*Standard* voltages

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Of course I know of many common voltages that seem to be industry standard either formal or informal -- 3.3, 5, 9, 12, 15, 120, 240, etc... --, I was curious as to how often other voltages are used, say 82 or 197?

 

Recognizing, of course, that settling on standard voltages makes interoperating with components / systems manufactured by others far easier and safer; but what if I wanted to use 31 volts for my design?

 

I just finished working through the serial circuit portion of the U.S. Navy's Electronic Engineering course and so have a very rudimentary and un-practiced understanding of the relationships in Ohm's law, and recognize there is a max power / max efficiency aspect to all of this as well. How much does that play in designing the power profile of a system?

 

Thanks!

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Many of the lower voltages, some of which you mention, some not, are at or near battery voltages, partly determined by chemistry.

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You might want to read about the "current war": There's a good reason why we use AC to transmit electricity: It can be transformed very easily. If you want to cover large distances, you want to save on material for the cables since metals are expensive.

 

If you have thin cables, you have great resistance. Because P_loss=I^2*R you want a small current. But you need a certain amount of power at the end point. And that's why you compensate with a higher voltage: P=U*I.

 

But high voltages are dangerous, you don't want 300kV in you house! So you convert it back to lower voltage an high current.

 

The same logic applies in most fields of electrical engineering. When it comes to semiconductors, things are a bit different though. Here, we can't use higher voltages because the structures are so small that they can't withstand more than a few volts and to conserve energy.

 

Most voltages we consider standard today have just proven to give a good compromise or were convenient at the time they were introduced and then they just stuck for compatibility reasons.

 

 

Of course I could go on and on, but I hope that's enough to give you an idea.

 

Cheers

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+1 for saving materials. Sometimes it goes to extremes. The venerable "The Art Of Electronics" a review question where you are given The energy draw of New York and shall compute the diameter of the wire needed to get that electrical energy in there. Turns out it must be ridiculously thick. Several hundred meters IIRC.

Enter transformation. Up goes the voltage. Down goes the current. And so does the energy dissipation due to conductor resistance.

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Voltages for power supplies do not need to be that precise, they are pretty much all +/-10% i think, so it is unlikely you are ever going to see 82 V.

 

Standards have to apply for batteries, mains supplies but outside that given the ease of converting voltages it is anything goes. All you need is some voltage to push enough current for the application. How it is generated depends usually on whatever is easiest or traditional, trains, ships, airplanes all have different ideas about that.

Bob. Engineer and trainee Rocket Scientist.

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There are standard voltages in military, aviation, automotive, telecomm. Military vehicles use 24V batteries. Aviation uses 28VDC, 26VAC 400Hz, cars are heading to 42V to run pumps instead of belts, telecom racks use 48VDC. Any of this news to anyone? Hope it helps.

 

Imagecraft compiler user

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pawi777 wrote:
Most voltages we consider standard today have just proven to give a good compromise or were convenient at the time they were introduced and then they just stuck for compatibility reasons.     Of course I could go on and on, but I hope that's enough to give you an idea.

 

This is kind of what I figured.And, I'm all ears (and eyes) if you have the time!

 

JohanEkdahl wrote:
The venerable "The Art Of Electronics" a review question

 

Great. Thanks for spending another $100 on my behalf!!  ;-) (ordering this now!)

 

donotdespisethesnake wrote:
Voltages for power supplies do not need to be that precise, they are pretty much all +/-10% i think, so it is unlikely you are ever going to see 82 V.

 

Right, 82 was just an out-of-my-butt value. But still possibly a valid value for a particular application I imagine. 

 

After playing with IR detection this weekend voltage dividers are next up on my list. So all of this is really valuable to me!

  • "Give me six hours to chop down a tree and I will spend the first four sharpening the axe."  -- Abraham Lincoln
  • "All right wise guy, where am I?"   -- Daffy Duck
  • "Well, we're safe for now. Thank goodness we're in a bowling alley."  -- Big Bob, Pleasantville
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Well, well.. Bingo got a new p/s with the outputs on the back. You top that easily, having voltages coming out your *rse! Beware of shorts. Actually any pants, unless made of rubber.. Got latex? ;-)

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"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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donotdespisethesnake wrote:
Standards have to apply for batteries

As already noted, battery voltages are defined by chemistry - rather than imposed by standards ...

