DIY Power Supply Build - Page 1
Forum section: electronics / general

author: Joshua
author_rank: Regular Contributor
timestamp: April 25, 2011, 02:49:03 am
content: Hello Everyone!You may have seen my other topic(s) about building a bench supply. I have decided to build a dual supply based on the schematic below.Here is the full pdf...http://www.elv-downloads.de/Assets/Produkte/2/225/22532/Downloads/22532_Universelle_Netzteilplatine_um.pdfI have a couple of questions regarding this design. According to the description(translated), by selecting some resistor values, I can either build a 0-15V 4A supply, or a 0-30V 2A supply. Why is the 30V version limited to 2A? If it is not possible to build a 0-30V 4A design, which version would be more useful? I am beginning to learn electronics, but know that I will want to deal with motors, robotics, audio circuits, etc...To build a dual supply, will I also have to have two transformers? I will want to be able to connect them in series, and in parallel, so I know they have to be isolated from each other. What kind of transformer do I need? When searching for transformer on digikey, I do not know what I need enough to filter the results.On the bottom left, there is some form of temperature measurement using a 'SAA965' which is actually a KTY81-151. - Datasheet:http://www.datasheetcatalog.org/datasheet/philips/KTY81-151.pdfWhat do I use this to measure the temperature of? The heat sink of the transistor? How do I attach it to what ever I am measuring? Also in the area of the temperature measurement, there is a 5V supply. Where is the 5V supply coming from, the 7805 at the top? And what are the the two lines coming out to the left, labeled 'ST6' & 'ST7' going to?I will want to have panel meters displaying voltage and current output. I think I want to incorporate possibly a uC into the project, for some 'fanciness' I have in mind, once I have the foundation, so maybe just a LCD is all I need. For the Panel meter, and micro ideas, can I use the 5V supply, that is also the 5V supply for the LM324, or will I need another small transformer, to power these items?Some people suggested in another thread, that I use a ten turn pot on my supply. I also agree that that is a good idea. In the LM317 datasheet, there is an example(below) about digitally selected outputs. Would this also work on this supply? I think I want a button for 5 and 3.3 volts, and the micro will select the correct resistance. What are the downsides of this?In Dave's recent video about the HP Supply, he mentioned that it had no 'load switch.' Is that just a normal toggle switch(that can handle the current), to just quickly disconnect the output? Would a beefy switch, or a small switch with a relay be better?What are the funny looking pots in the top right of the schematic? Why do they have a flat end, instead of an arrow-does this represent something significant?One last question: What are the transistors with two lines coming out of them? What do the two lines represent?My goal is to have a nice dual supply, that I can use for years as I continue to learn about electronics. I will greatly appreciate any advice, answers to questions, or just ideas I haven't thought about. Also, some of the above information is not 'set in stone'. I.E. if it is better to use a different design for the supply, than I am willing to use that one instead.Thanks in advance,Joshua

author: Unknown
author_rank: Unknown
timestamp: April 25, 2011, 12:35:05 pm
content: Quote from: PianoKid1994 on April 25, 2011, 02:49:03 amPower dissipation in the pass transistors. Max. dissipation with 0-30V, 2A is about 2A*30V(+drop over pass transistors at 30V), 0-15V, 4A is also about 60W. Max dissipation of a 0-30V, 4A supply is about 120W. You would probably need double the pass transistors, plus a heat sink with about half the thermal resistance.Quote from: PianoKid1994 on April 25, 2011, 02:49:03 amTwo transformers or one transformer with two separate secondary windings (not one center tapped). The transformer would obviously need twice the power in the latter case. Something like 30V/8A (7A) per power supply (extra current because of the rectification and smoothing) in your case. 2x15V/8A (put them in series) or 2x30V/4A (put them in parallel) would also work.Disadvantage of two secondary windings is that the isolation between secondaries is usually less than the isolation between primary and secondary. Commercial supplies from eg. Agilent are rated for 250VDC between the outputs, I wouldn't count on this for secondaries without any insulation in between.Transformer selection should be primarily driven by output voltage and current. Input should be your mains voltage (or center tapped windings which can be wired in parallel/series for 115V/230V) at 50/60Hz, this will be true for 95% of the mains transformers you find. I wouldn't worry about finding a transformer with the low-power center tapped 18V winding, you're unlikely to find this. Just get some small 2x9V transformers.Quote from: PianoKid1994 on April 25, 2011, 02:49:03 amIt's attached to the heat sink with some sort of clamp (Halteklammer / Schelle für den Temperatursensor). It's there to shut down the power supply if the heat sink gets too hot. This can be omitted if there is enough cooling, it's not critical to the operation, it's just an extra safety feature. ST6/ST7 are just solder terminals to connect the temperature sensor to the PCB.Quote from: PianoKid1994 on April 25, 2011, 02:49:03 amDigital panel meters usually need a supply that's floating relative to the voltage they're measuring, so you need a separate secondary windings for each. For a uC, it doesn't have to float, but the input voltage should be within the power supply range of the uC (check datasheet for exact range). If you connect uC ground to the ground of the reference voltage, this should work out fine for current (which is positive in respect to this potential, although only between 0-0.3V or so), but not so well for the voltage, ST9 is negative relative to this, so you would need to bring this within range with something like resistors or the spare op-amp (IC3D).Quote from: PianoKid1994 on April 25, 2011, 02:49:03 amVery coarse resolution. Something like a DAC would work fine, although it will probably require some modifications to the circuit. To keep things simple, I would probably first build it with regular pots.Quote from: PianoKid1994 on April 25, 2011, 02:49:03 amHaven't watched the video yet, my guess is that's indeed an output enable/disable switch, which is quite convenient because it saves you from turning of the whole power supply or disconnecting wires each time. Both solutions should work fine. If you're going for digital control, controlling a relay from the uC might have the advantage that it makes it easier to add remote control/programmability later.Quote from: PianoKid1994 on April 25, 2011, 02:49:03 amTrimpots. They are for setting the max. voltage/current, the procedure is described under 'Abgleich'.Quote from: PianoKid1994 on April 25, 2011, 02:49:03 amDarlington transistors (you should be able to look this up in any textbook like AoE or even Wikipedia). Used because of their high current gain.Quote from: PianoKid1994 on April 25, 2011, 02:49:03 amI like this design and I know multiple people who have build it and are happy with it. I'm sure there are other good designs out there, maybe even some documented in English, but I haven't found one yet, although I haven't looked very hard either.

