In this circuit, is it possible to switch a BC547 Transistor with a 2n2222a Transitor?

Thread Starter

anmolmaker

Joined Nov 10, 2017
2


I am currently trying to build this oscillator circuit for a project at school, but we don't have any BC547 transistors available. We do however have many 2n2222a transistors. Can I switch the transistors or modify the 2n2222a's to make the circuit work?
 

OBW0549

Joined Mar 2, 2015
3,566
I am currently trying to build this oscillator circuit for a project at school, but we don't have any BC547 transistors available. We do however have many 2n2222a transistors. Can I switch the transistors or modify the 2n2222a's to make the circuit work?
For the circuit you posted, with the component values shown, just about any NPN transistor should work just fine so long as it has an hFE greater than 10. When in doubt, consult the transistor's data sheet.
 

ebp

Joined Feb 8, 2018
2,332
If you are using the "plastic" version of the 2222, be careful - the pin sequence is opposite that for the BC547.

Just about any "small signal" NPN transistor will work just fine, possibly with a slight change in frequency. The external components in the circuit almost totally "swamp" differences among different transistors. \

some common types in North America:
2N2222A ("officially" the 2N2222A is in a metal case, which used to be very common but is now much less so and tends to be considerably more expensive; some manufacturers of plastic packaged versions use the 2N prefix, others use a prefix like PN; the actual semiconductor is the same, just the package differs
2N3904
2N4401
MPS-A06

[edit - lost my final sentence somehow]: ON Semiconductor data sheets and selection guides show some devices as being "preferred" - they are very popular so they tend to be more readily available and somewhat cheaper than less popular types.
 
Last edited:

Thread Starter

anmolmaker

Joined Nov 10, 2017
2
I ended up taking the suggestion of be80be and going with 3904. The circuit worked great! Thanks to everyone for all the help!
 

recklessrog

Joined May 23, 2013
985
My thought exactly. As previously stated, most small signal npn transistors would work, and as the bc547 is the plastic version of the old bc107, any of that range would be fine too. Incidentally, the gain spread of the bc107-108-109 is anything from 50-500!! I have dozens left over from a job in the early 70's and colour coded them for low/med/high/ Vhigh gain.
Also, If the components were all "perfect" and Identically matched, It would not start to oscillate. It's the differences that makes one transistor conduct a little heavier than the other that gets it going.
You don't even need to use the same transistors, try substituting other similar transistors for just one of them, 99.5% of them will still work.
 
Last edited:

be80be

Joined Jul 5, 2008
2,051
Well It's like this any one of them would work
But the 2n3904 in that circuit is posted everywhere.

The 2n2222 makes a better switch for things that need more current. But the 2n3904 seem to osculate easy LOL.

This kind of get's me I was the frist poster to say any would work 2n2222 2n3904 and the 2n4401 most any

Just because I said I would used the 2n3904 you all start with the bull here what's the deal the 2n3904 is a close match for the bc547 .

But i have make that circuit using the 2n3904 it worked fine
 
Last edited:

recklessrog

Joined May 23, 2013
985
Hi be80be,
I did see that you mentioned that any of the others would work ok, but in your next post you stated that the 2n3904 would be better and as Crutschow asked, I also thought "why"?. Had you qualified that by saying you found the 2n3904 Oscillated easier then we would not have asked the question.
Remember that there are many people who read the forum who may not have a great deal of experience and don't know that in very many simple circuits, specifically numbered parts can be substituted without causing problems.
I well remember when I was young desperately trying to locate the exact components to build projects without realising that I could have used other parts I already had on hand.
For sure, there are many many circuits that need very specific components to work correctly, equally, with simple circuits, often they are not. Guess it all comes down to experience learned over the years, (of which I have too many)
That is why I tried to give the T.S some general advice, not to criticise you in anyway, in fact just to expand on your statement a little. :)
 

dl324

Joined Mar 30, 2015
12,790
Just because I said I would used the 2n3904 you all start with the bull here what's the deal the 2n3904 is a close match for the bc547 .
The problem is that you made the following statement without qualification.
If you have some 2n3904 it would be better..
Why would they be better than 2N2222 or any other general purpose NPN transistor?

2N3904 are more common in the US. If you were in Europe, where BC transistors are more common, BC546/7/8 might be a better choice. If you were in Asia, 2SC are more common, something like 2SC380 might be a better choice.

Since the OP stated that he had 2N2222, they would have worked just fine.
 

dl324

Joined Mar 30, 2015
12,790
No one said 2N3904 wouldn't work. The OP's question was whether 2N2222 could be substituted for BC547. The answer was yes; just about any NPN transistor would work.

This is a peer reviewed site. Any incorrect or misleading information is subject to correction by the community; as it should be because someone might stumble across the information in the future.

If I make an incorrect or misleading statement, I'd welcome someone pointing it out so I have the opportunity to correct it.
 

be80be

Joined Jul 5, 2008
2,051
The problem is that you made the following statement without qualification
How about your read the datasheet and come back and go on about nothing.
Which is what is going on here I posted two post at the start

One stating that I think the 2n3904 is better I then posted any of them like the 2n2222
2n3904 and 2n4401 are ok to use for a bc547

The 2n3904 is the closes match tho if you read the datasheet.

I don't see where I said something wrong here. Just because I'm not going to write a book and post why

I think OWB post read the datasheet kind of covered that Becuse I started to post that very thing till I read his post.

Well why are you going on cause i said i think the 2n3904 is a bit better

Post #2 should work LOL
Post #3 works for me
Post #4 I think a 2n3904 is better
Post #5 any of them
2n2222
2n3904 and 2n4401 are ok to use for a bc547.

Then bull starts

As previously stated I was the first one to state that these are good for a bc547.
2n3904 and 2n4401.
But the poster needs to read the datasheet somethings one of them is better at.
2n2222
2n3904 and 2n4401 are ok to use for a bc547.

My statement is not misleading the 2n3904 is the best pick for his circuit and I done said that any of the 3 I listed would work long before anyone started the as been said stuff so I'm sure that helped everyone that reads this.

Then even the poster said he tried the 2n3904 and it worked great.

I'm not the smartest guy in the boat but I bet we make it to the shore if I'm in the boat.
 
Last edited:

be80be

Joined Jul 5, 2008
2,051
This is a little better then the one the TS posted figure I'd post it so they could try it out.
The better part is my opinion.

Screenshot from 2018-03-06 18-14-13.png
 

DickCappels

Joined Aug 21, 2008
7,270
With reference to the schematic in post #18, the diodes in series with the bases are probably there to protect against degradation from emitter-to-base reverse breakdown current, but what purpose could the diodes in series with the collectors serve?
 
Top