High-Side Switch Firing Circuit for Thermal Inkjet Nozzles
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Solution Overview
Problem
Current low-side switch firing circuits in thermal inkjet printers are prone to voltage leakage, which can damage other firing circuits if a heater resistor fails, leading to unintended damage to neighboring nozzles.
Innovation Solution
The implementation of a high-side switch firing circuit with a MOS transistor operating in constant current mode, where the switch is connected to the voltage source and the heater resistor is connected to ground, minimizing voltage leakage and isolating faulty circuits from others.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a low-side switch firing circuit is used, then the circuit design is simple and easy to manufacture, but voltage leakage occurs when a heater resistor fails, damaging other firing circuits
Solution Approach 1:
The patent applies segmentation by dividing the common power supply rail into individual isolated supply paths for each firing circuit. Each firing circuit has its own dedicated power supply path through the high-side switch, preventing voltage leakage from one circuit from affecting others. This segmented isolation maintains manufacturing simplicity while significantly improving reliability.
Solution Approach 2:
The patent introduces an intermediary isolation mechanism using individual power supply paths and body connections for each firing circuit. The body of each MOS transistor is connected to the source, creating an intermediary isolation barrier that prevents voltage leakage from propagating to neighboring circuits, thus protecting other firing circuits from damage.
2Reliability
If a high-side switch firing circuit is used, then voltage leakage is minimized and circuit isolation is improved, but the circuit complexity increases
Solution Approach 1:
The patent applies universality by using the high-side switch configuration to achieve multiple objectives simultaneously: circuit isolation, voltage leakage prevention, and consistent current delivery. The same circuit architecture that provides reliability also enables multi-functional operation across different firing circuits without requiring additional isolation components.
Solution Approach 2:
The patent utilizes parameter changes by operating the MOS transistor in constant current mode rather than switching modes. This parameter change allows the high-side switch to maintain stable current delivery while providing isolation benefits, effectively managing the complexity-reliability tradeoff through controlled electrical parameters.
3Productivity
If multiple firing circuits operate concurrently, then productivity increases, but parasitic resistance increases causing voltage drops
Solution Approach 1:
The patent applies segmentation by providing dedicated power supply paths for each firing circuit, isolating the current paths to minimize parasitic resistance interactions. This segmentation allows multiple circuits to operate concurrently without significant voltage drops affecting individual circuit performance.
Solution Approach 2:
The patent implements feedback through the constant current mode operation of the MOS transistor, which automatically compensates for voltage drops caused by parasitic resistance. The transistor adjusts its operation to maintain stable current delivery even when multiple circuits are firing concurrently, thereby maintaining productivity.
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 design ensures that only the affected firing circuit and nozzle are impacted by a malfunctioning heater resistor, preventing damage to neighboring circuits and maintaining consistent ink ejection current despite parasitic resistance increases during concurrent firing.
Implementation Method 1
The switch (102) operates in a constant current mode
Implementation Method 2
current flows through the heater resistor (104), which heats ink and causes it to eject from the corresponding nozzle
Data Source
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AI summary
A firing circuit (100) for a thermal inkjet-printing nozzle includes a heater resistor (104) and a switch (102). The heater resistor heats ink to cause the ink to be ejected from the nozzle. The heater resistor has a first end and a second end, the second end connected to a ground. The switch controls activation of the heater resistor. The switch has a first end connected to a voltage source and a second end connected to the first end of the heater resistor. The switch operates in a constant current mode, such that an at least substantially constant current flows through the heater resistor upon activation.