[GreenKeys] History - Why voltages and frequencies are chosen(5v & 3.3v l...

[Scott Johnson]

Logic voltages are kept low to conserve power and limit dissipation, and are
pushing even lower, core voltages in state of the art devices are now
considerably less than a volt.  This is enable by finer geometries and very
thin gate dielectrics.  Ironically, at the other end of the spectrum, high
voltage/power RF FETs are now available that operate on 160 VDC (Full wave
rectified 115VAC line voltage), this is convenient for obvious reasons of
economy on the power supply, but also makes matching the device to a 50 ohm
load much easier and more efficient.

Scott W7SVJ

 

From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of WA5CAB at cs.com
Sent: Thursday, November 22, 2012 7:37 PM
To: Greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] History - Why voltages and frequencies are
chosen(5v & 3.3v l...

 

I don't recall ever checking on why 5V or 3.3 V were used for logic but
always assumed it was at least in part because of inherent voltage ratings
of the components and/or was enough lower than 6.3 VDC to allow a regulator
to operate properly.

And the 50/60 cps subject has been beaten enough today so I won't add any
comment.

6.3V (and 12.6 V and 25.2V) for tube filaments is a result of the
characteristics of the lead-acid cell and the fact that early automotive
systems were nominally 6 VDC (then 12, then 24) (with engine off of course).
The fully charged voltage of a lead-acid cell (after removal of the surface
charge by a slight discharge) is 2.1 VDC.  Three cells in series yields 6.3
VDC and the heavy use in automotive applications made the batteries readily
available for battery operated radios (farm sets, and the like).  As the AC
operated sets had no particular technical reason (consumer stuff, anyway) to
prefer a different voltage, 6.3 volt filaments became common.  

On the 120/220 VAC question, there never has been a system with those
nominal voltages, whether single or 3-phase.  The standards over the years
have been 110/220, 115/230, 117/234 and 120/240 for single phase.  Because
the standard single phase pole pig has a center-tapped secondary and you
can't get 220 volts line to line if the line to CT is 120.  The most common
(probably) low voltage 3-phase system is currently 120/208 wye.

In a message dated 11/22/2012 18:18:10 PM Central Standard Time,
1oldlens1 at ix.netcom.com writes: 




----- Original Message ----- 
From: "Keith Lueck" <kwlueck at swbell.net>
To: <notbago at yahoogroups.com>; 
<i3detroit-public at googlegroups.com>; <acti at provide.net>
Cc: <Greenkeys at mailman.qth.net>
Sent: Wednesday, November 21, 2012 12:57 PM
Subject: Re: [GreenKeys] History - Why voltages and 
frequencies are chosen(5v &3.3v logic, 6.3v filaments, 
120/220 VAC, 50/60Hz etc)



Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

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