DIY power supply

[Pirateguy]

so i finally got around to building a proper psu, and am wondering what kind of features i should put in it.

what i have to work with:

-desktop PC ATX PSU @ 300 watt
-various (regular) wall warts and PSU, incl one with selectable output (1.5v, 3v, 4.5v, 6v, 7v, 9v, 12v)
-various linear PSU from various devices
 ZVS driver + flyback converter
-various small buck and boost converter
-lm317 regulators
-78xx regulators
-panel mount volt/amp meter (x2)
-panel mount thermometer
-pots, relays, knobs, jacks etc.



....i'd post link but for some reason my links keep getting molested.
just assume every item is the cheapest version of it on ebay.

[Pirateguy]

zvs psu:
https://www.ebay.com/itm/ZVS-Tesla-coil-Booster-High-Voltage-Generator-Plasma-Music-Arc-Speaker-Kits-20KV/112961131719?ssPageName=STRK%3AMEBIDX%3AIT&var=413340326271&_trksid=p2057872.m2749.l2649

volt/amp mater:
https://www.ebay.com/itm/Dual-Blue-Red-Red-Red-LED-Digital-Voltmeter-Amperemeter-Panel-Amp-Volt-Gauge-DC/322982162973?ssPageName=STRK%3AMEBIDX%3AIT&var=512120455709&_trksid=p2057872.m2749.l2649

function generators:
https://www.ebay.com/itm/XR2206-1HZ-1MHZ-Function-Signal-Generator-DIY-Kit-Sine-Triangle-Square-Output/272371567006?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
and
https://www.ebay.nl/itm/Signal-Generator-PWM-Pulse-Frequency-Duty-Cycle-Adjustable-Module-Kit-3-3V-30V/332615961616?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

thermometer:
https://www.ebay.com/itm/New-Digital-LCD-Thermometer-Temperature-Meter-Gauge-Molex-Panel-Mount-C-F-PC-MOD/122513357209?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

[Cliff Matthews]

so i finally got around to building a proper psu, and am wondering what kind of features i should put in it.

what i have to work with:

-desktop PC ATX PSU @ 300 watt
-various (regular) wall warts and PSU, incl one with selectable output (1.5v, 3v, 4.5v, 6v, 7v, 9v, 12v)
-various linear PSU from various devices
 ZVS driver + flyback converter
-various small buck and boost converter
-lm317 regulators
-78xx regulators
-panel mount volt/amp meter (x2)
-panel mount thermometer
-pots, relays, knobs, jacks etc.



....i'd post link but for some reason my links keep getting molested.
just assume every item is the cheapest version of it on ebay.

OK, "so i finally got around to building a proper psu" sounds like it's done.. So show this Franken-Supply 

[Pirateguy]

i got around to starting lol
still waiting for some stuff to come in and looking for an enclosure, and prolly will need to order some
final bits after deciding what all this thing will have to do.

but ready to start drawing up a plan.
for the moment the concept is:

-AC out 0-40v(ish)
-DC out 0-40v(ish)
-DC negative V out (?)
-AC constant current out
-DC constant current out
-DC out at typical battery voltages; 3, 5, 6, 7, 9, 12
-USB 5v out
-polarity inverting (with idiot proofing )
-volt/amp display
-thermometer display
-jack for connecting temp probe to thermometer
-function generator
-active cooling (have various sizes desktop pc fans for this)
-ZVS driver (?)

anything that should be on or not on this list?
also what would be the best ways to go about implementing?

[MarkF]

IMHO you need to refine your requirements.  You are setting yourself up for failure by trying to build the "be all" to "end all" psu.  Get back to the basics and think about just a +/- dual DC supply (fixed or variable).  You can go a LONG way with just a +/-12VDC supply for analog projects and a +5VDC for digital projects.

Afterward, build an independent function generator based on something like the AD9834 DDS and a small MCU.

i got around to starting lol
still waiting for some stuff to come in and looking for an enclosure, and prolly will need to order some
final bits after deciding what all this thing will have to do.

but ready to start drawing up a plan.
for the moment the concept is:

-AC out 0-40v(ish)
-DC out 0-40v(ish)  A 0-30VDC range would seem to be easier to obtain
-DC negative V out (?)  A negative supply would be necessary for analog (op-amps)
-AC constant current out
-DC constant current out
-DC out at typical battery voltages; 3, 5, 6, 7, 9, 12
-USB 5v out
-polarity inverting (with idiot proofing )
-volt/amp display
-thermometer display
-jack for connecting temp probe to thermometer
-function generator
-active cooling (have various sizes desktop pc fans for this)
-ZVS driver (?)

anything that should be on or not on this list?
also what would be the best ways to go about implementing?

[MarkF]

Some ideas for your project:

[Pirateguy]

IMHO you need to refine your requirements.  You are setting yourself up for failure by trying to build the "be all" to "end all" psu.  Get back to the basics and think about just a +/- dual DC supply (fixed or variable).  You can go a LONG way with just a +/-12VDC supply for analog projects and a +5VDC for digital projects.

Afterward, build an independent function generator based on something like the AD9834 DDS and a small MCU.

i got around to starting lol
still waiting for some stuff to come in and looking for an enclosure, and prolly will need to order some
final bits after deciding what all this thing will have to do.

but ready to start drawing up a plan.
for the moment the concept is:

-AC out 0-40v(ish)
-DC out 0-40v(ish)  A 0-30VDC range would seem to be easier to obtain
-DC negative V out (?)  A negative supply would be necessary for analog (op-amps)
-AC constant current out
-DC constant current out
-DC out at typical battery voltages; 3, 5, 6, 7, 9, 12
-USB 5v out
-polarity inverting (with idiot proofing )
-volt/amp display
-thermometer display
-jack for connecting temp probe to thermometer
-function generator
-active cooling (have various sizes desktop pc fans for this)
-ZVS driver (?)

anything that should be on or not on this list?
also what would be the best ways to go about implementing?

How would that be an improvement over the switching wallwart i am already using?
also some of the things u crossed out could be done super simple.
like the set voltages i mentioned are already on current crappy diy psu, which is the innards of a switching wall wart
with the switch broken out to an external switch and the output tied to a couple of bananna sockets.
oh and a pocket multimeter taped to the top of it...
an improvement over the wallwart to be sure, but i am ready to build something better.

and what is a usb out other then 5v with a usb connector?
the biggest challenge there seems to be mounting the usb socket.
and if it is better to keep that separate or current limited or something,
i could just use one of the usb wall plugs i am using now and wire a panel mounted
usb socket to a usb plug...

also i intend to do a lot of experimenting with wireless powering of leds n small motors and plasma arcs.
so i feel like some kind of AC out of some sort would come in handy...

i should prolly explain that my main focus atm is in using electronics to make special effects for miniature dioramas.
medieval high fantasy stuff, for example: tiny jacob's ladder = magical soul stealing device, magnetically levitating magnets + epoxy clay = magically floating artifact,
tiny marx generator = magical demon summoning machine...

also the whole thing doesn't have to be one build, i intend to deal with each thing in there individually
and add them one at a time.

[MarkF]

I don't even know how to respond.
The phrase "Jack of all trades:  Master of none" comes to mind.

You said it best yourself -  Do you really want a bunch of switchable voltages from a crappy wall wart??
In most cases you are only going to use a couple fixed voltages and maybe one variable voltage.

For digital logic you will probably need a 3.3VDC and/or 5VDC.  If you don't mix your logic here, a variable DC supply for doing your projects may be the ticket.  The power requirements of each will in most cases be low for the majority of your projects (unless they are very large). 

I believe for most small motors you would be looking at +12VDC.  And if you go that far add a -12VDC output for other analog projects.  I have no idea what your requirements would be for your medieval fantasy stuff might require.  Your biggest problem here is keeping motor emf and other high voltage noise out of your lower microprocessor logic.

Somewhere along the line, I think you really should purchase an adjustable lab power supply with current limiting capabilities.  Something like the Rigol or the Siglent of the single output variety as a minimum.

As far as USB goes, most modern USB chargers have circuitry to indicate current capabilities of charger.  In particular, Apple devices.  Depends on what you want.

Bottom line here - I'm suggesting you determine what your REAL requirements are.


On the function generator side:  I DO NOT recommend the function generator you linked to in your first post.  The sine output is a filtered triangle that in most cases needs adjustment to be symmetrical.  I saw a few reviews and complaints about it somewhere. I can't remember where I saw them.

[rdl]

That function generator is not bad for the price, okay for a starter, but if you buy one, watch these:


"Design errors in an XR2206-based function-generator from Ebay "



"Fixing the issues with the XR2206 Function-Generator from EBay "

[Pirateguy]

The phrase "Jack of all trades:  Master of none" comes to mind.

i'm a hobbyist of the type that i learn what i need to get what i want. not someone who wants to
become an electronics expert. (hence i have many blind spots when it comes to planning this kinda thing)

clarification: it's not the wall wart i used that is crappy, the psu i made of it is crappy.
it's basically a 'tabletop-wart' now with some banana plugs and a pocked mm taped to it.

i actually ordered 2 function generators.
any thoughts on this one?
https://www.ebay.nl/itm/Signal-Generator-PWM-Pulse-Frequency-Duty-Cycle-Adjustable-Module-Kit-3-3V-30V/332615961616?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

in any case a couple of points:
-i am too much of a noob still to really have a good idea of what my needs might be.
so far everything i have done is aimed at battery power or usb, but then this month i find myself messing around with kilovolts...
-my low skill level does restrict me, but you guys would know more about what that means in terms of what my needs are.
-i do know it means i will not be needing super accuracy or performance as i will not be doing anything particularly sensitive.
-my need for the func gen is really a matter of not having to build a 555 circuit every time a need a waveform. the waveforms i need are of the most basic kind:
pwm for driving motors and leds n stuff, and now i guess ill be needing it for tesla coils.
-like i posted above i have a bunch of power supplies i could use, including several non wallplug type linear ones from older heavier pc peripherals like older printers n stuff. i want the convenience of one big box that holds it all, but technically i could use a different supply for everything i put in the box.

so anyway right now i am thinking what i want is this:
3.3v, 5v, 12v fixed outputs + one variable.
as for amps, i was thinking 5 should have me covered? what would a pair of li-ion cells typically deliver?
i see no reason not to include the volt/amp and temperature displays. is there one?
i am not expecting accuracy, just a course indication and something to warn me of majorly wrong values
like when i have a short in a circuit or something like that and to reasure me that the psu is not about to catch fire.
i ordered that ZVS kit for experimenting with high voltage, any particular reason i should not build it into the same box?
i am not sure about the interface; does it make more sense to have an output for each voltage? or to have one and switch between them?
should i have multiple outputs for each voltage? i do have plenty of bananna jacks...
any particular traits i should look for when i look for an enclosure?

