JP2018088390A - Led lighting control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED lighting control circuit that exhibits a parabolic nonlinear curve by a current and a lighting control signal which are received.SOLUTION: An LED lighting control circuit 1 that outputs an LED current reference signal in a signal output terminal on the basis of a first PWM signal P1, comprises: a first signal adjustment circuit 10; a first branching circuit 11; a second branching circuit 12; a three resistance R3; and a first capacitance C1. The first signal adjustment circuit converts the first PWM signal into a second PWM signal P2. The first PWM signal becomes complementary of the second PWM signal. The first branching circuit includes a first resistance R1 connected in serial and a first switch Q1. One end is electrically connected to a first reference signal source 13, and the other end is electrically connected to the signal output end. The first switch is turned on/off on the basis of the second PWM signal. The second branching circuit 12 includes: a second resistance R2 connected in serial; and a second switch Q2.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an LED dimming circuit, and more particularly to an LED dimming circuit that exhibits a parabolic nonlinear curve in the current and dimming signal received by the LED.

  Light emitting diodes (LEDs) have advantages such as small volume, low power consumption, high luminous efficiency, and long lifetime, and thus are widely applied to display devices of various electronic products. In general, LEDs need to be dimmed by an LED dimming circuit, and there are various dimming methods in the LED dimming circuit. Among them, the PWM dimming method is one of the most commonly used dimming methods. One.

  In the PWM dimming method, the conventional LED dimming circuit has a single switch module, and the PWM dimming is performed by changing the duty ratio of the PWM dimming signal received by the LED dimming circuit. By adjusting the LED current reference signal output by the LED dimming circuit by controlling the operation of the LED, the LED drive circuit outputs the corresponding output current based on the LED current reference signal, and the LED brightness is adjusted To achieve. That is, the output current output from the LED drive circuit has a corresponding relationship with the LED current reference signal.

  Fig. 1 is a dimming curve diagram of the PWM dimming signal received by the conventional LED dimming circuit and the output current provided to the LED when the conventional LED dimming circuit dimmes using the PWM dimming method. is there. As shown in FIG. 1, the ideal dimming curve of the PWM dimming signal received by the conventional LED dimming circuit and the output current provided to the LED has an inverse linear relationship. In other words, the conventional LED dimming circuit, when the PWM dimming signal is reversed by the comparator and then supplied to the switch module, when the duty ratio of the PWM dimming signal becomes 0%, the LED While the 100% output current output by the LED driving circuit is received correspondingly, when the PWM dimming signal is 90%, the LED receives 10% output current correspondingly. However, in practice, as shown in Figure 1, when the duty ratio of the PWM dimming signal received by the conventional LED dimming circuit varies between 0% and 5%, other circuit functions have been added. The actual output current is 100%, and when the PWM dimming signal changes from 5% to 100%, the output current changes from 100% to 0%, and these stages have an inverse linear relationship.

  However, as can be seen from Fig. 1, the PWM dimming signal received by the conventional LED dimming circuit and the dimming curve of the output current provided to the LED are curves with an inverse linear relationship, so the user can do knob type dimming When it is necessary to adjust the LED brightness by a device such as a lighting device, if the duty of the PWM dimming signal transmitted by the dimmer is relatively small and the output current is relatively large, the LED brightness change is too slow. When the duty of the PWM dimming signal is relatively large and the output current is relatively small, the brightness change of the LED is too early. Thereby, the dimming effect becomes poor.

  Furthermore, the duty ratio of the dimming signal received by the conventional LED dimming circuit is actually only 90% at maximum, so the output current can only be adjusted to 10%, that is, the conventional LED dimming circuit The output current adjustment range is only 10% ~ 100%. With the development of science and technology, the luminous efficiency of LEDs has been further improved. For similar brightness, a smaller output current is sufficient. When the change range of the duty ratio does not change, it is expected that the adjustment range of the output current output from the LED drive circuit by the LED current reference signal is expanded from 10% -100% to, for example, 1% -100%. However, conventional LED dimming circuits cannot meet the demand.

  In view of the above circumstances, it is a problem to be solved by the present invention to develop an LED dimming circuit that can improve the above-described conventional technology.

  The present invention provides an LED dimming circuit, and the dimming effect of the conventional LED dimming circuit is poor, and the adjustment range of the output current received by the LED is too narrow to meet the demand. It aims at solving.

