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Thread: Adjustable bench power supply - buy or build yourself?

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    Default Adjustable bench power supply - buy or build yourself?

    A bench power supply with adjustable voltage and current limits, is one of those essential bits of kit if you're into hobbyist or technical level electronics. Years ago (1960's) when I first started out in electronics, building your own adjustable power supply, was one of the very first projects you would tackle. Back in those days, pretty much all bench power supplies were the linear type utilizing a large mains powered transformer, because switchmode types (SMPS) hadn't came of age at that time. In fact, the mains transformer was very much the most expensive part of your own bench power supply.

    Around 35 years ago in the early 1980's, Texas Instruments released the now ubiquitous TL-494 PWM driver IC - at the time (and maybe still today), this was really a mile-stone design, which reduced the complexity, component count, and circuit design requirements, for most all power control/regulation tasks, and was pretty much the 'go to' chip and first to give rise to the mains powered SMPS age. Over the next couple of decades, this IC ended up in everything and became so common place, it was expected the *all* modern designs would be using it. I'm sure a lot of folks here reading this, are familiar with the TL-494 life history, but what isn't widely known is that TI themselves discontinued production of this IC in 2008 or so. In 2005, TI signaled to the world this was going to happen, by announcing that the device will be discontinued, and a lifetime-buy period was in effect. ( see -> for the meaning of 'lifetime-buy' if you don't know the term) It was of course discontinued to make way for later, improved designs that obsoleted the venerable TL-494 product.

    I'm not sure of exactly when (I doubt anyone really is), but because I've worked in electronics repair for many years, by my reckoning there were no more 'genuine made by TI' TL-494 chips left in the wild by 2010. I say that, because at around the same time, I started seeing a lot more SMPS power supply PCB failures, from many different types of equipment, and it got to the point where I'd put the post 2008 TL-494 IC, on my 'pet hate' list...along with old tantalum caps, and a host of other 'known problematic components'.

    Why the short history recount? Well, here we are in 2020, and chinese knockoffs of the TL-494 are still being produced, and they're still the 'go to' chip for cheapest manufacture of antiquated mains SMPS designs. A few places in particular you will still see this IC being used, is in things like stand-alone SMPS power supply modules, DC->AC inverters, and cheap computer PSU units.

    Another place they turn up, is inside these things ;





    I have a few bench supplies, and I have one of those above, a made-in-china 0-30v/0-10A bench supply ; let me show you where I ended up using the thing;




    Yep, out on the battery charging/electroplating bench ..exactly where it belongs. There is so much noise, ripple and spikes on the DC output of these things, they're useless for any precision or technical application, but are a reliable source of power for electroplating it seems, at least, it hasn't exploded yet, but it's never anywhere near running full output.

    So come this human malware lockdown time, I started looking about for a replacement for my electronics bench. this unit was supposed to fill. and I came across a few YT vids from Dave Jones (EEVBlog) which I found really interesting -- these modules have been around for a few years, but I'd never really looked into them ->

    I did a bit more searching, and found someone had created open source firmware for the modules as well, which is very cool -->

    This got me thinking.... you could add some filtering to the regulator module to make the output cleaner (tried that with the cheap chinese made supply above, but the spikes were still a pita), so all one really needed to do to make their own adjustable supply, is find a suitable DC power source. Even though I have a few 300watt toroidal mains transformers on the shelf here, I'd still have to build a rectifier, add bulk capacitors, do all the wiring, find a case...etc etc, and I'm too old and lazy to be bothered anymore =) Plus the thing would end up weighing as much as my linear supply, that tips the scales at some 8kg.

    So I started hunting about on ebay, and found these ;





    Case kits for the control modules are out there if you want neat&tidy -->

    'Best match' for the 480watt PU brick, is either Riden Rd6006, or DPS50V15 ...I chose the latter.

    All these parts are on their way here, but best guess when it'll all arrive here - might still be weeks before the DPS module arrives -- when it all gets here, I'll post back with some of the build stuffs.

    Just thought I'd post this, in case anyone else here were interested in this sort of part hacking =)
    Last edited by wotnot; 29-04-20 at 01:35 AM.

