Vehicle Input Circuit for Stable Voltage Threshold Detection
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Solution Overview
Problem
Existing constant current drivers using transistors struggle with inefficient determination of high or low voltage thresholds due to variations in element temperature characteristics and resistor divider ratios, leading to inaccuracies and increased costs.
Innovation Solution
The on-board device employs a PNP bipolar transistor with a parallel connection of a pull-up resistance and base resistance to eliminate resistor divider effects, combined with an emitter follower circuit and level shift circuit to stabilize voltage thresholds and reduce variations, using relatively inexpensive components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a constant current driver using a transistor is used, then the device can drive loads by current, but the determination of high or low voltage thresholds becomes inefficient due to variations in element temperature characteristics and resistor divider ratios
Solution Approach 1:
The patent extracts the problematic resistor divider circuit from the voltage threshold determination path and replaces it with a direct reference to a stable voltage source (Vref). By removing the resistor divider ratio from the threshold calculation, the determination becomes independent of resistor variations and temperature characteristics, thereby improving both measurement precision and reliability
Solution Approach 2:
The patent changes the parameter used for threshold determination from a calculated value based on resistor divider ratios to a direct reference voltage value. This parameter change eliminates the accumulation of errors from resistor tolerances and temperature drift, providing stable and accurate threshold determination
2Adaptability or versatility
If resistor divider circuits are used for voltage threshold determination, then voltage levels can be scaled, but variations in resistor divider ratios lead to inaccuracies and increased costs
Solution Approach 1:
The patent removes the resistor divider circuit from the threshold determination path entirely. Instead of scaling voltage through resistors, the design uses a stable reference voltage source that directly provides the threshold value, eliminating resistor tolerance accumulation and improving accuracy
Solution Approach 2:
The patent introduces a reference voltage source (Vref) as an intermediary element that provides a stable, temperature-compensated voltage threshold. This mediator replaces the inaccurate resistor divider ratio calculation with a precise reference value, improving threshold accuracy while maintaining voltage scaling capability through the regulator circuit
Data Source
AI summary
An on-board device installed in a vehicle and is provided with an input circuit including an input end into which an input voltage is entered, and a drive power supply circuit that outputs a drive voltage to the input circuit. The input circuit includes a PNP bipolar transistor, a pull-up circuit, a second pull-up resistance, and a base resistance. The pull-up circuit includes a pull-up power supply, a first pull-up resistance, and a second diode with an anode facing the first pull-up resistance, which are connected in series and are provided between a base of the PNP bipolar transistor and the input end. The second pull-up resistance is provided between the base of the PNP bipolar transistor and the drive power supply circuit. The base resistance is provided between the base of the PNP bipolar transistor and the second pull-up resistance.