Yes but rail to rail o/ps are not need here plus the 741 is immune to lockups. Not that you couldn't use the other chips but the 741 is still cheaper. Although given the shorted gate you could use any opamp. j/k
To be realistic, you can make a reasonable pwm circuit with a single 555, a switching transistor and a few diodes, resistors and capacitors. Maplin's module RN41U is just that, and will probably give a better revs range to your fan than a 317T circuit. The more complex circuits with an extra 555, or an op-amp/comparator added, give a marginally wider range of control, and the specialised fan control ics like the MIC502 and TC54x have a few extra tricks like a kick-start, sleep control or a dead fan alarm. Good reasons to build a PWM controller are because you want a compact unit with no bulky heatsink. Like the use in macromans psu. Or for fun. Just don't tell me about energy-saving when your Athlon makes the house-lights dim running Super Pi.
is there an article somewhere that i could follow on how to build a PWM based fan controller? the MIC502 is not available here so this is out of the question. im not good at electronics so if possible a working circuit that i could follow.
I don't know where "here" is, but did you look at http://65.218.208.24/Rep-Dist_INT/FMPro?-db=Rep-Dist_INT_DB&-lay=Layout #1&-format=search.htm&-view to see if micrel has any distributors in your country?
You can get it in the US from Future-Active, but the minimum order is 50 pieces. I got mine in a group buy that was organized by some dude on [H].
There's so much 555 info on the web it's just astounding. Basically to set the duty cycle you manipulate the values of R1 and R2. this calculator illustrates how it works. I don't know offhand, but my instinct is that you'd only be able to adjust the duty cycle from a little over 50% to almost 99% with this circuit, but it's cheap and easy. But once you've sorted that, just drive a power transistor from the 555 output.
There are some cunning tricks you can do with steering diodes to greatly extend the duty cycle, claims of 5-95% are usual. An example with more bells & whistles (a kickstarter, even ) here I'm waiting for a few bits to build this one, so I'll report back :dude:
Will a 12 volt fan run off of 12 * 5% = 0.6 volts? Nope. (0.6 volts being the average DC value the fan would see).
Very doubtful, though they'll start at a lower average voltage than un-pulsed DC. Micrel suggest a 40% minimum, works fine on all my fans. However, if you want to use the same controller for model motors, PWM gives a smoother start than linear control, and it's a good way to dim leds or filaments, so the bottom end can be handy.
The above circuit won't work, but there's a variation on Uller's design here that might. You can put a led and its dropper resistor across the fan leads, but it may flicker at low speeds, depending on the pwm frequency.
Haha, I remember the threads on [H] where we all kinda contributed to that damn design. Probably gone now though, they pruned the database quite a bit. It's the same oscillator, a 555 without its output connected, just a tweak to the power transistor. I need to build my MIC502 circuits one of these days or sell them off to someone who will.
There's also a thread at Ars C&CF where Uller responds, Thought it rang a bell, I was pimping Bit-Tech/mm at the time...
no i know why others are having a hard time building a PWM fan controller without the MIC502. poor us newbies! no way we can build one. i really need one that works and tested.
Need a bleeding heart Smiley. There's a commercial kit (so virtually guaranteed to work) available in the US, or you can just download the circuit and description from here in the pdf file. It uses a 556 (2 555s) and a switching transistor, so cheap to build, parts easy to find.
I get a 404 and at http://www.electronickits.com I get "THIS IS DEFAULT SITE FOR MISCONFIGURATED REQUESTS." May just be temporary edit: working now/again
