LED Power Control Circuit for Traffic Signals
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Solution Overview
Problem
LED traffic signals experience varying light intensity due to temperature changes, leading to increased current at high temperatures and decreased current at low temperatures, which can stress the LEDs and affect their service life, and existing solutions fail to maintain constant power and light intensity effectively.
Innovation Solution
A power control circuit that supplies controllable DC voltage and current to LEDs, using a multiplier circuit to generate a variable power-representative signal and a feedback control loop to adjust the voltage and current, ensuring constant light intensity and power consumption across different temperatures and aging conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If constant voltage is maintained across LEDs, then voltage stability is improved, but LED current varies exponentially with temperature causing light intensity instability and LED stress
Solution Approach 1:
The patent implements a feedback control system that measures the actual LED forward voltage and adjusts the drive voltage dynamically to maintain constant LED current despite temperature variations. The controller continuously monitors LED parameters and modifies the output voltage to compensate for temperature-induced forward voltage changes, thereby stabilizing both current and light intensity.
Solution Approach 2:
The system dynamically changes the drive voltage parameter based on measured LED forward voltage characteristics at different temperatures. By adjusting the voltage parameter in real-time according to temperature conditions, the system maintains optimal LED operating current and prevents the exponential current variations that occur with constant voltage operation.
2Stability of the object's composition
If fixed LED output current is used, then current stability is improved, but light intensity varies with temperature due to forward voltage changes
Solution Approach 1:
The feedback mechanism measures actual LED forward voltage and adjusts the drive current dynamically. This ensures that despite temperature-induced forward voltage changes, the LED receives the optimal current required to maintain consistent light intensity, rather than using a fixed current that results in temperature-dependent brightness variations.
Solution Approach 2:
The system transitions from static fixed current operation to dynamic current adjustment. The drive current is continuously adapted based on real-time measurements of LED forward voltage characteristics, allowing the system to respond to temperature changes and maintain optimal light output across varying operating conditions.
3Illumination intensity
If LED current increases at high temperatures to maintain light output, then light intensity is maintained, but LED stress increases reducing service life
Solution Approach 1:
The feedback control system detects elevated temperatures through forward voltage measurements and automatically reduces the drive current to safe levels. This prevents thermal runaway and excessive LED stress that would occur with fixed current operation, thereby extending LED service life while maintaining acceptable light output through intelligent current management.
Solution Approach 2:
The system takes preliminary protective action by detecting temperature trends through forward voltage changes and preemptively adjusting current before damaging conditions develop. This prevents thermal stress accumulation and extends LED reliability by avoiding operating conditions that would accelerate degradation.
4Reliability
If LED current decreases at low temperatures to maintain safe operating levels, then LED stress is reduced, but light intensity becomes dim
Solution Approach 1:
The feedback system detects low-temperature conditions through forward voltage measurements and dynamically adjusts the drive current upward to optimal levels for that temperature. This compensates for the increased forward voltage at low temperatures, maintaining adequate light intensity while ensuring safe operating conditions through continuous monitoring and adjustment.
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 maintains light intensity and power consumption within +/- 10% of the stated value, effectively stabilizing LED performance across temperature variations and aging, reducing stress on LEDs and improving their service life.
Implementation Method 1
multiplying an output forward voltage and a variable current-representative signal from the light-emitting load to generate a variable power-representative signal
Implementation Method 2
feedback controlling the controllable dc voltage and current in relation to the variable power-representative signal to keep the light intensity produced by the light source substantially constant
Implementation Method 3
LED (light-emitting diode) lamps
Implementation Method 4
light-emitting diode
Data Source
Figure 1
Figure 2-A
Figure 2-B
AI summary
A light source with substantially constant intensity and power consumption is provided. The light source includes a controllable dc voltage and current source; a non-linear light-emitting load supplied with dc voltage and current from the controllable dc voltage and current source; a current sense circuit connected in series with the non-linear light-emitting load; a variable LED forward voltage (varying with temperature, binning batch, aging) sensor circuit; a multiplier operative to measure a power-representative signal; and a power consumption control feedback circuit through which the dc voltage and current source is controlled in relation to the variable forward voltage representative signal to adjust the dc voltage and then a current to amplitudes that keep the light intensity and power consumption produced by the light source substantially constant.