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Topic: I made a mistake with transistors. (Read 1 time) previous topic - next topic


I downloaded some transistor components for DesignSpark. I needed a 2N3904, well actually a MMBT3904 but that one wasnt included in the package. So being a n00b I chose the 2N3904 because it had a SMD footprint (along with the through-hole option). I figured it was the same. So I designed a fairly simple circuit and sent it off to be printed.

Now, tonight I was playing with the arduino and the breadboard and found i had a through-hole transistor whose leads wernt the common EBC configuration but rather ECB. So this got me curious. I pulled up the datasheet for my SMD transistors to check the leads and compared it with my PCB design. Yup. They're wired completely wrong. So, either the footprint is completely wrong or they actually make transistors with this footprint and I just need to substitute them for these...

Am I screwed? Or is there hope?

I attached a modified picture of what I need. The letters in red are what i need the leads to be. Can someone help me?

ps. i havent received my pcb yet - thats why i'm playing around with the breadboard haha.
pss. always check the datasheet.... sixteen million times before committing a design.


You could always solder wires to the legs and attach them to the proper pads.  Or, if it fits the footprint, you might be able to turn it at an angle and get C and E connected to the proper pads with B connected via jumper wire.  With only 3 pins, it shouldn't be hard to make it work.


well I fixed the problem in the design and emailed oshpark about my situation. AFAIK the board hasn't been printed yet so hopefully he'll let me swap out designs. Laen seems to be a nice guy.


just got a reply! he swapped it out! definitely gonna use oshpark again!


You could also have rotated the transistor 120 Deg. anticlockwise...
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard


You could also have rotated the transistor 120 Deg. anticlockwise...

yeah that may have worked, but might as well do it right. i dont really want a janky looking pcb. but since i got it all straightened out i dont have to worry about it :)
lesson learned though.

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