Power supply protection networks

Yeah, that's what I've heard for all of the couple of decades that I've been working. Hence I've never once gotten close to being asked to design an off-line switcher, although I have done a number of DC-input ones.

"I know someone in the states designing wall warts that get made in China. The products have no markings to trace back to them. They stay totally out of the lawsuit pockets. I don't know if the money is off- shored or not. The scheme seemed to me to be highly likely to get one's company ripped off by the Chinese, but hey, it's not my business."

Are they really esoteric designs or something? It seems like the standard

Out stock room is locked and only a few have access. We have to fill out a req to get any parts. Yes, it's a PITA to find our admin to fill out a req (she has all the charge numbers) to "buy" a $.0015 0603 resistor. If we're working after hours, it's time to go home.

Our Admin can look at costs and inventory. I don't have access to that system. All the rest of that information is available.

We only have one SMT line. When a board is run, they check out the reels they need and return them to stock when they're done. "Kitting" isn't required.

We have a small number of boards, perhaps 20 and they're usually run in smallish batches (20-50). Nothing, other than components, raw boards, and metal is done outside. Up until now, the business was

*very* seasonal. If a vendor pushed us off for a month we wouldn't lose just a month, but likely the whole year. Since the business was so seasonal we couldn't count on any leverage with vendors so everything possible is done in-house.

[...]

A guy on the German NG bought rechargeable batteries from various Chinese sources. Then he measure the thermistor. One always read 10K no matter what the temperature was ...

[...]

Last week I designed a 30W switcher where the main transistor gets to around 200mW. At least on SPICE. We'll see.

--
Regards, Joerg

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I'm always amazed how many engineering companies seem to actively withold cost information from their own design engineers.

The locked up parts bit I can understand a bit more in that the management might be figuring all the engineers will start building their own caches of commonly used parts over time anyway, so access to the "main supply lines" can be more restrictive. (It still doesn't make any sense though... as you point out, you spend $10 on an administrator to get a 1.5 cent part...)

---Joel

How can you build 15 boards without pulling the parts for 15 boards? You can't run into the stockroom for 45 resistors, solder them down, then run in for 60 capacitors, then go back for 15 diodes...

We have to load our p-n-p carousels for a production run. Sometimes we load the carousel for N boards when we only want to stuff N/3, knowing that we can set the entire carousel aside and pick it up later to do more boards. But that carousel load is still done from a picked kit, from a computer-generated set of kit labels for the N assemblies.

John

This was outsourced. They always loaded full reels and just reloaded when the machine beeped.

We had catheter and system production inhouse. When they needed to build

30 systems they started with the base, power supplies, fan assy and so forth and then built it up. So they pulled in as many chassis as they wanted, often like 10-12 at a time so they don't block pathways. Then they loaded carts with 15-20 transformers, fuse blocks, terminal blocks, wire and whatever else they wanted to have on the floor. Not what some list dictated them to cram into the place.

But I hope you don't snip 45 resistors off a reel and load it into the machine just because the standard operating procedure says so ;-)

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Not so much withholding parts costs as not having the purchasing systems linked to the engineering databases. Programming time to small companies is preciously scarce. They talk about doing a "back-annotate", but it never gets done.

That would be ten parts. ;-) The problem is that the manufacturing types don't know a $.0015 part from a $100 part. The rule is *no tickie, no partie" or the whole inventory control system leaks. Then it's not so much the parts cost as not having inventory when it's needed. I understand why. I don't like why, but it's the owner's money either way. He wants to waste my time, I guess that's his derogative. OTOH, weekends and nights aren't his time (the glory of being a salaried employee).

Does it have a drop ceiling? I always found them to be effective.

How can you pick parts without knowing how many are in stock, or what they actually cost?

Our semi-auto machines allow about 10 reels, and a lot of loose parts in carousel bins. And we may buy 25 or 50 parts at a time, not enough to wrap around a reel.

Some parts, like bypass caps, they can pull off a reel. Most parts have to be kitted into the carousel bins.

We have almost 5000 different parts in stock.

John

Our business philosophy is to trust all our employees. There are no locks inside the building except one fireproof safe for the checkbook and such. I think we gain a lot and, rarely, lose a little. If anybody wants modest amounts of electronic parts, wire, postage, or office supplies for personal use, well, just take them.

John

Usually, yes, that's exactly what we do. For cheap parts, we pull a few extra, and if there are any left after the boards are stuffed, we throw them away. It's too expensive and dangerous to return them to stock.

If, while placement is going on, for some reason we're short a couple of parts, the stockroom is 15 feet away, so go get what you need.

John

Then we have a totally opposite philosophy when it comes to production. Maybe that is because I usually design for larger production runs. Folks there would never cut anything off a reel. It costs too much labor to do that, and also waste. Or a trip to the stock area if coming up short (after all, some guys has to get up and do that). In my area of work the typical method is to always load whole reels and then return them to the storage area when no longer needed.

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Too bad you don't program? :-)

Yeah, I can see that... but such a policy suggests that basically engineers can't or won't properly document whatever it is they're taking, which is a bit disappointing from a "company culture" point of view.

Of course I agree that, well, if you take the job, you gotta play by the rules as spelled out by "da boss," and this kind of thing largely falls under "don't sweat the small stuff" in the grand scheme.

---Joel

I think they'd rather pay me to design products. ;-) ...and I don't suppose they'd like their inventory system written in assembler (or VHDL). ;-)

*That* is understandable. I doubt I'd document a $.0015 resistor. Other stuff, don't know. When the swam needs draining...

Yep. "If this is my biggest bitch, it must be a good place to work." ;-)

No ceiling at all.

That's a problem, huh? I know pretty much what the parts cost that I've specified. Other than that, it's a crap shoot.

Our pick-n-place machine has 135 "slots" (components are up to 5 or six slots wide for an audio transformer), which limits our component diversity to that per side. One board pushed that limit so I had to go back and choose resistors more wisely.

The issue is how many you stuff at once. We take full reels to the floor for the board being run and return them after. Sometimes they get intercepted for the next board, but that's really no difference. Most inventory is serialized by pick-n-place.

It's not so much philosophy. Our Essemtec machines can hold a maximum of 15 reels, and a pcb BOM might have 100 different items.

John

Hey Keith (and John?),

Do you guys keep 5% (or looser) resistors around anymore?

I've previously worked at a place that found that keeping both 1% and 5% resistors around cost more than the savings gained based on their price differences and hence switched to just using 1% for everything (I don't believe any of the engineers protested :-) ). My officemate also previously worked at such a place (not the same one).

---Joel

We have some in our inventory but I never use anything other than 1%. Why?

Do 5% 0603s exist? At five or six to the penny (for 1%), why bother? We don't have a full set of 1% values, so choosing resistors gets to be a problem. Again, it's not so much the cost of a reel ($8-$10), rather another SMT slot. I spent a few days figuring resistor ratios to eliminate a few stuffer slots.

Microdyne issued alternate stock numbers to the 5% resistors to phase them out. We were paying more for 55 resistors that the 1% because we used so few of them. Then purchasing decided to stop buying 10% rated inductors, and substituted 5% parts from a different, cheaper vendor without telling Engineering. We were bit in the ass with SRF and other problems by their folly. Some filters used the SRF to good effect in shaping the skirts.

--
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"Bulk medium" resistors are needed for some applications, like arc suppression. The resistance medium on 1% resistors (typically metal film) is far too thin for such transient suppression applications.

It is hard to find them, but they are out there, and are still being made.