Where to go from here - Page 1
Forum section: electronics / beginners

author: Mery128
author_rank: Newbie
timestamp: June 13, 2014, 10:38:14 pm
content: So I recently started watching Dave's videos, and have always had a bit of an interest in electronics but never really had the money to fund any "fiddling" or "tinkering" or getting any kind of decent equipment but have found that now I do. So I took Dave's advice and have gotten myself an oscilloscope and I have a cheapy "won hung-lo" meter which I plan on replacing with a pair of Extech EX330s soon(TM). But Im kinda running into a problem of "Where do I go from here" I have some projects in mind but I don't really have the experience designing circuits yet and was wondering if anyone had a suggestion of what to do to get familiar building and designing power supplies (a keen interest of mine actually). So, I have looked at some of the talking electronics projects but Im just really 100% sure where to go with things at the moment and had a bit of a "So I got my oscilloscope, now what?" moment last night and thought Id make my first post here on the forums and see about getting some input on it.Also as an aside I would like to say: Dave I love the videos I've seen on youtube, Im glad I found them and want to say thank you for making them, they inspired me to rekindle my interest in electronics.

author: Dongulus
author_rank: Regular Contributor
timestamp: June 13, 2014, 11:23:01 pm
content: Obtain some busted electronics and try to fix them. Repairing electronics is a great way to learn a lot quickly.

author: zapta
author_rank: Super Contributor
timestamp: June 13, 2014, 11:42:58 pm
content: What kind of projects do you think will be more interesting for you, audio (e.g. amplifiers), digital (counters, logic, blinking stuff), radio (transmitters or receivers), general analog (e.g. build your own power supply), etc.Once you figure out, you can find schemas for simple circuits that you can build and debug. This will force you to learn enough to complete the projects.

author: Mery128
author_rank: Newbie
timestamp: June 14, 2014, 12:06:47 am
content: I have some interest in digital, I snagged an arduino board and have fiddled with that some. Id say for the time being Im interested mainly in building test gear and power supplies and such. The idea of snagging some busted electronics and fixing them up sounds like it would be a good fun time. Would you guys say that throwing together pretty much any circuits I can find schematics for on a breadboard and then tinkering with them from there is a pretty worthwhile endeavor?

author: Flump
author_rank: Frequent Contributor
timestamp: June 14, 2014, 12:14:27 am
content: these two should get you started, the transistor one especially.editi just tried to attach two free pdf books but it failedso google these and download them.1-100TransistorCircuits.pdf50-555Circuits.pdf

author: Lee697
author_rank: Regular Contributor
timestamp: June 17, 2014, 03:43:45 am
content: I find more satisfaction in making circuits that have a purpose too... After I kept killing SLA batteries leaving lights on in my observatory, I made a timer switch, that turns off after a period. About to make another to cut power to the soldering iron after a few hours too....Lee

author: nsayer
author_rank: Regular Contributor
timestamp: June 17, 2014, 02:38:04 pm
content: One place I turn for inspiration is the shared projects feed at oshpark.com. They're not always documented very well, but there are some interesting ideas there.

author: Lee697
author_rank: Regular Contributor
timestamp: June 17, 2014, 10:13:01 pm
content: Quote from: Mery128 on June 13, 2014, 10:38:14 pmMy advice would be, if you haven't already - watch Daves video on how to not blow up your oscilloscope....(#279)....

author: GreyWoolfe
author_rank: Unknown
timestamp: June 18, 2014, 12:03:00 pm
content: Check out W2AEW's videos. I built the curve tracer circuit that he did and it is a handy little project.

author: malch
author_rank: Regular Contributor
timestamp: June 18, 2014, 03:34:55 pm
content: A useful project is a MegaSquirt kit to control your car's ignition and fuel.

author: Mery128
author_rank: Newbie
timestamp: June 21, 2014, 06:05:55 am
content: @Lee697 That actually is the very first video I watched. I was a little stunned to be honest, I had never thought about the fact that things you plug in all tie into the same ground line like that.@Flump I've actually read those and fiddled with the circuits some they're really interesting.I have been really wanting to build a power supply, I've been looking at some schematics that I've found on google. I somewhat would like to know if there's any good literature on power supply design, or maybe some suggested reading for that. I'm still somewhat shaky on the concept of why some components are selected for circuits. I have a feeling reading all of the art of electronics may make this more clear but something that's more concise would be awesome too.One more thing I'm somewhat curious about: Circuit Simulation.Is circuit simulation a valuable tool or is it more of a trap for new players? Half the time I've thrown diagrams into a simulator it seems like they don't function as described or it seems like most of the components are actually pointless in the simulation. (I am willing to accept this may also be me not understanding quite how everything is supposed to work together)Also thank you all for your input on this it's very much appreciated.Edit: Corrected spelling and added Circuit simulation paragraph.

