linear voltage regulator suggestion - Page 1
Forum section: electronics / beginners

author: Cali-Sam
author_rank: Contributor
timestamp: July 14, 2012, 01:08:12 am
content: can any body suggest a linear voltage regulator 0-15v and at least 3A current handling?doesnt have to be exact. anything similar would work.im trying to build a clean, riple free linear PSU for my tiny lab. too bad, i'm a poor bigenner, and i cant afford a pre-built one.please help!!

author: ivan747
author_rank: Super Contributor
timestamp: July 14, 2012, 01:16:51 am
content: Try with the LM350, as it is available from many manufacturers.

author: Cali-Sam
author_rank: Contributor
timestamp: July 14, 2012, 01:32:09 am
content: that sounds more like what i was looking for....i faild to mention that i would need a negative voltage regulator with the same or similar spesifications as well. any idea??

author: Unknown
author_rank: Unknown
timestamp: July 14, 2012, 01:42:53 am
content: The LM350 does not go below 1.25 V without introducing extra complexity. 3 A / 15 V without pre-regulator will also require serious cooling to get rid of ~55 W while keeping the junction temperature at a sane level.

author: Cali-Sam
author_rank: Contributor
timestamp: July 14, 2012, 01:55:22 am
content: heat might be somthing i can deal with. i can add a CPU heat sync with a fan.... but i really want voltages below 1.2v.... any other regulator that can go below 1.2v.

author: notsob
author_rank: Frequent Contributor
timestamp: July 14, 2012, 02:40:39 am
content: You may want a K version [T0-3 package] for better heat dissipation

author: ivan747
author_rank: Super Contributor
timestamp: July 14, 2012, 04:50:37 am
content: Quote from: alm on July 14, 2012, 01:42:53 amI am prototyping a DC-DC converter pre-regulator for this regulator. I only have a 7805 and an LM337 on hand, though.

author: Simon
author_rank: Unknown
timestamp: July 14, 2012, 10:36:02 am
content: you can do down to 0 volts but it complicates your circuit, the 1.25V limit is so because it is the reference voltage inside the chip. You need to play around with your regulators ground (0 reference) taking it under 0V by at least 1.25 so that when the reg thinks it is delivering 1.25 it is actually 0V

author: MikeNye
author_rank: Contributor
timestamp: July 14, 2012, 01:49:29 pm
content: Hi Cali-Sam,Have you had a look at Linear Technologies' LT3083?This looks like a very good regulator which is the bigger brother of the LT3080 that Dave has done some videos about with the first power supply project book, except it handles 3A and has a slightly lower voltage range (0V - 23V). It is low dropout.It is available in a TO-220 package, so perfect for breadboarding and easily mountable on a heat sink.The data sheet even shows you a lab supply with current limiting as one of the application examples:For your negative requirement, do you need dual tracking and a true earth reference? If not, could you not just reverse the output terminals when you need a negative supply?I hope this helps you out!-M

author: T4P
author_rank: Super Contributor
timestamp: July 14, 2012, 02:22:37 pm
content: You should be ashamed to even call that a "lab supply" IT'S NOT!

author: Simon
author_rank: Unknown
timestamp: July 14, 2012, 02:29:46 pm
content: Quote from: DaveXRT on July 14, 2012, 02:22:37 pmcare to qualify that ? or are you firing off blanks again ?

author: digsys
author_rank: Unknown
timestamp: July 14, 2012, 02:51:46 pm
content: Geeez, so much anal negativity .. LT make damn nice products. All it needs is a reverse OP to IP diode,Zener OV clamp on the OP, followed by a polyfuse, Current and voltage meters and you end up with anice bench P/Supply quite cheaply. Just need to decide on the heatsinking.

author: Cali-Sam
author_rank: Contributor
timestamp: July 14, 2012, 05:10:35 pm
content: Quote from: Simon on July 14, 2012, 10:36:02 amcan you provide the schematic for that please!! i would be thankful.

author: Simon
author_rank: Unknown
timestamp: July 14, 2012, 05:14:56 pm
content: I don't have a schematic to hand and it would need adapting to the specific regular. The topic is discussed in the book "the art of electronics"

author: Unknown
author_rank: Unknown
timestamp: July 14, 2012, 05:19:41 pm
content: See the '0 to 30V regulator' application example in the National LM350 datasheet.

author: T4P
author_rank: Super Contributor
timestamp: July 14, 2012, 05:40:53 pm
content: Quote from: Simon on July 14, 2012, 02:29:46 pmJust ask FE!

author: Simon
author_rank: Unknown
timestamp: July 14, 2012, 05:42:12 pm
content: Quote from: DaveXRT on July 14, 2012, 05:40:53 pmFE ?

