Long-distance low-distortion PWM dimming transmission system

Abstract

The invention provides a long-distance low-distortion PWM (Pulse Width Modulation) dimming transmission system, which comprises a CPU (Central Processing Unit), a first ADC (Analog to Digital Converter) sampling unit network and a second ADC sampling unit network, the first ADC sampling unit reads peak voltage of PWM signals within external 10V amplitude and judges whether the PWM signals are effective PWM signals or not through a 1M pull-up resistor, a 240K pull-down resistor and a 33P-100P small capacitor on the pull-down resistors. The second ADC sampling unit performs integral filtering on external PWM signals and reads average voltage through a 1M pull-up resistor, a 240K pull-down resistor and a 330NF-1UF large capacitor on the pull-down resistors, and the CPU unit processes the signals through a built-in algorithm, so that the effect of long differential transmission distance is achieved when the transmission distance of TTL level signals is short.

Description

Technical Field

[0001] The present invention relates to the technical field of LED lighting power supplies, and more specifically to a long-distance and low-distortion PWM dimming transmission technology. Background Art

[0002] In the existing LED dimming power supplies, when dimming with PWM signals, since TTL levels usually undergo significant signal distortion, attenuation, and distortion within a distance of usually less than 100 meters during long-distance transmission. This causes large brightness differences among lamps at different distances on the same line. Summary of the Invention

[0003] The present invention provides a long-distance and low-distortion PWM dimming transmission system. Aiming at the deficiencies and defects of the above prior art, the purpose of the present invention is to provide a PWM signal long-distance transmission technology, which effectively improves the transmission distance to more than 10 times that of the conventional TTL level PWM transmission scheme in actual tests in the field of LED dimming power supplies.

[0004] The technical solution of the present invention is implemented as follows: A long-distance and low-distortion PWM dimming transmission system includes a CPU unit, a first ADC sampling unit network, and a second ADC sampling unit network. The first ADC sampling unit reads the peak voltage of an external PWM signal within an amplitude of 10V and determines whether it is a valid PWM signal through a 1M pull-up resistor, a 240K pull-down resistor, and a 33P - 100P small capacitor connected in parallel with the pull-down resistor; the second ADC sampling unit reads the average voltage after integrating and filtering the external PWM signal through a 1M pull-up resistor, a 240K pull-down resistor, and a 330NF - 1UF large capacitor connected in parallel with the pull-down resistor. The CPU unit processes the signal through a built-in algorithm to achieve the effect of long differential transmission distance for the deficiency of short TTL level signal transmission distance.

[0005] The signal detection unit of the present invention includes two ADC samplings. One of them is used to collect and identify signal characteristics, and determine whether it is a PWM signal according to a software algorithm. If so, the PWM mode is locked. At this time, the second ADC is responsible for sampling the effective average voltage value.

[0006] As a preferred embodiment, the first ADC sampling network is connected to an external PWM dimming signal within an amplitude of 10V through a 1M pull-up resistor, a 240K pull-down resistor, and a 33P - 100P small capacitor to read the signal peak and determine whether the PWM signal is valid, and at the same time filter out high-frequency interference signals to prevent interference misjudgment. The sampling network has a very high input impedance and will not be damaged when accidentally connected to AC220V, ensuring system safety.

[0007] As a preferred embodiment, the second ADC sampling network is connected to the external PWM dimming signal after being integrally filtered by a 1M pull-up resistor, a 240K pull-down resistor, and a 330NF - 1UF large capacitor connected in parallel to the pull-down resistor, so as to obtain a stable average effective voltage value. The sampling network has a very high input impedance and will not be damaged when accidentally connected to AC220V, ensuring the safety of the system. Different from the first ADC sampling network, there is a 330NF - 1UF large capacitor in parallel on the pull-down resistor of this ADC, which forms an integral filtering relationship with the pull-down resistor. PWM signals above 300HZ will become stable pure DC voltage signals through this integral filtering.