[plazma]

Do you want the challenge of designing a working PSU or do you need a cheap one?

If the latter check out DPS5005 and similar modules. EEVblog also reviewed some models.

I have built few units with DPS5005 and DPS5015 modules. One unit got internal batteries for portability.

[Cliff Matthews]

Do you want the challenge of designing a working PSU or do you need a cheap one?

If the latter check out DPS5005 and similar modules. EEVblog also reviewed some models.

I have built few units with DPS5005 and DPS5015 modules. One unit got internal batteries for portability.

What's the ripple like on the DSP5005? I added a voltage boost winding to my Pace ADS200 to get 40vdc out the back and I'm looking for an add-on module (since the Pace station will always be on the bench, it's like having an invisible 80w PSU for $20).

[plazma]

 19.2V input (Dell laptop PSU). 5V 5A output.

[Cliff Matthews]

i actually ordered 2 function generators.
any thoughts on this one?

Yes, it would be nice if someone could comment, to know it's "flakey" I see alice1101983 has it listed at $3.26 USD
https://www.ebay.com/itm/Adjustable-PWM-Pulse-Frequency-Duty-Cycle-Square-Wave-Signal-Generator-Module/202085368556

[Cliff Matthews]

19.2V input (Dell laptop PSU). 5V 5A output.

Nice, doesn't look bad at all.. (even better add a choke and cap, "she'll be alright")
You could put two SMPS 19v in series with a big diode between (to go higher), since AFAIK the DPS5005 cannot boost..

Here's my Pace transfo: https://www.eevblog.com/forum/manufacture/my-first-pace-ads200-victim/msg1711994/#msg1711994

[Pirateguy]

maybe i haven't been clear enough about my motivation.

i do not do anything that warrants spending $300 on a psu, or anything else for that matter.
my oscilloscope is a first generation dso nano, and i don't own a single component that wasn't the cheapest
one i could find on ebay and so far those parts have served me perfectly adequately.
such is the simplicity of my projects.

i am JUST a beginning hobbyist who wants to upgrade from the complete ghetto psu i have now
to a more convenient one.
performance is not much of an issue, neither is accuracy. in terms of functionality the collection of wallwarts i have would have served me fine,
but i want more convenience.

so essentially my question to you is: what is convenient?
what can i put in this box, and what manner can i put it in there that will come in handy for a beginning hobbyist like me?

what features do i need?
what features do i want?
what features can i put in there cuz 'i might as well since i have these things lying around and i have the box open anyway'?
what would be the more practical way of setting up connectors and switches etc for the above?
what 'traps for young players' should i look out for?

keeping in mind i will NOT be designing missile guidance systems or medical equipment.
i just want a big box that gives me a more convenient way of powering stuff, and it would be nice if it
gave me some basic info on what it is doing.
THESE are my questions.

[StillTrying]

i actually ordered 2 function generators.
any thoughts on this one?

Yes, it would be nice if someone could comment, to know it's "flakey"

I've got one, the frequencies are only approx. mine runs about 2% fast.
The output TR and 1k pull-up rises ~50ns, falls ~10ns which means narrow pulses % at higher frequencies are off.
The + and - buttons and their acceleration work OK, but I'd describe it as set-able rather than adjustable.
I've only used it between 5V and 10V, which is enough for it to start getting warm.
So it's just about OK for the price.

[rdl]

Too bad you're not in the US. My recommendation for a beginner power supply is one of these:



They cover just about all beginner needs and are commonly found on ebay for $100-150 used. I would look for something similar as far as features and specs.

[HB9EVI]

It's really true: you want to do the 4th step before taking 1,2 and 3. You say it yourself: you are a beginning hobbyist. So why do you want to start all up with an advanced all-in-one device?

All you need in a labsupply is adjustable voltage with current limit and a voltage/current meter showing you the actual parameters.
So - why not to go - for example - with a LM723? The meters you get on aliexpress or you maybe already have them. You can even do 2 independent channels for opamp circuitry.

And: if you want a function generator to buy, watch at least out for a DDS-module with an AD9834. Nobody uses anymore those XR2206, ICL8038 or MAX038; they had their time, but these times are all over. A DDS is also a good diy project to get into uC-programming and the DDS-architecture.

[Jwillis]

Oh let him have his fun.
40 volts and 5 amps can be a tough nut to crack if using BJTs .Power BJTs safe operating area drops off a lot over 30 volts so even the trusty 2N3055 is only capable of a couple amps flat out at 40 volts .That can shorten the life of the transistor. So if you want them to last you'll have to parallel 4 or 5 to keep the things cool. MOSFETs don't respond well to linear applications but can handle much more amperage when pulsed. Are you going to use MOSFETs or BJTs.Of course this is assuming you would like to build from scratch.Most PSU circuits on the web will only go to 30 volts since most regulators are really only capable of around 35 volts .Even the lm317 has a max rating of 37 volts.There are regulators that go higher like the TL783 if your looking for direct regulation.
If I may suggest a floating regulator like the LM723 or similar .They tend to be much more stable and are easier to use.There are others that use op amps as well .
There are hundreds of ways to build a PSU .It just depends on how complex and how modern to want it to be.

[Doctorandus_P]

Turn it around. What sort of things do you do with electronics?
Then make a power supply for those things.
You like electroplating? You may need 3V @ 100A.
You like microcontrollers? 3V3 and/or 5V is all you need.
You like opamps? A dual supply of + and - 15V will be handy.
You like motors? You want lot's of amps from a simple unregulated power supply.

An important feature for any lab power supply in my opimion is an adjustable current limit.
30V 3A was a sort of standard for 40 years, but electronics has changed a lot and those power levels are hardly ever needed anymore.

If you want to design something yourself and want to keep it cheap then I suggest to keep your goals within reason. 20V @1A will be a very usefull power supply and designing such a power supply with adjustable voltage and current limit wil give you plenty to do for a few months of spare time.
There are at least 2 different very common kits with adjustable voltage and current limit you have to solder yourself from China in the price range of < USD 10. If you complement those with voltage and current meters you have a quite decent power supply.

DPS5005 is step down only. However the DPH series from the same manufacturer can also do step up, some go up to 80V.
They also have simpler designs with 7-segment display's and push buttons instead of a TFT and rotary encoders for a price of around USD12.

[Old Printer]

Too bad you're not in the US. My recommendation for a beginner power supply is one of these:



They cover just about all beginner needs and are commonly found on ebay for $100-150 used. I would look for something similar as far as features and specs.

Ditto on this, but I will add that this same PS was also sold by BK Precision as their model 1651. The ITT tech schools that went bankrupt a few years ago unloaded pallets of these on the liquidation market. This is a very solid PS and very easy to work on, and no fan so it is quiet. Tektronix just rebadged it, but in the process put together a very good service manual with full circuit description, troubleshooting, schematics and parts list. The manual is available on CD via ebay for about $12 and the scan is very good quality. In the last few months I picked up 3 of the BK flavor for under $35 each. One had a fault in the B supply, I got TEK's SM and tracked it down to a bad 10 cent diode. The seller replaced the PS for free and told me to keep the bad one I learned a lot tracking down that diode. Bottom line, the BK's are ugly compared to the TEK's, but are available far cheaper and it is the same hardware in a different color case.

[Pirateguy]

Oh let him have his fun.
40 volts and 5 amps can be a tough nut to crack if using BJTs .Power BJTs safe operating area drops off a lot over 30 volts so even the trusty 2N3055 is only capable of a couple amps flat out at 40 volts .That can shorten the life of the transistor. So if you want them to last you'll have to parallel 4 or 5 to keep the things cool. MOSFETs don't respond well to linear applications but can handle much more amperage when pulsed. Are you going to use MOSFETs or BJTs.Of course this is assuming you would like to build from scratch.Most PSU circuits on the web will only go to 30 volts since most regulators are really only capable of around 35 volts .Even the lm317 has a max rating of 37 volts.There are regulators that go higher like the TL783 if your looking for direct regulation.
If I may suggest a floating regulator like the LM723 or similar .They tend to be much more stable and are easier to use.There are others that use op amps as well .
There are hundreds of ways to build a PSU .It just depends on how complex and how modern to want it to be.

indeed let me have my fun! that's a big part of the motivation behind the elaborations.
but also my projects are really all over the place.
i do work with arduinos from time to time, battery operated devices using all kinds of cells, but i also screw around with jacob's ladders and recently i have
gotten a bit obsessed with tesla coils, particularly small ones. and then i'm also gonna be messing with low voltage AC when i get around to playing with this EL wire i have, and now recently i have been looking at diy spot welders.
my main focus though is on special effects for miniature dioramas, and for this i am looking at pretty much anything i can get done at a low cost, incl;
various high voltage spark thingies like the marx generator, and i want to see how small i can make a plasma ball, ultrasonic foggers to animate liquid,
electromagnets to mage items float in midair, tiny animatronics, floating water drops using a strobe, etc etc.

so yeah, variation is desirable.

and no i will not be building from scratch.
though i might do something similar from scratch for a specific project some time.

atm i am thinking of taking this approach:

step 1: build basic PSU out of old ATX psu with a single output that switches between the different voltages available from the ATX.
(-12 and -5 are on there, so why not inculde them) along with a volt/amp display and a temperature display.
possibly later i will expand this above 12v with some boost converters or something.
(so far everything should fit into the original ATX housing.)

step 1b: add a dedicated usb port or 2 on front and/or a series of them on the rear of the unit.

step 2: build second half of this unit in the form of a 317 based variable supply along with another volt/amp display.
i may use a different source for this, like the 32v 1.5A PSU i have (a particularly nice one from HP with lots of safety features)
in which case i would need a larger housing.

step 3a-z: over time add more features to the larger housing such as an AC output, func generator/pwm generator, dummy load, second temperature display (for ext), etc.

step 4: maybe integrate a ZVS driver in the thing.

i imagine this taking place over the course of a year or 2.

