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Forum Index : Microcontroller and PC projects : Small cheap switching supplies.
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| paceman Guru  Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
Hi Mick, How did you go with these switching supplies? I ordered one of each too and found the following. - the single LM2596 based adjustable supply was brand new and at $1.73 looks pretty good. Specs are: input 4.5-40v; output 1.5-30v; max current 2A without heatsink. Size is 43x20mm. - the dual adjustable IR3802A based supply (~$6.50) wasn't new and and the one I received was a bit worse for wear. It's claimed specs are: input 7-20v; output 1-16v; current 6A!. Single supply on the right. The dual supply has a blob of grey rubber on top of one of the inductors - maybe for spacing on the original component? 
The dual supply looks a bit kludged. It has a very small (28x25mm) pre-loved piggy back board with dual IR3802A chips, inductors and support SMD passives mounted on it, all sitting on top of a new looking 47x53mm board which mounts the smoothing caps, adjusting pots and screw connectors. The piggy-back control board has had several SMD's prised off at one end! - but both supplies still work, so presumably they were there for something else! The smoothing caps on the dual supply board unfortunately look rather worse for wear and one of the output ones on the one I received is badly corroded and pitted - it can be seen (centre cap) in the photo above. The output 270uF caps are only rated at 16v for a claimed 1-16v output range too, which is a bit iffy, but if you only want 5v or 3.3v out, I guess OK. (The single supply uses 35v caps). The dual supply's input cap is also only 20v rated for a claimed input range of 7-20v too, but again if you're feeding it with 9v or 12v that should be OK?. I did find though that one of the channels (Ch2) wouldn't work when set at 5v output and using a 9v input - it fired up OK with a 12v in though. The other channel was fine for 5v out with 9v in. Size-wise, the dual supply board is slightly bigger than two of the single boards so there's not much in that, but the dual supply does have screw terminals whereas the single supply board only has solder pads. I had a look at the "noise" on each of them - 'scope photos below, all taken at 12v in, 5v out and lightly loaded at 20 ma using a 1K pot. The Vrms of the AC component for each is shown on the bottom right of the screen and the Vmax & Vmin (AC component) are shown at bottom left and middle. There's quite a difference. (Note that the 3802 dual supply runs at 300Khz whereas the 2596 single supply runs at 150Khz.) I included a slower sweep shot of Ch2 of the dual supply because it's AC component had an additional lower frequency, higher amplitude component and this can be seen on the lower sweep rate shot. Single Supply: 
Dual Supply Ch1: 
Dual Supply Ch2: 
Dual Supply Ch2 - slower sweep: 
For comparison I also looked at Sparkfun's linear breadboard supply (P/No PRT 00114 - $10). It uses an LM317 and is a single supply switchable for 5v or 3.3v. SF don't quote current capability for this but I guess maybe 1A (?), without a heatsink. The "noise" component is pretty low compared to the others as I guess you'd expect. Physically it's a bit smaller than the others at 30x30mm. SparkFun LM317 based supply: 
I set each of the supplies to 3.3v (with 12v in) and hooked each up in turn to my Mini-Maximite. The Mini worked fine with all of them including both channels of the dual supply - current draw was 120 mA. Conclusion: They all do the job but I think if I wanted a switching supply with dual outputs I'd go for two of the single supplies because of the better quality of components. If you need the extra current capability claimed for the dual unit then you're on your own. I didn't try to load them up to their current specs - mainly because I didn't want to fry them! Greg |
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| ronee Newbie  Joined: 08/01/2012 Location: CanadaPosts: 20 |
Thanks Greg, excellent write up. Are these isolated supplies? Ron |
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Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
Just looking at these screenshots above, it looks like a useful application that someone could create for the Maximite. What we need is some form of adapter/input "thingy" to allow the input of voltages and signals (with protection) and then let the Maximite graph the data. In colour even when using a colour Maximite. Nick |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
