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Old 17th April 2013, 01:02 AM   #11
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Yes a linear reg def isn't efficient, but i plan on only dropping to 36v before using something like an lm317 for better load regulation, and then using that, get to say 24v (guess i should mention i ultimately am also going to use an lm7815/lm7915 to get +/-15v (or maybe using a pair of ALWSR's) but the big picture is i plan on making a lab power supply that outputs a variety of fixed levels, 42v (of crz, the main output of these PS's), 36v, 24v, 15v, 12v (also provided by the supply), 9v, 5v (also from the supply) and 3.3v (also via the supply). Same thing on the negative side from a 2nd supply (so i have -42v from the 2nd supplies ground (and the +42v of the 2nd will be tied to the ground of the first, e.g. parallel, as well as all the other voltage levels needed -36, -24v, -15v, etc..).. the result is a various level dual-rail supply thing.. best part is each 1300w version PS can supply ~27amps @ 42v that's a decent amount of audio!

The supplies i got as surplus from work (i work for a financial company and i'm an comp/hw engineer there and regularly work in the server/network lab there), they were getting rid of them (actually they initially had 6000watt supplies but those it turns out they needed still, DOH they're not light too!! i got them home then needed to lug them back, but i eventually then got some 1300watt i hopefully won't have to give back, they are still more than enough power output for hopefully ALL my audio and electronic projects).

I looked around online, they can be had for like 30-50 bucks a piece (that sometimes includes shipping).. with two them one has pretty much a great amount of flexibility (outputting 42/12/5/3.3v) and power headroom.. i also reached out to a contact i have at cisco for the secret elusive pinout of the 6500 series switch power connector so i have a good idea what you can get on what pin.. i didn't think to ask for the service manual as i would really rather not open these guys up (and cisco gives 3rd parties guidelines and other people actually build the supplies so they aren't always manufactered by cisco for there to be an official service manual anyway).

eventually i am looking to maybe create an open source hardware project that anyone can take some cisco 6500 series power supplies and hook them up to this contraption i'm designing, providing you a turnkey solution for various (and eventually variable) voltage lab power supply.

Of course may not be too surprising that i don't have much of an electrical engineer background (other than hobbyist, i did comp sci in school), so i'm picking things up as i go.. if anyone has any other input on the circuit i came up with, i'm all ears.. i actually am curious whether i sized the bypass caps properly on the input/output (i was kind of just pulling numbers out of the air without any scientific approach :-\ so could use some input there or other pointers
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Old 17th April 2013, 06:27 AM   #12
RJM1 is offline RJM1  United States
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If you look at the attachment in my last post the right hand schematic shows how to use the LM317HV as a negative regulator.
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Old 18th April 2013, 09:57 PM   #13
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RJM1, sorry didn't pay close enough attention to your post, that looks like it would work, but i am looking to do approx 6amp so i would need a series pass device to be able to handle that amount of current (and your post only had the HV lm317 doing all the heavy lifting).. guess what you posted could be adapted, but i'm rather proud of what i came up with as well
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Old 19th April 2013, 06:31 AM   #14
RJM1 is offline RJM1  United States
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Here is the schematic with the pass transistors. R1 and R5 are 1/2W.
The LM317HV wil pass about 668mA.
Attached Images
File Type: jpg LM317HV.JPG (73.7 KB, 67 views)

Last edited by RJM1; 19th April 2013 at 06:33 AM.
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Old 19th April 2013, 06:02 PM   #15
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Those two schematics (the pos/neg halves of your latest post) look eerily similar to each other.. why did they produce an LM 337 if you could just use an LM317 in almost the exact same way?

Can you help me understand the difference? Specifically my concern is, with the neg version, isn't it stepping down the common Ground (0v) of the neg half, lower toward the negative extreme? E.g. if you have a 0v @ gnd and -42v at the -Ve side, isn't it stepping down the 0v lower toward the -42v (instead of making the -42v go toward the 0, to -36v? I'm asking because this makes me think the gnd reference will be shifting between both supplies, and with my overall project, the Gnd on the +42v supply is going to be hooked up to the +42v of the second ground (to have that common point be the virtual ground).

I'm basically worried the neg version will make the Gnd really be, with an absolute reference, (as if it was an isolated 2nd supply), 0-42v becoming 0-36v (instead of what i think i need being 0-42v becoming "6-42v").

Sorry if i'm doing a crappy job explaining where i'm concerned, hopefully you get what i'm trying to ask
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Old 20th April 2013, 07:34 AM   #16
AndrewT is online now AndrewT  Scotland
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if you require a dual polarity supply and plan to use a centre tapped secondary, then you need a positive and a negative pair of regulators for the supply.
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regards Andrew T.
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Old 23rd April 2013, 04:19 AM   #17
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ok so that's kind of what i was thinking, that the use of the lm317hv in a neg regulator role would not work.. thanks for validating my concerns i think
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