LED Power Controller Soft-Start Noise Reduction
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Solution Overview
Problem
Power supplies for LEDs generate significant audio noise due to large load transitions during dimming operations, which are unpleasant and need to be suppressed or reduced in consumer products.
Innovation Solution
The implementation of a power controller with a soft-start mechanism and a soft-brake mechanism, along with a dual-driver gate-driving circuit, to manage the switching of power switch 15, reducing the energy allocated to harmonic frequencies and thus minimizing noise. This includes configuring the ON time during soft-start and soft-brake periods to limit power conversion and ensure smoother transitions between dimming-ON and dimming-OFF periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If dimming signal VDIM is used to control LED chains illumination, then brightness adjustment is achieved, but large load transitions cause audio noise due to energy allocated to harmonic frequencies
Solution Approach 1:
The soft-start mechanism is activated before the normal dimming operation to gradually ramp up the power switch duty cycle from zero to its target value. This preliminary action prevents sudden load transitions that would otherwise generate large harmonic currents and audio noise when the dimming signal is first asserted.
Solution Approach 2:
The power switch operates with periodic switching cycles during normal dimming operation, but during soft-start and soft-brake periods, the duty cycle is modified to create a smoother, more gradual periodic pattern. This reduces the amplitude of harmonic frequencies while maintaining the necessary illumination control functionality.
2Loss of energy
If power switch 15 is alternatively turned on and off to build up output voltage VOUT, then power conversion efficiency is improved, but large load transitions during dimming cause harmonic frequencies and noise
Solution Approach 1:
Before normal power conversion operation begins, the soft-start mechanism pre-charges the output capacitor and gradually increases the power switch duty cycle. This preliminary action ensures that when full-power operation commences, the load transition is minimized, reducing harmonic generation while maintaining efficient power conversion.
Solution Approach 2:
The duty cycle parameter of the power switch is dynamically modified during soft-start and soft-brake periods. Instead of abrupt transitions between 0% and 100% duty cycle, the parameter changes gradually through intermediate values, reducing the spectral content of harmonic frequencies while preserving the essential power conversion function.
3Illumination intensity
If current IIN is drained from input node VIN during dimming-ON period, then LED chains illuminate, but sudden current transitions generate noise unpleasant to human
Solution Approach 1:
The soft-start mechanism activates before the dimming-ON period to gradually establish the input current IIN at its target value. This preliminary current ramping prevents sudden inrush currents that would otherwise be converted to audible noise by the inductive device, while still enabling the LED chains to illuminate as required.
Solution Approach 2:
The soft-start and soft-brake mechanisms act as intermediary control stages between the dimming signal and the power switch. These intermediaries smooth out the abrupt current transitions by introducing gradual ramping phases, thereby eliminating the direct coupling between sudden load changes and audible noise generation.
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 effectively reduces audio noise by minimizing the energy in harmonic frequencies, resulting in a quieter operation of LED power supplies, enhancing user experience by reducing unwanted noise in consumer products.
Implementation Method 1
power controller 18 alternatively turns on and off power switch 15 to store electric power in inductive device PRM and to release the stored electric power such that output voltage VOUT with required specifications is built up
Data Source
AI summary
Disclosure has power controllers and control methods used therein. A disclosed power controller is adapted for a power converter to power at least one light emitting diode. The power converter includes a power switch with a control gate to make an inductive energized or de-energized. The power converter receives a dimming signal to substantially control the lighting of the light emitting diode. The power controller has a gate-driving circuit, for driving the control gate according to a pulse-width signal and the dimming signal. When the dimming signal is asserted the gate-driving circuit has a first driving force. When the dimming signal is deasserted the gate-driving circuit has a second driving force less than the first driving force.