[GreenKeys] GreenKeys Digest, Vol 106, Issue 42

[Gerry Block]

John,

  I can tell you in solid state the power supplies are generally dictated by the 
semiconductor processes used to build the components.  As the semiconductor 
demensions shrink the dielectrics shrink and the 'withstanding voltage' (to fry 
the part) (also called maximum ratings) go down and so lower power supply 
voltages are required  Just like capacitors.   In early days of logic there was 
12v and 5v.  Then 3.3v.  Then 1.8v.  Then 1.2v.  Now .9v (!).    The lower 
voltages have the additional benefit of increasing speed (the same volts/uS can 
slew through the logic switching level faster), lowering EMI,  and the smaller 
dies of course mean more $$$/wafer...  

  For analog circuits higher voltages (+/-15v) used to be pretty standard in 
order to drive real-world loads, but has progressively gone down depending on 
the required loads.  In today's battery operated equipment the voltages are very 
low.
  In vacuum tubes I believe the filament voltages chosen had something to do 
with the battery voltages available.  For instance 6.3v is four cells.  ALso for 
line voltage radios the filmaent strings had to e    equal the line voltage so 
you had 25v and 50v filments as well as 12v and 6v.
  In a modern cell phone the batteries and components are still closely 
related.  Battery life has gone up as voltage and power consumption has gone 
down.  

  The availability of very efficient switching regulators allows a single 
battery to provide many different internal rails.
  We make equipment with 28v, 13.v, +/-12v, 3.3v, 1.9v, 1.2v - all in the same 
box, which runs from anything between a +6 to +33v source.   If you look at each 
component and its operating voltage, you can usually deduce what year it was 
designed.

Gerry
AD6MC
  




________________________________
From: John Nagle <nagle at animats.com>
To: greenkeys at mailman.qth.net
Sent: Wed, November 21, 2012 1:54:30 PM
Subject: Re: [GreenKeys] GreenKeys Digest, Vol 106, Issue 42

On 11/21/2012 1:28 PM, greenkeys-request at mailman.qth.net wrote:
> I don't know if I ever asked this before.  I had a VERY interesting question 
> arise (yet again) the other day, and STILL haven't yet found a good 
> explanation for MANY of the "made choices" by the engineers yet.
> 
> Question - What is the history behind the CHOICES for voltages and 
> frequencies - for logic, batteries, tubes (filaments & plates), 
> mains V&F, etc?  
> If arbitrary, then why do power supplies and load needs often NOT MATCH?
> 
> Does anyone have a link to any good "history of power supply voltage 
> and frequency choices" stories, that covers these subjects?
> (I'm sure this could fill books, but I'm looking for the Cliff Notes 
>versions... :-)

    Google.

    There's an extensive literature on power line frequencies.
See

    http://en.wikipedia.org/wiki/Utility_frequency

For an early discussion of the design tradeoffs, see

http://www.nycsubway.org/wiki/The_New_York_Subway:_Chapter_05,_System_of_Electrical_Supply


which discusses the tradeoffs which led to 25HZ distribution for
the New York City subway.  The generators were driven by large
reciprocating steam engines at 75 RPM.  Power distribution was
three-phase 11KV, converted to 600 VDC for the third rail system
with synchronous converters at substations along the system.

                        John Nagle
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