Two different bipolar transistor symbols - what's the difference? - Page 1
Forum section: electronics / beginners

author: c4757p
author_rank: Super Contributor
timestamp: December 07, 2012, 02:01:46 am
content: (No, not NPN vs PNP)I've seen this a few times, and haven't been able to figure it out. Inthis datasheetand others, in the schematic, there are two different transistor symbols: one with a line for the base (e.g. Q1 on the far left), and one with an outlined rectangle (e.g. Q5 just above it). What's the difference?

author: Wytnucls
author_rank: Super Contributor
timestamp: December 07, 2012, 03:08:47 am
content: Darlington pair, perhaps?

author: Tube_Dude
author_rank: Regular Contributor
timestamp: December 07, 2012, 04:55:20 am
content: A normal PNP transistor, just with collector shorted to base, to behave like a diode...

author: IanB
author_rank: Super Contributor
timestamp: December 07, 2012, 05:20:37 am
content: I guess to clarify, this:vs this?I don't have a clue either.

author: Tube_Dude
author_rank: Regular Contributor
timestamp: December 07, 2012, 05:35:21 am
content: Quote from: IanB on December 07, 2012, 05:20:37 amThe one at the right in the pic...( this one is a NPN )

author: Shuggsy
author_rank: Regular Contributor
timestamp: December 07, 2012, 06:08:57 am
content: Quote from: Tube_Dude on December 07, 2012, 05:35:21 amDoesn't seem to make sense with the transistor pairs in the schematic c4757p linked to in the first post. Pairs like Q3/Q4, Q5/Q6, and Q15/Q17. Why have diode pairs like that? Then there's the question of why they marked some transistors like that and others with the base explicitly tied to the collector (Q7, Q22, Q27... Q27 even has the different schematic symbol already!). Very interesting.Maybe those require a larger Vbe to turn on? Some kind of insulated base or different doping concentrations?

author: IanB
author_rank: Super Contributor
timestamp: December 07, 2012, 06:22:32 am
content: Quote from: Tube_Dude on December 07, 2012, 05:35:21 amNo, not that. I clarified c4757p's question to make the specific symbols clear. The original question was about the symbol used for Q1 (or Q2) vs the symbol used for Q5 (or Q6). The difference is that for one transistor the substrate is drawn as a single line, whereas in the other it is drawn as a hollow rectangle. What is the significance of drawing the transistor with a hollow rectangle like that?To emphasize again, what is the significance of drawing a transistor with this symbol?

author: Tube_Dude
author_rank: Regular Contributor
timestamp: December 07, 2012, 06:31:41 am
content: I see! I have misunderstood the original question.Oh, my English!!

author: amyk
author_rank: Super Contributor
timestamp: December 07, 2012, 06:49:11 am
content: My guess is athicker base region.You can ask Linear about it, I think they were the ones who came up with that schematic.

author: Simon
author_rank: Unknown
timestamp: December 07, 2012, 09:29:47 am
content: could it just be that they are using two main types of transistors and that is their way of differentiating them, it's an internal code

author: alanb
author_rank: Frequent Contributor
timestamp: December 07, 2012, 10:02:10 am
content: could it be the diffrence between germanium and silicon?

author: Tube_Dude
author_rank: Regular Contributor
timestamp: December 07, 2012, 10:15:23 am
content: Quote from: alanb on December 07, 2012, 10:02:10 amDon't think so. Germanium in an integrated circuit substrate...

author: c4757p
author_rank: Super Contributor
timestamp: December 07, 2012, 12:05:14 pm
content: IanB is right, I was asking about the difference between those two symbols, not diode-connected transistors.

author: Gall
author_rank: Frequent Contributor
timestamp: December 07, 2012, 12:22:22 pm
content: Quote from: alanb on December 07, 2012, 10:02:10 amNo. Both are silicon.Looks like just two different IC mask layouts, i.e. a "small transistor" and "large transistor".

author: Arion02
author_rank: Contributor
timestamp: December 07, 2012, 05:11:42 pm
content: Could it be an Isolated Gate Bipolar Transistor (IGBT)?Sent from my SPH-L710 using Tapatalk 2

author: T4P
author_rank: Super Contributor
timestamp: December 07, 2012, 05:35:38 pm
content: Might mean some amount of capacitance

author: Simon
author_rank: Unknown
timestamp: December 07, 2012, 05:37:40 pm
content: like a more powerful transistor

author: AlfBaz
author_rank: Super Contributor
timestamp: December 08, 2012, 01:49:52 am
content: As far as I can see they're in pairs, more specifically "long tail" pairs. The symbol probably represents matched pairs