author: RazSlack
author_rank: Contributor
timestamp: June 21, 2014, 10:34:31 am
content: Quote from: Mery128 on June 21, 2014, 06:05:55 amThere's two kinds of power supplies: Feedback linear series pass transistor, and switch-mode. When designing a power supply, first you have to think what it has to accomplish. Does it have to go down to 0 volts? How many channels do you want? How much space can it take up?I'd recommend starting with a linear power supply, unless you want a PSU that can output at least 300 watts, and they're easier to understand.

author: tautech
author_rank: Super Contributor
timestamp: June 21, 2014, 12:01:04 pm
content: Quote from: Mery128 on June 21, 2014, 06:05:55 amJust build a simple PSU for starters. Hunt around for a pair or old 12V downlight transformers.(get proper transformers not SMPS)Wire their outputs in series, rectify, smooth and simple adjustable linear regulator and hey presto close to 30V @ 4 amps. Use a thermal and SC protected regulator.Stick it all in a nice case(not too small) and add panel meters, 10 turn pot, extra outlets etc later as you need/ can afford them.Don't worry about adjustable current current yet, you may find you don't need it.For the first power up of a circuit you have built, just add a small Auto bulb in series as over-current limiter/indicator. That will keep the magic smoke in.The Art of Electronics is an excellent reference/ideas book, but it is likely to do your head in until you are more experienced. Apply the KISS principle.From that you have posted it seems Power Electronics is your interest.Great fun controlling 100's to 1000's Watts with logic and power devices!Become confident with just glue logic and Fets etc then proceed to micros as your knowledge grows.Have fun and welcome to the forum.

author: radioFlash
author_rank: Regular Contributor
timestamp: June 21, 2014, 12:51:28 pm
content: As far as power supplies, you can look up datasheets / example circuits using voltage regulators such as LM317 and LM723.Here's an interesting document on Power supplies:DC Power Supply HandbookHP / Agilent Note 90Bhttp://cp.literature.agilent.com/litweb/pdf/5952-4020.pdf

author: Lee697
author_rank: Regular Contributor
timestamp: June 21, 2014, 02:19:42 pm
content: Quote from: Mery128 on June 21, 2014, 06:05:55 amI saw it after I tried to blow mine up! I was measuring the voltage across a resistor (not at ground) with one PSU no prob, then switched PSUs little did I know the second one was mains-earth referenced.... couldn't work out why every time I touched the ground clip to this resistor the PSU fan would power up and it would be delivering 2A... I'm glad I found out without destroying something....

author: Mery128
author_rank: Newbie
timestamp: June 21, 2014, 04:40:29 pm
content: This might be better for a new thread but, what I'm kinda not groking here is say in this circuit:http://www.rason.org/Projects/powsupply/powsupply.htmWhy would one use the 3055 transistors? it looks like they're hooking back straight into the output of that rectifier so ultimately they're just pulling the electricity straight through them, if thats the case 1) Wouldnt they just blow up? (I suppose they're beefy little buggers) 2) When you're designing a circuit what are you going to look for in a transistor data sheet to decide "This is the transistor I want".I suppose Im looking to learn how to fish with these things rather than just be handed a fish.@radioFlash I havent gotten to read that document yet, hopefully it will maybe make this more clear. Thank you@tautech Yep I think I am a power junky lol. I also somewhat feel that it would be a really good idea to understand what seems to be a fundamental part of any project before moving on to the other parts of projects. (IE: What do all electronics need. Power. \^.^/ )@RazSlack Im probably interested in something that can do around 100W~200W but I think for now Im going to get the parts to build the LM723 supply I linked and am going to fiddle with adjusting it some. To be honest I dont even know the benefit of being able to drop to zero volts on a power supply so Im sure I have alot to learn!

author: tautech
author_rank: Super Contributor
timestamp: June 21, 2014, 09:00:12 pm
content: Quote from: Mery128 on June 21, 2014, 04:40:29 pmThe 3 x 3055's are configured as 2 series pass and 1 driver.Really forget that build there are much better.Base your build on a 317 or 338 and let the IC do the work.Get the datasheets and have a study.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 21, 2014, 09:26:47 pm
content: Quote from: Mery128 on June 21, 2014, 04:40:29 pmThe LM723 is the voltage regulator driver chip. It was a predecessor for the chips that tautech is touting. Perhaps he is too young to remember the roots of the integrated circuit family.The CONTROL output from the 723 (pin 10) drives Q1, and then Q1 drives the main PASS ELEMENTS Q2 and Q3. The main path of current is from the output of the bridge rectifier (D1-D4), filtered by C1-C4, controlled through Q2 and Q3, through R6 and R7 in parallel, and out to the load. The 723 chip senses the voltage across R6/R7 which indicates the current.The three major parameters we look for when selecting a transistor are1) Voltage rating2) Current rating3) Current gainThe reason that circuit uses Q2 and Q3 in parallel is because a 2N3055 doesn't have enough current rating by itself, but two of them working together (in parallel) will meet the requirement.

