CMKT5088 - Dual NPN for *2*5*2*0* input

[Ethan]

I went to see an eye-doc earlier this year because of on and off blurriness in my right eye. The doc takes a look with all sorts of gadgetry, then says, "Hmmm, that's...that's...I've never seen that before!" (never a good sign). He then opens the office door and proceeds to yell out, "John, you've gotta come see this!" (at this point I feel like a circus freak show).

Apparently I have spots on my cornea. Nothing can be done for it. It comes and goes every few months, really strange and annoying.
Other than that it turns out I have "really dry eyes." (I paid $150 for that damn visit to be told that I have "really dry eyes." :shock: And here's the kicker, I was "prescribed" over-the-counter eye drops!

 

[PRR]

Keep your eyes wet.

The cells in the eye lens are alive (though barely). They need oxygen. But they can't have blood: that would pink-out your vision. They get oxygen mostly from the air.

And you know that damp iron oxidizes (rusts) much better than dry iron. And your lungs are wet inside, for the same reason. And your eyes need to be wet or they will suffocate. The cells in the lens live very slowly, and won't suffocate quickly, but over the years it hurts.

Astigmatism is, in principle, perfectly correctable with two numbers. I have the bare minimum astigmatism, the doc has to round-up to justify prescribing astig correction. And I really rather they wouldn't: I spend enough time without glasses that putting on astig-corrected lenses is disturbing.

My main problem is that "infinity" is about 13" away. So I will always be able to read without glasses. And though it is illegal, I can drive fine without glasses. I can't read street signs, but see stop signs/lights fine, I see where every car on the road is, and can often tell you make/model.

But while I used to be able to focus less than an inch, I'm out to 9" now. When I put on my "driving" glasses, infinity focuses fine, but even 15 feet is blurry. I'm actually wearing "computer glasses": corrected for about 30". This gives tolerable blur at infinity (I can read roadsigns, even pass the driving test again), hallways are sharp, and I lose focus around 24". Then glasses-off, I have my 13"-9" range. And if I need closer, I keep 50mm camera lenses for the 2" zone.

> why are those little tiny components an improvement?

Are they an improvement?

What can you do in SMT that you could NOT do on octal sockets and good old 1/2W 2"-leg resistors? What two products, one DIP/thru-hole the other SMT, prove that SMT is "an improvement"?

I hope I am not stepping on anybody's toe. I know some commercial promotion touts the advantages of SMT. And there is a point. Smaller total area and no through-leg solder blobs means tighter design, less parasitic couplings. GHz work must be much simpler in SMT. And hot audio amps do have GHz response.

I'm in favor of BIG surface mount; been doing it since it was "bad". I haven't drilled a PCB in decades. I leave a large pad, bend leads to a "J", and tack-solder. When I started, parts HAD to be through-hole for "mechanical support". And this may be true in shipping. But breadboarding on tack-solder PCB convinced me that tack-solder could be plenty strong enough for home use. And some of my "SMT" boards have been thrown in and out of gig-bags many times. The layout (using DIP and 1/2W resistors) ends up a little bigger than a fully optimized thru-hole board, because pads have to be large. But in one-off design, PCB area is not a big cost, no-drill is faster, and a wide-open layout is an advantage in debugging and tweaking. I'd much rather be debugging/tweaking than drilling.

In mass-produced stuff: yes, SMT is now better. One reason is that it is still a "bad idea", so proponents of SMT really worked to get those wee bits to stay on the boards when the crate falls off the forklift. Smaller area and lower parasitics too. And SMT is now "better" just because it is the industry standard. You can find many qualified outfits to assemble your SMT, fewer who can stuff a thru-board properly.

 

[SonsOfThunder]

[quote author="Category 5"]http://www.oselectronics.com/ose_p11.htm
The kit version of the FG500K is only $31. It takes about 30 minutes to build.'[/quote] Haven't used the model you are referring to but have used and measured the GF-800 on the same page. Pretty cheap and not too bad, really. Lower THD is this one, but not as adjustable obviously.
The October issue of Mix Magazine has a great primer on using a 'scope, written by my friend and G'DIY lurker Eddie Cilletti. Its not online just yet but soon.

