PWM Duty-Cycle Conversion Circuit Without Large Filter Capacitors
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Solution Overview
Problem
Existing LED dimming systems face challenges with complex peripheral circuits and high costs due to the need for large capacitors to convert PWM signals into analog signals, and digital implementations of duty cycle calculations are difficult.
Innovation Solution
A PWM signal conversion circuit and method that includes a detection module, addition module, switch signal generation, duty cycle ratio generation, and output voltage generation, allowing for the extraction of duty cycle ratios without large capacitors and enabling real-time response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low-pass filter with a large-capacity capacitor is used to convert PWM signal into analog signal, then the filtering effect is improved, but the device complexity and cost increase due to the inability to integrate the capacitor internally
Solution Approach 1:
The patent replaces the traditional RC low-pass filter (analog filtering mechanism) with a digital sampling and calculation system. The PWM signal is sampled digitally, and the duty cycle is calculated through digital operations (summing Ton and Toff values, performing division), ultimately generating an analog output voltage through a DAC. This substitution eliminates the need for large external capacitors and complex analog filtering circuits.
Solution Approach 2:
The patent introduces a digital intermediary system between the PWM input and the analog output. Instead of directly filtering the PWM signal with a capacitor, the system uses a microcontroller or processing unit to sample, calculate, and convert the signal. This intermediary digital processing layer replaces the direct analog filtering approach, allowing for more flexible and integrable solutions.
2Adaptability or versatility
If digital sampling techniques are used to obtain Ton and Toff values for duty cycle calculation, then the flexibility is improved, but the implementation difficulty increases due to the need for division operations in digital circuits
Solution Approach 1:
The patent segments the duty cycle calculation process into distinct modular steps: (1) sampling the PWM signal to detect high and low level durations, (2) accumulating the high-level duration (Ton), (3) accumulating the low-level duration (Toff), (4) performing the division operation to calculate duty cycle ratio, and (5) converting to analog output. This segmentation allows each step to be independently implemented and optimized, making the overall complex operation more manageable and implementable in digital circuits.
3Device complexity
If traditional RC filter circuit is used to convert PWM signal, then the circuit structure is simple, but the response speed is slow due to the requirement of large capacitor for low-frequency filtering
Solution Approach 1:
The patent employs periodic sampling of the PWM signal at a sampling frequency higher than the PWM frequency. By periodically capturing the signal state at defined intervals and using counter-based measurement of high and low level durations, the system achieves fast response without requiring large filtering capacitors. The periodic nature of the sampling and counting process enables rapid conversion while maintaining accuracy.
Data Source
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AI summary
Provided in the present invention are a PWM signal conversion circuit and method, and an LED dimming system. The PWM signal conversion circuit comprises: a PWM signal detection module (11), which outputs a first voltage corresponding to a low-level time of a PWM signal, and a second voltage corresponding to a high-level time of the PWM signal; an addition module (12), which sums the first voltage and the second voltage to obtain a third voltage; a switch signal generation module (13), which generates a switch signal on the basis of the third voltage; a duty ratio value generation module (14), which obtains a duty ratio value on the basis of a high-level count of the switch signal for the PWM signal; and an output voltage generation module (15), which obtains, on the basis of the duty ratio value, an output voltage related to the duty ratio of the PWM signal. In the present invention, there is no need to use a large capacitor, and a peripheral circuit of a chip is simple; only one PWM signal cycle is required for extracting the duty ratio of a PWM signal, thereby achieving rapidness and high efficiency; and the frequency of performing duty ratio counting on the PWM signal is a fixed multiple of the frequency of the PWM signal itself; therefore, the duty ratio count is always constant regardless of how the frequency of the PWM signal changes, and thus the accuracy is high.