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Old 13th August 2004, 09:34 AM   #1
alecwek is offline alecwek  Denmark
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Question DIY benchtop power

does anyone have schematics for one....any idea how you could control both the voltage and current...help would be greatly appreciated...also its gotta be dual polarity........hey what about signal generaors...anyone out there built one?
oh and of course would the cost compared to usability warrant going DIY on this...or should i just cough up the cash for a used one....hmmm?
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Old 13th August 2004, 01:20 PM   #2
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if you look at the datasheet for the LM317 on National Semi's website you will find a schematic for a "dual-tracking" regulator -- you follow the tracking voltage regulator with an another LM317 set up as a current limiter -- for the negative voltage use the LM337 devices.

I just bought a bunch of Lambda 422FM supplies for the lab for less than $50 each -- these are dual 0 - 40V with adjustable voltage and current, meters for voltage and current. there is no way that you can beat this price -- even with shipping from the US to Europe. I also bought some Tektronix PS503A's for the undergrad lab -- these run about $35 each and can track if so desired. They fit into the TM5XX series of mainframes which are also very inexpensive.
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Old 13th August 2004, 01:37 PM   #3
UrSv is offline UrSv  Sweden
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jackinj:
Just checked the datasheet and I must be blind. Where is the dual tracking PSU?

alecwek:
Providing some specs for what you need could be useful.
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Old 13th August 2004, 02:01 PM   #4
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http://wwwd.national.com/national/Po...4?OpenDocument

if you use a dual pot it will track

i've considered "tricking" the part -- but you really do want both error amps minding their own business.

you can get down to "zero" volts by bringing the "adjust" pin down below the reference voltage of 1.25 V -- in a lab supply it's helpful to be able to get close to zero.
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Old 13th August 2004, 02:40 PM   #5
UrSv is offline UrSv  Sweden
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Aha, you meant it's dual and tracking if you build two identical ones and use a dual pot? Sounds feasible.
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Old 13th August 2004, 08:21 PM   #6
alecwek is offline alecwek  Denmark
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need something ..yeah plus minus 40V would be good...i could say 5 amps...but thats really overkill....i will check up those ics thanks for the feedback guys.....
hey i got a question...when testing a large system of opamps transistors and the likes....should i just set the required voltage and then let the opams etc pull down the amount of current needed...or should i be able to control both voltage and current.....cause i remember those cool PSU at school where you could set both the voltage and the amperes...but im thinkin if u set the voltage to the required Vcc and Vee then u set a current...will that current be forced through the components at all time...or is that the maximum current available...forcing the current through sounds like a good contender for overheating devices.......please help feeling a bir confused....
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Old 13th August 2004, 09:27 PM   #7
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Quote:
Originally posted by alecwek
need something ..yeah plus minus 40V would be good...i could say 5 amps...but thats really overkill....i will check up those ics thanks for the feedback guys.....
hey i got a question...when testing a large system of opamps transistors and the likes....should i just set the required voltage and then let the opams etc pull down the amount of current needed...or should i be able to control both voltage and current.....cause i remember those cool PSU at school where you could set both the voltage and the amperes...but im thinkin if u set the voltage to the required Vcc and Vee then u set a current...will that current be forced through the components at all time...or is that the maximum current available...forcing the current through sounds like a good contender for overheating devices.......please help feeling a bir confused....
If it's 5 amps you're looking for, then you are in an entirely different class of power supply --

for testing operational amplifiers rarely will you need more than a few hundred milliamps --

for matching transistors you will need an supply capable of around 1.5 amps -- for this purpose a Lambda 15 volt supply would be fine.
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Old 13th August 2004, 10:19 PM   #8
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Hm, I need to make myself a bench supply one of these days. So, I'm wondering about the same as alecwek is.

If you use 2 LM317s, one to set the voltage and the second to set the current, what will happen? For example, let's say you set it to 12V 1A. Will the thing then continously give out 1A or will it cap the max output at 1A? (The latter seems more logical, since I don't really see how a supply could "force" more current though some resistors for example.)
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Old 13th August 2004, 11:11 PM   #9
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Tthe voltage will be reduced when the current exceeds the limit you set.
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Old 14th August 2004, 01:15 AM   #10
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this would work:
http://cgi.ebay.com/ws/eBayISAPI.dll...832822809&rd=1

or this:

http://cgi.ebay.com/ws/eBayISAPI.dll...832822073&rd=1
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