KR100979835B1 - Constant Current Driver for LED Lighting System - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for supplying a constant current to light emitting diodes used in various lighting systems. The present invention can easily supply a constant current to a light emitting diode without using expensive devices such as a constant current driver integrated circuit (IC) or a microprocessor. In particular, by using a feedback resistor element having a negative feedback effect on a load transistor supplying a constant current to the light emitting diode, the constant current can be supplied at all times by reducing the variation of the driving current which may appear due to the characteristics of each transistor. The diode can be driven stably.

Light emitting diode, constant current, supply, feedback resistor, transistor, lighting

Description

Constant Current Driver for LED Lighting {Constant Current Driver for LED Lighting System}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current supply device for light emitting diode lighting, and more particularly, to a device for supplying a constant current to a light emitting diode used in various lighting systems using light emitting diodes (LEDs).

Light Emitting Diode (LED) is a light emitting device manufactured using a semiconductor manufacturing process. Since the phenomenon of light emission occurs when voltage is applied to a semiconductor device in the 1920s, it has been put into practical use since the late 1960s. Research and development related to this have been done steadily.

Recently, due to various advantages of light emitting diodes, there is a growing interest in light emitting diodes that have light characteristics that can replace conventional incandescent lamps. Products that replaced light emitting devices used in conventional lighting systems with fluorescent diodes or incandescent lamps Are being released one after another.

Recently, a light emitting diode lighting system having brightness characteristics comparable to existing lighting devices has been announced. However, much research is still needed in various related fields such as light emitting diode devices, packages, optical systems including light emitting diodes, and light emitting diode control circuits.

On the other hand, since the light emitting diode is a device driven by a current, a constant current must be supplied to maintain the same brightness of the light emitting diode.

To this end, in general, a constant current driving circuit is generally configured using a constant current driving integrated circuit (IC) or a microprocessor, but there is a problem in that the production cost increases due to the price of such a device.

Accordingly, the present invention has been made to solve the above problems, it is possible to simply supply a constant current to the light emitting diode without using expensive devices such as a constant current driving integrated circuit (IC) or a microprocessor and to reduce the deviation of the driving current SUMMARY OF THE INVENTION An object of the present invention is to provide a constant current supply device for light emitting diode lighting that can efficiently drive a light emitting diode for lighting.

In order to achieve the above object, the constant current supply device for LED lighting according to the present invention, the input unit for generating a constant voltage control signal in accordance with the drive control signal input to drive the light emitting diode (LED); A constant voltage generator configured to generate a constant voltage according to the constant voltage control signal generated by the input unit; A load stage switching unit connected to a load including one or more light emitting diodes and having a conductive state determined according to a constant voltage generated by the constant voltage generator; And a feedback resistor element positioned between the load stage switching unit and the ground to form a path through which the current can flow through the load stage switching unit.

The input unit includes a transistor Q1 through which the driving control signal is input to a base terminal, a current limiting resistor R1 is connected between a collector terminal of the transistor Q1 and a power supply, and a current limit is connected between the emitter terminal and the ground of the transistor Q1. The resistance resistor R2 can be configured to be connected.

In this case, the voltage applied to the collector terminal of the transistor Q1 may serve as the constant voltage control signal.

The transistor Q1 may be configured using a bipolar transistor.

The constant voltage generator includes a transistor Q2 through which the constant voltage control signal is input to a base end, a collector end of the transistor Q2 is connected to a power supply, and a current limiting resistor R3 and R4 between the emitter end and the ground of the transistor Q2. Can be configured to be connected in series.

In this case, a voltage appearing at the common contact between the resistors R3 and R4 may be used as the constant voltage.

The transistor Q2 may be configured using a bipolar transistor.

The load stage switching unit may include a bipolar transistor.

In addition, the load stage switching unit may include a metal oxide semiconductor (MOS) transistor or a field effect transistor (FET).

In this case, the load stage switching unit is applied to a constant voltage generated by the constant voltage generator in the gate terminal of the transistor, the drain terminal is connected to the power supply through a load including one or more light emitting diodes, the source terminal is the feedback resistor element It can be configured to be connected to ground through.

The load stage switching unit may further include a voltage divider resistor connected in series with a load to prevent an excessive voltage from being applied to the transistor.

The constant current supply apparatus of each embodiment includes a plurality of pairs of the load stage switching unit and the feedback resistance element, and each pair of load stage switching unit and the feedback resistance element is configured to be commonly connected in parallel to the load, You can also adjust the magnitude of the current through the load.

According to the present invention, a constant current can be supplied to a light emitting diode without using expensive devices such as a constant current driver integrated circuit (IC) or a microprocessor.

