Switch Controller for LED Current Control Without Slope Compensation
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Solution Overview
Problem
Conventional buck converters for LED driving face limitations in Constant Current (CC) control, requiring complex circuits for duty cycle limitation and slope compensation to prevent sub-harmonics, and struggle with detecting voltage across high-voltage LED strings.
Innovation Solution
A power supply device with a switch controller that uses a sensing resistor to generate modulation sensing voltage, inverting-amplify it, and add an offset to control the power switch based on high and low peak references, synchronizing with the input voltage's zero crossing points to manage LED current limits effectively, eliminating the need for complex duty cycle limitation and slope compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional peak current control is used, then the power supply device can operate, but CC control characteristic is poor and sub-harmonics occur
Solution Approach 1:
The patent implements feedback control by detecting the current through a sensing resistor and using the detected signal to control the power switch. The controller adjusts the duty cycle based on the feedback from the current detection, enabling precise CC control and preventing sub-harmonics by continuously monitoring and adjusting the current waveform.
Solution Approach 2:
The patent replaces complex mechanical duty cycle limitation circuits and slope compensation circuits with an electronic control system. The controller uses electronic signal processing to achieve the same effects, eliminating the need for additional passive components and complex circuitry while improving control precision.
2Object-generated harmful factors
If duty cycle limitation and slope compensation are implemented, then sub-harmonics are prevented, but circuit complexity increases
Solution Approach 1:
The patent merges the functions of duty cycle limitation, slope compensation, and current control into a single integrated controller. The controller performs all these functions through electronic signal processing without requiring separate circuits, thereby preventing sub-harmonics while maintaining simple circuit architecture.
Solution Approach 2:
The patent extracts the essential control functions from complex passive circuits and implements them through active electronic control. By removing the need for separate duty cycle limitation and slope compensation circuits, the patent achieves sub-harmonic prevention with simpler overall circuit design.
3Measurement precision
If voltage sensing is used across high-voltage LED strings, then current can be detected, but measurement precision is difficult due to high voltage
Solution Approach 1:
The patent introduces a sensing resistor as an intermediary element to detect current. Instead of directly sensing the high voltage across the LED strings, the current flows through the sensing resistor and generates a proportional voltage that is much lower and easier to measure accurately. This intermediary approach enables precise current detection without the dangers and difficulties of direct high-voltage sensing.
Data Source
AI summary
The power supply device includes a power switch including one terminal to which an input voltage is transferred; an inductor including one terminal connected to another terminal of the power switch; a diode connected between a ground and a floating ground; a sensing resistor connected between the floating ground and the one terminal of the inductor. A switch controller compares a modulation sensing voltage depending on a sensing voltage generated from the sensing resistor with a high peak reference and a low peak reference when a LED string is connected between an inductor and the ground. The switch controller controls a switching operation of a power switch according to the comparison result. The high peak reference and the low peak reference are references for controlling an upper limit and a lower limit of an LED current flowing through the LED string, respectively.