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I got a request today for the impossible...

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Holes Flow

New Member
Experts,

A friend of mine travels a LOT, and they do it with 2, sometimes 3 laptops. He has about 5-10 pounds of converters & power supplies with him in a backpack, and he has been asking me for a solution. He's trying to go all USB-C (100w per spec), as many are, and these are the rough requirements, with low weight being #1. I really want to go transformerless, but I'm beginning to think this is impossible (hence the subject line).
USB-C is shown to supply 3A-5A @20V, or 60w-100w.

Must have enough power to power the following (simultaneously):
  1. Must be light.
    1. Traditional heavy transformers are out-too heavy.
    2. Size is less important than weight, so there is room for fans, etc.
    3. This is just for charging, so there is no need for tight ripple/noise specs.
    4. In other words, not a traditional hub with addressable endpoints-except for the situations where voltage (and current?) negotiation has to occur. I do realize that many devices don't like EMI on their DC supply, but I'll keep things loose until I get to that point.
  2. Input
    1. 110vac, normal current expectations for a hotel.
    2. No on-board battery to worry about, inverters, etc.
  3. Output
    1. As described below, it would by nice if all outlets could be loaded at once without overheating.
  4. Apple Macbook
    1. USB-C
    2. 20v @ 3A (60w)
  5. Dell laptop
    1. Dell-specific connector (thinking I could combine 3-4 of the below USB-C outlets into a Frankenstein/hydra?)
    2. 20v @ 9A (180w)
  6. USB-C outlets
    1. 4 outlets - USB-C as well, and as I understand there is voltage (and current?) negotiation once connected, I guess these should also be able to do just the minimum 3A @ 20V, or 60w each (240w total).
Unfortunately, this looks like, at full load, a demand of 480w in DC. Assuming lossless perfection, that is a draw of 4.3A @ 110vac. It's a lot, but only 1/2 of what you'd expect a hair drier to be.

Problem: All I know is traditional AC->DC power supply design, and that is from electronics school back when we learned about tubes(GAK!) & transistors, and how to solder. I'm totally lost, as I am trying to do this solid-state, without bulky transformers. He claims there is no product out there that can do this (there aren't even any all-USB-C hubs), and that it must be impossible-or else someone would have done it by now.

Q: Is this truly impossible to do?

I'm just looking to rough out a prototype, not make a slick product. If I can lay it out on the high-power equivalent of a normal breadboard (a piece of wood?), then it will be enough to prove it can be done. Transformerless is designed for low DC voltages, and switch mode information seems to be strictly DC-DC.

I don't need someone to do this for me. Really I'm just asking if it can be done, and if so, which design should I go after? With so many to study, I'd really enjoy someone's advice as to which architecture to go after-if any!

What do you guys & gals think?

Thanks!
 

dknguyen

Well-Known Member
Most Helpful Member
Hysteretic converters and their cousin, constant-on time converters are good for large step-down ratios. Drawback is it inherently requires ripple to function so you will always have some amount of ripple that you can't just arbitrarily filter out to infinitesmal levels. Also has a more unpredictable frequency spectrum than synchronous switching converters so filtering is more difficult.

I'm a bit confused...if you want transformerless why couldn't you just rectify the mains voltage and then step it down directly with a switching design that can handle large ratios? Or use multiple steps so you aren't so you don't have to compromise as much on a switch that is both high voltage and high frequency capable?

switch mode information seems to be strictly DC-DC.
I'm confused about why this is a problem? AC-DC is easy. Bridge rectifier and smoothing cap. The whole point of the transformer is to easily step down a high voltage to a lower one so you can work with it, regardless of whether you need AC or DC in the end. So find a switching design that can handle high voltage and has large step-down ratios to replace the role of the transformer.

EDIT: If your knowledge is old, then hysteretic converters are one of the easier switching designs to wrap you brain around and you don't need to worry about compensation for stability. In a sentence: disconnect the source when the voltage is too high and reconnect the source when the voltage is too low.

Even with a transformer, wouldn't this just end up being the size of a small computer power supply? I mean...that's basically what you're looking for with custom plugs and a 5V and 20V output. That's like what? 3 lbs in a 6" x 6" x 4" block? And those things are encased in steel which yours doesn't necessarily have to be (I think some of it is shielding but they are also full of fan and ventilation holes so maybe not.)

I don't know what you consider heavy, but that has to be beat 5-10lbs of multiple supplies and cords.

Like, aren't you basically looking for this?
http://www.buddyrc.com/efuel-550w-30a-12-18v-power-supply-with-pfc.html:
 
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KeepItSimpleStupid

Well-Known Member
Most Helpful Member
iGo was really neat until something happened. It was a nice laptop supply that had 12-24 V input (automobile/Aircraft) so at say 10 A, that's 120 W. A lighter socket might go to 15 or 20A. A separate power cord was used for this.

Then you had an AC input cord. Never tried both at the same time.

It gave you another port that would power cell phones, with another DC-DC converter and the correct tip. The tip also had a DC barrel connector to be used with DC-DC converters that would step down to cell phone devices.

The output cord used two make before break (seemingly custom) parts. that put resistors in the tips. These set the current and voltage of the converter.. as wel as the polarity.
iGo never gave the tip specs.

The resistance values needed are available online and some info can be had with a patent search.

Never had a problem with the converters. Always had problems with the cords and tips. Tips actually blew out the laptop too.

