Thermistor Feedback Fan Driving Circuit for Temperature-Stable Control
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Solution Overview
Problem
Conventional fan driving circuits fail to compensate for temperature variations in transistor components, leading to inconsistent fan control due to ignored characteristic changes caused by ambient temperature changes.
Innovation Solution
A fan driving circuit with a feedback unit that includes a thermistor and resistors, which adjusts the feedback current to compensate for changes in common emitter current gain of the transistor due to temperature variations, using a signal adjuster and transistors to generate and modulate the fan driving signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional fan control technologies increase fan rotating speed based on ambient temperature, then fan cooling capability is improved, but transistor characteristic variations due to temperature are ignored causing control inaccuracy
Solution Approach 1:
The patent introduces a feedback mechanism where the feedback unit samples the output signal and feeds it back to the input端 through a feedback resistor. This closed-loop feedback allows the system to automatically adjust and compensate for transistor characteristic variations, maintaining control accuracy while preserving the temperature-based fan speed adjustment capability
Solution Approach 2:
The patent utilizes temperature-dependent parameter changes of the transistor (specifically the base-emitter voltage Vbe and current gain β) to its advantage. By designing the feedback network to compensate for these parameter variations, the system transforms the temperature sensitivity from a source of error into a mechanism for automatic compensation, thereby maintaining precise control across different operating temperatures
2Reliability
If transistor operating temperature increases, then common emitter current gain increases, but fan control becomes inconsistent due to uncompensated characteristic changes
Solution Approach 1:
The feedback unit continuously monitors the transistor's operating state and adjusts the input signal accordingly. This real-time feedback compensation ensures that even as transistor characteristics change with temperature, the overall system maintains consistent control behavior, preventing the control inconsistency that would otherwise occur
Solution Approach 2:
The feedback network is designed in advance to anticipate and compensate for the expected temperature-induced characteristic changes. By pre-configuring the compensation parameters in the feedback path, the system proactively counteracts the inevitable transistor variations before they can cause control inconsistency
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
The circuit effectively compensates for temperature-induced changes in transistor characteristics, ensuring consistent fan control by adjusting the fan driving signal based on ambient temperature, thereby improving control precision and reliability.
Implementation Method 1
a compensation bypass connected in parallel with the first resistor or the second resistor, wherein the compensation bypass consists of a thermistor and a third resistor connected in series with the thermistor, and a resistance of the thermistor changes along with the temperature
Data Source
AI summary
A fan driving circuit with temperature compensation comprises a power input end, a power output end connected with a fan motor, a first transistor arranged between the power input end and the power output end, a signal adjuster connected with the first transistor and connected with a signal generating circuit, a second transistor connected with the signal adjuster, and a feedback unit. The feedback unit comprises a first resistor and a second resistor connected in series, and a compensation bypass connected in parallel with the first resistor or the second resistor, wherein the compensation bypass comprises a thermistor, a resistance of the thermistor changes along with the temperature and changes a magnitude of a feedback current which is provided to the second transistor, so as to compensate a change of a common emitter current gain in the second transistor generated by the temperature.