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    I made a couple of supplies this way a while back with ebay modules and no problems with them at all so far.
    Used the DPS5005 from memory (50V 5A) with a fan cooled 48V SMPS and built a plywood box to house it all.

    All much better than I expected considering the price

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    I've only ever built one PSU in my life. To replace the power supply in my old XT computer. I used a transformer Bridge rectifier and a various voltage regulator chips and mounted it all inside the case. The filter caps were almost as big as the Tranny itself! Weighed a ton, but it worked! The only problem I had was the there was not a lot of magnetic shielding so I could not place it near my monitor and could not leave floppy disks in the drives for too long. (could not afford a 10mb HDD back then)

    As I noted elsewhere, I have adapted a computer PSU to other uses, (power for downlights) and am in the process of convertin one to a benchtop supply to put out the usual +/-12v and 5v supplies.
    Last edited by lsemmens; 29-04-20 at 11:52 AM.
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    I have built many PSUs in the past but these days I have no time or money to build a 60V 5A regulated lab supply and sometimes I need stuff up to 20A, when China is cheaper and they work very well.

    I still have some old small linear supplies(max 2A) I built ages ago that I use for low noise pre amp designing and testing.
    This era of thoughtless consumption must end so we can encourage a world of creative geniuses rather than consumer idiots.


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    I've had mixed success with power supplies over the years. I have an ancient Dick Smith 5-15v linear PSU, bought in the late 1970s. Can't kill it - the thing just keeps soldiering on, but it's not at all a precision device. I always seem to need just a little more current or just that little bit more or less voltage than what it can deal with.

    In the early 2000s I built a massive 30v / 10A power supply out of an electronics magazine. For the safety of their readers, it was a bit peculiar, in that it had a massive toroidal transformer on the mains side, then a switchmode regulator on the low voltage side of the transformer. It goes alright, but every once in a while something happens that causes it to "take off". The SMPS makes a weird squealing sound and the current limiting stops working. Not nice at all.

    I bought a GW Instek power supply a few years back - quite like that and it's probably my best one. There's also a cheap chinese one rebadged as a "Tenma" programmable PSU that I bought on sale from Element 14. I believe it's a re-badged "Korad KA3303P". It goes ok, but seems to have slightly glitchy firmware and occasionally does funny things. Like the kit electronics magazine PSU, I don't fully trust it. Being programmable, you can't just grab a knob and twist it for more/less voltage/current. It's good for when I need more than 30v, or for split +12/-12 (or whatever) rails - e.g. playing with Op Amps.

    I've followed some of the Eevblog posts on the cheap Chinese modules. I have a few good laptop computer power adapters floating around and thought a 19v / 4A (or more) power supply might go well with one of the Chinese power supply modules - bearing in mind the limitations re output noise etc. I'll be interested to see what you find.

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    If you want a constant voltage / constant current adjustable power supply for a specific and precise control, then buy the lab power supply.
    But if you're just doing blunt 5,6,9,12,24,48V kind of brute force power supply then build your own.
    Yes I am an agent of Satan, but my duties are largely ceremonial.

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    Quote Originally Posted by shred View Post
    I've had mixed success with power supplies over the years. I have an ancient Dick Smith 5-15v linear PSU, bought in the late 1970s. Can't kill it - the thing just keeps soldiering on, but it's not at all a precision device. I always seem to need just a little more current or just that little bit more or less voltage than what it can deal with.

    Lol.. Same as me, mixed success and now have a Lab supply and the old Dick Smith electronics Vk power master which I built many years ago and it's still going strong.

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    I've followed some of the Eevblog posts on the cheap Chinese modules. I have a few good laptop computer power adapters floating around and thought a 19v / 4A (or more) power supply might go well with one of the Chinese power supply modules - bearing in mind the limitations re output noise etc. I'll be interested to see what you find.
    Those longwei K3010D units are evil things, depends on exactly which odm makes them I think. When I was testing those ebay LED lights, I dragged that thing inside for the sake of an easy video ; the LED lights have a buck driver inside, that'll swallow anything from 8v to 32v.