Greg Thanks Greg, excellent write up. Are these isolated supplies? Ron Hi Ronee, They're both non-isolated "Adjustable DC-DC Step-down modules" as quoted from the suppliers. I just checked resistance from negative-in to negative-out on them both and my DVM says 1 ohm - pretty much a dead short. The dual supply also has a common negative for both channels - three screw terminals; Ch1, Ch2, Gnd. There's very little info for the dual supply - and some of what they say doesn't make sense. The single supply has a lot more info. I actually bought mine from "Alice 1101983" on e-Bay for $1.73. I've bought from her before and haven't had any problems. Took two weeks to get here from HK, postage zero! The full specs given for the single unit are: Conversion Efficiency: up to 92% Frequency: 150 KHz Rectifier: Non synchronous Module: Non-isolated step-down (Buck) Short Circuit Protection: current limiting, since the recovery (their words!) Operating Temp: Industrial grade (-40 to +85) output power 10W or less. Full Load Temp Rise: 40 (all degrees C presumably) Load Regulation: +/- 0.5% Voltage Regulation: +/- 2.5% Dynamic Response: 5% 200uS Input Voltage: 4.5-40V Output Voltage: 1.5-35V (adjustable) Output Current: Rated 2A, max 3A with additional heatsink. Dimensions: 43x20x14mm I also bought a nice SPI interface SD card reader/writer module from her for $3.98 that looks good for Maximite purposes. Specs are: "All SD SPI pins output, MOSI, SCK, MISO & CS." "Support 5V/3.3V input." "Size: 51x31 mm Greg |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
Hi Nick, Yes I've thought the same thing for some time ($25 4" colour TFT screen, Maximite, fancy electronics  battery, box and Bob's your Uncle) but from what I've read it's "non-trivial" on the "electronics" side and a lot of programming involved - both well beyond me at this stage I'm afraid. You and a few of the rest of the forum could handle it though I reckon 
I thought about buying one of the ones mentioned in the links below but then decided I'd go the full monty and got a standalone "proper" 100MHz Rigol DS1102E (Geoff G has a review on his site) from Emona Instruments here in Melb - cost me a bomb ($450 with GST) but I guess if I get bored with my retirement hobby I could resell it. So far no likelihood of that! DPScope PicAxe forum poscope Greg |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Hi Greg, I havent done anything with mine yet but I concur with your belief that the Dual supply looks used.. the output caps look shot blasted to me... Your review was great... I put it in the Cheap for the price they charge category.. I would use two of the new single modules instead of the dual if I needed a dual voltage.. I want to load it up to 1A amd see if there is any heat driving off 12v(or 13.8v) Great effort Greg. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
Hi Greg, I havent done anything with mine yet but I concur with your belief that the Dual supply looks used.. the output caps look shot blasted to me... Your review was great... I put it in the Cheap for the price they charge category.. I would use two of the new single modules instead of the dual if I needed a dual voltage.. I want to load it up to 1A amd see if there is any heat driving off 12v(or 13.8v) Great effort Greg. Regards, Mick Thanks Mick - wait till I figure how to get photos off the 'scope!! I set the single supply up again for you and loaded it up with....ta daaa...an old jug element - full resistance 33 ohms, 1800 watts! It was easy to just clip onto different parts of it to load things higher. Anyway - it looks pretty good. Fed it with 12v from my bench supply and set the output first at 3.3v, then 5v and in both cases ran it at one amp for 15 mins or so. It stayed pretty cool in both cases - scientifically tested by the tip of my little finger on the chip, inductor and capacitors. They were warm but that's all. Mind you it was sitting out in the open on my desk with room temp at 19 deg C. How it'd be in an enclosure I don't know - you'd have much more idea than me. I took some pictures again with the same 'scope conditions as before. The order of the Vmax, Vmin & Vrms have changed for some reason but the info's there. Errr... having trouble here; don't seem to be able to upload pictures at the moment. Anyway the AC component at 1A output just shows an increased Vrms to about 27mV and the waveform now looks pretty much saw-tooth (2uS rising & 4uS falling) with a fast blip about half the total sawtooth amplitude at each transition. Re "caps looking shot-blasted" - yes, I'd say marine environment corrosion! I think the bad one of mine (worst of a bad bunch in fact) actually has a hole in one section of the top edge - amazing it's working! Hope this helps, Greg |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6098 |
Take a look at the DSO Nano. I have the V1 and for the price and size, it is very handy. http://www.seeedstudio.com/depot/dso-nano-v2-p-681.html?cPat h=174 (I do still bring out the Tektronicx for serious work. Jim VK7JH MMedit MMBasic Help |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
Hi Jim, I remember seeing that one when I was looking around but couldn't find my bookmark. For $89 it looks good but I remember thinking then that the 200 KHz bandwidth was likely to be a problem at times and I still wouldn't have what I wanted. In the end I was trying to make up my mind between the DS1102E Vs the DS1102D version of the Rigol. The "D" version is also a 16 channel logic analyser but the bandwidth is dropped to 50MHz whereas the "E" version is 100MHz but without the logic analyser. I'm still wondering if I made the right choice but... Greg |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
About scopes.... http://www.youtube.com/watch?v=JTG6jWL0ZqA comparing a few: http://www.youtube.com/watch?v=Ev121xAt_k4 Microblocks. Build with logic. |
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