Watch Constant Current Circuit Using Fuse Tap Selection
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Solution Overview
Problem
Existing constant current circuits in watches suffer from significant variations in current due to off-leakage current from transistors, which is exacerbated by temperature changes, particularly in circuits supplying small constant currents.
Innovation Solution
The implementation of a constant current circuit with a current mirror circuit, regulating transistors, connection wiring lines, selecting fuses, simulation disconnecting transistors, and disconnection determining transistors, which allows for the selection and regulation of transistors to minimize off-leakage current by simulating disconnection and determining the state of selecting fuses, thereby stabilizing the current output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a transistor-based switch circuit is used to select taps of a resistor ladder, then the constant current can be regulated, but the off-leakage current increases with temperature and causes significant variation in the constant current
Solution Approach 1:
The patent extracts and removes the problematic transistor switch from the current path by replacing it with a fuse-based selection mechanism. The fuse connects the power supply to different taps of the resistor ladder, eliminating the transistor's off-leakage current while maintaining the ability to select different resistance values for current regulation.
Solution Approach 2:
The patent uses fuses, which are disposable one-time-use components, to replace the transistor switch. Once a fuse is blown to select a particular tap, it remains in that state, providing stable connection without the temperature-dependent leakage characteristics of transistors. This disposable approach ensures reliable current stability.
2Reliability
If multiple connection wiring lines are provided for each transistor to enable fuse selection, then the ability to minimize off-leakage current is improved, but the device complexity increases
Solution Approach 1:
The patent merges the functions of multiple connection wiring lines into a single integrated structure. Instead of having separate complex switching mechanisms for each connection, the design combines power supply connections, resistor ladder taps, and fuse mounting points into a unified circuit architecture where fuses directly connect power supply to selected taps, simplifying the overall structure.
Solution Approach 2:
The fuse acts as an intermediary component that simplifies the connection between power supply and resistor ladder taps. Rather than using complex transistor switches with multiple wiring lines, the fuse provides a simple binary connection state (connected or disconnected), reducing circuit complexity while achieving the same functional goal of current regulation.
Data Source
AI summary
A watch is provided that includes a constant current circuit including: a plurality of transistors coupled in series between a first power supply and a second power supply, the first power supply being a power supply of a high potential side power supply, the second power supply being a power supply of a low potential side power supply; a plurality of connection wiring lines each provided for each of the plurality of transistors, and configured to couple the first power supply and a terminal on the first power supply side of each of the plurality of transistors; a non-disconnected fuse provided in a non-disconnected state to one connection wiring line of the plurality of connection wiring lines, and a disconnected fuse provided in a disconnected state to a connection wiring line other than the one connection wiring line of the plurality of connection wiring lines.