author: tautech
author_rank: Super Contributor
timestamp: June 21, 2014, 09:51:37 pm
content: Quote from: Richard Crowley on June 21, 2014, 09:26:47 pmNot at all Richard. I cut my teeth on octal base valves.I respect your detailed circuit analysis, however the OP and the thread name suggests limited knowledge and experience so IMO it is best to apply the KISS principle.With a 317/338 it is possible to build a "rats nest" PSU to get him started, try that with a 723.

author: Mery128
author_rank: Newbie
timestamp: June 21, 2014, 10:19:05 pm
content: While KISS is a good idea. Im not afraid to go look up complicated concepts as need be. I personally learn better in my opinion from the "this is why we do this" than "just do it this way" approach. All of the input is greatly appreciated, I think Im going to pick up a few of the components discussed here and see what I can throw together.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 21, 2014, 10:22:06 pm
content: Quote from: tautech on June 21, 2014, 09:51:37 pmNo offense meant, tautech.I agree that 723 is pretty long in the tooth and there are more modern (easier/faster/better/cheaper) solutions to that problem.That is, indeed, a decades-old ham-radio solution.@Mery128, you would probably be better off with a more modern circuit design with modern components.For example, here is a more modern version of that circuit...http://www.circuitdiagram.org/12v-10a-power-supply.html

author: Mery128
author_rank: Newbie
timestamp: June 21, 2014, 10:36:51 pm
content: Can that be re-designed pretty simply with swapping the LM7812 for a variable voltage regulator? Perhaps having to change out the transistors to match the new parameters of the new regulator? Or maybe that's more of my mystery to solve looking through datasheets. Also for what its worth, I wasn't really married to that design I linked, it just seemed like a good starting point to try and figure out "why are these parts picked?"

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 21, 2014, 10:40:33 pm
content: Yes, there are variable-voltage versions of that same circuit. Use the image search feature of Google and look for variable-voltage power supply circuit or schematic diagram. You will find enough to keep you busy for the rest of the day.

author: Mery128
author_rank: Newbie
timestamp: June 21, 2014, 10:48:16 pm
content: One more question on that, is circuit simulation a worthwhile endeavor on these kinds of circuits or is it ultimately a waste of time and I'd be better served buying real components and blowing them up on my breadboard?

author: tautech
author_rank: Super Contributor
timestamp: June 21, 2014, 10:59:50 pm
content: Fuse the AC supply and let a modern regulator give you the additional protection needed.ie. thermal and SC.Once built you can use your scope to measure ripple and fine tune the main smoothing cap value at full load. Use Auto bulbs for loads.That way you won't need to shell out for larger than necessary E-caps at crazy prices.Think also of paralleling 2 or more caps to get the results desired.Sure you can do the calcs but at this stage its about getting up and running.Many use simulation and it is a worthwhile tool for complex stuff.Use the tools you have to gain understanding.Use datasheet typical applications as a gospel of stuff that works.

author: G0HZU
author_rank: Super Contributor
timestamp: June 21, 2014, 11:35:37 pm
content: Quote from: Richard Crowley on June 21, 2014, 10:22:06 pmThat 'modern' 12V PSU circuit looks pretty hideous to me (for several reasons) and I don't think it will even work properly because the component values are obviously wrong anyway.The overall design is so bad it isn't even worth considering and this is one to avoid IMO

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 21, 2014, 11:37:21 pm
content: Quote from: G0HZU on June 21, 2014, 11:35:37 pmWhat do YOU think is wrong with it? I have seen manufacturers' application notes with virtually identical circuits. That arrangement is quite common. Perhaps you are only seeing it for the first time.

author: G0HZU
author_rank: Super Contributor
timestamp: June 21, 2014, 11:43:10 pm
content: Are you serious? It obviously won't work (as a 10A PSU) with the 0.1R resistor at the input to the regulator. I can see how it's 'supposed' to work but even if you correct the obvious component errors it's an awful design. The 470uF cap is too big.... there is no soft start... the fuse protection is shite...It's complete crap.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 21, 2014, 11:48:44 pm
content: It is a minor variation of the circuit right out of the LM78xx series application notes. Perhaps you don't understand how it works.http://www.ti.com/lit/an/snoa660a/snoa660a.pdf

author: G0HZU
author_rank: Super Contributor
timestamp: June 21, 2014, 11:53:45 pm
content: QuotePerhaps you don't realise the impact of the 'minor variations' ?

