LED Driver Circuit Switched Constant Current Source Dimming
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Solution Overview
Problem
Existing LED power supply systems face inefficiencies due to disproportionate increase in electrical losses with reduced switch-on time, particularly when using constant current sources for dimming, which affects power delivery to LEDs.
Innovation Solution
A control unit adjusts the switch-on time and DC supply voltage of a clocked constant current source, such as a buck converter, to minimize power losses by specifying a target DC output voltage and reducing switch-on time to a minimum, while changing the operating mode of a Power Factor Correction (PFC) circuit to optimize power delivery based on load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the switch-on time of the switch is reduced to dim the LEDs, then the light output is reduced, but the electrical losses increase disproportionately
Solution Approach 1:
The patent changes the DC supply voltage level in addition to adjusting the switch-on time. By modifying the voltage parameter of the constant current source, the system can reduce power delivery (P=VI) without relying solely on reduced switch-on time, thereby avoiding the disproportionate increase in electrical losses that occurs when duty cycle is reduced alone.
2Loss of energy
If the switch-on time is reduced to minimize power delivery, then power consumption is reduced, but the control becomes less efficient due to minimum on-time constraints
Solution Approach 1:
The patent dynamically adjusts two control variables (switch-on time and DC supply voltage) instead of relying on a single variable. This dynamic approach allows the system to maintain control efficiency even when switch-on time approaches its minimum value, as the voltage adjustment provides an additional degree of freedom for power control.
3Loss of energy
If the DC supply voltage is lowered to reduce power delivery, then power consumption is reduced, but the constant current source operation becomes less stable
Solution Approach 1:
The patent employs feedback control in the constant current source that adapts to varying DC supply voltage levels. The control unit monitors the actual current through the LEDs and adjusts the switch-on time accordingly to maintain the desired current level, ensuring stable operation even when the DC supply voltage is reduced.
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
This approach reduces power supply by minimizing switch-on time and adjusting voltage, thereby minimizing electrical losses and optimizing power delivery to LEDs, especially during dimming operations.
Implementation Method 1
an actively clocked PFC circuit (Power Factor Correction Circuit) can be used, for example, to provide the supply voltage for the constant current source
Implementation Method 2
The power delivery can be changed by changing the clocking of a switch of the PFC circuit
Data Source
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AI summary
The invention relates to an LED driver circuit comprising: a circuit block for providing an adjustable DC voltage and a clocked constant current source, e.g. a DC/DC converter that is supplied with the DC voltage, comprising a switch that is clocked by a control circuit in such a way that a reduction of the activation period t0N of the switch leads to a reduction in the provision of power. One or more LEDs can be supplied from the constant current source and in addition to reducing the activation period t0N, the control unit is designed to change at least one other control variable of the constant current source or the circuit block in order to provide the direct current.