KR101008432B1 - Digital dimming driving circuit for led - Google Patents

Abstract

The present invention relates to a digital dimming LED driving circuit that separates the control loop frequency and the PWM frequency differently. More specifically, the control loop frequency is 1/4 times the PWM frequency, and the initial inrush current is removed by using predictive control. The present invention provides a digital dimming LED driving circuit capable of constructing a digital control system even at a high frequency PWM while reducing costs by using a control board unit (eg, MCU) having a relatively low performance as compared with the related art.

In particular, the digital dimming LED driving circuit according to the present invention comprises: a control loop frequency to control power to DC-DC converters for red, green, and blue LEDs, and to control current flowing through the red, green, and blue LED arrays. And a control board unit for supplying a PWM frequency different from the control loop frequency.

Dimming, PWM Frequency, Predictive Control

Description

DIGITAL DIMMING DRIVING CIRCUIT FOR LED}

The present invention relates to a digital dimming LED driving circuit that separates the control loop frequency and the PWM frequency differently. More specifically, the control loop frequency is 1/4 times the PWM frequency, and the initial inrush current is removed by using predictive control. According to the related art, a digital dimming LED driving circuit capable of constructing a digital control system even at a high frequency PWM while reducing costs by using a control board unit (eg, MCU) having relatively low performance can be provided.

LEDs have a high color reproducibility, and the color temperature and brightness can be adjusted in detail, so they have recently been applied to emotional lighting. In addition, the LED is a light source with a low heat loss, so the power consumption is very small compared to the incandescent bulb, and energy saving is possible. In addition, the illumination light source using the LED can realize the color of the full-color light source by the combination of the LED, excellent mechanical strength and consumes less power.

High power LEDs, on the other hand, require a driver circuit with stable operation and efficiency because the power rate exceeds 1W, unlike conventional small LEDs. In addition, since lighting products consume power of tens to hundreds of watts, driving techniques using resistors are not suitable for high efficiency LED lighting systems.

In general, driver control circuits have mainly used analog control circuits, and have externally implemented dimming digitally to construct LED lighting systems. Recently, how to digitally control the internal structure of the LED driver with the improvement of the MCU function was introduced. In particular, the digital method has its advantages as the number of LED modules increases.

Conventional digital control methods have the same control loop as the PWM frequency, providing the maximum control loop frequency that can be used digitally. This method guarantees the best performance, but is difficult to apply due to the limitations of the computational speed of the microcomputer unit (MCU) in systems with switching frequencies of several hundred kHz. This is because, when configuring the LED driver for color temperature control, the frequency is designed to be very high by digital dimming. For this reason, the frequency of the PWM is designed to be higher than the typical SMPS, and designed to be hundreds of kHz or more. As a result, when the system is configured in the conventional manner, the amount of computation of the MCU becomes too large, which increases the price of the MCU.

1 is a timing block diagram illustrating a prior art in which a control loop period and a PWM period are the same. PWM output changes from cycle to cycle. The PWM duty d ₁ to d ₉ may be the same or different depending on the situation. This method requires an ADC with a fast conversion time in a system requiring a high frequency PWM such as LED, which causes the specification of the MCU to increase.

In order to solve the above-mentioned problem, an object of the present invention is to provide a digital dimming LED driving circuit that separates the control loop frequency and the PWM frequency differently. In addition, the control loop frequency is 1/4 times the PWM frequency, the initial inrush current is eliminated by using predictive control, and the cost is reduced by using a control board part (eg, MCU) which is relatively low in performance compared to the conventional method. In addition, an object of the present invention is to provide a digital dimming LED driving circuit capable of constructing a digital control system even in a high frequency PWM.

In order to achieve the above object, the digital dimming LED driving circuit of the present invention comprises: at least one red LED array in series with a plurality of red LEDs emitting red light and at least one in series with a plurality of green LEDs emitting green light A light source unit including a green LED array and at least one blue LED array connected in series with a plurality of blue LEDs emitting blue light; DC-DC converter for red LED converts the DC voltage received from the outside into a DC voltage of a size suitable for driving the red LED array, and the DC voltage received from the outside of the size suitable for driving the green LED array. SMPS unit including a DC-DC converter for converting the DC voltage into a DC, DC-DC converter for converting the DC voltage received from the outside into a DC voltage of a size suitable for driving the blue LED array ; And supplying a control loop frequency to control power to the DC-DC converters for the red, green, and blue LEDs, and controlling the current flowing through the red, green, and blue LED arrays, and a PWM different from the control loop frequency. It includes a control board for supplying a frequency.

The control board unit may independently control power of the DC-DC converters for the red, green, and blue LEDs, and independently control currents flowing through the red, green, and blue LED arrays, respectively.

In addition, the control loop frequency is preferably 1/4 times the PWM frequency.

The control board unit may further include a prediction control table in which a sampled current value is stored to supply an initial inrush current flowing in the red, green, and blue LED arrays step by step.

