Want to by variable power supply  - Page 1
Forum section: electronics / general

author: Ian
author_rank: Contributor
timestamp: December 27, 2010, 10:53:04 pm
content: HII am looking to by a variable power supply that has like 1amp of power and 0-12v or so. It would be nice if it had a meter to show voltage. thank you

author: Zero999
author_rank: Super Contributor
timestamp: December 27, 2010, 11:08:08 pm
content: I'd build one using the LM317.The problem is it's generally limited to 1.25V minimum but there are ways round this, here's an example:http://www.silicontronics.com/index.php?action=ezportal;sa=page;p=19

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: December 28, 2010, 01:16:19 am
content: Here's alink to an LM-317-based designI built using an 18-volt switcher as the source. It only goes do to 1.25 volts but it's pretty handy for the cost.

author: Mr J
author_rank: Regular Contributor
timestamp: December 28, 2010, 05:11:20 am
content: Quote from: Hero999 on December 27, 2010, 11:08:08 pmthere is an easier wayI love the 317, check out the data sheet athttp://www.national.com/profile/snip.cgi/openDS=LM317Okay you have to change r1 to get 12 voltssome math:Vout = 1.25 (1+R2/R1)Define Vout = 12V, R2 5K Pot, R1 is unknown12V = 1.25 (1+5K/R1)12/1.25 = (1+5K/R1)9.6 = 1+5K/R19.6 - 1 = 5K/R18.6 = 5K/R1R1= 5K/8.6R1=581 ohms, (use a 560 it's a standard value, it will give you 12.41Vout)you can use any pot as long as you keep the ratio of r2/r1 the same. I would also suggest a 10 or 25 turn precision pot, it makes it easier to get the voltage you want dead on.for a meter I would use the PM-128E (e is the enhanced version you can use with a common ground to supply the meter)http://www.web-tronics.com/panelmeter.html

author: Mr J
author_rank: Regular Contributor
timestamp: December 28, 2010, 05:19:56 am
content: let me know if you need a full schematic, I can draw one up in gEDA.

author: Zero999
author_rank: Super Contributor
timestamp: December 28, 2010, 08:39:12 am
content: Quote from: Mr J on December 28, 2010, 05:11:20 amYes, I've seen that on the datasheet and I've decided it's not a very good idea.It's simpler but not so good as using an op-amp to null it. The problem is the LM317's reference is 1.25V whilst the LM113 is 1.22V so 0V won't be exactly 0V which is made even worse by the LM317 having a tolerance of 4% so even if you used a reference of exactly 1.25V you're still going to be out.The op-amp will provide a greater degree of accuracy, ensuring 0V is really 0V by measuring the reference voltage and subtracting it from the LM317's negative rail. If you need more accuracy, use a better op-amp with better resistors.The LM113 might also be obsolete, Farnell don't have it, RS and Digikey do but it's really expensive, even a decent op-amp and 0.1% resistors is much cheaper!http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=LM113http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556223&k=LM113

author: saturation
author_rank: Super Contributor
timestamp: December 28, 2010, 11:25:32 am
content: Those are fairly low cost and very prolific. I have a model similar to this and it can deliver stable output voltage down to 0.3001V under load.Full reviews, just search my name and 'mastech'.http://www.mastechpowersupply.com/dc-power-supply/linear-power-supply/mastech-regulated-variable-dc-power-supply-hy1503d-15v-3a/prod_64.htmlThere are many clones of it and similar makes to it, and its scattered around the world. Just find one easy for you to buy and post the link here and let us review it.good luck!

author: Bored@Work
author_rank: Super Contributor
timestamp: December 28, 2010, 12:25:16 pm
content: Quote from: Hero999 on December 28, 2010, 08:39:12 amThat isn't really a valid argument. Voltage references, more precisely shunt voltage regulators, even adjustables, are a dime a dozen. It should be easy to find a replacement, probably for 0.25 ct or maybe 1 € (single qty).

author: Mr J
author_rank: Regular Contributor
timestamp: December 28, 2010, 06:48:52 pm
content: Quote from: BoredAtWork on December 28, 2010, 12:25:16 pmYep a LT1634CCZ-1.25 (1.25V) looks good, also free samples. if you really want to be exactly 0 volts use an adjustable like a TS4436ICT. Or even use a LM337 in a pinch, just use a good meter to calibrate it with the tolerance of the LM317. the specs on the lm317 says any where from 1.2 to 1.3 V for the internal reference voltage. But for the hobbiest this is splitting hairs, have I needed to go below 1.2 volts? Rarely. When I do just put a pot between the output and ground, chances are I'm only pulling a few mA and a pot will work nicely.

