C't-Lab - Page 1
Forum section: electronics / projects

author: Alfons
author_rank: Regular Contributor
timestamp: January 02, 2016, 08:13:31 pm
content: Over the years, gathered a lot of components, resistors, ICs, capacitors, etc. I then came across an older project of the german journal Ct, the CT-Lab. After some reading, I decided to build a few parts of this project: the power supply and the electronic load.It takes some experience to realize the whole. You have to wade through all the reading material really. Construction, programming, calibration, etc., must be understood first time.Here in the forum, the project was not heeded. I'll report back when I take the parts in operation.If someone components integrated the CT Lab in operation, I would welcome contributions.For those interested: Unfortunately, everything is in German-Language:http://www.heise.de/ct/projekte/machmit/ctlab/wiki

author: prasimix
author_rank: Unknown
timestamp: January 03, 2016, 03:20:15 pm
content: Hi, since I don't know more then ten words in German, could you please let me know if anywhere on that site is discussed per-regulation part of the power supply. I'm interesting to see how it is built, maybe some schematic exists and text I can try to check with an online translator.

author: Kalvin
author_rank: Super Contributor
timestamp: January 03, 2016, 03:25:40 pm
content: Quote from: prasimix on January 03, 2016, 03:20:15 pmGoogle translate does pretty good job for translating technical text from German to English.

author: dom0
author_rank: Super Contributor
timestamp: January 03, 2016, 04:05:40 pm
content: Here is the list:http://www.heise.de/ct/projekte/machmit/ctlab/wiki/AlleModuleE.g. power supply module =>https://shop.heise.de/katalog/kleinkraftwerk=> Leseprobe (= _full_ article) =>http://www.heise.de/ct/artikel/Kleinkraftwerk-291224.html.PDF schematic:http://www.heise.de/ct/projekte/machmit/ctlab/browser/Schematics/schem_DCG2.pdf?format=rawHonestly I can't say it's a well-drawn schematic. Looks very messy.First analysis:Two regulator low-side design with diode OR made up from LED2/D1 and U13/D4 (optocoupler) for mode indication.Reference voltages seem to come from only one DAC multiplexed with S/H stages and muxes.Similarly one ADC is used and some muxes to select input.Level shifting stage, arguably the most important design detail, is done with a common base stage Q4 and a somewhat temperature compensated constant current load Q5. This together with the output driver (which is an additional load at the collector of the common base stage) basically determine how fast the supply is.A good design detail is the additional fast current limit / SOA limit by Q7.Q5 is controlled by Q3. No collector current in Q3 = no output drive.U5a/b are a differential voltage sense amplifier.This stage will likely be the limiting factor in voltage regulator performance, since varying load currents appear as a common mode signal at this stage. CMRR is inherently poor when the S+/S- are only connected by the internal 100 ? protection resistors.Current sensing is quite complicated with no less than four switched shunt resistors up to 470 ?. Clearly a trade off amplifier complexity vs. cheaper shunts. With a more advanced zero-drift amplifier, likely multiple stages for bandwidth or a feed-beside scheme, this should be possible to be simplified quite a bit, even with the aim of 30 nA(!) resolution.I don't expect good offset performance out of the box, since power FETs like the IRF540 used are not really low leakage types, you can expect (ballpark wise) 1 µA or so of leakage current. Calibrating this out is easy, as long as the leakage drift stays low. Zeroing this automatically during operation is not possible.Also consider 200 nA or so bias current of U5b, which adds another offset.

author: Alfons
author_rank: Regular Contributor
timestamp: January 03, 2016, 06:00:14 pm
content: dom0, thank you for your contribution.Some of you mentioned points were in the forums already identified and discussed, but the circuit seems to work quite well without modifications. That there is a lot to improve, the developers also fell on the passage of time. So then came even added a small daughterboard, fielded the overshoot during load shedding. Some, of course, as the Multiplexing of V/A can not be changed.However, a resolution in the range of 0.1mV and 0.1mA should be possible without further modifications, which already are good values for a power supply.LT sent the expensive 16-bit AD / DA converters and reference ICs offered free of charge as samples. So you can keep the price of the whole very low. I feel that the project is very well suited to learn.

author: prasimix
author_rank: Unknown
timestamp: January 03, 2016, 11:32:44 pm
content: Thanks dom0 for assistance. Maybe I cannot see it, but there is no pre-regulator circuit on that schematic. What is on thePowerIn+/PwrIn+(PL6) input of this circuit, just rectified AC from main transformer?

