Programmable Constant Current Circuit for LED Intensity Control
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Solution Overview
Problem
LED light intensity is inconsistent due to variations in manufacturing process variables and ambient temperature, leading to undesirable intensity variations when using a fixed resistor for current limiting, which adds cost and complexity to products.
Innovation Solution
An integrated circuit device with a programmable constant current circuit that eliminates the need for an external current limiting resistor, allowing for adjustable current sink or source from 5 to 25 mA, enabled by internal control registers and FET gate voltage, to maintain constant light intensity across various operating and manufacturing variables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed resistor is used to limit current through the LED, then the circuit is simple to implement, but the LED light intensity becomes inconsistent due to variations in manufacturing process variables and ambient temperature
Solution Approach 1:
The patent implements a dynamic current limiting mechanism using a programmable constant current circuit that actively adjusts the current through the LED based on feedback from sense resistors and control logic, replacing the static fixed resistor approach. This allows the system to adapt to variations in LED forward voltage, manufacturing process variables, and ambient temperature while maintaining consistent light intensity.
Solution Approach 2:
The patent changes the operating parameters by introducing programmable current limit values that can be adjusted through software control rather than being fixed by hardware components. The constant current circuit modifies the current parameter dynamically based on programmed settings, enabling consistent LED operation across different operating conditions without requiring physical component changes.
2Ease of manufacture
If a fixed resistor is used for current limiting, then the implementation is straightforward, but additional cost and complexity are added to the product
Solution Approach 1:
The patent merges the current limiting function with the existing digital device output driver by integrating the constant current circuit, sense resistors, and control logic into the same device. This consolidation eliminates the need for separate external current limiting resistors and reduces overall product complexity while maintaining implementation simplicity through unified control.
Solution Approach 2:
The patent implements a self-service mechanism where the digital device automatically regulates its own output current through the programmable constant current circuit, eliminating the need for external passive components like fixed resistors. The device monitors its own output through sense resistors and adjusts the current accordingly, reducing external component requirements and overall product complexity.
3Adaptability or versatility
If the output driver current varies with power supply voltage and operating temperature, then the circuit responds dynamically to voltage changes, but undesirable LED intensity variation occurs
Solution Approach 1:
The patent implements a feedback mechanism using sense resistors that monitor the actual current flowing through the LED and feed this information back to the constant current control logic. This feedback loop enables the system to detect and correct current variations caused by power supply voltage changes and temperature variations, maintaining stable LED intensity while preserving the ability to respond dynamically to operating conditions.
Data Source
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AI summary
A constant current output sink or source eliminates a current limiting series resistor for a light emitting diode (LED) and maintains a constant light intensity from the LED for all operating and manufacturing variables of a digital device since the current through the LED is maintained at a constant value. The constant current output sink or source may be programmable for selection of a constant current value from a plurality of constant current values available.