 

[SonsOfThunder]

[quote author="PRR"]Keep your eyes wet...They get oxygen mostly from the air.[/quote] Most interesting!

Astigmatism is, in principle, perfectly correctable

You bet! I used to have 20/15 vision with my glasses and I could shoot a target rifle with great accuracy IF I got my "eyeballs" on just right...Haven't tried this in a few years though...

> why are those little tiny components an improvement?
Are they an improvement?

Here's my take on this, if anyone's interested.

SMT is an improvement...(overall, not really but keep reading), as PRR says regarding parasitic effects and such because of tight layout. It is touted in manufacturing because it is an "easier" process once set up. You load up the machine with PCBs, parts, and the locator program for the design you are doing and if the hot-air reflow oven is in tune, your yield will likely be >98%. A lot of money can be saved in manual rework costs. The machines that do this can be expensive, but they show up for work every day, they don't take vacations, they can work 24hrs...etc.

Otherwise SMT is inferior in many respects: Thermal capacity, service-ability, trouble-shooting, danger of stray solder bridges, etc. When was the last time you encountered a ckt that took hours to troubleshoot and it turned out to be a cracked thru-hole cap? Tons of hours have been spent on cracked SMT resistors and caps...not visible until you hit them with an iron...then its obvious! Doh!

Typical SMT designs are going to take up less space but the PCB designer has to think clearly to avoid vias which can consume a "lot" of space. Vias are sort of built-in when using thru-hole.

Btw, that part about thru-hole giving mechanical support is IMO only going to be true for a PCB with plated thru-holes. Single-sided PCBs...you are at the mercy of the bond between copper and the PCB substrate...sometimes its good...sometimes, its just not. Sometimes, its okay until the PCB gets cooked for a few years. I've got a Samson headphone amp in need of some simple repairs, but I'm afraid to touch it for fear of every trace in the middle of the board falling off because the o/p devices have cooked the traces and they are ready to fall off!

HTH!
Charlie

 

[tk@halmi]

The original reason for using this part was the convenience of pre-matched transistors when making a larger quantity of the opamp. At this point I am starting to think that just spending a few hours on matching good ole' 2N5088s in TO-92 cases is more productive than handling this SMD component. :grin:

Tamas

 

[PRR]

> that part about thru-hole giving mechanical support

When I was young, parts were tight against the board when soldered. Resistors hard against the PCB, transistors sitting tight on little nylon spacers to keep the seals out of the solder. There was no lift on the copper.

Yeah, nobody has obsessed about that in decades.

 

[Dan Kennedy]

Part of the tightness to the board issue now raises problems in production, in fact many parts have built in risers, or spacers that keep the bulk of the body up off the board by .5mm or so to allow thorough cleanup after soldering.

The water washable fluxes now used leave a very conductive residue that needs to be completely removed, and tight parts don't help.

De-fluxing used to be done with some very effective and fairly nasty flourocarbon products that are no longer permitted, but they'd clean up anything...

 

[SonsOfThunder]

[quote author="Dan Kennedy"]De-fluxing used to be done with some very effective and fairly nasty flourocarbon products that are no longer permitted, but they'd clean up anything...[/quote] And now they use...a fancy dishwasher!

Peace!
Charlie

 

[CJ]

Wait til you guys have to solder PLASTIC surface mount transistors!
I'd like to murder the genius who thought up that packaging technique.

 

[SonsOfThunder]

[quote author="cjenrick"]Wait til you guys have to solder PLASTIC surface mount transistors![/quote] SMT film caps are quite the challenge.

HTH!
Charlie

 

[BradAvenson]

I do alot of very small SMD work by hand. My only advice is a metcal and solder flux. Without those two I would be hard pressed to do most of the really small stuff.

I like the density that you can acheive with SMT. And of course, being the eternal optimist, I dont' build stuff to be repaired. :wink: