# Voltage Linear ramped speed control circuits

Discussion in 'General Electronics Chat' started by Tree1, Nov 30, 2010.

1. ### Tree1 Thread Starter Member

Nov 30, 2010
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I have been researching fan control in an effort to understand how voltage linear ramped circuits are used to increase/decrease the speed of a fan however, despite reading many articles, I seem disconnected or rather confused.

So, a fan has settings ( e.g off, low, med, high) that allows the user to change the speed of the fan. Whenever a user selects a particular setting does the control circuit ramp to particular voltage then levels off to keep it running at that speed. What if the person selects the highest speed right after, does the ramp further increase to higher voltage and levels off ?? What would the waveform look like for that particular action ? Would it look like a linear line that levels off after it reaches a peak and the increases linearly again and then levels off again?

What does the commanded signal ( input signal) that allows the voltage to ramp look like ?

Does the rate of ramp affect the speed of the fan ?? Is the rate of the ramped voltage different everytime the user selects a different speed setting?

I would def. be grateful if someone could assist me.Thanks!!!!!!!

Apr 5, 2008
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3. ### Tree1 Thread Starter Member

Nov 30, 2010
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Thanks Bertus! will check it out.

4. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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Are you referring to small fans, such as in a PC power supply, or "3 Speed" 120VAC household fans?

5. ### Tree1 Thread Starter Member

Nov 30, 2010
46
0
Actually trying to gather a graphical picture as to the operation of the blower motor in a certain vehicle and I was reading that HVAC module sends the commanded blower motor speed to the control processor through a 0-12 volt-linear ramped blower motor speed control circuits. Was wondering how the output of that speed control circuit would look like every time the speed varies or if it is increased to a certain speed ( say medium speed) and remained at that speed for a duration of time and then increased to higher speed. Would it be a series of different linear ramp waves? Basically if I were to observe the output waveform of that ramp speed control circuit using an oscilloscope what would I see ?

6. ### retched AAC Fanatic!

Dec 5, 2009
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It depends.

If it is a PWM device, you would see the Pulse Wave sized to the "speed" that is set.

The 0-12v speed control signal is most likely windowed so engine revs do not "change" the speed from medium to high.

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