In particular, since the transistor and the resistance element can be easily configured, and the feedback resistance element is used, the variation of the driving current due to the difference in the characteristics of the transistor appearing in the manufacturing process can be minimized, thereby providing a stable constant current to the light emitting diode. Accordingly, the present invention may be applied to various electronic products such as a refrigerator, an air conditioner, a television set, and provide a high quality lighting effect to a user.

In addition, since it can be composed of only general-purpose devices, it is possible to increase the interchangeability of the components used, easy design changes, and reduce the production cost of the product.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, in a system for performing any illumination using a light emitting diode, at least one light emitting diode 12, which emits light as a current flows, allows a constant current to flow through the light emitting diode 12. A constant current supply device 11 is included to allow 12 to emit light of a constant intensity.

That is, since the light emitting diode 12 is a device driven by a current, the constant current supply device 11 must supply a current having a constant magnitude in order to maintain the constant brightness of the light emitting diode 12.

Referring to FIG. 2, the constant current supply device 20 according to the present invention may include an input unit 21, a constant voltage generator 22, a load stage switching unit 23, and a feedback resistor element 24.

The input unit 21 serves to generate a constant voltage control signal according to a drive control signal input to drive the load 12, and the constant voltage generator 22 according to the constant voltage control signal generated by the input unit 21. It plays a role of generating constant voltage.

The conduction state of the load stage switching unit 23 is determined according to the constant voltage generated by the constant voltage generator 22. The load stage switching unit 23 together with the feedback resistance element 24 supplies a current flowing through the load 12. Adjust.

The load 12 connected to the load stage switching unit 23 includes one or more light emitting diodes (# 1 to #n: n is an integer of 1 or more) as shown in FIG. 3. The load 12 is connected between the power supply and the load stage switching unit 23, and the current flowing in the load 12 is also determined according to the conduction state of the load stage switching unit 23.

The feedback resistor element 24 is positioned between the load stage switching unit 23 and the ground.

Therefore, when the load stage switching section 23 is in a conducting state, current flows along a path composed of the power source, the load 12, the load stage switching section 23, and the feedback resistance element 24.

Referring to FIG. 4, a specific embodiment of configuring a constant current supply device using a transistor and a resistance element will be described.

The input unit 21 can be configured using the transistor Q1 and the resistors R1 and R2. A driving control signal is input to the base terminal of the transistor Q1, a current limiting resistor R1 is connected between the collector terminal and a power supply, and a current limiting resistor R2 is connected between the emitter terminal and ground.

In such an embodiment, the voltage applied to the collector terminal of the transistor Q1 may serve as a constant voltage control signal.

Transistor Q1 may be configured using a bipolar transistor.

For example, the transistor Q1 may be configured using an NPN bipolar transistor. In this case, when the driving control signal is high, the NPN transistor is in a conductive state, and the constant voltage control signal is in a low state.

If the transistor Q1 is configured using a PNP bipolar transistor, the PNP transistor becomes conductive when the drive control signal is low, and the constant voltage control signal is low.

Here, the high state and the low state refer to voltages required to switch the transistor to an on state or an off state, and resistance values of the current limiting elements R1 and R2 are determined so that the constant voltage control signal has a voltage according to each situation.

The constant voltage generator 22 may be configured by using the transistor Q2 and the resistors R3 and R4. A constant voltage control signal is applied to the base terminal of the transistor Q2, the collector terminal is connected to a power supply, and between the emitter terminal and the ground. Current limiting resistors R3 and R4 are connected in series. In such an embodiment, a constant voltage may be generated at the common contact of the resistors R3 and R4.

Transistor Q2 may be configured using a bipolar transistor.

For example, transistor Q2 can be configured using a PNP bipolar transistor. In this case, the constant voltage becomes high because the PNP transistor is in a conductive state when the constant voltage control signal is low. At this time, the high state is a voltage obtained by subtracting the emitter-collector terminal voltage of the PNP transistor Q2 from the power supply voltage to R4 by the resistors R3 and R4.

If transistor Q2 is configured using an NPN bipolar transistor, the NPN transistor will be in a conductive state when the constant voltage control signal is high.

4 illustrates an example in which the load stage switching unit 23 is constituted by FETs, the load stage switching unit 23 may be constituted by a bipolar transistor or a MOS transistor, if necessary. This can be applied as it is.

In the illustrated example, the constant voltage generated by the constant voltage generator 22 is applied to the gate terminal of the FET Q4 (hereinafter referred to as transistor Q4) of the load stage switching unit 23, and the drain terminal includes one or more light emitting diodes. It is connected to the power supply via the load 12, and the source terminal is connected to the ground through the feedback resistor element R6 (24).

