Cooling Fan Control Module: An In-Depth Guide to Voltage Regulation
In the world of electronics, engineers frequently face the challenge of efficiently controlling cooling fans. The Cooling Fan Control Module subject addresses a challenge. This challenge arises because the Microcontroller Unit (MCU) operates at either 3.3V or 5V. Cooling blowers often demand voltages as low as ~3V (below which they won’t even spin) and as high as 12V or even 24V. This article explores methods and circuits for efficient Cooling Fan Control, providing valuable insights to those seeking solutions.
The Op-Amp and Transistor Solution
One straightforward solution is to employ an operational amplifier (op-amp) in combination with a PNP transistor or a P-channel MOSFET in the positive rail. This circuit can help bridge the voltage gap between the MCU and the cooling blower. Even though it seems obvious, let’s look at some of the alternative possibilities that local experts have thought about.
The ADI Circuit: A Unique Approach
When searching the internet for solutions, one circuit that catches attention originates from Analog Devices Inc. (ADI). In this circuit, they substitute the traditional op-amp with a current mirror and a buffer transistor. This approach appears in the ADM1028 ‘remote thermal diode monitor with linear fan control’ data sheet. It’s an appealing option since it operates within a voltage range of 3V to 5.5V and delivers a substantial signal processing capability with a 0–2.5V analog output swing.
Exploring Circuit Variations
There’s also a MOSFET output variant of the current mirror design within the same data sheet. However, it’s essential to note that these current mirror circuits typically have a low input impedance. This can be problematic, especially without an op-amp buffer. The low-pass smoothed 3.3V or 5V PWM signal that an Arduino generates, instead of an analog voltage, might get excessively loaded by such circuits.
Practical Considerations
Considering practicality, it might make sense to stick with the op-amp circuit. You can choose a suitable op-amp meeting both MCU output and fan Vcc voltage requirements without being overly exotic. This is an efficient and cost-effective approach while maintaining a reliable cooling fan control module.
A DIY MCU Solution
For those looking to create a custom cooling fan control system using an MCU like Arduino, here’s an innovative suggestion. This method involves utilizing two or three MCU pins and an internal digital feedback loop. The MCU generates different PWM ratios into the RC network until it measures the desired voltage at the ADC input.
For example, when dealing with a 12V fan, target 8V (12V – 4V = 8V) for one-third of the voltage. For precision, connect a fan voltage monitoring potentiometer to another ADC input to fine-tune voltage control. Because fans primarily control temperature, utilize temperature as feedback, eliminating the necessity for voltage monitors.
Exploring MOSFET Options
The PWM range for fan speed spans a small range, positioned in the middle, between fan-not-rotating and fan-full-speed. Finding a MOSFET for 12V x 160mA power handling with enough gate voltage swing for the feedback loop. You might consider using a cheap op-amp for simplicity.
When PWM Is the Answer
Certain fans, known as ‘4-wire’ fans, accept a 25kHz 5V PWM signal, simplifying direct MCU control of fan speed. 5015 blower fans (snail fans, not axial) usually have 2-wire or occasionally 3-wire setups, complicating direct PWM control.
Conclusion
You can address the challenge of regulating cooling fans with varying voltage requirements using diverse approaches. These approaches include op-amp circuits, current mirrors, and MCU-based solutions. Ultimately, your choice hinges on your project’s specific needs, considering factors such as voltage range, precision, and component availability.