MOS Transistor Drive Circuit for Light Emitting Thyristors
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Solution Overview
Problem
Conventional drive devices for light emitting thyristors experience oscillations due to negative resistance, leading to fluctuations in drive current pulse width and exposure energy, and signal reflections through long cables increase rising and falling times of the drive current waveform, hindering high-speed switching control.
Innovation Solution
A drive device with a MOS transistor-based drive circuit that includes a substrate bias to operate in a saturation region, increasing output resistance beyond the negative resistance of the light emitting thyristor, and a terminating circuit with a termination resistance connected to the common terminal of the light emitting elements to minimize signal reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current limiting resistor is used to drive the light emitting thyristor array, then the drive current can be limited, but the resistance value is lower than the absolute value of the negative resistance of the light emitting thyristor, causing oscillation in the drive current
Solution Approach 1:
The patent changes the resistance parameter by replacing the conventional current limiting resistor with a MOS transistor-based drive circuit. The MOS transistor operates in saturation region with substrate bias, providing a dynamically adjustable output resistance that exceeds the absolute value of the negative resistance of the light emitting thyristor, thereby eliminating oscillation while maintaining current limiting functionality.
Solution Approach 2:
The patent substitutes the simple resistive current limiting mechanism with an active MOS transistor-based electronic control system. The MOS transistor circuit provides intelligent current regulation through gate voltage control and substrate bias, replacing the passive resistor approach and enabling stable drive current without oscillation.
2Ease of operation
If the current limiting resistor and anode are connected via a long cable, then the components can be physically separated, but signal reflection occurs multiple times between the drive device and light emitting thyristor array, increasing rising and falling times of the drive current waveform
Solution Approach 1:
The patent introduces a terminating circuit with termination resistance as an intermediary element at the end of the long cable. This termination resistance matches the cable's characteristic impedance, absorbing signal reflections and preventing multiple reflections between the drive device and light emitting thyristor array, thereby maintaining high switching speed despite the long cable connection.
3Device complexity
If the MOS transistor operates in linear region, then the circuit is simpler, but the output resistance is not high enough to exceed the negative resistance of the light emitting thyristor, causing oscillation
Solution Approach 1:
The patent utilizes the dynamic characteristics of the MOS transistor by operating it in the saturation region with substrate bias. This dynamic operation mode enables the MOS transistor to provide a high output resistance that exceeds the negative resistance of the light emitting thyristor, ensuring stable drive current. The substrate bias dynamically adjusts the threshold voltage to maintain optimal operating conditions.
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
The solution prevents oscillations and maintains constant drive current, ensuring high-quality image formation with uniform print density and enabling high-speed switching control even with long cables.
Implementation Method 1
a substrate terminal set to have a potential different from the potential of the second power supply in the direction of increasing threshold voltage of the first MOS transistor
Implementation Method 2
a plurality of three-terminal light emitting elements each including: a first terminal connected to a first power supply; a second terminal configured to enable drive current flow to the first terminal from the second terminal
Data Source
AI summary
A drive device to drive a plurality of three-terminal light emitting elements, comprising: a drive circuit including a first MOS transistor and configured to drive conducting three-terminal light emitting elements among a plurality of three-terminal light emitting elements based on a received drive signal. The first MOS transistor includes: a third terminal connected to a second power supply having a potential different from a potential of the first power supply; a fourth terminal connected to the second terminals connected in common, a second control terminal configured to control a conduction state between the third terminal and the fourth terminal based on the drive signal; and a substrate terminal set to have a potential different from the potential of the second power supply in a direction of increasing threshold voltage of the first MOS transistor.