dplatt@coherent.com (Dave Platt) (10/10/89)
I need a small circuit with which to control the speed of a 12V DC
cooling fan. I can take a guess at what sort of circuit might do the
job, but I'm not enough of a hardware-hacker to be sure that it will
work or which components would be the most appropriate. If anybody out
there can offer a quick critique of my ideas, suggest alternate ones, or
recommend appropriate parts, I'd much appreciate it.
I have a hard-disk cabinet that includes a 2.5" 12VDC cooling fan. The
fan runs at a high rate of speed, and emits a very annoying whine. It's
moving much more air through the cabinet than seems necessary... the
tape mechanism I'm using doesn't draw much power. I believe the fan
could be quieted down by dropping its voltage... but I don't want to
risk overheating.
A similar fan I saw at Fry's says "8-15V, 12V nominal, 1 watt". The fan
in my case is being run off of the +12 line from the power supply. I'd
like to install a temperature sensor and voltage controller in line with
the fan. The controller would need to handle a max of about 150 ma, I
believe, and must run from the single-sided 12V supply.
My guess as to an appropriate circuit would be an op-amp driving a
pass-transistor of some sort. The noninverting input of the op-amp
would be connected to a voltage-divider between +12 and ground; the
bottom leg of the divider would be a thermistor with a positive
temperature coefficient, and the top leg would be a ten-turn trimpot.
The inverting input of the op-amp would be fed from the slider of
another ten-turn trimpot wired between the op-amp's output and ground.
The op-amp's output would also drive a small power transistor (MOSFET?
bipolar? whatever's appropriate...) hooked in series with the fan's +12
lead.
The two trimpots would, I think, enable me to tweak the circuit's
parameters... I could adjust the speed of the fan at power-on (when the
cabinet was cold), and also adjust the rate at which the fan's speed
would increase as the temperature rose. There would be substantial
interaction between the two trimpots, so I'd have to iterate on the
adjustment a few times.
Does this sound like a reasonable approach? Is there a better one?
What parts should I use? [preference given to simple jellybean
components that I can buy at a local Radio Trash, Fry's, or a similar
outfit.]
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USNAIL: Coherent Thought Inc. 3350 West Bayshore #205 Palo Alto CA 94303vaso@mips.COM (Vaso Bovan) (10/11/89)
In article <36251@coherent.coherent.com> dplatt@coherent.com (Dave Platt) writes: >I need a small circuit with which to control the speed of a 12V DC >cooling fan. I can take a guess at what sort of circuit might do the >job, but I'm not enough of a hardware-hacker to be sure that it will >work or which components would be the most appropriate. If anybody out >there can offer a quick critique of my ideas, suggest alternate ones, or >recommend appropriate parts, I'd much appreciate it. > >I have a hard-disk cabinet that includes a 2.5" 12VDC cooling fan. The >fan runs at a high rate of speed, and emits a very annoying whine. It's >moving much more air through the cabinet than seems necessary... the >tape mechanism I'm using doesn't draw much power. I believe the fan >could be quieted down by dropping its voltage... but I don't want to >risk overheating. > Several companies make "integrated" fan controllers. One thermistor- controlled package is the "DC-100", made by Quality Thermistor, at (208) 377-3373 Fax: (208) 376-4754