Switchable Current-Sensing Resistor for LED Driver
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Solution Overview
Problem
Existing LED driver circuits face limitations in achieving a wide dimming range without using pulse-width modulation, which can cause stroboscopic effects, and analog current control struggles with low current measurement accuracy and thermal issues due to high power dissipation in current-sensing resistors.
Innovation Solution
A driver circuit that switches the current-sensing resistor to two different values, using parallel resistors with electronic switches to adapt to different current ranges, ensuring accurate measurement and minimizing power loss and thermal issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed current-sensing resistor is used in analog current control, then the circuit is simple, but the measurement precision deteriorates at low current values and power dissipation increases at high current values
Solution Approach 1:
The patent applies the dynamics principle by making the current-sensing resistor value changeable based on operating conditions. The circuit switches between different resistor values (R_CS1 and R_CS2) depending on the current range, allowing optimal measurement precision at low currents and minimal power dissipation at high currents. This dynamic adaptation resolves the contradiction between measurement precision and power dissipation.
Solution Approach 2:
The patent implements parameter changes by varying the resistance value of the current-sensing resistor according to the current magnitude. The control unit selects between different resistance values based on detected current levels, enabling the system to maintain high measurement precision at low currents while minimizing power dissipation at high currents through parameter adaptation.
2Measurement precision
If a higher current-sensing resistor value is used to improve low current measurement, then measurement precision improves, but power dissipation and thermal issues increase
Solution Approach 1:
The patent uses dynamics by switching the current-sensing resistor value based on current magnitude. When low current is detected, the higher resistance value (R_CS1) is selected to improve measurement precision. When high current is detected, the lower resistance value (R_CS2) is selected to minimize power dissipation and prevent thermal issues, thus resolving the contradiction between measurement precision and temperature control.
3Adaptability or versatility
If pulse-width modulation is used to achieve low current levels, then the dimming range is extended, but stroboscopic effects and potential health issues occur
Solution Approach 1:
The patent replaces the mechanical switching approach of PWM with an analog current control system that uses variable resistance. By substituting the PWM switching mechanism with continuous analog control through switchable current-sensing resistors, the system achieves low current levels without the stroboscopic effects associated with pulse-width modulation, thus resolving the contradiction between dimming range and harmful effects.
4Adaptability or versatility
If combined PWM and analog control are used to provide wide dimming range, then the dimming range is improved, but stroboscopic effects persist at low current levels
Solution Approach 1:
The patent applies segmentation by dividing the current control into different ranges, each handled by appropriate circuit configurations. The circuit segments the control strategy by using different current-sensing resistor values for different current ranges, enabling wide dimming range while avoiding PWM at low currents where stroboscopic effects occur, thus resolving the contradiction between dimming range and harmful effects.
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
Enables a wide dimming range with precise current control across varying current levels, reducing power dissipation and preventing LED flickering by adapting the resistor value to the current range, thus improving reliability and efficiency.
Implementation Method 1
The voltage drop across R CS is measured in the integrated circuit and used to regulate the desired current for the LED load
Implementation Method 2
the current-sensing resistor is formed either by only one of the two resistors (when the switch is open) or by both resistors connected in parallel (when the switch is closed)
Data Source
Figure 1~2
AI summary
The invention relates to a driver circuit for supplying power to one or more LEDs, comprising an adjustable constant current source for connecting one or more LEDs connected in series, and a current-sensing resistor connected in series with the one or more LEDs, wherein the driver circuit is configured to determine the current through the one or more LEDs via a voltage drop across the current-sensing resistor in order to regulate the current to a predetermined value, wherein the driver circuit is further configured to switch the current-sensing resistor to at least two different values, wherein the lower of the two values is used to measure the current through the one or more LEDs in a higher current range and the lower of the two values is used to measure the current through the one or more LEDs in a lower current range.