author: Joshua
author_rank: Regular Contributor
timestamp: April 25, 2011, 02:07:37 pm
content: Alm, thanks for the reply!If I wanted to build a 30V 4A design, would a pass transistor like this be suitable?http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=BDX33CGOS-NDor this, in a To-3 package for heatsinkinghttp://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MJ11012GOS-NDFor the transformer, where do I buy these things at? A simple search on digikey returned a toroid for $100! (I don't want to pay that much for a transformer, especially if I need two of them) Can I get these cheap somewhere or something?For the temperature sensing, can I just take it out like below? (assuming I use adequate cooling as you mentioned.)For the panel meters, if I get a small transformer, just for the meters, would this work? Also, how would I measure the current with a panel meter, would I have to put it in series? Is it possible to some how use a resistor, and actually measure the voltage?In practice, is there a difference between Constant voltage, with current limit; or constant voltage with constant current? If so, which is this supply? How will I set the constant current/limit with a panel meter? I think dave mentioned something in his recent video about shorting the output terminals-how does this apply?For the BC558 PNP Transistor, will any general-purpose PNP work, or does it need to be the BC558?For the 5V, and 3.3V buttons I was talking about, what I had in mind, was some trimpots set for 5V, and 3.3V output, and also the regular 10 turn pot for full scale adjustment. The micro would 'select' the 5V resistor when I pressed the 5V button, and likewise for the 3.3V. I could then have the output from the 10 turn pot going to an analog input of the micro. If the micro sensed that the pot was changing, it would then select that resistance,and leave it selected, until one of the buttons was pressed. Would that work?Thanks again,Joshua

author: Unknown
author_rank: Unknown
timestamp: April 25, 2011, 06:53:12 pm
content: Quote from: PianoKid1994 on April 25, 2011, 02:07:37 pmI expect issues with the SOA of the BDX33. At DC, max ICwith VCE=30V is slightly over 1A. This should be just OK for this design (1A per transistor in their design at 30V/2A), but is a bit too close for my comfort. The MJ11012 looks like it should work fine, but is a lot more expensive than the TIP142.Quote from: PianoKid1994 on April 25, 2011, 02:07:37 pmSomeone that lives in the same country as you (wherever that is) is probably going to be more helpful. You can sometimes buy surplus transformers.Quote from: PianoKid1994 on April 25, 2011, 02:07:37 pmYes. It's basically an OR gate with three 'inputs', and you just remove one of those, which is logically equivalent to the temperature protection always being off.Quote from: PianoKid1994 on April 25, 2011, 02:07:37 pmSmall transformer will work, remember one secondary winding (so 2x9V can power two panel meters) per DPM. Also need rectification/smoothing/regulation for each.Quote from: PianoKid1994 on April 25, 2011, 02:07:37 pmI believe current limit / constant current is explained in the Agilent appnote 90B I linked to earlier. Constant current is more useful in my opinion (it allows the supply to operate as a current source), but more complex. Yes, for most cheap supplies, you have to short the outputs (to force it into constant current mode) to set the current limit.Quote from: PianoKid1994 on April 25, 2011, 02:07:37 pmSure, nothing critical, it's just a constant current source.Quote from: PianoKid1994 on April 25, 2011, 02:07:37 pmThat should work, although it seems overly complex to me.

author: david77
author_rank: Frequent Contributor
timestamp: April 25, 2011, 10:37:09 pm
content: If I wanted more power from that circuit, say 30V/4A, I'd double the number of series transistors, each with their own emitter resistors, of course. That way you can spread the heat dissipation over a larger area of heatsink and you'd still be able to use the cheap TIP142s.Only thing I'm not quite sure about are R30 & 31. Would they need to be another value?Btw. I'd leave the overtemp protection in, it certainly doesn't hurt. Powerfull linear supplies like that can double as heaters under some extreme load conditions. You could always glue the sensor to the heatsink using epoxy glue or something similar.PS. A good decision to use this circuit I reckon. ELV has a very good name in Germany, their kits and other stuff are at the top end of the line. If something in the German description needs clarification - just shout.

author: Joshua
author_rank: Regular Contributor
timestamp: May 13, 2011, 03:07:56 pm
content: Hey Everybody!It's been a while (I've been really busy), but I managed to build it up on a breadboard. It took me a couple weeks working on it about 5 minutes at a time.ItKINDAworked. I was using many(somewhat dead) 9V batteries instead of a transformer and rectification. I was able to get some voltage adjustment, like from 20-23v. I thought about trying to see what was wrong with the circuit to get full voltage adjustment, but figured it would be pretty much impossible to troubleshoot it without just starting from scratch. I've decided to just go with this circuit and trust that it works, based on you guys' recommendation. (not that I didn't trust that it works, I just wanted to test it out first just for the fun of it)I am now on a quest for transformer(s). I would like to build two of these supplies of 30V 4A. I will connect them in series or parallel based on what I desire at the moment. I am in the U.S. so I will need a transformer rated(?) for 120V (110, 115, whatever). My meter actually measures 123.4V at my outlet.I do not know what kind of transformer I need. Should I get a regular(?) or a toroidal? What should be the ratings I need? Where is the best, cheapest place to get these. I do not want to spend $80 a piece, when I need to transformers. However, I could justify $40 a piece.Once I get my transformer(s) I will probably build up one supply on perfboard as a test. I will then determine what enclosure I want, and figure out my cooling system. I will then try and lay out my own board, and either etch it, or have one professionally made.Any advice on the project, or more specifically the transformer, is greatly appreciated!Thanks,Joshua

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 13, 2011, 04:49:03 pm
content: i wonder how to test high power capability of this thing before putting it in pcb?

author: Zad
author_rank: Super Contributor
timestamp: May 13, 2011, 06:29:48 pm
content: Car lamps, not halogen ones though, just the usual 20W tail lamp types.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 13, 2011, 06:47:51 pm
content: i mean without burning the tracks/breadboard. and i mean at max 120W (say 12V 10A), including stability and heat analysis.

author: Excavatoree
author_rank: Frequent Contributor
timestamp: May 13, 2011, 07:42:54 pm
content: It looks like one would have to go ahead and design the installation for the heatsink-mounted components, (or at least mock it up to be close enough) as well as the transformer and rectifiers. The rest of the circuit could still be on the breadboard for testing/tweaking. Once the design was certain, then a board could be made.EDIT: See the post below mine - that's what I'm trying to say.Interestingly, this is similar in design to the Kepco power supply I've been working with. I am considering posting a thread similar to the Lamda PS thread about it.

author: johnmx
author_rank: Frequent Contributor
timestamp: May 14, 2011, 12:26:20 am
content: I’m also designing my own quad bench power supply (4x 20V@3A). The circuit is not the same as yours. It’s based on an Elektor article but with some modifications.Right now I finished the analog control circuit. The complete power supply will have 2 toroidal transformers. Each one has dual outputs. I added 4 more windings to each transformer which will supply the analog and digital control circuit. Each transformer is rated for 150VA and the biggest advantage over normal laminated steel transformers is the size and weight, almost half.As you can see in the attached image, the pass transistor (2N3055) is mounted on a heat sink. This is crucial for the tests. The 3A conductors don’t pass in the breadboard, just in terminal blocks. Also note the sensor resistor mounted on a terminal block.My next step is to replace the potentiometers by two DACs.Later I can post the schematics if someone would be interested.

author: nukie
author_rank: Frequent Contributor
timestamp: May 14, 2011, 01:05:05 am
content: Isn't E type core better than toroid in terms of noise coupling? We want our PS output to have least noise as possible right? Can anyone explain this?

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 14, 2011, 04:25:58 am
content: yea! thats it! separate the power line and control line.

author: johnmx
author_rank: Frequent Contributor
timestamp: May 14, 2011, 11:56:15 am
content: That’s true, but I will use them anyway because I want to reuse them. 0€ costI could use another transformer for the control line, but I want to keep the power supply the small as possible in terms of size. Since it's a quad isolated bench power supply, I need 4x 12Vac + 4x 8Vac lines for the analog and digital section. So I prefer to have all windings in the same transformer and filter the control supply (after being rectified) with an LC filter.This post explains some differences between both types:http://www.diyaudio.com/forums/power-supplies/45348-toroidal-e-i-core-transformer.html#post509909Also check this white paper about noise reduction in toroidal transformers:http://www.dalitech.com/Resources/Narow%20Bandwidth%20Technology.pdf

author: Wim_L
author_rank: Regular Contributor
timestamp: May 14, 2011, 08:52:27 pm
content: I'll note that using those large power transistors on a solderless breadboard is not a good idea. Even ignoring the ability of the breadboard to deal with large currents, the pins on those big devices are thicker than most, and can cause permanent damage to the springs in the breadboard. That can lead to bad contact on thinner wires later.

author: Joshua
author_rank: Regular Contributor
timestamp: May 16, 2011, 05:44:57 pm
content: Hey everyone,Thanks for the replies! I will get back to them later(I am in the process of re-imaging my computer because of a virus)Anyway, I saw these transformers on ebay, and was wondering if they would be 'approved' by you guys for the project. I believe he has 2 available of each one.150W 110V Toroid Transformer 17V + 17V & 33V + 33Vhttp://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190533592999&ssPageName=STRK:MEWAX:IT#ht_1597wt_1139300W 110V Toroid Transformer 17V + 17V & 38V + 38Vhttp://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190533594073&ssPageName=STRK:MEWAX:IT#ht_1229wt_1139Which one, if any, should I get. If the 300W is a good deal, and I could build a larger power supply, like a 30V 8A, then I don't care to change the design.Thanks for the replies so far. Like I said I will get back to them hopefully tonight, I just had to push these transformers to the top because there is only a day left on them.Thanks,Joshua

author: Excavatoree
author_rank: Frequent Contributor
timestamp: May 16, 2011, 06:05:09 pm
content: Being a Yank, I'm not familiar with the markings on those transformers - do any of them indicate approval from a reputable agency?Because this is connected directly to the mains, I'd be concerned about getting something safe.I need to do more studying about this.......

