Switched-Capacitor Ripple Filter Circuit for LED Drivers
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Solution Overview
Problem
Existing ripple filters in AC-DC driving circuits, such as those used in LED drivers, face challenges in integrating large capacitors due to size constraints, leading to increased costs and reduced service life from power frequency ripples.
Innovation Solution
A ripple filter circuit utilizing a switch capacitor circuit and filter capacitor, controlled by clock signals, simulates the characteristics of an RC low-pass filter, allowing for reduced capacitance values that can be integrated into a single chip, and an error amplifying circuit generates a compensation signal to regulate the output current and eliminate ripples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large capacitors are used in traditional ripple filters, then filtering effectiveness is improved, but device size and integration difficulty increase
Solution Approach 1:
The patent changes the operating parameters by using a switch capacitor circuit operating at high frequency (clock signals) to simulate the behavior of a large capacitor. The switch capacitor circuit effectively provides large capacitance values through switching action, while the actual physical capacitors required are much smaller than traditional filter capacitors, enabling chip integration.
Solution Approach 2:
The patent replaces the traditional passive RC low-pass filter with an active switched-capacitor filter circuit. The mechanical/passive filtering approach is substituted with an active electronic switching mechanism controlled by clock signals, allowing the simulation of large capacitance values with small physical components.
2Reliability
If traditional RC low-pass filters are used, then ripple filtering is achieved, but the circuit complexity and cost increase due to large capacitor requirements
Solution Approach 1:
The switch capacitor circuit serves multiple functions: it acts as both the filtering element and the impedance-setting component. The same switching mechanism that creates the effective large capacitance also determines the filter characteristics, reducing the need for separate large-value passive components and simplifying the overall circuit structure for integration.
Solution Approach 2:
The patent employs periodic switching action using clock signals to control the switch capacitor circuit. This periodic switching creates the equivalent of a large capacitor through charge transfer cycles, replacing the need for large static capacitors with a dynamic switching mechanism that achieves the same filtering effect with much smaller components.
3Duration of action of stationary object
If power frequency ripples are not filtered, then circuit simplicity is maintained, but load service life is reduced
Solution Approach 1:
The error amplifying circuit provides feedback control by comparing the output voltage with a reference and adjusting the power switch duty cycle to eliminate ripples. This closed-loop feedback mechanism ensures accurate ripple filtering and load current regulation, extending load service life through precise control while using a compact integrated circuit structure.
Solution Approach 2:
The patent replaces traditional mechanical/passive filtering with an active controlled switching system. The ripple filtering function is achieved through electronic switching and feedback control rather than large passive components, reducing circuit complexity and enabling integration while effectively extending load service life by eliminating harmful ripples.
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
This approach effectively reduces capacitance values, enabling chip integration and eliminating power frequency ripples, thus extending the service life of loads like LEDs by maintaining a constant DC current without AC components.
Implementation Method 1
the filter circuit includes a switch capacitor circuit and a filter capacitor
Implementation Method 2
generating, by a filter circuit, a filter voltage signal by filtering the sense voltage signal
Data Source
AI summary
A method of filtering a ripple can include: (i) generating, by a sampling circuit, a sense voltage signal that represents an output current flowing through a load; (ii) generating, by a filter circuit, a filter voltage signal by filtering the sense voltage signal, where the filter circuit includes a switch capacitor circuit and a filter capacitor; and (iii) generating, by an error amplifying circuit, an error compensation signal by amplifying a difference between the sense voltage signal and the filter voltage signal, where the error compensation signal is configured to compensate and regulate the output current flowing through the load by controlling a power switch that is coupled to the load and the sampling circuit.