Therefore, the constant voltage generator 22 should be able to apply an appropriate constant voltage to the gate terminal of the transistor Q4 in accordance with the type of the transistor Q4.

In the illustrated example, when the constant voltage generated by the constant voltage generator 22 is in a high state, the transistor Q4 is in a conductive state, and is in a non-conductive state when in a low state.

In addition, the load stage switching unit 23 may be configured to further include a voltage dividing resistor R5 connected in series with the load 12 in order not to apply an excessive voltage to the drain terminal of the transistor Q4.

As described above, the feedback resistor R6 (24) is located between the load stage switching unit 23 and the ground, when the load stage switching unit 23 is in a conductive state, the power supply, the load 12, the voltage divider resistance element. Current flows through the path of R5, transistor Q4, and feedback resistor R6 (24).

Now, the embodiment described with reference to FIG. 4 will be described in more detail.

When a high state voltage is applied as the drive control signal to the base of the transistor Q1 constituting the input unit 21 as the drive control signal, the transistor Q1 is turned from the OFF state to the ON state and the resistors R1, Current flows through the transistor Q1 and the resistor R2.

At this time, if the resistance values of the current limiting resistors R1 and R2 are properly distributed, a low voltage (constant current control signal) is applied to the collector stage of the transistor Q1 to enable the transistor Q2 of the constant voltage generator 22 to conduct. The transistor Q2 is also turned on from the off state.

As a result, a current flows from the power supply via the transistors Q2, the resistors R3 and R4, and a high voltage constant voltage is applied to the resistor R4.

This constant voltage is applied to the gate terminal of the transistor Q4 constituting the load stage switching section 23 and maintains the drain current I _{D ( Q4 )} of the transistor Q4 at a constant value.

At this time, since the voltage-dividing resistor R5 as well as the load 12 is positioned at the drain terminal of the transistor Q4, an excessive voltage can be prevented from being applied to the collector terminal of the transistor Q4.

The reference voltage (constant voltage: V _{G ( Q4 )} ) applied to the gate terminal of the transistor Q4 and the drain current I _{D ( Q4 )} of the transistor Q4 may be represented by the following equations (1) and (2).

As such, the feedback resistor R6 24, which is a source resistor of the transistor Q4, may perform a function of minimizing a current error caused by the variation of the transistor Q4.

FIG. 5 is for explaining the bias stabilization function of the feedback resistance element R6 24, and is a measurement graph when transistors having different characteristics are used as the transistor Q4.

5A is a V _{GS ( Q4 )} −I _{D ( Q4 )} curve in the absence of the feedback resistor R6 (24), and the current I _{D ( Q4 )} flowing in the transistor Q4 can be expressed by the following equation (3).

Here, K _{( Q4 )} is a constant representing the characteristics of transistor Q4, and 't' represents 'threshold'.

As shown in Equation 3, when the K value and the V _t value of the transistor Q4 are the same, each transistor maintains the same current with respect to the same reference voltage V _{GS ( Q4 )} . However, as shown in FIG. 5A, each transistor Q4 (FET1, FET2) has a deviation of the V _{GS ( Q4 )} -I _{D ( Q4 )} curve due to the variation in the manufacturing process, and I _D1 , I for the same reference voltage V _G1 . Current error occurs as in _D2 .

In addition, since the drain current of the transistor Q4 is proportional to the square of the reference voltage as in Equation 3, the current error increases as the current is increased and driven.

5B is a V _{GS ( Q4 )} −I _{D ( Q4 )} curve with the feedback resistive element R6 24. The load line I _{D (Q4)} by the feedback resistance element R6 24 is as shown in Equation 2, and as a result, it can be seen that the current errors I _D3 to I _D4 are reduced.

FIG. 6 is a measurement graph when several transistors having different characteristics (O1 to O4) depending on the presence or absence of the feedback resistance element R6 (24) are used as the transistor Q4.

6A relates to the V _{GS ( Q4 )} -I _{D ( Q4 )} curve in the absence of the feedback resistor R6 (24), where the drain current of the transistor varies from about 40 to 60 mA with respect to the reference voltage V _G1 . It can be seen that there is a deviation of about 20mA.

Figure 6b shows the V _{GS (Q4)} -I _{D (Q4)} curve with a feedback resistor R6 (24) with a resistance of 10 ohms, draining the transistor for a reference voltage V _G2 equal to V _G1. It can be seen that the current varies from about 40 to 44 mA, resulting in a deviation of about 4 mA in the drain current. In other words, the variation with respect to the drain current of the transistor Q4 is greatly reduced.

