What kind of strange beast is Q5? It appears to have an insulated gate and be depletion mode as the source-substrate-drain are drawn solid but the presence of the bipolar emitter in the source lead is puzzling. Is it some new-fangled depletion mode IGBT?
I only ask because the datasheet uses the conventional symbol for an enhancement n-channel mosfet ;}
piglet
John has a bad habit of drawing idiotic* symbols, I guess as shorthand. :)
*I'm justified in making such an accusation, because whether people realize it or not, arrows in symbols were placed there because they mean something. And damn it, that makes me right!Tim
-- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
I also have the bad habit of designing lots of stuff that works.
There are many ways that people draw mosfet symbols. We like that one.
The arrow in the "usual" mosfet symbol makes no sense to me. And it's ugly.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
I do that all the time. It often makes the schematics look much nicer.
Depends on your CAD software. It won't do that in PADS.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
I actually like the arrow: it reminds me of the channel polarity and sorta like a jfet which way the gate gets driven and it reminds me which way round the source-drain parasitic diode is (which I am often too lazy to explicitly draw in). The arrow can make a lot of sense.
Having broken line vs solid line to distinguish enhancement vs depletion mode is also good, especially now that both flavors are more available.
Nothing stops you drawing your mosfets as curly-tailed-elephants but then everyone outside your circle would be baffled :>
piglet
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:)
Most of it much the same stuff, slightly tweaked. A new product ever two we eks doesn't leave much room for extensive innovation.
If you had paid attention to more of your lectures back at Tulane, the arro w might makes sense to you now. Then again, I managed to soak up the distin ction between N-type and P-type semiconductors without ever having listened to a lecture on the subject, and the fact that you haven't might suggest t hat you weren't so much uninterested in acquiring an education, as sea-gree n ineducatable.
-- Bill Sloman, Sydney
Absolutely! As long as the dot is clear, it's no big deal. With modern fonts and printers this shouldn't be an issue.
It would be a RPITA and really mess up some schematics.
PADS won't let you near-miss a connecton, like some other schematic programs, and like LT Spice. There are no dangling or floating or single-ended wires in PADS.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Sure, but my arrow makes more sense. It looks just like an NPN transistor with an insulated base.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Like an IGBT?
I don't use IGBTs, but if I did I'd probably use the same symbol.
The people who design ICs often use the simplified mosfet symbol.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
People who design ICs tend not to write the application notes. Bob Widlar may have been an exception, but he tended to be so far ahead of the pack that it made sense to get him to spend time writing the occasional application note.
-- Bill Sloman, Sydney
Exactly! It's telling you *what's inside*! What could be more useful? The arrow is explicitly the substrate-to-channel junction...which is shorted to source, so, yep, that's the D-S body diode!
Specifically, the arrow always tells you minority carrier flow. Which is forward for BJTs and junction diodes (minority carrier devices) and reverse for FETs (majority carrier devices).
Thus, drawing an "emitter" arrow on what otherwise appears to be a field-effect device is explicitly telling the reader that there's a diode junction pointing "this-a-way". Which is patently absurd for a MOSFET, and if it were real, would be... almost always bad, I would think.
The MOSFET variant with the antiparallel diode (usually a zener) always amuses me: it's explicitly redundant. It might make sense if it were a co-pack*, but they're never done that way; and the avalanche (technically not zener) capability is just an optimization tradeoff against switching / amplification performance, so it doesn't make sense to attempt to indicate an avalanche-capable MOSFET this way.
*It actually makes both a semantic and physical difference with IGBTs, which don't have intrinsic reverse handling, so you will see symbols drawn both ways and for meaningful reason.Or he could just use IEEE/ISO symbols. :^)
Tim
-- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
I use the body diode enough that I like to see it on the schematic, e.g. in the PMOS input polarity protection trick.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
The common symbol shows the body diode hitting the middle of the perforated channel, when it actually connects low-impedance source to drain.
The common symbol is just too busy. And ugly.
I have seen symbols that show the usual body diode and an additional s-d diode, even busier.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Never?
(interesting nfet symbol on that one)
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
The Vishay datasheet does use correct symbols. There is some sense to explicitly showing the body source-drain diode - it is not necessarily the same as the substrate-d/s diode, just think of devices like 3N163 where substrate is not internally connected to source?
piglet
Correct? Who gets to define correct?
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
That's an independent diode. I suppose you call it "beernuts" when you buy a pack of nuts taped to a six-pack? :-)
Ditto.
Ironically, it's arguably *not* a co-pack, as that indicates two dies in the device. Like so;
That said, they probably fabricate it as a "co-pack", reserving a seperate corner of the die for the schottky.
That's closer to the mark, *maybe*. But they still get the symbol wrong, and I believe even your schematic standards don't mistake zeners for schottkys. :)
I don't know offhand if they are able to integrate a schottky junction directly within a MOSFET structure (without making a MESFET or whatever in the process), so it may well be that those devices (antiparallel schottky) are, at best, the monolithic expression of "co-pack". But for the regular (PN junction or "zener") style, the point stands; it's already there in the symbol.
Tim
-- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
No problem there. I draw schottkies as
| \ | | \ | | \ |
-------| . \|--------- | /| | / | | / |
where the dot in the middle is the hot carrier.
All the mesfets and phemts and GaN fets that I've tried behave like jfets, namely D-S diode effect. Such parts are, as far as I can tell, not avalanche rated and will die a quick and horrible death at high drain voltages.
Haven't tried SiC yet. I haven't had a use for it so far.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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