In addition, the sampled current values stored in the prediction control table are preferably independent of the red, green, and blue LED arrays, respectively.

According to the present invention, a control board unit (eg, MCU) having a relatively low performance compared to the conventional method by removing initial inrush current by using predictive control in the digital dimming LED driving circuit and differently separating the control loop frequency and the PWM frequency. ), It is possible to reduce the cost, to build a digital control system even at high frequency PWM, and to control the idle time of the MCU due to the low control loop frequency. Can provide.

The digital dimming LED driving circuit according to the present invention will be clearly understood by the detailed description with reference to the following drawings showing a preferred embodiment of the present invention, including the technical effect for the above object.

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

2 is a block diagram of a digital dimming LED driving circuit according to an embodiment of the present invention.

The digital dimming LED driving circuit includes an external power supply 10, an SMPS unit 20, a light source unit 30, and a control board unit 40.

The external power supply 10 is a device for supplying DC power to the LED drive circuit.

The SMPS unit 20 converts the DC voltage received from the external power supply 10 into a DC voltage having an appropriate size to drive the light source unit 30. The SMPS unit 20 is a DC-DC converter 21 for red LEDs that converts a DC voltage of an appropriate size to drive a red LED array, and a DC for green LEDs that converts a DC voltage of an appropriate size for driving a green LED array. A direct current converter 22, and a direct current to direct current converter 23 for a blue LED which converts the direct current voltage of a size suitable for driving the blue LED array.

The light source unit 30 includes at least one red LED array 31 connected in series with a plurality of red LEDs emitting red light, at least one green LED array 32 connected in series with a plurality of green LEDs emitting green light, and blue light. A plurality of blue LEDs emitting light includes at least one blue LED array 33 connected in series.

The control board unit 40 controls the power supplied to the DC-DC converters 21, 22, and 23 for the red, green, and blue LEDs, and the red, green, and blue LED arrays 31, 32, and 33. To control the current flowing in the control loop frequency, a control frequency and a PWM frequency different from the control loop frequency are supplied. For example, such a control board unit 40 may be a microcomputer unit (MCU) serving as a controller capable of controlling a light source and a power supply.

In addition, the control board unit 40 independently controls the power of the DC-DC converters 21, 22, and 23 for the red, green, and blue LEDs. As shown in FIG. 2, the control board unit 40 supplies a signal S421 to control the power supply of the DC-DC converter 21 for a red LED, and the DC-DC converter 22 for a green LED. The signal S422 is supplied to control the power supply, and the signal S423 is supplied to control the power supply of the DC-DC converter 23 for the red LED. For example, the switching PWM frequencies of the signals S421, S422, and S423 are supplied at 350 kHz.

In addition, the control board unit 40 independently controls the current flowing through the red, green, and blue LED arrays 31, 32, and 33, respectively. As shown in FIG. 2, the control board 40 supplies the signal S431 to control the current flowing through the red LED array 31, and the signal S432 to control the current flowing through the green LED array 32. It supplies the signal S433 to control the current flowing in the blue LED array (33). For example, the dimming PWM frequency of the signals S431, S432, S433 is supplied at 100 kHz.

In addition, the red, green, and blue LED arrays 31, 32, and 33 transmit feedback signals to the control board unit 40. As shown in FIG. 2, the red LED array 31 transmits a signal S314, which is a padback signal, to the control board unit 40, and the green LED array 32 transmits a signal S324, which is a feedback signal, to the control board unit 40. ), The blue LED array 33 transmits a signal S334 which is a feedback signal to the control board unit 40.

On the other hand, the control loop frequency of the LED dimming circuit according to an embodiment of the present invention is preferably 1/4 times the PWM frequency. That is, the period of the control loop is preferably four times the PWM period.

3 is a timing block diagram illustrating a control loop period and a PWM period according to an embodiment of the present invention. The control loop period is different from the PWM period, and the control loop period is four times the PWM period. In other words, the sampling period required to control the LED is designed to be different from the PWM period. The PWM frequency can be limited to the minimum frequency value for digital dimming in the LED, so use this method to separate the control loop frequency from the PWM frequency.

In particular, in the case of lighting LEDs, the control loop frequency does not need to be fast, and thus the cost can be reduced by lowering the specification of the control board (eg, MCU). On the other hand, when the control loop frequency and the PWM frequency are differently set, when the LED array is turned off and then turned on again because the control loop frequency is reduced, it is difficult to reduce the initial inrush current requiring fast dynamic characteristics.

Accordingly, the control board unit 40 includes a prediction control table in which a sampled current value is stored to supply an initial inrush current flowing through the red, green, and blue LED arrays 31, 32, and 33 step by step. In addition, the sampled current values stored in the prediction control table have independent values for the red, green, and blue LED arrays 31, 32, and 33, respectively.

