MOSFET schematic symbol

ScottWang

Joined Aug 23, 2012
7,397
When I draw the symbol with paint that I always like to follow the datasheet, but I'm not sure since when that I drawn the bjt symbols didn't including the circles and the mosfet did, maybe I should add the circles to the bjt, but there is a good situation that if the bjt and mosfet putting in the same circuit, the mosfet may very easy to identify.

TheBjtAndMosfetSymbols_ScottWang.gif
 

atferrari

Joined Jan 6, 2004
4,764
I draw schematics in a way it would look most pleasing to the viewer.So If I have a bunch of connections going around the transistor then I would make sure it gets noticed,so I would just a draw a circle around it or a dashed box.

I recall seen the dashed box for transistors requiring heat sink.
 

ISB123

Joined May 21, 2014
1,236
I recall seen the dashed box for transistors requiring heat sink.
I never heard about it,I'm pretty sure that there is no official heat sink symbol.
If a component requires a heat sink I would just make a list on bottom part of the schematic where it says which ones do,like this:
Heatsink: Q1,Q2,U4,etc...

On PCB design I draw a dashed square which points where heat sink is needed and required.
Like so:
heatsink.PNG
 

Thread Starter

AnalogKid

Joined Aug 1, 2013
10,986
An RCA manual, dated 1971, shows BJTs, FETs and diodes with a circle.
And that is where I was headed with this. I am of retirement age, which means that the majority of EE, techs, hobbiests, etc. in the US are younger than me, which means that a large, but decreasing, subset grew up reading Popular Electronics, the RCA and GE manuals, etc., and we all had a common baseline exposure to how the pro's did it. The two reference magazines, PE and Electronics World, both circled semiconductors, including specialty diodes like zeners and tunnels. Clearly that has changed over the years for BJTs and diodes, but not so consistantly for JFETs, and even less so for MOSFETs. In college there was no course in schematic drawing, and it never was addressed specifically in classes. The textbooks had small schematics, never anything large or complex, and the assumption was that everyone in electronics at that level already just sorta knew.

My original question paraphrased a string of TV ads: What's in your library? Everyone can find dozens of conflicting examples on the innergoogle, but that speaks more to a lack of common exposure than to a lack of standards. So I'm making the hasty freshman generalization that a CAD program with international distribution, support, and user base is a pseudo-indicator of current industry "best practices", and I'm asking about the native symbols supplied with the program.

ViewDraw / DX Designer MOSFET's have circles. Yours?

ak
 

Thread Starter

AnalogKid

Joined Aug 1, 2013
10,986
I never heard about it,I'm pretty sure that there is no official heat sink symbol.
Agree. It isn't an electronic component, but it is something that needs to be a controlled aspect of the design. Like mounting holes, fiducials, etc.

ak
 

Russmax

Joined Sep 3, 2015
82
I can post dozens of exceptions to that rule.
So can I. Doesn't mean anything. I can post dozens of examples of engineers violating the rules of spelling and grammar, too. This isn't even a rule, anyway, or even a guideline. Really just a convention or a trend. I'm just stating there is a logical reason why the circles around devices started going away in the 60s and 70s, even if engineers at the time weren't aware they were doing it. And for any given convention, not everyone is going to follow it. At least not until the Cadence and Mentor standard libraries for IC process transistors come out sans circles. Then we all follow it.

Engineers get so used to not drawing circles, now, much of the time, they don't draw them for discrete transistors either.

Regards
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
The old JIC (Joint Industrial Council) Electrical Standards shows Electrical and Electronic graphic symbols for Electrical Diagrams dated 1967-71. Since replaced or updated by IEEE315-1975 (Latest update 1993).
In the early version all tubes are shown with a circle, various semiconductors, transistors diodes etc are shown without.
The 1995 IEE-315 version shows semiconductors with a circle.
Max.
 
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ScottWang

Joined Aug 23, 2012
7,397
So that's the IEEE change the symbols?
If the symbols have the circles then how a symbol with circle can represent mje2955 and mje3055?
So should we depending on which kind of the bjt that we use and draw the symbol?
 

Russmax

Joined Sep 3, 2015
82
Better follow the IEEE standards or the schematic police will haul you away.
Hey, there's a funny example: diodes. They rarely follow my observed convention of discrete devices drawn with a circle. But I've seen them in circles, especially LEDs. I've also seen discrete resistors and caps drawn inside boxes, but that's just weird.

I'm going to still offer as evidence for what I'm claiming the fact that darlingtons and matched pairs are usually drawn inside a circle or oval enclosing both transistors.
 

Thread Starter

AnalogKid

Joined Aug 1, 2013
10,986
Max -
1. I knew someone had the docs. Been too long since I've seen the MIL DTL on this. Thanks.
2. Exactly the opposite of what I would have guessed.

ak
 
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Thread Starter

AnalogKid

Joined Aug 1, 2013
10,986
I'm going to still offer as evidence for what I'm claiming the fact that darlingtons and matched pairs are usually drawn inside a circle or oval enclosing both transistors.
Yeah, but that sorta makes sense since is is very common for those circuits use two separate devices. If you follow that logic, it makes sense to circle a power MOSFET because of the included zener diode.

ak
 

crutschow

Joined Mar 14, 2008
34,280
Whether on not the transistors I draw have circles depends upon whether the drawing program I use incorporates circles in their transistor symbols. ;)
 

tindel

Joined Sep 16, 2012
936
Interesting discussion. I always thought that circles on bipolars indicated a metal case and the connection to the case which is important to not let float. And the circle on tubes depicted the glass case... Often with both amplifies of a dual tube being in the same circle (oval).
 

ErnieM

Joined Apr 24, 2011
8,377
I am fine for the most part with leaving the circles off, and telling those entering the field such is preferred but not demanded for "reasons of history."

The exception to this is the modern trend to stuff more stuff into SMD packages, such as "pre-biased" transistors where resistors (series base and/or base to emitter) are included in the device. When I draw these I include the resistors in the symbol and then box it, either solid or dashed lines, so both the schematic and package properties are both clear.
 

DerStrom8

Joined Feb 20, 2011
2,390
I am fine for the most part with leaving the circles off, and telling those entering the field such is preferred but not demanded for "reasons of history."

The exception to this is the modern trend to stuff more stuff into SMD packages, such as "pre-biased" transistors where resistors (series base and/or base to emitter) are included in the device. When I draw these I include the resistors in the symbol and then box it, either solid or dashed lines, so both the schematic and package properties are both clear.
That brings up a very good point. Darlington transistors in a single package should probably be drawn with a circle as well. Otherwise it may look like two separate transistors, which may have different specs than a packaged Darlington pair.
 

ErnieM

Joined Apr 24, 2011
8,377
That brings up a very good point. Darlington transistors in a single package should probably be drawn with a circle as well. Otherwise it may look like two separate transistors, which may have different specs than a packaged Darlington pair.
That reminds me of one of my stories: I was working for a hybrid company that won a bid for a power device in a TO-3 package, two transistors with a small cap and perhaps a resistor or such. I got the package after we won a gov't contract to make these obsolete devices. As I reviewed the package something seemed familiar. I cracked up a Motorola data book and found our spec was written around a Motorola data sheet for a darlington device. (The cap was paralytic.)

We found some somewhere in obsolete stock, bought them, had them replated and retested, and sold our $50 devices for $750 each.

Good work when you can get it.
 
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