author: dom0
author_rank: Super Contributor
timestamp: January 03, 2016, 11:38:22 pm
content: There is no pre-regulator on that module. The article of the circuit speaks about an input voltage switch, but it isn't in the schematic. Could be part of the optional power output stage.edit: Indeed, there is arelayswitch on the DCP module....sorry guys, it isn't 1940 anymore...Fan control via LM75 overtemp shutdownsoundslike it would tend to continuously turn the fan on and off (overtemp => fan on => cools down below hysteresis => fan off => heats up again, a two point regulator).

author: prasimix
author_rank: Unknown
timestamp: January 04, 2016, 12:03:43 am
content: Ok, thanks again, so main transformer with multiple secondars and relays. I hope that it is equipped with something more advanced.

author: station240
author_rank: Unknown
timestamp: January 04, 2016, 09:55:32 am
content: Anyone else think the location of FS1 is odd ? Shouldn't it just protect the transformers instead of also being connected to the 230V output ?Also 20mm what, nail ?

author: Kleinstein
author_rank: Super Contributor
timestamp: January 04, 2016, 01:59:56 pm
content: Those small 2-5 VA transformers are rather high impedance. So a fuse on the secondary may not even blow in case of a short. So F1 is there to prevent a desaster after a transformer is burnt.You are free to add one at the 5 VA transformer secondary, not shure it helps much.Should be a small medium fast one. Maybe they though about 20 mA medium speed.

author: dom0
author_rank: Super Contributor
timestamp: January 04, 2016, 02:43:00 pm
content: 20 mm => fuse size (5x20 mm)The small transformers often don't need a fuse at all (the primary wire is so thin it acts like a single long fuse), whether or not is specified in the data sheet.

author: Alfons
author_rank: Regular Contributor
timestamp: January 04, 2016, 06:48:01 pm
content: Here are a few links:http://www.thoralt.de/wiki/index.php/Hauptseitehttp://www.segor.de/#/ct-lab/Segor lists cleanly ordered the placement lists (the most recents), and also offers the boards as individual pieces, which are otherwise not get. The prices for this are OK, because the microprocessors are already soldered.The complete kits are very expensive.Short for info: the DCG as a standalone solution can be powered by an external DC voltage source and then supplies 30V - 1A. But you have to note that each of the CT Lab module for the galvanic separation among themselves their own power supply (+/- 15V and 5V) required. The DCP module then adopts the one hand the power to the circuit and can provide a suitable AC source up to 2A (with component changes to 48V possible). The module can be controlled completely without control panel via the computer, LabView drivers exist. The control panel allow controlling the device, however, the PC control offers a lot more, also this is also necessary for commissioning. So you need at least still the IFP module and a (cheap) ISP Progammer. There is a lot to be found on other software, including open source code.With a farther module a tracking operation is possible...

author: Alfons
author_rank: Regular Contributor
timestamp: January 04, 2016, 08:21:24 pm
content: Here are some first pictures:The IFP module, the control panel and the DCG board. On the IFP module is at the bottom yet a IC soldered, a RS232-USB converter IC. So one saves an external converter.On the underside of the control panel also is an IC, a PCA9555D which takes over the control of the encoder, the keyboard, etc..

author: prasimix
author_rank: Unknown
timestamp: January 05, 2016, 08:13:47 am
content: Quote from: Alfons on January 04, 2016, 06:48:01 pmThanks alfons for sharing that with us. Could you please let us know the location of the open source code. LabView if mentioned and I'm curious if they are also using SCPI for control or not.Also if I understood you correctly the DCP module can be used as an pre-regulator for the DCG? When I say pre-regulator I mean a circuit that should prepare power input that in an way that we have lower power dissipation on regulating (linear) element in post-regulator, let say not more then 10-15W for the output current of 3 to 5A regardless of the output voltage (e.g. 0-30V).

author: prasimix
author_rank: Unknown
timestamp: January 05, 2016, 08:22:10 am
content: Quote from: Alfons on January 04, 2016, 08:21:24 pmLooks nice, BUT from my experience I can say that when you have one SMT component on the board it's time to think about removing THT components completely out of the picture. Migration to SMT could spare PCB space (regardless of the fact that here is the Eurocard format chosen, in that case you can pack more thing on the same board) and also could spare on components. Also experimenting is far simpler because the desoldering from 2 (or more) layer PCB is much harder then with SMT. Therefore it could also spare some time and lots of nerves.

