smoothing circuit - help needed

[BigBadger]

Hi,
I'm building a Pulse Width Modulated fan speed controller to control a noisy
high speed cooling fan in my PC. I'm following this article:
http://www.bit-tech.net/article/51/ It uses a Micrel MIC502 chip.
One thing about the design bothers me: the pulsing output disables the fans
built in speed monitoring function.
I would have thought it would be possible to build some sort of smoothing
circuitry to get rid of these pulses. I would guess such a circuit would
consist of capacitors and possible a torroid, however I've no idea how to go
about sizing the components. The output would be 0 - 12V and the pulse
frequency 30Hz.
Any advice gratefully received.

thanks

 

[cpemma]

Hi,
I'm building a Pulse Width Modulated fan speed controller to control
a noisy high speed cooling fan in my PC. I'm following this article:
http://www.bit-tech.net/article/51/ It uses a Micrel MIC502 chip.
One thing about the design bothers me: the pulsing output disables
the fans built in speed monitoring function.
I would have thought it would be possible to build some sort of
smoothing circuitry to get rid of these pulses. I would guess such
a circuit would consist of capacitors and possible a torroid, however
I've no idea how to go about sizing the components. The output would
be 0 - 12V and the pulse frequency 30Hz.
Any advice gratefully received.

Get the MIC502 Application Note 34, shows an opamp circuit to recover the
sensor signal.

 

[BigBadger]

Get the MIC502 Application Note 34, shows an opamp circuit to recover the
sensor signal.

Thanks, that is useful information. However I was hoping that a smoothing
circuit would be relatively simple (I'm a bit of a novice at this stuff!).
My fan already has speed sensing built in feeding back to the 3rd pin on the
motherboard fan header and I would like to keep that working if at all
possible.

 

[Genome]

Hi,
I'm building a Pulse Width Modulated fan speed controller to control a noisy
high speed cooling fan in my PC. I'm following this article:
http://www.bit-tech.net/article/51/ It uses a Micrel MIC502 chip.
One thing about the design bothers me: the pulsing output disables the fans
built in speed monitoring function.
I would have thought it would be possible to build some sort of smoothing
circuitry to get rid of these pulses. I would guess such a circuit would
consist of capacitors and possible a torroid, however I've no idea how to go
about sizing the components. The output would be 0 - 12V and the pulse
frequency 30Hz.
Any advice gratefully received.

thanks

Cheap Fan
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Cheap Self Tappers
Cheap Motherboard

Is this the new Hi-Fi?

Maniacal Laughter!

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DNA

 

[R.Legg]

Hi,
I'm building a Pulse Width Modulated fan speed controller to control a noisy
high speed cooling fan in my PC. I'm following this article:
http://www.bit-tech.net/article/51/ It uses a Micrel MIC502 chip.
One thing about the design bothers me: the pulsing output disables the fans
built in speed monitoring function.
I would have thought it would be possible to build some sort of smoothing
circuitry to get rid of these pulses. I would guess such a circuit would
consist of capacitors and possible a torroid, however I've no idea how to go
about sizing the components. The output would be 0 - 12V and the pulse
frequency 30Hz.
Any advice gratefully received.

thanks

This application circuit pulses the fan's negative terminal. Because
the tach output of the fan will typically be related to the negative
terminal, a filter would not allow recovery of this signal, as it
would not be safely read by the motherboard while level shifted.

If you change the TIP122 to a small signal part, in order to drive a
TIP125/6/7 or pchannel mosfet, with the fan as a grounded load for the
pnp darlington, then there is a small chance that the tach output
might respond without a filter.

Most likely the tach output requires a regulated DC fan supply, and a
filter would have to be added. Unfortunately the frequency produced by
your chosen app circuit (100 to 300Hz) is much too low to filter with
small, easily-obtained parts.

Try some other circuit.

http://wwwd.national.com/national/PowerMB.nsf/

A fan speed that is controlled by a pot, in a PC, is not a practical
idea. The aim of the fan is to keep temperatures manageable. If it is
to be adjustible, it must recognise and react to this information.

RL

 

[Spajky]

I'm building a Pulse Width Modulated fan speed controller to control a noisy
high speed cooling fan in my PC.

There are many other simplier ways to reduce fans RPM w/o having
problems with revealing RPMs ...; see my site under Electronics ...


-- Regards, SPAJKY
- http://freeweb.siol.net/jerman55/HP/Spajky.htm
Celly-III OC-ed,"Tualatin on BX-Slot1-MoBo!"
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