DIY bench power supply  - Page 1
Forum section: electronics / beginners

author: Fermín
author_rank: Newbie
timestamp: April 15, 2015, 02:05:25 am
content: Hi, I've decided I'm going to build my own bench power supply based on Mjlorton's design.As I don't have rail to rail opamps and I want to reach 0V at the output I think (correct me if I'm wrong) I need a negative rail, but I don't need a symmetric power supply i just want something like -10Vcc with a small amount of current so I don want to use a center tap transformer.I've been thinking about using tho different transformers, a big one (with the necessary voltaje and current regarding the specs of my power supply) and a small one (with just the necessary voltaje and current to gibe the opamp a negative rail). Or in a more efficient way, one with different windings.I came up with the attached design. I want to know if it is correct or if is there any other (more efficient) way to do it.Thank you.

author: ivan747
author_rank: Super Contributor
timestamp: April 15, 2015, 02:44:41 am
content: There is a more efficient way to do it. Here is an example of a power supply that does it. It does it using a capacitive charge pump, similar to a capacitive voltage inverter. I frankly can't remember its name.

author: Fermín
author_rank: Newbie
timestamp: April 15, 2015, 02:54:09 am
content: Quote from: ivan747 on April 15, 2015, 02:44:41 amthank you.I'd prefer a linear power supply because of the noise. Is there any problem with my design, would it work? I have no idea

author: rs20
author_rank: Super Contributor
timestamp: April 15, 2015, 03:11:57 am
content: Quote from: Fermín on April 15, 2015, 02:54:09 am?? The rectified output of your negative transformer supply is going to be a rectified sine wave, so you still need to filter it, and put it through a linear regulator anyway. So, if you really want a very smooth supply, just use ivan's suggestion of a charge pump, coupled to a linear regulator.

author: rdl
author_rank: Super Contributor
timestamp: April 15, 2015, 03:16:32 am
content: Just go ahead and make a full dual polarity power supply. Having a usable negative rail comes in handy sometimes. The free to download chapter 9 of the Art of Electronics 3rd edition has a good schematic and great information about power supplies in general.

author: Fermín
author_rank: Newbie
timestamp: April 15, 2015, 03:23:43 am
content: thank you very much.

author: skyjumper
author_rank: Regular Contributor
timestamp: April 15, 2015, 03:43:51 am
content: I need to do a similar thing, and along these lines, did Dave ever make a kit of his battery powered power supply, that he designed in a multi-part blog entry?

author: Cliff Matthews
author_rank: Unknown
timestamp: April 15, 2015, 11:12:06 am
content: Quote from: ivan747 on April 15, 2015, 02:44:41 amThe whole project around that schematic seems to be athttp://electronics-lab.com/projects/power/001/I have two things I just can't visualize in my head:1 - U2 and U3 must draw very little current - How do C2 C3 and D5 D6 magically invent that negative rail?2 - I don't see any trusty shunt resistor in the path from rectifier and the final series-pass 3055 (so how's that possible?)

author: rs20
author_rank: Super Contributor
timestamp: April 15, 2015, 11:36:19 am
content: This video is far more relevant than it might first appear. If you understand this video properly, and then go back to the schematic you posted, it'll make sense:Sure. the video is a doubler rather than the negative rail that you want, but just flip the diodes around the other way and you'll get your negative rail instead. And the circuit in this thread uses AC as the oscillating signal, rather than a microcontroller pin. Same principle.If you're wondering why a doubler looks so similar to an inverter, you just have to realise that a doubler and an inverter are exactly the same thing. Think about it: you have 12V (or whatever) and 0V, and you want to generate -12V. Now, measure those voltagesrelative to the top rail-- the top rail is 0V, the old ground is -12V, and you want -24V. You want a voltage doubler, albeit one that operates on negative rails. Just flip those diodes around.

author: Thor-Arne
author_rank: Unknown
timestamp: April 15, 2015, 11:56:03 am
content: Quote from: Cliff Matthews on April 15, 2015, 11:12:06 amThere's a update on this projecthere.Also read the electronics-lab forum, there's a lot of comments on this design there.

author: Fermín
author_rank: Newbie
timestamp: April 15, 2015, 12:59:54 pm
content: Thank you all for te info, I'll start reading and decide how to do it in the best way possible.

author: Cliff Matthews
author_rank: Unknown
timestamp: April 15, 2015, 01:06:58 pm
content: Quote from: Thor-Arne on April 15, 2015, 11:56:03 amThanks - yeah I saw that note about pushing the TL081's over the brink at the bottom - it's good to see peer review around some of these designs - without it, some of us would be toasting-up too many IC's!

author: Sbampato12
author_rank: Regular Contributor
timestamp: April 15, 2015, 01:40:55 pm
content: It is important to read the forum and updates on that project because they got some corrections.And they changed the OpAmp, because the phase reversal problem with the TL081...I've built this circuit, looked good, but I almost never used these power supply. When I was about to use, I found the forum showing the problems, and started I project on my own.

author: rdl
author_rank: Super Contributor
timestamp: April 15, 2015, 03:40:49 pm
content: I personally wouldn't waste any time on that circuit from electronics-lab.com, it's been debated and modified for years. The last time I looked there were two threads about it with thousands of posts where people have been trying to fix it. It would take days to sort through it all. I would at least start from a circuit that's known to work well.For anyone thinking about building their own supply I'd highly recommend getting a copy of the free preview pdf of the Art of Electronics third edition. It includes chapter 9 on power supplies, which is over a hundred pages - almost a book on its own. I'm sure there are other places to get it, where you don't need to request a password, but here's the official link:http://www.cambridge.org/us/academic/textbooks/art-electronics

author: Fermín
author_rank: Newbie
timestamp: April 15, 2015, 05:22:46 pm
content: I've been reading and I've decided that I'll use MJlortons schematic but I'll add a capacitive charge pump in the supply, like attached.what do you think?

