Key Matrix Wake-Up Circuit With Voltage Division for IC Protection
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Solution Overview
Problem
Key matrix circuits used in devices like image forming apparatuses face challenges when operating with power source voltages higher than the upper limit voltage that can be input to information processing apparatuses, such as ICs, which can lead to damage and operational limitations.
Innovation Solution
A key matrix circuit device that includes voltage dividing resistors and a wake-up circuit, allowing the use of higher power source voltages by ensuring the sense terminals are connected to a predetermined voltage or less, and utilizing a wake-up circuit to switch the mode from sleep to normal when a switch is activated, thereby protecting the IC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a power source voltage higher than the upper limit voltage is used, then the power supply capability is improved, but the information processing apparatus may be damaged
Solution Approach 1:
The patent introduces voltage dividing resistors as intermediary elements between the high voltage power source and the sense terminals of the key matrix circuit. These resistors act as mediators that automatically divide the high power source voltage to a safe level for the IC, allowing the system to utilize high voltage power sources without damaging the information processing apparatus.
2Reliability
If voltage dividing resistors are added to protect the IC, then the safety is improved, but the device complexity increases
Solution Approach 1:
The patent merges the voltage dividing resistors with the existing key matrix circuit structure by connecting them between the sense terminals and the switches. This integration approach allows the protective function to be added without requiring separate protection circuits, thereby minimizing the increase in device complexity while ensuring IC protection.
3Reliability
If the sense terminal voltage is limited to predetermined voltage or less, then the IC safety is improved, but the power source voltage utilization is restricted
Solution Approach 1:
The patent changes the voltage parameter at the sense terminals through the voltage dividing resistors, transforming the high power source voltage into a safe voltage level for the IC. This parameter transformation allows the system to maintain adaptability with various high voltage power sources (such as 12V vehicle batteries) while ensuring the IC always receives voltage within its safe operating range.
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 the use of higher power source voltages safely within the operational limits of the IC, ensuring reliable operation and power-saving mode transitions without damaging the information processing apparatus.
Implementation Method 1
The plurality of voltage dividing resistors have respective resistance values that make voltages of the plurality of sense terminals connected to respective sense ports of the information processing apparatus to a predetermined voltage or less
Data Source
AI summary
A key matrix circuit device includes a key matrix having scan terminals, sense terminals, switches arranged in a matrix, and voltage dividing resistors connected between the sense terminals and the switches, and a wake-up circuit having an output terminal outputting a switch signal causing a switch unit to switch a mode of an information processing apparatus to a power-saving mode or a normal mode, a power source terminal connected to a power source, and a connection terminal connected to the power source terminal and the scan terminals. The voltage dividing resistors have resistance values that make voltages of the sense terminals to a predetermined voltage or less. The wake-up circuit outputs a switch signal to switch the mode to the normal mode when at least one of the switches is turned on and a potential of the connection terminal is brought into a first level in the power-saving mode.