[Pirateguy]

on the topic of function generators, i do have some ICL 8038 ICs that i could build one with.
i also have various arduinos and one of those cheap arduino starter kit LCD displays, as well as a small tft screen.

how would u rate the challenge level of such a project?

incidentally i have put together that XR2206 thing and BOY does it suck! lol
i might try to implement those improvements in those videos posted, but i'm not sure it's worth it.
prolly end up using it in some project for some specific task or something...

[Jwillis]

Sounds like you have a version 1 ATX.Version 2 has no -5V.
A simple rotary switch would work or individual output terminals up to you .A variable supply can be wired from the -12v and  +12v and common ground using split rail regulation.Check around for split rail PSU or you can get assembled + and - adjustable power modules on Ebay.  But you will only get the maximum current available of the Negative rail  (-12V).  Or just use an adjustable module from the +12V and common .The USB can be wired directly from the +5V and Com.
A simple digital volt meter ,amp meter and temp meter with sensor can be powdered from appropriate voltage source .Either +12V and common or +5V and common check the meters specifications.
If you intend on a high voltage output I would keep that as a separate isolated output from the low voltage outputs.I would even go as far as a separate transformer .There are modules available based on the TL494 IC that run off of 12VDC .These are low amperage from around a few micro amps to a few milli amps.   

The sense wire on the ATX just needs to be switched to ground to turn the unit on usually a green wire but check the pin outs for your specific PSU.All the same polarity and voltage wires can be tired together. Yellow for +12V .Blue for -12v.Red for +5V, white for -5V and orange for 3.3V .Black wires are ground . Grey wire can be tied to a LED and resistor to indicate the unit is on.Again check the pin outs for your specific PSU.Wire colors may be different.

The total current available is dependent on the ATX. I've not seen version 1 ATX power supplies over 500W.

[MarkF]

on the topic of function generators, i do have some ICL 8038 ICs that i could build one with.
i also have various arduinos and one of those cheap arduino starter kit LCD displays, as well as a small tft screen.

how would u rate the challenge level of such a project?

incidentally i have put together that XR2206 thing and BOY does it suck! lol
i might try to implement those improvements in those videos posted, but i'm not sure it's worth it.
prolly end up using it in some project for some specific task or something...

It looks like the ICL8038 works in a similar fashion to the XR2206.  I would predict a similar result.  But, it maybe a worth while exercise to gain experience since you already have the chips and they only need a few external parts and NO microprocessor required.

If you want to build a function gen, I still feel a modern DDS like the AD9834 will give you better results.  However, they are $12.00 each and have a SPI interface.  Since you already have an Arduino and some small displays, you could start by just programming the display and controls with no initial monetary investment.  Here is the display I did for my function generator to give you a starting point (There is a PIC hidden under the display):

You are definitely going to need a scope to do some debugging.

   

[Pirateguy]

i'm not sure what is more practical, but for limited room for jacks n stuff i think i am gonna
go with the rotary switch.

my ATX has lots of red, black and yellow, but only 1 white, blue and orange wire.
there is a thick shielded bundle of wire connected to the board and power jacks that has a big switch on the other end
to be mounted in the PC case.
maybe the sense wire is in there?

i also read something about having a load resistor on one of the outputs for some reason.
thinking about pulling one off this $1 usb dummy load thing i have.

if i ever put in a high voltage output i intend to have a separate transformer, inside it's own compartment in the housing,
fully isolated from all other stuff.
maybe something like a halogen ballast or a neon sign transformer or something like that. though more likely it will just a ZVS driver,
keeping the actual high voltage stuff external.
my ATX is just a 200 watt one.


---

on the topic of fin gens: from what i understand the xr2206 is not that terrible up to 12v, and it is mainly design flaws in the
board that make this module crappy, aside from already being cheap.
hopefully i wouldn't make those mistakes and maybe i could use multiple chips for better performance.
like dedicate a chip to each waveform, or have different chips for frequency ranges or something like that...

unfortunately i don't have a proper scope.
i do have a OSD nano (first gen) but i think maybe i should hold off on this till i get a proper bench one.

[MarkF]

I think you have that backwards -

• Power Supply  I can think of lots of projects that would require multiple voltages. Essentially, any analog project that includes a microcontroller.  A function generator for example could require +5V, +12V and -12V.  I currently have six power supplies on my bench.
  
  Old ATX Power Supplies required a load on the 5V rail to start. An adapter I bought (never used) included a 10 ohm 10 watt resistor.  The adapter also included fuses.  An ATX power supply DOES NOT have any current limiting and can ruin your day.   http://dangerousprototypes.com/docs/ATX_Breakout_Board   
  
  IMHO: An ATX power supply is not a replacement for a proper lab supply.
  
  
• Function Generator  In almost every case you will only use one signal at a time.  The only case I can think of would be if you needed some kind of modulation.

[Pirateguy]

well i have some 0.9A poly switches, but i also have some breakout boards
with step down converters for arduino. they have 3.3 and 5v.

also the rotary switch i have has 12 positions

[MarkF]

I do like these little HP Supplies.  Not a lot of power but without a fan, they are quiet and don't take up much space.
   HP 6216A Power Supply

Also, an AD9834 DDS Signal Generator Sine/Triangle/Square Wave Generator module that you could interface your Arduino to.
   AD9834 Module

[Old Printer]

I do like these little HP Supplies.  Not a lot of power but without a fan, they are quiet and don't take up much space.
   HP 6216A Power Supply

Ditto on the little HP's. The 6216A is good for about a half amp at 24 volts. Has both voltage and current modes, each having coarse and fine adjustments. Very well documented which is easily available online. Operation, service & schematics. With a little patience they can be had in nice shape for $50 shipped on ebay. I bought three last winter like that for my bench in a spare bedroom. Quiet and compact, built like a tank and easy to repair.

[Pirateguy]

 

[Jwillis]

Seems when you start to make progress you get cornered by more salesmen .I feel your pain.....Anyway.
Ok so your +5V and +12 volt will give you the most current .3 volt will probably only be a few miliamps .You can load one of the +5 volt lines with a 5 to 10 Watt power resistor connected to ground.
Difficult to say what the potential current is. Current limiting is nice to have, but not completely necessary.Unless you create dead shorts your projects will only draw as much current as it requires .You can always put in short circuit protection later if you like.
We can start by tying the yellow wires together and the black wires together.tie all the red ones together except one .We'll use that for the 5-10 Watt 10 Ohm resistor.If  yours has a switch you can use that one or shorten the bundle and use a similar switch put through the ATX case.You can use a LED and a 1 or 2k resistor for each voltage if you like to indicate which voltage you switched to.Will also indicate power on.For variable power try a buck boost variable regulator..
Maybe consider a larger enclosure than the stock enclosure.Things will most likely get pretty cramped inside.

[MarkF]

Seems when you start to make progress you get cornered by more salesmen .I feel your pain.....Anyway.
Ok so your +5V and +12 volt will give you the most current .3 volt will probably only be a few miliamps .You can load one of the +5 volt lines with a 5 to 10 Watt power resistor connected to ground.
Difficult to say what the potential current is. Current limiting is nice to have, but not completely necessary. Unless you create dead shorts your projects will only draw as much current as it requires .You can always put in short circuit protection later if you like.
We can start by tying the yellow wires together and the black wires together.tie all the red ones together except one .We'll use that for the 5-10 Watt 10 Ohm resistor.If  yours has a switch you can use that one or shorten the bundle and use a similar switch put through the ATX case.You can use a LED and a 1 or 2k resistor for each voltage if you like to indicate which voltage you switched to.Will also indicate power on.For variable power try a buck boost variable regulator..
Maybe consider a larger enclosure than the stock enclosure.Things will most likely get pretty cramped inside.

Fuses or No Fuses?

An ATX Power Supply has almost the same current capabilities as my MIG Welder!  If you drop a wire into a project you're testing, short the wrong pins with a probe, or a wire comes loose on a solderless breadboard -- FIREWORKS.  Accidents happen.  The polyfuses the OP has would be a must in my book.  As I mentioned earlier the ATX Breakout board has the polyfuses, ATX power connector, load resistor (if needed), On/Off Switch and LED power on indicator.  Just plug and play. No need to modify the power supply or cutting off connectors and dealing with tying off unused wires.

   

From everything the OP mentioned, the ATX power supply would probably be the cleanest way to go over the wall-warts.  I can also envision projects that require multiple voltages.  NOT a rotary switch with a single output.

The OP has a lot of suggestions of what "to do" and "not do".  Plus several options of low cost items that are available to purchase.  If this all seems like too much to take in, I would stay far away from the high voltage projects mentioned!  I'm sorry if this comes off mean spirited.  It's not meant to be.  Just trying to point out the dangers.

