Collaborative power supply design -- benchtop 30V-3A - Page 1
Forum section: electronics / general

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 03, 2014, 10:26:57 pm
content: I watched a tear down of a big 1U PS (xantrex) that Dave did and he pointed out that there are separate areas for a PS or maybe separate subsystems is a better description. High-voltage section, conversion from ac-to-dc, then there's dc-to-dc, control, remote control(optional), there's the display and the cv (constant volts) and cc (constant current) knobs. I think that's about it.I realize that there are lots of PS designs around so this is probably a boring topic for most. But after seeing all the problems with Rigol and Korad PS it seems to me that an alternative could be made for less with fewer features. Am I wrong about this? Perhaps naive but some of the "commercial" PS are really poorly designed and I bet over time they will show themselves to be more inadequate at best and maybe much worse.With a target of 30V-3A these subsystems would need to be designed1) ac-to-dc2) dc-to-dc3) control4) display -- lcd or edp (e-paper/e-ink)5) knobs and chassis/case6) remote control (ethernet or usb or rs-232)7) stuff I forgotI realize due to the huge quantities involved that PS makers can get much better component pricing but the idea here is to come up with a solid design that avoids the currently seen pitfalls of the "commercial" products.And the final product would be one that we would have confidence in because the design was scrutinized and once made, any problems found, would be out in the open and resolved quickly.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 04, 2014, 09:59:00 am
content: QuoteThis one hasn't been finished, but has lots of the rights ideas.Dave also had a couple of designs on the go.

author: Thor-Arne
author_rank: Unknown
timestamp: March 04, 2014, 05:43:22 pm
content: I have been tinkering with variations on this design using parts I have laying around.Just ordered some parts specific to the original design to test that out to.Pre-regulator based on LM2596 is more or less done, only needs some filtering.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 04, 2014, 10:25:20 pm
content: Quote from: HackedFridgeMagnet on March 04, 2014, 09:59:00 amIt started in 2012 and the OP went missing about a year later. I didn't read the whole thread but I see an iterative process.I also saw some links to other sites with PS designs.Is the heavy lifting in the final output design?QuoteI need to look at these.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 04, 2014, 10:28:40 pm
content: Quote from: Thor-Arne on March 04, 2014, 05:43:22 pmIt looks like you picked up where the OP left off. I'm not sure what a pre-regulator is so will have to look at the lm2596.What is the current state of the PS? What's left that needs to be completed?

author: Thor-Arne
author_rank: Unknown
timestamp: March 05, 2014, 12:31:46 pm
content: The pre-regulator is a switching regulator (noisy) that holds the source voltage for the regulator at 3-4 volts above the regulated output.For the record, I hacked aDC-DC modulefrom China as this was the cheapest solution to me.Note that the LM2596 comes in both fixed and variable versions, the fixed voltage ones is unusable as a tracking regulator.I use a transformer that delivers 1A@24VAC on this design, no other transformer has been tested.And I'll use a current shunt resistor in TO220 package instead of the ten 10ohm resistors suggested, this will save quite some space on the PCB and provide more accuracy. This is the most expensive part on the regulator board so far.The output stage that Richard (Amspire) designed seems to be usable as-is.I spent most of the time trying out variations on the design, using parts that I had in-house.My attempt to use a single 2N2955 pass transistor resulted in oscillation when there was put a load on it.Current status:I've made a input board with transformer, rectifier, pre-regulator, op-amp supply and reference voltage. Still some tweaking to do with this to get everything perfect.The regulator itself is still on breadboard (using BC337/BC327 transistors). I've ordered some 2N2222/2N2907 to compare to the original design.As far as I can see it seems to be function as intended.On the regulator board I need to do some filtering of the pre-regulated source voltage as the noise is quite bad from the switcher, and just putting a large cap there is out of the question as the pre-regulator needs to "track" the output voltage. To high difference between input and output voltage will fry R10, and probably a few more parts.Also, I need to address the issue with the current limit led. And I need to make a adjustable maximum current limit since I need to set this according to the available current.I intend to post the schematic when I've got everything in place.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 05, 2014, 10:32:14 pm
content: Quote from: Thor-Arne on March 05, 2014, 12:31:46 pmIs this the essence of the difference between a switching and linear PS?Is there a part # for this "current shunt resistor in TO220"? I don't know what it is?I see now that Dave did a complete design too and looked at his schematic, did anyone ever make one? It seems to have stopped at a part 6 video and no more discussion on the forum after part 5. Looks like it was destined to become a kit. But that would be a whole lot of work to sell kits like that!!

author: calexanian
author_rank: Super Contributor
timestamp: March 06, 2014, 05:57:08 am
content: Some companies make power resistors in TO220 transistor style packages for easy heat sink mounting. Caddock and Dale come to mind. Some of them are high precision.