So, you bring everything up to a given buss voltage and then step down to whatever the device wants. Negotiation would be better than make before break power supply swapping IC's.
 

ronsimpson

Well-Known Member
Most Helpful Member
"Tranformerless" is a term we use to say there is no isolation from the power line. This is very dangerous.
This picture is a witching power supply. It has a transformer that runs at 100khz not 60hz. It is very small.
Supplies like this come with or without the metal cage.

http://www.us.tdk-lambda.com/ftp/Specs/ls.pdf
I could not find very many "20" volt supplies. Every one makes "24 volt" and most can be adjusted down to 22 volts.
Input is 110/220 VAC.

This link should take you to a place where you can look at 100s.
https://www.digikey.com/products/en...ower+supply&pageSize=25&pkeyword=power+supply
 

dknguyen

Well-Known Member
Most Helpful Member
Experts,

A friend of mine travels a LOT, and they do it with 2, sometimes 3 laptops. He has about 5-10 pounds of converters & power supplies with him in a backpack, and he has been asking me for a solution. He's trying to go all USB-C (100w per spec), as many are, and these are the rough requirements, with low weight being #1. I really want to go transformerless, but I'm beginning to think this is impossible (hence the subject line).
USB-C is shown to supply 3A-5A @20V, or 60w-100w.

Must have enough power to power the following (simultaneously):
  1. Must be light.
    1. Traditional heavy transformers are out-too heavy.
    2. Size is less important than weight, so there is room for fans, etc.
    3. This is just for charging, so there is no need for tight ripple/noise specs.
    4. In other words, not a traditional hub with addressable endpoints-except for the situations where voltage (and current?) negotiation has to occur. I do realize that many devices don't like EMI on their DC supply, but I'll keep things loose until I get to that point.
  2. Input
    1. 110vac, normal current expectations for a hotel.
    2. No on-board battery to worry about, inverters, etc.
  3. Output
    1. As described below, it would by nice if all outlets could be loaded at once without overheating.
  4. Apple Macbook
    1. USB-C
    2. 20v @ 3A (60w)
  5. Dell laptop
    1. Dell-specific connector (thinking I could combine 3-4 of the below USB-C outlets into a Frankenstein/hydra?)
    2. 20v @ 9A (180w)
  6. USB-C outlets
    1. 4 outlets - USB-C as well, and as I understand there is voltage (and current?) negotiation once connected, I guess these should also be able to do just the minimum 3A @ 20V, or 60w each (240w total).
Unfortunately, this looks like, at full load, a demand of 480w in DC. Assuming lossless perfection, that is a draw of 4.3A @ 110vac. It's a lot, but only 1/2 of what you'd expect a hair drier to be.

Problem: All I know is traditional AC->DC power supply design, and that is from electronics school back when we learned about tubes(GAK!) & transistors, and how to solder. I'm totally lost, as I am trying to do this solid-state, without bulky transformers. He claims there is no product out there that can do this (there aren't even any all-USB-C hubs), and that it must be impossible-or else someone would have done it by now.

Q: Is this truly impossible to do?

I'm just looking to rough out a prototype, not make a slick product. If I can lay it out on the high-power equivalent of a normal breadboard (a piece of wood?), then it will be enough to prove it can be done. Transformerless is designed for low DC voltages, and switch mode information seems to be strictly DC-DC.

I don't need someone to do this for me. Really I'm just asking if it can be done, and if so, which design should I go after? With so many to study, I'd really enjoy someone's advice as to which architecture to go after-if any!

What do you guys & gals think?

Thanks!
"Tranformerless" is a term we use to say there is no isolation from the power line. This is very dangerous.
This picture is a witching power supply. It has a transformer that runs at 100khz not 60hz. It is very small.
Supplies like this come with or without the metal cage.

http://www.us.tdk-lambda.com/ftp/Specs/ls.pdf
I could not find very many "20" volt supplies. Every one makes "24 volt" and most can be adjusted down to 22 volts.
Input is 110/220 VAC.

This link should take you to a place where you can look at 100s.
https://www.digikey.com/products/en/power-supplies-external-internal-off-board/ac-dc-converters/133?FV=17d40094,17d40174,17d4003d,ii1|2211,ffe00085,1180042a,1180008f,118000b3,1180077b,118000c8,118000de,118000e8,118000f2,118009fd,11800100,1180014d,11800176,11800187,1180018d,11800193,118001a6,118001aa,1180002b,1180002f,118001ec,11800204,11800218,11800036,1180021f,11800234,1180025a,1180003d,11800273,11800288,11800362&quantity=&ColumnSort=1525&page=1&k=power+supply&pageSize=25&pkeyword=power+supply
I just bought the TDK-Lambda LS for work. Not that it's too big or heavy, but if size and weight are your concerns, then the

https://www.mouser.ca/datasheet/2/400/cus200ld-1154816.pdf

is half the volume and half the weight for the same power. It feels better built too in my hand than the LS. It does, however, cost double.
 

blort1961

Member
I would think that its simply rediculous carrying around more tham 1 laptop. Just figure out exactly the voltages you need, and get a Labda for each.
BUUUUTTTT...............
This household has 4 laptops in it, all from different manufacturers, and includes an Apple, a Google, a Monsterous Gaming unit, as well as others....and each has a power supply no bigger than 3x4x2 inches, and each weighs only a few ounces...why the need for such grotesquely huge, heavy power supplies????.
Each laptop here outweighs its power supply by about 10:1....maybe even more.
Are his Laptops 90's Military Surplus???...or maybe even Radio Shack units???
I think that the money that would be invested in this project would be better spent on 1 computer, and its associated itty bitty supply.
 
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