SMT replacement for BC549

[aballen]

I'm working on a buffer that uses a BC549, but I want to go SMT with it.

I'm not sure if any old NPN will do in a buffer.  Any decent substitutions out there that are SMT?

[kothoma]

The SMD ones are called BC849.

[aballen]

Why not use the same part number?  Does the 849 have the same specs or just a suitable replacement in a buffer?

[kothoma]

It's the same silicon in a different package. Looks like it is a convention to add 300 on BC transistor part numbers to get the SOT-23 equivalent.

[aballen]

Ok, I figures out viable replacements for all the other parts except one.   any idea what would be a good replacement for a 1N5401?

[muddyfox]

If you can live with 1A instead of 3A, I'm using S1B-13.

[aballen]

Awesome, I think my layout is done... just can't get it single sided though, damn transistor!

Thanks for pointing me to the correct parts, this is my first SMT design, but I'm hoping to get it correct on the first try though.

[aballen]

I still need to label this up, but I'm wondering how small I can make it?  This is 1.25" square, I can get it down to a 1" square, which I want to, but I'm concerned about the components being too close... should I worry?

The tant caps and diode are the biggest components, I could shrink the remaining caps/resistors to 0603.
I'm I leaving too much space?

[muddyfox]

I never worry about shrinking the board it there's nothing significant to be gained by it. If it's borderline-1590A-squeezable, I'd probably make an effort. Likewise if it'd get me into a lower fab price bracket.
Otherwise, I just find it a hassle to solder cramped smd boards that are cramped just for the heck of it.
YMMV.

[aballen]

I want to get it in a 1590LB, its really my main driver for going SMT, lower the height.  Dropping from 1.25" square to 1" square mean about 50% less surface area as well.  I'm going to try it with 0603 and see how it works out.

Thanks a bunch for the assist!

[stevie1556]

I never worry about shrinking the board it there's nothing significant to be gained by it. If it's borderline-1590A-squeezable, I'd probably make an effort. Likewise if it'd get me into a lower fab price bracket.
Otherwise, I just find it a hassle to solder cramped smd boards that are cramped just for the heck of it.
YMMV.

Same here, unless I can get the board into a cheaper pricing bracket, I generally don't bother making it smaller if I don't have to.

What program are you using to do your layout in? If it's Eagle, there is a really easy way that I've found to get a via inside a SMD pad to make a duel layer board and keep the layout small and looking neat.

Keep us updated on how the layout goes.

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[aballen]

I think it looks ok, I just ordered a set to test.

http://www.oshpark.com/shared_projects/bLeuzZAo

[garfo]

The SMD ones are called BC849.

I was also looking for this and had a look and both data sheets. They don't seem to be exactly the same.

[Jay]

Can I be a bit pedantic here for the sake of learning? SMT is the method of attaching SMD components to the board.

That is all. Said with love. I'll see myself out.


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