Vehicle Lamp PWM Phase Shifting for Lower Peak LED Current
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Solution Overview
Problem
The power supply circuit in existing Adaptive Driving Beam (ADB) lamps experiences a sudden increase in load current due to simultaneous turning on of multiple LEDs, requiring a large current supply capacity and favorable load regulation characteristics.
Innovation Solution
A controller is used to pulse width modulation (PWM) control multiple light-emitting pixels in an array, employing a common counter and signal processing unit to generate individual PWM signals with offset values, shifting their phases to smooth current flow and reduce peak current demand.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple LEDs are turned on simultaneously at the start of the PWM period, then all LEDs can be illuminated with the required light intensity, but the load current suddenly increases requiring a power supply circuit with large current supply capacity
Solution Approach 1:
The patent applies periodic action by using PWM (Pulse Width Modulation) control to illuminate LEDs in a periodic manner rather than continuously. The controller turns on LEDs at specific periods with controlled duty cycles, which allows the power supply circuit to handle current in periodic pulses rather than requiring continuous high current capacity, thus resolving the contradiction between maintaining light intensity and reducing current supply capacity requirements.
Solution Approach 2:
The patent applies preliminary action by pre-calculating and storing optimal PWM duty cycle values for each LED in a lookup table before operation. This preliminary preparation allows the controller to quickly retrieve and apply appropriate duty cycles during operation, enabling smooth current control without sudden load increases, thereby reducing the power supply circuit's current capacity requirements while maintaining required illumination intensity.
2Ease of operation
If multiple LEDs are turned on simultaneously, then the light distribution can be controlled according to the pattern, but the power supply circuit requires favorable load regulation characteristics
Solution Approach 1:
The patent uses PWM periodic control to manage LED illumination, where each LED is controlled with specific duty cycles within each PWM period. This periodic action allows the power supply circuit to experience controlled, predictable current variations rather than sudden simultaneous load changes, improving load regulation characteristics while maintaining ease of light distribution control through the controller's programming.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the PWM duty cycle parameters for each LED based on pre-stored optimal values. This allows the system to change illumination parameters smoothly over time rather than making abrupt changes, which improves load regulation characteristics of the power supply circuit while maintaining flexible light distribution control capability.
Data Source
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AI summary
A controller 300 pulse width modulation (PWM) controls multiple light-emitting pixels PIX1 through PIXn arranged in an array that form a variable light distribution lamp 200. A common counter 310 is provided in common for the multiple light-emitting pixels PIX1 through PIXn, and generates a common count value cv having a ramp waveform. A signal processing unit 320 generates multiple duty cycle instruction values for specifying the duty cycles of the multiple light-emitting pixels PIX1 through PIXn according to a light distribution instruction S1. Furthermore, the signal processing unit 320 stores multiple offset values that correspond to the multiple light-emitting pixels, generates an individual count value for each light-emitting pixel by adding the corresponding offset value to the common count value, and generates individual PWM signals pwm1 through pwmn that correspond to results of comparison between the individual count values and the corresponding duty cycle instruction values.