A PWM phase control method for multi-channel LED driving

Abstract

The present application belongs to the technical field of LED driving, and particularly relates to a PWM phase control method for multi-channel LED driving. The scheme of the present application divides phases into four kinds in a PWM cycle, wherein the phases of two kinds of phases (channels 3 / 4) are just opposite in opening and closing to offset the up and down rush effects, and meanwhile, channels 1 / 2 can offset the up and down rush effects at the end of the first PWM cycle and the beginning of the first channel in the next PWM cycle, and the processing of the switching positions of the PWM signals of the four groups of phases can greatly reduce the influence of the opening and closing of the channels on the power supply.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of LED driving, and particularly relates to a PWM phase control method for multi-channel LED driving. BACKGROUND

[0002] In a multi-channel LED driver, the PWM method is generally used to control the brightness of LEDs, and the LED driver controls the brightness of the LEDs driven by each channel by controlling the PWM signal of the channel, such as a commonly used LED chip and application structure as shown in Figure 1 If there is no phase processing, the PWM opening of the four channels is the same clock cycle, and the undershoot problem is very serious, such as Figure 2 A hardware solution is to add a capacitor at the power supply to reduce the overshoot / undershoot problem of the power supply, which causes power supply interference and EMI problems, thus increasing the system cost.

[0003] Figure 3 A commonly used 90-degree phase processing method is shown in the figure, and the four groups of PWM are self-differentiated by 1 / 4 PWM period. In this way, the misplacement can be achieved when the PWM is opened. This method avoids the PWM opening situation, but it does not solve the problem of 4 PWM simultaneous undershoot. From Figure 4 , this phase processing method does not have any improvement in the worst case. SUMMARY

[0004] In view of the above problems, the present application provides a PWM phase control method for multi-channel LED driving.

[0005] The technical scheme of the present application is:

[0006] A PWM phase control method for multi-channel LED driving, defining the number of LED channels as 4, providing PWM signals for the four channels through a PWM control module, the PWM phase control method comprising:

[0007] S1, obtaining the PWM duty cycle value according to the input signal of the PWM control module, and then generating the original PWM phase according to the internal clock counting, defined as PWM_CNT;

[0008] S2, defining the PWM period parameter PWM_PERIOD, so that in a PWM period, the value range of PWM_CNT is represented as 0~PWM_PERIOD-1, and the value of PWM_PERIOD is 2 n , n is the number of bits;

[0009] S3, generating the PWM_CNT values corresponding to the four channels respectively:

[0010] PWM_CNT1 = PWM_CNT;

[0011] PWM_CNT2 = PWM_PERIOD - 1 - PWM_CNT;

[0012] PWM_CNT3 = (PWM_CNT < PWM_PERIOD * 1 / 2)? (PWM_CNT + PWM_PERIOD * 1 / 2) :

[0013] (PWM_CNT - PWM_PERIOD * 1 / 2) ;

[0014] PWM_CNT4 = (PWM_CNT < PWM_PERIOD * 1 / 2)? (PWM_PERIOD * 1 / 2 - PWM_CNT) :

[0015] (PWM_PERIOD * 1 / 2 + (PWM_PERIOD * 1 / 2 - 1 - (PWM_CNT - PWM_PERIOD * 1 / 2))) ;

[0016] S4, compare the PWM duty cycle value of each channel with the corresponding PWM_CNT value to obtain the PWM signal of the channel, and the specific comparison method is that the PWM signal of each channel can be obtained by comparing the size of the PWM duty cycle value of each channel with the corresponding PWM_CNT value, when the PWM_CNT of the channel is smaller than the PWM duty cycle value, the PWM signal is 1, otherwise, the PWM signal is 0.

[0017] The scheme of the application divides the phase into four kinds in a PWM period, wherein the phases of two kinds of channels (channels 3 / 4) are exactly opposite in opening and closing to offset the up and down rush effects, and channels 1 / 2 can offset the up and down rush effects when the first PWM period ends and the first channel starts in the next PWM period, and the processing of the switching positions of the PWM signals of the four groups of phases can greatly reduce the influence of the opening and closing of the channels on the power supply.

[0018] The application has the beneficial effect of effectively reducing the influence of the opening and closing of the LED channels on the power supply. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a commonly used LED chip and application structure;

[0020] Figure 2 It is a schematic diagram of the down rush problem without processing the PWM phase;

[0021] Figure 3 It is a schematic diagram of the PWM phase 90 degree skew processing method;

[0022] Figure 4 This is a schematic diagram illustrating one of the worst-case scenarios for power supply impact in the 90-degree phase edge misalignment handling method.