author: Unknown
author_rank: Unknown
timestamp: May 16, 2011, 06:21:41 pm
content: Quote from: Excavatoree on May 16, 2011, 06:05:09 pmThese transformers look like US spec to me, from which country do you believe the markings are? Or is this the standard 'pardon my ignorance, I'm a product of the US public school system' excuse?As far as I know, they indicate isolation class and that they're for indoors (dry) environments only. Not sure about the left one.One thing to be careful about is the max current per winding. They don't appear to specify it, so it may be something like 2x38V/4A and 2x17V/100mA. 33V, let alone 38V is a bit high for my taste, about 44-45V after rectification. That means lots of heat dissipation for something like 5V. 2x17V should be fine for something like 2x15V or 1x30V, provided it can deliver enough current. Don't forget to divide AC current by two (multiply by 0.6something) to get the correct DC current after rectification.

author: Excavatoree
author_rank: Frequent Contributor
timestamp: May 16, 2011, 06:32:02 pm
content: It's difficult to do a google search for an icon.I meant agencies such as UL, but I know there are others in the world, and a good part may not have the UL symbol, but still be reviewed by someone.I speak in words, not pictograms. Ever hear of people who have trouble with words but can read pictures? I seem to have the opposite problem.I have never built a power supply, mainly out of laziness, and because I've been able to accumulate a collection of relatively cheap power supplies. I guess I need to do a post about my collection.

author: johnmx
author_rank: Frequent Contributor
timestamp: May 16, 2011, 06:35:00 pm
content: You need to know the current rating of each secondary winding. Request this information from the seller.If the efficiency is 100% (ideal):Isec(ac)= 150/(17+17+33+33)=1.5AIsec(ac)= 300/(17+17+38+38)=2.7ABut probably the two windings have different current ratings, it depends of the diameter of the copper wire. From the photograph it looks that the 33V windings are thicker.

author: tekfan
author_rank: Frequent Contributor
timestamp: May 16, 2011, 09:08:04 pm
content: Quote from: AcHmed99 on May 16, 2011, 07:19:52 pmA neat idea is to connect a variac and a potentiometer together so that the variac always supplies the filter caps and series pass transistors with a few volts more than the desired output. You can get a really efficient linear power supply that way.

author: Joshua
author_rank: Regular Contributor
timestamp: June 05, 2011, 10:26:05 pm
content: I'm Back! Sorry for the delays everyone, some things came up, and I ended up having to go out of town, blah, blah, blah.Johnmx, I would love to see a link/schematic to the psu you are a building!Anyway, about the eBay transformers, the seller never responded to my multiple questions - Screw You! I'll give my money to someone else.Alright, so I've found a couple of transformers that might be viable.http://www.newark.com/jsp/search/productdetail.jsp?SKU=38K4930&CMP=AFC-OP&CMP=AFC-OPDatasheet:http://www.farnell.com/datasheets/74774.pdfTOROIDAL TRANSFORMERPower Rating:300VASecondary Voltages:30Transformer Type:ToroidalSecondary Current AAC:5AOutput Current, Secondary Series:5ASupply Voltage:115Vhttp://www.antekinc.com/details.php?p=66Datasheet:http://www.antekinc.com/pdf/AN-3230.pdfOutputs 2xPower 300VAOutput Voltage Current30V 5.0ATorroidSince these are both transformers with dual secondaries, I believe I can actually use just one transformer that will take care of both supplies. Am I correct in that?Also, they are both rated at 5A. Does that mean 5A total, as in both secondaries together can not pull more than 5A? Or does it mean 5A per secondary, giving a total possible current draw of 10A?Also, here is a link to the product listing of Antek. Are they a quality brand?Also, when multiplying 30V x 1.414 I get ~42V peak to peak. Is that to high-should I go with like a 24V secondary output, to get ~33V?Joshua

author: bilko
author_rank: Frequent Contributor
timestamp: June 05, 2011, 10:59:16 pm
content: Quote from: PianoKid1994 on June 05, 2011, 10:26:05 pmYes, you can use 1 transformer for both suppliesTransformer is rated at 300VA, that's 150VA per winding, so at 30V you can draw 5A from each winding

author: Joshua
author_rank: Regular Contributor
timestamp: June 05, 2011, 11:26:54 pm
content: Well that seems like it might be the 'dope' ! I neglected to think through the ratings logically like you did...Does anybody have any thoughts on these particular brands?

author: Unknown
author_rank: Unknown
timestamp: June 07, 2011, 12:16:20 am
content: Keep in mind that isolation between secondaries tend to be much less than isolation between secondary and primary. This means that you may get troubles if there is a significant potential difference between the two outputs. The closest commercial lab supply I have allows 350V DC + peak AC between ground and any output. The rating would be much less with just two secondary windings only separated by some enamel.

author: Joshua
author_rank: Regular Contributor
timestamp: June 11, 2011, 02:53:02 am
content: Quote from: alm on June 07, 2011, 12:16:20 amIs this something that is spec'd in the datasheet?(I can't seem to find it) Also, for my own learning, how does this happen. Does one secondary actually induce a small voltage in the other, causing a potential?Say I order one and there is a potential, how much are we talkin about, what are the ill effects, and is there a way to work around it?Joshua

author: Zero999
author_rank: Super Contributor
timestamp: June 11, 2011, 10:50:14 am
content: It's often not specified but 350V seems reasonable, although that's not enough to ensure safety when working with the mains i.e. you shouldn't connect one secondary to the mains and expect the other one to be safe to touch.

author: Joshua
author_rank: Regular Contributor
timestamp: June 12, 2011, 01:23:30 am
content: Quote from: Hero999 on June 11, 2011, 10:50:14 amThat makes sense.Okay, so how does this affect my application? Is it a safety thing, or a practical thing? In other words, is this a problem, in my application, because it might somehow be unsafe, or because it will cause the dual supply to function correctly?For either of the two above, is there a way to fix the problem, as in work around it?