[0008] As a preferred embodiment, when the CPU unit starts to work, it continuously reads the first ADC signal every 10US without interruption, and continuously compares it with the previously read value, selects the larger value to retain, and discards the smaller value. After sampling for 1MS, the maximum value is selected and saved. If there are multiple pulse signals higher than 2.5V and multiple pulse signals lower than 2.5V, the PWM dimming mode is entered. This algorithm can fully identify PWM signals of 300 - 2KHZ after testing. The reason for adopting the above processing method is that the internal reference voltage of the ADC is 2V. Therefore, after voltage division by the 1M and 240K resistors, a PWM signal with a maximum amplitude of 10V can be read. Considering that the PWM dimming signals of dimmers on the market are basically between 3.3V and 10V, the software takes special processing for peak signals below 3.3V. Due to various common-mode and differential-mode interferences generated during long-distance signal transmission, as well as signal distortion interferences caused by capacitive and inductive reactances of the line and signal zero-point drift, after actual testing, these interference signals hardly exceed 2.5V. Therefore, the final strategy is that if the signal peak is less than 2.5V, even if the signal is in a pulsating state similar to PWM, the CPU will consider the PWM signal invalid and will not enter the PWM dimming mode. This greatly enhances the system's ability to identify long-distance interference signals and enables the system to be compatible with all 3.3V - 10V dimming signals. Once the CPU unit enters the PWM dimming mode, it will continuously read the voltage of the second ADC, and calculate the average value after multiple readings. Finally, the average value is divided by the signal peak obtained from the first ADC sampling to obtain the duty cycle of the PWM signal.

[0009] As a preferred embodiment, the 2.5V voltage setting eliminates the common-mode and differential-mode interferences formed by inductance and capacitance on long-distance lines and can ensure the adaptation of PWM signals with amplitudes of 3.3V - 10V; the first ADC sampling unit network and the second ADC sampling unit network sample at the same point, and the result obtained after division is a relative value, which is not affected by the line distance.

[0010] After adopting the above technical solution, the beneficial effects of the present invention are as follows: The structure of the present invention is simple and requires fewer electronic components. Since both channels of ADC sample at the same point and the distances from the sampling point to the external dimmer are the same, the result obtained by dividing the average value of the second channel by the peak value of the first channel (i.e., the PWM duty cycle) is a relative number, and signal attenuation has no effect on it. Similar to differential transmission, it has the anti-interference ability of differential transmission. In actual engineering, the communication distance of this system exceeds 1 kilometer, far exceeding the 100 meters of ordinary TTL-level PWM on the market. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0012] Figure 1 It is the structural schematic diagram of the present invention.

[0013] Figure 2 It is the electrical schematic diagram of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0015] Embodiment:

[0016] As Figures 1-2 shown, a long-distance and low-distortion PWM dimming transmission system includes a CPU unit, a first-channel ADC sampling unit network, and a second-channel ADC sampling unit network. The first-channel ADC sampling unit reads the peak voltage of the external PWM signal within an amplitude of 10V and determines whether it is a valid PWM signal through a 1M pull-up resistor, a 240K pull-down resistor, and a small capacitor of 33P - 100P connected in parallel with the pull-down resistor; the second-channel ADC sampling unit integrates and filters the external PWM signal and reads the average voltage through a 1M pull-up resistor, a 240K pull-down resistor, and a large capacitor of 330NF - 1UF connected in parallel with the pull-down resistor. The CPU unit processes the signal through a built-in algorithm to make up for the shortcoming of the short transmission distance of the TTL-level signal and achieve the effect of the long transmission distance of the differential transmission.

[0017] The system includes four parts: an external PWM dimming signal 10, a first ADC sampling network 20, a second ADC sampling network 30, and a CPU unit 40.

[0018] When the system works, the CPU unit 40 enables the first ADC sampling network 20 to sample the external PWM dimming signal 10 once every 10 microseconds, continuously sampling 100 times for a total of 1 millisecond. Save the peak value among them. And analyze whether there are signals higher than 2.5V and signals lower than 2.5V that appear multiple times in the signal. If both exist, it is considered that the PWM signal is valid and enters the PWM dimming mode.

