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Everything posted by liquibyte

  1. So, you come to a board that posts schematics regularly for projects and post a project without any real information and then request peoples email addresses to send them information? Does anyone here think this is a good idea to get information on the project given that a quick ebay search shows entire projects with code and all as downloadable material. My spidey sense tells me something's amiss here.
  2. I'm sorry, I should have said I think it's the wrong value for this configuration. I'd have to work out the math for it but I think you'd do better with a much lower value at 10A output. Doing that would require also adjusting the resistor values around the voltage reference and current regulation circuit.
  3. I tried my best to fix a few of the more glaring issues that I had while I was testing. The one thing that always bothered me was the current sense heater. I felt like I should be using this as an on demand water heater. I'm actively working on prototyping out the changes to see what works and what doesn't. The one thing we lose is getting voltages close to 0V but I don't think anyone really needs that either. I haven't looked at different op amp solutions yet because the TLE214x family worked so well but my guess is that a nice rail-to-rail could go in there now without issues due to the 36V regulator circuit and come close to addressing that issue. My focus was on the transient issues and a better current sensing scheme. I'm planning a voltmeter/ammeter for this using modern parts. 12bit ADC, Atmel microcontroller (up for debate but I've got some blank 328P-PU's), and a MAX7219 to drive the displays, and a 4-wire sense resistor. Doing the meter is more for the educational value than anything else for me but some folks might find it useful so I plan on releasing everything all at once when testing is complete.
  4. You can do a search for output decoupling caps to ground and you will find several references to 1uF to 2.2uF for the values in an effort to solve oscillation. I used these because of that actual problem I was having. I do understand each component in the circuit having studied it extensively and having modelled it in LTSpiceIV extensively to arrive at the circuit that I posted. Bringing in linear regulators to the circuit added nothing to the conversation whatsoever. I did not copy that other circuit, I based mine off of that configuration. By the way, the 0-30V circuit uses the same principles and quite a bit of the same configuration. I don't know if you've noticed but I posted a modified version of that circuit that I'm working on as well. I removed the part of the circuit that was the negative regulator because it really added nothing to the circuit and introduced issues that has made it hard to fix. We now have a 10V reference and a 0.1 ohm current sense resistor that suffers from much less heat than before. Still think I don't understand what's going on?
  5. Really, 20mV p/p is worse stability? I've got a nice scope trace I'd like you to look at then.
  6. The fact that you even suggested that circuit tells me that you either know nothing and are trying to fake it or that what you think you know is entirely wrong. Linear regulators as a lab supply is just stupid and I'm tired of seeing that dumbass circuit all over the net being suggested as so.
  7. Your change adds significant oscillations to my simulation output on the positive side of things. As for the 2.2u cap, it could have just as well been 1uF but 2.2uF is what I had on hand that solved the issue I was working on also in regards to oscillations. I got the value from doing some research into problems I was having and this was a recommended solution and, no offence, it worked. I'd link what I was reading but I can't find it again. Suffice to say that it was from a reputable source and not instructables or the like. I think it was actually an ap note and I'll link it if I find it. The bottom line is that while math and theory can go a long way, up until you build something you never know what you're going to get. Oh, and always run board checks. The missing trace was a dumb mistake on my part. The pic of the board shows the fix I had to do. This is a redesign of something I found online and wanted to see if I could simulate it an manipulate it to do what I wanted. My changes worked so well that I wanted to put it on a manufactured board so I did.
  8. You guys are late to the conversation. I've had the boards made and from my testing things work rather nicely. I did make a mistake on the gerbers and forgot to connect D2 to R2 but since it was a short hop, I left the lead on the zener long, folded it over and soldered it to the lead of the resistor on the bottom. I have no way to vary the current dynamically and I'd not imagine anyone doing that so I'd say, all in all, things work as expected with no oscillation at all. I've got less than 20mV ripple at full load on the output. For what I designed this for, I'd say it works nicely.
  9. Yeah, I know. I did the math from the datasheet and given what the simulation is giving me, I'd say the device can probably handle it. I don't have the equipment to lay this out and test in the real world but PD from both amps only total around 300mW and if I'm reading things right, the 2142 can probably handle it. It turns out that I was under a wrong assumption about the power handling capabilities of op amps in general.