author: Zero999
author_rank: Super Contributor
timestamp: June 12, 2011, 08:12:06 am
content: It's only a problem if you connect one output of the dual power supply to a dangerous voltage source and expect the other to still be safe to touch or if you connect the outputs to different parts of a circuit with more than around 350V between them.

author: Joshua
author_rank: Regular Contributor
timestamp: June 13, 2011, 02:28:34 am
content: Quote from: Hero999 on June 12, 2011, 08:12:06 amOk, so as long as I am careful, then I guess I should be fine. (?) Anyway, does anybody have any additional thoughts regarding these two transformers, such as one brand is totally better, or anything? Or anything about the project in general...I think I will order one of these, but haven't decided which one yet, unless someone brings a third option into the pile.

author: Joshua
author_rank: Regular Contributor
timestamp: June 17, 2011, 02:57:57 am
content: Well I ordered the AnTek transformer, and some other odd parts from Mouser. I might've ordered from element14, but last time ordered like 40 capacitors that were tiny, they charged me like $13 shipping, every value came in it's own padded envelope and all of them came in a box. It was outrageous. Anyway, I am awaiting the parts to build up a test(safely, of course!).

author: hannobisschoff
author_rank: Contributor
timestamp: June 17, 2011, 09:21:35 am
content: Hey man. I don't actually want t give you advice or anything, but I just want to wish you luck in your project. A power supply is one of the projects (if you built it well) that will last you a long time.

author: Joshua
author_rank: Regular Contributor
timestamp: June 20, 2011, 03:59:44 am
content: Quote from: hannobisschoff on June 17, 2011, 09:21:35 amThanks for the kind words!Ok, so I am trying to layout a board so I can try and etch it for this project. Basically I want to build a board for the 4 rectifier diodes and large 4700uF Capacitor. Here is the datasheet for the cap I will probably order:http://products.nichicon.co.jp/en/pdf/XJA043/e-vr.pdfHere's the problem, I can't figure out the dimensions. It says on the second page that the cap could be 22x50, or 25x40. However, when I go back up to the actual drawing I cannot tell how this correlates in anyway. Is there something I am missing?Also, when posting a url, how do people make it so that the url is different words. For instance instead of sayinghttp://www.google.com, How do I make it sayGooglebut still be a hyperlink?Joshua(Oh, in case you missed my other thread, I have changed my 'username' to Joshua. I felt that PianoKid1994 was somewhat childish, and not very professional. Also, I figured I might as well make it my real name since that's what I sign my posts anyway with...)

author: joelby
author_rank: Frequent Contributor
timestamp: June 20, 2011, 05:27:53 am
content: Quote from: Joshua on June 20, 2011, 03:59:44 amI find it safest to wait until you've actually got the parts in hand. There are some very ambiguous datasheets out there, and some details are only obvious once you can check the part. If they're cheap, order a few different sizes - it never hurts to have spares!QuoteHave a look at theAdvanced BB Codespage. Basically, you do:Code:[url=http://example.com/]Link text

author: johnmx
author_rank: Frequent Contributor
timestamp: June 20, 2011, 09:19:44 am
content: Quote from: Joshua on June 20, 2011, 03:59:44 amThe data sheet is clear about that. What is the order code of the capacitor that you are going to buy?I believe you want 4700uF/63V, so there are two options:Order code: UVR1J472MRD -> 22x50 -> Rated ripple current = 3.4AOrder code: UVR1J472MRD6 ->25x40 -> Rated ripple current = 3.2A

author: Joshua
author_rank: Regular Contributor
timestamp: June 21, 2011, 03:16:58 am
content: I got the transformer today fromAntektoday! Pictures are below...Overall I am satisfied with the company. I have yet to form an opinion on the actual transformer as I am not experienced in such things. Only time will tell about the performance. Cost of the transformer: $47.00 USD shipped. I placed the order Thursday morning, and received it this Monday morning. It was very well packed for shipping.I also ordered some parts from Mouser today, and will hopefully receive them in a couple of days. In the mean time, I am working on trying to layout a board in DesignSpark(because it is free and does 3d) so I can do some testing. Does it look alright? or does it look like it's gonna blow up in my face...

author: johnmx
author_rank: Frequent Contributor
timestamp: June 21, 2011, 09:22:05 am
content: Joshua, don’t do those tests on top of the bed, it can catch fire with the smallest electric arc.

author: Joshua
author_rank: Regular Contributor
timestamp: June 21, 2011, 02:54:57 pm
content: Oooooh good point. I guess I was so careful as to not get shocked, I had neglected the issue of fire. Thanks for pointing it out.

author: Joshua
author_rank: Regular Contributor
timestamp: June 23, 2011, 03:33:49 am
content: Hey everybody, while I'm waiting on a couple of parts to arrive(hopefully tomorrow), I decided I might as well learn a CAD software and route a board to etch.I decided to use DesignSpark for this one because it's free, and will give me a 3d cad file I can pop into AutoDesk Inventor to view in my enclosure when I get to that point. Anyway, the purpose of this board is to get me the rectified DC so I can build the rest of the circuit on my breadboard.Basically I have two boards in one.The first(left) has a 3 pin terminal block with 30V AC coming in from my transformer, and gets rectified with the diodes, and is smoothed by the large capacitor.30V Dc then exits with another 3 pin terminal block. Both the input and output terminal blocks are connected to the two outside connections, for maximum isolation.The second(right) also has two 3-pin terminal blocks, and this one has 18v ac, center tapped, coming in to the three pins from another transformer. It is then rectified and smoothed as well. (This 9v,0,-9v is the supply for the op amp)I have made all my tracks 60 mil wide, and the ground plane has an isolation of 90mil. Are these amounts enough, or do I need to beef it up a little? There is also half an inch between the two sides. I put a ground plane on so I didn't have to etch as much copper away. However, is it bad to have a ground plane around both the 30v ac input, and the 30v dc output? The ground plane for the left side isn't actually connected to anything, because I can't figure out how to make two different ground planes in DesignSpark. Although DesignSpark is more intuitive on somethings, I think I'll go back to playing with Eagle, it is definitely more powerful, and this is the first board I've ever laid out.Below is the same board, with and with the copper pour, for clarity of the tracks.The top copper layer represents jumper wires I will install.NOTE: DesignSpark exported it small, working on making it larger...Joshua