[0023] Figure 5 This is a schematic diagram of the four phase combinations proposed in this invention;

[0024] Figure 6 This is a schematic diagram of the phase control processing of the present invention;

[0025] Figure 7 This is a schematic diagram illustrating the power supply interference situation under the four PWM duty cycles <50% of the present invention;

[0026] Figure 8 This is a schematic diagram of power supply interference under the condition that the duty cycle of the four PWMs is >50% according to the present invention. Detailed Implementation

[0027] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0028] like Figure 5 As shown, these are the four phase combinations proposed in this invention:

[0029] Group 1 PWM: The PWM signal progresses from front to back as the PWM duty cycle increases.

[0030] Group 2 PWM: The PWM signal proceeds from back to front as the PWM duty cycle increases.

[0031] Group 3 PWM: The PWM signal is divided into two parts. As the PWM duty cycle increases, the signal first increases from the middle to the end. When the PWM duty cycle exceeds 50%, the excess portion will increase from the first cycle onwards (segment 2).

[0032] Group 4 PWM: The PWM is divided into two parts. The PWM signal increases from the middle to the front as the PWM duty cycle increases. When the PWM duty cycle exceeds 50%, the excess part will increase from the last cycle to the front (segment 2).

[0033] like Figure 6 The diagram illustrates the phase control processing of this invention. First, the PWM duty cycle value is obtained and calculated. Then, the original unadjusted phase PWM_CNT is generated based on the internal clock count. Within one PWM cycle, the value of PWM_CNT ranges from 0 to PWM_PERIOD-1. PWM_PERIOD represents different values ​​depending on the number of bits in the PWM signal. For example, if the data is 8 bits, then PWM_PERIOD is 256. The PWM_PERIOD corresponding to 9 bits of data is 512.

[0034] According to the PWM_CNT, four PWM_CNT values corresponding to four different phases (PWM_CNT1, PWM_CNT2, PWM_CNT3, PWM_CNT4) are generated

[0035] Specifically as follows:

[0036] PWM_CNT1 = PWM_CNT

[0037] PWM_CNT2 = PWM_PERIOD - 1 - PWM_CNT;

[0038] PWM_CNT3 = (PWM_CNT < PWM_PERIOD * 1 / 2)? (PWM_CNT + PWM_PERIOD * 1 / 2) : (PWM_CNT - PWM_PERIOD * 1 / 2);

[0039] PWM_CNT4 = (PWM_CNT < PWM_PERIOD * 1 / 2)? (PWM_PERIOD * 1 / 2 - PWM_CNT) : PWM_PERIOD * 1 / 2 + (PWM_PERIOD * 1 / 2 - 1 - (PWM_CNT - PWM_PERIOD * 1 / 2));

[0040] Finally, the PWM signals of the control channels are obtained by comparing the PWM duty cycle values of each group with the corresponding PWM_CNT.

[0041] As can be seen from the above, in any 1 / 2 PWM period, the maximum number of PWM signals that are simultaneously turned on and off is two groups. For an LED system divided into four groups of PWM, the worst-case overshoot / undershoot effect can be reduced by 50%, and in most cases, the effect can be reduced to 25%. Figure 7 and Figure 8 The interference of four groups of PWM duty cycles on the power supply in the case of <50% and >50% is shown.

Claims

1. A PWM phase control method for multi-channel LED driving, defining the number of LED channels as 4, and providing PWM signals to the 4 channels through a PWM control module, characterized in that, The PWM phase control method includes: S1. Obtain the PWM duty cycle value based on the input signal of the PWM control module, and then generate the original PWM phase based on the internal clock count, which is defined as PWM_CNT; S2. Define the PWM cycle number parameter PWM_PERIOD, such that within one PWM cycle, the value of PWM_CNT ranges from 0 to PWM_PERIOD-1, and the value of PWM_PERIOD is 2. n where n is the number of bits; S3. Generate the PWM_CNT values ​​corresponding to the 4 channels respectively: PWM_CNT1 = PWM_CNT; PWM_CNT2=PWM_PERIOD-1-PWM_CNT; PWM_CNT3=(PWM_CNT <PWM_PERIOD*1 / 2)?(PWM_CNT+PWM_PERIOD*1 / 2): (PWM_CNT - PWM_PERIOD * 1 / 2); PWM_CNT4 = (PWM_CNT) <PWM_PERIOD*1 / 2)?(PWM_PERIOD*1 / 2-PWM_CNT): PWM_PERIOD*1 / 2+(PWM_PERIOD*1 / 2-1-(PWM_CNT-PWM_PERIOD*1 / 2)); S4. Compare the PWM duty cycle value of each channel with its corresponding PWM_CNT value to obtain the PWM signal of that channel. The specific comparison method is: when the PWM_CNT value of the channel is smaller than its PWM duty cycle value, the PWM signal is 1; otherwise, the PWM signal is 0.

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