A Circuit, Method and Computer Program Medium for Adjusting Color Temperature with Single PWM

Abstract

The present invention relates to the technical field of LED adjustment, and discloses a circuit, a method and a computer program medium for adjusting color temperature with single PWM. The circuit includes at least two parallel-connected LED strings, and each path has at least one series-connected switching component; the present invention also discloses a method for adjusting color temperature with single PWM. The present invention is composed of at least two LED strings and at least two switching components, realizing a simple, efficient and low-cost color mixing solution for a constant-current LED driver. At the same time, the color temperature of the LED can be freely adjusted continuously between two extreme color temperatures by only controlling the duty cycle of one PWM signal. Therefore, it can be applied not only to small current or large current, but also to dimmable or non-dimmable constant-current LED drivers, effectively solving the problems of high cost and large ripple of traditional color temperature adjustment circuits.

Description

Technical Field

[0001] The present invention relates to the technical field of LED adjustment, and more specifically, to a circuit, method, and computer program medium for adjusting color temperature with a single PWM. Background Art

[0002] Nowadays, LED lighting has been widely popularized in the market, which greatly reduces the cost for users to switch to LED lamps. As the number of users increases, their requirements also increase. Currently, users not only regard dimming as a basic function but also hope to meet the needs of different scenarios and freely adjust the color temperature of the lamps.

[0003] Currently, the mainstream color temperature adjustment schemes on the market can be broadly divided into two categories: passive and active. Passive means that there is at least one passive component on the LED string, usually a resistor. By adjusting the impedance, the current flow through the LED is controlled to achieve color temperature adjustment. However, due to circuit limitations, this scheme generally adjusts the color temperature in segments, such as 2700K, 3000K, 3500K, 4000K, etc., and the number of segments is not large. In addition, because a resistor is added to control the current flow, the LED current cannot be too large, otherwise the power consumption will be relatively high, generally several hundred milliamperes. For applications that require a large current, the color temperature is generally reduced to three segments, such as 2700K, 4000K, and the color temperature when both are lit simultaneously, which is approximately 3400K, but the color temperature cannot be finely adjusted. For multi-segment or stepless color temperature adjustment, a dual-PWM active scheme is generally adopted. This scheme includes at least two switched LED constant current drive circuits to independently drive at least two strings of LEDs with different color temperatures. By controlling the current of the LED string through the dimming pins attached to the control chip, the color temperature adjustment function is achieved. For low-current applications, such as dozens of milliamperes, a linear dual-PWM scheme is also adopted.

[0004] Figure 1 For a general passive segmented color temperature adjustment circuit application, the circuit includes a group of WW yellow LED strings, such as 2700K; another group is CW white LED strings, such as 4000K. Both are connected in series with a resistor, namely R1 and R2, to adjust the current ratio of the two to achieve the required color temperature. S1 is a switch, such as a slide switch, for selecting gears.

[0005] Figure 2 For a high-current application of a general passive segmented color temperature adjustment circuit, the circuit includes a group of WW yellow LED strings, such as 2700K; another group is CW white LED strings, such as 4000K. Only a switch S1, such as a slide switch, is used to select the color temperature output.

[0006] Figure 3It is a general dual-PWM active stepless high-current color temperature adjustment circuit. This circuit includes a group of LED strings with warm white (WW) light, such as 2700K; another group is LED strings with cold white (CW) light, such as 4000K. Each group of LED strings is controlled by a switching-type LED constant current driving circuit. The current of the LED string is adjusted by the dimming pin attached to the control chip, thereby adjusting the proportion of light output to achieve the color temperature adjustment function.

[0007] Figure 4 It is a general dual-PWM linear stepless low-current color temperature adjustment circuit. This circuit includes a group of LED strings with warm white (WW) light, such as 2700K; another group is LED strings with cold white (CW) light, such as 4000K. Each group of LED strings is controlled by a linear-type LED constant current driving circuit. The current of the LED string is adjusted by the dimming pin or enable pin attached to the control chip, thereby adjusting the proportion of light output to achieve the color temperature adjustment function.

