What are the lowest cost transistors out there

[Rochey]

Hello folks,

In an effort to find the easiest and cheapest parts to do things like switch LED's on in circuit etc, I would like to discuss and share what transistors people are using.

Sounds silly, but I hope that some of you may be using low cost transistors for switching etc.


So, I'll go first.

I use PN2222 transistors for switching LED's and relays. They are cheap ($0.05 at mouser for 1) and can handle the current easily (can support up to 600mA)
They are also available in surface mount too.

Can anyone suggest a MOSFET or JFET in the same price range?

Also, can the base-emitter pins be used as a diode for simple rectification?

Cheers

/R

Cheers

/R

 

[PRR]

5 cents each is mighty close to what the packaging and handling costs. (Ask your production engineers what it costs to make these things... probably over a penny each, and 5X markup to ship around the world and break crates to single parts isn't unreasonable).

So no matter WHAT is inside, you won't find much cheaper unless it "fell off a truck" or you buy whole crates.

MOSFETs may not need a base resistor.

Use the collector-base junction: 40V instead of 7V reverse rating.

 

[jdbakker]

Not to derail the thread in the first response, but I personally find it much more interesting to find a small set of parts to cover as many as sockets as possible. That way you can buy them in bulk, and having to stock a smaller set of parts is always a Very Good Thing.

My picks would be:
BC550C/560C: 100mA, high hFE, low capacitance, $0.037/$0.042 in qty100.
2N4401/4403: 500mA, low-noise audio and/or switching, $0.034 in qty100.

(IMNSHO, unless you're buying millions a month having one part that can replace half a dozen others is much more useful than paying even a dollar less per hundred)

Also, can the base-emitter pins be used as a diode for simple rectification?

If you can live with the reverse breakdown of only ~6V, sure.

JD 'TUP/TUN, anyone?' B.

EDIT: Crossed posts with PRR

 

[JohnRoberts]

I though this was a joke question..  The cheapest transistor is probably inside some large memory chip, or processor.

These days it cost more to place a small signal transistor than the part itself, and if through hole, it cost to drill the holes too.

ROHM and probably others make transistors with base resistors built in to save manufacturing touches...

2n3904/3906 low end general purpose small signal transistors.. 2n2222 sounds kind of old.. perhaps more expensive.

JR

 

[Svart]

I'm with JDB, I'd spend a little more per part to get something that I can use in more places and therefor order larger quantities and keep a tighter BOM.

I also second the BC550/560 stuff, I've been using them for a lot of things and find them pretty versatile.

 

[PRR]

> 2n2222 sounds kind of old..

He said PN2222.

I doubt he could find a ready supply of genuine 2N2222 today. I had a box of genny early-production 2N2219, thick gold plate, but long gone now.

The "PN2222" has become a generic spec for stuff bigger than 3904 and smaller than 4401. And always in the cheap TO-92 or now the teensy legless bugs.

 

[owel]

I use a BC546C  (same family as the BC550). 
The BC546C is 65V rated. (the BC550 only 45V rated, Vce)

250 pcs for about $16.

 

[Rochey]

I use a BC546C  (same family as the BC550). 
The BC546C is 65V rated. (the BC550 only 45V rated, Vce)

250 pcs for about $16.

Just want to check, the S0t-23 version of that device is the BC846 from the looks of things. Can someone confirm?
It's a pity it's only rated to 100mA.

/R

 

[Rochey]

also, I see lots of NPN recommendations... no-one like mosfet switches?

Keith was talking to me about J111 and J112

 

[volker]

Those are JFETs intended for switching purposes. You won't get any JFET or MOSFET for the price of a small signal bipolar transistor. I use JFETs only for audio switching. And MOSFETs tend to make more sense, once you want to switch higher currents.


Volker

 

[BradAvenson]

2N7000 and 2n7002 (smd) are cheap mosfet options.

 

[sahib]

I have a good stock of 2N2222 and use it like asprin for switching purposes.

 

[Rochey]

I have a good stock of 2N2222 and use it like asprin for switching purposes.

I started with metal can 2n2222's, but didn't need the power dissipation quality of the metal can... so I switched to the PN2222 (got a bagful at a great price in China).
Since then, I've moved to SOT-23's of the device (MMBT2222?)

Whats your experience with JFET audio switching? Any suggested devices that won't break the bank?

 

[JohnRoberts]

I'm using a small Pch MOSFET as a high side switch in a battery powered design, it's not bipolar cheap but not bad (DMG3415?), and it is the right part for the job.

I think we all share the judgement of keeping the BOM as small as possible... Back in the early days of automation there were only a finite number of reels you could put on an insertion machine. Not as much of an issue today, but probably an issue in the margins. Certainly when having to order 5k reels, using that one oddball transistor makes a lot less sense.

