Fan Control Circuit PWM to DC Conversion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional fan control circuits fail to provide the lowest driving voltage required for fans, leading to ineffective operation and inability to precisely stop the fan, due to limitations in converting PWM voltage signals and amplifying them to suitable driving voltages.
Innovation Solution
A fan control circuit comprising a filter circuit, an amplifier circuit, a current expansion circuit, and a feedback circuit, which converts PWM signals into DC signals, amplifies them with a static voltage, and uses a current expansion mechanism with transistors in cascade configuration to generate a driving voltage signal that is directly proportional to the PWM duty cycle and sufficient to drive the fan, even at zero duty cycle, and includes a comparison circuit to stop the fan operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the control circuit converts PWM voltage signal to DC voltage signal using conventional filter and operational amplifier, then the circuit structure is simple, but the driving voltage cannot reach the lowest driving voltage value of the fan when duty cycle approaches zero
Solution Approach 1:
The patent changes the voltage parameters by introducing a static voltage signal (e.g., 5V or 12V) that is added to the PWM signal after filtering. This parameter change ensures that even when the PWM duty cycle approaches zero, the resulting driving voltage remains at least equal to the fan's lowest driving voltage value, solving the problem of insufficient driving voltage at low duty cycles
Solution Approach 2:
The patent introduces a static voltage signal as an intermediary element that mediates between the filtered PWM signal and the fan driver. This static voltage acts as a baseline that guarantees the minimum driving voltage requirement is met, while still allowing PWM control functionality to operate
2Ease of operation
If the control circuit uses operational amplifier output to control transistor switch, then the circuit can amplify the DC voltage signal, but the fan operation cannot be effectively stopped because the operational amplifier output voltage cannot reach the supply voltage
Solution Approach 1:
Instead of using the operational amplifier output directly to control the transistor switch (which cannot reach supply voltage), the patent inverts the control approach by using the filtered PWM signal combined with static voltage to directly control the switch. This inversion allows the switch to be fully turned off when duty cycle is zero, enabling precise fan stop control
3Use of energy by moving object
If the control circuit directly converts PWM signal to driving voltage without static voltage addition, then the circuit consumes less power, but the driving voltage is insufficient to drive the fan at low duty cycles
Solution Approach 1:
The patent changes the voltage parameter by adding a static voltage component to the PWM signal. This parameter change increases the minimum driving voltage to meet fan requirements while maintaining reasonable power consumption through efficient circuit design and transistor switching
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 solution ensures the fan operates effectively across the entire PWM duty cycle range, including at zero duty cycle, and provides precise control over fan operation, enhancing stability and response speed while avoiding the limitations of conventional circuits.
Implementation Method 1
The filter circuit 21 is composed of a first resistor 21R and a first capacitor 21C. The input end of the filter circuit 21 is electrically connected to the processing unit 3 in order to receive a PWM voltage signal from the processing unit 3 and convert the PWM voltage signal into a DC voltage signal
Implementation Method 2
The positive input end of the amplifier circuit 22 is separately connected to a first power supply unit V1 and the output end of the filter circuit 21 in order to receive the DC voltage signal and a static voltage signal from the first power supply unit V1. The amplifier circuit 22 performs addition on the DC voltage signal and the static voltage signal and then amplifies the combined signal
Implementation Method 3
The input end of the current expansion circuit 23 is connected to the output end of the amplifier circuit 22, and the output end of the current expansion circuit 23 is connected to the fan 4. The current expansion circuit 23 performs current expansion on the amplified voltage signal and thereby generates a driving voltage signal and a driving current signal
Implementation Method 4
The two ends of the feedback circuit 24 are respectively connected to the negative input end of the amplifier circuit 22 and the output end of the current expansion circuit 23 so that the magnitude of the driving voltage signal, which is derived from the DC voltage signal through the amplifier circuit 22, the current expansion circuit 23, and the feedback circuit 24, is in direct proportion to the duty cycle of the PWM voltage signal
Data Source
AI summary
The present invention is to provide a fan control circuit, which includes a filter circuit for converting a pulse-width modulation (PWM) voltage signal into a DC voltage signal; an amplifier circuit having an input end for receiving the DC voltage signal and a static voltage signal and generating an amplified voltage signal at an output end thereof; a current expansion circuit configured to perform current expansion on the amplified voltage signal and thereby generate a driving voltage signal for a fan; and a feedback circuit connected between another input end of the amplifier circuit and an output end of the current expansion circuit so that magnitude of the driving voltage signal is in direct proportion to the duty cycle of the PWM voltage signal and is greater than or equal to a lowest driving voltage value of the fan when the duty cycle of the PWM voltage signal approaches zero.