author: prasimix
author_rank: Unknown
timestamp: January 05, 2016, 08:27:11 am
content: Quote from: prasimix on January 05, 2016, 08:13:47 amHuh, I now realized that DCP is actually mentioned in dom0's post above.

author: Alfons
author_rank: Regular Contributor
timestamp: January 05, 2016, 12:58:40 pm
content: Quote from: prasimix on January 05, 2016, 08:22:10 amYou have to keep in mind, the project was published in 2007, as is nearly 10 years old. It was intended from the outset as DY project. At that time there were many with the soldering SMD unfamiliar, and the error rate would have risen sharply. After all, had also a comercial background and you wanted and keep the whole thing probably as secure easy as possible. In addition, all is sized in European card format for 19"-rack. Place is so there.After all, one has a functioning and tested basis. As a basis for your own project are indeed an all doors are open. After all, one has a functioning and tested basis.

author: Alfons
author_rank: Regular Contributor
timestamp: January 05, 2016, 01:00:58 pm
content: Quote from: prasimix on January 05, 2016, 08:13:47 amThere is no pre-regulation. You can connect two transformer windings to keep power dissipation low.

author: prasimix
author_rank: Unknown
timestamp: January 05, 2016, 02:40:30 pm
content: Quote from: Alfons on January 05, 2016, 12:58:40 pmYes, that is correct, I started my project not a decade but a little bit then a year ago and was think that SMT is a big no-no for DIY ... that was mytheory. Fortunately inpracticeI learned that is not true.Anyway, possibly any info regarding source code and SCPI support exists? I'd like to hear to what extent is covered power supply functionality.

author: Alfons
author_rank: Regular Contributor
timestamp: January 10, 2016, 12:08:15 pm
content: I have finally managed to put the device into operation. First, still missing a few pieces, and then a lot of time i have not always. Although the whole thing does not look so complicated, you have to find the right from the amount of information. Everything a little messed up. There were improvements and changes and since you have to get visitors find times. Well, and then it creeps in an error, even though you think you have made it very conscientiously. So I had mistaken for a 330R resistor with a 330K and it took me hours before I had finally found the error. The advantage here is that you can then learn to understand the circuit.I have roughly adjusted with the V-A-Offset trimming potentiometers , not yet calibrated. This happens via a Labview Vi, being 25 !!!!! Remeasure parameter and must set. Simple is different. However, I'm amazed at how well run the device itself without calibration already. Power ranges from 500µA to be relatively accurately displayed (510µA on multimeter, 534µA instrument) on which the last digit is no longer remain quiet. It goes well in the noise floor down. But not bad. The voltage indicator is apart from the last location very stable. But, as I said, I still have to calibrate.The charge injection of multiplexers hit a few millivolts of the output voltage. This could be alleviated by changed filter parameters at the outputs, so that they are practically no longer be seen at low load. This will surly rise by high load. At low load, the noise voltage at the output at less than 1 mV, the more I could not test. This will certainly look different under high load... I reports then and pictures will follow.Here a link...https://www.heise.de:444/svn/ctlab/Schematics/Look for schem_DCG2_mit_bugfix2.pdf. This is the latest Version.

author: Alfons
author_rank: Regular Contributor
timestamp: January 10, 2016, 09:37:20 pm
content: Here are some first pictures. As I said, everything without calibration. I can do that only in one of a few days ago. But I think, that an accuracy of 0.1%. is feasible. The device can be remotely controlled easily. New for me is, that both goes parralel: you can simultaneously adjust values on the PC and on the panel of the device. This is handy if you want to record data, for example in the background. However, much can not be adjusted on the panel, certainly a drawback of the device.

author: Alfons
author_rank: Regular Contributor
timestamp: January 12, 2016, 05:10:10 pm
content: For the first time the instrument is calibrated by software and I am satisfied with the result. I think, a little more can still get out, but the adjustment is time-consuming. In addition, I had to understand first time the software. For a PS, the values are OK. The values on the panel display are shown with four digits, in software then five digits.Here is briefly a picture with a light load, but the values remain at a higher load and voltage are OK. I hope, you can see something.

