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frostmeister said:I'll never understand the obsession with potentiometers - or rheostats - that people on here seem to have. From an electronics engineers point of view, it's an extremely inneficient way of doing a simple job, as all you need is a small switching regulator - I can make one and post the circuit diagram if you like. This way, you don't have to deal with 30watts of heat in you case, degrading nearby drives / components through it's heat emmision, especially if it's in a baybus of some kind. I'm not trying to have a go at you personally TyRex, but wouldn't it be much nicer if you used less electricity, produced less heat, and could control more devices more reliably as well?
frostmeister said:a 1n5821 would do fine, seal. And TyRex, the LM2577 is pretty much non-subsitutable. Hope this helps.
frostmeister said:Well, here's the circuit. Build it and test the output with a voltmeter first, so you can verify you're getting the correct output. This thing is 80% efficient - translates to 1 watt of heat for every 5 watts it supplies. The output current depends on the inductor and resistor. Inductors will usually come with a current rating, and check the diode you're using as well. I can't find a 1N5820 in my electronics catalogue, but you could use a 1N5822 which has a 3A current rating, and will be good for an output of up to 40 volts. 3 amps is the max the LM2577 can supply by the way, which should be ok for about 4 standard 12volt fans quite safely.
Have fun
Let me know if there's anything you're unclear on by the way