LED Forward Voltage Measurement for Power Multiplexer Threshold
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Solution Overview
Problem
LEDs require adaptive forward voltage measurement to maintain system efficiency due to variations caused by process, temperature, aging, and usage factors, necessitating a method to set the lowest possible headroom while ensuring desired current delivery.
Innovation Solution
A method and apparatus for measuring anode and cathode voltages of LEDs, calculating the forward voltage, and setting a voltage multiplexer switch threshold to optimize LED operation, incorporating a processor, analog-to-digital converter, and pulse-width modulator to adaptively manage power supply switching based on measured values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed voltage threshold is used for power supply switching, then the system is simple to implement, but it cannot adapt to LED forward voltage variations caused by process, temperature, aging, and usage factors
Solution Approach 1:
The system performs preliminary measurement of LED forward voltage during initialization or calibration phase. The voltage multiplexer measures the actual forward voltage of each LED and stores this information in non-volatile memory. This preliminary action allows the system to adapt to individual LED characteristics without requiring continuous complex measurement during operation.
Solution Approach 2:
The system uses the LED's own forward voltage characteristic to determine the optimal power supply switching threshold. By measuring the actual forward voltage of each LED and using this self-information to set the threshold, the system eliminates the need for external calibration equipment or complex adaptive algorithms during normal operation.
2Loss of energy
If the power supply switching threshold is set low to maximize efficiency, then system power efficiency improves, but current roll-off occurs due to insufficient headroom
Solution Approach 1:
The system dynamically adjusts the power supply switching threshold parameter based on the measured forward voltage of each LED. Instead of using a fixed threshold, the threshold is set to Vf + headroom, where Vf is the actual forward voltage measured during calibration. This parameter change allows the system to optimize efficiency for each specific LED while maintaining sufficient headroom to prevent current roll-off.
3Loss of energy
If individual LED forward voltage measurement is performed, then optimal power efficiency is achieved, but measurement time and system complexity increase
Solution Approach 1:
The forward voltage measurement is performed during initialization, boot-up, or calibration sequences rather than continuously during operation. This preliminary timing allows the system to establish accurate LED characteristics early in the device lifecycle without impacting normal operational performance or requiring continuous measurement overhead.
Solution Approach 2:
Once the forward voltage is measured and stored in non-volatile memory, the system can reuse this information across multiple operation cycles without re-measuring. This allows the measurement action to be performed once and continuously benefit the system, eliminating repeated measurement time and energy consumption during normal operation.
Data Source
AI summary
A method and apparatus for optimizing a light emitting diode (LED) operation range is provided. The method comprises the steps of: turning on at least one LED; and then measuring an anode voltage of the at least one LED; then measuring a cathode voltage of the at least one LED. Once the measurements are completed, a forward voltage of the at least one LED is calculated. After the calculation, the at least one LED is turned off and a power multiplexer switch threshold is set for that LED based on the measured anode and cathode voltages.