KR102248072B1 - Method and apparatus for driving light emitting diode using average current control - Google Patents

Abstract

The present invention relates to light-emitting diode lighting, and more particularly, to a light-emitting diode driving apparatus and method using average current control. The present invention provides an average current-controlled light-emitting diode driving apparatus, comprising: a light source including at least one light-emitting diode; A power supply for supplying power to the light source; A current control unit connected to the power supply unit and including a switch element and a sensing resistor for driving the light source PWM; It may be configured to include a control unit connected to the current control unit to control the duty value of the PWM driving so that a current value having a constant average current is applied to the light source.

Description

TECHNICAL FIELD [Method and apparatus for driving light emitting diode using average current control]

The present invention relates to light-emitting diode lighting, and more particularly, to a light-emitting diode driving apparatus and method using average current control.

Research on a light source, light emission method, driving method, etc. for lighting equipment is being conducted, and recently, a light emitting diode (LED), which has advantages such as efficiency, color diversity, and design autonomy, has been attracting attention as a light source for lighting. .

These LEDs are semiconductor devices that emit light when a voltage is applied in the forward direction, and have a long lifespan, low power consumption, and have electrical, optical, and physical properties suitable for mass production.

In order to use such an LED for lighting, a driving circuit capable of stably driving the LED is required.

The power characteristic that can implement LED lighting is one of the main factors that determine the overall performance. Since the light output of the LED varies according to the fluctuation of the power supply, power safety is very important to keep the light output constant. In addition, due to the characteristics of LED lighting that must stably and constantly control its brightness, a constant current control method is preferred in the driving circuit of the LED lighting.

However, a situation in which the current applied to the LED fluctuates together with fluctuations in the input voltage and the temperature of the LED, and there is a need for a way to efficiently control this.

1. Patent Publication No. 10-2014-0053651 (2014.05.08)

The technical problem to be achieved by the present invention is to provide a light emitting diode driving apparatus and method using average current control that enables a light source to be driven at a constant luminous flux.

As a first aspect of achieving the above technical problem, the present invention provides an average current control light emitting diode driving apparatus, comprising: a light source including at least one light emitting diode; A power supply for supplying power to the light source; A current control unit connected to the power supply unit and including a switch element and a sensing resistor for driving the light source PWM; It may be configured to include a control unit connected to the current control unit to control the duty value of the PWM driving so that a current value having a constant average current is applied to the light source.

Here, the control unit may use an MCU including an ADC terminal.

In this case, applying a current value having a constant average current may be performed by detecting a peak current flowing through the light source through the sensing resistor and applying an average current function.

In this case, the peak current may be sensed by applying a voltage value applied to the sensing resistor to the ADC terminal of the MCU.

In addition, the average current function may be applied such that the product of the peak current and the duty is constant.

Here, a current sensing terminal connected to the control unit may be further included between the switch element and the sensing resistor.

Here, the power supply unit includes a transformer having a primary winding and an auxiliary winding on a primary side and an output winding on the secondary side; A rectifier connected to the primary winding of the transformer and rectifying AC power; A secondary rectifier connected to the secondary output winding of the transformer; And a capacitor that transfers the voltage rectified through the secondary rectifier to the light source.

In this case, it may further include a photo coupler connected between the capacitor and the control unit to adjust the amount of energy transferred from the primary side to the secondary side of the transformer.

As a second aspect of achieving the above technical problem, the present invention provides a method of driving a light emitting diode using average current control, the method comprising: receiving a voltage value flowing through a light source and converting it into a digital signal; Detecting a peak current flowing through a light source using the voltage value; Applying an average current function to the light source such that an average current is applied to a constant current value; It may be configured to include the step of PWM driving the light source by adjusting the duty value by applying the average current function.

Here, the average current function may be applied so that the product of the peak current and the duty is constant.

Here, in the detecting of the peak current, a voltage value applied to a sensing resistor connected to the light source may be digitally converted and sensed.

The present invention has the following effects.

Regardless of fluctuations in the input voltage and LED temperature, the LED can be driven with a constant current value with an average current, so a constant current can be supplied to the LED at all times.

In addition, since there are no additional parts, the circuit is simple and it is possible to implement a miniaturized circuit at a low cost.

On the other hand, it is possible to control the LED current by applying a specific function, so it is possible to implement the lighting applied with the desired designed current value.

1 is a circuit diagram showing a first example of a current control circuit of a light emitting diode driving device.
Fig. 2 is a schematic diagram showing a current waveform when driving an LED by the circuit of Fig. 1;
3 is a circuit diagram showing a second example of the current control circuit of the light emitting diode driving device.
4 is a circuit diagram showing a third example of the current control circuit of the light emitting diode driving device.
5 is a circuit diagram showing a fourth example of a current control circuit of a light emitting diode driving device.
6 is a circuit diagram showing a fifth example of the current control circuit of the light emitting diode driving device.
7 is a schematic diagram showing a current waveform when driving an LED by the circuit of FIG. 6.
8 is a flowchart illustrating a method of driving a light emitting diode using average current control.