On the other hand, the feedback resistor element 24 is adjustable to obtain a constant value of drain current as shown in Equation 2, and in a circuit requiring a current of several tens of mA or more, such as a light emitting diode, the feedback resistance element 24 is equal to or less than 100 ohms. It may be desirable to configure to have a resistance value of.

In addition, the feedback resistor element 24 may exhibit a negative feedback effect on temperature change or power supply fluctuation as well as the above-described bias stabilizing role.

In general, when the transistor increases in temperature or the drain voltage increases, the drain current increases even if the same gate voltage is applied.

However, when the feedback resistance element 24 is present, if the drain current increases due to an increase in temperature or drain voltage, the voltage applied to the feedback resistance element 24 also increases due to the increased drain current. When the voltage applied to the feedback resistor element 24 increases, the voltage V _GS between the gate and source terminals of the transistor decreases (since the gate voltage of the transistor is constant), so that the drain current decreases again.

As a result, when the drain current of the transistor increases due to an increase in temperature or drain voltage, the feedback resistance element 24 exhibits a negative feedback effect, thereby reducing the drain current again. It becomes insensitive to the fluctuation of the drain voltage.

Meanwhile, the constant current supply device 20 according to the present invention uses a pair of load stage switching unit and feedback resistor elements 71-1 and 72-1 to 71-k and 72-k as shown in the embodiment shown in FIG. It can be comprised so that a plurality may be included.

In this embodiment each pair of load stage switching and feedback resistor elements 71-1 and 72-1 to 71-k and 72-k are commonly connected to the load 12 in parallel and belong to the load 12. The current flowing through the light emitting diode is the sum of the currents that can be supplied through the pair of load stage switching units and the feedback resistance element.

The above-described embodiments are intended to help the understanding of the present invention, and the present invention is not limited to the above-described embodiments and can be variously modified and implemented by those skilled in the art without departing from the spirit of the present invention. to be.

1 is an overview of driving a light emitting diode;

2 is an embodiment of a constant current supply device according to the present invention,

3 is an example of a load,

4 is a specific embodiment of a constant current supply device according to the present invention;

5 and 6 are graphs of measurement of the current deviation depending on the presence or absence of a feedback resistance element when using transistors having different characteristics;

7 is another embodiment of a constant current supply device according to the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

11,20: constant current supply 12: load

21: input unit 22: constant voltage generator

23,71-1 to 71-k: load stage switching unit

24,72-1 to 72-k: feedback resistor

R1 to R6: resistor elements Q1, Q2 and Q4: transistors

Claims (10)

An input unit for generating a constant voltage control signal according to a driving control signal input to drive a light emitting diode (LED); A constant voltage generator configured to generate a constant voltage according to the constant voltage control signal generated by the input unit; A load stage switching unit connected to a load including one or more light emitting diodes and having a conductive state determined according to a constant voltage generated by the constant voltage generator; And A feedback resistor element disposed between the load stage switching unit and the ground to form a path through which the current flows through the load stage switching unit; The load stage switching unit includes a metal oxide semiconductor (MOS) transistor or a field effect transistor (FET), A constant voltage generated by the constant voltage generator is applied to a gate terminal of the transistor, a drain terminal is connected to a power source through a load including one or more light emitting diodes, and a source terminal is configured to be connected to ground through the feedback resistor element. A constant current supply for light emitting diode lighting, characterized in that. The method of claim 1, The input unit includes a transistor Q1 through which the driving control signal is input to a base terminal, a current limiting resistor R1 is connected between a collector terminal of the transistor Q1 and a power supply, and a current limit is connected between the emitter terminal and the ground of the transistor Q1. The resistance element R2 is connected, And a voltage applied to the collector terminal of the transistor Q1 serves as the constant voltage control signal. The method of claim 2, And the transistor Q1 is configured using a bipolar transistor. The method of claim 1, The constant voltage generator includes a transistor Q2 through which the constant voltage control signal is input to a base end, a collector end of the transistor Q2 is connected to a power supply, and a current limiting resistor R3 and R4 between the emitter end and the ground of the transistor Q2. Is connected in series so that the constant voltage is generated at a common contact between the resistor elements R3 and R4. The method of claim 4, wherein And the transistor Q2 is configured using a bipolar transistor. delete delete delete The method of claim 1, And the load stage switching unit further comprises a voltage divider resistor connected in series with the load to prevent an excessive voltage from being applied to the transistor. The method according to any one of claims 1 to 5, And a plurality of pairs of the load stage switching unit and the feedback resistance element, wherein each pair of the load stage switching unit and the feedback resistance element are connected in common to the load in parallel. .

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