MOSFET takeover - Page 1
Forum section: electronics / general

author: goldcoin
author_rank: Contributor
timestamp: July 07, 2016, 05:43:06 pm
content: Will MOSFET transistors become the only transistor type to be used in the foreseeable future in integrated or discrete form or are there still applications where the BJTs cannot be replaced or is a better choice ?

author: Zero999
author_rank: Super Contributor
timestamp: July 07, 2016, 08:50:21 pm
content: Quote from: goldcoin on July 07, 2016, 05:43:06 pmNo. BJTs will always be there, unless a totally new type of transistor is developed which is much better than MOSFETs and BJTs.BJTs have a much higher transconductance and much better matching so are much more suited in analogue applications. MOSFETs are generally used more as switches.Try building a discrete op-amp from MOSFETs such as the 2N7000 and BS250 and compare it to one made with BJTs such as the BC338 and BC328. You'll find the BJT one gives a much better common mode rejection ratio and higher open loop gain, for the same number of parts.

author: uncle_bob
author_rank: Unknown
timestamp: July 07, 2016, 08:52:27 pm
content: HiSeems that you have already written off JFET's ....There are areas of RF design that will continue to use JFET's and bipolar for a long time. Their noise and overload performance are different than a MOSFET.Bob

author: rfeecs
author_rank: Frequent Contributor
timestamp: July 07, 2016, 09:13:40 pm
content: Yes, for RF there's HBTs (Heterojunction Bipolar Transistor), a form of bipolar.HEMT (High Electomobility Transtor) as in GaN power HEMTs, a form of MESFET.Super low noise GaAs pHEMTs.Some analog applications, like translinear circuits also come to mind. Circuits that depend on exponential or log characteristics of the junction like log amps or analog multipliers. The band gap voltage reference is another one perhaps.

author: uncle_bob
author_rank: Unknown
timestamp: July 07, 2016, 09:16:21 pm
content: HiOk, so let's flip this around. Since bipolars, jfets, and mosfets have all been around for .... errr .... nearly 50 years:Why *would* mosfets wipe out all the rest?Bob

author: Kilrah
author_rank: Unknown
timestamp: July 07, 2016, 09:22:37 pm
content: Because we now make class D amplifiers?

author: uncle_bob
author_rank: Unknown
timestamp: July 07, 2016, 09:30:29 pm
content: Quote from: Kilrah on July 07, 2016, 09:22:37 pmHiThe whole D,E,F,G amp thing is at least 30 years old. To the extent we make them mostly with MOSFETS at audio, ok. That's maybe 5% of the semiconductor market .... at most.Still trying to get a feel from the original poster to see if we simply have missed the point of the question. It happens pretty often around here ....Bob

author: Kilrah
author_rank: Unknown
timestamp: July 07, 2016, 09:38:55 pm
content: Quote from: uncle_bob on July 07, 2016, 09:30:29 pmSure, but given this kind of example it isn't too far-fetched to imagine more and more applications could shift to similar approaches.

author: uncle_bob
author_rank: Unknown
timestamp: July 07, 2016, 09:42:24 pm
content: Quote from: Kilrah on July 07, 2016, 09:38:55 pmHiAgain, the approach is hardly new or revolutionary (any more). It didn't hit the market last week or even in the last few years. It also is a bit of a low end / low cost approach with a lot of limitations. You still see audio done with vacuum tubes ....So still back to the "why the question?" question.Bob

author: janoc
author_rank: Super Contributor
timestamp: July 07, 2016, 10:15:17 pm
content: Quote from: Kilrah on July 07, 2016, 09:22:37 pmEhm, transistors are not used only for audio amplifiers.

author: lem_ix
author_rank: Regular Contributor
timestamp: July 07, 2016, 10:26:16 pm
content: To someone new in electronics the difference probably isn't quite apparent. They can both(fet/bjt) switch, amplify and buffer but of course that's not all there is to it. Previous posters covered most of it, lots of technologies with various advantages and disadvantages. There are even semiconductor technologies like BiCMOS and BiFET. Also keep in mind it's not just the performance that is of concern, rather the fabrication technology can be a deciding factor for popularity.Bottom line if you're interested there's a LOT of reading to do.

author: bitslice
author_rank: Frequent Contributor
timestamp: July 07, 2016, 11:46:31 pm
content: They will need to keep making 2N3055's forever, so that people can continue to repair all the stuff that was made with 2N3055's.It's a marketing dream.

author: uncle_bob
author_rank: Unknown
timestamp: July 07, 2016, 11:49:25 pm
content: Quote from: bitslice on July 07, 2016, 11:46:31 pmHiThey still make vacuum tubes ...Bob

author: sarepairman2
author_rank: Frequent Contributor
timestamp: July 08, 2016, 12:19:34 pm
content: all electronic parts will have application specific uses that would make it unwise to discontinue anything, really.the more you learn the more you see the utility and beauty in stuff that you thought was outdated

author: uncle_bob
author_rank: Unknown
timestamp: July 08, 2016, 01:08:07 pm
content: HiSo we've all had a fun time here ... except where is the person who started the thread?Bob

author: calexanian
author_rank: Super Contributor
timestamp: July 08, 2016, 07:16:58 pm
content: The only thing that really comes to mind where BJT's are kinda hard to replace is linearity and stable on/off characteristics.

author: elgonzo
author_rank: Unknown
timestamp: July 08, 2016, 08:04:26 pm
content: Instead of thinking about MOSFETs replacing BJTs, why not think about marrying them: IGBTs...

author: VK3DRB
author_rank: Super Contributor
timestamp: July 09, 2016, 07:58:42 am
content: Quote from: elgonzo on July 08, 2016, 08:04:26 pmLGBTIs are becoming more popular these days. They are AC/DC and don't require any bias.

author: JoeN
author_rank: Frequent Contributor
timestamp: July 09, 2016, 08:31:50 am
content: Quote from: VK3DRB on July 09, 2016, 07:58:42 amhttps://en.wikipedia.org/wiki/2016_Orlando_nightclub_shooting

author: G7PSK
author_rank: Super Contributor
timestamp: July 10, 2016, 09:25:49 am
content: IGBT are now taking over from MOSFETS in welding inverters as they are more robust.

author: David Hess
author_rank: Super Contributor
timestamp: July 10, 2016, 08:47:51 pm
content: Quote from: G7PSK on July 10, 2016, 09:25:49 amThey are more robust for a given cost. Like bipolar transistors, IGBTs have higher current densities and this advantage grows at higher voltages.

author: uncle_bob
author_rank: Unknown
timestamp: July 10, 2016, 08:56:34 pm
content: HiOk, so I decided to actually try to answer my own question --- who asks these questions and what is the basis for the question?If you take a look, the OP has never re-posted to any thread he has started. It's simply a "toss up a nutty question and run" sort of thing.Bob