  In order to achieve the above object, in a preferred embodiment of the present invention, an LED dimming circuit that outputs an LED current reference signal at a signal output terminal based on a first PWM signal, the first signal adjustment Circuit, a first branch circuit, a second branch circuit, a third resistor, and a first capacitance, wherein the first signal conditioning circuit converts the first PWM signal to the second PWM signal The first PWM signal is complementary to the second PWM signal, and the first branch circuit includes a first resistor and a first switch connected in series, and the first PWM signal is complementary to the second PWM signal. One end of the branch circuit is electrically connected to the first reference signal source, the other end of the first branch circuit is electrically connected to the signal output terminal, and the first switch is based on the second PWM signal The second branch circuit includes a second resistor and a second switch connected in series, and one end of the second branch circuit outputs a signal. And the other end of the second branch circuit is electrically connected to the ground end, and the second switch is turned on / off based on the first PWM signal, and the third resistor is The LED capacitance is electrically connected between the signal output end and the ground end, and the first capacitance provides an LED dimming circuit electrically connected between the signal output end and the ground end.

FIG. 10 is a dimming curve diagram of a PWM dimming signal received by a conventional LED dimming circuit and an output current provided to the LED when the conventional LED dimming circuit performs dimming by the PWM dimming method. 1 is a circuit block diagram of an LED dimming circuit according to a first preferred embodiment of the present invention. FIG. 2 is a dimming curve diagram of a first PWM signal and an output current generated by the LED drive circuit based on the LED dimming circuit shown in FIG. FIG. 3 is a circuit block diagram of an LED dimming circuit according to a second preferred embodiment of the present invention. FIG. 5 is a waveform schematic diagram of an RC triangular wave signal output from the RC circuit of the LED dimming circuit shown in FIG.

1, 2: LED dimming circuit
10: First signal conditioning circuit
11: First branch circuit
12: Second branch circuit
13: First reference signal source
20: Rectifier circuit
21: Separation circuit
22: RC circuit
23: Second signal conditioning circuit
3: Knob type dimmer
R1: first resistor
R2: Second resistance
R3: Third resistor
R4: 4th resistor
R5: 5th resistor
C1: first capacitance
C2: Second capacitance
Q1: 1st switch
Q2: Second switch
G: Grounding end
P1: 1st PWM signal
P2: Second PWM signal
P3: Square wave signal
P4: RC triangular wave signal
S1: LED current reference signal

  Examples illustrating the features and advantages of the present invention are described below. Various modifications of the embodiments of the invention should be included within the scope of the invention. The description and drawings relating to the embodiments of the present invention are merely illustrative of the present invention and do not limit the present invention.

  FIG. 2 is a circuit block diagram of the LED dimming circuit of the first preferred embodiment of the present invention. As shown in FIG. 2, the LED dimming circuit 1 of the present invention receives the first PWM signal P1 as an input signal to the dimming circuit, and based on the first PWM signal P, the LED dimming circuit By outputting the corresponding LED current reference signal S1 at the signal output terminal of 1, the LED drive circuit (not shown) electrically connected to the LED dimming circuit 1 is based on the LED current reference signal S1, A corresponding output current is output to drive an LED (not shown) and adjust the brightness of the LED. Here, the LED current reference signal S1 and the output current output from the LED driving circuit may be proportional.

  In the present embodiment, the LED dimming circuit 1 includes a first signal adjustment circuit 10, a first branch circuit 11, a second branch circuit 12, a third resistor R3, and a first capacitance C1. The first signal adjustment circuit 10 receives the first PWM signal P1 and converts the first PWM signal P1 into the second PWM signal P2, where the first PWM signal P1 is the second PWM signal P1 Complementary to the PWM signal P2, that is, when the first PWM signal P1 is high level, the second PWM signal P2 is low level, and conversely, the first PWM signal P1 is low level In this case, the second PWM signal P2 is at a high level. The first signal adjustment circuit 10 further includes a comparator, which makes the first PWM signal P1 in the reverse direction. The present invention is not limited to this.

  The first branch circuit 11 includes a first switch Q1 and a first resistor R1 connected in series, and one end of the first branch circuit 11 is connected to the first reference signal source 13 (for example, 5V or 3.3 V voltage source), the other end of the first branch circuit 11 is electrically connected to the signal output terminal of the LED dimming circuit 1, the signal output terminal outputs the LED current reference signal S1, The 1 switch Q1 is turned on / off based on the second PWM signal P2.

