Buck Converter Current Sensing for High-Voltage LED Control
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Solution Overview
Problem
Existing converter technologies for LED lighting systems face challenges in providing multichannel output functions with high precision current control, low switching losses, and wide voltage operation range while maintaining cost-effectiveness and compact size, particularly when controlling peak current at high output voltages.
Innovation Solution
A converter device with a control strategy that includes an electronic switch, a diode for current recirculation, and a current-detection circuitry using resistors and capacitors to detect and control peak current referenced to ground, operating in quasi-resonant mode to reduce losses and enhance precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current transformer is used to detect peak current, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the peak current detection function from the main power circuit by using a separate sensing resistor Rs connected in series with the LED string. This allows independent optimization of the detection circuit without affecting the main power conversion circuit, reducing overall system complexity while maintaining detection precision.
Solution Approach 2:
The patent introduces an intermediary sensing resistor Rs that converts current information into voltage information (Vr = Io × Rs). This intermediary element enables precise current measurement through voltage comparison by the operational amplifier, avoiding the need for complex current transformers while maintaining measurement accuracy.
2Measurement precision
If feedback voltage is referenced to output voltage, then control precision is improved, but adaptability to high voltage applications deteriorates
Solution Approach 1:
The patent creates a virtual ground reference at the inverting input of the operational amplifier that maintains a stable reference potential independent of output voltage variations. This allows the feedback network to maintain precise control ratios across a wide voltage range, enabling the circuit to adapt to both low and high voltage applications while preserving control precision.
Solution Approach 2:
The operational amplifier acts as an intermediary that compares the feedback voltage Vf with the reference voltage Vr and generates an error signal that drives the PWM controller. This intermediary comparison mechanism decouples the control precision from the absolute output voltage level, allowing precise control across varying voltage conditions.
3Productivity
If switching frequency is increased to improve response speed, then productivity is improved, but energy losses increase
Solution Approach 1:
The patent employs periodic PWM switching control where the MOSFET is switched on and off at optimized frequencies. The PWM duty cycle is dynamically adjusted based on the error signal from the operational amplifier, allowing the system to achieve fast response through periodic control while minimizing switching losses by avoiding excessive frequency operation.
Solution Approach 2:
The patent implements a closed-loop feedback system where the operational amplifier continuously monitors the output current through the sensing resistor and adjusts the PWM duty cycle accordingly. This feedback mechanism enables fast response to load changes without requiring high switching frequency, as the system can make precise incremental adjustments to the duty cycle based on real-time error signals, thereby reducing switching losses.
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
The solution achieves high precision current control, low switching losses, and wide voltage operation range with simplified control, suitable for high output voltages, and is applicable to various converter topologies including buck, forward, and bridge converters.
Implementation Method 1
a first resistor Ra and a first capacitor Ca arranged in series with respect to one another and connected in parallel to the buck inductance or coil Lb... configured to detect a current ILb flowing through the inductance Lb
Implementation Method 2
an electronic switch S1 set between an input node at a voltage Vinput and a driver node N... an inductance Lb coupled between the driver node N and an output node OUT
Implementation Method 3
a diode D configured to enable a current flow between ground GND and the driver node N
Data Source
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AI summary
A converter device (10), such as a buck converter, that can be used for driving LED lighting sources (L) comprises: an input node configured to receive an input signal (Vinput) and an output node (OUT) configured to have an electrical load (L) coupled thereto; an inductance (Lb, RLb) between the output node (OUT) and a driver node (N); and an electronic switch (S1) between the input node (Vinput) and the driver node (N), wherein the driver node (N) is electrically coupled to the input node (Vinput) in response to the electronic switch (S1) being conductive, with a current-recirculation diode (D) configured to facilitate the flow of current between ground (GND) and the driver node (N). Current-detection circuitry (Ra, Ca, Cb, Rb) is provided, comprising the series connection of a first resistor (Ra) coupled to the driver node (N) and a first capacitor (Ca) coupled to the output node (OUT), a second capacitor (Cb) having a first end coupled between the first resistor (Ra) and the first capacitor (Ca) and a second end coupled to a current-detection node (P), with a second resistor (Rb) between the current-detection node (P) and ground (GND). Zeroing circuitry (S2) is likewise provided between the current-detection node (P) and ground (GND), the zeroing circuitry (S2) being configured to force the current-detection node (P) to ground in response to the electronic switch (S1) being nonconductive.