For this mod linky I need a power supply/fanbus capable of adjusting between about 5 and 12 volts, providing about 5 amps while @ 12v. If that isnt feasable, a way to drop the voltage down to around 5 volts, so I can use a switch. Can anybody help me with the designing and/or making of such a circuit please?
Hmm, could you mod in a second PSU to the case. maybe Matx would do as you're after 60W on the 12V line. Maplin sell 10A switches, DPDT so you can have some indicators.
Easy-peasy, but for a linear control you've up to 13W of heat to waste, so a PWM controller might be cooler. With them motors you'll need a nice fat diode (1N5401, 10p to you) across the motor, connected as shown in the circuit on this page. /50 bonus points for triple pimp
rapidelectronics sell lm338T 5A variable regulator which would do it. they also sell "MIC45xx 200kHz step down voltage regulators" here but I dont know how to use them. They cost a lot more in comparason but waste a lot less heat - 77% efficient.
You wouln't really need a PWM step down regulator since they are mean't for outputting smooth voltage, but when you PWM a fan, you dont need smooth voltage. So you can use something as simple as a 555 and a mosfet (though you won't get 100% power with a single 555, you can get 100% with two somehow).
How about a simple PIC PWM generator + MOSFET driver. somthing like a 16F6xx built in 1 channel PWM is all that would be needed. LED + Switch control. Maby even try and make it seek an RPM n replicate this for the mobo?
Or better yet use a small PIC12F675 with a pot connected to one of the A/D inputs, and code your own PWM routine. Velleman make a PWM kit for controlling loads upto about 6.5A. Kit - K8004. I have one here pre-built if you want to buy...
Yes but you could smooth the output after with caps.. If its not smooth then the fan will be almost more niosy than without being turned down, because the stopping and starting makes it niosyer. How can a mosfet and 555 timer be used to do pwm?
