LED Driver Circuit Dynamic Current Reduction for Thermal Management
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Solution Overview
Problem
Direct-to-mains LED lighting circuits experience high power dissipation and thermal issues due to varying mains voltage, leading to poor light quality and increased heat, especially during startup and high-voltage periods.
Innovation Solution
A driver circuit with a controllable current source and controller that adjusts current based on the voltage difference between the series arrangement and the rectified AC supply, providing a lower current during high voltage conditions to reduce power dissipation and heat, and dynamically adjusts charging current during startup to minimize IC temperature increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a high charging current is used to charge capacitors quickly during startup, then the charging time is reduced, but the power dissipation and temperature increase in the IC becomes significant
Solution Approach 1:
The patent applies dynamic current adjustment by switching between a first current value (higher current) when the capacitor voltage is below a reference voltage, and a second current value (lower current) when the capacitor voltage exceeds the reference voltage. This dynamic adjustment optimizes both charging speed and thermal management, resolving the contradiction between fast charging and temperature control.
2Adaptability or versatility
If the number of LED strings is increased to match higher peak mains voltage, then the voltage matching is improved, but the power dissipation in the IC increases due to excess voltage
Solution Approach 1:
The patent dynamically adjusts the LED string configuration based on the rectified mains voltage level. When the voltage is high, more LED strings are connected in series to match the voltage, reducing the voltage difference and power dissipation. When voltage is lower, fewer strings are active. This dynamic adaptation resolves the contradiction between voltage matching and energy loss.
Solution Approach 2:
The patent changes the operating parameters (number of active LED strings, current values) based on the mains voltage conditions. By adjusting these parameters dynamically, the system achieves better voltage matching while minimizing power dissipation in the IC.
3Illumination intensity
If capacitors are added in parallel with LED strings to reduce current ripple, then the light quality is improved, but the device complexity and cost increase
Solution Approach 1:
The patent uses capacitors selectively - not with all LED strings simultaneously, but only with specific strings depending on the operating conditions and mains voltage level. This partial application of capacitance provides sufficient ripple reduction to improve light quality while avoiding the full complexity and cost of adding capacitors to every string.
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 solution reduces power dissipation and heat management challenges, allowing for smaller, less expensive transistors and simpler thermal design, while maintaining acceptable charging times and light quality.
Implementation Method 1
the dissipation in the current source can be high even if a low to moderate charging current is used... the power dissipated in the IC would be approximately Vrect.ILED... this can already lead to a significant temperature increase
Implementation Method 2
capacitors C1, C2, and C3 may be included in parallel with respective LED string LED1, LED2 and LED3... the charge stored in the capacitors can be used to power the respective LED string, reduce the current ripple
Data Source
AI summary
There is disclosed a driver for driving a series arrangement being a variable number of strings of LEDs wherein each string has a capacitance connected in parallel with the respective string; the driver comprising: a controllable current source adapted to be connected in series between the series arrangement and a rectified AC supply to and source a controllable current (Istr) through the series arrangement; and a current source controller adapted to control the controllable current source; wherein the current source controller is operable to source a relatively lower current (ILED′) when a difference (Vstr3A) between the voltage across the series arrangement and the voltage of the rectified AC supply is relatively higher and a relatively higher current (ILED) when the difference is relatively lower. Associated driver circuits and lighting circuits, and methods are also disclosed.