author: johnmx
author_rank: Frequent Contributor
timestamp: June 23, 2011, 12:57:48 pm
content: My advice:

author: ivan747
author_rank: Super Contributor
timestamp: June 23, 2011, 01:11:04 pm
content: Quote from: johnmx on June 23, 2011, 12:57:48 pmYou can have that trace below the diodes. It is safer to keep away from the edges.

author: Joshua
author_rank: Regular Contributor
timestamp: June 23, 2011, 02:40:17 pm
content: I thought about putting the track under the diode, but since I have never etched a board before, I wanted to keep everything away from each other as much as possible. Is it dangerous because it's easier for me to touch and get shocked?It never occurred to me to route the track that way, John. Thanks for the suggestion, I like it.

author: Richard W.
author_rank: Regular Contributor
timestamp: June 23, 2011, 04:35:19 pm
content: My suggestion:Use a bridge rectifier instead of 4 separate diodes. Cooling the flat package is much easier.(something like this one:http://www.conrad.de/ce/de/product/161041/)A few smaller capacitors are better than one large.C3, C4, C5, C6 should be as near as possible to the 78/79 regulator.

author: Joshua
author_rank: Regular Contributor
timestamp: June 24, 2011, 03:47:50 am
content: John, I have taken your advice and moved the track, as demonstrated below.Richard, I have removed the smoothing caps, and will put them on the breadboard next to the regulators.How does it look now?

author: Richard W.
author_rank: Regular Contributor
timestamp: June 24, 2011, 08:58:42 am
content: How do you want to cool D1...D4? Cooling will be necessary.Use a rectifier which you can screw onto a heatsink.I don't understand why do you want a second board with D5...D8?Put the diodes, the smoothing-capacitors and the filter-capacitors on the same board as the 78/79 regulators. Avoid long distances between the filter-capacitors and the regulators and it will be fine.

author: Joshua
author_rank: Regular Contributor
timestamp: June 24, 2011, 02:37:42 pm
content: Richard,Thanks again fior the reply. I like the idea of using a rectifier as you have suggested. The reason I have not already moved forward with this idea is that this board is just for testing. On the final board I will have everything together and close to where it should be as you say. This board is just so I can finalize my circuit and everything on my breadboard. It also gives me a chance to practice etching a board.

author: johnmx
author_rank: Frequent Contributor
timestamp: June 24, 2011, 02:43:39 pm
content: Joshua, you can make that PCB with half of the size.

author: Joshua
author_rank: Regular Contributor
timestamp: June 26, 2011, 03:11:21 am
content: Quote from: johnmx on June 24, 2011, 02:43:39 pmVery True. I have now made it a 3x4" instead of a 4x6". I also went back to eagle because it is much more powerful, even though designspark was somewhat more intuitive on things. Anyway here's my 'new' board. I will probably make do with using some 1n4001 diodes on my breadboard for right now, while I gather the materials to etch this board. I would put it all on my breadboard, but the capacitor and diode leads are too large for the holes. So does it look good to everybody? What is the minimum trace width I should feel comfortable with on my first board, specifically the text?Also, when I print out the board on my laserjet, the drill holes for the p600 diodes(the large ones on the left) do not show up. Does anyone know what could cause this?Joshua

author: Joshua
author_rank: Regular Contributor
timestamp: September 05, 2011, 12:14:36 am
content: Hello Everyone!It's been a loooonnnnnggggg time! Anyway, I got the above mentioned boards done on perfboard, and am actually troubleshooting the supply on breadboard.Here is the situation.I have everything connected on the breadboard, and the voltage regulation works great! I can go from 30V all the way down to around 15-17mV. First is that normal, to only be able to go that low? I can't get it to go any lower than that and my OCD desires 0.00 volts.The main problem is that anytime I connect the smallest of loads the power supply totally drops out down to ~15mV. And when I say a small load, I mean even just a small little light bulb(incandescent). Since I do not fully understand how the circuit works, I can't really begin to trouble shoot it. Since I can't read german, that makes it hard as well. Is this a common problem with an easy fix? Also, would somebody that understands the circuit care to explain what the two LEDs represent? Sometimes they are on, and sometimes they are not.I can post pictures if necessary to help aid in the guessing of the problem.Thanks,Joshua

author: IanB
author_rank: Super Contributor
timestamp: September 05, 2011, 12:47:08 am
content: What circuit do you have that will work successfully off a 15 mV supply? (Hint: it will be no circuit with transistors in it.)There is no practical reason I can think of to go below a supply voltage of about 0.5 V.I'm even more interested in what circuits you have that will work off a 0 V supply? Do you have plans to invent free energy?

author: Joshua
author_rank: Regular Contributor
timestamp: September 05, 2011, 12:50:50 am
content: Thanks for the reply. I understand your point. The perfectionist in me wants to 0.00 - 30.00I guess I just thought that when looking about making my own supply, I seen alot...'A supply that goes down to zero is very useful.' I suppose that when they said 'zero' they just meant 'zero-enough'.Also, I have done some measurements and found something that appears to be significant. I will post shortly...

