BC547 and BC557 Transistor Replacement in TO-220 package?

[Adam60]

Does anyone know what transistor in a TO-220 package would substitute for a BC547 and BC557?
I have students knocking legs off these like crazy and would like to substitute with something a little beefier. Thoughts?

[IconicPCB]

Not a TO220... but may be BD139/149? might be convinced to play nice

[Yansi]

BD139/140 is TO126.


Whats the deal with TO92? Have the students pay for the components, ya'll see how quickly they learn to not break your stuff.

Those trannies  are dirt cheap, but still. Making students pay for them will certainly learn them a lesson

[bd139]

Just buy a ton of them and throw them away. Or use 2n3904/6 which are fractionally cheaper

Legs break off to220 packages easier and they wreck breadboards and the packages are way more expensive

[soldar]

What use? Breadboarding? Maybe put them in some kind of holder or reinforcement?

[Benta]

Just buy TO-220 transistors from China, they'll have BC547/557 die inside.   

[Kleinstein]

BC547 and similar are cheap - one may even consider not to reuse them between groups.
If they brake so easy one may consider a different manufacturer - it could be just a bad batch with legs already bend a lot.

Some other TO92 parts (e.g BC635) may have thicker legs to get rid of heat better.

[edavid]

I do think BD139/BD140 is a good choice.

The package leads are smaller than TO-220, so not as rough on the breadboards.

Also, you can get them with reasonably high beta, so you won't have to change the circuits too much.

[bd139]

They are pretty good if I do say so myself. However to insert into the average breadboard you need to twist the legs at 90 degree angle or it’ll kill it instantly. Breadboards are more expensive than transistors.

[T3sl4co1l]

Alternate option: train your students to show some care for the kit they're using.  Put damaged components on their grade.  Industry certainly won't stand for such behavior!

Tim

[Adam60]

Thanks for all the great responses. My favourite is to either charge the students for the transistors or teach them to respect our equipment.
1)  We can't charge our students for supplies as they are apparently under a lot of financial stress from going to school in the first place.
2)  I taught two of my own to respect other peoples property and I think they turned out okay. There is not enough time in the day to teach 30 more the lessons their parents should have taught them, and get their lessons in as well.
In all fairness to the students, they are just learning about transistors and breadboarding and probably not their favourite subject so bending transistor legs to fit and breaking the odd one are probably not on their list of priorities for the day. I am just looking for something that will stand up a little better. Perhaps I should pre-populate the boards for them and then they won't have to worry about that either? 

[IanMacdonald]

Training should always be realistic in nature, and should follow industry practices as far as possible. 

Train people to do things wrong, and it will be much harder to get them to unlearn that later!

Look for an Ebay or AliBaba supplier - These transistors are very cheap if bought direct from Chinese manufacturers. The reject rate is not all that much either.

On a related issue, a useful instructional aid is a PCB on a box with a pinball machine solenoid (or similar) inside it. The trainee is told to measure the voltages on a few transistors, an IC, resistors, etc.  If s/he slips with the probe and causes a short there is a loud CLONK  and power to the PCB is reduced. After that the student gets wrong voltages for every test.

This brings home the message that once they have caused a short, the equipment is likely damaged and will no longer work. 

Of course the 'damage' is actually just a latching relay which the instructor can reset.

I found that a couple of rounds of this completely cured our students of causing shorts. After that they were careful.

[Kleinstein]

It might already help to get the transistors with the leads bend in a suitable way to better fit the breadboard. There are different variants on how the leads are bend.

When buying the transistors in something like 100-1000 piece quantities the price should be rather low.

I would be more worries about the time needed to pre-populate. For learning it tends to be better to do things by them-self. Some learn better when they actually move there fingers and not just the eyes and ears.

[spec]

You can mount the transistors on a three pin header strip that just plugs straight into the breadboard without any bending- gives a better connection too

[rsjsouza]

I see the annoyance; especially due to the lack of care from students that should know better.

However, being pragmatic, for about US$80.00 you can buy 2000 BC547s.

[Whales]

I've spent time in classes where burning, breaking or damaging a transistor was frowned upon.  Some that would even mark students down.

From an intentionalist perspective it makes sense: "treat things well" and "do it right the first time".  "It's horrible to see students breaking things all the time, what are we teaching them?".  Culture and customs.

From a consequentialist perspective it's garbage.   Students learn far more effectively if they make mistakes and break things with their own hands.  If a student is afraid of breaking a part then they won't engage anywhere as well with the problem solving process and will be afraid to try different things.  Encouraging them to destroy transistors is a very cheap way (compared to their course fees!) of increasing educational value.

I've also seen students try and hide their work from from tutor/lab/etc staff during class because of this.  Meanwhile I blow all my stuff up at home instead and gain an advantage.  You don't ever want to make a student afraid to ask for help, and you do not want to de-value the time students have in their labs.

Please, please consider the whole picture when looking at policies around damaging electronics in education.  Artists are not punished for breaking brushes, lawyers are not punished for breaking pens and you don't punish your students for crossing things out in an exam paper.  Transistors are dirt cheap, education is not.

[David Hess]

Do you need performance similar to the BC547 and BC557?  If not, I would just look for the least expensive TO-126 or TO-225 parts which are less expensive than the least expensive TO-220 parts.  But even these are much more expensive than TO-92 packaged transistors and I doubt they are proportionally more rugged.