author: Alfons
author_rank: Regular Contributor
timestamp: January 15, 2016, 07:22:24 pm
content: Here are some pictures:The first shows the Calibration tool, the second the LabVIEW Vi. to control the device. Here, as the Panel itself, ripple signals can be switched on. With a somewhat modified firmware can also output signals aribitäre. More pictures to follow, showing the noise at the output, and the ripple function.A few details:Standard DCG - DC: 30V 1AWith DCP: 30V 2A - with modified components up to 48V - 2.5AInterference voltage at output: ca 2,5 mV / RMSabout 100us CV-CC response timeOnly CC-operation, no CV-operationResolution in the range 2mA: 1µA (can not be used - from approximately 50µA relatively accurately)Resolution in 200mV: 100µV relatively accurately and stably.Charge Injection (1KHz pulse) beats by the output of up to 20mV / pp - which can be solved by a dual DAC option - which it altered firmware exists.Tracking of two modules possible (parallel and serial mode).

author: Alfons
author_rank: Regular Contributor
timestamp: February 07, 2016, 08:00:23 pm
content: Now in addition to the DCG / DCP, the electronic load is finished. The part also belongs to the CT Lab and is called EDL.Here schematics can be found:http://www.heise.de/ct/projekte/machmit/ctlab/browser/SchematicsUnlike the DCG the part does not require many improvements. It works very satisfactory and provides a very good range of functions. In my configuration 10A are possible, but only at low voltages. 10A can be used only to 5V. 30V and approximately 3A are possible in this configurations. I have partially used other components because a lot is possible. The EDL is easy upgradeable to 250W. Connections for an external power stage are available.The part can be both internal and external triggers. A trigger output for an oscilloscope is also available. Adjustable are an upper and a lower limit, so that the load regulation of a power supply can be beautifully seen on the oscilloscope.Bugs: the sense outputs must be bridged hard at the device input. There are a few changes needed to ensure that sense inputs can be used properly.The picture shows an EDG / EDP and right the EDL can be seen. because of the galvanic isolation are numerous power supplies needed.

author: Alfons
author_rank: Regular Contributor
timestamp: February 08, 2016, 07:11:20 pm
content: Here are some pictures, that show the electronic load (EDL) and the power supply (DCG) together during operation.You can see the transition from CV to CC mode and the CC to CV mode in the second image. In the first picture, the trigger out signal of the electronic load can be seen.

author: Alfons
author_rank: Regular Contributor
timestamp: February 08, 2016, 07:22:20 pm
content: And here is a picture that show the greatest disadvantage of the DCG (Power supply). The charge injection of the multiplexer. Meanwhile, I have the whole thing replaced by two DAC's, the multiplexer for DA-current and DA-voltage is then not necessary. This was developed in a neighboring forum from a reader, who adapted then also the software. Thus, the charge-injection signals are of course no longer exists. But you need 2 DAC's per board.

author: quarks
author_rank: Frequent Contributor
timestamp: February 09, 2016, 08:48:46 am
content: I have had this on my projects to build wish list for many years, but unfortunately never started.Thanks for sharing and please keep on posting

author: Alfons
author_rank: Regular Contributor
timestamp: February 09, 2016, 03:24:29 pm
content: What a pity, that the project is little known, because it really is expandable and offers plenty of room for improvement. Anyway, it was really fun to build the parts. However, you have to work extremely carefully, because even instantaneously performs smallest error interference. In went hours for debugging my mistakes. Only the panels ran for me completely right the first time. The circuits reacts extremely sensitive.The whole thing is so extensive that it is difficult for me to report the project, because unfortunately the time lacks.

author: Alfons
author_rank: Regular Contributor
timestamp: February 12, 2016, 06:38:29 pm
content: Here are a few pictures of the power supply (DCG) to the external power stage (DCP).On the DCP is not more than the power supply of the circuit (+ 15V / -15V / + 5V) and the power transistor BD249. Two relays switches a 2x15V/4A transformer depending on the requirement in series, so that loss of power remains limited. The small heat sink I've cut myself. The in the picture above on lying small 4cm fan comes later in front of the heatsink. It was a bit tricky to mount the small heatsink, since under that there are still a few SMD, including a LM75, which is read by the processor continuously. From 50 degrees then the fan switches. 60-70Watt are possible.Then a few pictures of the DCG, in which the small bug fix board is that makes for a heavily modified CC control. Thus, without overshoot control times of about 100us possible.Tracking operation. In addition, a ripple function to generate, for example. rectifier signals or other interference. In an extended firmware, a simple ARB-operation is possible.

author: Alfons
author_rank: Regular Contributor
timestamp: February 12, 2016, 06:46:17 pm
content: Ripple-Function. This is configurable, High, Duty-Cycle...