author: IanB
author_rank: Super Contributor
timestamp: September 05, 2011, 12:55:33 am
content: This is an area where you would switch to a more specialized tool. Generating regulated voltages in the mV or uV range may have uses, but you would not use a general purpose bench supply for that, you would use a more specialized power supply specifically for that job.

author: Joshua
author_rank: Regular Contributor
timestamp: September 05, 2011, 01:16:23 am
content: Quote from: IanB on September 05, 2011, 12:55:33 amAaaah, gotcha. Thanks for clearing that up.I connected an led across the output in series with a 220R resistor. Here is a graph of the mA over voltageThe only thing that was adjusted to create this graph was the voltage-regulator potentiometer. As the voltage grew, so did the current. Once the current got to about 20mA, it grew no further. Also, at that point the voltage was about 6.4. I could not increase the voltage any further as well. Turning of any pots availed nothing. I could not increase the voltage at all, or the current. Only by lowering the voltage below ~6.4 could anything change. What could this mean?When there is no load connected I can adjust the voltage all the way up to 30v.Joshua

author: Richard W.
author_rank: Regular Contributor
timestamp: September 05, 2011, 08:01:50 pm
content: QuoteLED D13 is on, when the power supply operates in constant voltage mode. (In this case you controll the output voltage. The current is only limited by the load or the capatibilities of the supply)This led should be on, even if you have connected a load or not.LED D12 is on, when the power supply operates in constant current mode. (In this case, you controll the current which flows to your load)This led is on, when you have connected a load, and reduce the current with the current controlThis LED also indicates, when you want to draw more current than possible.For the troubleshooting:What's the voltage at C12?What's the voltage at C7?What's the voltage at C8?Have you chosen the right resistors from "Tabelle 2" ?Which resistors have you used as R30 / R31 ?

author: Joshua
author_rank: Regular Contributor
timestamp: September 06, 2011, 01:10:01 am
content: Quote from: Richard W. on September 05, 2011, 08:01:50 pmThanks for the reply. So D13 is on when I am in constant voltage mode. I can adjust the voltage all the way up from 0 - 30v and the light should be on regardless of load or no load. D12 is on when the current limiting has come into play. If I lower the current level with the pot, it should come on when I reach that value. I.E., if I connect a load that will pull 1A and I have my current limit set to 500mA, the supply will only allow 500mA to flow, and the led will light indicating that it is actually limiting current. Is all that right? To clarify, is the current functionconstantcurrent, or currentlimit?I mean, will the supply only cap the max amount of current allowed, or will it try and supply the designated current continuously and change the voltage to make that happen(within the limits of the supply)?Quote from: Richard W. on September 05, 2011, 08:01:50 pmThe voltage at across C12 is 43VVoltage across C7 and C8 are 5V, giving me a 10V split supply for the op amp.I have chosen the resistors from Table 2 based on the 30V/2A version and have checked that the values are correct. Just to make sure, do Germans use commas instead of periods for decimals? For instance, for R8 it says to use 6,8k. I am assuming that this equates to 6.8k but just wanted to make sure.Before I wasted any more of someone's time, I went through with the schematic and highlighted each connection after ensuring that it was correct. I found 2 or so problems and corrected them. I am not absolutely, positively guaranteeing that there are no errors, but am pretty sure there is not. Here is the problem now. D12 is constantly lit, and the voltage adjustment no longer works. I can vary the voltage from -0.5v to -150mV . Turning the current adjust pots do not do anything except the trimpot(R6), when I bring it do the far end of its travel on one side it dims D12 to about half of what it was. What could cause this? A fried component, an incorrect setup,...??The current source(R1,2,3; and the transistor) is sourcing ~8mA but I guess it is all being sunk through D12? Also, I traded out the TIP142's just to make sure that they weren't blown or anything.Here is my somewhat vague understanding of the circuit. The current source supplies a constant current of ~8mA to the bases of the pass transistors. If/when the voltage or current needs regulating, the op-amp sinks some of this 8mA to itself, effectively 'stealing' the current from the transistors. I have a couple of (possibly silly/stupid) questions. I understand how to use a transistor as a current source(as used in this circuit), but I don't understand how the change in base current of the transistors can change the voltage. Also, how does the op amp know how much current is flowing, in order to regulate it. One more: Based on my(very limited) op amp knowledge, the op amp has to have some sort of feedback, otherwise a few nV difference between the 2 inputs would make it swing immediately to the respective power rail. How are the two op amps getting their feedback? Could someone recommend some reading material on the subjects. I could not find anything to help me understand these things.Thanks so much,JoshuaP.S. here is another copy of the schematic so you don't have to go to page 1

author: IanB
author_rank: Super Contributor
timestamp: September 06, 2011, 01:14:08 am
content: Quote from: Joshua on September 06, 2011, 01:10:01 amYes. Most European countries use this convention, with the exception of the UK.

author: Richard W.
author_rank: Regular Contributor
timestamp: September 07, 2011, 09:04:42 am
content: voltages and resistors seem to be okay.Quote from: JoshuaIt is constant current, NOT just limit. The maximum voltage is the voltage which you have set with the voltage-pot.Asumed you set the current to 500mA and the voltage to 5V:with a 1Ohm resistor connected there is a current of 500mA and a voltage of 0,5Vwith a 100 Ohm resistor conntected, there will be a current of 50mA at a voltage of 5V

author: Joshua
author_rank: Regular Contributor
timestamp: September 08, 2011, 02:36:16 am
content: Quote from: Richard W. on September 07, 2011, 09:04:42 amAlright, but how do I tell it which mode I am want-constant voltage or constant current? Also, with the voltage set to 5V in constant voltage mode, can I limit the current to, say, 200mA? Same with constant current, can I set the current to 200mA and limit the voltage to,say, 3V?

