PWM Filter Circuit for Duty-Ratio Threshold Switching
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Solution Overview
Problem
Traditional voltage comparison circuits cannot determine output signals based on the variation of the duty ratio of PWM signals, restricting the usage of PWM signals by outputting a constant 0 V voltage regardless of changes in the duty ratio.
Innovation Solution
A filter circuit comprising an RC circuit, a comparator circuit, and an output control circuit that generates a ripple voltage and compares it with a reference voltage to output a switch signal, allowing the output signal to correspond to the PWM signal when the duty ratio is above a predetermined threshold, and not correspond when below, enabling filtering based on duty ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a traditional voltage comparison circuit is used to determine output signals, then the circuit structure is simple, but the circuit cannot respond to duty ratio variations of PWM signals and outputs constant voltage
Solution Approach 1:
The circuit is divided into three functional modules: RC circuit for generating ripple voltage, comparator circuit for comparing with reference voltage, and output control circuit for generating final output. This segmentation allows each module to perform a specific function, enabling duty ratio detection while maintaining clear signal processing stages.
Solution Approach 2:
The RC circuit performs preliminary action by generating ripple voltage from the PWM signal before the comparison stage. This preprocessing transforms the PWM signal into a form that reflects duty ratio variations, enabling the subsequent comparator to detect these variations effectively.
2Adaptability or versatility
If a traditional voltage comparison circuit outputs constant 0 V voltage, then the circuit operation is simple, but the usage of PWM signal is restricted
Solution Approach 1:
The output control circuit dynamically adjusts the output signal based on the comparison result between ripple voltage and reference voltage. When ripple voltage exceeds the reference voltage (indicating duty ratio above threshold), the output follows the PWM signal; otherwise, it outputs zero voltage. This dynamic behavior enables flexible PWM signal usage while maintaining simple operational control.
Solution Approach 2:
The circuit changes its operational parameters based on the duty ratio of the PWM signal. By comparing the ripple voltage (which varies with duty ratio) against a reference voltage, the circuit transitions between different output states, thereby adapting its behavior to the input signal characteristics without complex control logic.
3Adaptability or versatility
If the filter circuit compares ripple voltage with reference voltage to generate switch signal, then the filtering based on duty ratio is achieved, but the circuit complexity increases
Solution Approach 1:
The comparator circuit serves multiple functions: it compares the ripple voltage with the reference voltage, generates the switch signal, and implicitly determines whether the duty ratio exceeds the threshold. This multi-functionality reduces the need for additional separate components, balancing the filtering capability with acceptable circuit complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the filtering of PWM signals according to their duty ratio, allowing for the manipulation of secondary stage circuit operations by adjusting the duty ratio, such as controlling the luminance of a light bulb, without the need for specific control ICs, thereby facilitating the usage of PWM signals.
Implementation Method 1
The RC circuit is configured to generate a ripple voltage according to the PWM signal
Implementation Method 2
The comparator circuit couples with the RC circuit, and is configured to compare the ripple voltage with a first reference voltage, and to output a switch signal according to a comparison result
Data Source
AI summary
A filter circuit comprises a resistor-capacitor (RC) circuit, a comparator circuit, and an output control circuit. The RC circuit is configured to generate a ripple voltage according to the PWM signal. The comparator circuit couples with the RC circuit, and is configured to compare the ripple voltage with a first reference voltage, and output a switch signal according to a comparison result. The output control circuit couples with the comparator circuit and the RC circuit, and is configured to generate an output signal according to the switch signal and the PWM signal. When a duty ratio of the PWM signal is larger than a predetermined threshold value, the output signal is corresponding to the PWM signal. When the duty ratio of the PWM signal is smaller than the predetermined threshold value, the output signal is not corresponding to the PWM signal.