  The second branch circuit 12 includes a second resistor R2 and a second switch Q2 connected in series, and one end of the second branch circuit 12 is electrically connected to the signal output terminal of the LED dimming circuit 1 Then, the other end of the second branch circuit 12 is electrically connected to the ground terminal G, and the second switch Q2 is turned on / off based on the first PWM signal P1.

  The third resistor R3 is electrically connected between the signal output terminal of the LED dimming circuit 1 and the contact terminal G, and is connected in parallel to the second branch circuit 12. The first capacitance C1 is electrically connected between the signal output end of the LED dimming circuit 1 and the contact end G, and is connected in parallel to the second branch circuit 12 and the third resistor R3. .

  FIG. 3 is a dimming curve diagram of the first PWM signal and the output current generated by the LED drive circuit based on the LED dimming circuit shown in FIG. As shown in FIG. 3, the LED dimming circuit 1 of the present invention includes not only the first switch Q1 of the first branch circuit 11, but also the second switch Q2 of the second branch circuit 12, and When the first switch Q1 is turned off and the second switch Q2 is turned on because the first switch Q1 and the second switch Q2 are controlled by the complementary second PWM signal and the first PWM signal. Since the voltage level of the LED current reference signal S1 output from the LED dimming circuit 1 is pulled down by turning on the second switch Q2, the voltage level between the first PWM signal P1 and the output current provided to the LED is reduced. The dimming curve is not an inversely linear curve but a parabolic non-linear curve. The duty of the first PWM signal P1 is relatively small and the output current is relatively large (for example, in the region close to the left in FIG. 3, the slope of the change in the output current is large and the brightness of the LED becomes faster. When the duty ratio of the first PWM signal P1 is relatively large and the output current is relatively large, the slope of the change in the output current is small and the change in the luminance of the LED is slow, so the LED dimming circuit of the present invention 1 can improve the dimming effect of the LED and is more suitable for sensing the dimming luminance change of the human eye.

  In some embodiments, as shown in FIG. 2, the first resistor R1 is electrically connected between the first reference signal source 13 and the first switch Q1. The first switch Q1 is electrically connected between the first resistor R1 and the signal output terminal of the LED dimming circuit 1. The second resistor R2 is electrically connected between the signal output terminal of the LED dimming circuit 1 and the second switch Q2. The second switch Q2 is electrically connected between the second resistor R2 and the ground terminal G. In other embodiments, the connection position of the first resistor R1 and the first switch Q1 may be exchanged with each other, and the connection position of the second resistor R2 and the second switch Q2 may be exchanged with each other. Good.

  Further, as shown in FIG. 3, the change of the LED current reference signal S1 with respect to the duty ratio of the first PWM signal P1 is actually a non-linear continuous change.

  In another embodiment, the LED dimmer circuit 1 can be coupled to a knob dimmer 3, which provides the first PWM signal P1 and the knob dimmer By turning 3, the duty ratio of the first PWM signal P1 is adjusted. Further, in the embodiment, the maximum duty ratio of the first PWM signal P1 provided by the dimmer 3 is smaller than 0.95 due to its own characteristics. However, in the present invention, the source of the first PWM signal is not limited to the knob-type dimmer, and may be another dimmer such as a slide-type dimmer. There may be. For example, an output signal by another dimming method such as a 0-10V dimming method or a variable resistance dimming method is further converted into a PWM signal.

  FIG. 4 is a circuit block diagram of the LED dimming circuit of the second preferred embodiment of the present invention. As shown in FIG. 4, a part of the structure of the LED dimming circuit 2 of the present embodiment is similar to the LED dimming circuit 1 shown in FIG. To do. Compared with the LED dimming circuit 1 shown in FIG. 2, the LED dimming circuit 2 of the present embodiment further includes a rectifier circuit 20 and a separation circuit 21. The rectifier circuit 20 receives the square wave signal P3 and rectifies the square wave signal P3 into the first PWM signal P1. The input side of the separation circuit 21 is electrically connected to the rectifier circuit 20, receives the first PWM signal P1, the output side of the separation circuit 21 is electrically connected to the first signal conditioning circuit 10, and the separation circuit 21 A coupler may be included, but is not limited to this. The separation circuit 21 transmits the first PWM signal P1 to the first signal adjustment circuit 10 by a separation method.

