CPU fan buck converter, miniature

Here's why this is a miniature buck converter. It's in the little green circle at the lower right corner, of a fairly-small 3x3-inch PCB.

Save yourself a copy, you might need it oneday. I imagine it's got about 5W of capability.

We did one box recently that has a temperature sensor on the main PCB, which was a good idea anyhow, so now the uP can control fan speed. That is less noisy usually, and to some extent reduces the delay tempcos.

The uP output is PWM, lowpass filtered into an LM317. The algorithm is a simple slow up/down counter based on temp high/low compared to the setpoint. That's simple and stable and has no acoustic drama.

On this one, each amplifier board has its own fan, plus one for the box. All run full blast.

On your little board, in one place two traces make a V where they hit a pad. One of our high-PITA customers wants us to change a board layout to eliminate any not-90-degree pad entries, mumbling something about "acid traps", which I think may have happened a few times around

I use a fair number of those AOZ parts--they're cheap and they just work.

There's also the AOZ1282CI-1, which gives you half the current at twice the frequency, but is hard to get.

Cheers

Phil Hobbs

Alpha & Omega makes lots of interesting parts. And they seem determined to sell them at very low prices.

They want you to purchase full reels? Twice the frequency, that would have put it in good contention with the LM2842Y part. But the extra 6V also helped in this case. Most of the 20V parts are synchronous, save the space of a sod-123 diode.

Do you follow the principle on your layouts? Or only for that customer? Most of the time a 90-degree rule isn't a problem. But there are times I prefer a mecca approach, where all traces must meet only at the pads, despite whatever room around the pad is available.

A few years ago I starting worrying about flaring any narrow traces as they reached a large pad, to reduce the possibility of trace breakage or lifting. If you start worrying about outlier cases, is there any end?

This is an example. I manually added the flaring.

A 90 degree entry rule is not the right solution. The right rule would be to have no internal corners less than 90 degrees. I often use traces enter ing at a corner which the 90 degree entry rule would exclude even though it has larger than 90 degree internal corners.

I have no idea if acid traps are a real issue or not, but this is easy enou gh to deal within general, so I design as if it were a real issue. It woul d be even easier if the software had a design rule to check for that, which mine doesn't. Manual inspection is not so easy when your boards have hund reds of pads.

I don't typically worry with that, but then my traces are typically not muc h smaller than the pad. Sometimes I have to reduce a trace width to match the pad. Pad for digital components are often 0.5 or even 0.4 mm pitch. T he pad is less than 8 mils, so a 6 mil trace matches pretty well.

PADS will do teardrops automatically, but I think they're ugly so don't do them on my boards.

We very rarely have a board problem. We buy from known good vendors and specify bare-board testing.

We have had some bad cheapie-quick-proto Chinese boards.

I'm confused, no 45-degree direction changes in traces?

Perhaps they'd permit 135 degree instead :)

piglet

Winfield Hill wrote in news: snipped-for-privacy@drn.newsguy.com:

I like the old, hand routed traces with nice, smooth transitions. No corners anywhere. Even the 45s had rounded lead ins and lead outs.

Piglet wrote in news:r0mdcn$pm4$1@dont- email.me:

Squiggly wiggly PCB layout pigly

I've read that Altium has brought those back in its last version 20. They can be automatically invoked in tight ball-grid-array via wiring, improving the trace clearances. Not having installed 20, I'm not sure if they help the user employ them elsewhere.

PADS can do rounded corners, but it's a nuisance.

I was told to not bend the tape on tape-and-mylar boards because the stress on the tape would allow the corners to slowly creep, and change clearances. That, like a lot of other things, like acid traps and right-angle reflections and a zillion bypassing rules, may have been folklore. Layout people seldom understood electronics (still don't) so developed a lot of lore.

BGAs with radiused bends does sound interesting.

Funny how so many ads and articles about technology are illustrated with pics of ancient thru-hole DIP boards with rounded traces.

that would not make an internal corner less than 90

snipped-for-privacy@highlandsniptechnology.com wrote in news: snipped-for-privacy@4ax.com:

There's nothing wrong with 45 degree traces if they join the pad at the corners. The problem is not 45 degree traces. The problem is internal corners of less than 90 degrees... if there is a problem at all.

Bad?: internal corner at =90 degrees. \ \ \ \ \ \ \+-------+ | | | PAD | | |

Is that more clear?

Why do YouTube videos follow me around now? When I scroll the window to read comments the video stays on the screen. I can close it, but as soon as I scroll to the top and back down it returns.

Why are they making it hard to read the comments?

Exascale processing in Europe seems to use 32-pin thru-hole CPUs.