Constant-Current Circuit for LED Drive with Voltage Regulation
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Solution Overview
Problem
Conventional constant-current circuits for LED drive face issues with high power consumption and systemic errors due to voltage fluctuations, which affect the precision of output current and increase chip area requirements.
Innovation Solution
A novel constant-current circuit design featuring NMOS transistors with a voltage regulation unit, current detector, and controller to maintain equal drain voltages and precise current output, eliminating systemic errors and reducing power consumption by lowering the minimum output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a cascode-type current mirror circuit is used to maintain high precision in outputting constant current, then the output current precision is improved, but the minimum output voltage becomes high and power consumption increases
Solution Approach 1:
The patent changes the operating parameters of the MOS transistors by controlling their drain voltages to be equal, allowing them to operate at optimal points that reduce the minimum output voltage requirement while maintaining precision. This is achieved through the voltage regulation unit that actively adjusts transistor parameters.
Solution Approach 2:
The patent employs feedback mechanisms where the voltage regulation unit continuously monitors and adjusts the drain voltages of the MOS transistors to maintain equality, thereby optimizing the operating point and reducing the minimum output voltage while preserving current precision.
2Measurement precision
If the output transistor is formed by connecting MOS transistors in series to operate in saturation region, then the constant current precision is maintained, but the chip area substantially increases
Solution Approach 1:
The patent introduces dynamic control through the voltage regulation unit that actively adjusts the drain voltages of the MOS transistors during operation. This dynamic adjustment allows the transistors to maintain saturation region operation for precision while optimizing the voltage distribution to reduce the number of series transistors needed, thereby reducing chip area.
3Adaptability or versatility
If MOS transistors with different drain-source voltages are used in the current mirror circuit, then the circuit can operate with voltage fluctuations, but systemic errors are generated in outputting the output current
Solution Approach 1:
The patent applies the equipotentiality principle by ensuring that the drain voltages of the MOS transistors in the current mirror circuit are maintained at equal levels. The voltage regulation unit actively adjusts the voltages to achieve this equipotential state, which eliminates the systemic errors that would otherwise occur due to voltage differences while maintaining adaptability to external voltage fluctuations.
Data Source
AI summary
A constant-current circuit includes a first transistor for supplying a current based on a control signal input to a gate of the first transistor so as to serve as a current source, a second transistor for supplying a current to a load based on the control signal input to a gate of the second transistor, a voltage regulation unit for controlling a drain voltage of the first transistor according to a drain voltage of the second transistor, a current detector for detecting a value of a current flowing through the first transistor and output a current according to the detected value, and a controller for controlling each gate voltage of the first and second transistors according to the value detected by the current detector so that the current flowing through the first transistor becomes a predetermined value. The first and second transistors are MOS transistors having the same conductivity.