By using the prediction control table, the duty of the initial n steps can be sequenced to eliminate time consumption by ADC conversion and control, and the initial inrush current can be reduced by directly applying a PWM command. Find the optimized duty sequence with the simulation sequence. The process of finding a sequence takes advantage of the MCU's idle time. Designed much slower than the control loop frequency, the slow control loop eliminates steady-state error while the duty sequence prevents initial inrush current. As a result, it can behave like a system with fast dynamics, and the LED can be applied because it already knows the load variation.

Therefore, the operation overhead of the control board 40 may be reduced, and the specification of the control board 40 may be lowered, thereby achieving the same effects as in the prior art, thereby reducing the cost. The factor that can reduce the overload of the calculation of the control board unit 40 is because the control loop frequency of the circuit is lowered as described above (see FIG. 3), which can reduce the amount of calculation of the control board unit 40.

4 is a timing block diagram illustrating an algorithm for finding an initial duty sequence according to an embodiment of the present invention. The initial sequence creates an optimized duty sequence that limits the magnitude of the inductor current, thus solving the problem of inrush current in systems with slow dynamics.

First, the process of finding the duty sequence of FIG. 4 finds the duty by d ₁ to d ₈ using the current value stored in the prediction control table. According to an embodiment of the present invention, since the control loop period corresponds to four times the PWM period, the same duty d ₈ is repeated four times. Thereafter, the same duty d ₉ is repeated four times. Accordingly, the present invention has an advantage of reducing the problem that the amount of calculation of the control board unit 40 (for example, MCU) increases in proportion to the PWM in the digital power system using the high frequency PWM.

5 is a flowchart showing the effect of the initial inrush current removal of the LED driving circuit according to an embodiment of the present invention.

As the current i _L flowing through the inductor increases, the current value i _LED flowing through the LED increases step by step. That is, the section in which the current value (i _LED ) flowing in the _LED increases step by step corresponds to the section in which the duty sequence of FIG. 4 is found, and the section in which the current value (i _LED ) flowing in the _LED is constantly maintained It will be seen that the control loop period corresponds to each of four times the PWM period.

Accordingly, the present invention provides a control board unit having a relatively low performance compared to the conventional (for example, MCU) by removing the initial inrush current by using predictive control in the digital dimming LED driving circuit and differently separating the control loop frequency and the PWM frequency. ), It is possible to reduce the cost, to build a digital control system even at high frequency PWM, and to control the idle time of the MCU due to the low control loop frequency. Can provide.

Preferred embodiments of the present invention described above are disclosed for the purpose of illustration, and various substitutions, modifications and changes within the scope of the technical spirit of the present invention for those skilled in the art to which the present invention pertains. Changes may be made, but such substitutions, changes and the like should be regarded as belonging to the following claims.

1 is a timing block diagram illustrating a prior art in which a control loop period and a PWM period are identical.

2 is a block diagram of a digital dimming LED driving circuit according to an embodiment of the present invention.

3 is a timing block diagram according to an embodiment of the present invention in which a control loop period and a PWM period are different.

4 is a timing block diagram illustrating an algorithm for finding an initial duty sequence in accordance with an embodiment of the present invention.

5 is a flow diagram illustrating initial inrush current removal in accordance with an embodiment of the present invention.

<< Detailed description of the major symbols in the drawings >>

10. External supply power 20. SMPS part

21. DC-DC converter for red LED 22. DC-DC converter for green LED

23. DC-DC converter for blue LED 30. Light source

31.Red LED Array 32.Green LED Array

33. Blue LED Array 40. Control Board Section

Claims (5)

At least one red LED array in series with a plurality of red LEDs emitting red light, at least one green LED array in series with a plurality of green LEDs emitting green light, and at least in series with a plurality of blue LEDs emitting blue light A light source unit including one blue LED array; DC-DC converter for red LED which converts DC voltage received from the outside into DC voltage driving the red LED array, and green converts the DC voltage received from the outside into DC voltage driving the green LED array. A SMPS unit including a DC-DC converter for LEDs and a DC-DC converter for converting a DC voltage received from the outside into a DC voltage for driving the blue LED array; And Supply a control loop frequency to control power to the DC-DC converters for the red, green, and blue LEDs, and control the current flowing through the red, green, and blue LED arrays, and a PWM frequency different from the control loop frequency. Digital dimming LED driving circuit comprising a control board for supplying the. The method of claim 1, And the control board unit independently controls power of the DC-DC converters for the red, green, and blue LEDs, and independently controls the current flowing through the red, green, and blue LED arrays. The method of claim 2, And said control loop frequency is one quarter of said PWM frequency. The method of claim 3, wherein And the control board unit further comprises a predictive control table in which a sampled current value is stored to supply an initial inrush current flowing in the red, green, and blue LED arrays step by step. The method of claim 4, wherein And the sampled current values stored in the prediction control table are independent of the red, green, and blue LED arrays, respectively.

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