Which N Or P Power MOSFETs ?

Yeah, I was thinking about the engineering required for 5G and such. That must suck up most of the smartest people on this planet.

tirsdag den 24. november 2020 kl. 00.57.43 UTC+1 skrev snipped-for-privacy@highlandsniptechnology.com:

that's all software-defined radio any way so you can control it all digitally no need for analog delays

I find tht the diode recovery problems are way worse with higher voltage applications... i.e. Low voltage, less than around 200V or

And the higher voltage Schottkys with low forward voltage (> ~200V) aren't available at real high V so doesn't do much good, if any, in parallel with the HV FETs... And, the HV Schottkys have a positive temperature-voltage coeffiient so they don't share or over-share the reverse current as they heat up. Damn. Can't have anything !

My experience as I remember anyway.

What was your motor driver voltage ? That might complicate things just being a motor drive. I don't know

I think that Space-X has a lot of those smart people. Would be great to be a bug on the wall watching them talk about their work.

There are lots of different ways of being smart, and smart people with other interests aren't all that likely to retrain to get the skills needed to work on 5G and 6G.

There are also quite a lot of other uses for smart people - quite a few of them are busy working up vaccines and other defenses against Covid-19 at the moment.

If you were deluded and smart, you might be working on a way to defeat 5G so that it doesn't propagate the Covid-19 virus (not that it does, but there are lunatics who seem to think that it does).

It was a 24 volt supply, and two fets in half-bridge, driving a motor whose other end was grounded. We reversed with a real DPDT switch. It was sort of a charity project.

Higher-voltage diodes tend to be pin structures, and often have a doping profile that makes them drift step-recovery (Grehkov) diodes. I guess a fet substrate diode could do that to. Maybe those moto mosfets were oddballs.

My current project is a full h-bridge, running from 48 volts, driving a transformer. The schottkies across the fets might increase efficiency a tiny bit too.

Nah, they don't pay enough for that.

The idea of working on a project that large gives me the screaming heebie-jeebies. An optical table, an interesting problem, one or two colleagues, and somebody to sign purchase requests without giving me agita is the ticket. ;)

Cheers

Phil Hobbs

We lost an interesting redesign to an in-house team specially assembled to do it, two groups totalling about 20 engineers on two continents. Might have taken us 4 months. Three years later, theirs still isn't done. At some point, more engineers and especially more management turns the progress rate back down. Approaching a man-year per square inch.

It's sad how they have to keep buying the old stuff from us.

;)

From our point of view the main problem working with large groups at clients is that they're generally seriously underdamped. We've learned to nitpick every specification document they send us--not so much so we can understand what they want, but so _they_ all have to understand it.

Awhile back we lost a potentially good customer by being too polite about their specifications document for an ultraquiet laser. Turned out that the guy who wrote it (and illustrated it profusely) thought we were replacing one vendor's lasers, whereas the rest of their team wanted us to replace their other vendor's laser. They just hadn't read their own document carefully. :(

We actually fished that one out, and built greatly improved replacements for _both_ vendors' lasers within the specified budget, but then their project lead left the company and the project got cancelled. On the plus side, we now have this super quiet laser system that we can sell to other folks. :)

Cheers

Phil Hobbs

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all that I found it can't work. The drawing was on the bench and I saw the problem immediately, at a glance. Damn.

This looks pretty much non-negotiable.

er ?N channel or P channel. The difference it the power supply. Which is ea sier to design, but what if the better choice need negative, ? Then I draw it upside down, so what ?

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It's a fairly well known problem

talks about software engineering, but it reflects a general problem - the m ore people you've got working on a project, the more time gets spent on mak ing all the contributions fit together (or on complaining that they can't b e made to fit).

They have my deepest sympathies. One of the problems of replacing a bought- in solution is that the existence of that solution gives the design team t unnel vision.

If the problem is tackled from scratch, there's a fair chance that somebody will comes up with a rather different solution that wouldn't have evolved from up-grading the existing solution.

John's four month development time presumably reflects doing such an evolut ion. Throwing twenty engineers at the problem suggests the the customer was more ambitious, but if you can't find the right engineers having twenty en gineers squabbling about the right way to go can waste a lot of time.

The bigger any group (engineers, soldiers, rabbits) the more powerful group dynamics becomes. Peer approval becomes the dominant force. Fun things can happen, like wars.

If it's an accident, it's a discovery, not a design.

After that, everybody actually knew it, all along . . . .

RL

Depending how well run they are.

Peers aren't the whole group. What matters is the approval of the people who know what they are talking about - or at least that is what matters in a well run group - and they do tend to agree.

When people who think they know what they are talking about start throwing their weight around the situation can - and frequently does - deteriorate.

If a basic concept comes from a rarely or never explored place in the solution space, it's a discovery. Deliberate, organized searches for ideas tend to miss those places.

If it involves parts soldered to a board that people buy, it's a design.

The combination can be good.

At least those searches organised by John Larkin may. Not that he's ever re ported doing such a search.

If it's documented, you can tell people it's a design, even if you got ther e by a process of incremental modification, which is actually evolution, ra ther than design.

If accident is the only way that you can get away from the familiar corner of the solution space, it's better than nothing. Design involves actually l ooking for alternate solutions, and usually means ripping up quite a few of them. Doing it before you've soldered parts to boards is cheaper.

Huh? Deliberate, organized searches do NOT miss items in the searched space. It's just that some folk miss possibilities because of predispositions. This is a variant on the classic XY scenario.

Deliberate, organized searches work just fine. Beware, though, attempting to find a cheap D-to-A solution by searching IC merchants' offerings for "DAC" because that misses the R-2R ladder. It's not an IC...

Looking for ideas like looking for your car keys? Riiiiiggghhhhtttt.

Cheers

Phil Hobbs

Inventing things and finding bugs in things are similar mental processes. Both require letting your brain diffuse far and wide, and not trusting data sheets or experimental observations or what everybody knows. Both can be done in background, like when you are asleep.

But you don't find novel ideas (or car keys) if you keep looking incrementally in all the usual places.

I once found my car keys underwater, under a layer of ice, in the parking lot at Sugar Bowl. That took a while, and the electronics in the fob was destroyed. That's about a $270 or so fix for an Audi.

This may be true for John Larkin. I've inverted stuff that has got patented, and it doesn't line up with my experience.

Once you've put in the hard work to get the information (lots of it) into your head, your sub-conscious will work on it in background. My father had 25 patents, and claimed that his best ideas came to him when he was shaving. He was well aware that he'd been sleeping on the problem, and that the answer that "came to him" had been sitting in a queue.

Obviously not, unless "incrementally" means progressively increasing the area searched - as opposed to going back over areas already searched, time and time again.