Tripple limited bench PSU ( digital ) from wall adapter - Page 1
Forum section: electronics / projects

author: Jan Audio
author_rank: Frequent Contributor
timestamp: March 19, 2019, 05:56:10 pm
content: Hi, i made this topic in search of a cheap tripple bench PSU :https://www.eevblog.com/forum/testgear/3-channel-psu-without-problems/I got the suggestion to build something to save money ( page 3 ).I,m not doing any 220volt ( i have my reasons ), so i like to use a wall adapter as power source for this adjustable PSU.Here are the specefications i like to build :0 to 15 volt output on 2 channels0 to 5 volt output on 1 channelCurrent limitedAccurate measuring ( per 1 milliamp )Digital controlWall adapter inputSo it can be really simple with 20x4 display and a few rotary encoders.So how does all this works ?, what parts do i need per section.Will there be expensive parts ?Programming the LCD is no problem.Can it be done without earthing ?A wall adapter has no earth, i like to make -15 volt and +15 volt.thanks

author: Cliff Matthews
author_rank: Unknown
timestamp: March 20, 2019, 01:48:28 am
content: I posted with a 1ma spec panel meter, but after realized there's more you'll need to know:A) You want to avoid mains, so it's going to be messy (and off-the shelf SMPS's often supply dirty power)B) The 2 or 3 wall adapters you'll need are missing a maximum current spec (for still unknown expectations)C) Wall adapters will require galvanic output isolation from the mains (for all to function as a cohesive whole)D) You'll need to read other project posts regarding bench supplies with good Vref, DAC's and digital control.

author: not1xor1
author_rank: Frequent Contributor
timestamp: March 20, 2019, 07:27:38 am
content: as a non-native English speaker I was wondering what the heck does TRIPPLE means... when I realized it was just a misspelling matter

author: Jan Audio
author_rank: Frequent Contributor
timestamp: March 20, 2019, 02:57:10 pm
content: I dont like the idea of 3 wall adapters.I want all from 1.

author: Cliff Matthews
author_rank: Unknown
timestamp: March 20, 2019, 04:09:45 pm
content: Today's wall adapters rarely have 2 outputs, still fewer are isolated from both the mains and one another. and you want 3?FWIW, source power complexity is only where the fun begins.. digital control and measurement of all 3 supplies at your specified 1ma resolution is tricky. There's lots of projects on the forum.. spend time reading and asking questions. Good luck!

author: Jan Audio
author_rank: Frequent Contributor
timestamp: March 20, 2019, 04:26:10 pm
content: Looks like i,m spending €500,-

author: Cliff Matthews
author_rank: Unknown
timestamp: March 20, 2019, 05:06:23 pm
content: Quote from: Jan Audio on March 20, 2019, 04:26:10 pmI don't live in the EU but maybe two of these will work..https://www.ebay.es/itm/MLINK-DPS3005-30V-5A-Fuente-Alimentacion-Digital-regulable-con-display-digital/251954125552and you can regulate the 5v from one of them (if you're willing to share a common ground..)Also:https://www.welectron.com/Korad-KD3005D-Benchtop-Power-Supply

author: tautech
author_rank: Super Contributor
timestamp: March 21, 2019, 12:39:40 pm
content: Quote from: Jan Audio on March 20, 2019, 04:26:10 pmReally ? €370 is enough to get more you than you want.

author: nctnico
author_rank: Super Contributor
timestamp: March 21, 2019, 12:44:25 pm
content: If you use wall-warts make sure they have a transformer. The switching ones very likely have filter capacitors which bias the output to half the mains voltage. This will kill your circuit.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: March 21, 2019, 02:12:29 pm
content: This is all hocus pocus to me.Quote from: tautech on March 21, 2019, 12:39:40 pmPlease advice me here :https://www.eevblog.com/forum/testgear/3-channel-psu-without-problems/msg2280686/#msg2280686No siglent spam please.

author: Cliff Matthews
author_rank: Unknown
timestamp: March 21, 2019, 03:47:52 pm
content: Quote from: tautech on March 21, 2019, 12:39:40 pmUgh! Where's the brutha luv? Man you've been tributing for ages.. now you spam bro?