[Pirateguy]

well my ATX is onlu 200watt, but that still plenty to set my projects (and me) on fire.
some years there was a death in the family and i inherited a bunch of electronics stuff from this person.
including a bunch of fuses.

do those things age when not in use?
and what kind of values am i looking for?

to clarify: i want BOTH a selectable fixed voltage that i can dial in with a switch AND
a variable output that i can set with a pot.
the variable output at least will have a little panel v/a meter to tell me what is going on and the unit will have a temp display.

if i understand correctly you are saying it is better to have each output with it's own binding posts
cuz i might need to use several at the same time?

i have some breakout boards for stepping down to 3.3 and 5v for arduino. i am considering including one of those
and drawing the 3 and 5v from there instead of directly from the atx.
and for the variable output i have 317 and 338 regulators.

maybe i should make it so i can switch between a 5amp 338 one and another limited to lower current?

right now the only high voltage stuff i am screwing around with is all powered by those cheapo stun gun modules off ebay:
particularly these 2:
https://www.ebay.com/itm/15KV-High-Frequency-Inverter-Generator-High-Voltage-Electric-Ignitor-Coil-Arc/382475346892?ssPageName=STRK%3AMEBIDX%3AIT&var=651230490166&_trksid=p2057872.m2749.l2649
https://www.ebay.com/itm/High-Voltage-Pulse-Generator-Inverter-Module-Super-Arc-Pulse-Ignition-Coil-DH/362195494965?ssPageName=STRK%3AMEBIDX%3AIT&var=631407328312&_trksid=p2057872.m2749.l2649

neither of those have the cap built in and they are basically like arc lighters and will run off 2xAA.

what i want right now is to see how i can incorporate sparks as special effects for dioramas, so
it's gotta be low power anyway. dioramas tend to be fairly flammable
so part of the scope of my high voltage projects is to see how low i can get the amps and still have cool looking sparks.

this stuff is indeed overwhelming, especially for me as i have ADD.
that's kinda why i came here; to plan things out ahead of time (after having it checked for stupidity)
and work systematically, 1 step at a time.

[Pirateguy]

just remembered: i still have a couple of UK wall plugs.
harvested 2x 3A fuses from those.

[MarkF]

well my ATX is onlu 200watt, but that still plenty to set my projects (and me) on fire.

Mine too.  Just trying to drive home the point with those who think fuses are not necessary.   

to clarify: i want BOTH a selectable fixed voltage that i can dial in with a switch AND a variable output that i can set with a pot.
the variable output at least will have a little panel v/a meter to tell me what is going on and the unit will have a temp display.

if i understand correctly you are saying it is better to have each output with it's own binding posts
cuz i might need to use several at the same time?

Exactly.  Separate posts for each voltage.

i have some breakout boards for stepping down to 3.3 and 5v for arduino. i am considering including one of those
and drawing the 3 and 5v from there instead of directly from the atx.
and for the variable output i have 317 and 338 regulators.

Why?  Just use the 3.3V, 5V, +12V and -12V directly from the ATX supply.
You could tap off one of the ATX +12V lines to drive a LM317/LM338 to create a 0 to 10V variable output. (I believe the cutoff for the LM317 and LM338 is around 2V.  So, you won't be able to go above 10V with a 12V input.)

maybe i should make it so i can switch between a 5amp 338 one and another limited to lower current?

You can go a long way with the ~1A polyfuses (or normal fuses) on each output voltage.  I would wait a see what your real needs are and proceed from there with something more at that point.  You may wish to buy a proper lab power supply with current and voltage adjustments.

[rstofer]

Difficult to say what the potential current is. Current limiting is nice to have, but not completely necessary.Unless you create dead shorts your projects will only draw as much current as it requires .You can always put in short circuit protection later if you like.

I would think that adjustable over-current protection would be the second most important criteria for a power supply right after voltage.  I don't always care if voltage is adjustable, I just need +- 15V and 5V but current limiting at a low level seems terribly important.  Having current foldback on a 5A supply doesn't do much to protect things.

The other day I was bringing up a Z80 project and there was an address conflict.  In effect, two sources were driving the data bus at the same time.  Not good!  I had set the current limit to 100 mA and, sure enough, the limit kicked in and the output voltage dropped to about 1V.  This potentially saved a lot of chips.

Even adding fuses doesn't do much good if they are of some high value.  I want to limit current at low mA, not low Amps.

If I didn't have the money for a real lab supply, I might try these $6 Chinese supplies just to see if they would work.

https://www.ebay.com/itm/Red-0-30V-2mA-3A-Continuously-Adjustable-DC-Regulated-Power-Supply-DIY-Kit-PCB/201751652278

There are dozens of these supplies around, maybe some of them are satisfactory.

[rstofer]

well my ATX is onlu 200watt, but that still plenty to set my projects (and me) on fire.

Mine too.  Just trying to drive home the point with those who think fuses are not necessary.   

if i understand correctly you are saying it is better to have each output with it's own binding posts
cuz i might need to use several at the same time?

Exactly.  Separate posts for each voltage.

Spaced exactly 3/4" on centers so that double plugs will fit.

[Pirateguy]

i was thinking i would have a selector switch between differently rated fuses.
one limited to something appropriate for micros and something a little stronger for motors n stuff like that.

i was thinking of using the breakout boards cuz they come with a regulator for each output.
isn't that also a way to limit the current?

[MarkF]

i was thinking i would have a selector switch between differently rated fuses.
one limited to something appropriate for micros and something a little stronger for motors n stuff like that.

I don't know if that would be worth while.  If you really want different current capability outputs, I would have separate output jacks.  It is far too easy to overlook a switch position. 
You could put a high current output and the variable voltage output off to the side to distinguish the difference.

i was thinking of using the breakout boards cuz they come with a regulator for each output.
isn't that also a way to limit the current?

The current limiting capabilities of those breakout boards is probably only a thermal shutdown.  Far too late to save you.  Just stick with the ATX outputs and fuses.  Just speculation not knowing the exact boards you are referirng to.

I prescribe to the K.I.S.S. (keep it simple stupid) theory.

[MarkF]

Here's is a possible panel layout:

   

I agree with having a 3/4" horizontal spacing between the jacks. 
There is a high chance you would use the double banana plugs at some point.

[sureshot]

Once you've done your wire grouping and or binding posts, preload options...
If you choose the atx route how about this below.
Rotary switch is break before make configuration.

[rhb]

I suggest visiting thrift stores and looking for an old piece of audio gear that's cheap.  Those will usually have a good transformer for a linear supply.  Another option is to rewind the secondary of a microwave oven transformer.  That will certainly give you 0-40V at 5 A provided you add a *large* pass transistor to the LM317 with a big heatsink. For the fixed stuff just use the ATX.

Adjustable current limiting is not difficult.  For the ATX, use a comparator, a sense resistor voltage divider pot and flip flop so if overcurrent is detected it toggles the flip flop and disables the PSU power enable line until you press a reset button.

I think it would be wise to start with the ATX as a base, but in a large enough case that you can add an adjustable linear supply later.  The layout by MarkF looks very practical.  Get some cheap DMMs and add switching to monitor voltage and current using those minus the cases.

[Pirateguy]

these are the boards i was talking about:
https://www.ebay.com/itm/5Pcs-DC-DC-12V-To-3-3V-5V-Buck-Step-down-Power-Supply-Module-For-Arduino-/352280409059?var=&hash=item0

my thinking was that instead of blowing a fuse when u use too much this would just limit the current and not deliver more then it can.
seems to make more sens then replacing fuses... although i would include those too in case of anything malfunctioning in the PSU or something like that.

so i went over the fuses i have, and looked up the codes n stuff.
apparently they come in speed ratings, are the slow ones ok for this?

also lemme see if i got anything wrong here:
remove access wires, combine multiple rails of the same output, run a wire for each output to a fuse, and from there to the jacks?
and for the variable the fuse goes between the atx and the regulator?

I suggest visiting thrift stores and looking for an old piece of audio gear that's cheap.  Those will usually have a good transformer for a linear supply.  Another option is to rewind the secondary of a microwave oven transformer.  That will certainly give you 0-40V at 5 A provided you add a *large* pass transistor to the LM317 with a big heatsink. For the fixed stuff just use the ATX.

Adjustable current limiting is not difficult.  For the ATX, use a comparator, a sense resistor voltage divider pot and flip flop so if overcurrent is detected it toggles the flip flop and disables the PSU power enable line until you press a reset button.

I think it would be wise to start with the ATX as a base, but in a large enough case that you can add an adjustable linear supply later.  The layout by MarkF looks very practical.  Get some cheap DMMs and add switching to monitor voltage and current using those minus the cases.

could i just yank the whole setup out of an extension cord that has that feature?

with large pass transistor, do you mean one that lets through a lot of current?
i have some 2N3055 ones that look pretty beefy...

for power monitoring i have a couple of panel units that show volts and amps at the same time.

for now i think i will build it all into the original ATX case as i don't have anything else right now,
and i want to take my time finding something that looks nice.
there is enough room though for a regulator circuit to do a limited variable output of 10v as suggested below.

[MarkF]

DO NOT TAKE THE ATX CASE APART.
The extra space is needed for air flow.

Just use the wires on the connector for the motherboard.
Cut out the wires you want to use from the connector and leave the rest.
You may wish to use the leftover wires in a future mod. Or power your function generator.
Leave the disk drive connectors alone.

You said you have polyfuses. 
I would recommend them for the low current outputs and the variable output.
They reset after the load is removed.

I would save your breakout boards for something else. 
They don't have any special current limiting.
You're not going to gain anything over using the ATX outputs with some polyfuses.

The slow-blow fuses will react slower and will take a little more current.
I would suggest 0.5A for the low current outputs and 5A for the high current output.