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JohanEkdahl wrote:
Beware of shorts. Actually any pants, unless made of rubber.. Got latex? ;-)
 

 

This should cover me, right?

 

  • "Give me six hours to chop down a tree and I will spend the first four sharpening the axe."  -- Abraham Lincoln
  • "All right wise guy, where am I?"   -- Daffy Duck
  • "Well, we're safe for now. Thank goodness we're in a bowling alley."  -- Big Bob, Pleasantville
Last Edited: Fri. Apr 29, 2016 - 06:10 PM
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^ Can't tell from the picture if they're using 1.8V or 3.3V there.

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In practice when doing low power stuff I tend to look at the lowest voltage all the components I need will work at and use that. For example, I used 2.7V in one project because a flash memory needed 2.5V, and the XMEGA has a limit of Vcc-0.6 for AREF and 2.048V is convenient.

 

This is possible because modern LDOs are really, really efficient at low current. In the above scenario I was running from a 3.6V lithium cell, and the 0.5uA loss in the regulator was offset exactly by a 0.5uA reduction in sleep mode current from the micro. When active, running at a lower voltage tends to bring bigger savings than the LDO losses.

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on some US fishing boats I have been on I have seen a lot of different voltages, 208 460 480 V AC, and on one of them the 110V AC was made between two phases!.

 

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Is 208 just 240V rectified and smoothed?

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Many different forces have lead to "standard" voltages. At the low end, it has tended to be what various semiconductor processes yield in terms of optimum operating voltage. For a long time, 5V was the de-facto standard, and that seems to have been driven by the optimum voltage for bipolar (eg, transistor) TTL logic. 15V was also common, being sort of the analog IC optimum (including +15/-15). All this was before CMOS. Early CD4000 CMOS logic could work from 5V to 15V. Process shrinks and thinning of oxide layers has pushed the maximum voltage down and down. Now, we are working with logic that does not even require gate voltages as high as the threshold voltage. 

 

In the end, these common voltages are just that - common voltages. There are no standards, at the low voltage end, anyway. But, since TI's CMOS logic needs to work with Fairchild's and NXP's and Toshiba's, we end up with these widely used voltages.

 

Jim

 

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No it's a "real" AC voltage, and now I can't remember the colour code (as I remember 208 had a red phase) it had to be marked different than 460-480V

Last Edited: Thu. May 12, 2016 - 04:23 PM
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mojo-chan wrote:

Is 208 just 240V rectified and smoothed?

 

208v is the phase to phase voltage of a 120V 3-phase system.

 

It is sqrt(3) times 120V.   The two 120V lines are not in phase so they don't add up to 240v.

 

Kevin

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ka7ehk wrote:
Now, we are working with logic that does not even require gate voltages as high as the threshold voltage.

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ciroque wrote:

Of course I know of many common voltages that seem to be industry standard either formal or informal -- 3.3, 5, 9, 12, 15, 120, 240, etc... --, I was curious as to how often other voltages are used, say 82 or 197?

 

Recognizing, of course, that settling on standard voltages makes interoperating with components / systems manufactured by others far easier and safer; but what if I wanted to use 31 volts for my design?

 

Those numbers you quote as standard voltages, are more accurately, already Voltage Ranges.

 

Any 5V supply comes with a tolerance spec, used to be +/- 10%, but these days +/-2% is affordable.

 

You also will see wider supply is a trend : Common now to see Micro's Specd for 1.8~5.5v, or power supply chips from sub-5V to > 40v, so you can choose anywhere you like, within that range. 

 

'Using less copper' tends to drive voltage up, but there is also a human-safety threshold at around 36~48V that can determine what is chosen.

 

 

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mojo-chan wrote:

 

Is 208 just 240V rectified and smoothed?

 

kevin_white wrote:
208v is the phase to phase voltage of a 120V 3-phase system.

 

Smoothing a rectified AC voltage tends to give you the peak voltage; so 240V rectified and smoothed would give ~340V

 

That's sqrt(2) times 240V

 

The "240" is the RMS, and it's a sine wave - so the peak is sqrt(2) times the RMS.

 

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