Any of you electronics guys ever build or modify a power supply?

[Spook50]

My laptop came with a linear power supply that is only capable of a maximum 7.7A current. Output voltage is 19VDC. The 7.7A is always right at its limit powering my laptop, which causes it to heat up a great deal, and they just don't last long. As a fix, ASUS now sells a 9.5A power supply (also linear) that doesn't heat up as badly and provides plenty of current for the laptop.

Ideally, I'd like to build a switching power supply that'll give me the 9.5A 19VDC that the upgraded supply provides and keep it at home as a permanent setup for my laptop. Unfortunately I don't see that as feasible for now since I haven't done much work with power supplies and we haven't covered them yet in school.

Since I can at least order a replacement if I damage the 7.7A supply I've already got, I'm curious to find out what would have to be changed in a linear supply to increase its available output current from 7.7A to 9.5A. I'm more using it as a learning experience for myself than anything else, but I'm not sure what exactly to start looking at in the circuit.

 

[george_tlc]

What laptop do you have, is it vacuum tube based???

9.5A at 19VDC is close enough to 180W. I've never seen a laptop that needs much more than about 60W... Linear power supply - I haven't seen laptops use a linear power supply since - hmm... ever...

Do not even think about designing a offline switching power supply unless you know what you are doing. This kind of project isn't a novice diy type project.

cheers,
george.

 

[e9999]

no expert on power supplies here, but I'll confirm that just about all my laptops have power supplies that are either about 65W or 90W. Mostly the latter, but I just got a 17" screen i7 monster that has only a 65W supply, which presumably should still be enough to cover it fully functioning and charging the battery some on top of that. We got some Dells that came standard with a 65W IIRC but you could get an extra-cost optional 90W, presumably for faster charging.

I do have a smaller ASUS, which has the usual smallish inline power supply brick -also 19V- out but only 2.1A.

I think I do remember something about linear supplies being very inefficient -and also very big- but that would not come into play since your 9A is presumably after the supply anyway.

Of course, all my laptops are consumer or business laptops. No fancy super duper milspec NSA affairs with built-in rail guns here... (unfortunately)...

 

[Spook50]

Aye, it's an ASUS G74 series laptop. Stock power supply output is 19.5VDC with a max of 7.7A (give or take a wee bit, but commonly acknowledged to be 150W max current). Problem is, the laptop will consume even more power than that and can end up being unstable when running demanding stuff, not to mention the 150W power supply getting damn hot, probably close to thermal shutdown if it has any kind of safety circuitry built in (I'm assuming it does). ASUS solved the problem by releasing a near identical power supply that has a maximum wattage of 180W. It operates much cooler since it's not being stressed, and solved a lot of stability issues with G74 laptops being run full tilt.

Really it just comes down to I want to tinker with something, power supplies are a curiosity to me and this had a potentially beneficial outcome, as long as everything went right when testing it, which would happen before it even came near my laptop

Edit: just realized I kept saying linear in my first post. Meant to say switching. At least I assume it's a switching power supply, given how much heavier I expect it should be if it were a linear type.

 

[george_tlc]

....

Really it just comes down to I want to tinker with something, power supplies are a curiosity to me and this had a potentially beneficial outcome, as long as everything went right when testing it, which would happen before it even came near my laptop

Edit: just realized I kept saying linear in my first post. Meant to say switching. At least I assume it's a switching power supply, given how much heavier I expect it should be if it were a linear type.

Firstly, you do NOT want to "tinker" with an offline switcher unless you have full schematics/spec sheets and know what you are doing. You may as well decide to "tinker" with the ECU in your cruiser....

Secondly, the amp rating is due to the choice of components in the power supply that were made when it was designed, it is very unlikely you can just go in there and change out a diode or resistor to achieve higher output current. It would require changing many components and more than likely also the magnetics and power elements (FETs etc). Thermal issues would need to be evaluated. PCB layout may even need to be changed to deal with increased current flow in various paths.

Thirdly, the mere fact that you were talking about Linear versus Switching tells me and should tell you as well, to LEAVE IT ALONE

I design DC : DC switching supplies (LED drivers up to the 100W range) for a living - these are not simple devices that you can "tinker" with...

cheers,
george.

 

[rusty_tlc]

What George said.

If you want to tinker in the virtual world try playing around with Webench

http://www.ti.com/lsds/ti/analog/webench/overview.page

 

[Spook50]

Firstly, you do NOT want to "tinker" with an offline switcher unless you have full schematics/spec sheets and know what you are doing. You may as well decide to "tinker" with the ECU in your cruiser....

Secondly, the amp rating is due to the choice of components in the power supply that were made when it was designed, it is very unlikely you can just go in there and change out a diode or resistor to achieve higher output current. It would require changing many components and more than likely also the magnetics and power elements (FETs etc). Thermal issues would need to be evaluated. PCB layout may even need to be changed to deal with increased current flow in various paths.

Thirdly, the mere fact that you were talking about Linear versus Switching tells me and should tell you as well, to LEAVE IT ALONE

I design DC : DC switching supplies (LED drivers up to the 100W range) for a living - these are not simple devices that you can "tinker" with...

cheers,
george.