[0008] Figure 5 It is a waveform display of the color mixing signal of dual-PWM. The duty cycle of PWM1 is 0.2; the duty cycle of PWM2 is 0.8. The sum of the duty cycles of the two must be 1. When taking Figure 4 the scheme as an example, PWM1 is used to control the yellow light; PWM2 is used to control the white light. Because the share of PWM2 is larger, the color temperature will tend to be white. The waveform of the current flowing through the LED string depends on the design and can be a chopping type or a current reduction type. The chopping type can be applied not only to the switching-type constant current circuit but also to the linear constant current circuit, but the current ripple is large. The current reduction type of regulation circuit can be applied to high-current designs and can achieve zero ripple, but the cost is high.

[0009] Regarding the problems in the related art, no effective solution has been proposed yet. Summary of the Invention

[0010] Regarding the problems in the related art, the present invention proposes a single-PWM color temperature adjustment circuit, method, and computer program medium to overcome the above technical problems existing in the existing related art.

[0011] For this reason, the specific technical solutions adopted by the present invention are as follows:

[0012] According to one aspect of the present invention, a single-PWM color temperature adjustment circuit is provided. This circuit includes at least two parallel LED strings, and at least one switching component is connected in series in each path.

[0013] Preferably, this circuit includes a string of yellow light LEDs, a string of white light LEDs, field effect transistor Q1, and field effect transistor Q2;

[0014] Wherein, the string of yellow LED is connected in parallel with the string of white LED, and the field effect transistor Q1 and the field effect transistor Q2 are respectively connected in series on the string of yellow LED and the string of white LED.

[0015] Preferably, the field effect transistor Q1 is used to control one color temperature lamp string, and the field effect transistor Q2 is used to control the other color temperature lamp string.

[0016] Preferably, both the field effect transistor Q1 and the field effect transistor Q2 are N-channel enhancement mode field effect transistors.

[0017] Preferably, the circuit further includes a diode D1 and a diode D2, and the diode D1 is connected in parallel at both ends of the string of yellow LED, and the diode D2 is connected in parallel at both ends of the string of white LED.

[0018] Preferably, the diode D1 is used for overvoltage protection of the field effect transistor Q1 of the string of yellow LED, and the diode D2 is used for overvoltage protection of the field effect transistor Q2 of the string of white LED.

[0019] Preferably, during the process of adjusting the color temperature, only one channel is a PWM signal to drive one of the field effect transistors, and the other field effect transistor is at a high potential to keep it conducting. The color temperature is controlled according to the duty cycle of the PWM, from white light to warm white light. When it is adjusted to warm white light, the PWM is switched to the other field effect transistor, and the duty cycle is controlled so that the color temperature can be adjusted from warm white light to yellow light.

[0020] According to another aspect of the present invention, a method for adjusting the color temperature with a single PWM is provided, and the method includes:

[0021] Using a single PWM signal to drive one of the field effect transistors, while the other field effect transistor is at a high potential for keeping it conducting;

[0022] Controlling the color temperature through the duty cycle of the PWM, so that it is modulated from white light to warm white light. When it is adjusted to warm white light, the PWM is switched to the other field effect transistor, and the duty cycle is controlled so that the color temperature is adjusted from warm white light to yellow light.

[0023] Preferably, the method further includes using the diodes connected in parallel at both ends of the LED lamp string to provide overvoltage protection for its field effect transistors.

[0024] According to still another aspect of the present invention, a computer program medium is provided, on which a computer program is stored, and when the program is executed by a processor, the steps of the above method for adjusting the color temperature with a single PWM are implemented.

[0025] Compared with the prior art, the present invention provides a circuit and method for adjusting color temperature with single PWM, having the following beneficial effects:

[0026] The present invention is composed of at least two LED strings and at least two switching components, realizing a simple, efficient and low-cost color mixing scheme for a constant current LED driver. At the same time, the color temperature of the LED can be freely adjusted continuously between two extreme color temperatures by only controlling the duty cycle of one PWM signal. Thus, it can be applied not only to small current or large current, but also to dimmable or non-dimmable constant current LED drivers, effectively solving the problems of high cost and large ripple of the traditional color temperature adjustment circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings described herein are used to provide a further understanding of the present application, and constitute a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application, and do not constitute an improper limitation to the present application. In the drawings:

