Low-pass Filter Circuit with Dynamic Time Constant Control
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Solution Overview
Problem
Existing low-pass filter circuits are prone to malfunctions due to variations in control circuit elements, leading to delayed startup and reduced noise elimination capabilities, especially when the cutoff frequency is set low, resulting in slow restoration of output voltage.
Innovation Solution
A low-pass filter circuit configuration featuring a capacitance element connected to an output terminal and a resistance circuit with a MOS transistor and amplifier, where the amplifier controls the time constant based on the voltage difference between input and output terminals, allowing for stable and high-speed startup and noise elimination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the cutoff frequency of the low-pass filter circuit is set low to enhance noise elimination capability, then the noise elimination capability is improved, but the startup speed of the output voltage becomes slow
Solution Approach 1:
The patent applies dynamics by making the time constant of the low-pass filter circuit variable rather than fixed. The control circuit dynamically adjusts the time constant based on the operational state: using a first time constant during startup to ensure fast response, and switching to a second time constant during normal operation to enhance noise elimination. This dynamic adjustment resolves the contradiction between fast startup and effective noise filtering.
Solution Approach 2:
The patent changes the parameter of the time constant from a fixed value to a variable parameter that can take different values (first time constant and second time constant) depending on the operational phase. By changing the time constant parameter according to the circuit's state, the system achieves both fast startup (with smaller time constant) and effective noise elimination (with larger time constant), resolving the technical contradiction.
2Object-affected harmful factors
If the time constant of the low-pass filter circuit is made large to improve noise elimination, then the noise elimination capability is improved, but the restoration speed of output voltage after fluctuation becomes slow
Solution Approach 1:
The control circuit dynamically adjusts the time constant based on the operational state: using a smaller first time constant when startup or restoration is needed to ensure fast response, and switching to a larger second time constant during stable operation to enhance noise elimination. This dynamic adjustment resolves the contradiction between fast restoration and effective noise filtering.
Solution Approach 2:
The patent changes the time constant parameter from fixed to variable, allowing the system to switch between a first time constant for fast response (startup/restoration) and a second time constant for noise elimination. This parameter change enables the system to achieve both fast restoration after voltage fluctuation and effective noise elimination during normal operation.
3Speed
If a control circuit is used to switch the time constant, then the startup speed can be improved, but the system becomes vulnerable to malfunctions due to variations in control circuit elements
Solution Approach 1:
The patent employs feedback mechanisms where the control circuit monitors the output voltage and automatically adjusts the time constant accordingly. The feedback ensures that the switching between first and second time constants occurs at appropriate moments, improving startup speed while maintaining reliability through automatic adjustment rather than manual or external control.
Solution Approach 2:
The control circuit is designed to automatically determine when to switch between time constants based on the operational state of the power supply device, without requiring external intervention. The circuit self-adjusts the time constant based on internal voltage levels and operational conditions, improving both startup speed and reliability by eliminating dependence on external control signals that may be affected by variations.
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
The solution enables stable and high-speed startup of the output voltage, independent of control circuit variations, and rapid restoration of output voltage even with large fluctuations, enhancing noise elimination capabilities.
Implementation Method 1
a capacitance element (12) connected to an output terminal (2)
Implementation Method 2
a low-pass filter circuit formed by the resistor 211, the capacitor 212 and the NMOS transistor 213
Implementation Method 3
a resistance circuit (11a) connected between an input terminal (1) and the output terminal (2), and equipped with a MOS transistor (13)
Implementation Method 4
an amplifier (14) having a first input terminal (3) to which the input terminal (1) is connected, a second input terminal (4) to which the output terminal (2) is connected
Data Source
AI summary
To provide a low-pass filter circuit which is high in noise elimination capability and starts its output stably and at high speed, and a power supply device. A low-pass filter circuit is provided which is equipped with a capacitance element connected to an output terminal, and a resistance circuit connected between an input terminal and the output terminal, and in which the resistance circuit is equipped with a first MOS transistor connected between the input terminal and the output terminal, and an amplifier which has a first input terminal to which the input terminal is connected, a second input terminal to which the output terminal is connected, and an output terminal to which a gate of the first MOS transistor is connected, and which controls a time constant of the low-pass filter circuit.