Something in the 0.5A to 1A range for the variable output.
Put the fuse on the output of the variable supply. Also, you will need a heat sink and cooling.
You will need to carefully consider the grounds for this if you drive the input from something other than the +12V of the ATX supply.

You are probably okay not having fuses for the internal things you power from the ATX.  Just for lines leaving the box.

You also need to be careful how you wire those volt/amp panel meters. 
You especially need to check the low sides of the input power, volt meter and amp meter. 
Some have the low sides tied together and will short what you're trying to measure if connected wrong.

Like I said before, I would not get overly ambitious for a first project with unknown needs.  Just the basics for now.

[Pirateguy]

lol i already cut off the connectors, but no worries, i may be a noob but this isn't the first time i heat up a soldering iron.
(and i have several half finished robots to show for it )
and don't worry, i know all about discharging the caps n stuff. u could safely shower with this thing right now.
i intend to desolder the wires i don't need instead of cutting them, and will have no trouble adding new ones if needed.
and the case, once i find a larger enclosure for it all, i will ditch entirely.

with the room i have available, and some reworking of the wiring, changing yuge connectors for solder connections,
i think there is more then enough room for air flow and the circuit for the regulator for the variable output
shouldn't take up too much space.
only the interface will take up space, and it's not too terrible (again after taking care of some unnecessarily bulky plugs n stuff.)
also there will be a thermometer on the thing, so if i run into trouble i should get fair warning, and i can always drill some holes and add another fan if needed.

also i think right now i will just do the fixed outputs in the ATX box, and make the variable a separate unit for now until i find
a proper housing for it all. i have a nice looking HP 32V 1.550A linear psu with what looks like ample protection.

also there is a yuge heatsink already in the atx and i was thinking of making use of that. though i do have other heatsinks if needed, incl specific to220 ones.

once my brain gets done booting up ill post some pics.

[Pirateguy]

[MarkF]

The 32V HP Supply and a LM317 would make a very nice variable supply.
However at low output voltages and a 1A load, the LM317 would need to dissipate 30W. 
You could use a bypass transistor to handle the load. There is a two transistor configuration in the datasheet if you want to use the 2N3055.

I saw a thread last week discussing a LM317 and a TIP36C PNP bypass transistor.  I would opt for the PNP single transistor.
   https://www.eevblog.com/forum/beginners/lm317hv-and-heatsink/

I would also use a 10-turn potentiometer to adjust the voltage.
   https://www.mouser.com/ProductDetail/Bourns/3590P-2-103L/?qs=sGAEpiMZZMvygUB3GLcD7uCOAMig3YAGHWGOtVZsEa0%3d

[Pirateguy]

what about lm338?
i have some of those coming my way.

edit:
that pot is a bit pricey for my budget, how about this one:
https://www.ebay.com/itm/1PCS-3590S-Precision-Wirewound-Potentiometer-Pot-10Turn-500R1K2K5K-10K-20K-50K/302098816720?hash=item46567e1ed0:m:mEC_-G0YRedjCMHo_CI84VQ

[MarkF]

The LM338 would work as well. 
The thread I pointed to has a few extra parts than normally shown in the datasheets. 



Here is another thread discussing bypass transistors:
   https://www.eevblog.com/forum/beginners/resistors-purpose/

That eBay 10-turn pot looks like the same Bourns one with different type pins.  I rarely buy from eBay and put together larger orders with Mouser. 
You will have to go over the design for your voltage range and pick the pot value you will need.

[Pirateguy]

do i need those transistors? if i am reading the datasheet correctly the 338 can do 5 amps, and that's about as much as i can imagine myself needing.
i have a ZVS driver kit and a stungun module that ask for 12v, and those are the only times i have needed to account for amps beside limiting resistors for leds.

if yes, anything with the right power capabilities will do?

[MarkF]

It's not the current that is the limiting factor.  It's the heat the LM338 will have to dissipate. 30W or more is going to generate a lot of heat.  You will need a big heatsink and a fan.  The worse case will be the voltage drop across the LM338 and the current drawn by the load.  You can calculate the power the LM338 will need to handle by the worse case you expect to use.  You could try with just a LM338 and see if it can handle power levels you want to use.

Even with a PNP bypass transistor, you will be transferring (I should say sharing) the power dissipation from the LM338 to the transistor.  The TIP36C transistor in the other thread comes in a TO-247 package which is almost twice the size of a TO-220.  Much better to dissipate the heat.

Most power supplies will have relays to switch to different input voltages so the regulators don't have to dissipate all the heat.

[Pirateguy]

i was thinking of attaching them to the top of the big heatsink that's in there, which is right in line with the fan.

what about the MJ2955?
it is the compliment to the 2n3055 i have and comes in a to-3 package.
also i have some ceramic plates to go in between the heatsink and transistor.

[MarkF]

Let's not jump off the cliff just yet.
Let's take a look at what you are trying to do here and what your options are.

  1)  Using the 32V 1.5A HP Supply, you could design something in the 0-30V @ 250mA to 500mA range without a bypass transistor.  It would be a simple construction and in most cases it would be all you would need.  For example, I have a 60V @ 250mA maximum supply.

  2)  Using the 32V HP Supply, you could add a bypass transistor to reach the 0-30V @ 1.5A range.  Maybe limit to 1A to make it easier.  A more involved build.

  3)  Using the 12V from the ATX Supply, you could get  in the 0-10V @ 5A range.  I think it would be rare that you would use these current levels.  In the two cases you mentioned, you would used your 12V high current output directly from the ATX supply.

To answer your question:  You could build with a MJ2955.  You could probably make almost any power PNP transistor work.  You will need to adjust the resistor values to get the desired bias voltage.

As for a variable power supply:  Is this something you want to build or buy?  How much effort do you want to do in the design and build?  Personally, this is one item I would buy.  Possibly with a LAN interface to automate some project testing.

In reference to using the ATX heatsink.  It is NOT something I would recommend.  You have already compromised the cooling and airflow by removing the case.  The saving grace is that you are NOT using anything near the capabilities of the supply.  It is still to be seen if it gets hot during use.

[Pirateguy]

i want to build my own for now, and either improve it over time or replace it with a commercial unit
if/when my projects and needs get more sophisticated. though i have a bunch of things still higher up on my wishlist.
including a DSO (currently have only a 1st gen dso nano) and moving to another house.

as for the ATX case, my intention was to put it back in the original case and build all the externals into the side.
all that will change in the end is there will be fewer wires, some room made by removing bulky connectors and soldering
wires to the board, and the back side of all the binding posts and display etc.
which, on that side should not effect airflow too much.

if i add another heat sink though that will change i think.
so right now i think maybe going with the HP one for the variable might be better.
though i don't have a case for it that can fit the additional stuff.

so for now i think i will build the ATX with the fixed outputs and a temperature display.
ill use the polyswitches for protection, and add LEDs on each output to let me know if i popped one.

and i will set aside the HP one for the variable unit, and treat that as a separate project.
prolly end up going for suggestion 1) with an option to upgrade to suggestion 2) later.

so for the ATX fixed output unit, for the load resistor on the 5v, could i use one of the ones from this thing?:

[MarkF]

Try it first without a load resistor. Some supplies don't need it. Depends on when it was made.

[coldfiremc]

Sorry but I can't resist

[MarkF]

Fantastic 
But the sword is jealous

[MarkF]

I do like these little HP Supplies.  Not a lot of power but without a fan, they are quiet and don't take up much space.
   HP 6216A Power Supply

Ditto on the little HP's. The 6216A is good for about a half amp at 24 volts. Has both voltage and current modes, each having coarse and fine adjustments. Very well documented which is easily available online. Operation, service & schematics. With a little patience they can be had in nice shape for $50 shipped on ebay. I bought three last winter like that for my bench in a spare bedroom. Quiet and compact, built like a tank and easy to repair.

Great minds think alike Old Printer.
I also bought three of the HP-6216A power supplies for my bench in a spare bedroom. In addition, I bought a HP-6217A which is 50V@200mA.
I also built a +/-15V@1A using the PCB I posted above for an analog project needing clean power rails.

[Pirateguy]

oh for crying out loud!

lol ok i get it, can't beat em...

so wat do you guy think of these modules?:

[plazma]

oh for crying out loud!

lol ok i get it, can't beat em...

so wat do you guy think of these modules?:

I already suggested them. I favor the DPS5005 module because it is the most powerfull of the compact ones (pcb in display module).

[MarkF]

I watched Dave's video a while back.  But that is all I know about them.
They look promising if you want to buy something.  One would probably be a better choice to pair up with your HP power supply or the ATX depending on the voltage range you're interesting in.

Edit:
After watching the videos again, my only concern would be that the output is noisy.  It may or may not be an issue depending on what you're using it for at the time.

[Pirateguy]

i don't mind some noise, it will just force me to learn about putting filters in my projects n stuff when it comes up.
(does that make sense?)
i like the panel type setup, leaves a lot of freedom over the placement of the binding posts n stuff.
ill keep these in mind for later. for now ima diy it. i feel like this is all stuff i'm gonna need to know about
anyway to progress in my hobby. so itll be worth it just for the experience.

speaking of dave's videos, i found the perfect one for me and this project:

i haven't watched the whole thing yet, but it looks like this will teach me the math i need
for the adjustable one.

anyhoo, wat do you guys mean when u talk about 'double bananna plugs'?
and does the 3/4" measurement have to be exact? or is it a minimum?

[Old Printer]

About a year ago when I was needing my first decent power supply I ran across this series of videos where Dave designs a PS. I had a look inside some good quality supplies and was amazed at the complexity of the circuit and components. I realized I was not going to be able to come up with anything like that on my own and started watching Dave's. I don't recall which video number it was, but 3 or 4 into the series he started running into complications. As I recall he kind of lost interest in finishing, or at least overcoming all of the problems to his satisfaction. This is very loose recollection on my part so don't quote me, but it was at that point I set my sights on a good commercial PS. The nice HP's were too expensive so I headed to the used market. Seven PS's later I think I have enough for now They can be an addiction.

