and the LED module 11-15 to convert the pulsed DC voltage source into a pulsed DC current source in phase with it. Current source circuit 30 provides loop current to each LED module 11-15 to achieve a satisfactory power factor.

FIG. 3B is a diagram showing the ON / OFF state of each LED module in half of the waveform period of supplied AC power. The first LED module 11 receives sufficient current and starts emitting light when the voltage of the power supply reaches the Vs1 level. Before the voltage of the power supply is further increased to the Vs2 level to allow the second LED module to receive power, it is applied to the fourth resistor 250 coupled between the base B and the emitter E of the transistor 252. Since the applied voltage is insufficient to make this transistor conductive, the second transistor 252 in the first current guide control circuit is operated in the cut-off region and switched off. As a result, the second output terminal 258 is in an electrically separated state. On the other hand, the first transistor 251 receives the voltage from the second input terminal 256 through the third resistor 259 and thus operates in the saturation region and is switched ON so that the current is switched to the first transistor 251. Through emitter (E) and collector (C), it flows directly to the LED module immediately downstream and the current guide control circuit immediately downstream.

Similarly, the second transistor in the immediately downstream current guide control circuit is not biased conductively since the input voltage is lower than Vs2. As a result, the first transistor is turned on and allows current to flow to the next downstream LED module and the next downstream current guide control circuit.

If the voltage of the power supply rises to a level higher than Vs2 that causes current to flow to the second LED module, the applied voltage is sufficient to bias the fourth resistor 250 in the first current guide control circuit 21, and thus The two transistors 252 are forward biased and operate in the saturation region. This causes the closed circuit between the emitter E and the collector C of the second transistor 252. At this moment, the first transistor 251 is unbiased and therefore operates in the cut-off region and is switched OFF to place the first input terminal 255 in an electrically isolated state. Thus, current flows from the positive electrode of the second LED module 12 to the negative electrode through the conductive path, thereby turning on and illuminating the first and second LED modules 11 and 12. The remaining current guide control circuit has insufficient voltage to supply, so that current flows through the first transistor to the downstream LED module and then the downstream current guide control circuit. Within the time interval from t2 to t3, as shown in FIG. 3B, the voltage level of the power supply (Vs2 to Vs3) is higher than causing the current to flow to the second LED module 12, so that the first and second LEDs Only modules 11 and 12 are turned on, emitting light (as indicated in zones 1 and 2). The rest can be deduced similarly.

In order to manufacture the device according to the invention, each current guide control circuit is mounted on a circuit board and then electrically connected to each LED module. Alternatively, each current guide control circuit and each LED module are packaged together in an integrated circuit package.

The present invention employs at least two transistors to form at least two switch circuits, and serves as a current guide control circuit for controlling the LED module. The present invention provides a rectifying circuit for receiving power from a voltage source to provide a pulsed direct current (DC) voltage source, providing a loop current corresponding to different voltage levels of the positive portion of the voltage source, and being driven by each current guide control circuit. If so, provide a current source circuit that allows each LED module to emit light. Each current guide control circuit can selectively allow current to flow in response to a predetermined voltage level applied. The current guide control circuit has a fourth resistor for setting a voltage threshold level, each of which controls the flow of current through the LED module under current control. Thus, each LED module is driven to emit light within one cycle of AC main power when the corresponding current guide control circuit reaches a predetermined current threshold level. Due to the disclosed invention, the maximum number of LED modules are driven to emit light at a given voltage level, thereby achieving the object of efficient power utilization and reducing power loss.

In conclusion, the LED driving method and apparatus according to the present invention can achieve the objects and effects intended by the present invention due to the above-described structural arrangement. Although the present invention has been described with reference to the above preferred embodiments, the preferred embodiments are merely illustrative and are not intended to limit the scope of the present invention, and various modifications and changes may be made by those skilled in the art without departing from the spirit of the present invention. It will be apparent that the scope is defined in the appended claims.

11, 12, 13, 14, 15: LED module
21, 22, 23, 24: control circuit
251: first transistor
252: second transistor
253: first resistance
254: second resistance
255: first input terminal
256: second input terminal
257: first output terminal
258: second output terminal
259: third resistance
250: fourth resistance

Claims (8)

A method for driving a light emitting diode,
Providing a rectifying circuit for receiving power from the voltage source to provide a pulsed direct current (DC) voltage source;
Providing a current source circuit for providing a loop current corresponding to a different current level of the positive portion of the voltage source; And
Placing a plurality of LED modules under the control of a plurality of current guide control circuits so as to emit light when each LED module is driven by each current guide control circuit, wherein each of the current guide control circuits has a predetermined current applied thereto. At least two transistors for configuring at least two switch circuits for selectively passing current in response to the level, each current guide control circuit comprising the steps of responding to a different predetermined current level:
And when the voltage level applied to the corresponding current guide control circuit reaches the predetermined current level, each LED module is driven to emit light within one cycle of AC main power. The method of claim 1, wherein the current source circuit converts the pulsed DC voltage source into a pulsed DC current source in phase to provide the loop current to each LED module. An apparatus for driving a light emitting diode,
A voltage source for providing an AC voltage;
A rectifier circuit for converting an AC voltage from said voltage source into a pulsed direct current (DC) voltage source;
A current source circuit coupled between the rectifier circuit and a plurality of LED modules, the current source circuit adapted to convert the pulsed DC voltage source into a pulsed DC current source in phase to provide a loop current to each LED module;
At least two LED modules each comprising a plurality of LEDs connected in series, in parallel or in a combination of the two; And
At least two current guide controls coupled between adjacent LED module entities, each having first and second transistors, first to fourth resistors, first and second input terminals, and first and second output terminals. Circuit
The first input terminal is connected in parallel to the positive electrode of one LED module, upstream of the one LED module, connected in series to the negative electrode of the other LED module, the second An input terminal is connected to the voltage source through the third resistor, the first output terminal is connected to the negative electrode of the one LED module, and the second output terminal is the other one downstream of the one LED module. The LED driving device connected to the positive electrode of the LED module. The method of claim 3, wherein each of the first and second transistors includes a first terminal, a second terminal, and a control terminal, wherein the first input terminal is connected to a first terminal of the first transistor, and the first transistor is used. The control terminal of is connected to one end of the first resistor, the other end of the first resistor and the first terminal of the second transistor is coupled to the second output terminal through a common line, the control of the second transistor A terminal is connected to one end of the second resistor, the other end of the second resistor and the second terminal of the first transistor are connected to the first output terminal through a common line, and the second terminal of the second transistor is Coupled to the second output terminal, wherein the fourth resistor is coupled between a control terminal and a second terminal of the second transistor. The device of claim 4, wherein the first and second transistors are NPN-type bipolar junction transistors (BJTs), and the first terminal, the second terminal, and the control terminal are emitter, collector, and base, respectively. The LED driving device according to claim 3, wherein the LEDs mounted on each LED module gradually increase and decrease in quantity while going from upstream to downstream. The device of claim 6, wherein each of the current guide control circuits is mounted on a circuit board and electrically connected to each LED module. The device of claim 6, wherein each said current guide control circuit and each said LED module are packaged together in an integrated circuit package.

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