Capacitive Pre-converter for LED Current Regulation
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Solution Overview
Problem
Existing LED supply circuits for automotive applications face challenges in maintaining precise current regulation due to varying supply voltages, leading to high power losses and increased costs, particularly in linear controllers and complex switching converters.
Innovation Solution
A capacitive pre-converter with a controlled longitudinal switch, controlled by a microcontroller using PWM and a look-up table, converts the primary DC voltage into a desired intermediate circuit voltage, reducing component complexity and power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If linear controllers are used to maintain precise current regulation, then current accuracy is improved, but power loss increases significantly
Solution Approach 1:
The voltage regulation function is divided into two stages: a pre-converter stage that performs coarse voltage reduction and a linear controller stage that performs fine current regulation. This segmentation allows each stage to operate in its optimal efficiency range, reducing overall power loss while maintaining current accuracy.
Solution Approach 2:
The pre-converter performs preliminary voltage reduction before the current reaches the linear controller and LED circuit. By reducing the voltage beforehand, the linear controller operates with a smaller voltage differential, significantly reducing power loss in the form of heat while maintaining precise current control capability.
2Loss of energy
If switching converters are used to reduce power loss, then power efficiency is improved, but device complexity and cost increase
Solution Approach 1:
The system segments the voltage regulation task between a simple pre-converter and a linear controller, avoiding the need for a complex switching converter while achieving similar power efficiency. The pre-converter uses basic components (capacitors, resistors, transistors) rather than complex switching converter topology.
Solution Approach 2:
The pre-converter uses inexpensive, simple components that can be easily replaced or adjusted. Rather than investing in a complex, expensive switching converter, the patent employs a simpler, cheaper pre-converter stage that achieves the same power loss reduction goal with lower component cost and complexity.
3Power
If a DC/DC converter with transformer and rectifier is used for voltage conversion, then voltage regulation is achieved, but manufacturing cost and device complexity increase
Solution Approach 1:
The patent extracts only the essential voltage conversion function from the traditional DC/DC converter, removing the transformer and rectifier components. The pre-converter achieves voltage conversion using a simpler circuit topology with capacitors, resistors, and transistors, eliminating expensive magnetic components and complex rectification circuits.
Solution Approach 2:
The patent replaces the mechanical/magnetic transformation approach (transformer-based DC/DC conversion) with an electronic approach (capacitive voltage division and switching control). This substitution eliminates the need for physical transformers and complex rectifier circuits, reducing manufacturing cost and device complexity while maintaining voltage conversion capability.
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 achieves low component complexity, high current accuracy, and reduced power loss, making it suitable for efficient LED supply in motor vehicle headlight systems at a lower cost.
Implementation Method 1
an intermediate circuit capacitor (CZ) which is supplied with the primary DC voltage (UB) via the controlled series switch (S)
Implementation Method 2
a controlled series switch (S) which is located between the primary DC voltage (UB) and the intermediate circuit capacitor (CZ) and which is controlled by a PWM output of a microcontroller (µC)
Data Source
Figure 1~3
Figure 4~5
AI summary
A power supply circuit for supplying LEDs (LED1, LED2) from a primary DC voltage (UB), wherein a control transistor (T) and a current sensor (RS) are located in the circuit of at least one LED, and a comparator (K) is provided whose output is connected to the control input of the control transistor, wherein a setpoint (ss) for the current (IS) in the LED circuit is supplied to a first input of the comparator, and an actual value (si) of the LED circuit detected by the current sensor is supplied to a second input of the comparator, wherein a capacitive pre-converter (KV) is arranged between the LED circuit, which comprises the series connection of the LED circuit (LED1, LED2), the control transistor (T), and the current sensor (RS), and the primary DC voltage (UB), which converts the primary DC voltage to an intermediate circuit voltage (UZ) with a fixed value desired for the LED circuit, depending on the magnitude of the primary DC voltage.The capacitive pre-converter (KV) comprises a controlled linear switch (S) located between the primary DC voltage (UB) and an intermediate circuit capacitor (CZ), which is controlled by a PWM output of a microcontroller (µC), wherein an input of the microcontroller is supplied with a voltage value proportional to the primary DC voltage, and the microcontroller contains a look-up table (LUT) with a relationship between the value of the supplied voltage value and the duty cycle of a signal at the PWM output in order to convert the primary DC voltage to the intermediate circuit voltage (UZ) with the fixed value desired for the LED circuit, wherein the LED circuit is connected to the intermediate circuit capacitor.