[MarkF]

anyhoo, wat do you guys mean when u talk about 'double bananna plugs'?
and does the 3/4" measurement have to be exact? or is it a minimum?

There are a lot of varieties.  The spacing is 3/4".  Just Google them.  Here are a few:

[MarkF]

speaking of dave's videos, i found the perfect one for me and this project:
      _{Video removed}
i haven't watched the whole thing yet, but it looks like this will teach me the math i need
for the adjustable one.

Yes.  Dave's video would be a perfect learning experience.  Follow it with two LM338's and get it working on a breadboard.
Then layout a PCB and get it made.  You can expand on the layout I showed above by adding the current limit stage.
The 4 diodes form a full-wave bridge for an AC input.  Or, you can bypass them and feed in DC via a wall-wart plug.
You can get five 100mm x 100mm PCBs made for $5.00 US at Elecrow.

     

[Pirateguy]

lol but postage would be $8
for now i think ill just use some perfboard.

so i had an idea:
using this calculator: http://diyaudioprojects.com/Technical/Voltage-Regulator/
i determined that i need 5.9k to get exactly 32v. so i was thinking
what if i just put a 10k multi turn pot parallel with a small 20k pot on the pcb, and use the 20k to tune the max resistance
till it gives me 30V?

[MarkF]

If you do two LM338 in series (1st doing current limit, 2nd setting the voltage), you are probably only going to get 28V for the output. That's assuming 2V drop-out volts for each LM338.  Designing for 25V would be more realistic.

Using that calculator, you have R1=240 and R2=5K.  I would only use a 5K ohm 10-turn pot mentioned earlier for the voltage control.

I built an Electronic Load with a 10K 10-turn pot and it gave me plenty of sensitivity to set the current.  One 10-turn pot for each LM338 should be enough for the current and voltage adjustments.  You would probably only use two pots if they were the 3/4 turn type. If you want two pots, they would be in series with one big (say 5K) and one small (say 500).  Parallel pots would be a NO NO.

You will need to determine the value for the current limit pot.

Dave's video mentioned that the LM338 needs a minimum load and to adjust R1 and R2 to provide that load.  I haven't worked through the math to determine the best values to use.


I know the postage would cost more than PCBs from Elecrow if you only get one design made.  I try to order more than one PCB design to make the postage worth while.  But, I suggested it so you have the experience of going through the whole process and learn how to do a PCB layout and get it built.  Maybe even a second board with all your polyfuses and whatever meter switching you want to do.

[Pirateguy]

yeah i'm not quite at the point where i want to order commercial boards like that yet (though i am excited about these options we have now).
i want to be better at designing circuits first so i can have some confidence of not having to order the same board 5 times due to tiny mistakes.
and also i want to transition from THT to SMD first, at least to the point of having confidence in being able to solder a board full of 0805.

y no resisters in parallel?
with what i had in mind the 2nd one is just for fine tuning the range and then maybe fixing it in place.
the idea was that i would not be bound by standard values for resistors...

anyway i totally spaced on the 2nd 338 for the current
back to the drawing board...

still, you sound like no pots parallel is a bad idea in general?
if so, how so?

also the minimum load, isn't that what the 240ohm resistor is for?
my circuit would have been the diode protected version that is in the datasheet, only adding that sencond pot...

[rstofer]

Pots in parallel:  Spend some quality time with Excel.  Compute, say, every 10% of the first pot in parallel with every 10% of the second pot.  Rerun for different pot values...  Remember:  The parallel combination of resistors is always less than the smallest value.

'Fine' and 'Coarse' adjustment pots are often in series.  It might be marginally faster to adjust two single-turn pots than a single 10 turn pot but just how often does the voltage need to change?  Three supplies may be set for +-15V and 5v and never changed.  Ever!

I suppose an adjustable supply could be used as a signal source and speed dialing might be handy but I would still prefer the 10 turn pot.

[Pirateguy]

what i mean is that i only mount 1 pot on the panel and one inside the case that cannot be accessed.

i would turn the panel pot up all the way and then dial the pcb pot in to the max voltage i want.
after that i would never touch the pcb pot again and only use the panel pot to change the voltage.

[ricktendo]

I already suggested them. I favor the DPS5005 module because it is the most powerfull of the compact ones (pcb in display module).

And also there is a open source version firmware called OpenDPS for the DPS5005 (also controllable via WiFi (ESP8266) or via a serial port)

https://johan.kanflo.com/upgrading-your-dps5005/

https://johan.kanflo.com/hacking-the-dps5005/

And it seems like the OpenDPS firmware is also compatible with my DPS5015

https://gojimmypi.blogspot.com/2017/04/opendps-with-dps5015.html

Edit: I wish somebody could post some instructional videos on the whole compiling and flashing process!

[MarkF]

I just ran across this video that is of interest in doing the current limit.

   


Which would look something like:
R_SC=10,  R2=110,  R3=1K  ==>  125mA<=I_OUT<=1.26A
Remembering that our minimum voltage is going to be 1.25V because we don't have a negative voltage source.
I'm afraid that the voltage drop across R_SC will not make this a viable solution.

   

   

[MarkF]

I forgot all about this:
  You might consider this power supply by Peter Oakes:

   

   

[MarkF]

Okay...   Here is a cross between your original two LM338 design and Dave's current limiting case.  There are still a few odds and ends to work out.

   

[Pirateguy]

i wasn't actually thinking of using 2 lm338 or an adjustable current limit,
but rather that using a regulator would cap the max current at whatever the
regulator's max capability is.

is this wrong?

i like the idea of having an adjustable current, but that might be a bit over my head at the moment.
i am decent at basic math, but i never learned any kind of shorthand in school or anything, so i still need
to learn to interpret these formulas n stuff.

like when it says '(stuff)morestuff', does that mean i calculate '(stuff)' and then multiply the result by 'morestuff'?
there seems to be a missing symbol there...
is there a guide or something out there that happens to focus on specifically those kinda questions?
i bet i can do it if i can just learn to translate it into english...

anyhoo, for now maybe i should build a variable voltage one for now and separate the variable current limit to
a later upgrade project?
in which case, single 338 +bypass transistor +polyswitch?

in that last pic, what is REF02?

[MarkF]

You can build the adjustable voltage part of the last circuit (It's just like in the datasheets) and then add the variable current limit later.  The variable current section just monitors the current through a 1 ohm resistors and pulls the LM338 adj pin to gnd, which sets it's output to minimum, when the current reaches the set point.  Identical to Dave's video.  Just watch his explanation and think LM338 where he has the LT3080.

The REF05 is a 5V reference.  You would need the variant that has a 40V input capability.
   www.analog.com/media/en/technical-documentation/data-sheets/REF01_02_03.pdf

i wasn't actually thinking of using 2 lm338 or an adjustable current limit,
but rather that using a regulator would cap the max current at whatever the
regulator's max capability is.

is this wrong?

Do not depend on any chip for current limiting.  That's the same as not using any fuses and just waiting for the meltdown.
I would still use a polyfuse on the adjustable supply just like you're doing for the fixed outputs from the ATX.

[MarkF]

Here's an initial cut at what the LM338 Adjustable Voltage and Current Limit Power Supply PCB might look like:

   


Updated for AC or DC inputs (not all parts would be populated).

[JS]

I forgot all about this:
  You might consider this power supply by Peter Oakes:

   

   

  That looks quite unstable, I run a simulation and it behaves awfully, specially with a little bit of capacitance at the load. Adding some resistance at the output makes it better but that screws regulation even further than the already badly placed current sense. Some inductance in parallel with the resistors helps but now it's getting tricky, not as simple as it looks. output wire parasitics might be enough in some cases but relying on that isn't good practice. I think Peter showed this as a first approach, to show a working prototype with a minimalistic approach but it doesn't mean it's a good design. It does work on steady conditions but will overshoot every time it can.

  Something similar would happen with the LM338 example, it might work but once in the real world it will catch a condition when it becomes  as current limiting doesn't look particularly stable. It's quite easy to make one or the other condition stable but the transition between both gets tricky to get right. I've explained this in a topic, I designed a CC/CV dummy load which simulates stable under a wide range of conditions, I haven't found one where it behaves erratically, overshoots badly or starts oscillating, I did build a prototype for the first attempt and it was ok, the second attempt after some math and more time on the sim looks even more promising but I haven't got around to build it yet. In the meanwhile it showed the possibility of adding constant resistance mode which looks nice so I might add that before finally building and for simple tests I have the first one which does an ok job for general testing.
  Going from there to a power supply adds a few challenges, they are similar but the load isn't designed to reject ripple for instance or accomodate for input voltage variations as it's only looking at the voltage across the pass elements, turning that around swaps all the control configuration bringing new stability issues so is not a straight forward conversion.
  There's a design around here of a dynamic load which seems great, much faster than mine, only current but with a pulsed current on top of the DC, so you can look at the dynamic response of the DUT.

  In all this time looking for a simple design of a lab PS which meets my desires I haven't found a project up to the task. I'm not being too picky about voltage and current ranges as I am with dynamic response under different loads. I expect my lab PSU to behave as it should with capacitive or inductive loads, avoiding overshooting and oscillations which might bring problems to the table later on when I'm testing something and trusting the PSU.
  One thing I'm considering is using two power devices to regulate current and voltage independently, which makes control much easier but that doesn't scale up nicely as two small devices are cheap and easy but once you get into higher powers needing multiple bigger devices it gets expensive and having twice as much as needed doesn't play nice.

JS

[Pirateguy]

man, i thought this was gonna be simple. lol.
this and some other stuff i been reading lately suggests that power supplies in general are kind of an advanced project
the moment you make any kind of demands of it's performance.

i think i'm gonna have to just build the fixed output ATX one, then the variable voltage one, and then
reassess if i want to diy anything more complicated after using that for a while.