  10. Many, many questions keep getting asked about this thing and people keep attempting to build it without even knowing the basics, why I don't know. The power supply suffers from a couple of issues that have never really been adequately addressed so this is going to be my attempt at bringing this thing into the modern age. What follows is just preliminary work to right several wrongs I've noticed with the design. It's not complete but I'm posting it to get opinions and suggestions. This paragraph is for the newbies: DO NOT ATTEMPT TO BUILD THIS YET. If you don't know what you're doing, do not even try and breadboard this. Once I have a final design, I promise that I'll post it. Now, onward. I'm posting my spice simulation for anyone that wants to try and give this a go. One of the things that concerns me is the power dissipation in the op amps but I'm not sure how to get this down to a more acceptable level because I don't think 150mW at load is very good so suggestions are most welcome. First, the voltage reference in the old version was an extremely odd thing to me so what I wanted to do was get a precision reference in there to work with. 10V seemed like a nice round number so that's what I went with and I actually have one on hand to use. Second, the sense resistor. 0.47 ohms? Once again, odd. Plus, it suffers from extreme power dissipation as well. My idea is to have a nice 0.1 ohm 3W 4 wire resistor in there to hook a meter to so I adjusted things around the reference to get me to where I wanted to be and I also have some of these. What I'd like to eventually do is design the meters along with the supply so that what we end up with is a relatively complete project with all the nice bits people seem to be after. No one, I repeat, no one ever offers a suggestion as to what to build to replace this, not one single engineer. They will, however, be the first people to tell you how bad the design is but never offer any sort of advice as to why. I know, I've asked and so have many other people. 0-30V-0-3A-redesign.zip
  11. Seriously? https://www.google.com/search?q=control+pic+through+internet&ie=utf-8&oe=utf-8
  12. I guess one of the learning experiences when one gets into this hobby should be blowing things up so that you learn how not to. I just posted these from the archive that the user posted because just about everything was a pdf file save the schematic. I have no idea what format the design files were in or what program they open with so ymmv. I get why you'd want to use a linear regulator for a quick and dirty supply but I don't understand their ubiquitous use with newbies. You don't really learn anything designing with them in my opinion. Trying to design one with discrete components on the other hand...
  13. This has been done over and over again all over the internet.
  14. I don't know about function but it certainly seems like it's trying to look like it. I get why he wants everything integrated and looking the same but I despise the web 2.0 look. The first person to do this was doing something unique, everyone else, not so much.
  15. Then I'd have to say that the software switch was a bad idea. It shouldn't take javascript to post, ever. I have it blocked by default on most sites unless I whitelist it and I hadn't done that yet here because things changed and I'm personally wary of things changing just for the sake of change. I think that this is probably going to have me going back to anonymous lurker status. To be honest, there's not much in relevant content here anymore and I don't see it being brought back to life any time soon without new content. It's one of the reasons I came up with this supply but since the software can't be used without arbitrary and unnecessary js usage, I don't think I want to bother with it anymore.
  16. I hit the submit button and I was taken back to the post but it was if I hadn't done anything in the first place, no changes.
  17. I hate this new forum software. I just did an edit and it lost its mind. I had forgotten to add that you will have to install http://ltwiki.org/files/LtSpiceIV_Plus_12_2009.exe for the extra parts I used. I'm not sure if the OP07 comes with LTSpiceIV by default or not but I do know the bridge rectifier I used doesn't. If you don't want to install them, just replace the rectifier with 4 diodes. I usually use the MUR460's.
  18. I have come up with what seems a fairly decent power supply using a minimal of parts that are easily obtainable and cheap. The idea is to have a power supply for working with dual supply op amps. The schematic in the picture differs from the LTSpiceIV simulation file for clarity. I've got this sitting on a breadboard and it works but I've only loaded it down to 200mA so far due to my not having had boards made yet and the transistors not being on heatsinks. Once I've got this completed I'll put up a BOM with everything I've used including the case, meters, heatsinks etc. Updated to reflect reality. I'm probably going to just put in analog meters for this project. 0-18V-Independently-Variable.zip
  19. I agree. I've always thought that SMF was an amateurish production though. My recommendation was to try a move to PHPBB as it's mature and stable. I've worked with a fair number of the forum software and I've always gravitated that way as it just seems more intuitive to administrate and the codebase is easier to hack on. I also prefer the layout as I've never been a fan of the web 2.0 look but then again, I'm old and crusty.
  20. I can see some not coming through due to the user base size, but your mods?
  21. Man, I go away for a little while and everything changes. I didn't even have a login anymore.
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