Author Topic: BJTs being phased out?  (Read 8887 times)

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Online rsjsouza

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Re: BJTs being phased out?
« Reply #25 on: October 15, 2020, 07:13:13 pm »
I'm much more worried about the JFET, which is a dying species.

I'm feeling a Save the JFET T-Shirt coming on...
The UJTs are a much more endangered species...  :-DD

2N2646 forever!

(I still have a bunch from the ol' days)
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Offline coppice

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Re: BJTs being phased out?
« Reply #26 on: October 15, 2020, 07:13:35 pm »
The electret mic market was mostly phones and cell phones.
Uhhhh… electret mikes were in practically every tape recorder. They're still widely used in webcams, laptops, and all manner of audio devices. They're still in every landline or VOIP phone and headset.

Phones have almost gone.
At home, yes, they're going that way. In businesses, not really. They may not be true circuit-switched landline phones any more, they're VOIP, but they still use handsets with electrets. Call center style headsets also use electrets.
Have you been in an office lately? The VOIP phones are mostly ageng. Call centre still need them, but a huge number of desks no longer have a phone on them. Webcams and laptops seems to be using MEMS mics now, and the better ones use multiple mics for beam forming, so they need them to be very small.
 

Offline coppice

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Re: BJTs being phased out?
« Reply #27 on: October 15, 2020, 07:14:13 pm »
The UJTs are a much more endangered species...  :-DD

2N2646 forever!

(I still have a bunch from the ol' days)
I miss the UJT. Its such a fun, flexible device.
 

Offline tooki

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Re: BJTs being phased out?
« Reply #28 on: October 15, 2020, 07:46:41 pm »
Nice of you to just ignore everything else I said, coppice… :(

Have you been in an office lately?
Yes, frequently.

The VOIP phones are mostly ageng. Call centre still need them, but a huge number of desks no longer have a phone on them.
And a huge number still do. In some companies, phones have gone away, but in many, they're still widely used. Industries and companies vary wildly in their communication styles.

Webcams and laptops seems to be using MEMS mics now
Certainly not universal. I could only find three webcam models that use them. On the other hand, even high-end webcams (like my Logitech Brio 4K) use electrets.

and the better ones use multiple mics for beam forming, so they need them to be very small.
I saw that in a live streaming camera (which connects to a phone, not a computer), but not webcams. Would make sense though!


Again, not saying that MEMS mikes aren't stealing a lot of sales volume from electrets. Just that electrets are FAR from obsolete, at least right now.
 

Offline Benta

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Re: BJTs being phased out?
« Reply #29 on: October 15, 2020, 08:17:38 pm »
I'm much more worried about the JFET, which is a dying species.

I'm feeling a Save the JFET T-Shirt coming on...

Not a bad idea. Just printing the JFET symbol on a T-Shirt would make 99.999999% of the population wonder what it's about.
I love it!   :-DD

 

Offline Cerebus

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Re: BJTs being phased out?
« Reply #30 on: October 15, 2020, 08:55:12 pm »
I'm much more worried about the JFET, which is a dying species.

I'm feeling a Save the JFET T-Shirt coming on...

The JFET Preservation Society.

Even got a ready made Society song, just mash-up "The Self Preservation Society" from The Italian Job.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 

Offline bsfeechannel

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Re: BJTs being phased out?
« Reply #31 on: October 15, 2020, 10:03:17 pm »
The UJTs are a much more endangered species...  :-DD

2N2646 forever!

(I still have a bunch from the ol' days)

You're rich!

Digi-Key sell them for almost 6 bucks a pop.
 
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Offline tszaboo

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Re: BJTs being phased out?
« Reply #32 on: October 15, 2020, 10:06:16 pm »
Electrets are still omnipresent in pro audio such as broadcast TV. Because of the poor performance and longevity of early electrets, pro audio distanced itself from the word "electret" and just calls them condenser mikes, because electrets are a subtype of condenser mikes. (It simply means a condenser mike that is pre-polarized, as opposed to ones that need external polarization power.) As such, I think it's eminently possible that a significant percentage (perhaps even a majority?) of "condenser" mikes are actually electret condensers.
I was under the impression, that condenser mikes are the ones, that have no built in circuits. Just a metallized sheet hanged in a frame. While electrets have a small metal tube, one end open, and typically they have a JFET or other transistor built in. Electret is actually the name of the material that is used as the dielectric, and for condenser microphones the dielectric is air. So they need more voltage.
 

