Author Topic: Do they exist? SOT-23 PNP transistors with non-standard pinout  (Read 5966 times)

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Offline GiantGnome

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Hi All

I have designed a small PCB (a 4 digit 7-segment display backpack with a MSP430 uC), and I have discovered that I have made a terrible mistake. I seem to have made all the transistor footprints with the base and the emitter swapped  |O

The transistor I tried to use (S9012), and all other PNP transistors I have checked on mouser.com seems to be like this:

 3
 |
SOT
| |
1 2

1: Base
2: Emitter
3: Collector


Do PNP transistors exist with emitter and based swapped? I would think that, for prototyping needs, I could just turn the sot-23 around and bend the leads the best I can.
But that's not very reflow-soldering friendly, and that was one of the educational goals of this board.
 

Offline Unixon

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Re: Do they exist? SOT-23 PNP transistors with non-standard pinout
« Reply #1 on: April 23, 2014, 06:25:31 pm »
According to my EDA (Eagle) database they exist. I don't remember exact numbers but you can check this.
 

Offline mikeselectricstuff

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Re: Do they exist? SOT-23 PNP transistors with non-standard pinout
« Reply #2 on: April 23, 2014, 06:33:15 pm »
It's not hard to bend the leads to mount SOT23's upside down - just need a couple of spiky implements - one to hold the body down, the other to push the leads down flat - reflows no problem
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Offline Richard Head

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Re: Do they exist? SOT-23 PNP transistors with non-standard pinout
« Reply #3 on: April 23, 2014, 07:45:16 pm »
It's frustrating isn't it? I did the same thing a couple of months ago with a prototype board. I had to bend the legs over as you suggest and rotate the body 45 deg. There were 18 devices on each board! It really pays to double/triple check the layout before having it manufactured. But, at the end of the day mistakes happen (all too often with me) so don't feel too bad about it.

Dick
 

Offline theatrus

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Re: Do they exist? SOT-23 PNP transistors with non-standard pinout
« Reply #4 on: April 24, 2014, 02:34:45 am »
Had the same problems.

Also, putting too much faith in TI's footprint names ("PQFP!"), without checking the other code (i.e., PJT) which means its a smaller-pitch TQFP.

I've saved a few board goofups by printing board artwork 1:1 on a laser printer, ordering all the parts, and "building" the design by laying parts on the paper checking footprints. Granted this wouldn't catch the swapped pins.
Software by day, hardware by night; blueAcro.com
 

Offline free_electron

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Re: Do they exist? SOT-23 PNP transistors with non-standard pinout
« Reply #5 on: April 24, 2014, 03:13:09 am »
jes they do the order code typically has a suffix R for Reverse

bc847  and bc847R  emitter base swapped.
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Offline calexanian

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Re: Do they exist? SOT-23 PNP transistors with non-standard pinout
« Reply #6 on: April 24, 2014, 04:16:30 am »
jes they do the order code typically has a suffix R for Reverse

bc847  and bc847R  emitter base swapped.

I have fallen victim to the newbie at the vendor seeing that in the alternate part number and sending us those parts. Unfortunately they were respooled and the marker on the part was the same.. Frustrating day...
Charles Alexanian
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Offline GiantGnome

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Re: Do they exist? SOT-23 PNP transistors with non-standard pinout
« Reply #7 on: April 25, 2014, 02:22:42 am »
Turning the transistors upside down worked like a treat. I have proof  :D :


I can't seem to find bc847r (or S9012R) on mouser's nor digikey's site.

But now, the prototype seems to work. I'll give it a test, and then maybe have another batch of 10-20 or so made.

Another thing I discovered during design and soldering: If you only have tweezers (ie no suction pen), you need to place components with enough space for said tweezers :clap:
 

Offline free_electron

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Re: Do they exist? SOT-23 PNP transistors with non-standard pinout
« Reply #8 on: April 25, 2014, 03:15:58 am »
not all parts have this reverse pinout version avaialble

here is one i know has a reverse pinout :

http://www.nxp.com/documents/data_sheet/BF998.pdf

both parts have marking MOp  but, the reverse pinout has an inversion sign above the small p

Code: [Select]
          _
MOp  vs MOp

hard to see the bar sometimes
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Offline theatrus

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Re: Do they exist? SOT-23 PNP transistors with non-standard pinout
« Reply #9 on: April 27, 2014, 03:47:01 am »
Or get smaller tweezers :)
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