The A92 or mpsa92 is a popular 300V pnp transistor in a TO-92 package, with a number of sot-23 SMD versions also manufactured, most commonly the mmbta92. Most of these 300V transistors have breakdown voltages of 400 to 450V, in my experience, and on occaision I've used them in designs right up to 300V. But I didn't realize until recently that there was an official 400V version, the mpsa94, with a number of sot-23 offerings: e.g., the mmbta94, cmpta94, hmbta94 and fhta94.
However, a quick look failed to turn up any distributor carrying any of these parts. Does anyone here have any experience with these, or know of other 400V sot-23 pnp transistors that might be readily available?
Ah, I found the Zetex FMMT558 and FMMT560 sot-23 parts, with 400 and 500V ratings. How'd I miss those? Hmm, Fairchild offers their FMMT560 rated at 60V -- oops!
Digikey shows >1K in stock of both Panasonic 2SB14880PA and Zetex FMMT558TA both in full and broken reels. A bit pricey, though (
0.282/2K and 0.1728/3K vs. 0.06/3K for the jellybean MMBTA92).
Best regards, Spehro Pefhany
--
"it\'s the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
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The Panasonic isn't a sot-23, but the Zetex fmmt558 is an ideal replacement for the A92. According to the datasheet it has less capacitance, a higher fT, and better gain over a wider current range. What's not to like? Later today I'll make the change in my 2.2kV amplifier and find out.
Sometimes money is no object. That's easy to say when only 11 cents is involved. :-) Well, actually, with 16 per board it's $1.76, but that's on a large PCB with 600 parts and a $400 per board cost in a run of 40 boards.
Oops. Not even SMT, but at least a pleasant ~0.1" pitch through-hole package with good power dissipation. ;-)
Sounds like an interesting circuit.
I didn't think it would matter much to you, but it's interesting that there's a 280% price increase for a 25% improvement in Vceo.
Best regards, Spehro Pefhany
--
"it\'s the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
But the Zetex part is a 825% increase in Vceo over the Fairchild's one, for 0% increase in part#.
Let see the scene: Design some nice 400V gadget... Prototype, blah... Run into prod. First runs OK. Purchase dep.: Oh, but why would we pay Zetex that much. Fairchild has the same one. No pb.
Designer: what part did you get mounted? Prod: FMMT560 Board: still Kaboum! Designer: wait! That's not possible. Prod: Yes, but the board doesn't say so: Kaboum! Designer: Are you sure it's FMMT560? Purchase: Sure! Look at the delivery note. Designer: scratch... Board: Kaboum!
2 weeks later: Customer: Hey, where are my boards? Board: Kaboum! Sales dep.: Oh, your order must have got lost by the postal service. We never received it. We'll send you all our stock tomorrow. Boss: What's the f..k, designer? You're fired. Designer: but... Board: Kaboum! ... ... Tech: Idea!...FMMT560->MMBT560... Eureka! Tech: Look! That FMMT560 is a 60V part! Purchase dep.: Those designers are really nothing but morons. Prod: Hmmm, but the first board runs worked OK. Boss: You know, components have some tolerances. First ones must have been very good. Prod: Amen. Purchase dep. : Amen. QA dep.: Amen. QA dep.: Ouch, but that's a huge Vceo variation. Those FMMT560 are really crap. Mark them as forbidden, or don't use them with more than 6V VCE. ...
Zetex: Why don't we sell our nice transistors anymore?
... ...
Win: Too bad... Zetex has just dropped that wonderful FMMT560 I was fond of.
I'm sure both the fmmt558 and the A92 can turn off in well under a usec, if it's current sinking or steering you're thinking of. But do you mean the output has to slew 400V in under 1us, or > 4x10^8V/s? Assuming an external node capacitance of 5pF plus an estimated 3pF for the transistor over most of the excursion, the load current would have to be i >= C dV/dt = 3.2mA. Since that's quite reasonable, it would seem these transistors may meet your requirement.
Indeed. It's the nature of high-voltage series-cascode applications to use a lot of transistors per circuit. For example, in my circuit I used four for each amplifier, but I should have used five. If I had added the rail-current monitoring circuit I envisioned, it would have been 15 per amplifier. If I had then beefed up the HV amplifier to a full push-pull configuration, to improve speed, it could have meant 35 of the A92 or A42 transistors per amplifier (thanks for machine assembly). And if I had then increased the voltage range to beyond 2.5kV, it would have been...
I was thinking about usage in a boost or SEPIC converter. A microsecond can be quite painful when the whole conduction phase is 5usec or so. There are some FETs but the smaller ones in SOT23 or SOT223 are mostly from EU companies and they can be an absolute pain to deal with from over here. May last attempt at that was with the BSP297 and after two hours on the phone I vowed to never do that again. Being fluent in German did not help one bit, they simply couldn't get them to us. Or maybe sales volume didn't matter...
That's the beauty of today's jelly-bean parts. People say that our youth doesn't have the available resources to build electronics projects. That's nonsense. Sure we had a radio store in the next town (one hour by bicycle) but one of those transistors would have cost a fortune. There was no Digikey.
Well, in some ways it is better; in others worse. I used to be able to just go to any of several local stores and persuse through table after table of parts and components in a warehouse kind of place; or go through Radio Shack (even before Tandy bought them) and see most of the entire store with parts; and so on. I seem to recall at least two or three RS stores in the city area (good part sources), an Allied Radio electronics warehouse store with a huge resource I could go through by hand; a United Radio store with parts everywhere; and two other "surplus" electronics stores I would frequent.
