Predictive LED Forward Voltage Slew Rate Control
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Solution Overview
Problem
LED lighting systems generate substantial electromagnetic interference (EMI) due to abrupt changes in current and high series inductance, which can affect nearby electronic communication systems, and existing solutions like filter circuits and shielding compromise system efficiency and increase costs.
Innovation Solution
The implementation of a light emitting diode (LED) lighting system with a current source connected to series-connected LED modules, each equipped with a slew rate control circuit and a shunt transistor, along with a ramp generator circuit and amplifier to manage voltage and current transitions smoothly, reducing EMI by controlling the slew rate of voltage changes across the modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If filter circuits and shielding are used to reduce EMI, then electromagnetic interference is reduced, but system efficiency is compromised and cost increases
Solution Approach 1:
The patent applies preliminary action by predicting the future forward voltage of LEDs before switching occurs. The system uses a ramp generator and amplifier to pre-establish a controlled voltage ramp that anticipates the voltage change needed, allowing the LED current to transition smoothly without abrupt changes. This predictive approach prevents EMI generation at its source rather than filtering it afterward, maintaining system efficiency without requiring additional shielding or filter circuits.
Solution Approach 2:
The patent changes the voltage transition parameter from abrupt to gradual by implementing a controlled ramp function. Instead of instant voltage switching that causes high di/dt and EMI, the system varies the voltage parameter continuously over time using a ramp generator. This parameter transformation smooths current transitions and eliminates the need for energy-consuming filter circuits while maintaining LED drive functionality.
2Object-affected harmful factors
If filter circuits and shielding are used to reduce EMI, then electromagnetic interference is reduced, but system cost increases
Solution Approach 1:
The patent extracts the EMI reduction function from external components (filters and shielding) and implements it within the existing LED driver circuitry. By incorporating a ramp generator and predictive forward voltage circuit into the LED driver itself, the system eliminates the need for separate filter circuits and shielding components. This extraction approach reduces both component count and system cost while maintaining EMI reduction effectiveness.
Solution Approach 2:
The LED driver circuit serves itself by generating the controlled voltage ramp internally through its own ramp generator and amplifier components. The system uses its existing power supply and control infrastructure to create smooth voltage transitions without requiring external EMI filtration or shielding. This self-service approach eliminates additional components and reduces overall system complexity and cost.
3Ease of operation
If abrupt current changes occur in series-connected LEDs, then PWM control is simple, but substantial EMI is generated
Solution Approach 1:
The patent introduces a ramp generator and amplifier as intermediary components between the PWM control signal and the LED array. This intermediary circuitry translates the simple PWM control signal into a smooth, controlled voltage ramp that drives the LEDs. The intermediary preserves the simplicity of PWM control while eliminating abrupt current changes that generate EMI, effectively decoupling control simplicity from EMI generation.
Data Source
AI summary
A light system is disclosed. The light system includes a light emitting diode (LED) and a shunt transistor having a current path connected to the LED. A ramp generator circuit generates a ramp voltage. An amplifier has a first input terminal connected to the LED, a second input terminal coupled to receive the ramp voltage, and an output terminal connected to a control terminal of the shunt transistor.