DC Voltage-Limiting Circuit for Wide-Range Low-Loss Power Input
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Solution Overview
Problem
Existing DC voltage-limiting circuits, such as those using voltage dividing resistors or voltage regulator diodes, suffer from high electricity loss, inability to support variable input voltages, and limited output capacity, making them unsuitable for electronic devices with high power requirements like thermostats with Wi-Fi modules.
Innovation Solution
A DC voltage-limiting circuit employing three transistors with specific resistor connections and voltage regulators, along with a bridge rectifier and a BUCK circuit, to provide a wide input voltage range (25VDC-42VDC) with low power consumption and design flexibility, allowing for fast and slow charge paths and preventing high-frequency interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a high-capacitance capacitor is used to store sufficient electricity for the BUCK circuit, then the electricity supply capacity is improved, but the capacitor size becomes large and exceeds the limited PCB space
Solution Approach 1:
The patent changes the voltage parameter by introducing a DC voltage-limiting circuit that reduces the rated voltage requirement of the capacitor. By limiting the input voltage to a lower level (e.g., converting 42V DC to a lower voltage), the capacitor can have the same capacitance value but operate at a lower voltage rating, thereby reducing its physical size and fitting within the limited PCB space while still providing sufficient electricity storage capacity.
2Device complexity
If a voltage dividing resistor based method is used to limit voltage, then the circuit is simple and cheap, but electricity loss is high and variable input voltage is not supported
Solution Approach 1:
The patent replaces the passive resistor-based voltage division method with an active transistor-based voltage-limiting circuit. This substitution uses transistors (Q1, Q2, Q3) controlled by voltage regulators (Z1, Z2) to actively regulate and limit the voltage, replacing the purely passive and wasteful resistor network with an active control system that minimizes power loss while maintaining circuit simplicity.
3Device complexity
If a voltage regulator diode based method is used to limit voltage, then the circuit is simple and cheap, but the output capacity is limited by the dissipation power of the diode
Solution Approach 1:
The patent merges multiple components into an integrated voltage-limiting circuit that combines transistors, resistors, and voltage regulator diodes working together. The transistors Q1, Q2, and Q3 are configured in a specific arrangement with associated resistors (R1-R4) and voltage regulators (Z1, Z2) to create a unified circuit that provides both voltage limiting and sufficient current output capacity, overcoming the limitation of single-diode solutions where output capacity is constrained by the diode's dissipation power.
Data Source
AI summary
A DC voltage-limiting circuit generally includes first, second, and third transistors. The first transistor is connected between a voltage input terminal and a voltage output terminal. The first transistor has a collector connected to the voltage input terminal, an emitter connected to the voltage output terminal, and a base connected to the voltage input terminal via a first resistor. The second transistor has a base connected to the voltage input terminal via a first voltage regulator and a second resistor, a collector connected to the base of the first transistor, and an emitter connected to the voltage output terminal. The third transistor has a collector connected to the base of the first transistor via a third resistor, an emitter grounded, and a base connected to the voltage output terminal via a second voltage regulator and a fourth resistor.