Tomáš Svoboda's Dual Channel 30V 2A power supply? - Page 1
Forum section: electronics / projects

author: Chris56000
author_rank: Frequent Contributor
timestamp: January 12, 2019, 03:43:24 pm
content: Hi!Has anyone had a go at building Tomáš Svoboda's excellent 0–30V 2A Laboratory Power Supply?I was looking at the oscillograms this chappie provided and it looks like a very well–designed low–noise unit, with nothing out of the ordinary involved in its construction!The boards are single–sided as well, making it a very useful psu for the newcomer to electronics construction, or home–made pcb manufacture!I'll amend this post to attach the package later once I've extracted the files off my old 'fone!Note – unfortunately the chap wrote the thesis for this entirely in Czech, but I have started work on an English translation!Chris Williams

author: Hydrawerk
author_rank: Super Contributor
timestamp: January 12, 2019, 04:42:32 pm
content: Linkplease?

author: Cliff Matthews
author_rank: Unknown
timestamp: January 12, 2019, 06:56:15 pm
content: I tried searching through his work, but it got so distracting.. so much genius in one man!http://cmp.felk.cvut.cz/~svoboda/

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 13, 2019, 04:32:03 am
content: Quote from: Hydrawerk on January 12, 2019, 04:42:32 pmMaybe this onehttps://www.vutbr.cz/www_base/zav_prace_soubor_verejne.php?file_id=126067

author: JacobPilsen
author_rank: Regular Contributor
timestamp: January 13, 2019, 07:41:04 pm
content: Quote from: Cliff Matthews on January 12, 2019, 06:56:15 pmCimrman...

author: Chris56000
author_rank: Frequent Contributor
timestamp: January 13, 2019, 08:43:14 pm
content: Hi!Board design files, oscillograms & code:-Chris Williams

author: Chris56000
author_rank: Frequent Contributor
timestamp: January 13, 2019, 09:01:00 pm
content: Hi!Written Thesis (unfortunately in Czech!) and construction pictures:-https://www.dropbox.com/s/rhcmrewrapd03o2/svoboda_tomas_BBCE.zip?dl=0I've started unravelling the Czech into English on his thesis but it's a very long job as all the diagrams have to be extracted from the PDF and relabelled!Chris WilliamsPS!I think it's possible to buy the case Tomas used (U-KK12-30221) online from the "GM Electronic" e-shop in the Czech Republic - it's about 20€ + 21% VAT plus P & P!

author: Yansi
author_rank: Super Contributor
timestamp: January 13, 2019, 09:06:34 pm
content: To be honest, I do not see there anything special, with this supply and I do not think it was very well engineered.Trying to read the opponents opinion on the thesis, I got the idea the work done by the student may have been above average (compared to what typically leaves our junk school system), but the power supply itself is far from ideal and far from what one should really copy 1:1, without making corrections for the mistakes present.I agree with what the thesis reviewer (opponent) said. Here is the version corrected for the gibberish, from the university web. The review is kinda critical, but I think in a very reasonable manner.Here you are, so you can translate into whatever you prefer:QuoteI could add lot of other notes on the circuit. Skimming through the work, I see the concept is really not well thought out (the need for analog voltage isolation amplifiers, etc), and the circuit topology the IL300 optocouplers are used in, is known to be notoriously bad in linearity. Even the application note/datasheet of IL300 tells you not to use the IL300 in photoconductive mode.The opponent is also spot on, regarding the missing dynamic characterization of the power supply.

author: Chris56000
author_rank: Frequent Contributor
timestamp: January 13, 2019, 09:56:03 pm
content: Hi!Czech is not a language that can be translated roughly "on sight", hence me not having chance to study the design in detail yet, but that's an interesting note made about the IL300 optocoupler - I'll certainly read up on that!All the crosses, marks and other artifacts you get on native Eagle schematics & PCB layouts don't make for easy reading and comprehension either!Chris Williams

author: Yansi
author_rank: Super Contributor
timestamp: January 13, 2019, 10:00:57 pm
content: To read more about the IL300 designs, check here:https://www.vishay.com/docs/83708/appnote50.pdfIf you read through thoroughly, you will quickly realize, that trying to design one in is the last thing you want in any design. The parameter variation is just too big and buying tighly binned IL300 for the K factor gets expensive fast, especially when there is so eaaaaasy solution: Just place an ADC on the floating side and then isolate just the few digital signals.Something as cheap as MCP3202 plus a suitable digital isolator (like for example a Si8441AA) might do just well. Adding a DAC (MCP4922) on the same isolated SPI bus is also very simple and may add great value to the overall PSU: Being able to set the voltage/current digitally, for example through a serial port/SCPI interface. Substantial functional addition, for very small investment.I have not noticed crosses in the schematics, but as a long time Eagle user, I know what you mean. But these should not be present there. They are there because the student couldn't export the images correctly and probably just took print screens. Correctly exported schematics from Eagle do not contain any crosses.