[0019] After the system enters the PWM dimming mode, the CPU unit 40 enables the second ADC sampling network 30 to read several times and then calculate the average value. Finally, divide the obtained average value by the peak value obtained by the first ADC sampling network 20 to obtain the duty cycle of the PWM signal. Then adjust the brightness of the lamp.

[0020] Although the external PWM dimming signal 10 received by this system is still at TTL level. However, the two ADCs sample at the same point and are at the same distance from the external PWM dimming signal 10, so the signal attenuation degree is the same. Moreover, since the second ADC sampling network 30 has been integrally filtered by a large capacitor of 330NF - 1UF and a resistor of 240K, the relative value obtained by dividing the signal average value by the signal peak is not affected by signal attenuation and is a true restoration of the PWM signal duty cycle. Therefore, it has the characteristic of differential transmission. It is measured that the brightness difference of all LED power supplies within 1 kilometer under the control of this PWM dimming signal is not significant, and it has the ability of high anti-interference over long distances. It is especially suitable for LED energy-saving lighting projects.

[0021] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A long-distance low-distortion PWM dimming transmission system, characterized in that: It includes a CPU unit, a first ADC sampling unit network and a second ADC sampling unit network. The first ADC sampling unit reads the peak voltage of an external PWM signal within an amplitude of 10V and judges whether it is a valid PWM through a 1M pull-up resistor, a 240K pull-down resistor and a small capacitor of 33P-100P on the pull-down resistor; the second ADC sampling unit integrates and filters the external PWM signal through a 1M pull-up resistor, a 240K pull-down resistor and a large capacitor of 330NF-1UF on the pull-down resistor, and then reads the average voltage. The CPU unit processes the signal through a built-in algorithm, so that the shortcoming of TTL level signal transmission is achieved by differential transmission at a long distance.

2. A long-distance low-distortion PWM dimming transmission system as claimed in claim 1, characterized in that: The first ADC sampling network described is connected to an external PWM dimming signal with an amplitude of less than 10V through a 1M pull-up resistor, a 240K pull-down resistor, and a 33P-100P small capacitor on the pull-down resistor, reads the signal peak value and determines whether the PWM signal is valid, and at the same time filters out high-frequency spike interference signals. The sampling network has a very high input impedance and will not be damaged when mistakenly connected to AC220V, thereby ensuring system safety.

3. A long-distance low-distortion PWM dimming transmission system as claimed in claim 1, characterized in that: The second ADC sampling network is connected to the external PWM dimming signal through a 1M pull-up resistor, a 240K pull-down resistor and a 330NF-1UF large capacitor on the pull-down resistor for integration filtering to obtain a stable effective average voltage value. The sampling network has a very high input impedance and will not be damaged when mistakenly connected to AC220V, thereby ensuring system safety.

4. The long-distance low-distortion PWM dimming transmission system as claimed in claim 1, characterized in that: The CPU unit samples the first ADC sampling unit network at a frequency of 10 microseconds. If multiple pulse signals higher than 2.5V and multiple pulse signals lower than 2.5V occur within 1 millisecond, the peak voltage data of PWM is saved and the PWM dimming mode is entered. Subsequently, the second ADC sampling network is sampled multiple times and the average voltage is calculated. The PWM duty cycle is restored by dividing the average voltage by the peak voltage.

5. A long-distance low-distortion PWM dimming transmission system as claimed in claim 4, characterized in that: The setting considerations of the 2.5V voltage value eliminate the common-mode and differential-mode interference formed by the inductors and capacitors on the long-distance transmission lines and can ensure that the PWM signal with an amplitude of 3.3V-10V mainstream in the industry can be adapted; the first ADC sampling unit network and the second ADC sampling unit network are sampled at the same point, and the result obtained after division is a relative value, which is not affected by the line transmission distance.

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