Offset Voltage Eliminating Circuit for LED Dimmer Accuracy
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Solution Overview
Problem
Conventional converting circuits for LED dimming face issues with voltage offset due to current-limiting resistors, affecting the accuracy of dimming control signals when used with traditional dimmers, particularly resistive dimmers.
Innovation Solution
An offset voltage eliminating circuit structure incorporating a constant current source, a subtractor formed by operational amplifiers and resistors, and a hysteresis comparator, which uses an offset reference voltage to subtract the voltage drop across the current-limiting resistor, ensuring the dimming signal voltage is not affected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current-limiting resistor is added for circuit protection, then circuit reliability is improved, but voltage offset is introduced affecting dimming control accuracy
Solution Approach 1:
The patent segments the voltage measurement function by introducing a subtractor circuit that separates the dimming signal voltage from the voltage drop across the current-limiting resistor. This allows independent measurement and compensation of the offset voltage, resolving the contradiction between needing protection (resistor) and maintaining accuracy (measurement precision).
Solution Approach 2:
The patent implements feedback by using the subtractor to continuously monitor and compensate for the voltage offset caused by the current-limiting resistor. The offset reference voltage is fed back to eliminate the measurement error, maintaining dimming control accuracy while preserving circuit protection functionality.
2Adaptability or versatility
If a converting circuit is connected between traditional dimmer and LED, then compatibility is improved, but voltage offset affects control signal accuracy
Solution Approach 1:
The patent introduces an intermediary subtractor circuit between the traditional dimmer and LED that acts as a mediator. This subtractor removes the voltage offset component while passing through the dimming control signal, enabling compatibility with traditional dimmers without sacrificing control accuracy.
3Measurement precision
If offset reference voltage is used to compensate voltage drop, then dimming signal accuracy is improved, but circuit complexity increases
Solution Approach 1:
The patent extracts only the essential offset compensation function by using a subtractor circuit that specifically removes the voltage drop component. This targeted approach achieves dimming signal accuracy without implementing a fully complex compensation system, balancing precision with circuit simplicity.
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
Effectively eliminates the voltage offset created by current-limiting resistors, allowing for precise control of LED brightness by isolating the dimming signal voltage, thus enhancing the reliability and accuracy of the dimming control mechanism.
Implementation Method 1
a subtractor formed by a third operational amplifier OPA3 and second, third, fourth and fifth resistors R2, R3, R4 and R5
Implementation Method 2
the constant current source A is controlled to output a current I = V1/R1. The current flows through the variable resistor RT to create a voltage VT=RT*V1/R1
Implementation Method 3
The non-inverting input of the hysteresis comparator CMP1 is connected to the output Pout (i.e. the dimming signal input ADJ_in), while the inverting input is input with a saw-tooth wave
Data Source
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AI summary
An offset voltage eliminating circuit structure for a protection mechanism of a dimmer includes a constant current source, a subtractor and a hysteresis comparator. The constant current source is used for outputting a stable current, the output of the constant current source is connected with a dimming signal input through a current-limiting resistor, and the dimming signal input is connected with an output of an external traditional dimmer. A voltage that causes an offset voltage is created across the current-limiting resistor when a current flows through the current-limiting resistor. An input of the subtractor is connected with the constant current source, and another input of the subtractor is input with an offset reference voltage. A non-inverting input of the hysteresis comparator is connected to the output of the subtractor, while the inverting input of the hysteresis comparator is input with a saw-tooth wave. By setting the offset reference voltage to be the same as the voltage of the current-limiting resistor, the subtractor eliminates the voltage of the current-limiting resistor, so that the hysteresis comparator is able to obtain the correct dimming signal voltage and output a GD pulse signal for adjusting the brightness of a LED.