Offline coppice

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Re: BJTs being phased out?
« Reply #33 on: October 15, 2020, 10:30:13 pm »
Electrets are still omnipresent in pro audio such as broadcast TV. Because of the poor performance and longevity of early electrets, pro audio distanced itself from the word "electret" and just calls them condenser mikes, because electrets are a subtype of condenser mikes. (It simply means a condenser mike that is pre-polarized, as opposed to ones that need external polarization power.) As such, I think it's eminently possible that a significant percentage (perhaps even a majority?) of "condenser" mikes are actually electret condensers.
I was under the impression, that condenser mikes are the ones, that have no built in circuits. Just a metallized sheet hanged in a frame. While electrets have a small metal tube, one end open, and typically they have a JFET or other transistor built in. Electret is actually the name of the material that is used as the dielectric, and for condenser microphones the dielectric is air. So they need more voltage.
Condenser mics, electret or otherwise, are impractical without some electronics close to the sensor. The impedance of a condenser mic is very high, so as soon as you pass its signal through some mic cable it would be heavily low pass filtered by the capacitance of the cable. Therefore you need electronics to bring down the impedance. The usual solution is based on a JFET.

Condenser mics usually consist of a rigid metal plate close to a thin plastic sheet coated in a thin metal film. This structure is chosen to be as light and flexible as possible. Sound waves vibrate the plastic sheet. There needs to be a polarising voltage between the two plates, which the sound wave can modulate. This is produced either by an external high voltage, or by using a plastic film consisting of highly polar molecules, which is produced in a strong electric field. This film is an electret, and has a permanent high voltage across the film. This removes the need for an external polarising voltage.

« Last Edit: October 16, 2020, 02:52:51 am by coppice »
 
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Offline tooki

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Re: BJTs being phased out?
« Reply #34 on: October 15, 2020, 11:04:39 pm »
Electrets are still omnipresent in pro audio such as broadcast TV. Because of the poor performance and longevity of early electrets, pro audio distanced itself from the word "electret" and just calls them condenser mikes, because electrets are a subtype of condenser mikes. (It simply means a condenser mike that is pre-polarized, as opposed to ones that need external polarization power.) As such, I think it's eminently possible that a significant percentage (perhaps even a majority?) of "condenser" mikes are actually electret condensers.
I was under the impression, that condenser mikes are the ones, that have no built in circuits. Just a metallized sheet hanged in a frame. While electrets have a small metal tube, one end open, and typically they have a JFET or other transistor built in. Electret is actually the name of the material that is used as the dielectric, and for condenser microphones the dielectric is air. So they need more voltage.
coppice does a great job answering in detail. But the upshot is, no, those construction details aren’t what defines an electret vs non-electret condenser mike.

Most other mics are condenser or dynamic. There were once some very high quality electret mics, but they seem to have gone, and now we only have condenser, ribbon and dynamic mics for high quality applications. Condenser mics also use a JFET, but their volumes are millions, not the hundreds of millions we see with cellphones.
That is categorically untrue. Electrets are still omnipresent in pro audio such as broadcast TV. Because of the poor performance and longevity of early electrets, pro audio distanced itself from the word "electret" and just calls them condenser mikes, because electrets are a subtype of condenser mikes. (It simply means a condenser mike that is pre-polarized, as opposed to ones that need external polarization power.) As such, I think it's eminently possible that a significant percentage (perhaps even a majority?) of "condenser" mikes are actually electret condensers. (In pro audio, you'll see reference to "true condenser" to try and signify an externally polarized condenser mike, even though that phrase is technically imprecise since it attempts to mislead one into thinking that electrets aren't truly condenser mikes.)
It seems my hunch was right: while reading up on electrets to try and answer NANDblog’s question, I came across a statement from Shure (one of the big names in pro audio mikes) claiming that “probably 95% of the condenser microphones on the market are the electret type”.

Another source found during the same trawl says that MEMS overtook electret capsules in sales in 2014, but that most MEMS microphones are also electret-based! “ The MEMS microphone designed is largely based on the design of the electret condenser microphone capsule.” (This I did not know.)
« Last Edit: October 15, 2020, 11:08:33 pm by tooki »
 

Offline David Hess

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Re: BJTs being phased out?
« Reply #35 on: October 16, 2020, 01:36:32 am »
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.

Some high performance switching designs still do that when an IGBT is not fast enough.

Quote
- Bipolar transistors have a higher current density than FETs, which leads to less area (cost) for a given current.

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.

IGBTs take advantage of the same thing; have you ever seen a 100 amp IGBT?  Where this matters is at high voltages where MOSFET die size becomes huge.
 

Offline etiTopic starter

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Re: BJTs being phased out?
« Reply #36 on: October 16, 2020, 02:06:11 am »
Pendant hour is it? These point by point, pick-apart multi-quoting reply posts truly smack of "no no no, no matter what you say, I'm going to pick apart, analyse and refute absolutely everything you've said, wait and see, and I WILL be right!"