author: IanB
author_rank: Super Contributor
timestamp: September 08, 2011, 02:45:35 am
content: Quote from: Joshua on September 08, 2011, 02:36:16 amYou don't really have a mode that you can select with a switch or anything like that. There is a limiting voltage and a limiting current. At any given point in time either the voltage limit is active or the current limit is active. It is not possible for any other situation to exist.Basically what will happen is that if you turn up the voltage, the current will increase until either the current limit is reached or the voltage reaches the maximum setting.On the other hand, if you turn up the current the voltage will increase until either the voltage limit is reached or the current reaches the maximum setting.If you carefully think through the way this works (the way thismustwork), you will see that all eventualities are catered for.

author: Joshua
author_rank: Regular Contributor
timestamp: September 08, 2011, 03:15:53 am
content: Quote from: IanB on September 08, 2011, 02:45:35 amAwesome! That makes sense. Thank you for the great explanation.Now back to seeing what is wrong with my circuit. Might be a day or so though, got to go to a funeral tomorrow so probably no more progress tomorrow. I'm getting really excited/anxious because I really want to move to the 'fun' stuff, like playing around with a working circuit and trying to improve it, not troubleshoot. (I know, I know, I learn so much more from troubleshooting. Don't get me wrong, I love this stuff, but some stuff just seams more 'appetizing') Also, I've got some other projects in the pipeline, but there's no way I can probably do them without some sort of variable supply.Somewhat unrelated, whats the protocol on this circuit I'm using. What I mean, is that this circuit, from what I gather, is from a kit(?) by ELV in germany. If I take this circuit as a base, and slightly modify it to fit me a little better, can I then release all of the design files/mechanical case drawings, etc... and it be true 'open hardware'? I am definitely doing all of my projects as open hardware so I just wanted to know what the technicalities were.Joshua

author: Joshua
author_rank: Regular Contributor
timestamp: September 19, 2011, 03:34:55 am
content: Okay, so I think I've got it working on the breadboard, but now have to order some higher wattage resistors.Anyway I have a question: This power supply is made to built in two configurations: 15V 4A or 30V 2A.My original plan was to mod the circuit to do 30v 4A. Note: I will be building two identical versions to have a dual supply.That means that I can either have one of these three setups. The first two are the one specified in the circuit.I. 15V 8A parallel or 30V 4A seriesII. 30V 4A Parallel or 60V 2AIII. 30V 8A parallel or 60V 4AI am leaning toward one of the first two right now. It just seems like it would be too difficult for me right now with all of the high power design, and heat sink design, etc.... Anyway, my question to you is, which one would you build? In other words, what do/would you use more often?I've added a poll.Joshua

author: Lawsen
author_rank: Frequent Contributor
timestamp: September 19, 2011, 04:57:50 am
content: I would use the Bourns potentiometers to adjust voltage and current.http://www.bourns.com/ProductFamily.aspx?name=potentiometersToroidal power transformers are usually very compact, efficient transfer of energy between input primary winding to the output secondary winding and the magnetic flux is confined to the center of the core, "doughnut hole." I have seen expensive stereo amplifier with the French "Atoll" brand uses these toroidal power transformers.http://www.tabtronics.com/TECHNOLOGY/ElectromagneticBasics/ToroidalTransformerBasics/tabid/112/Default.aspx#the_toroidal_coreI have built a non adjustable linear, regulated power supply in my experience. Reading your project is exciting. Are you going to etch your own printed circuit with wide traces for lots of current?

author: Lanman
author_rank: Contributor
timestamp: September 20, 2011, 12:25:30 am
content: Great project Joshua. It's been interesting following your progress.Dave

author: mrflibble
author_rank: Super Contributor
timestamp: February 08, 2014, 09:23:10 am
content: This is an interesting design, looks like fun to try! I went over the schematics yesterday, and IthinkI more or less understand it. Except for one thing.I take it D9 & D10 are meant as protection against fast transients on the load? But it looks like in the current configuration it's not going to do very much. Either that, or I am missing something.Shouldn't the cathode of D9 be connected toST8(low side of the 1 Ohm sense resistors)? That would clamp the sense voltage across the resistors to about 2 diode drops, which would correspond to about 4.2 A per transistor.Any ideas?

author: jkf1000
author_rank: Regular Contributor
timestamp: April 20, 2014, 09:59:30 am
content: Hi all, first time post on the forum but wanted to add my bit, I found this circuit from a google search and am very impressed by it, I found this thread when the first build was almost complete, really interesting reading. I didn't bother breadboarding, but instead went first to veroboarding. Worked first time out, which was a suprise given a few changes I implemented. Firstly a full wave bridge rectifier was used after the secondary, much easier to cool, and instead of the recommended 3X 1ohm emitter resistors I used single 0.22ohm 5 watt ceramics, not sure if the 0.11ohm change makes a significant difference or not to the current sensing but seems to work fine.I am still undecided which final range to use, so the resistors used to set the range for either the 30v or 15v variant have been mounted on vero pins so if I decide to just use the vero built version, I can easily change the options around without lifting the board. My recycled transformer has secondary taps for 32v or 16v, so I have the option to change if I need to, my primary concern is the heat generated by the output transistors running a moderate load at lower voltages, say from 3.3v to 12 volt range. That is a significant voltage drop/dissipation accross the pass transistors.Next up is a case design, but initial impressions of the circuit into my adjustable load are very promising, I will try and post some pictures as my project progresses..Karl