lodestar wrote:This has been done commercially, most recently by Nanoxia with the PWMX. It was quite a neat device, and included a variable fan speed control. As it disappeared fairly quickly I assume it was not a sales success. The issue, as always, is that it may be cheaper to replace a 3 pin fan with a 4 pin PWM rather than pay for a separate controller and keep the 3 pin fan. Before the Nanoxia PWMX there was a device available from a British company called PaQ . They continue to advertise it at
http://www.paqt.co.uk/store/index.php?a ... roductId=5. There is a data sheet here
http://www.paqt.co.uk/docs/PaQ_PWM.pdf.
Yes, that's the one that PCY makes. For some reason, I never looked carefully at the picture of it. Rather I tried, but couldn't make anything meaningful from it. My design is similar, but it uses an op-amp instead of the NPN and PNP transistors, and it uses only one NPN transistor for the current amplification. Given the cost of transistors vs op-amps, the PaQ is probably cheaper to build, especially en masse.
I sorta fell into this as curiosity. I recently got a new video card, but replaced the heatsink with the Gelid Icy Vision that MikeC recommended. Unfortunately, I found the fan to be far too loud and even my regular fan controller couldn't make it quiet enough (it bottoms out to probably around 6v). I daisy chained a zalman fanmate to bring it to acceptable levels, but in all honesty, I want my video card to take care of its fan speed. The capability is already there, but the fan is not. It's not really easy to swap out the fan on this, and it generally makes me nervous to even think about.
I saw the PWMX, but also saw that it was out of stock pretty much everywhere. The PaQ seems good, but I don't know if I want to pay 10 quid plus shipping to the US for something that I can put together myself (with all due respect to PaQ). Besides, I'd need a different connector anyway for the video card, since it's not your typical header.