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| BJTs being phased out? |
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| coppice:
--- Quote from: tooki on October 13, 2020, 02:11:22 pm ---Aren't those all shifting to IGBTs? I mean, an IGBT is essentially a hybrid of the two, so the real answer is even more complex! :D --- End quote --- 1200V IGBTs get expensive. For higher power levels they may be the better choice. However, low power 1200V BJTs are super cheap, so for low power supplies in a lot of 3 phase control, monitoring and metering applications they are a great choice. That market is big enough that there are SMPS controller chips specifically designed to drive a high voltage BJT. For single phase 240V work you have a lot more choices of good cheap transistors with adequate voltage headroom. This is just an example application. There are others where the price of a suitable MOSFET or IGBT starts to rise rapidly above about 700V, and a simple BJT is an excellent choice. |
| David Hess:
Just adding to your list: - Bipolar transistors have a higher transconductance than FETs. This also leads to a higher gain-bandwidth product. - Bipolar transistors have a higher current density than FETs, which leads to less area (cost) for a given current. - Bipolar transistors have a lower voltage noise than FETs. |
| Benta:
--- Quote from: eti on October 13, 2020, 02:50:03 am ---I'm watching an electronics fundamentals lecture series, and the tutor seemed to be implying that BJTs are being phased out; he said "BJTs are slowwwwwly being replaced by MOSFETS" ... or maybe I've put words into his mouth through misinterpreting what he said... Is this the case? I find it extremely hard to believe. --- End quote --- This will happen the same day that the 555 gets phased out. According to most posts on this forum (from my feeling, every third), the 555 will cure Corona, world hunger, overpopulation and global warming as well as solve almost every electronic issue imaginable. :-DD Don't worry, the BJT will survive. I'm much more worried about the JFET, which is a dying species. |
| NiHaoMike:
There was a device called the "ESBT" (Emitter Switched Bipolar Transistor) many years back, it's literally just a high voltage bipolar transistor with a low voltage MOSFET in series with the emitter. --- Quote from: David Hess on October 13, 2020, 08:14:52 pm ---- Bipolar transistors have a higher current density than FETs, which leads to less area (cost) for a given current. --- End quote --- MOSFETs that can switch on the order of 100A are not that uncommon (they're found on every modern motherboard), but a 100A bipolar is pretty exotic. |
| T3sl4co1l:
--- Quote from: NiHaoMike on October 13, 2020, 11:12:56 pm ---There was a device called the "ESBT" (Emitter Switched Bipolar Transistor) many years back, it's literally just a high voltage bipolar transistor with a low voltage MOSFET in series with the emitter. --- Quote from: David Hess on October 13, 2020, 08:14:52 pm ---- Bipolar transistors have a higher current density than FETs, which leads to less area (cost) for a given current. --- End quote --- MOSFETs that can switch on the order of 100A are not that uncommon (they're found on every modern motherboard), but a 100A bipolar is pretty exotic. --- End quote --- Not exotic, just old. They reigned in motor drives and such, alongside SCRs, until IGBTs displaced them (in all but the biggest applications, where SCRs and GCTs still reign supreme). BJTs of 300A (or more?) and 1200V, often with triple-Darlington configuration, are common salvage items. I wouldn't call it "exotic", but "obsolete" is appropriate. :) Incidentally, ESBTs are still available (for exactly what applications, I do not know?), and they made a bit of a resurgence when SiC broke onto the market with JFETs and BJTs -- what's old is briefly new again, then old again as SiC MOSFETs and IGBTs were introduced. :) Tim |
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