[0028] Figure 1 is a schematic application diagram of a general passive segmented color temperature adjustment circuit in the prior art;

[0029] Figure 2 is a schematic application diagram of a large current of a general passive segmented color temperature adjustment circuit in the prior art;

[0030] Figure 3 is a schematic application diagram of a general dual-PWM active continuous large current color temperature adjustment circuit in the prior art;

[0031] Figure 4 is a schematic application diagram of a general dual-PWM linear continuous low current color temperature adjustment circuit in the prior art;

[0032] Figure 5 is a schematic waveform display diagram of a color mixing signal of dual-PWM in the prior art;

[0033] Figure 6 is one of the schematic circuit diagrams of a circuit for adjusting color temperature with single PWM according to an embodiment of the present invention;

[0034] Figure 7 is another schematic circuit diagram of a circuit for adjusting color temperature with single PWM according to an embodiment of the present invention;

[0035] Figure 8 is a schematic output total actual current waveform diagram of a color temperature adjustment control scheme using single PWM in a circuit for adjusting color temperature with single PWM according to an embodiment of the present invention;

[0036] Figure 9It is a schematic diagram of the total actual current waveform output by using the dual-PWM color temperature adjustment control scheme in a single-PWM color temperature adjustment circuit according to an embodiment of the present invention;

[0037] Figure 10 It is a schematic diagram of the actual test data by using the single-PWM color temperature adjustment control scheme in a single-PWM color temperature adjustment circuit according to an embodiment of the present invention. Specific embodiments

[0038] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0039] According to an embodiment of the present invention, a circuit, a method and a computer program medium for adjusting color temperature by single-PWM are provided.

[0040] Now, the present invention will be further described in conjunction with the accompanying drawings and specific embodiments. As Figures 6 - 10 shown, according to an embodiment of the present invention, a circuit for adjusting color temperature by single-PWM is provided. The circuit includes at least two LED strings and at least two switching components, such as MOSFETs, realizing a simple, efficient and low-cost color mixing solution for a constant current LED driver.

[0041] The above circuit includes at least two LED strings with different color temperatures in parallel, and at least one switching component, such as a MOSFET, is connected in series to each path. In order to streamline the circuit, the present invention uses an eight-bit single-chip microcomputer as the PWM signal generator, and can freely adjust the color temperature of the LED as needed by only controlling the duty cycle of one PWM signal.

[0042] Specifically, the circuit includes a string of WW yellow LEDs, a string of CW white LEDs, a field effect transistor Q1 (MOSFET Q1) and a field effect transistor Q2 (MOSFET Q2);

[0043] Wherein, the string of yellow LEDs is connected in parallel with the string of white LEDs, and the field effect transistor Q1 and the field effect transistor Q2 are respectively connected in series to the string of yellow LEDs and the string of white LEDs.

[0044] The field effect transistor Q1 is used to control one color temperature lamp string, and the field effect transistor Q2 is used to control the other color temperature lamp string.

[0045] Both the field effect transistor Q1 and the field effect transistor Q2 are N-channel enhancement type field effect transistors.

[0046] The circuit further includes a diode D1 and a diode D2, and the diode D1 is connected in parallel across both ends of the string of yellow LEDs, and the diode D2 is connected in parallel across both ends of the string of white LEDs.

[0047] The diode D1 is used for overvoltage protection of the field effect transistor Q1 of the string of yellow LEDs, and the diode D2 is used for overvoltage protection of the field effect transistor Q2 of the string of white LEDs.

[0048] When adjusting the color temperature, only one channel will have a PWM signal to drive one of the MOSFETs, and the other MOSFET will be at a high potential to keep it conducting. As Figure 6 shown, the color temperature is controlled according to the duty cycle of the PWM, from white light to warm white light. When adjusted to warm white light, switch the PWM to Q2 and control the duty cycle, and the color temperature can be adjusted from warm white light to yellow light, as Figure 7 shown.

