Homemade AC Adapter??

S

SpangeMonkee

[H]ard|Gawd
Joined
Dec 18, 2001
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I've be tryin' to find a 20v AC adapter so that I can convert an old Apple 15" CRT from ADC to DVI, but I need 20v. I can only seem to find 18/24v switching ac adapters from the usual places (fry's, radioshack etc..) The only 20v I see are for laptops and those are way past my budget for this. After searching in vain for some kinda of kind, I'm empty handed. Any help would be appreciated.
 
1) You need to know how much current

2) I would expect that if you were capable of converting DVI to an analog signal, then you would have no issue with creating a 20v powersupply.
 
That thing is only good for 200 ma. A crt is going to need quite a bit more juice. An older CRT will probably have even higher power requirements.

Mister X said:
How much current do you need?


There is a sort of tutorial on how to make your own AC adapter located here----->
http://www.smallbearelec.com/Projects/SmWart2/SmallWart2.htm

if you wanted to streamline that whole thing you could always use one of the "plug in enclosures" they sell at Jameco
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Whatsisname said:
That thing is only good for 200 ma..
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No shit. :rolleyes:

Now just imagine how much current you could get if you used a different transformer.
That is why I said it was a sorta tutorial. ;)
 
get a transformer that can step down 120VRMS (that's 170V amplitude) to about 24 or 28 VRMS...

use a diode bridge to rectify it.. then what i like to do is a two stage filter.. it's just two LC (DC choke) filters.. then you can run it through a linear regulator.. ro a switching regulator...

if you want a lot of current just get a transformer with a high VA (volt amp) rating

i'm extremly busy.. i would like to help you more.. i've build power supplies before.. but i'll check back every so often.. ther's tons of info out there..

you can get a transformer from.. hammon manufactureing (just google it).. there a tons of transformer makes that come in all sorts of voltages.. you can get a dribe rectifire from digikey. just make sure it's rated for over 200RMS.. at least.. just my personal thing..

then for the CAps just get large electrolytics (since it's only 60Hz you're gona filter out)

it will all turn out pretty big.. andi would suggest making a PCB for.. well you're gonna have to.. for hte bridge rectifier and caps and stuff.. plus you need to earth groun it right.. you don't want to make a dangerous supply lol..

sorry for the grammar errors and typos... gotta go
 
A transformer for any decent amount of juice is going to weigh a ton and waste a good amount of power. He'd be better off buying or building a switching power supply.

Mister X said:
No shit. :rolleyes:

Now just imagine how much current you could get if you used a different transformer.
That is why I said it was a sorta tutorial. ;)
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Yes, a switching power supply will be the way to go for a high current draw when convering AC to DC. A linear regulator would generate A LOT of heat as they are very inefficient. So I second that switching idea.
 
Royicus said:
Yes, a switching power supply will be the way to go for a high current draw when convering AC to DC. A linear regulator would generate A LOT of heat as they are very inefficient. So I second that switching idea.
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linears are more stable.. and have less noise... though :(
 
That is true, but they are so inefficient that once you get beyond some certain power rating (depending on application), they are just too bad to use. That is why your computer's power supply is switching, not linear. Also, that shows that you can normally get "good enough" voltage from a switching regulator/supply. And by good enough, I mean you run sensitive electronics off of it.
 
Royicus said:
That is true, but they are so inefficient that once you get beyond some certain power rating (depending on application), they are just too bad to use. That is why your computer's power supply is switching, not linear. Also, that shows that you can normally get "good enough" voltage from a switching regulator/supply. And by good enough, I mean you run sensitive electronics off of it.
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sometimes designers use a switching regulator as a "pre-regulator" and then they run it through a linear regulator.. hehe...
 
RancidWAnnaRIot said:
sometimes designers use a switching regulator as a "pre-regulator" and then they run it through a linear regulator.. hehe...
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Yup. The more voltage you drop, the less the efficiency, I think. If you take the voltage down via switching to about what you want, you can then pass it through a linear regulator and get a lot better efficiency :p
 
I believe that's exactly what computer PSUs do--they have a switching regulator to take the voltage down to a certain level, then use a smoothing capacitor and a linear regulator to give a nice, smooth voltage out.
 
Yes, this could be true. I've not looked into it at all, so I'm not sure what kind of techniques they employ. But as far as capacitors to eliminate some of the ripple in the DC voltage, yes, nearly all electronics devices use that.
 
thanks for the advice guys.

just in case anyone wants to know; ADC carries digital, analog, usb and power.
 
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