Blower Motor Current Regulation Using Transistor Temperature Coefficients
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Solution Overview
Problem
Existing circuit arrangements for controlling blower motor current in motor vehicles fail to efficiently regulate current as a function of both voltage and temperature without requiring expensive temperature sensors, leading to suboptimal performance and increased power consumption.
Innovation Solution
A circuit arrangement using base-coupled transistors with discrete components, where the load current is regulated through a differential amplifier with a defined temperature coefficient, eliminating the need for temperature sensors by leveraging the temperature-dependent behavior of the circuit components, and adjusting collector quiescent currents to adapt to temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a temperature sensor is used to regulate load current as a function of temperature, then the current control precision is improved, but the device complexity and cost increase
Solution Approach 1:
The circuit uses the intrinsic temperature-dependent behavior of bipolar transistors (specifically the variation of base-emitter voltage with temperature) to automatically sense and compensate for temperature changes. The transistor parameters themselves serve as the temperature sensing mechanism, eliminating the need for external temperature sensors and complex control circuits.
Solution Approach 2:
The invention exploits the natural parameter changes of bipolar transistors with temperature - specifically the change in base-emitter voltage (Vbe) and collector current characteristics. By designing the circuit to utilize these inherent parameter variations, the system achieves temperature-compensated current control without requiring separate temperature sensing components.
2Reliability
If the maximum load current is kept constant regardless of temperature, then the short-circuit protection function is maintained, but the power consumption increases at low temperatures and the control precision deteriorates
Solution Approach 1:
The circuit dynamically adjusts the maximum load current based on temperature conditions. At low temperatures, the circuit allows higher current to compensate for increased motor efficiency, while at high temperatures it reduces the current limit to prevent overheating. This dynamic adaptation is achieved through temperature-dependent transistor parameter variations that automatically modulate the current limit.
Solution Approach 2:
The invention changes the current limit parameter as a function of temperature by utilizing the temperature-dependent characteristics of bipolar transistors. The base-emitter voltage and collector current of the transistors naturally vary with temperature, and the circuit is designed to translate these parameter changes into corresponding adjustments of the maximum load current, optimizing power consumption across different temperature ranges.
3Device complexity
If base-coupled transistors are used in the differential amplifier, then the device complexity is reduced and cost is lowered, but the input impedance decreases
Solution Approach 1:
The invention extracts and utilizes the temperature-sensitive properties of bipolar transistors directly within the differential amplifier circuit. By taking out the need for separate temperature sensing functionality and embedding it in the transistor characteristics themselves, the design achieves temperature compensation with simpler components, accepting the trade-off of lower input impedance as an acceptable consequence.
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 solution allows for efficient control of blower motor current as a function of both voltage and temperature, reducing power loss and preventing thermal stress on components, while being cost-effective and robust enough to operate in a wide temperature range without additional sensors.
Implementation Method 1
leveraging the temperature-dependent behavior of the circuit components, and adjusting collector quiescent currents to adapt to temperature changes
Data Source
Figure 1~2
Figure 3~4
AI summary
The circuit arrangement (1) has a differential amplifier provided for the amplification of the control deviation (W-X) between a command variable (W) and a control variable (X). A transistor (Q4), a collector resistor (R2) and an emitter resistor (R6) are provided for the regulation of the load current (IL) as a function of the load voltage (VL). The series connection of the base-emitter section of the fourth transistor and emitter resistor is arranged parallel to a load (RL). The tapping point (P) for the reference voltage (Vref) is arranged between the collector resistor and the transistor. A resistor (Rs), through which the load current flows and across which a voltage (Vs) drops, serves as the control variable for the regulation of the load current. The tapping point for reference voltage serves as the command variable for the regulation of the load current.