  The LED dimming circuit 2 may further include a fourth resistor R4 electrically connected between the first reference signal source 13 and the LED dimming circuit two-signal output terminal. The fourth resistor R4 may be configured by a variable resistor, and the resistance ratio of (fourth resistor R4 / third resistor R3) :( first resistor R1 / third resistor R3) is 19: The resistance ratio of the fourth resistor R4: the first resistor R1 may be greater than 19: 1, but the present invention is not limited to this. As can be seen from the installation of the fourth resistor R4, the maximum value of the LED current reference signal S1 is actually generated by the divided voltage of the first resistor R1, the third resistor R3, and the fourth resistor R4 ( On the other hand, the minimum value of the LED current reference signal S1 is the second resistor R2, the third resistor R3, and the fourth resistor Q1 is generated with the first switch Q1 turned on and the second switch Q2 turned off. Is generated by voltage division of the resistor R4 (generated in a state where the first switch Q1 is turned off and the second switch Q2 is turned on).

  Further, when the duty ratio of the first PWM signal P1 is larger than 90%, the output current received by the LED can be adjusted to be smaller than 10%, for example, 1%. The LED dimming circuit 2 further includes an RC circuit 22. The RC circuit 22 is electrically connected between the first signal adjustment circuit 10 and the control end of the first switch Q1, and modulates the second PWM signal P2 based on the RC time constant to By generating the triangular wave signal P4, the first switch Q1 is turned on / off based on the RC triangular wave signal P4. By filtering the second PWM signal P2 by the RC circuit 22, an RC triangular wave signal P4 having a voltage level lower than that of the second PWM signal P2 can be generated, and thus the first PWM signal P1 is gradually increased. When the voltage level of the second PWM signal P2 is gradually lowered, for example, greater than 90%, the first switch Q1 is turned off early by the RC circuit 22. In this case, since the minimum value of the LED current reference signal S1 is generated by the voltage division of the second resistor R2, the third resistor R3, and the fourth resistor R4, the third resistor R3 and the fourth resistor R4 By adjusting the resistance value, the output current received by the LED can be controlled to be smaller than 10%, for example, 1%.

  FIG. 5 is a schematic waveform diagram of an RC triangular wave signal output from the RC circuit of the LED dimming circuit shown in FIG. As shown in FIG. 5, the RC triangular wave signal P4 actually includes an approximate triangular waveform having a curve. Also, when the duty ratio of the first PWM signal P1 is greater than 90%, the RC time constant is equal to the period of the first PWM signal P1 so that the first switch Q1 is turned off earlier by the RC circuit 22. It is preferably 5% to 20%. As can be seen from the above, when the duty ratio of the first PWM signal P1 is larger than 90%, as long as the first switch Q1 is turned off, the output current received by the LED is smaller than 10%, for example, 1%. be able to. Therefore, when the duty ratio of the first PWM signal P1 is larger than 90%, the peak voltage of the RC triangular wave signal P4 becomes smaller than the ON threshold value of the first switch Q1. Thereby, the first switch Q1 can be turned off only when the duty ratio of the first PWM signal P1 is larger than 90%.

  As shown in FIG. 4, in some embodiments, the RC circuit 22 includes a second capacitance C2 and a fifth resistor R5. One end of the fifth resistor R5 is electrically connected to the first signal adjustment circuit 10, and the other end of the fifth resistor R5 is electrically connected to the control end of the first switch Q1. One end of the second capacitance C2 is electrically connected to the control end of the first switch Q1 and the other end of the fifth resistor R5, and the other end of the second capacitance C2 is electrically connected to the ground end G. .

  Further, in another embodiment, the LED dimming circuit 2 further includes a second signal adjustment circuit 23, the second signal adjustment circuit 23 receives the first PWM signal P1, and the second switch Electrically connected to the control terminal of Q2, the second signal adjustment circuit 23 is configured by a comparator, and the comparator of the second signal adjustment circuit 23 receives the first PWM signal P1, Since the signal actually output from the signal adjustment circuit 23 matches the first PWM signal P1, the second signal adjustment circuit 23 is actually used to improve the transmission accuracy of the first PWM signal P1.

