New project idea - give me your suggestions - Page 1
Forum section: electronics / projects

author: brabus
author_rank: Frequent Contributor
timestamp: May 04, 2013, 05:19:44 pm
content: Hello everybody,I was about to begin my new electronic project, and I realized that a large amount of my bench space was occupied by the power supply. I made this sucker some years ago, and it worked fine since now:http://peresperienza.blogspot.com/2008/05/lalimentatore-da-banco.htmlSorry for the website only in Italian, I hope the pictures are clear enough.I have a small bench, so I basically need a smaller (yet flexible and powerful) power supply. So I had this new idea:I'd like to make an universal power supply, which can be supplied from virtually any DC source, such as your laptop charger, or that useless 12V transformer you have hangin' around in your basement, and so on.I have in mind a 9 - 24V DC input. Maybe also down to 5V, if you only have USB as power source. The outputs are going to be a 5V fixed, plus a variable 0 - 15V dual (for opamp projects), let's stick with 1A maximum. Panel and controls TBD, but let's keep it small and functional.The question is: does anyone know about existing projects like this? Does it make sense to spend some work on it? Would you buy it if it was a kit, or even a complete product? How much money would you spend to buy it? What additional features should it absolutely have (i.e. galvanic insulation, USB interface, graphic or 7-seg display...)?Thank you for your time and for any comment.--Alberto

author: ivan747
author_rank: Super Contributor
timestamp: May 05, 2013, 03:44:55 pm
content: It's your lucky day. Take a look at Amspire's "General purpose power supply design" and the PCB I made for it. Due to the lack of a Dremel (I lost mine) and some inconveniences I haven't been able to build my PCB, but I believe it will work flawlessly.Here are the links:https://www.eevblog.com/forum/projects/general-purpose-power-supply-design-7488/15/https://www.eevblog.com/forum/projects/amspire's-power-supply-in-a-pcb/You can power the supply form almost any source, as long as you comply with the requirements. Read Amspire's thread until he presents his "Mark 3" supply. I don't recommend that one because it uses a pre-regulator and complexity goes up a lot.If you have any questions just ask.Edit: I must add this power supply is flexible enough to use analog and digital displays, pre-regulator or not, potentiometers or DACs, microcontrollers or not, etc.

author: Harvs
author_rank: Super Contributor
timestamp: May 05, 2013, 11:35:47 pm
content: Quote from: brabus on May 04, 2013, 05:19:44 pmThe problem with that, is most DC source you'll find around are not isolated from mains ground.

author: gxti
author_rank: Frequent Contributor
timestamp: May 06, 2013, 01:07:53 am
content: Unearthed laptop chargers are easy to find by the boxfull. That's exactly what I was thinking of when I found amspire's thread.

author: Harvs
author_rank: Super Contributor
timestamp: May 06, 2013, 01:24:49 am
content: There you go, you learn something new every day. I always thought they had some connection to neutral, but I just checked a few and clearly not (albeit there's about 30Mohms resistance between them).So anyone know how far away from neutral (i.e. ground) the output can be operated? Would 100VDC still be ok? I'm guessing there's a Y-rated cap across the isolation or something?

author: Harvs
author_rank: Super Contributor
timestamp: May 06, 2013, 06:35:17 am
content: I was intrigued so I tested a couple for leakage current between output and earth.I hooked a meter on uA range between the negative output and mains earth on half a dozen laptop power supplies I had around the house. All were sold with laptops or by retail stores in Oz, so they should be reasonable quality (i.e. no ebay specials.)I got anywhere between -5 to 35uA, and when a DC bias was applied up to 60VDC, it added around 2-3uA in each case.Just something worth knowing.

author: gxti
author_rank: Frequent Contributor
timestamp: May 07, 2013, 12:28:13 am
content: Admittedly I didn't think too hard before replying either. In the USA the unearthed ones are easy to spot because they use an unearthed plug, which is common for simple appliances. I'd always assumed that the adapters with the 3-pin molex connector are earth-referenced but it might be the case that those float too, as you seem to have found. I guess in other countries unearthed plugs are probably much more rare, in which case the 3-pin adapters would be the only type sold.