Switched Converter Voltage Scaling for LED Current Selection
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Solution Overview
Problem
Galvanically isolated switched converters, such as flyback converters, face challenges in easily adapting output current selection from the secondary side to the primary side, particularly due to high current loads and noise introduced by long wires when modifying shunt resistor values.
Innovation Solution
Incorporating a voltage scaling unit in the feedback path with at least two different scaling factors, allowing for modification of the voltage signal and control of the switch's clocking, enabling selection of different output currents without the need for modifying shunt resistor values, and optionally using different mains connection terminals to select output currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If shunt resistor values are modified to change output current on the primary side, then output current selection is achieved, but high current load and noise from long wires are introduced
Solution Approach 1:
The patent introduces an intermediary circuit between the shunt resistor and the control unit that includes a first switching element and a second switching element. This intermediary circuit allows the shunt resistor to remain in a high-impedance state during normal operation, preventing it from bearing high current loads. The switching elements act as mediators that enable current measurement when needed while isolating the shunt resistor from continuous high current flow, thereby reducing noise and heat generation.
Solution Approach 2:
The patent changes the operational state of the shunt resistor from continuously low-impedance to dynamically switching between low-impedance (during measurement) and high-impedance (during normal operation) states. This parameter change allows the system to achieve output current selection functionality while minimizing the harmful effects of high current load and noise by keeping the shunt resistor in high-impedance state most of the time.
2Adaptability or versatility
If shunt resistor values are modified to enable output current selection, then different output currents can be selected, but the control unit must be close to the shunt resistor, introducing long wires and noise
Solution Approach 1:
The patent introduces an intermediary circuit between the shunt resistor and the control unit that includes a first switching element and a second switching element. This intermediary circuit allows the shunt resistor to remain in a high-impedance state during normal operation, preventing it from bearing high current loads. The switching elements act as mediators that enable current measurement when needed while isolating the shunt resistor from continuous high current flow, thereby reducing noise and heat generation.
Solution Approach 2:
The patent changes the operational state of the shunt resistor from continuously low-impedance to dynamically switching between low-impedance (during measurement) and high-impedance (during normal operation) states. This parameter change allows the system to achieve output current selection functionality while minimizing the harmful effects of high current load and noise by keeping the shunt resistor in high-impedance state most of the time.
3Reliability
If galvanic isolation is used in feedback path, then galvanically isolated converter is achieved, but optical coupler is needed increasing cost and component count
Solution Approach 1:
The patent extracts and removes the optical coupler from the feedback path while maintaining galvanic isolation through alternative means. By using a transformer with primary and secondary windings and utilizing the relationship between primary and secondary currents, the system achieves galvanic isolation without requiring an optical coupler, thereby reducing cost and component count while maintaining reliability.
Solution Approach 2:
The patent replaces the optical coupling mechanism with an electromagnetic coupling mechanism using a transformer. Instead of using light to transfer feedback signals across the galvanic barrier, the system uses magnetic coupling through the transformer to achieve the same feedback function while eliminating the optical coupler and its associated costs and complexity.
4Measurement precision
If secondary side regulation is used, then feedback information is accurately obtained, but more components and higher cost are required compared to primary side regulation
Solution Approach 1:
The patent makes the primary side regulation circuit multi-functional by enabling it to perform both the regulation function and the output current selection function. By incorporating the voltage scaling unit and switching elements into the primary side regulation circuit, the system achieves accurate feedback information obtained through primary side sensing while also providing output current selection capability, eliminating the need for separate secondary side regulation components.
Solution Approach 2:
The patent merges the output current selection functionality with the primary side regulation circuitry. By combining the voltage scaling unit, switching elements, and shunt resistor into the primary side regulation path, the system achieves both accurate regulation and current selection in a single integrated circuit, reducing overall component count and cost compared to separate secondary side regulation approaches.
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 easy selection of output currents by adjusting scaling factors, reducing noise and component complexity, and eliminating the need for galvanic isolation in feedback paths, thus improving efficiency and reliability.
Implementation Method 1
a sensing path with a shunt resistor for sensing a voltage drop at the shunt resistor representing the current through the switch
Implementation Method 2
Incorporating a voltage scaling unit in the feedback path with at least two different scaling factors, allowing for modification of the voltage signal
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A switched converter (1) for driving LEDs (16) or for supplying a further LED converter stage comprising a switch (2), a control unit (3) for controlling the switch (2), a sensing path with a shunt resistor (4) for sensing a voltage drop at the shunt resistor (4) representing the current through the switch (2) in the closed state of the switch (2), and a feedback path for feeding back a voltage signal to the control unit (3) that represents the voltage drop at the shunt resistor (4) of the sensing path, wherein the control unit (3) is configured to use the voltage signal, which is fed back on the feedback path, to control the clocking of the switch (2), and wherein the switched converter (1) further comprises a voltage scaling unit (5) in the feedback path for scaling the voltage signal, which is fed back on the feedback path, by at least two different scaling factors, or wherein the switched converter (1) further comprises for at least one phase of a mains voltage different mains connection terminals (15) for connecting with the corresponding phase and a voltage scaling unit (5) in the feedback path for scaling the voltage signal, which is fed back on the feedback path, by at least two different scaling factors depending on to which mains connection terminal (15) the phase is connected, or a voltage scaling unit in the sensing path for scaling the voltage drop at the shunt resistor unit by at least two different scaling factors depending on to which mains connection terminal (15) the phase is connected.