LED Drive Circuit Ramping Current to Reduce EMI
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Solution Overview
Problem
Conventional LED drive circuits for pulse-lighting LEDs generate high-frequency currents that lead to electromagnetic interference (EMI), requiring costly components and measures to mitigate EMI, which increases development costs.
Innovation Solution
An LED drive circuit that uses a pulse-shaped drive current, incorporating an oscillator, up/down counter, digital-to-analog converter (DAC), and transistor to control the ramping up/down of the drive current, allowing for adjustable frequency and resolution to reduce EMI effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PWM-based switching operation is used to turn on/off many LEDs at the same time, then LED pulse-lighting characteristics are achieved, but high-frequency LED drive current generates electromagnetic interference (EMI)
Solution Approach 1:
The patent applies periodic action by using PWM (pulse width modulation) to periodically switch the LED drive current on and off. The up/down counter generates a periodic waveform that ramps up and down in a cyclic manner, creating controlled periodic current flow that maintains LED lighting efficiency while reducing EMI through gradual transitions rather than abrupt switching.
Solution Approach 2:
The patent implements dynamics by replacing fixed switching operations with dynamic ramping up/down of the LED drive current. The current transitions smoothly from zero to maximum and back to zero through the DAC converting digital counter values to analog current levels, creating a dynamic current profile that reduces electromagnetic interference while maintaining effective LED pulse-lighting.
2Object-generated harmful factors
If shield or filter components are added to reduce EMI emission, then electromagnetic interference is reduced, but component cost and development cost increase
Solution Approach 1:
The patent converts the potentially harmful abrupt switching action into a beneficial gradual ramping up/down action. By transforming the sharp edges of PWM switching into smooth triangular waveforms through the up/down counter and DAC, the circuit inherently reduces EMI generation at the source, turning what would have been a harmful electromagnetic emission problem into a controlled, low-interference operation without requiring additional filtering components.
Solution Approach 2:
The patent extracts the EMI-generating abrupt switching action from the LED drive circuit by replacing it with smooth ramping up/down current transitions. The up/down counter and DAC combination removes the harmful high-frequency components associated with traditional PWM switching, isolating and eliminating the EMI source while preserving the essential pulse-lighting function.
Data Source
AI summary
A LED drive circuit equipped with oscillator 18, up/down counter 20, and DAC 22 in order to drive multiple LEDs 10(1)-10(m) in a block. Up/down counter 20 carries out count-up/down operations in sync with clock CLK sent from oscillator 18 during the ramping up/down of pulse-lighting of the LEDs. DAC 22 converts counter count value DN into analog voltage signal VDAC and supplies it to the gate terminal of NMOS transistor 14 via low-pass filter 28 and buffer amplifier 24.