[edavid]

I see the annoyance; especially due to the lack of care from students that should know better.

However, being pragmatic, for about US$80.00 you can buy 2000 BC547s.

You can get 2000 for $36 with free shipping:  https://www.arrow.com/en/products/bc547cg/on-semiconductor

I'm not sure if that's exactly the issue.  Maybe OP could clarify.

[mariush]

TME.eu has BC547 at 0.01$ : https://www.tme.eu/en/details/bc547-cdi/npn-tht-transistors/cdil/bc547/

100+       $ 0.0147
500+       $ 0.0132
2000+       $ 0.0117
12000+       $ 0.0105

23$ for 2000pcs , plus vat and shipping

You could just ask each class to contribute 1$ per student, or 10$ per class, at the start of each year, in the "purchase components" fund.

[Ian.M]

'Jellybean' To-92 transistors are much cheaper than the labour costs for any of the technical 'solutions' offered above.  Even if you coopt 'free' student labour, you still have to supervise, and one hour of teacher's salary, + classroom overhead costs + admin costs to organise it will buy a *LOT* of 'jellybean' transistors.

You cant ask for money from the class in a school with a significant proportion of disadvantaged kids.  The non-discriminatory way round that is a volunteer fundraising activity.  If you end up with surplus funds  consider getting one semiconductor analyser (digital transistor/diode tester) and make up a board of labelled quick test sockets for it in all the pinouts your class assignments use, so any student having problems can quickly check their parts.

For the 'no respect for parts and equipment' issue, you could set an assignment of a short  group presentation on what each student has leaned from stuff failing,  breaking or otherwise going wrong, either their own or their bench neighbours, with a prize of electronics related maker kits for the group with the best presentation.

Part of the problem may be poor tools.  If there aren't as many pairs of miniature smooth jawed short flat nose pliers (not needle nose) as breadboards in use, to use for pin and lead straightening and lead bending, and preferably also slotted lead bending jigs to support the leads next to the component body, even careful students will break more components than the unavoidable minimum.   When working on a densely packed breadboard I certainly can't live without such a pair of pliers - they pay for themselves solely in time saved inserting and removing discrete components and wires without disturbing adjacent connections.

[sleemanj]

I don't imagine you need precise specs, probably you are just using them as "generic NPN" and "generic PNP". 

I'd just splurge and buy a few hundred of each from Aliexpress, you could buy a thousand of each and spend less than $20 I'm sure.

Here is a search for 1000 piece of 547
https://www.aliexpress.com/wholesale?minPrice=&maxPrice=&isBigSale=n&isFreeShip=n&isNew=n&isFavorite=n&minQuantity=1000&maxQuantity=1000&shipCountry=NZ&shipFromCountry=&shipCompanies=&SearchText=BC547&CatId=0&g=y&initiative_id=SB_20190203025028&needQuery=n

and 1000 piece of 557
https://www.aliexpress.com/wholesale?minPrice=&maxPrice=&isBigSale=n&isFreeShip=n&isNew=n&isFavorite=n&minQuantity=1000&maxQuantity=1000&shipCountry=NZ&shipFromCountry=&shipCompanies=&SearchText=BC557&CatId=0&g=y&initiative_id=SB_20190203025028&needQuery=n

probably enough to last you for years, perhaps the school can manage to reimburse you that $20, if not maybe just consider it your good deed for the year.

[johnkenyon]

BC547 and similar are cheap - one may even consider not to reuse them between groups.

Give each student (say) four transistors each for free at the start of the of the series of labs/classes, and tell them that they will have pay for any replacements (without telling them the cost...)

Sit back and watch as the disadvantaged students take care to avoid damaging the components (and you quietly use your discretion to issue free replacements when accidents happen).
Meanwhile the students who have enough money not to care, can pony up.

[Doctorandus_P]

BD139 / BD140 is indeed not TO220 but smaller and fits a Breadboard better.
They are almost as cheap as the TO92, and TO-220 is bound to be a lot more expensive still, so in the end you won't save much, and the thicker pins are also harder on the breadboards. Higher power BJT's tend to have a lower Hfe and this is also clearly starting to show with the BD139 (Which is also a 40+ year old design).

But instead of trying to save some transistors, I advise to go the other way around.
You can get assortment boxes of different transistors for cheap:
https://www.aliexpress.com/wholesale?SearchText=transistor+assortment
And in bulk probably still cheaper.

Devise some tests (to high voltage, current, or power) that will let some smoke out of some of these transistors, but not from others.
There is no better way to learn than to see the differences of these transistors, and a bit of smoke makes it fun too.
Tests also do not have to be destructive. What happens if you put 2 different transistors in a long tailed pair, and why does that happen?
There are also grey area's where e (saturated) BJT refuse to conduct more current without it recassarily getting damaged.
Examining such areas are very educational. In education, the why is always more important than the how.
For keeping the different transistors apart you can dip them in some paint, instead of reading the small numbers, or just write them off as single use.

But it aso depends on the age group and what you want to learn them about transistors.
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[edit] Removed text below the cut line [/edit]

[bd139]

Just a point on bd139 specifications. fT is only about 75Mhz on ST branded ones. Not the original 150MHz or the old philips ones.

[Doctorandus_P]

Just a point on bd139 specifications. fT is only about 75Mhz on ST branded ones. Not the original 150MHz or the old philips ones.

And why would that be important with first year students on a breadboard?
My guess is that the intention is to use it from DC to audio here.