Fan Voltage Control via PWM Startup Current Limiting
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Solution Overview
Problem
Existing power supplies for devices with integrated electric fans are often oversized to handle the high startup current of the fans, leading to increased costs, space requirements, and variability in airflow due to supply voltage fluctuations.
Innovation Solution
A method and circuit arrangement that control the voltage applied to the fan motor during startup using pulse-width modulation, limiting the Root Mean Square (RMS) current to the rated current, allowing the power supply to be dimensioned for continuous operation rather than startup power, with a capacitor and choke to stabilize and limit current, and a current measurement shunt for additional functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power supply is dimensioned to handle the high startup current of the fan, then the fan can start up reliably, but the power supply size and cost increase
Solution Approach 1:
The patent applies pulse-width modulation (PWM) to switch the power supply output periodically during fan startup. By rapidly switching the power supply on and off with controlled duty cycle, the fan receives pulsed power that limits the RMS current to the rated current level, preventing excessive startup current while maintaining adequate average power for reliable startup. This periodic action transforms the continuous high-current problem into a controlled pulsed delivery system.
Solution Approach 2:
The patent changes the electrical parameters delivered to the fan during startup by implementing PWM control. Instead of providing continuous full-voltage power that causes high startup current, the system varies the effective voltage and current parameters through duty cycle control, maintaining the RMS current at or below the rated current level. This parameter transformation allows the power supply to be sized for continuous rated current rather than peak startup current.
2Reliability
If the power supply is dimensioned for startup current, then the fan can start up, but the cost and space requirements increase
Solution Approach 1:
The PWM switching mechanism delivers power in controlled pulses during fan startup, maintaining RMS current at rated levels. This periodic power delivery enables reliable fan startup while allowing the power supply to be compact, as it only needs to handle continuous rated current plus device load rather than being oversized for peak startup current.
Solution Approach 2:
By transforming the power delivery from continuous full-voltage to PWM-controlled pulsed voltage, the system changes the effective current parameters. The power supply is designed for rated current conditions, and PWM modulation achieves the necessary startup performance without requiring a larger, more expensive power supply unit.
3Speed
If full voltage is applied to the fan during startup, then the fan starts quickly, but supply voltage fluctuations cause variability in airflow
Solution Approach 1:
The PWM control system applies power to the fan in regulated pulses rather than continuous full voltage. By controlling the duty cycle to maintain RMS current at rated levels, the system achieves smooth fan acceleration and stable airflow from startup. This periodic controlled power delivery eliminates the voltage fluctuations and airflow variability that occur with direct full-voltage startup.
Solution Approach 2:
The system changes the voltage application method from direct full-voltage to PWM-modulated voltage with controlled RMS current. This parameter transformation ensures smooth current buildup and stable fan operation, eliminating supply voltage fluctuations and ensuring consistent airflow characteristics during startup and operation.
4Weight of stationary object
If pulse-width modulation is used to limit RMS current, then the power supply can be smaller, but additional control circuitry is required
Solution Approach 1:
The PWM control circuitry generates periodic switching signals to control the power MOSFET, enabling RMS current limiting without oversized power supply components. The control circuit includes a microcontroller or dedicated PWM controller that generates the switching waveform, along with minimal supporting components (current sensing resistor, feedback circuitry, and power switching transistor), achieving compact overall design despite the added control function.
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 approach reduces the power supply's size and cost, maintains consistent airflow, and allows for efficient operation without the need for large chokes or high computing power, enabling the power supply to be designed for rated current only, saving resources and ensuring the fan operates within safe limits.
Implementation Method 1
a switching-on and switching-off of the output voltage of the power supply applied to the fan by a switch pulse-width-modulated-controlled by a control unit so that the Root Mean Square (RMS) value of the current flowing through the fan is lower than a startup current of the fan
Implementation Method 2
with a capacitor and choke to stabilize and limit current
Implementation Method 3
with a capacitor and choke to stabilize and limit current
Data Source
AI summary
Methods for controlling a voltage present at an electric fan during a startup of the fan are disclosed herein. The fan serves to generate a flow of air for cooling a device. The method includes applying an output voltage of a power supply, which serves to supply voltage to the device, to the fan; and switching on and switching off the output voltage of the power supply applied to the fan by a switch pulse-width-modulated-controlled by a control unit so that the Root Mean Square value of the current flowing through the fan is less than a startup current of the fan.