Being right is hugely overrated, and also a great waste of one's time. It makes me think many people have naff all better to do than "prove" their (supposed) ability to know more than the other man.

Lighten up - it's not that important in the overall scheme of life, and will you recall who "won" on a forum conversation, when you're in the final hours of your life?

I also sense a disproportionate dose of confirmation bias is present in a lot of these types of threads, and I don't just mean EEVblog, this bullshit is epidemic net-wide from people who can't accept they're not THAT clever all the time, are only human and make mistakes and miscalculations like everyone else.

Calm down, get off your chairs and go for a walk.
« Last Edit: October 16, 2020, 02:09:34 am by eti »
 

Offline coppice

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Re: BJTs being phased out?
« Reply #37 on: October 16, 2020, 02:46:05 am »
It seems my hunch was right: while reading up on electrets to try and answer NANDblog’s question, I came across a statement from Shure (one of the big names in pro audio mikes) claiming that “probably 95% of the condenser microphones on the market are the electret type”.
Interesting. The fairly modern mics I've seen schematics for, or seen inside, had pumps to push the 48V phantom power up to a high voltage. Electrets have real benefits. They can create a really big bias voltage. I had a pair of Pioneer electret headphones in the early 70s. Condenser headphones, like the Stax models, could produce wonderful sound, but struggled to reach high volumes, because they didn't want an extreme bias voltage running down the cable. No problem with the Pioneer electret headphones. They would reach pain levels while maintaining high fidelity.
 
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Online NiHaoMike

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Re: BJTs being phased out?
« Reply #38 on: October 16, 2020, 03:19:42 am »
Some high performance switching designs still do that when an IGBT is not fast enough.
Isn't that the realm of SiC and GaN transistors nowadays?
Quote
IGBTs take advantage of the same thing; have you ever seen a 100 amp IGBT?  Where this matters is at high voltages where MOSFET die size becomes huge.
Actually have a few of those in an assembly on the bench. Rated for quite a bit more than 100A, I got it instead of something closer to the 50A or so I actually need for my application because it's cheap.
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Offline schmitt trigger

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Re: BJTs being phased out?
« Reply #39 on: October 16, 2020, 03:31:08 am »
Indeed, the 2N2646 UJT, being in a metal can is expensive and essentially in the brink of extinction.
But the 2N4870/1 in a plastic TO92 package is significantly cheaper.

PUTs like the 2N6027/8 are another nifty device, although more closely related to thyristors than transistors.

Neither is, or will become, a mainstream device anymore.
 

Offline tooki

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Re: BJTs being phased out?
« Reply #40 on: October 16, 2020, 08:49:41 am »
It seems my hunch was right: while reading up on electrets to try and answer NANDblog’s question, I came across a statement from Shure (one of the big names in pro audio mikes) claiming that “probably 95% of the condenser microphones on the market are the electret type”.
Interesting. The fairly modern mics I've seen schematics for, or seen inside, had pumps to push the 48V phantom power up to a high voltage. Electrets have real benefits. They can create a really big bias voltage. I had a pair of Pioneer electret headphones in the early 70s. Condenser headphones, like the Stax models, could produce wonderful sound, but struggled to reach high volumes, because they didn't want an extreme bias voltage running down the cable. No problem with the Pioneer electret headphones. They would reach pain levels while maintaining high fidelity.
Given how mature both electret and non-electret microphone technology is today, I think that what ultimately matters is how carefully the capsule (and the device it’s in) has been designed, and that top quality can be achieved with either technology, when low cost isn’t the primary decision driver.
 

Offline tom66

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Re: BJTs being phased out?
« Reply #41 on: October 16, 2020, 09:41:59 am »
Up until a few years ago discrete BJTs (e.g. MMBT3904) used to be half the price of equivalent NMOS transistors (e.g. 2N7002), useful for small loads. I see now the price has reached parity so it seems that for most applications any cost advantage there is now gone.
 

Offline coppice

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Re: BJTs being phased out?
« Reply #42 on: October 16, 2020, 09:49:03 am »
Up until a few years ago discrete BJTs (e.g. MMBT3904) used to be half the price of equivalent NMOS transistors (e.g. 2N7002), useful for small loads. I see now the price has reached parity so it seems that for most applications any cost advantage there is now gone.
From my experience with small ICs, I assume the cost of packaging a small discrete, like a 2N7002, now greatly exceeds the cost of the silicon itself. So, the cost of the device is only marginally affected by which transistor is inside.
 

