Light-Emitting Thyristor Circuit With Level-Shifted Turn-Off Control
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Solution Overview
Problem
Existing image forming apparatuses face issues with turn-off failure and erroneous turn-on states of light emitting thyristors due to fixed voltage levels, limiting the variable ranges of reference and turn-on potentials.
Innovation Solution
A light emitting device with a level shift circuit that adjusts the low-level voltage of the turn-off signal based on the turn-on potential, using a turn-off thyristor switched from OFF to ON when the signal reaches a low level, and a level shift circuit with an undershoot circuit to prevent turn-off failure and erroneous turn-on states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed voltage level is used for the turn-off signal, then the circuit operation is simple, but the variable ranges of reference potential and turn-on potential are limited
Solution Approach 1:
The patent applies dynamics by making the low-level voltage of the turn-off signal variable rather than fixed. The level shift circuit dynamically adjusts the low-level voltage based on the turn-on potential value, allowing the system to adapt to different operating conditions while maintaining reliable turn-off operation across a wider range of potentials.
Solution Approach 2:
The level shift circuit acts as an intermediary between the turn-off signal generator and the turn-off thyristor. It translates the fixed high-level/low-level signal into an adjusted voltage level that is appropriate for the current turn-on potential, thereby enabling broader potential ranges without directly modifying the original signal generation logic.
2Illumination intensity
If the turn-on potential is increased to increase light intensity, then the light exposure amount increases, but turn-off failure or erroneous turn-on of the turn-off thyristor may occur
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the low-level voltage parameter of the turn-off signal based on the turn-on potential. When the turn-on potential increases to boost light intensity, the level shift circuit proportionally increases the low-level voltage, maintaining a safe voltage difference that prevents turn-off failure and erroneous turn-on while allowing higher operating potentials.
Solution Approach 2:
The level shift circuit implements feedback by monitoring the turn-on potential value and using it to determine the appropriate low-level voltage for the turn-off signal. This feedback mechanism ensures that the turn-off signal characteristics are continuously adapted to match the current operating conditions, preventing reliability issues that would occur with fixed voltage levels.
3Illumination intensity
If the reference potential is decreased to reduce light intensity, then the light exposure amount decreases, but the turn-off thyristor may be erroneously turned ON
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the low-level voltage parameter of the turn-off signal based on the turn-on potential value. When the turn-on potential decreases to reduce light exposure, the level shift circuit proportionally decreases the low-level voltage, maintaining a sufficient voltage difference that prevents erroneous turn-on of the turn-off thyristor while allowing lower operating potentials for reduced intensity operation.
Data Source
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AI summary
A light emitting device includes: plural light emitting elements including anode terminals to which a reference potential is applied, and cathode terminals connected to a first end of a current limiting resistor in common; a turn-on instructor configured to sequentially output turn-on instruction signals to the plural light emitting elements to sequentially turn ON the plural light emitting elements; a turn-on potential applier configured to apply a turn-on potential to a second end of the current limiting resistor; a turn-off instructor configured to, when turning OFF a light emitting element in an ON state, output a turn-off signal while changing the turn-off signal from a high level to a low level; a level shift circuit configured to change a low-level voltage of the turn-off signal according to the turn-on potential; and at least one turn-off thyristor including an anode terminal to which the reference potential is applied, a gate terminal connected to the first end of the current limiting resistor, and a cathode terminal to which the turn-off signal having the low-level voltage changed by the level shift circuit is input, the at least one turn-off thyristor being configured to be switched from OFF to ON when the turn-off signal reaches the low level, and change potentials at the cathode terminals of the plural light emitting elements to potentials at which the plural light emitting elements are turned OFF.