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

While the present invention allows various modifications and variations, specific embodiments thereof are illustrated and shown in the drawings, and will be described in detail below. However, it is not intended to limit the present invention to the particular form disclosed, but rather the present invention includes all modifications, equivalents, and substitutions consistent with the spirit of the present invention as defined by the claims.

When an element such as a layer, region or substrate is referred to as being “on” another component, it will be understood that it may exist directly on the other element or there may be intermediate elements between them. .

Although terms such as first, second, etc. may be used to describe various elements, components, regions, layers and/or regions, these elements, components, regions, layers and/or regions It will be understood that it should not be limited by these terms.

1 is a circuit diagram showing a first example of a current control circuit of a light emitting diode driving device.

FIG. 1 is an example of a current control circuit for driving a light emitting diode (LED), and power applied from a power supply unit may be controlled by a switch element Q1 controlled by the MCU 10. A sensing resistor R1 may be connected to the switch element Q1.

In this way, by controlling the on/off of the switch element Q1 by the PWM (pulse width modulation) signal output from the MCU 10, the current flowing through the LED (LED current; I _LED ) can be controlled. I can.

At this time, by controlling the on/off of the switch element (Q1), the LED can be dimmed, and when the switch element (Q1) is turned off, the current flowing through the _LED (I LED) is blocked, and the switch When the device (Q1) is turned on, the LED voltage (V _LED ) _{divided by the input voltage (V IN} ), the switch device voltage (V _MOSFET ), and the resistance (R1) voltage (V _{R) as shown in Equation 1 below.} The LED current (I _LED ) is controlled by the and LED temperature.

However, in this case, accordingly, the LED current may also fluctuate according to fluctuations in the input voltage and the LED temperature.

Fig. 2 is a schematic diagram showing a current waveform when driving an LED by the circuit of Fig. 1;

As mentioned above, since the LED current may also fluctuate according to fluctuations in the input voltage and the LED temperature, etc., as shown in FIG. 2, the average current of the LED may not maintain a constant value. In FIG. 2, P is an LED peak current, and D is a duty during PWM driving.

Therefore, the luminous flux of the LED lighting device may fluctuate according to fluctuations in the input voltage and the LED temperature.

3 is a circuit diagram showing a second example of the current control circuit of the light emitting diode driving device.

3 shows a linear LED current control circuit, and by controlling a constant current to flow through the resistor R2 by an operational amplifier (OP AMP; OP1), the LED current I _LED can be controlled at a constant current. .

By such control, the current flowing through the LED (I _LED ) can be constantly controlled. That is, the average current and the light flux can be kept constant.

In this current control circuit, since all voltages other than the LED voltage and the constant resistance R1 voltage are applied to the switch element Q2, it is advantageous to use the switch element Q2 such as a high-power MOSFET.

However, in the case of a high-power MOSFET, the price is high and the size is large, so there may be limitations in designing a small and inexpensive circuit.

Fig. 4 is a circuit diagram showing a third example of the current control circuit of the light emitting diode driving device, and Fig. 5 is a circuit diagram showing the fourth example of the current control circuit of the light emitting diode driving device.

Here, FIG. 4 shows a buck converter type LED current control circuit, and FIG. 5 shows a high-side buck converter type LED current control circuit.

The step-down converter-type circuit as shown in FIGS. 4 and 5 shows a method of controlling _{the LED current I LED with a constant current using the LED driver IC 30.}

The step-down converter-type circuit as shown in FIGS. 4 and 5 controls the switch elements Q3 and Q4 using the LED driver 30, and the power delivered from the power source is stored in the inductors L1 and L2, and then the diode ( It is induced and transmitted to the output (LED) side by D1, D2).

As described above, a DC-DC converter type control circuit or a linear control circuit such as a step-down converter has high efficiency and can stably maintain an average current and a light flux stably.

However, such a circuit may have limitations in designing a small low-cost circuit because components such as the LED driver IC 30, inductors L1 and L2, and capacitors are essentially used.

6 is a circuit diagram showing a fifth example of the current control circuit of the light emitting diode driving device.

Referring to FIG. 6, the current control circuit includes a light source including at least one light emitting diode (LED), a current controller including a switch element Q5 and a sensing resistor R4 for PWM driving the light source, and the LED. It may be configured to include a control unit 100 for controlling the duty value of the PWM driving so that the average current applies a constant current value.

Here, a current sensing terminal 110 connected to the controller 100 may be connected between the switch element Q5 and the sensing resistor R4.

Here, as the power supplied to the LED, various power units capable of supplying DC power capable of driving the LED may be used.

For example, the power supply unit 20 as published in the prior art document may be used as the power supply unit, and this power supply unit 20 may be connected to an LED to supply an _{LED driving current (I LED).} Hereinafter, reference numerals of the power supply unit 20 refer to FIG. 2 of the prior art document.

As a specific example of such a power supply unit 20, an insulation type using a transformer T1 may be used.

An AC power supply of 100 V or 220 V is connected to the input power supply 21, and a rectifying unit 23 is connected to the power supply 21. The rectifying unit 23 may use a full-wave rectifying circuit using a bridge diode.

