Two-Wire LED Dimming Pre-Charge Circuit for Inrush Current Control
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Solution Overview
Problem
High inrush currents during PWM-controlled dimming in two-wire LED lighting systems can damage switches and capacitors, and trigger protection mechanisms, making the systems unreliable and prone to power supply interruptions.
Innovation Solution
A pre-charge stage is introduced between the switch and capacitance to limit inrush currents, using a buck converter with a low-pass LC module and a control switch that adjusts the charging current to prevent peak values from exceeding safe limits, ensuring stable power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a two-wire PWM-controlled dimming system is used to simplify the circuit and reduce cost, then the circuit complexity is reduced, but high inrush currents occur when the switch closes, damaging components and triggering protection mechanisms
Solution Approach 1:
The patent applies preliminary action by introducing a pre-charge phase before the main power switch closes. During this pre-charge phase, a separate pre-charge switch closes first to charge the capacitance C through a controlled path, limiting the inrush current. Only after the capacitance is charged does the main switch close, preventing the harmful inrush current peak that would otherwise damage components.
Solution Approach 2:
The patent uses an intermediary element - a pre-charge switch - that mediates between the power source and the capacitance during the initial charging phase. This intermediary switch provides a controlled current path, preventing direct connection of the power source to the capacitance through the main switch, thereby limiting inrush current while still enabling the two-wire dimming functionality.
2Illumination intensity
If the switching frequency is increased above human eye sensitivity range to achieve smooth dimming, then the dimming quality improves, but the inrush current peak intensity increases, risking component damage
Solution Approach 1:
The pre-charge phase performs preliminary action by charging the capacitance before the main switch operates. This separates the capacitance charging function from the PWM switching function, allowing high-frequency PWM switching for smooth dimming without generating harmful inrush currents, since the capacitance is already charged and no large current peaks occur during switching.
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 pre-charge stage effectively limits inrush currents, preventing damage to components and ensuring reliable operation by maintaining average current within safe limits, thus stabilizing power flow and reducing the risk of protection triggers.
Implementation Method 1
The peak value of this current is nominally limited only by the parasitic resistance of the power supply line including the switch T and the capacitance C
Implementation Method 2
the capacitance C observable as a whole downstream of the switch T, capacitance which may also include at least one capacitor included in the input stage of the driver D
Implementation Method 3
using a buck converter with a low-pass LC module
Implementation Method 4
The peak value of this current is nominally limited only by the parasitic resistance of the power supply line
Data Source
Figure 1~3
Figure 4~6
Figure 7a~7d
AI summary
A light source (S) is powered by a two-wire power supply line (10) in which is interposed a switch (T) to control the transfer of said power supply to said light source (S), thus regulating the luminosity of the source (S). Downstream of the switch (T) there is a capacitance (C) crossed by a charge current when said switch (T) is closed. A pre-charge stage (P) that limits such a charge current to a given value is interposed between the switch (T) and the capacitance (C).