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Help with output transistors

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Sceadwian
You make a valid point about system impedance. The motivation for this project is to reduce the noise signature of a PC. DC brushless blowers do indeed produce higher static pressures than axial fans, but at a cost of increased noise. In my builds static pressure is only a concern for the CPU cooler, however with careful component selection axial fans are suitable for the task. For moving air through the chassis, negative pressure is more desirable from a noise perspective and axial fans are up to this task as well.

unclejed613
1] Will be using a PNP power transistor for the final output in a TO-247, TO-251, TO-262 or TO-220 package.
2] The low-pass filter at the input and the capacitor on the output will minimize transients and ripple to the fan motor.
3] varying the voltage to a standard 3-wire brushless fan will control the speed of the fan.
4] I have also disassembled a number of brushless fans and everyone of them had a hall sensor and a driver IC. An emerging trend is the use of internal PWM to to enable the output transistors to be integrated on die. If you would like more information Google 'fan motor driver' and explore some of the data sheets from Rohm, Sanyo and Zetex.
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trident
 

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Odd, I thought blowers were quieter than axial fans at the same CFM?
 
blowers are quieter measured from the intake side, probably because they're enclosed. but on the exhaust side, air motion is air motion, and not much difference there.
 
I'm an open minded person, if you know of a brushless blower that can produce 20CFM with a noise level of 20dBA@1m or less, please do tell. All of the following 120mm axial fans can.

Antec TRI-COOL 120, 21CFM @ 870RPM, 20dBA@1m

ebmPapst 4412 F/2GLL, 23CFM @ 980RPM, 20dBA@1m

Nexus D12SL-12, 23CFM @ 850RPM, 20dBA@1m

Scythe SFF21E, 23 CFM @ 910RPM, 20dBA@1m
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trident
 
i'll have to check out what some of the home audio manufacturers use inside their home theater receivers. the axial fans that use are quiet, but keep amplifiers cool.....
 
Damn those are quiet fans =O
I don't think I've seen blowers that quiet, least not at those ratings. I'll have to keep that in mind, I've always thought blowers were better.
 
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