author: Ian
author_rank: Contributor
timestamp: December 28, 2010, 09:46:20 pm
content: thank you all i dont need 0v 1.25 or 1v or 2v is fine really. thank you all so much

author: dealexcel
author_rank: Contributor
timestamp: December 29, 2010, 06:47:24 am
content: Buy DC power supply here:http://www.dealexcel.com/-electronic-instruments-dc-power-supply_c2372

author: Ian
author_rank: Contributor
timestamp: December 29, 2010, 03:46:03 pm
content: yikes way to much

author: Mr J
author_rank: Regular Contributor
timestamp: December 29, 2010, 06:10:56 pm
content: here is onehttp://elexp.com/tst_1802.htmVariable DC Power SupplyLCD DisplayModel HY1802D - 0-18V; 0-2A Model HY1803D - 0-18V; 0-3A* Voltage Adjustable: 0-18Vdc* Current Adjustable: 0-2A (HY1802D); 0-3A (HY1803D)* Constant voltage or current operation* LCD displays both current and voltage* Current limiting and short circuit protection.* Load Effect: less than or equal to 0.01% + 5mV* Dimensions: 9" x 6.3" x 3.7"* Weight: ~10 lbs.$58.95 USD*****************************Or thishttp://elexp.com/tst_3010.htm(this one is on my bench) Works great but horrible instruction to assemble if you get the kit.DC Power Supply Model 3010 / 3040The 3010 DC Power Supply features 3 regulated DC supply outputs. One output is fixed and 2 are continuously variable. All 3 supplies are fully current limited and shortcircuit protected. Available assembled or in kit form.SPECIFICATIONSFixed Output:5V DC at 3 amps maximum line regulation of 0.2% load regulation of 1% with a maximum ripple of 10mV p-p.Variable Output:+/- 1.5V DC to +/- 15V DC at 1 amp maximum, line regulation of 0.5%, load regulation of 1% with maximum ripple of 10mV p-p.65.00 as a kit or 79.00 Assembled***********************************************

author: Ian
author_rank: Contributor
timestamp: December 29, 2010, 06:47:50 pm
content: thank you i like your ideas does any one know of a kit that can output say 1.25 or so to like at least 12v. and at least 1amp? I was thinking of just buying a kit and building my own box .

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2010, 08:01:32 pm
content: It's so easy to build that I don't think there's much point in buying a kit.Here's an example circuit:http://www.electronicecircuits.com/electronic-circuits/lm-317-power-supply/Although I'd recommend making the following modifications to the parts list:T1 = 15V, this will be better for lower voltages (what you need) and IC1 will dissipate less power but the downside it will stop regulating >12V >1A.R1 = 100R, the LM317 might not regulate properly with a light load, if R1 is 220R.R2 = 1k, the value of R1 is reduced so we need to reduce R2 proportionally.D1 a 5A rectifier will do although it's a bit overkill, 2A will be fine.C1 can be rated to 35V, 50V is overkill for a 15V transformer.Mount IC1 on a good heat sink, preferably one with a thermal resistance of 2.3°C or better.Note that 1A probably won't be available when the voltage is set to below 5V because IC1 will protect itself against the large amount of power being dissipated.Build the circuit on a piece of strip board or etch your own PCB. Construction isn't critical although keeping the trace between pin 2 on IC1 and R1 as short as possible will help to improve the regulation.

author: Longhair
author_rank: Regular Contributor
timestamp: December 29, 2010, 09:50:17 pm
content: Quote from: Ian on December 29, 2010, 06:47:50 pmElenco K-11Adding a LCD display shouldn't be too hard.

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2010, 10:26:08 pm
content: Quote from: Longhair on December 29, 2010, 09:50:17 pmDid you look at the schematic?It's a simple zener regulator buffered with a Darlington pair. The regulation, ripple rejection will be horrible compared to the LM317 and there's no protection so a short circuit will burn out the transistor which is not what you want from a lab power supply. The only advantage it has is the output will be able to go down to 0V but the regulation will be worse at lower voltages so that's not much use.

author: Ian
author_rank: Contributor
timestamp: January 02, 2011, 02:25:56 am
content: thanks