author: Yansi
author_rank: Super Contributor
timestamp: January 13, 2019, 10:34:25 pm
content: Just reading random chapter from the thesis: For example: I see he has designed a secondary voltage of 30V. But that is not enough. Considering the mains can fall -10%, the resulting voltage will be 27V. That still produces 36V peak voltage, but that is a no load voltage. Considering the voltage ripple at the filter cap, at 3A load the voltage will fall few volts, ie. to about 33V, leaving not enough room for the preregualtor to operate correctly. That is a fail.The filter capacitance of 2x 4700uF I consider a little bit on the high side (that will lead to unnecessary lowering of the power factor, drawing more RMS current from the transformer). The optimum secondary voltage should be like a 35V or more, I have not studied the minimum operating voltage difference accross the stepdown IC. With the raised input voltage, and the pre-reg in place, the filter capacitance could be likely lowered to just half that, a single 4700 uF cap, rated at 63V, with about 50V no load voltage nominal present there.The circuit topology is not the greatest either. I do not know, what had lead him to use the high side current sensing (LT6105). If the supply is completely floating, there is no reason to not use the obligatory current sense resistor in the OUT- terminal, well closed within the voltage regulation loop so the voltage drop will be compensated for.Also, for DAC controlled power supplies (not the case here, but assuming that as a quite advantageous), it is way more easier to implement the topology, where the whole control circuitry is grounded to the OUT+ terminal. All control and measurement signals are then present readily as a positive voltages referenced to a single point, the OUT+ terminal.

author: Yansi
author_rank: Super Contributor
timestamp: January 13, 2019, 10:51:09 pm
content: Lookin at the LT1085 used as the voltage regulator: I was wondering how the current loop was closed around it: Jeez! No compensation, no nothing. Just a shit ton of hacks, requiring negative voltages, for it to work. Thats a topology out of the last century.The positive rail-referenced control circuitry, could be realized with a single 5V supply and a couple of cheap RRIO opamps.The more power supply rails a circuit is dependent on, the more problems you have to solve, when a rail goes missing, or with regards to power rail sequencing: If for example you switch on the PSU by the mains switch, different rails get to the correct voltages in different times, leading very likely to unwanted dangerous transients at the PSU output (That yould easily damage the connected circuit!). Which probably I think may be also the case here.Attaching the PSU schematic, for clarity and other to easily access it to have a look.

author: Sparky49
author_rank: Regular Contributor
timestamp: January 13, 2019, 11:00:43 pm
content: Unfortunately the PDF in the dropbox link doesn't want to extract for me... Is this just a problem on my end?

author: Yansi
author_rank: Super Contributor
timestamp: January 13, 2019, 11:07:27 pm
content: Why don't you use the direct link provided in the thread to download the thesis directly from the school website?https://www.vutbr.cz/www_base/zav_prace_soubor_verejne.php?file_id=126067Or here is it complete, with the appended data and the opponents review:https://dspace.vutbr.cz/handle/11012/60435Mmm... The whole thesis looks like a copy of this. He cited it, okay, but still... I would expect better than to copy a simple circuit from an application note, and copy it so thoroughly so even all values and component types match.See page 7 Figure 15. Looks familiar?https://www.analog.com/media/en/technical-documentation/application-notes/an35f.pdfOn the other hand, most of bachelor students haven't seen a soldering iron and those who did, haven't probably touched it. So one can't expect too much.//EDIT: Another notice: The power supply in the thesis does not have ANY protection against any external voltages to be connected to the power supply terminals. Reverse polarity voltage will certainly damage it, so will connecting voltage to output terminals when the PSU is powered off, or set to lower voltage, than connected. The LT1084 will sublimate in both cases.

author: Chris56000
author_rank: Frequent Contributor
timestamp: January 04, 2023, 12:19:41 am
content: Regarding the Technical Review being critical about the means by which the MCU measures "UMEAS1", "IMEAS1", etc, could the +5V reference points and the MCU power supply be obtained from something like a REF02CP, or is the current drain too much for that?Are there any example designs of SPI–Controlled Linear Regulators (pref. Open Source or Creative Commons Licensed!) that will operate over 0–30 V and 0–3 A I can look at for inspiration so I don't run into Vishay's objections about using the IL300 in linear "photo–conductive" mode?Regarding the suggestion posted by Member "Yansi" three years ago to use (for example!) a Skyworks Si8441AA 4 channel Digital Isolator, the only trouble with that one is all the listings are those stupid bloody Chinese "Ask for quote" with "£480 postage" appended to them, but I can find UK supplies of the ISO7241X in the same package – could one of these do as an alternative?I'm afraid my expertise has always been repair rather than design from scratch!Chris Williams

author: DavidKo
author_rank: Frequent Contributor
timestamp: January 04, 2023, 09:08:17 am
content: It is LM317 power supply with switched voltage pre-regulation to improve efficiency. Probably not to make it too simple for bachelor work, it goes from 0V to 30V. Otherwise I do not see anything special on the design.