author: Zero999
author_rank: Super Contributor
timestamp: April 15, 2015, 05:44:40 pm
content: Quote from: Cliff Matthews on April 15, 2015, 11:12:06 amThat circuit contains many errors.There are many threads on that site with corrections. Unfortunately the webmaster won't update the circuit on the site.http://www.electronics-lab.com/forum/index.php?topic=7317.0http://www.electronics-lab.com/forum/index.php?topic=39481.0

author: Cliff Matthews
author_rank: Unknown
timestamp: April 15, 2015, 06:38:45 pm
content: I finally saw the shunt resistor R7 - a bit uncommon on the negative rail?...

author: DarkZero
author_rank: Regular Contributor
timestamp: April 15, 2015, 07:02:36 pm
content: hello !this is how i would generate -voltage with one transformeralso i have my own design that works pretty well, where you can see how i made charge pump with the help of a user on this forumhttp://www.filedropper.com/labpowersupply020v10ma2a

author: timofonic
author_rank: Frequent Contributor
timestamp: April 15, 2015, 07:42:10 pm
content: Quote from: Hero999 on April 15, 2015, 05:44:40 pmThere are a zillion "forks" of it, that made me to doubt about what one to do.There's a Dutch design in another forum thread and it seems to be a good one.Any EE expert to make a forum post collection of DIY power supplies with an extensive and pedagogical review? It would be awesome!

author: mstck
author_rank: Contributor
timestamp: April 16, 2015, 12:25:42 am
content: Quote from: rdl on April 15, 2015, 03:40:49 pmI have made several attempts to download this free file, but so far I have not not received a password. Is this something you can post here or alternately suggest another link. So far my searches on Google have drawn a blank or pointed at the link you provided.Thanks

author: BradC
author_rank: Super Contributor
timestamp: April 16, 2015, 02:00:16 am
content: Quote from: Cliff Matthews on April 15, 2015, 06:38:45 pmActually, it's mostly seen in the negative rail. Very rarely implemented in the positive rail as the sensing and amplification is much easier low side.

author: Cliff Matthews
author_rank: Unknown
timestamp: April 16, 2015, 02:10:03 am
content: Quote from: mstck on April 16, 2015, 12:25:42 amI will buy the book soon but it's been several days for me and, like you, still no password...Today I stumbled on the sample chapter (online file deleted) see the link RDL posted at the bottom of this thread...

author: mstck
author_rank: Contributor
timestamp: April 16, 2015, 02:37:42 am
content: CliffThanks for the link. Appreciate your help.

author: Cliff Matthews
author_rank: Unknown
timestamp: April 16, 2015, 11:12:34 am
content: Quote from: mstck on April 16, 2015, 02:37:42 amMy pleasure, but I have to bring up a question since the publisher is giving this chapter away...Should a six-part zip of this be posted to "Electronics primers, course material and books" section?I don't want to get hoofed from box.com (or this site!) on legalities, can anyone advise?

author: Cliff Matthews
author_rank: Unknown
timestamp: April 16, 2015, 12:35:51 pm
content: Some progress: I just got my password for the free TAoE sample chapter 9 (on power supplies).I replied, asking Fran Robinson (frobinson@cambridge.org) for permission to post it in the books section.If we get permission, I will post a 6-part zip file for everyone there.MSTCK: did Cambridge.org give your password yet?

author: rdl
author_rank: Super Contributor
timestamp: April 16, 2015, 03:44:42 pm
content: Sorry, I didn't notice this post until today. I guess you already found the file, but just in case - I got it from a link in this review:http://www.wisewarthog.com/electronics/horowitz-hill-the-art-of-electronics-3rd-edition.htmlQuote from: mstck on April 16, 2015, 12:25:42 am

author: Cliff Matthews
author_rank: Unknown
timestamp: April 16, 2015, 03:53:18 pm
content: Quote from: rdl on April 16, 2015, 03:44:42 pmThat's the site! (I cleared my cache and forgot where I got it....) ThanksNote: To avoid any legal problems, I will remove the file. (already 20 people have downloaded it)

author: mstck
author_rank: Contributor
timestamp: April 16, 2015, 03:56:53 pm
content: Quote from: Cliff Matthews on April 16, 2015, 12:35:51 pmCliff, I just checked and realized that the password finally arrived. The subsequent post byRDLand the link provided appears to answer the question surrounding the right to share the file.

author: rdl
author_rank: Super Contributor
timestamp: April 16, 2015, 08:56:05 pm
content: I can't imagine why they would care if someone made the file available elsewhere since they're providing it for free. Maybe requiring a password was just to avoid excess traffic on their server or something like that.

author: Zero999
author_rank: Super Contributor
timestamp: April 17, 2015, 12:51:43 pm
content: Quote from: Cliff Matthews on April 15, 2015, 11:12:06 amThey form a voltage doubler to make the negative rail.

author: ivan747
author_rank: Super Contributor
timestamp: April 19, 2015, 07:22:04 pm
content: Quote from: Thor-Arne on April 15, 2015, 11:56:03 amAWESOMEGreat find!