  As described above, the present invention provides an LED dimming circuit. The LED dimming circuit includes not only the first switch of the first branch circuit but also the second switch of the second branch circuit, and the first switch and the second switch are each complementary. Since it is controlled by the second PWM signal and the first PWM signal, the dimming curve between the first PWM signal and the output current provided to the LED becomes a parabolic non-linear curve. The dimming circuit improves the dimming effect of the LED. In addition, since the LED dimming circuit of the present invention turns off the first switch early by the RC circuit, when the duty ratio of the first PWM signal is larger than 90%, the output current received by the LED is 10 It can be controlled smaller than%. Thus, the LED dimming circuit of the present invention meets the current demand for LED dimming.

  Those skilled in the art can make various changes and modifications to the present invention, and these changes and modifications are included in the protection scope of the present invention.

Claims (12)

An LED dimming circuit that outputs an LED current reference signal at the signal output terminal based on the first PWM signal, the first signal adjustment circuit, the first branch circuit, the second branch circuit, A third resistor and a first capacitance;
The first signal adjustment circuit converts the first PWM signal into a second PWM signal, and the first PWM signal is complementary to the second PWM signal,
The first branch circuit includes a first resistor and a first switch connected in series, and one end of the first branch circuit is electrically connected to a first reference signal source, and the first branch circuit The other end of the branch circuit is electrically connected to the signal output end, and the first switch is turned on / off based on the second PWM signal,
The second branch circuit includes a second resistor and a second switch connected in series, and one end of the second branch circuit is electrically connected to the signal output terminal, and the second branch circuit The other end of the circuit is electrically connected to the ground end, and the second switch is turned on / off based on the first PWM signal,
The third resistor is electrically connected between the signal output terminal and the ground terminal,
The LED dimming circuit, wherein the first capacitance is electrically connected between the signal output terminal and the ground terminal.   A separation circuit; and a rectification circuit, wherein the rectification circuit receives the first PWM signal, an input side of the separation circuit is electrically connected to the rectification circuit, and an output side of the separation circuit is 2. The LED dimming circuit according to claim 1, wherein the LED dimming circuit is electrically connected to the first signal adjustment circuit.   3. The LED dimming circuit according to claim 1, further comprising a fourth resistor electrically connected between the first reference signal source and the signal output terminal.    4. The LED dimming circuit according to claim 3, wherein a resistance ratio between the fourth resistor and the first resistor is larger than 19: 1.    The maximum value of the LED current reference signal is generated by dividing the first resistor, the third resistor, and the fourth resistor, and the minimum value of the LED current reference signal is the second resistor. 5. The LED dimming circuit according to claim 3, wherein the LED dimming circuit is generated by dividing a voltage of the third resistor and the fourth resistor.    The RC circuit further includes an RC circuit, and the RC circuit is electrically connected between the first signal adjustment circuit and a control terminal of the first switch, and the second PWM signal is converted based on an RC time constant. The LED adjustment according to any one of claims 1 to 5, wherein an RC triangular wave signal is generated by modulation, and the first switch is turned on / off based on the RC triangular wave signal. Optical circuit.    7. The LED dimming circuit according to claim 6, wherein the RC time constant is 5% -20% of the period of the first PWM signal.   7. The LED dimming circuit according to claim 6, wherein when the duty of the first PWM signal is larger than 0.9, the RC triangular wave signal is smaller than an ON threshold value of the first switch. The RC circuit further includes a fifth resistor and a second capacitance;
One end of the fifth resistor is electrically connected to the first signal conditioning circuit, and the other end of the fifth resistor is electrically connected to the control end of the first switch,
One end of the second capacitance is electrically connected to the other end of the fifth resistor and the control end of the first switch, and the other end of the second capacitance is electrically connected to the ground end. The LED dimming circuit according to claim 6, wherein the LED dimming circuit is provided.   2. The LED dimming circuit according to claim 1, wherein the first signal adjustment circuit further includes a comparator that reverses the first PWM signal.   The LED dimmer circuit is coupled to a knob dimmer or a slide dimmer, the knob dimmer or the slide dimmer providing the first PWM signal, and the first dimmer circuit. The LED dimming circuit according to claim 1, wherein a maximum duty ratio of the PWM signal is less than 0.95.   2. The LED dimming circuit according to claim 1, wherein a change in the duty ratio of the LED current reference signal with respect to the PWM signal according to any one of the first to eleventh aspects is a non-linear continuous change.