Three-Terminal Light Emitting Thyristor Array for Print Head
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Solution Overview
Problem
Conventional LED print heads with thousands of LEDs in a matrix pattern face challenges due to high current requirements, leading to increased chip size and cost of power MOS transistors, making it difficult to reduce the size and cost of the print head.
Innovation Solution
A light emitting element array with three-terminal light emitting thyristors, where the gates are driven using consolidated gate drive circuits with a level shift function, eliminating the need for a power MOS transistor and reducing interference between concurrently driven elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a power MOS transistor is used to drive a large current for all LEDs, then the LEDs can be switched in time division, but the chip size and cost of the power MOS transistor increase
Solution Approach 1:
The patent segments the gate drive function by providing individual gate drive circuits for each light emitting element rather than using a single power MOS transistor for all elements. This segmentation allows each element to be controlled independently with smaller, more efficient drive circuits, resolving the contradiction between switching capability and chip size.
Solution Approach 2:
The patent transitions from a two-terminal LED structure to a three-terminal light emitting thyristor structure, adding the gate terminal as a new dimension of control. This enables independent gate control that eliminates the need for large current-carrying power MOS transistors while maintaining time division switching capability.
2Productivity
If a power MOS transistor is used to drive a large current, then time division switching is achieved, but the cost of the power MOS transistor increases
Solution Approach 1:
By segmenting the gate drive function into individual circuits for each light emitting element, the patent eliminates the need for expensive high-current power MOS transistors. Each individual gate drive circuit is much cheaper to manufacture while collectively achieving the same time division switching capability.
Solution Approach 2:
The patent replaces the expensive power MOS transistor with multiple inexpensive individual gate drive circuits. While there are more individual circuits, each is much cheaper to manufacture, resulting in overall cost reduction while maintaining the required switching functionality.
3Device complexity
If conventional two-terminal LEDs are used, then the structure is simple, but it is difficult to reduce the size and cost of the print head
Solution Approach 1:
The patent adopts three-terminal light emitting thyristors instead of two-terminal LEDs, adding the gate terminal dimension. This additional terminal enables independent control that eliminates the need for large power MOS transistors, thereby reducing print head size while the modular circuit design keeps overall complexity manageable.
Solution Approach 2:
The patent changes the fundamental electrical parameters of the light emitting element from two-terminal LED characteristics to three-terminal thyristor characteristics. This parameter change enables gate-controlled operation that reduces the size requirements for drive circuits and overall print head dimensions.
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
This solution allows for efficient driving of light emitting elements with minimized interference, reducing the size and cost of the optical print head and image forming apparatus while maintaining high-quality light emitting efficiency.
Implementation Method 1
a light emitting element array 200 including a plurality of light emitting elements 210; a drive circuit 100 for driving the light emitting element array 200... each having a first terminal, a second terminal, and a third terminal... A drive signal is supplied to the first terminals... control signal is applied to the third terminals, so that the light emitting elements are driven
Data Source
AI summary
A light emitting element array includes a plurality of light emitting elements each having a first terminal, a second terminal, and a third terminal. The light emitting elements are arranged next to each other to form a group. The first terminal receives a drive signal, the second terminal is connected to ground, and the third terminal has a threshold voltage or a threshold current controllable from outside so that the light emitting elements are driven in a time division way.