ALL (every single one) of these are essentially gone. The RS stores are no longer a resource to speak of, even though there are more of them now. There is a Norvac Electronics store here. And it has parts
-- but high priced "replacement brand" (read: NTE) parts for the larger part of it. Some interesting things once in a while.
This, in a city metro area with now 1.5 million people.
Of course, there are really great new options, too. I would never have been able to afford quality boards made for 1, 2, or 4 off kinds of things. My selection of parts are fantastic, and so on. So many more things are sincerely possible to consider realistically doing than there is time for, as a hobbyist with family pressures and a profoundly autistic child can manage.
However, I'm finding that transistors the size of salt grains without the possibility of any markings (unless they placed the letters on them pixel-atom by pixel-atom), the need for more expensive soldering tools and magnifiers (as I age), and the relative higher difficulties of actually finding and using parts I can put on a protoboard meaning that I really need those board houses more.
Some of it, though, at least for young kids, is that access to those who know a little about electronics (and I'm not talking about experts, just folks with some "playing around" experience who are there when a kid has a simple question coming to mind) seems to be in a diminishing ratio. There are more folks in the business, but fewer neighbors to ask, it seems. Certainly, when I was growing up there were many with at least some military experience in electronics you'd meet and others, too. I used to also have several neighbors in an easy 4-5 mile bicycle riding radius of me working on building their own telescopes. Also, into rocketry. And so on. I can't say I know where any of that is going on within many more miles of here, now. If at all. (I've lived in the same community my entire life.)
On the other hand, there is the internet, too. So that's to the good side of this.
Both parents working, or one working two jobs, the intrusion of TV and gaming systems into our time, the hours applied per individual adult and child for hobby learning has diminished, I suspect. People don't build their own barns, replace their own rooftops, repair their own plumbing or lines coming into the house, etc. They hire it, if they can. A transition from broad to specialized knowledge, a dependance upon a surrounding supports in society, etc.
I used to know lots and lots of neighbors by the hobbies they were into, in fact. "Oh. That's Joe. He's really into model planes a lot." That kind of thing. Now, often when I ask a parent or adult I know, "What kind of hobbies do you like to do?" I get a blank stare, much more often than I ever used to.
Our RS has shut down a few years ago. Because a, gasp, cell phone store :-(
Same here. My last designs contain lots of 0402. Very tough, even with #3 glasses plus magnifier.
Well, they should learn using usenet :-)))
Ham radio club meetings are a good opportunity to find those who still build stuff from scratch. That's how I found mentors when I was a kid because there was nobody else to ask in our neighborhood. Having a ham radio license helps even more. You can go onto the local 2m channel and ask. Chances are that someone will respond "Oh, that's a tough one but I've got a Tek scope. Come on over and we'll figure it out.".
No with me. I've laid lots of tile, re-did a bathroom, then another, then another. Many times hiring out results in huge costs. A neighbor was just quoted a whopping $33k (!) just to replace a deck.
Ok, we did hire out the re-roofing but we needed a rather complicated metal roof. Plus my back isn't that good and it gave out when I helped on a re-roof project for church outreach. We were so close to the ridge that I pushed myself too far, happens easily when roofing. Couldn't get up the next morning.
Sad, most people just hang out in front of the TV. That's their "hobby". In our neighborhood it's a lot better. People build cars, several airplanes, huge sea-going sailboats etc. There isn't one weekend where you don't hear some drills or sanders going.
On Sat, 14 Oct 2006 17:43:28 GMT, Joerg wrote in Msg.
The youth certainly has resources, more than ever before, but no incentive. When I was 15 I built my own stereo amp and loudspeakers because I wanted to have one, and commercial stuff was a lot more expensive. Now a kid can buy a $10 PC speaker set that sounds about as good as my amp back then.
A must-have must-build category of stuff were things that blink and generate noise. Nowadays we have computers and other cheap gadgets that do more noisy blinking than we can stand.
Another driving force behind hobby electronics was wireless communication. I vividly remember my first home-built matchbox-sized FM transmitter. What delight! The fact that operating it was kind of illegal was icing on the cake. Now every kid has a damn cell phone with which it can call every other kid in the industrialized part of the globe within seconds.
Where's the fun in doung stuff yourself if you can just buy it better and cheaper? I mean, it's still fun, but the main driving force for kids is gone.
The first computer games we played we had to invent and code ourselves because there were no games, at least not on the three $10000 computers my school had in 1985.
Of course nowadays 2-year-olds have those ultra-cool wooden bicycles which hadn't yet been invented back then.
I must say that I still do not have enough spare time to build all the stuff that we could use around here. Not even the stuff on the honey-do list: A decent level meter for X10, a non-mechanical pool timer that doesn't cost $500, low power AM transmitter to get web radio to other radios, X10 receivers that really work, and so on.
Shhhht... :-)
Oh, there would be. If I were a kid today I'd still do what I had done back in school. Build the biggest honking amp that a 15 amp circuit could sustain. Except this time it would be class-D for even more oomph. Instead of scavenging tubes and TO3 transistors I'd be prying FETs out of discarded computer power supplies.
They often just have to many toys, don't have to be creative anymore. When I grew up my favorite place was grandpa's shop.
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