Variabl Regulated Power Supply

[ArcaneDreams]

Well I'm looking to make one for benchwork, and I came arcross this:

**broken link removed**

I think I can find all the parts...except I cannot find a 24vac, 3A transformer. I am going to be plugging it into a standard 120Vac outlet.

I don't think I will need the meter either...If I were to use a meter, it would be digital, however I dont want to spend money on a digital meter. It will be easy enough to hook a DMM up to it to adjust my output voltage.

Would there be much difference between any old trim-pot, and the Bourns brand that they use? I'm going to guess that it is just more accurate.


On a side note I would like to add that MultiSim seems to always be missing something. I have yet to actually simulate anything outside of school work with it due to not haveing the components.

In this case, the LM317 is nowhere to be found in multisim...

 

[mkh]

why don't you use a circuit that uses 723 ic??? u could provide foldback protection

 

[Hero999]

Also you'll never get a smooth 30VDC output from this circuit with a 25V transformer and the current will be reduced at lower voltage settings due to the power dissipation of the LM317.

Oh and unless you're planning to use the more expensive LM217 R2 needs to be dropped to 110hm: and p1 to 2.5K.

 

[audioguru]

If you try to get 1.5A at 15V then the LM317 must dissipate 22.5W which is impossible with the TO-220 package on a huge heatsink. A fan or liquid nitrogen must also be used to cool it. If it gets too hot then it shuts down without melting, then starts working again when it has cooled.

If the voltage is set to 5V then the load current must be reduced to avoid shutdown due to heat. If you do manage to cool it then the LM317 will limit its current to 1A to protect itself.

 

[ArcaneDreams]

hmm then I see that guy has no idea what he is doing.

Perhaps I should just try to design my own!

 

[Sceadwian]

Ebay. The good deals are hard to come buy but if you lurk there for a few weeks you should find a decent deal on a benchtop current/voltage limited power supply.

 

[ArcaneDreams]

The whole point was to build one to become more familiar with designing circuits at home.

Is there a one stop shop that has all of these odd IC chips for purchase? It really sucks having to look through 500 different sites just to get parts.

I would also be interested in a site that has a listing of spec sheets ALONG with a reasonable description about what they actually DO!

I mean.. I for instance "LM317" translates into.......________

It would be helpful if everything wasnt named with random numbers and letters! Why can't they be named something that pertains to what they actually do? Or perhaps they are & I just have no idea what the letters stand for.




Oh, and I have searched google for some time now and all of the designs I see for variable power supplys use the LM317. Why would all these people use it, if it doesn't work?!

 

[audioguru]

www.digikey.com and www.newarkinone.com are about the largest electronics parts distibutors in North America. You can search for parts on their sites or have them send you a printed catalog.

You will learn that an LM317 is an adjustable voltage regulator IC. "LM" means it was invented by National Semiconductor but many other companies make it by licence.

 

[ArcaneDreams]

I see, I will have to check those sites out. I am going to have to take a class just on memorizing the names of components it seems....


BTW, any response to the question I had about lots of people using the LM317 in variable power supplies?

 

[audioguru]

The LM317 works fine if you use it within its limits. Mine is a tiny adjustable 1.25V to 9V/1A supply and it works perfectly. The wall-wart AC-DC adapter for it is 12V/1A. The LM317 has a medium-small heatsink that gets warm sometimes.
If more current is needed then use the LM350 for 3A or the LM338 for 5A. Follow their limitations for a good circuit. Their datasheets explain everything.

 

[kchriste]

It would be helpful if everything wasnt named with random numbers and letters! Why can't they be named something that pertains to what they actually do? Or perhaps they are & I just have no idea what the letters stand for.

You'll get used to it. Just like you know the difference between a Porche 911 and a Chevy Sprint....

Oh, and I have searched google for some time now and all of the designs I see for variable power supplys use the LM317. Why would all these people use it, if it doesn't work?!

They do work! They all have their uses. The LM317 is a nice, cheap, easy to use IC. The only problem comes when you want to draw alot of current out of it and the input voltage is much higher than the output. You may not exceed the maximum current rating, but it's maximum power dissipation rating may be exceeded ( Watts=(Vin-Vout)*Amps). One thing to remember with electronic parts is that you never want to run them at their "absolute maximum" ratings and always design in a safety margin.

I am going to have to take a class just on memorizing the names of components it seems....

Just start browsing some circuit diagrams at http://www.discovercircuits.com/list.htm Soon the more common parts will stick in your mind.

 

[audioguru]

Some older common parts stick in my mind:
1) LM324 quad opamp and its sister the LM358 dual opmp: Horrible crossover distortion and very narrow bandwidth. It is "low power" which means low performance.
2) 741 opamp. Terrible noise and narrow bandwidth.
3) Chevy Sprint. A piece of junk for a tiny car. Suzuki? A 4-wheel motor-bike.

 

[ArcaneDreams]

I know the 741! That is mainly what we have been using in my Opamp class all semester.

Thanks for the help guys. Information is best when it comes straght from people who know what they are talking about.

 

[Hero999]

1) LM324 quad opamp and its sister the LM358 dual opmp: Horrible crossover distortion and very narrow bandwidth. It is "low power" which means low performance.
2) 741 opamp. Terrible noise and narrow bandwidth.

But they're great cheap DC amplifiers , they don't oscillate when driving capacitive loads like the TL07x and they aren't as noisy as you think. The :mu:A741 has an equilivalent noise voltage of 23nV/√Hz and the TL07x is only 5nV better at 18nV/√Hz. If you're building a voltage regulator or AM radio there's no real reason to use a TL07x over the old :mu:A741, you won't be able to hear that noise above the static on the AM radio.

 

[audioguru]

The last time (the only time) I made a DC amplifier I used a lousy old 741 opamp.
I have used TL07x opamps ever since.