[0049] According to another embodiment of the present invention, there is provided a method for adjusting the color temperature with a single PWM, the method comprising:

[0050] Using a single PWM signal to drive one of the field effect transistors, and the other field effect transistor is at a high potential for keeping it conducting;

[0051] Controlling the color temperature through the duty cycle of the PWM, so that it is modulated from white light to warm white light. When adjusted to warm white light, switch the PWM to the other field effect transistor, and control the duty cycle so that the color temperature is adjusted from warm white light to yellow light.

[0052] In addition, the method further includes using a diode connected in parallel across both ends of the LED string to provide overvoltage protection for its field effect transistor.

[0053] According to still another embodiment of the present invention, there is provided a computer program medium, on which a computer program is stored, and when the program is executed by a processor, it implements the steps of the above method for adjusting the color temperature with a single PWM.

[0054] In summary, by means of the above technical solutions of the present invention, the present invention is composed of at least two LED strings and at least two switching components, and provides a simple, efficient and low-cost color mixing solution for a constant current LED driver. At the same time, it is possible to freely adjust the color temperature of the LED continuously between two extreme color temperatures only by controlling the duty cycle of a single PWM signal, so that it can be applied not only to small current or large current, but also to adjustable or non-dimmable constant current LED drivers, effectively solving the problems of high cost and large ripple of the traditional color temperature adjustment circuit.

[0055] The technical features of the above-described embodiments may be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification. Those of ordinary skill in the art can understand that all or part of the steps in implementing the above-described embodiment methods can be completed by instructing relevant hardware through a program. The program can be stored in a computer-readable storage medium. When the program is executed, it includes the steps described in the above methods. The storage medium, such as: ROM / RAM, magnetic disk, optical disk, etc.

[0056] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for adjusting color temperature with single PWM, characterized in that, it includes a circuit for adjusting color temperature with single PWM, the circuit includes at least two parallel-connected LED strings, and each path has at least one series-connected switching component; the circuit includes a string of yellow light LEDs, a string of white light LEDs, field effect transistor Q1 and field effect transistor Q2; wherein, the string of yellow light LEDs is connected in parallel with the string of white light LEDs, and the field effect transistor Q1 and the field effect transistor Q2 are respectively connected in series on the string of yellow light LEDs and the string of white light LEDs; the field effect transistor Q1 is used to control one color temperature lamp string, and the field effect transistor Q2 is used to control the other color temperature lamp string; both the field effect transistor Q1 and the field effect transistor Q2 are N-channel enhancement type field effect transistors; the circuit further includes diode D1 and diode D2, and the diode D1 is connected in parallel at both ends of the string of yellow light LEDs, and the diode D2 is connected in parallel at both ends of the string of white light LEDs; the diode D1 is used for overvoltage protection of the field effect transistor Q1 of the string of yellow light LEDs, and the diode D2 is used for overvoltage protection of the field effect transistor Q2 of the string of white light LEDs; During the process of adjusting the color temperature, only one channel is a PWM signal to drive one of the field effect transistors, and the other field effect transistor is at a high potential to keep it in the conducting state. The color temperature is controlled according to the duty cycle of the PWM, from white light to yellowish white light. When it is adjusted to yellowish white light, switch the PWM to the other field effect transistor and control the duty cycle, and the color temperature can be adjusted from yellowish white light to yellow light; It includes the following method: using a single PWM signal to drive one of the field effect transistors, and the other field effect transistor is at a high potential to keep it in the conducting state; Controlling the color temperature through the duty cycle of the PWM, so that it is modulated from white light to yellowish white light. When it is adjusted to yellowish white light, switch the PWM to the other field effect transistor and control the duty cycle so that the color temperature is adjusted from yellowish white light to yellow light; The method further includes using a diode connected in parallel at both ends of the LED string to provide overvoltage protection for its field effect transistor; Only by controlling the duty cycle of a single PWM signal, stepless adjustment of the color temperature of the LED can be achieved between two extreme color temperatures. It can be applied not only to small currents or large currents, but also to adjustable or non-adjustable constant current LED drivers.

2. A computer program medium, characterized in that, A computer program is stored thereon, and when the program is executed by a processor, the steps of the method for adjusting color temperature with single PWM described in claim 1 are implemented.

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