author: tautech
author_rank: Super Contributor
timestamp: March 21, 2019, 07:48:52 pm
content: Quote from: Cliff Matthews on March 21, 2019, 03:47:52 pmWell it's a lot more than what you think is spam.Quote from: Jan Audio on March 19, 2019, 05:56:10 pmThese are all basic PSU requirements for all but one: Wall adapter inputYes something could be built on the likes of a laptop power brick until you need -15 volt and +15 volt. Then it get tricky to provide a -15V rail with any sort of current capabilities.Then we have this:Quote from: Jan Audio on March 21, 2019, 02:12:29 pmWhich might indicate Jan has insufficient understanding to take a project like this on.Don't get me wrong, as a hobbyist I know only too well the value of a good PSU and I've built a couple some years back. The best is 30V 5A capable but without current limiting. Current limiting added another level of complexity that I wasn't prepared to undertake after researching it. So I used a LM338 in TO-3 and relied on the 5-7A foldback limiting. I spent more time and effort building it than what a new off the shelf Siglent costs.Yes I sell these things and those I've sold haven't given one ounce of problems and provide such a range of features that one couldn't possible replicate in a home build for anything like the price they are offered at.So my recommendation for what it's worth as an experienced hobbyist and equipment dealer is the €370 SPD3303X-E and up-hack it to the €509 X model to provide the 1 mV/mA resolution.The info on how to do this is in the Siglent ads thread.These are a good PSU and built like a tank.

author: 2N3055
author_rank: Super Contributor
timestamp: March 21, 2019, 09:19:21 pm
content: On occasion I myself did comment on Tautech's tenacity in promoting Siglent, where I felt he went a bit overzealous ..But in this occasion, I will support him and say that SPD3303X-E is probably best buy for OP... Other one would be Rigol DP831, (more money though), that has 3rd channel that is also fully regulated and settable like (0-8V / 0-5 A). Rigol has Ethernet, and supports programmed ramps, recording of measurements etc.. Also via SCPI, you can read measurements from PC like you would from meter.. I believe SPD3303X-E also has some of those capabilities.I have Rigol DP831 and it works very well..Both can be easily unlocked to more expensive model with increased resolution and capabilities.Jan, laboratory PSU is not simple project, and by your own estimate and by what knowledge you demonstrated, I think you are not in a position yet to design and make safe and high quality PSU of the type you would like. By all means, make it your learning project, but if you want reliable workhorse PSU you'll have to buy one, either one of the two I mentioned, or maybe and used old brand name one, in which case you might get a broken one that you will have to repair.Regards.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: March 22, 2019, 02:34:12 pm
content: Quote from: 2N3055 on March 21, 2019, 09:19:21 pmWIthout the extra functions, why would you buy the rigol over the itech ?How is the itech/keithly quality then ?I decided for the itech, hope they come with 3 sets of cables when i,m broke.

author: 2N3055
author_rank: Super Contributor
timestamp: March 22, 2019, 02:38:47 pm
content: I don't have one but people that have Itech are quite happy.It is a good PSU. It should serve you well..

author: Jan Audio
author_rank: Frequent Contributor
timestamp: March 23, 2019, 03:22:35 pm
content: Quote from: nctnico on March 21, 2019, 12:44:25 pmThis i dont understand, how can a 12v switching adapter give 110volt ?, that is not safe.

author: Cliff Matthews
author_rank: Unknown
timestamp: March 23, 2019, 03:54:51 pm
content: Although output (-) isn't DC-coupled to mains, blue Y cap beside transformer pulls its avg to about half (w/ resect to GND).

author: Jan Audio
author_rank: Frequent Contributor
timestamp: March 23, 2019, 04:23:57 pm
content: So when does this happen with switching adapters ?

author: Cliff Matthews
author_rank: Unknown
timestamp: March 23, 2019, 04:41:37 pm
content: Most are like this. The isolated output side of the adapter can be like a radio transmitter with square wave pulses from 30 to 300khz broadcasting switching harmonics. The Y cap effectively shunts this to meet EMI requirements (keeping your neighbors radio's happy..). If your project uses an SMPS psu, clip out the Y cap and encase it in a shielded box with isolated binding posts at front.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: March 24, 2019, 02:22:56 pm
content: I mean when.

author: Cliff Matthews
author_rank: Unknown
timestamp: March 24, 2019, 04:22:02 pm
content: When a device connects to a switching adapter, its negative supply rail can be adversely affected by the mains connected Y-cap. An issue more serious (IMO), can be found in poorly wound Asian SMPS transformer's where primary and secondary conductors crossover each other (sometimes exiting the bobbin en-route to solder terminals) with only a thin enamel to spare human life..A very hands-on tech in CZ (DiodeGoneWild) shows a dangerous adapter with poor winding's at the end of this video. Enjoy!