Back when I used more thru hole and discrete circuitry, I standardized on MPSA06/MPSA56, as a nice slightly higher current GP  npn/pnp pair, as a step up from 4401/4403.

PN2222? yup, my bad... the 2n2222 is kind of like the small signal version of 2n3055, got to keep that popular number alive even if the old part is archaic. 2222/2907, 4014/2915-2917??  . Old school small signal part numbers.

Speaking of repurposing old numbers, I vaguely recall a VN2222 part that was offered as a high volume go to (MOS?)FET for general purpose (Nch) switching use.

I'm not familiar with the BC series but I suspect they are in the same ballpark as others here. One possible consideration is how do you plan to use these.? For simple switching, with no passing if audio, noise is not much of a consideration... Probably breakdown voltage, current handling, and beta, in that order (with cost in there of course). I don't even recall what the standard PNs were I used at PV for small signal GP. These parts are pretty much interchangeable.

If you are worried about the price of small signal transistors, you are probably using too many, and there may be a higher level integrated circuit to do the task more effectively. For onsey twosey, the small signal component cost should not be a big deal, unless there's a bunch of different onesy twosey parts, then inventory management rises as an issue.

JR

PS: Using JFETs for audio switching gets a little parts intensive to do well (low distortion), CMOS transfer gates are easier for budget stuff. JFETs do not mimic low impedance mechanical switches.

 

[Rochey]

Hello John,

thanks for the detailed reply.

My main reason for looking for the low cost is that I tend to buy in reels/ammo boxes from a disty I have in China.
e.g. the PN2222's were really really low cost per unit, but the MOQ (Minimum Order Quantity) was quite high.

When the MOQ is in the 3K range (e.g. for a small reel of SOT-23 parts) then every penny begins to count

As we're also gearing up for production soon (under the expat audio brand), so I'm looking for the lowest COB, at a performance quality that is the best I can get.
For digital stuff, the PN2222's are fine I think. They drive relays and LED's beautifully, and can do the job of an inverter a lot easier than an 8pin SOIC.
I'm still scratching my head on the audio routing/switching route.

in this Pro space, I may be better of sticking to relays. However, that does add size and power consumption.

*sigh*

Thanks for letting me vent

 

[sahib]

I have a good stock of 2N2222 and use it like asprin for switching purposes.

I started with metal can 2n2222's, but didn't need the power dissipation quality of the metal can... so I switched to the PN2222 (got a bagful at a great price in China).
Since then, I've moved to SOT-23's of the device (MMBT2222?)

Whats your experience with JFET audio switching? Any suggested devices that won't break the bank?

I do not have a vast application experience with Jfet switches but I used 2N5459 few times. Because almost all of the work I do is one-off or very small quantity the cost is not particularly very much of a concern. However, I can symphatise with your peny pinching but at the end of the day you have to think of the sound quality too. Most guitar effect units use Jfet for switching, and take Boss for example. Great majority uses 2SK30 for switching and I bet it is so cheap that they almost pay you back when you buy them. But put a couple of those effects in series and see what happens to the sound of your guitar. Therefore for the stuff that you are doing at this stage the relay is costly but gives you no headache.

 

[Svart]

I think we all share the judgement of keeping the BOM as small as possible...

Not only that but around here, once we do a circuit and layout, we use the piece like Lego blocks.  We keep a store of ready-to-go blocks that we can just place into schematics or PCB layouts.  

That way we minimize low level testing of the same things over when we do different boards.  

I wonder how new power mosfets would do in an audio situation with their very low RDSon.

I rarely use BJTs for switching applications because, not only am I a FET lover at heart, I'm not limited to using the cheapest parts.

I would choose a .25$ FET over a .10$ BJT and it's biasing resistors.

 

[Dan Kennedy]

Problem with most power devices is the intrinsic reverse diode.

 

[Svart]

True, but there are a still a few parts out there that don't have a body diode.

 

[severus_snape]

I live in Shanghai at the moment and I've been buying loads of transistors to take with me when I move home. I've been buying them on Taobao.com which is like Chinese Ebay. I've bought 5087, 5088, 3904, 2222, bc550, bc560, bd139, bd140 and a few more. I paide 3-5 cents a piece in quantities anywhere from 10-100. I think the most I've paid for a transistor is 10 cents or so for a 5457. Regulators can be had for 10 cents. Most ICs are dirt cheap too. I also just bought 4 pounds of random surplus film caps for 2 bucks. It doesn't get much cheaper than this.

I've bought almost all the parts to build a pair of 1176s, a GSSL, 8 Green Pres, a load of stomp boxes and a Megadrum setup for my brother. I think I've spent $300 including rack boxes ($10 each).

My wife has been really cool about it all, but she's starting to eye my pile a little suspiciously now that its grown to weigh about 50 lbs.