Author Topic: Eagle PCB Layout Editor PNP Transistor E and C pins swapped?  (Read 3252 times)

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Offline DrifterNL

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Device -> BC557B-PNP-TO92-EBC (*-PNP-)
Package -> TO92-EBC
Library -> transistor

Are the E and C pins swapped somehow when you design the board?
The orientation of the transistor (silk screen) on the board doesn't comply to datasheets of the above mentioned device.
It was quite frustrating after I soldered the electronics in according to the silkscreen just to find out something didn't work and after looking up a data sheet on the BC557B that the transistor had to be turned around 180 degrees (flat face toward the round part of the silkscreen) while the schematic is good.
 
 

Offline Karel

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Re: Eagle PCB Layout Editor PNP Transistor E and C pins swapped?
« Reply #1 on: June 19, 2016, 05:37:44 pm »
The library is correct. The problem must be somewhere else.

Edit: This part is not in transistor.lbr, it's in transistor-pnp.lbr.

Also, never use libraries which aren't made by yourself. And if you do insist on using second or third party libs, check them twice!

« Last Edit: June 19, 2016, 05:43:07 pm by Karel »
The difference between theory and practice is less in theory than
the difference between theory and practice in practice.
Expensive tools cannot compensate for lack of experience.
 
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Offline jpanhalt

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Re: Eagle PCB Layout Editor PNP Transistor E and C pins swapped?
« Reply #2 on: June 19, 2016, 06:25:05 pm »
Are you sure there is not a mirroring problem as can be created by inadvertently switching between top and bottom layers?  Can you snip the portion of the board with the problem and post it here?

John
 
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Offline rob77

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Re: Eagle PCB Layout Editor PNP Transistor E and C pins swapped?
« Reply #3 on: June 19, 2016, 06:40:31 pm »
i bet on the mirrored component too ;)
if you mirror a component in board editor you effectively switching the mounting side of that component (e.g. when doing a single-sided THT + SMD mixed design, you mirror all the SMD parts to get them to the bottom side).
 
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Offline DrifterNL

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Re: Eagle PCB Layout Editor PNP Transistor E and C pins swapped?
« Reply #4 on: June 19, 2016, 08:29:58 pm »
Thanks for the responses.
I believe the library came with the software but I'm not completely sure anymore.
I also checked if I had inadvertently switched the component side (mirrored) but it's all good.
It has been confirmed by two members on another forum that that library is indeed incorrect with one member finding even more PNP transistors with the TO92 package that are incorrect and the other member stating it has been incorrect for a long time.
Picture below shows part of the schematic, board (blue top left is Vcc) and transistor in the working circuit.
« Last Edit: June 19, 2016, 08:51:07 pm by DrifterNL »
 

Offline jpanhalt

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Re: Eagle PCB Layout Editor PNP Transistor E and C pins swapped?
« Reply #5 on: June 19, 2016, 08:58:34 pm »
Interesting.  The Fairchild datasheet shows CBE going left to right looking from the top w/ flat facing you:



My version of Eagle (7.2) shows the same pinout.



I then drew a schematic with a capacitor attached to the emitter and resistor attached to the collector:



The connections look OK.  The attachments are in the order mentioned in text.   How do we insert in text as is done on most other sites?

John
 
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Offline DrifterNL

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Re: Eagle PCB Layout Editor PNP Transistor E and C pins swapped?
« Reply #6 on: June 19, 2016, 09:24:44 pm »
Found this datasheet with a good drawing of the transistor with pinouts and symbol -> http://pdf.datasheetcatalog.com/datasheet2/5/0qsl0963l7i0pw6dwpsgdj3890wy.pdf

EDIT:
With the PNP Emitter (3) connected to Vcc (+5V), Collector (1) connected to the relay and then through to GND, the flat side of the transistor would be facing right but the silkscreen shows it facing left (post #5) .  :-//

If the Transistor was an NPN, the silkscreen would have been correct.
« Last Edit: June 19, 2016, 10:17:41 pm by DrifterNL »
 

Offline Karel

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Re: Eagle PCB Layout Editor PNP Transistor E and C pins swapped?
« Reply #7 on: June 20, 2016, 12:35:20 am »
It has been confirmed by two members on another forum that that library is indeed incorrect with one member finding even more PNP transistors with the TO92 package that are incorrect and the other member stating it has been incorrect for a long time.

Can you please point me to the library that comes with the Eagle program that has an incorrect footprint for this transistor?
Because at least with V6 and V7, the footprint of this transistor is correct.

Again, always create your own libraries or double check.
It's never the fault of the library, it's the fault of the person who didn't check twice.

Edit: Found it, there's indeed an error in transistor.lbr.

« Last Edit: June 20, 2016, 01:58:06 am by Karel »
The difference between theory and practice is less in theory than
the difference between theory and practice in practice.
Expensive tools cannot compensate for lack of experience.
 
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