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 21, 2014, 11:57:11 pm
content: If you want to publish a "correction" or "improvement" feel free to do so.ANY circuit can use "improvement" for some factor that you consider more important than the original designer.Meanwhile many people have used THAT circuit quite successfully.Youmay not like it, but that doesn't prevent it from working.

author: G0HZU
author_rank: Super Contributor
timestamp: June 22, 2014, 12:03:39 am
content: QuoteNo they haven't.How much current does the regulator have to pull through the 0.1R resistor to turn on the TIP2955s? If the 7812 pulls an AMP then there's only 0.1V drop across the 0.1R resistor.How can it possibly work as a 10A PSU with a 0.1R resistor at the input to the regulator?

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 22, 2014, 12:07:17 am
content: If you have actually shown that it doesn't work, suggest that you notify the website where it was published.Did you actually read the datasheet and the app notes?

author: G0HZU
author_rank: Super Contributor
timestamp: June 22, 2014, 12:18:21 am
content: QuoteThere's no need really... variations of this circuit (developed from the Fairchild 7812 datasheet) are all over the internet and there's no shortage of people who think their variation works properly. There's another popular 'variation' below and it is also riddled with basic design flaws.http://www.zen22142.zen.co.uk/Circuits/Power/1230psu.htm

author: theatrus
author_rank: Frequent Contributor
timestamp: June 22, 2014, 04:33:27 am
content: While we may have gone off track, this does represent a learning opportunity.Mery: build some of the variants, and discover why they do and don't work.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 22, 2014, 05:45:56 am
content: Go directly to the manufacturer's application notes. Even G0HZU can't argue with them.

author: Mery128
author_rank: Newbie
timestamp: June 22, 2014, 08:14:40 am
content: Well its like Dave said in that one video. "I hope your project doesn't work!" Best way to learn.At this point I've got alot of reading and some simulating to do. Which is a perfect way to kill time while parts I ordered take their sweet time to get here.

author: G0HZU
author_rank: Super Contributor
timestamp: June 22, 2014, 10:53:08 am
content: Quote from: Richard Crowley on June 22, 2014, 05:45:56 amWhy don't you practise what you preach?Maybe if you read the manufacturer's application notes and analysed the circuit below then you wouldn't find yourself posting up a circuit that doesn't work as you claimThe arrowed resistor is 0.1R.This resistor is a key part of the PSU design. It's value depends on the max design current for the PSU, the max design current of the linear regulator and the current gain of the pass transistors and the Vbe drop. There is a simple design equation for this.It isn't going to work as a 10A PSU if you fit a 0.1R resistor here. Your circuit below is WRONG.It doesn't work as a 10A PSU. It will presumably work up to the limit of the LM7812 which will be typically much less than 2A. Also, once the 0.1R resistor value is corrected, the 470uF cap next to this resistor is about a thousand times bigger than it should be and this will screw up the response time of the feedback loop. This will cause all manner of voltage spikes on the output.Even if you fix both of these issues the circuit is still crap. The spread in current gain of the pass transistors, the lack of overvoltage protection, the lack of soft starting mean that this PSU is a disaster for a beginner to build.It isn't a 'modern' design either. The application note these designs are based on in the Fairchild datasheet dates back many, many years.

author: G0HZU
author_rank: Super Contributor
timestamp: June 22, 2014, 07:21:42 pm
content: Quote from: Mery128 on June 22, 2014, 08:14:40 amIf you want to analyse a bad PSU circuit then analyse Richard Crowley's suggested circuit (that he still seems to be defending?). The first thing you will find is that is doesn't work properly because the 0.1R resistor is too small in value.So it will only perform about the same as a standard 7812 regulator on its own.The next step is to download the latest Fairchild datasheet for the LM7812 (eg the 2013 version) and look up the design equations for the regulator when used with PNP pass transistors.This will help you design a more realistic value for the 0.1R resistor feeding the regulator although you also have to factor in the other 0.1R resistors used is series with the TIP2955s. However, the circuit suggested by Richard still has a serious design flaw because of the large 470uF capacitor across the input to the LM7812. This huge value capacitor is NOT there in the Fairchild app note and for very good reason...Try simulating the circuit with a step change (down) in load from several amps to a light load of a few mA. You will then see the circuit develop very significant overshoot spikes on the 12V output. These could easily kill the device the PSU is powering. The large 470uF cap causes this problem because it is a about a thousand times bigger than it should be.It's an awful 'variation' of the original app circuit from Fairchild. Even if you correct the 0.1R resistor and the 470uF capacitor the circuit is still not recommended. I can tell you why this is so if you like but my best advice is to run away from this circuit and design something better. eg something with decent short circuit protection, decent overvoltage protection and a decent/adjustable current limit featureWhat is really sad is that if you google TIP2955 then the first images you see are of various PSU circuits showing hobbyist developed variations of the Fairchild app note. Many of them have the 470uF capacitor across the LM7812 regulator and I guess all these circuits are derived from the original 'variation designer' (idiot?) who put the huge 470uF cap there in the first place