Battery Lab supply - Page 1
Forum section: electronics / projects

author: John40131
author_rank: Newbie
timestamp: October 24, 2020, 11:06:58 am
content: Hi,I love watching Daves Videos, I am a retired Electronics engineer so just a hobby but I mainly consentrate on Model Railways and accosiated electronics ... I live in UK ...I was very interested in the Lab supply he designed and built back in 2012 and was wondering if the sketch is available ... also checking on IC's and a lot seem to be surface mount knowadays so may be a re-design in Eagle Cad or Altium ...Regards John Marshall

author: homebrew
author_rank: Frequent Contributor
timestamp: October 24, 2020, 10:12:55 pm
content: Is that the file you are looking for?http://www.eevblog.com/files/uSupplyBenchRevC.pdfWhy not try out KiCad when re-designing?

author: John40131
author_rank: Newbie
timestamp: October 25, 2020, 11:57:37 am
content: Yes I have the Revision C board PDF... but was wondering if the Gerber files were available and the sketch for the Atmega328P was available ...I can redesign the board from Schematics but the sketch would be a no no for me ..Regards John

author: homebrew
author_rank: Frequent Contributor
timestamp: October 25, 2020, 01:31:24 pm
content: I haven't found that either, but maybe Dave will provide these files if you ask him?But if you would be interested in (re-)designing such a supply I would be all in to help.Writing some firmware for AVR controllers would be absolutely no problem. And while electronics is a hobby for me, too, I would consider myself at least somewhat experienced when it comes to multilayer PCB layouts and SMD only designs. I can assemble down to 0402 without any problems in at my home bench.That said, I would definitively want to improve a some aspects (Oh dear, who am I to suggest an 'improvement' to a design done by Dave ...):* Adding battery protection / fuse* Getting rid of the R/C PWM DACFurther I do think that the current limiting circuitry has a design weakness for low ohm loads (but maybe I just don't get it - so please correct me if I mistaken):Given the following scenario (an output set voltage of 5V, a current limit of 0.5A and a load of 0.1Ohm connected).- Depending on the firmware, and according to the comment in the schematic, V+ could sit at as low as 9V.- Therefore current limiting will be active and Q2 will be turned on. Its base will be supplied by 9V through R13 (10K). Hence Q2s I_B will be 0.82mA , assuming V_BE=0.8V.- As U3A is pulled out of regulation by Q2, it will output 9V. As this is the only current source (neglecting the 10uA from LT3080), Q2 needs to handle an I_C of 9mA, given R11 (1K).- According to the data sheet of the 2N3904 this would result in a V_CE of around 0.11V- Therefore, the output can't go to 50mV as required to meet the set current limit.However, maybe I'm just stupid and misinterpret that circuit ...For me a redesign would be interesting with a focus on small dimensions and operational safety.Of course such a design would be open hardware, too and ideally be designed with open source software only (i.e. KiCad), with fully published schematics, gerbers, cad files and firmware sources.

author: John40131
author_rank: Newbie
timestamp: October 25, 2020, 02:12:05 pm
content: That would be great if you had another go at Daves Awesome design ...I dont have a lot of test equipment ... I think cost mainly and Model Railway build takes most but I want to get hold of an old Oscilloscope and was considering contacting my local University Electronics Dept to see if they are throwing out any...The PCB design you say you use Kicad ... not heard of that but I use Eagle Cad and got hold of a later version 9 as I was having trouble getting gerbers to work on the version 8 I have ... anyway I just did 2 boards and sent to JLCPCB and they are traversing the globe at this moment ... Model Railway PCB's ...I did a BOM for Daves version C power supply ... most I costed from Digi Keys and FarnellsI do have a Bench 30 volt 3 amp which is okay but a portable one would be greatNot sure best method in contacting Dave could try on his FB page unless you know a better way...Nice to chat with you best wishesRegards John

author: homebrew
author_rank: Frequent Contributor
timestamp: October 25, 2020, 09:22:39 pm
content: Hi JohnI did switch from Eagle to KiCad two years ago. Simply because it is open source, thus free of cost and has no cloud/subscription stuff ...Just give it a shot:https://kicad-pcb.orgHere are some wonderful video-tutorials provided by Contextual Electronics:https://www.youtube.com/playlist?list=PLy2022BX6EsphFLOoGI_fQRpew1i28Y02And it does have VERY cool plugins:Anyway, back to the topic.I think I will redesign this completely around a slightly different LDO component (LT3081). That regulator one has a built in I_limit function and AD has even built a lab power supply around it (for demonstration?):https://www.analog.com/cn/technical-articles/high-performance-portable-dc-bench-power-supply.htmlHence, I think that their internal I_limit really is up to the job. Further, this part has a built in current monitor that could easily be read out using an ADC.As I do want digital control, I'll do the same as Dave did in his design and have a DAC to set the V_set of the regulator. However, I'll have to use a digital potentiometer (e.g. AD5245) plus an I2C isolator to replace the I_limit pot as it is riding on V_out. 256 steps would give approx. 7mA increments to the I_lim. For my applications, that would be sufficient precision.Let's see where this will lead to ...Ideas are welcome ...

author: John40131
author_rank: Newbie
timestamp: October 26, 2020, 12:21:24 pm
content: Can't really help you with ideas, as my knowledge on this type of electronics is limited ... I was in electronics until 1988 and PCB design and Production but that company went and had to take a job to live which wasnt electronics related ... retired in Jan 2015 and strated small time again ... so appart from what I am doing know I built 3 versions of a CNC machine last version runs Mach3 on a computer ... also 3D printing and I then built a Dbot Core XY 3D printer last year and also started building a model railway which has loads of Arduino control ... BUT ... sketches are a challenge ...Regarding Daves Usupply i am very interested to build your design to get a Precision power supply ...Also watched Daves video on the cheap chinese modules DPH3205 Adjustable Power Supply Module Digital Board Programmable £37 and DPS3003 PSU Module £21 .. they are cheap and chearful but may get one of these as well...Keep me in touch on your progress ... ohh and this is my Model railway layout if picture will post ... 2nd Picture is the 4 way crossing board ..Regards John