An EMI filter 22 for reducing electromagnetic interference (EMI) may be provided between the power source 21 and the rectifier 23.

A transformer T1 is connected to the rectifying part 23, and a fly-back transformer may be used as the transformer T1.

Such a transformer T1 has a main winding P1 and an auxiliary winding P2 on a primary side, and an output winding S1 on a secondary side.

A power controller 24 for controlling a discontinuous current mode (DCM) is connected to the main winding P1 and the auxiliary winding P2 of the transformer T1.

The secondary output winding S1 of the transformer T1 is connected to a secondary rectifying unit 25 and a capacitor 26 for transferring the rectified voltage to the load side through the secondary rectifying unit 25.

A feedback circuit 28 connected to the control unit 24 through a photo coupler 27 is connected to the secondary rectifying unit 25 and the capacitor 26.

The feedback circuit 28 adjusts the amount of energy transferred from the primary side to the secondary side by setting a reference voltage to generate a current in a photo coupler composed of a photodiode and a phototransistor.

Here, the power control unit 24 may be the same as described above, that is, the control unit 100 that controls the duty value of PWM driving so that the average current applies a constant current value to the LED.

On the other hand, as the power supply unit, a simpler type of power supply unit other than the power supply unit 20 may be used. That is, any power source capable of supplying DC power capable of driving LEDs may be used. In addition, if a plurality of LEDs are properly arranged, AC power may be directly connected and used.

Here, the controller 100 may use a micro controller unit (MCU) including an analog to digital convertor (ADC) terminal. Hereinafter, the control unit 100 will be described as an example of an MCU.

In this case, applying a current value having a constant average current may be performed by detecting a peak current flowing through the LED through the sensing resistor R4 and applying an average current function.

This peak current can be sensed by applying a voltage value applied to the sensing resistor R4 to the ADC terminal of the MCU 100.

The application of the average current function can be applied so that the product of the peak current and the duty is constant.

As described above, in the configuration of the circuit as shown in FIG. 6, the voltage of the sensing resistor R4 is input through the ADC terminal of the MCU 100, and the peak current detection function and the average current function of the LED are applied to the PWM duty value. By changing, the average current of the LED can be controlled to a constant value or a value to which a specific function is applied. Therefore, it is possible to maintain the light flux of the LED at a constant light flux.

7 is a schematic diagram showing a current waveform when driving an LED by the circuit of FIG. 6.

As shown in FIG. 7, it can be seen that the duty is changed from D to D'as the peak current P is changed (P').

In this way, when the average current function is applied, the product of the peak current (P) and the duty (D) can be controlled to always be a constant value.

As mentioned above, since the average current can drive the LED with a constant current value regardless of fluctuations in the input voltage and LED temperature, it is possible to always supply a constant current to the LED.

In addition, since there are no additional parts, the circuit is simple and it is possible to implement a miniaturized circuit at a low cost.

On the other hand, it is possible to control the LED current by applying a specific function, so it is possible to implement the lighting applied with the desired designed current value.

8 is a flowchart illustrating a method of driving a light emitting diode using average current control.

As shown in FIG. 8, a method of driving a light source including an LED may include the following steps.

First, a step of receiving a voltage value flowing through the light source and converting it into a digital signal (S10), and detecting a peak current flowing through the light source using the voltage value (S20).

As described above, in these steps S10 and S20, a voltage value applied to the sensing resistor R4 is applied to the ADC terminal of the MCU 100 and converted into a digital signal to be sensed.

Thereafter, a step S30 of applying the average current function may be performed so that the average current applies a constant current value.

The application of the average current function can be applied so that the product of the peak current and the duty is constant.

Next, the step (S40) of PWM driving the LED by adjusting the duty value by applying the average current function may be performed.

On the other hand, the embodiments of the present invention disclosed in the specification and drawings are merely presented specific examples to aid understanding, and are not intended to limit the scope of the present invention. In addition to the embodiments disclosed herein, it is obvious to those of ordinary skill in the art that other modified examples based on the technical idea of the present invention may be implemented.

10, 100: MCU, control unit 20: power supply
30: LED driver 110: current sensing stage

Claims (10)

In the average current control light emitting diode driving device,
A light source including at least one light emitting diode;
A power supply for supplying power to the light source;
A current control unit connected to the power supply unit and including a switch element and a sensing resistor connected in series with the light source for PWM driving the light source;
A current sensing terminal provided between the switch element and the sensing resistor;
And a control unit connected to the current control unit through the current sensing terminal to control a duty value of the PWM driving so that a current value having a constant average current is applied to the light source,
Applying a current value of which the average current is constant,
It is performed by detecting a peak current flowing through the light source through the sensing resistor and applying an average current function,
The average current function is applied so that the product of the peak current and the duty is constant. The light emitting diode driving apparatus according to claim 1, wherein the control unit uses an MCU including an ADC terminal. delete The light emitting diode driving apparatus according to claim 2, wherein the peak current is sensed by applying a voltage value applied to the sensing resistor to an ADC terminal of the MCU. delete delete delete delete delete delete

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