[MarkF]

@JS:

I'm a little confused as to which circuit you are referring to or both.

If Peter's design, he makes heavy design changes by the end.  It's been a while since I've watched the series and I don't remember what all he does.  The last I looked he was redesigning the entire thing and his Electronic Load.  I built his Electronic Load and it performs well even when driving it externally with pulsed control.

If my last Frankensteined design of the adjustable voltage circuit in the datasheet with Dave's current limit approach in his video.  To me it looks okay on paper but I have not built it up and performed any testing.  If you see any specific issues with the design, I would like to hear them.

[MarkF]

man, i thought this was gonna be simple. lol.
this and some other stuff i been reading lately suggests that power supplies in general are kind of an advanced project
the moment you make any kind of demands of it's performance.

i think i'm gonna have to just build the fixed output ATX one, then the variable voltage one, and then
reassess if i want to diy anything more complicated after using that for a while.

This thread has been throwing a lot of things around.  Don't get put off yet. 

• Your ATX fixed output should be in the can with just a few fuses.  This is going to be your workhorse 90% of the time.
• The Adjustable Supply is a good project to cut your teeth on.  Build it up and do some tests.
• Then, try building an Electronic Load.  About the same difficulty or easier then the Adj Supply.   
• After, tackle a Function Generator.  It would be a mix of analog design controlled by a microcontroller. (The Arduino's you already have for example.)

[plazma]

This thread has been throwing a lot of things around.  Don't get put off yet. 

• Your ATX fixed output should be in the can with just a few fuses.  This is going to be your workhorse 90% of the time.
• The Adjustable Supply is a good project to cut your teeth on.  Build it up and do some tests.
• Then, try building an Electronic Load.  About the same difficulty or easier then the Adj Supply.   
• After, tackle a Function Generator.  It would be a mix of analog design controlled by a microcontroller. (The Arduino's you already have for example.)

It depend if you want to use time and build your own gear or buy ready made ones and  use them for the hobby straight away.

Current limit is so important I would not bother with an ATX supply. The DPS modules are so cheap and work well.

[JS]

  By all means, build a variable PS with an LM317, or two... The ATX looks a bit dangerous for the projects as it can source quite a bit of current and blowing fuses testing projects is not my thing. It is useful to power a few things and I have a bunch I use every now and then when I need to test something, like feeding the input of your variable PS to test it. As Plazma just said, the "LAB SMPS" option is now available looks great and are cheap, with that and a laptop power bank you get quite a bit out there, I'm considering to get those but as SMPS doesn't quite get to a linear one I'm still with my project, even if I do get some of those.

  The circuit with 2 LM317 with a switch for selecting a few different current limits seems nice, I never build one but I wish I did, now I'm trying to get a more advanced one as I see I should be to the task.

  The frankie with Daves approach tends to be unstable, Dave stabilized it making it really slow to climb and fast to go down, with some big capacitance on the Vadj pin. The voltage being FF shouldn't overshoot which is nice. When he shows the Vadj pin on his you can see quite some oscillations going on in a few different situations. CC is one of them and you might get a noisy output there, put the shunting transistor to some abuse or be too slow and have quite a big current overshoot, you choose.

  Now, after my last post one idea came to mind that looks promising at a first glance in the simulator, more testing should be done there before addressing the real world design, ideally my design should be scalable to higher voltages and currents. Decent currents could be archived with a single big mosfet without worrying much about redesign other than stability tweaks to compensate for gate capacitance, for an extended voltage range the opamps rails becomes a problem, like 0-30V range you want the opamps to be able to run a bit wider than the range, and low dropout from the main supply for efficiency and better range from the same pass device. I'd like to run all that from a single transformer, which combined with the last few points makes for the need of some higher rail likely using a multiplier, to archive a higher voltage rail for the opamps. Last but not least, I want to be able to control it with a µC. On top of all that I want to use all standard components, nothing fancy or special. All of that put a lot of restrictions, I'm not to fancy about precision and stability, to makes things easier but that mostly comes to the µC side of things, where you could choose better reference and converters to improve on that, as well as opamps if going to the limit.
  Just for kicks, the difference in the new approach is using what Dave shown on the first video designing a lab PSU, in EEVBlog #221 as the constant current control, a conventional approach to control the voltage using a second opamp and a diode to select between both. As I have the current sense resistor in the high side after the pass device for the current mode it makes easy to stabilize the voltage mode under different loads without introducing new losses and keeping a good load regulation. An N-channel pass transistor looks like the more promising device but as has been discussed around here getting a proper transistor to work in this kind of circuits inside the SOA and not shortening it's life is a harsh problem, it looks like I can get an IRFP064 like the one in the Peter Oakes's design for about $3 which seems like a suitable part for a nice range, not needing to go for IXYS which could cost many times that. I'd probably start with some smaller IRF part to test around as I've been doing with my dummy load, if all comes together I'd get a few of those so shipping doesn't cost more than the devices.

  Going too long with this, I just hope to find some time for it and finally get to something, I want to get this right and test it to then share it with all of you, with a flexible design that anyone can build with it's own specs, right now I'm moving the lab in a new room in my house so it's all been quite messy plus some big projects on my day job eating all my time. I need this supply for myself too, I'm setting up the lab quite a bit lately and if I could save the $ for the supply I'd like to have and settle with this the $ could go to some other toy as I'm collecting quite a few lately and building some others.

JS

[JS]

One thing you might like to know... CC dummy loads are a much simpler to build than a lab PSU, same thing for a variable power supply, but if you have both and connect the dummy load between the source and the variable supply you get pretty much a lab PSU. That's what I meant when I said using two power devices for a lab PSU. Remember to put first the CC load and then the variable PSU, otherwise it won't work. The other possible way to do it is to put it on the low side, using the high side of the CC load as the ground for the variable PSU.

CC load is basically a mosfet, a sense resistor and an opamp. The variable PSU is just an LM317 with the standard circuit around it. If you want to go this way (which I totally recommend to get something up and running for a beginner to have something to work with) let us know so we can help you choosing the right CC load to build, as it's the part that might get unstable under certain conditions, the classic simplistic design gets unstable, but just adding a resistor and a cap to make it slower makes it work fine.

JS

[MarkF]

@JS:

Could you post the circuit you're tossing around so we can see your thoughts? 
I believe that @Pirateguy going to setup his ATX Supply with polyfuses so that he just needs to remove the overload condition and the fuses will reset for him.  As a start, I think he will just build the basic LM338 adj voltage in the datasheet with a polyfuse for current protection.  Then add adj current at a later date as his knowledge grows.

I actually did build Peter's Electronic Load.  The IRFP064 in a TO-247 package is a beefy MOSFET.  I have no problems with it.  However, I lowered the current capability to 1.5A for mine.  That's all I really need.

[JS]

  The picture is the basic design, I've just found it on google, at least has some compensation as I said which makes it usable but the values are wrong, at least R14 which should be 1Ω or maybe lower, depending on the expected current range, properly rated for power, much higher than the actual power the resistor will dissipate to get better stability and not get too toasty. 1k there seems way off unless going for really low currents, in which case the mosfet makes no sense as a single opamp could do the job for a few mA. R1 could be 100Ω, R15 10k and C10 something like 1n should roughly work, depending on the mosfet and some other factors, like expected speed and loads. Iset will be Vref/R14

  This is the topic of my dummy load. https://www.eevblog.com/forum/projects/cccv-dummy-load/msg1589761/#msg1589761
  As you see mine is quite more involved, having CV and CC modes, and thermal shut down and a more involved compensation to keep it relatively fast and stable under many conditions. It will be in CV till the CC limit is reached. The funny connected transistor is the temp sensor which I didn't had the lib for.

JS

[MarkF]

Looks nice. But, I thought we were talking about adj power supplies.

[JS]

Looks nice. But, I thought we were talking about adj power supplies.

They have a lot to do... specially once you start talking about current limiting. As I said, with a simple variable supply and a CC dummy load you basically have a lab supply.
Also, a related but simpler project that you would need to test the power supply you build so why not build it first... is kind of the egg and the chicken as what are you testing each with, but I tested mine with a 9V battery just to check so you don't need the PS to build it.

JS

[MarkF]

Here's the Electronic Load and values I used.  This does need a fan for the heat sink at currents over 500mA.
Maybe @Pirateguy would want to put the chicken before the egg.  It's just a matter of putting it together as I already tested it.

   

[Pirateguy]

This thread has been throwing a lot of things around.  Don't get put off yet. 

• Your ATX fixed output should be in the can with just a few fuses.  This is going to be your workhorse 90% of the time.
• The Adjustable Supply is a good project to cut your teeth on.  Build it up and do some tests.
• Then, try building an Electronic Load.  About the same difficulty or easier then the Adj Supply.   
• After, tackle a Function Generator.  It would be a mix of analog design controlled by a microcontroller. (The Arduino's you already have for example.)

lol i'm not put off, but i know my limits and the adjustable current is presently one step too far for me.
the ATX one is definitely gonna get built, as well as the volt regulated one.
but after that i think ill switch it up and work on some other projects before coming back to the psu.

however one of the things i wanna do next is build some mini tesla coils, and i want at least 1 that can
be modulated n stuff with an audio jack and a built in func gen, so that will help when i get back to the psu.
(i guess ill also be learning much about tiny faraday cages... )

[rstofer]

man, i thought this was gonna be simple. lol.
this and some other stuff i been reading lately suggests that power supplies in general are kind of an advanced project
the moment you make any kind of demands of it's performance.

i think i'm gonna have to just build the fixed output ATX one, then the variable voltage one, and then
reassess if i want to diy anything more complicated after using that for a while.