Offline tom66

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Re: BJTs being phased out?
« Reply #43 on: October 16, 2020, 10:10:03 am »
Up until a few years ago discrete BJTs (e.g. MMBT3904) used to be half the price of equivalent NMOS transistors (e.g. 2N7002), useful for small loads. I see now the price has reached parity so it seems that for most applications any cost advantage there is now gone.
From my experience with small ICs, I assume the cost of packaging a small discrete, like a 2N7002, now greatly exceeds the cost of the silicon itself. So, the cost of the device is only marginally affected by which transistor is inside.

Still, there was a price difference, 2N7002 being about twice the price of MMBT3904. We are talking about parts with a sub 1-2p BOM cost though.
 

Online NiHaoMike

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Re: BJTs being phased out?
« Reply #44 on: October 16, 2020, 12:40:34 pm »
From my experience with small ICs, I assume the cost of packaging a small discrete, like a 2N7002, now greatly exceeds the cost of the silicon itself. So, the cost of the device is only marginally affected by which transistor is inside.
Perhaps the next step is some sort of simple IC designed to take the place of a small transistor, the value add being built in protection against ESD, overcurrent, and overheating? Such a device, if cheap enough, would work nicely for interfacing sensitive logic to the external world.
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Offline tom66

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Re: BJTs being phased out?
« Reply #45 on: October 16, 2020, 01:00:54 pm »
From my experience with small ICs, I assume the cost of packaging a small discrete, like a 2N7002, now greatly exceeds the cost of the silicon itself. So, the cost of the device is only marginally affected by which transistor is inside.
Perhaps the next step is some sort of simple IC designed to take the place of a small transistor, the value add being built in protection against ESD, overcurrent, and overheating? Such a device, if cheap enough, would work nicely for interfacing sensitive logic to the external world.

Such ICs already exist.  MOSFETs with built in pull down resistors, ESD protection etc., or NPN transistors with base resistors on the same die.  Then you have things like load control devices that can switch a high side load with overcurrent and slew rate protection, for instance TI TPS22919. Many of them are sub 20 cents in volume which when you consider placement costs of the passive components required to replicate them is not bad at all.
« Last Edit: October 16, 2020, 01:03:31 pm by tom66 »
 
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Offline schmitt trigger

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Re: BJTs being phased out?
« Reply #46 on: October 16, 2020, 01:30:18 pm »
A positive development in the small signal bipolar transistor are the built-in bias resistors.

Makes using them a breeze.
« Last Edit: October 16, 2020, 01:39:47 pm by schmitt trigger »
 
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Offline tszaboo

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Re: BJTs being phased out?
« Reply #47 on: October 16, 2020, 07:13:21 pm »
From my experience with small ICs, I assume the cost of packaging a small discrete, like a 2N7002, now greatly exceeds the cost of the silicon itself. So, the cost of the device is only marginally affected by which transistor is inside.
Perhaps the next step is some sort of simple IC designed to take the place of a small transistor, the value add being built in protection against ESD, overcurrent, and overheating? Such a device, if cheap enough, would work nicely for interfacing sensitive logic to the external world.
What you describe is called "load driver", "relay driver", and MOSFET driver, solid state driver, and so on
 

Offline bsfeechannel

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Re: BJTs being phased out?
« Reply #48 on: October 20, 2020, 02:15:46 am »
Almost no major semiconductor manufacturers have them in their portfolio. And the ones that still have them are "pruning" their availability list.

The truth is that JFETs have never enjoyed the widespread use that BJTs or MOSFETs have. This is the 1976 transistor catalog of IBRAPE, a subsidiary of Philips.



You can see some audio signal-, power-, horizontal output- and radio signal transistors among them. But the only JFET is the venerable BF245. So the "pruning", if it ever existed in fact, started long ago.



What is ironic is that the bipolar transistor was discovered when physicists were trying to build the first FET, but failed. The BJT appeared as an enhancement over the original transistor and provided the ideas to finally create the (J)FET. However, despite the fact that JFETs most closely resemble the behavior of a pentode, by that time the BJT was already established as the semiconductor replacement for tubes. A few years later the MOSFET came up and rendered the JFET further irrelevant as a general purpose solution. Had they succeeded in inventing the JFET before the BJT, who knows how different history would be.

In all those years what I've seen JFETs do was to work as LF/RF front ends, RF oscillators, switches for analog signals, electronically controlled resistors and constant current sources or sinks. And some obscure or very specialized applications.

My hope is that in 20 year's time baking your own JFET, or any other semiconductor, be as inexpensive as producing your own PCB and you will be able to have it done to your specs for 2 bucks.
« Last Edit: October 20, 2020, 02:21:31 am by bsfeechannel »
 
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