I would if I could afford (and acquire) a replacement ECU as easily as a replacement power supply for my laptop
I'm early in the electronics engineering program at ITT and we've touched on power supplies but haven't covered them much. Really just the differences between linear and switching and pros and cons of each design. I know there would be alot of changing out of parts in either to allow for higher wattage capabilities, and alot more in depth for switching versus linear.

I'm mainly trying to learn more beyond just the basic workings of power supplies, and I learn best by tearing into stuff and messing with it.

Maybe one day I'll get a spare ECU and mess around with mine, but not until I can afford to buy a backup part....

 

[rusty_tlc]

I would if I could afford (and acquire) a replacement ECU as easily as a replacement power supply for my laptop
I'm early in the electronics engineering program at ITT and we've touched on power supplies but haven't covered them much. Really just the differences between linear and switching and pros and cons of each design. I know there would be alot of changing out of parts in either to allow for higher wattage capabilities, and alot more in depth for switching versus linear.

I'm mainly trying to learn more beyond just the basic workings of power supplies, and I learn best by tearing into stuff and messing with it.

Maybe one day I'll get a spare ECU and mess around with mine, but not until I can afford to buy a backup part....

You would probably be better off following the link I posted and building something from scratch than modifying an existing design. It's pretty easy to get free samples from the major semiconductor companies.

 

[Spook50]

I think building one from scratch might be a better way to go for a functional supply, which would be nice to have at home for a permanent setup so I can just plug it into my laptop whenever I sit down. Only real expensive part I'd have to try to source from something else would be the transformer to step down the voltage close to the 19.5V I need.

 

[rusty_tlc]

I think you should learn a little more about switch mode power supplies before you start trying to build one.

 

[Spook50]

I think you should learn a little more about switch mode power supplies before you start trying to build one.

Building and tinkering is how I learn best

And surprisingly I still have my eyebrows.....

 

[george_tlc]

Switching supplies run at high frequency, they aren't something you tinker with. Beyond the basic schematic/design there's the whole issue of the PCB layout which is critical for such a design.

Rusty & I are trying to be 'nice' and steer you to learning via good simulation tools versus hacking into something that will either (or all) fry/electrocute you or blow up your laptop.

A laptop switch supply does NOT have a transformer to step down to ~19.5V etc. It will be an offline switcher that has electronics on both the 110-240VAC side, magnetics, optoisolators etc and electronics on the DC side.

Please spend some (lots of) time reading and simulating with free tools. By the time you really understand what is involved you will also understand why attempting to modify your existing laptop supply is NOT something you want to do.

Anyhow, feel free to ignore the advice of an EE that designs DC : DC switching supplies for a living...

cheers,
george.

 

[Spook50]

Switching supplies run at high frequency, they aren't something you tinker with. Beyond the basic schematic/design there's the whole issue of the PCB layout which is critical for such a design.

Rusty & I are trying to be 'nice' and steer you to learning via good simulation tools versus hacking into something that will either (or all) fry/electrocute you or blow up your laptop.

A laptop switch supply does NOT have a transformer to step down to ~19.5V etc. It will be an offline switcher that has electronics on both the 110-240VAC side, magnetics, optoisolators etc and electronics on the DC side.

Please spend some (lots of) time reading and simulating with free tools. By the time you really understand what is involved you will also understand why attempting to modify your existing laptop supply is NOT something you want to do.

Anyhow, feel free to ignore the advice of an EE that designs DC : DC switching supplies for a living...

cheers,
george.

I know a laptop's switching supply doesn't use a transformer. What I was referring to a couple posts ago was building a regulated linear supply since it'd be much simpler than trying to jump right into messing with switched supplies. Now if I end up building something that works reliably and am able to integrate appropriate safety features into it, and then it tests kosher on the equipment at school (they've got oscilloscopes and good DMMs in the labs), then maybe I'd get ballsy enough to power my laptop with it. Maybe.

My original idea was too ambitious for my current skillset, so I'm going to try and start simple and work my way up to the more advanced stuff.

 

[Elbert]

Why not just buy the updated power cord from ASUS.... and call it a day. Laptops get hot...

 

[Spook50]

Why not just buy the updated power cord from ASUS.... and call it a day. Laptops get hot...

For just $60 I will be. I'll stick dick around with the stock power supply to learn more about them. One of our instructors is going to go over the individual components and construction of it once I take it into school and take it apart. I'm going to design and build a linear supply just to challenge myself. I'll build it to the specs needed to power my laptop (with the instructor's input and help) and add safety features to it and run a bunch of tests on it to see if I actually did stuff right.

In all honesty I expect it'll end up being a throw-away project that I'll save components from and just 86 the over all thing, but if it ends up working and proves reliable, then I'll use it as a keep-at-home supply and keep the $60 replacement in my travel bag so it's always ready to go.

 

[rusty_tlc]

Start watching the curb on trash day for an old microwave. It will have many of the parts you need for a linear power supply.

 

[e9999]

I did look up that ASUS. Sure enough it mentioned 150W. Amazing. Where does all that power go? Fast display processing maybe?

 

[Spook50]

Start watching the curb on trash day for an old microwave. It will have many of the parts you need for a linear power supply.

Ha, good idea. We've got a couple junked microwaves in the garage right now that I just haven't taken in for recycling. Time to clear off the work bench!

e9999, yeah this is by far the most power draw I've seen in a laptop. And the 150W supply is the one that ends up really getting pushed and heating up, so ASUS started selling the 180W supply for the next generation of G series laptops.