Re: Slow CPU Fan frequency doubler

On Thu, 18 Aug 2005 15:23:28 -0400, nospam@xxxxxxxxxx (Paul) wrote:

>In article <mp14g1t1aluclcck756gjsmpujt5i4uhvr@xxxxxxx>, Butch@xxxxxxxxx wrote:
>
>> Out of interest i opened up a three wire fan to see how the speed
>> sensor works. Below the motor there is an IC (with 4 connectings
>> wires, i believe a Hall effect sensor) a transitor and two resistors
>> and a capacitor. On the IC is printed "276 fB4". Looking at the
>> internet i could not find a specific datasheet of this IC.
>> Also i could not deduce the function of the transistor but i believe
>> its function is either voltage stabilazation (input voltage fluctuates
>> depending on speed setting) or an amplifier/emitter follower for the
>> output.
>>
>> Has anybody more information on the IC?
>>
>> Ofcource you can increase the sensors output frequency with some fancy
>> circuitry. But it is maybe easier just to put a second Hall effect |C
>> (180 degrees opposite) in the fan and put the two circuits in
>> parallel (assuming the output is an open collector).
>>
>> Anybody any suggestions or comments?
>>
>> Butch
>
>The buffer transistor is likely the open collector driver
>to the (motherboard provided) pullup structure. An amplifier
>of sorts.
>
>As for tracking down chips like that, a company logo would
>help. Small parts may not have a complete part number
>printed on them. Or the number may be a code, used to
>look up the part number. Using search engines, all I can
>find, is info on larger brushless motors. Maybe my
>search terms suck :-(
>
>This is as close as I could get to an example chip.
>
>http://www.melexis.com/prodfiles/US90_US91_rev005.pdf
>
> Paul

Thanks for the info.
I can not spot any more data on the chip without disassembling the
blower motor more (which i do not want to do).

I had found on the internet the following hall effect IC:
http://www.anachip.com/eng/product/search/datasheets/ATS276_277.pdf

'Your' chip has more potential because it has a seperate tachometer
output. If you mount this chip at 180 degrees you only need to connect
in parallel this tachometer output with maybe a diode in series
(or-gate). Also you need to use some dummies for the coils to provide
Vc to the chip).

Question now is; Which chip is it?
My interest (and time) does not go that far to do some more research
and experimenting so maybe somebody else tries to build the double.

succes
Butch

.

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