author: BravoV
author_rank: Super Contributor
timestamp: March 06, 2014, 06:52:45 am
content: Quote from: GiskardReventlov on March 05, 2014, 10:32:14 pmExample, Cadock MP series, bought these years ago when they're dirt cheap at ebay, if I'm not mistaken 4 or 5 pcs/$1. To my surprised the temp co is much better than datasheet and also accuracy even though stated at 1%, mine mostly < 0.5%.

author: Thor-Arne
author_rank: Unknown
timestamp: March 06, 2014, 10:01:38 am
content: Quote from: GiskardReventlov on March 05, 2014, 10:32:14 pmWikipediahas several articles on switch mode powersupplys.The reason for using a switching regulator is the heat generated compared to a linear regulator.Quote from: GiskardReventlov on March 05, 2014, 10:32:14 pmThere was some issues with the LT3080, and the project was put on hold.

author: awallin
author_rank: Frequent Contributor
timestamp: March 06, 2014, 07:48:54 pm
content: Quote from: GiskardReventlov on March 03, 2014, 10:26:57 pmmy 2 cents:3) control: use a common cheap uController or single-board computer. Arduino Due or Beagle-bone-black comes to mind. The BBB has built-in ethernet while the arduino needs an ethernet shield. Some will say these are over-priced, but the availability of the boards as well as programming examples/help is superior to almost anything else. A full linux install for a PSU is maybe overkill so maybe the Arduino is a better fit.Interface DACs and ADCs using SPI. This allows changing the ADC/DAC chips with little or no modification to the software.4/5: Character LCD would be simple - graphics if a display is cheap and there's a software library available. I'd use rotary encoders for controls that can be used for anything (navigating menus etc). A minimal design would use just a rotary encoder with built-in pushbutton.6) forget RS-232 and use Ethernet.There was a post elsewhere on the forum about digital vs. analog control loops for CV and CC. Fast loops obviously need to be all analog. But the setpoints and feedback for display/remote-control in a software controlled instrument should come from DACs/ADCs.Over time probably a few different power-stages could be developed that use the same digital control section of the circuit. Not everyone will have the same voltage/current requirements, as well as multi-output options etc.No I'm not volunteering to design & build this! sorry I probably will not have timeWorking on a DDS prototype currently, with the above mentioned arduino+ethernet SPI + 20x2 LCD + rotary-encoder/pushbutton controller.AW

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 06, 2014, 10:42:28 pm
content: @calexanian, BravoV, caddock and dale, will have a look@Thor-Arne, will read some more about the linear vs. switching regulator. I swear I read all of that part5 thread here, but I must have missed the part about LT3080. Surprised that I didn't read about it but I'll look some more, Dave probably did a video on just that. Was it a product defect? A documentation "bug"?

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 06, 2014, 11:09:22 pm
content: Quote from: awallin on March 06, 2014, 07:48:54 pmI like the idea of keeping things generic, I would lean away from a single-board computer. The choice for uC is large now. (maybe that's not good??)QuoteWell there are a ton of cheap color tablet things around now (with ARMs usually) but I have no idea how hard it would be to repurpose for this use. Maybe just rip the guts out intact and put a stripped down OS on it just to handle the display. Besides the usual, maybe have ambient temp., and other vital temps. of the PS. Could also add some statistical data. Sampling voltage/amperes over time and temp.QuoteI like this idea, but would it be difficult to set an exact V or A and then press the button? Maybe the button is separate from the knob?QuoteI'm ok with ethernet, but it seems too much, but maybe in the long run it just makes sense to use ethernet though. Makes it future-proof too.Expandability/flexibility sounds like a good idea.QuoteDDS? You're making a robot dentist? You mean R. DDS? What part for the rotary/push button?

author: Thor-Arne
author_rank: Unknown
timestamp: March 07, 2014, 12:09:53 am
content: Quote from: GiskardReventlov on March 06, 2014, 10:42:28 pmDave mentioned the problem several places, and it's discussed in other threads on the forum to. Can't remember the exactly where.As far as I can remember it was a design flaw in the chip that caused it to fry in certain circumstances.Just to mention it, the design by Amspire can be controlled by a mcu, either by pwm or by a dac. That design just overs the driver, regulator and feedback circuit.I recommend reading that thread, a lot of useful information there.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 07, 2014, 12:53:44 am
content: Quote from: Thor-Arne on March 07, 2014, 12:09:53 amWhere's Amspire? I will check that thread. Interesting about the LT3080. Was there ever any public mention by the maker of the LT3080 that it had issues? Or are they too big to fail? (too big to jail)

author: Thor-Arne
author_rank: Unknown
timestamp: March 07, 2014, 12:18:33 pm
content: I have no idea, Amspire hasn't been on since June 2013.I didn't read all the threads with LT3080 designs, have been focusing on the op-amp based ones.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 07, 2014, 06:10:38 pm
content: Quote from: Thor-Arne on March 07, 2014, 12:18:33 pmI will do the same, it's too painful to read through those threads.