    Noisy spiky chinesium SMPS on one side ; noisy spiky DC-DC buck converter on the other side, and start sweeping the voltage, and both LED buck and power supply start making twilight zone noises, and you hope neither hits some resonate frequency that shatter their own wafers =)



    See the 2 heatsinks on the left adjacent the fan? That's the mains switchers - those heatsink are hot, as in rectified mains AC hot, here;



    When the unit is used in normal orientation, gravity is trying to have both heatsink fall, with the possibility of the top heatsink falling (sagging) and contacting the lower heatsink and you get a mains potential + bulk capacitor dump like I welding arc. If bugs or the right sort of dust/lint gets in the space between those heatsinks, you'll be in for a blammo. In long, high usage conditions, the silastic holding the heatsink to the goes soft, on some designs the PCB tracks lift with the heat as well, and gravity does the rest. There's a fire extinguisher under that bench, but by most reports they typically only go into meltdown if run at near full rating for long periods of time and explode well after you've walked away from them thinking all was a ok =)

    Those little laptop power brick supplies, I've built up a small box of them, from units sent for repair but which turned out to be BER instead. I ended up buying some 2.1 Class-D audio amp boards to make use of them.



    The current Toshiba brick powering one board, is just an amp shy of what it needs at high volume with a subwoofer going hard at it, and I remembered I had a cheap multivoltage brick powering the lipo charger, so I switched it to 24v and hoped the extra amp would help.

    Turned it on, immediate loud switching noise from the brick on the speakers even with the volume down, turn it off and go back to the underpowered Toshiba unit -- some many of those things are junk. It's little wonder I see repairs come in with blown PMIC chips, or lipo charger mosfets chernobyled all the time...

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    My lucent power supply arrived this morning. I think I have done my dough on that.
    Should have checked it out more.

    The only connector is this triple row thing with a stack of little pins that goes straight to the board. I ( ignorantly) assumed it would have a regular 3 Pin 240 inlet and some sort of terminals for the output. That's bitten me on the arse. Unless there is a connector for that to wire the 240 and output to, the thing is going to be a door stop to me. Should have looked at it closer and been more sus as to why they were so cheap. :0( Very bummed out now. Once again the legit purchases I have made are the ones I get stung on.

    Any Connectors you know of Wotnot that can make this thing viable??

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    Quote Originally Posted by george65 View Post
    My lucent power supply arrived this morning. I think I have done my dough on that.
    Should have checked it out more.

    The only connector is this triple row thing with a stack of little pins that goes straight to the board. I ( ignorantly) assumed it would have a regular 3 Pin 240 inlet and some sort of terminals for the output. That's bitten me on the arse. Unless there is a connector for that to wire the 240 and output to, the thing is going to be a door stop to me. Should have looked at it closer and been more sus as to why they were so cheap. :0( Very bummed out now. Once again the legit purchases I have made are the ones I get stung on.

    Any Connectors you know of Wotnot that can make this thing viable??

    Oh...I knew what I was(am) getting, I thought you did too.... the situation with the rectifiers was summarized by the item image ;



    I'm familiar with this gear, that's all I needed...that part of the pinning. This was always going to be a DIY connection loom job, all this gear is sliding rack mounted with backplane connectors. Mine haven't arrived yet, but I'm going to end up crimping a few tails together anyhow, it'd be no problem for me to make a couple extra if you want. Haven't seen the connector yet..seen pics of the chassis they suit, but need wait until the austpost mule get here to be sure.

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    Quote Originally Posted by wotnot View Post
    Oh...I knew what I was(am) getting, I thought you did too.... the situation with the rectifiers was summarized by the item image ;
    Well no, my fault, seemed I didn't know what I was getting and didn't pay enough attention. You said they were good which I'm sure they are but I didn't and really, couldn't, have known what I was getting because there are, I surmise quite deliberately, no pics of the connectors on the ad.

    I'd be interested in how you are going to connect these because for my skills, it looks near impossible to do with any safety and reliability. Those pins are pretty Fine and pretty close together and the connections on the board itself are even smaller and closer still. I'm surprised they can handle the power they do actually.