author: darrylp
author_rank: Regular Contributor
timestamp: July 14, 2012, 08:54:34 pm
content: Free Electron?Sent from my HTC Desire using Tapatalk 2

author: digsys
author_rank: Unknown
timestamp: July 15, 2012, 01:15:41 am
content: Quote from: DaveXRT on July 14, 2012, 05:40:53 pmThat's all we'd need, another 200 post rant on how dumb everyone else is :-)

author: Monkeh
author_rank: Super Contributor
timestamp: July 16, 2012, 02:11:45 am
content: Quote from: Electroalek on July 16, 2012, 02:07:41 amAn ATX PSU, especially the cheap crap usually butche^W converted, is not a lab supply. And they most certainly cannot provide 10A on -12V. Most don't even have -5V.

author: digsys
author_rank: Unknown
timestamp: July 16, 2012, 02:41:58 am
content: Agree with Monkeh - besides this is a VERY dangerous path for a "beginner". Having had to repair 1 or 2,I wouldn't go near these dangerous beasts unless Vitally necessary !!

author: Monkeh
author_rank: Super Contributor
timestamp: July 16, 2012, 02:45:02 am
content: Quote from: digsys on July 16, 2012, 02:41:58 amI've repaired and modified a few myself, never thought of them as dangerous. Take the same precautions you do around anything with mains charged caps in it and you'll be fine.Mind you, I started with mains electrics long before playing with electronics.

author: Cali-Sam
author_rank: Contributor
timestamp: July 17, 2012, 02:19:09 am
content: Can i wire two of the lm350 in parallel and double the current?

author: digsys
author_rank: Unknown
timestamp: July 17, 2012, 03:26:35 am
content: QuoteAbsolutely, check the application ccts for info. I am testing a 10X parallel prototype right now,sharing is excellent. You can also use LM338 (5A) or LT1083 (7.5A), all work the same.

author: Cali-Sam
author_rank: Contributor
timestamp: July 17, 2012, 05:39:10 am
content: LM338 is only a dollar each on ebay, packaged as TO-3. could this be fake?as far as heat dissipation, efficiency, and performance ,which package is better To-3 or To-220?

author: Unknown
author_rank: Unknown
timestamp: July 17, 2012, 05:54:24 am
content: TO-3 has a lower thermal resistance to the heat sink, but is larger and usually more expensive. It's also harder to directly mount on a PCB. Hence the popularity of TO-220 (and similar packages like TO-3P). TO-3 would require a (slightly) smaller heat sink due to the lower thermal resistance. Performance and efficiency would be identical if the junction temperature is the same.

author: shebu18
author_rank: Frequent Contributor
timestamp: July 17, 2012, 05:58:02 am
content: Why not use the LT1083 instead. It also has a 1.25V minimum voltage but is rated to 7.5A

author: Cali-Sam
author_rank: Contributor
timestamp: July 17, 2012, 06:07:10 am
content: where can i buy the LT1083 from? and how much is it?

author: digsys
author_rank: Unknown
timestamp: July 17, 2012, 06:35:23 am
content: Quote from: Cali-Sam on July 17, 2012, 05:39:10 amYIPES, that sounds like bad silicon, IF it's NEW. There are some trusted places where I buy surplus lots,usually quite cheap. egwww.x-on.com.auSearch your part # and check ALL the hits.If you're not doing production, TO3 is better thermally plus larger transfer area (as suggested).In production, it's a pain in the ass, which is why I'm designing them all out of a product range, too much labour.The LT1083 also comes in a TO264 package, which is my MOST favourite package for assembly !!!They are much dearer than LM338s, but an awesome regulator. Check X-ON

author: Cali-Sam
author_rank: Contributor
timestamp: July 17, 2012, 08:06:06 am
content: this might sound strange!!!i was thinking about dumping my voltage regulator in a small contater filled with car engine oil instead of ataching a heat sink... is engine oil an insulator?forgive my ignorance, im just trying to come up with better solutions.

author: digsys
author_rank: Unknown
timestamp: July 17, 2012, 12:41:11 pm
content: QuoteThey do that for seriously large transformers and similar units that have large surface area. You can't use any oil,you'd have to check specs (google will tell you). But for small devices, you have no hope. Practicalities of containment and sealing,just a lot of effort for little value. Besides, the MOST important spec is how FAST you can get the heat away from the regulator.If you want to try it, go for it, practical is the best way to learn. The theory itself is fine.Added: Some of the new EVs are cooling their Lithium battery packs with liquid !! ie Tesla etc Actually pumping it OVER the 44-66lithium cells @ 180-280VDC 100-300A. We're still considering it ... lots to worry about :-)

author: SeanB
author_rank: Super Contributor
timestamp: July 17, 2012, 03:38:55 pm
content: Using transformer oil to remove heat will work, but you will need to still attach a heat spreader to the device, and arrange the oil to flow past it. Otherwise it will just cook. You can try using a flat aluminium plate to increase surface area, and keep it vertical to assist convection. Then you will have to keep the oil cool.