author: awallin
author_rank: Frequent Contributor
timestamp: March 07, 2014, 08:06:41 pm
content: Quote from: GiskardReventlov on March 06, 2014, 11:09:22 pmFront panel for the 19" rack 1U enclosure arrived today. This blog post also lists the user-interface parts for the DDS box:http://www.anderswallin.net/2014/03/dds-front-panel/A rotary encoder that only has 16 or 24 pulses per rev, with detents and a pusbhutton, will usually not rotate when you push it.I like the rotary+pushbutton because for a simple instrument no other buttons or knobs are required. The wheel can be used for both setting values and navigating menus.I hope the generic things I learn with the control + UI part of the DDS-box can be applied for other instruments also. Given endless time&resources I would build e.g. TEC-controller, multi-channel (slow) DAC/ADC, or even hybrid analog/digital PID-controller or lock-in amplifier, frequency-counter/TDC, etc. In reality we'll see what happensAW

author: neslekkim
author_rank: Super Contributor
timestamp: March 22, 2014, 09:16:23 am
content: Quote from: GiskardReventlov on March 07, 2014, 06:10:38 pmGoogle then, this:https://encrypted.google.com/search?q=LT3080#q=LT3080+site%3Aeevblog.comleads to this:https://www.eevblog.com/forum/projects/lt3080-wierdness-dave's-power-supply-(eev224)-gone-mad/

author: neslekkim
author_rank: Super Contributor
timestamp: March 22, 2014, 09:18:47 am
content: This also seems like an nice build, but no action since forever:http://gerrysweeney.com/fully-programmable-modular-bench-power-supply/

author: Thor-Arne
author_rank: Unknown
timestamp: March 22, 2014, 10:32:45 am
content: IanJ'sdesignis also interesting.Above all, it seems to be finished.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 22, 2014, 05:04:59 pm
content: Quote from: awallin on March 07, 2014, 08:06:41 pmYep, know what you mean, and my sights are set much lower (to match my skill level I suppose)Nice project. Looks like a great attention to detail and high quality.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 22, 2014, 05:14:23 pm
content: @neslekkim (mikkelsen??), good find on the LT3080 thread, will have a look.I think I looked at that other link (sweeny) but I don't remember what I concluded.@Thor-Arne, I think I may have looked at ianj PS, will check again.I think there's lots of room for an expandable, open sourced design, easily repairable PS that can be bought as a kit. Someone with the means could also sell pre-made PS but that's heavy lifting and probably very slim profit margins. I'm not sure if selling a kit is worthwhile. My be more trouble than it's worth.

author: rollatorwieltje
author_rank: Unknown
timestamp: March 22, 2014, 06:29:59 pm
content: Build a PSU that's actually good, that's enough of a challenge. No garbage on switch on/off, CC mode that is actually usable, no 1000uF cap on the output to stabilize the damn thing...All these projects seem to die on feature creep. It's easy to program in a million features, but it's all completely useless when the power supply isn't stable.

author: neslekkim
author_rank: Super Contributor
timestamp: March 22, 2014, 06:57:47 pm
content: Quote from: GiskardReventlov on March 22, 2014, 05:14:23 pmCorrect

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 22, 2014, 08:19:01 pm
content: Quote from: rollatorwieltje on March 22, 2014, 06:29:59 pmIt's not easy to program in a million, but it distracts (from your other well made point) of a usable PS.As a neophyte enthusiast I think a design should separate each of the sub-systems of the PS onto separate boards. Then use interconnects. This way might be more expensive and more work but it also would provide a path to augment with new features later. And also allow replacement of one sub-system that had to be altered due to problem parts, like the entire LT308x series.I lack the knowledge to know if this is a feasible approach but the feature creep is definitely a death trap. And I think a modular (based on the PS sub-systems) design would keep the feature creeps quiet as it would allow future additions.

author: LukeW
author_rank: Frequent Contributor
timestamp: April 07, 2014, 11:08:50 pm
content: Perhaps the 0-40V 100W power supply published in this month's (and next month's) Silicon Chip might be of interest?

author: Marco
author_rank: Super Contributor
timestamp: April 08, 2014, 03:18:14 pm
content: How hard would it be to modify the feedback loop in one of the many One Hung Low Meanwell clone power supplys? (In and of itself that wouldn't give a useful bench supply, but maybe with some filtering and a linear regulator.)