    Hope I can make this useable but I have my severe doubts at this time.
    Live and learn. :0)

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    I'll know more when I get a es460c here to check, but pretty sure it's this one ->

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    Yes, I can see PC 612 F on the connector on the unit.

    That connector looks easy to wire as well.... Not! :0(

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    The rectifier bricks arrived today, but instead of typing I decided to do a cover off & walk-through with the handicam.

    Before that though, I wanted to address george65's concerns about terminating the back-plane connector 'safely', in consideration the units have 240VAC input (via 2 adjacent pins), and over 400watts of DC output (however that output utilizes 3 commoned pins, so the actual current loading of the contacts is thus shared/spread). The 'PC 612 type F' connector is all part of DIN 41612 ; their are many different types, ratings, classes. Here, when using a 125VAC supply, the input max current is 5A.... on two pins. That means you'll need to use the 6A rated contact type (also referred to as high current type, 4A type would work too for 240VAC). Many of that type are only rated to 125VAC, so you have to select the higher voltage rated types to maintain your die-electric separation across the contact/connector housing. Next is the pin pitch/spacing, and these are 5.08mm pitch, on a 3.81mm pin spacing, 48pins, 3 rows. Once you have that sorted out, you can find a female connector all done with solder tails, with pins for PCB mount, or as cable mounted type which includes an unpopulated connector housing, and a set of crimps to suit, but again, the assembly housing must be rated @ 240VAC, and the crimp contacts to 6Amps. I'll dig out some RS part numbers later & order what I need..be here by Thursday.

    I think you could get away with soldering/hardwiring stuff into place as per normal hardware hacker practice, but when you see how these things are made inside, that'd be a bit of an... insult I guess, to the quality of the unit build/engineering -- the Made in Italy way, circa 2000

    Last edited by wotnot; 05-05-20 at 07:09 PM.

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    So is there any chanced you are impressed and satisfied with these Don?? :0)
    Shows the difference between Italian and Chinese engineering.

    If you could show how to connect them up one way or the other, that would be great! Don't care how it is, on the board or with a connector, as long as it's secure.
    I imagine these things would really do well with a fan on that heat sink as well. I like fans on heat sinks. Makes the oC/W rating much better.

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    Quote Originally Posted by george65 View Post
    So is there any chanced you are impressed and satisfied with these Don?? :0)
    Shows the difference between Italian and Chinese engineering.

    If you could show how to connect them up one way or the other, that would be great! Don't care how it is, on the board or with a connector, as long as it's secure.
    I imagine these things would really do well with a fan on that heat sink as well. I like fans on heat sinks. Makes the oC/W rating much better.
    There's usually only one reason these kind of things appear as NOS, despite the fact they're no longer needed because the equipment they were in have been decommissioned/upgraded -- no one needed spare rectifiers as replacement parts ; brick shithouses last a long long time =) Even when one questions the presence of a made in china bridge rectifier being there, a quick check reveals it's rated at 800volts/25amps with a 300amp peak...talk about generous over-rating.

    Connectors....one could do this, but you're paying as much for the connector as you did for the PU brick;




    A more cost effective & flexible idea, is this combo (which is what I've ordered)




    That's just the connector shell, so you need to also buy contacts



    I actually ordered a combination of solder tail and crimp for the pins I need to deal with, and you can buy the crimps in 3 sizes to suit different wire gauges.

    As I'm only going to use 11 or 12 pins on each connector, I can populate the shell with just the contacts I need, so I'll have all 3 units sorted for connections for under $20 =)

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    Agreed, that is an impressive bit of kit. What is it's "Official" rating? i.e. input/output power and voltages. I have no need of such a thing, so I am just curious?
    I'm out of my mind, but feel free to leave a message...

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    I found an old pic of my workbench psu.. Huge transformer and a heavy mother f^*k^r - 10 AMP


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    I've got a few P/Ss, but my big Bertha is this one

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    Awesome examples both, bench supply pr0n.. gotta love it
    Last edited by wotnot; 06-05-20 at 07:31 PM.

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