Temp control of DC fan

[sargan]

Just on the off-chance someone may have done this before.
My Comms cabinet get quite warm in summer, mainly from PSU and the ADSL modem & Ethernet switch.
Maybe if I use a variable speed DC brushless fan (as in PC cases) and a tenp sensor I could get a simple fan that kicks in above a set temp and varies it's speed dependent of how hot it is above threshold.

Seen one such cct:
http://www.bit-tech.net/modding/2001/12 ... ntroller/1
(option 3 )

Anybody got anything easier.
Read that using a MIC502 might be simpler but have no experience of that device.

[KMoffett]

The variable-speed, brushless-DC fans I'm familiar with have 4 speeds: off/low/medium/high. They have two leads for power and two leads that select the three speeds. Brushless DC fan speeds are controlled by internal oscillators, not supply voltage. Changing supply voltages will affect the speeds, but that is not how they are designed. Straight DC fans do work with PWM/supply voltage.

Ken

[sargan]

The variable-speed, brushless-DC fans I'm familiar with have 4 speeds: off/low/medium/high. They have two leads for power and two leads that select the three speeds. Brushless DC fan speeds are controlled by internal oscillators, not supply voltage. Changing supply voltages will affect the speeds, but that is not how they are designed. Straight DC fans do work with PWM/supply voltage.

Ken

2 leads fans are controlled by supply voltage, as are 3 lead fans .... (3rd lead gives tacho output) ..... so intended using a 2 lead fan.