LED Switched Converter Current Sensing at High Switching Frequency
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Solution Overview
Problem
Existing methods for sensing LED current in resonant flyback converters are inaccurate at higher switching frequencies and require secondary side current sensing, which is not feasible for all converter topologies.
Innovation Solution
A switched converter with a sensing transformer and control circuitry that operates in alternating cycles, using a sampling and hold circuitry to sense current across output terminals, independent of converter topology, and eliminates the need for secondary side sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard galvanically isolated sensing methods with current transformer are used, then current sensing is achieved, but accuracy deteriorates at higher switching frequencies due to reverse recovery charge of secondary side rectifier diodes
Solution Approach 1:
The patent introduces an intermediary capacitor connected to the secondary winding of the current transformer. This capacitor compensates for the reverse recovery charge of the rectifier diodes by providing additional charge during the diode's reverse recovery period, thereby maintaining accurate current sensing at higher switching frequencies. The capacitor acts as a mediator that bridges the gap between the transformer output and the sensing circuit, eliminating the accuracy degradation caused by diode reverse recovery effects.
2Device complexity
If primary side indirect sensing is used in resonant flyback topology, then secondary side current sensing is eliminated, but sensing accuracy deteriorates because resonance current makes simple calculation of LED current very difficult
Solution Approach 1:
The patent uses the capacitor connected to the secondary winding as an intermediary element that enables accurate primary-side sensing in resonant flyback topology. By measuring the voltage across this capacitor, the control circuit can indirectly determine the LED current with high accuracy, despite the complex resonance waveforms. This approach maintains the simplicity of primary-side sensing while overcoming the accuracy limitations imposed by resonant currents.
3Adaptability or versatility
If primary winding of sensing transformer is switched in series to capacitor, then current sensing becomes independent of converter topology, but device complexity increases
Solution Approach 1:
The patent implements a universal sensing approach where the sensing transformer with its primary winding switched in series to the capacitor can be applied to multiple converter topologies (flyback, resonant flyback, and other isolated converters). The same sensing circuit configuration provides accurate current measurement across different topologies, eliminating the need for topology-specific sensing designs. This multi-functional sensing solution achieves adaptability while maintaining reasonable complexity through standardized implementation.
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
Enables accurate and efficient LED current sensing across various converter topologies, including resonant and non-resonant types, without the inaccuracies associated with secondary side sensing.
Implementation Method 1
the primary winding of the sensing transformer is switched in series to the capacitor and the secondary winding of the sensing transformer is configured to generate an output signal
Data Source
AI summary
The invention relates to a switched converter, comprising: at least one switch, output terminals for supplying an LED load, a capacitor arranged in parallel to the output terminals, a sensing transformer, a primary winding of the sensing transformer, a secondary winding of the sensing transformer; and a control circuitry controlling the operation of the at least one switch. The switched converter is configured to operate in alternating cycles between phases of supplying energy from a node on a potential of the at least one switch to the output terminals and phases of supplying energy to output terminals of the capacitor but not from said node. The primary winding of the sensing transformer is switched in series to the capacitor and the secondary winding of the sensing transformer is configured to generate an output signal supplied to the control circuity of the switched converter, wherein the control circuity is configured to sense the current flowing across the output terminals supplying the LED load based on said output signal.