LED Driver Circuit Using Transformer Feedback for Current Regulation
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Solution Overview
Problem
Existing LED driver circuits face challenges in accurately regulating LED current due to indirect current detection on the primary side, which includes variable magnetizing current, requiring potential isolation and optocouplers, leading to inefficiencies and increased costs.
Innovation Solution
The solution involves a transformer-based decoupling method on the secondary side to detect LED current indirectly, using a detection winding to reflect the LED current as an AC signal to the primary side, eliminating the need for costly optocouplers and improving regulation by directly measuring the LED current through a current transformer and evaluation circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If LED current is detected on the secondary side and fed back to the primary side, then current regulation accuracy is improved, but potential isolation and optocouplers are required, increasing device complexity and cost
Solution Approach 1:
The patent introduces an intermediary transformer coupling mechanism that transfers current information from the secondary side to the primary side without requiring direct electrical connection or optocouplers. The secondary-side detection winding generates a voltage proportional to LED current, which is coupled through the transformer to the primary side control circuit, enabling accurate current regulation while avoiding complex isolation components.
Solution Approach 2:
The patent replaces the traditional optocoupler-based feedback mechanism with a transformer-based electromagnetic coupling system. Instead of using optical isolation components, the invention uses magnetic field coupling through the transformer to transfer current information, simplifying the feedback circuit while maintaining regulation accuracy.
2Device complexity
If LED current is detected indirectly via primary side current, then device complexity is reduced, but measurement precision deteriorates due to variable magnetizing current
Solution Approach 1:
The patent segments the detection function by adding a separate secondary-side detection winding that is specifically dedicated to measuring LED current. This separates the current detection function from the main power transformation function, allowing accurate measurement of LED current without being affected by primary side magnetizing current variations.
Solution Approach 2:
The patent uses the transformer's magnetic coupling as an intermediary to transfer the secondary-side detection signal to the primary side. This allows the control circuit to obtain accurate LED current information through electromagnetic induction, eliminating the need for direct ADC measurement while maintaining measurement precision.
3Measurement precision
If direct ADC measurement of LED voltage is implemented, then current regulation accuracy is improved, but device complexity increases due to ADC and optocoupler requirements
Solution Approach 1:
The patent replaces the ADC-based direct measurement system with a transformer-based electromagnetic coupling system. Instead of using ADC converters and digital processing, the invention uses the transformer to directly couple the secondary-side detection signal to the primary side control circuit, simplifying the hardware while maintaining regulation accuracy.
Solution Approach 2:
The transformer acts as an intermediary that transfers the detection signal from secondary to primary side without requiring digital conversion. The electromagnetic coupling mechanism provides direct analog signal transfer, eliminating the need for ADC components and reducing overall system complexity.
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 enhances current regulation accuracy and reduces the need for potential isolated feedbacks, providing a more efficient and cost-effective method for controlling LED driver circuits by directly measuring the LED current, thus improving the overall performance of the LED converter.
Implementation Method 1
a resonant circuit, such as an LLC converter, responsible for transferring current across a galvanic barrier from a primary side to a secondary side of the galvanic barrier
Implementation Method 2
a detection winding to reflect the LED current as an AC signal to the primary side
Data Source
Figure 1~2
Figure 3~5
AI summary
The invention proposes a driver circuit (1, 20) for illuminants, particularly LEDs, having: – a circuit (2), such as an inverter in the form of a half-bridge circuit that has a resonant circuit (3), that is clocked by means of at least one switch (FET1, FET2), – a transformer (L2) that follows the resonant circuit (3) and from whose secondary winding (L2b) the illuminants can be supplied with power, and – a control circuit (ST) that clocks the switches (FET1, FET2) of the clocked circuit (2), wherein an actual signal (ILED_PRIM) that indirectly reproduces the current through the illuminants and that is inductively output on the secondary side (L2/2) of the transformer (L2) is fed back to the control circuit (ST), wherein the control circuit (ST) is designed: – to regulate the current through the illuminants by clocking at least one switch (FET1, FET2) of the clocked circuit (2) on the basis of the actual signal (ILED_PRIM), and/or – to use the actual signal (ILED_PRIM) to record a fault state following the secondary winding (L2b) of the transformer (L2) and/or the illuminants and to take this as a basis for outputting a fault signal and/or for altering the actuation of the clocked circuit (2).