Why 3.3v? - Page 1
Forum section: electronics / projects

author: BiOzZ
author_rank: Regular Contributor
timestamp: January 13, 2014, 11:14:59 pm
content: sorry im just purly curious why 3.3v, 5v and 1.8v was chosen they seam to be fairly random! but im sure its not!any greybeards have any ideas?

author: Zbig
author_rank: Frequent Contributor
timestamp: January 13, 2014, 11:33:28 pm
content: My guess regarding 3.3V would be... well, because it's approximately 10/3, perhaps?Plus, a single fresh alkaline cell has little more than 1.5V initially so maybe they wanted some safety headroom for 2*AA in series applications?

author: c4757p
author_rank: Super Contributor
timestamp: January 13, 2014, 11:40:42 pm
content: I've also seen 1.2V and 1.5V.What do 1.2, 1.5, 1.8, and 3.3 have in common?They're all in theE12 series!

author: sync
author_rank: Frequent Contributor
timestamp: January 14, 2014, 12:18:34 am
content: For the reasons for 5V read this good post:https://www.eevblog.com/forum/chat/so-why-ttl-logic-uses-5v-again/msg185501/#msg185501

author: BiOzZ
author_rank: Regular Contributor
timestamp: January 14, 2014, 12:25:23 am
content: Well c4757p has all the answers as usual XPthanks guys now i can act like a smartass at work!

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 14, 2014, 01:02:53 am
content: Quote from: c4757p on January 13, 2014, 11:40:42 pmBut oddly enough, 2.5V is not, while 2.4V (not a common voltage) is part of E24...

author: tesla500
author_rank: Regular Contributor
timestamp: January 14, 2014, 10:24:49 am
content: Quote from: NiHaoMike on January 14, 2014, 01:02:53 amProbably because half of 5V is convenient.

author: Kjelt
author_rank: Super Contributor
timestamp: January 14, 2014, 11:19:43 am
content: Unsure if this is the real answer but guessing about the choice of a lower voltage is in the power used, which is the square of the voltage.If you want to save power and put expense in a new standard the factor you want is probably at least 50% extra powersavings then the previous one (why all the expenses for only a 10% savings does not make sense).So look at the power not the voltage and you see that each step is between a factor 1,4 and 1,9 lower1,2V P = 1,44factor dP=1,561,5V P = 2,25factor dP=1,441,8V P = 3,24factor dP=1,922,5V P = 6,25factor dP=1,743,3V P = 10,89Another reason could be that the frontiers in the silicon manufacturing process, some firm like Intel or Altera/Xilinx were designing such large chips that they had to reduce the power significantly. How much reduction would depend on the design so maybe they choose for a particular chip the voltage it should use and others adopted it.

author: nctnico
author_rank: Super Contributor
timestamp: January 14, 2014, 12:06:49 pm
content: 3.3V = 0.666 * 53.3V may be an arbitrary choice (5 isn't in the E12). Lower voltages are probably the result of a specific IC process. Nowadays every voltage goes.

author: c4757p
author_rank: Super Contributor
timestamp: January 14, 2014, 12:47:40 pm
content: I still suspect that the choice of 3.3V over, say, 3.4V, has to do with the fact that as an E12 number, many EEs will think of it as a "nice" number. It's the same reason programmers tend to pick powers of two even when it doesn't make a bit of difference.5V is obvious - it's the biggest "nice" number under Vebo.2.5V is "nice" in that it is half of 5.It's all pretty arbitrary I think, but still related to various reasons we think numbers are "nice".

author: mariush
author_rank: Super Contributor
timestamp: January 14, 2014, 02:42:19 pm
content: 3.6v is also very common in microcontrollers and other devices. 3 x 1.2v ...2.8v is also relatively common.

author: c4757p
author_rank: Super Contributor
timestamp: January 14, 2014, 02:46:08 pm
content: Quote from: mariush on January 14, 2014, 02:42:19 pmIs it? I don't think I've seen 2.8 before.

author: mariush
author_rank: Super Contributor
timestamp: January 14, 2014, 02:51:54 pm
content: Now that I think about it, I don't know any IC running at 2.8v, but plenty of PIC microcontrollers specifying 1.8-3.6v input range.I was saying 2.8v is common simply because I see a lot of fixed 2.8v linear regulators available.

author: narch
author_rank: Newbie
timestamp: January 14, 2014, 04:11:51 pm
content: As I recall, it had to be > 3v to meet the requirement of being compatible electrically with both the 4000 series CMOS chips and the various 74 families that were around at the time. Beyond that, I suspect it was chosen as a 'nice number', although I recall seeing 3.5v stuff in the 80s as well.The 3.6v you see on a lot of microcontrollers is almost certainly an artifact of 3.6v being the nominal voltage from a single lithium ion (NMC) cell.

author: BBQ
author_rank: Regular Contributor
timestamp: January 14, 2014, 06:16:40 pm
content: It seems you all have mentioned all the reasons.JEDEC Standard No. 8C.01 :http://www.jedec.org/sites/default/files/docs/jesd8c-01.pdfAah, now i'm gonna sift through other JEDEC documents O0.

author: wilheldp
author_rank: Regular Contributor
timestamp: January 14, 2014, 06:17:47 pm
content: Quote from: c4757p on January 14, 2014, 12:47:40 pmPun intended?

author: dfmischler
author_rank: Frequent Contributor
timestamp: January 14, 2014, 09:50:04 pm
content: Quote from: c4757p on January 14, 2014, 12:47:40 pmOr prime numbers, even when that doesn't make a difference.

author: tszaboo
author_rank: Super Contributor
timestamp: January 16, 2014, 12:44:13 pm
content: Quote from: wilfred on January 13, 2014, 11:29:25 pmThe voltage needed to drive NFETs out the linear region for any reasonable currents, back in the day. Later that become less, so new logic families were made.

author: Cdngreybeard
author_rank: Contributor
timestamp: January 16, 2014, 02:40:58 pm
content: Go far back to the time ICs were first developed. DTL and RTL logic of the early 1960s used BJTs. DTL required 5 volts and RTL required 3.3 to 3.6 volts. These requirements were based on the gate construction, transistor saturation requirements, and the minimum noise threshold to go between logic 0 and 1 states.