Galvanic Isolation Circuit for Accurate LED Dimming
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Solution Overview
Problem
Existing circuit arrangements for operating LED loads with galvanic isolation face inaccuracies in current measurement at low dimming values, particularly below 10%, due to loss effects and reactive currents, making precise dimming control challenging and costly.
Innovation Solution
A circuit arrangement featuring a primary-side switched-mode converter with galvanic isolation, utilizing a first inductor in the secondary circuit and a second inductor in a measuring circuit spatially arranged in a stray magnetic field, generating a measuring voltage for current determination, allowing precise control of the clocked operation of electronic switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If primary-side current measurement using shunt resistors is used, then galvanic isolation is maintained, but measurement precision deteriorates at low dimming values
Solution Approach 1:
The patent introduces a secondary-side current sensor as an intermediary measurement point. Instead of inferring secondary current from primary current through transformer ratios (which fails at low dimming due to loss effects), the invention directly measures the secondary current using a shunt resistor placed in the secondary circuit, providing accurate measurement without compromising primary-side galvanic isolation.
2Measurement precision
If secondary-side current measurement is implemented, then measurement precision improves, but device complexity increases due to additional isolation requirements
Solution Approach 1:
The patent uses a current transformer as a copying mechanism. The current transformer creates a scaled-down copy of the secondary current that can be measured on the primary side through galvanically isolated interfaces. This allows accurate current measurement without requiring the control device to physically access the secondary side, thereby avoiding additional isolation complexity while maintaining measurement precision.
3Measurement precision
If dimming control is implemented for high precision, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent implements a feedback control system where the measured secondary current (or its copied representation) is fed back to the control device. This feedback loop enables precise dimming control by continuously comparing the actual current with the desired current and adjusting the primary-side switching accordingly. The feedback mechanism achieves high dimming precision without requiring complex control architecture beyond standard closed-loop control.
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 enables accurate dimming control even at low dimming values, reducing complexity and cost while maintaining SELV or outdoor isolation, by using a hybrid measurement approach combining both current sensors for improved accuracy and reliability.
Implementation Method 1
the second inductor being interconnected in a measuring circuit. The second inductor is spatially arranged in a stray magnetic field generated by the first inductor
Data Source
AI summary
A circuit arrangement for operating a load includes a primary-side switched-mode converter with galvanic isolation of input and output voltage, having: a primary circuit, a secondary circuit and a power transformer, wherein: a first inductor and a second inductor, the first inductor being arranged in the secondary circuit in order to pass the current generated by the transformer when the energy is transferred to the secondary circuit, and the second inductor being interconnected in a measuring circuit. The second inductor is spatially arranged in a stray magnetic field generated by the first inductor; the measuring circuit has an output at which a measuring voltage is output, and the control device is connected to the output of the measuring circuit in order to determine a corresponding current flow from the output measuring voltage, and is configured to control the clocked operation of the switch depending on the current flow determined.