LED Driver Circuit Using Pre-charged Capacitors for Sequential Color Display
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Solution Overview
Problem
Color displays using sequentially-driven LEDs require separate driver circuits for each color due to differing power requirements, leading to increased cost, size, and weight, particularly problematic in helmet-mounted or head-mounted displays.
Innovation Solution
A power input system with current sensing units and pre-chargeable capacitors to provide controlled current and forward bias voltage to LEDs, allowing for efficient operation and reducing the need for multiple driver circuits by selectively connecting capacitors to apply appropriate voltages and currents based on the color being displayed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate driver circuits are used for each LED color, then each LED can be driven with appropriate current and voltage, but the device complexity, size, and weight increase significantly
Solution Approach 1:
A single driver circuit is designed to control multiple LEDs of different colors (red, green, blue) by dynamically switching between them using MOSFETs. The driver circuit performs multiple functions: current regulation, voltage switching, and sequential LED control, eliminating the need for separate dedicated driver circuits for each color while maintaining reliable LED operation.
Solution Approach 2:
The driver circuit uses dynamic switching elements (MOSFETs) to change the electrical connection state between the power supply, capacitors, and LEDs based on which color needs to be displayed. This dynamic reconfiguration allows one circuit to adaptively serve multiple LED colors with different electrical requirements, reducing overall system complexity.
2Reliability
If separate driver circuits are used for each LED color, then appropriate current control is achieved, but the size and weight of display circuitry increase
Solution Approach 1:
The driver circuits for red, green, and blue LEDs are merged into a single integrated driver circuit. This unified circuit shares common components including the power supply connection, current sensing resistor, control logic, and switching elements. By combining these previously separate circuits, the overall weight of the display circuitry is significantly reduced while maintaining accurate current control for each LED color through the shared current regulation mechanism.
3Loss of energy
If forward bias voltage is quickly changed for different colors, then power efficiency improves, but voltage switching delays occur
Solution Approach 1:
Capacitors are pre-charged to the appropriate forward bias voltages for each LED color before they are needed. The driver circuit maintains charged capacitors ready for immediate connection to any LED color. When a color needs to be displayed, the pre-charged capacitor is quickly switched to the LED, avoiding the time-consuming process of generating the voltage from scratch and reducing power loss during transitions.
Solution Approach 2:
Capacitors are introduced as intermediary energy storage elements between the power supply and the LEDs. These capacitors act as voltage buffers that can be quickly connected or disconnected from LEDs using MOSFET switches. This intermediary approach allows rapid voltage switching without directly drawing power from the main supply during transitions, thereby reducing power loss and switching delays.
4Device complexity
If uncontrolled current is supplied to LEDs, then circuit simplicity increases, but LED damage occurs due to power spikes
Solution Approach 1:
The driver circuit incorporates current sensing through a sensing resistor that monitors the actual current flowing to the LED. This feedback information is used by the control logic to regulate the current supplied to the LED, preventing overcurrent conditions that could damage the LED. The feedback mechanism maintains LED protection while keeping the circuit design relatively simple by using basic sensing and control elements.
Solution Approach 2:
The circuit includes protective elements such as current-limiting resistors, fuse components, and controlled switching mechanisms that are built into the driver circuit design beforehand. These protective measures are in place before any potential overcurrent event can occur, cushioning against power spikes and preventing LED damage. The protection is integrated into the normal circuit operation rather than being an afterthought.
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
Enables higher frame rates, prevents damaging power spikes and electromagnetic emissions, and reduces heat generation, while minimizing the size and weight of the display circuitry.
Implementation Method 1
a plurality of capacitor units connected to the input part to be provided with charge from a power supply for generating a respective one of a plurality of different respective forward bias voltages for application to the LEDs
Implementation Method 2
a plurality of light-emitting diodes (LED) each respectively operable to emit light to display a respective one of the plurality of different colours
Data Source
AI summary
A light source for a color display apparatus (1) for displaying light at optical wavelengths corresponding a plurality of different colors sequentially, comprising a plurality of light-emitting diodes (3, 4, 5) each respectively operable to emit light to display a respective one of the plurality of different colors, a power source (26) connected to the plurality of LEDs for supplying power thereto a plurality of capacitor units (7, 8, 9) connected to the power source to be provided thereby with charge for generating a respective one of a plurality of different respective forward bias voltages for application to the LEDs to operate the LED. A control unit (10) is operable to selectively connect a capacitor unit to an LED for applying a desired one of the different said forward bias voltages thereto according to the color of light which the LED is operable to display.