This happens all the time.  It seems obvious that a power supply should be a first project and many folks recommend it to newcomers.  Then reality hits the wall.  A REAL lab power supply with a wide range of voltage and current capability coupled with adjustable current limit is a really big project.  Dave's project is substantial and I think he got to a dead end (I stand to be corrected on that, I just watched a couple of videos).  When you look inside a REAL lab supply you get an understanding of just how complex the project can be.

The ATX is a common next idea.  The problem is, it doesn't have current limit and current limit is a really important feature.  It saves so much on smoked parts.

So, one approach that I used for decades is to use wall warts or batteries.  I could always put in a 7805 or whatever if I wanted a clean source.  Dedicated supplies for each project is one way to go.  Even a fixed voltage power supply using 7805,7815 and 7915s will do the job.  The output current won't be much but we really don't need 30V at 3A these days.

OTOH, Dave did a video or two on these Chinese supplies and they look really capable at about $20 per channel.  I don't know anything about them and I did notice that nobody linked them earlier.  I don't know why.



These are neat looking supplies.  There are at least 2 videos because there was a design problem with the earliest models, since corrected.

Here's the failure video:



And the fix:

[Pirateguy]

yeah i was looking at those and ill prolly go with that if i ever decide i need a better psu.
a loose panel like that provides a lot of freedom over the configuration of the externals.

[Pirateguy]

quick last question:

can i put n led on a negative volt rail?
also: what about the polyswitch?

[MarkF]

can i put n led on a negative volt rail?
   Yes.  But you need to reverse the polarity of the LED.

what about the polyswitch?
   Do you mean polyfuses?
   These:  https://www.mouser.com/ProductDetail/Littelfuse/60R065XPR?qs=sGAEpiMZZMsxR%252bBXi4wRUCTGuoKQj3D%2fWlrADHdQXLA%3d

This diagram might help (Again you may not need the load resistor for the supply to turn on):

   

[havewattwilltravel]

One thought: You can get really cheap low voltage digital voltmeter+ammeter boards on Ebay, which allows you to watch several channels simultaneously and still have a meter free.

[Pirateguy]

can i put n led on a negative volt rail?
   Yes.  But you need to reverse the polarity of the LED.

what about the polyswitch?
   Do you mean polyfuses?
   These:  https://www.mouser.com/ProductDetail/Littelfuse/60R065XPR?qs=sGAEpiMZZMsxR%252bBXi4wRUCTGuoKQj3D%2fWlrADHdQXLA%3d

This diagram might help (Again you may not need the load resistor for the supply to turn on):

   

ahh thanks

One thought: You can get really cheap low voltage digital voltmeter+ammeter boards on Ebay, which allows you to watch several channels simultaneously and still have a meter free.

yeah mean the panel mount ones?
yeah i got 2 of those, but for the fixed outputs i don't really need one i think.
anyways i'd have to either have 3 of them or have a switch for it, and i have no room for that.
i did put in a temp display though, and the variable psu ill make after this will have a meter in it.

[MarkF]

I missed the 3.3V Sense wire (Brown).
It needs to be tied to one of the 3.3V Output wires (Orange).

   

[Pirateguy]

lol no worries. my atx has neither 3.3v nor 3.3v sense wires
i added a step down module to get the 3v.

i also don't have a power on wire that i can see...

so it looks like my first planned upgrade will be a double pole version of the power switch
hopefully the chinese won't make me wait too long...

in any case here she blows:

[MarkF]

Looks good.   

Two questions:
   1)  Are the two yellow posts the temperature probe inputs?
   2)  On the power switch, I believe it's backwards?  The'O' is the OFF position and the '|' is the ON position.


Edit:
Third question:
   3)  Can you tell me what the power supply model is?

[Pirateguy]

ehhh not anymore since i removed the sticker and painted it.
but i did google the model number before and couldn't find anything.

in any case no 3.3v or sense, but also no power on line, and only a power good indication line.
it is running without the resistor OR having to short anything at all.
all it needs is for power to be applied to the input and it runs.

the yellow posts are the negative outputs. the temp meter is internal only for now.
i think ill add the external temp later, but it will have it's own display.

the power switch is ST; it only has 2 terminals. i guess i have it mounted upside down

[MarkF]

I believe you have an older AT Power Supply and NOT an ATX Power Supply

   

[Pirateguy]

now that you mention it, lol yeah i guess you're right.
that pinout is an exact match.

[Pirateguy]

and now it's f#$cked.
when i turn it on the fan starts blowing like mad, and the -12v polyswitch pops.

checked out all my handiwork, no problems there.
and even with everything disconnected it still does it.

ill check for shorts on the board later, but i'm pretty sure i can mark this down to
the old psu's decrepitude.

hell, an AT psu... this thing must be from the P1/2 era...
i didn't recognize it, cuz i didn't remember them, lol.

anyway on to option 2:
using 2 sources like the HP one for fixed and variable, the breakout board i have for the
3.3 and 5v, and a 7812 for 12v.
which has me back with my original problem: the housing...

[MarkF]

Maybe tbe resistor you choose for the LED is too small and the LED shorted out? Try disconnecting it.

[Pirateguy]

oh i disconnected everything but the mains in, it still does it.

and i can't find a damn thing wrong with the pcb either.
all caps look good, no brown spots anywhere, nothing.

so screwit, i'm stripping this thing for parts and moving on.

[exe]

It seems I'm late to the party. I don't know if you still need a schematic, but here are two designs that are not too bad and can serve while you making something better. Although, honestly, designing a PSU is a hard topic, even a linear one. Me too was trapped into "best beginner's project is a DIY psu" (unless it's a pair of lm317 in serial, one for CC, another one for CV).

For DIY power supply one can take a typical "0-30V 0-3A" PSU. I mean this one: . Can be bought from China as a kit. Don't know its performance. It holds well in my lab, but I don't do much with it. Just be sure to read on the forum how to modify it be more robust, etc. It's worth derate it to 15V max and install a very beefy heatsink.

Another one is mine https://www.eevblog.com/forum/beginners/please-critique-this-linear-psu/ . Didn't test how well it switches between CC/CV modes, but step response is excellent (thanks to lt3080). It's my main workhorse so far. Not perfect, worth replacing lm334z with something else as it drifts with temperature. Output current is limited to what lt3080 can provide (1.1A).

[Wolfgang]

When I look at the picture, and when I see 90W of regulated output and this ridicuously small line transformer, storage capacitor and cooling, i would suggest
that you put all this in a flameproof environment. In case of a prolonged short circuit at full current this will not last long.

Play safe !

[exe]

Oh, god, I didn't even watch the video. Yep, don't do that. Or tune resistor values to limit maximum current. I'd say it's better to change the capacitor anyway as it looks too cheap to be good.

[MarkF]

I thought the BEST part is that the pots are so close together that you can NOT put any knobs on them. That alone turned me off.

RUN AWAY....   

[exe]

I think pots meant to be wired (that's what I did). Anyway, didn't check if the pcb is well routed (probably not).

[Jwillis]

I wouldn't want it anyway because he took all the fun out by building it.

[Atom]

soooo....i  didnt read all the 5 pages of post but please .... do not use the peter oakes psu is really unstable and gave me nightmares as beginner.... do you want a sturdy psu ...look for the hp3610 series or similar, you can find the schematics and make your own copy , now what i would reccomend is the Blackdog psu, that thing is a beast the voltage moves of a couple of millivolts at 4 amps load , you can find the post and the schematics on eevblog , than  this guy made a drive folder with all the info

https://drive.google.com/drive/folders/1iKNivHfgNfMc6xBsww707_LqQOR2TIin?usp=sharing

if you are a beginner beginner i would suggest to toy whit linear reg and simple switcher from ti . if you are ready to make the next step take a schematic and understand it, do not blindly copy it you will learn a lot as i did and if you have any problem you have an entire community to ask to. good luck

[Pirateguy]

soooo....i  didnt read all the 5 pages of post but please .... do not use the peter oakes psu is really unstable and gave me nightmares as beginner.... do you want a sturdy psu ...look for the hp3610 series or similar, you can find the schematics and make your own copy , now what i would reccomend is the Blackdog psu, that thing is a beast the voltage moves of a couple of millivolts at 4 amps load , you can find the post and the schematics on eevblog , than  this guy made a drive folder with all the info

https://drive.google.com/drive/folders/1iKNivHfgNfMc6xBsww707_LqQOR2TIin?usp=sharing

if you are a beginner beginner i would suggest to toy whit linear reg and simple switcher from ti . if you are ready to make the next step take a schematic and understand it, do not blindly copy it you will learn a lot as i did and if you have any problem you have an entire community to ask to. good luck

thanks

i have decided that power supplies are out of reach for me atm and
am just going to make a simple fixed output one with some 78 series regulators.

for a variable output i am tempted to go with one of these:
https://www.ebay.com/itm/RD-DPS3012-LCD-Constant-Voltage-Current-Step-down-Programmable-Power-Supply-S1I8/253019740400

[MarkF]

I just finished laying out a triple fixed output power supply using MC78xx and MC79xx.  I have in mind a +5V and +/-15V fixed outputs using two transformers.  That way the +5V will be independent of the +/-15V outputs.  Each output would be capable of 1A.

You could build it up to replace your AT Power Supply that died.  You would have to get the PCB made.

   

   

[Pirateguy]

I just finished laying out a triple fixed output power supply using MC78xx and MC79xx.  I have in mind a +5V and +/-15V fixed outputs using two transformers.  That way the +5V will be independent of the +/-15V outputs.  Each output would be capable of 1A.

You could build it up to replace your AT Power Supply that died.  You would have to get the PCB made.

   

   

looks simple enough, could you post the schematic?
i might try to build this on some perfboard.

[MarkF]

You can buy dual +/- linear supplies from eBay.  But, the heat sinks are so small that you could not pull much current from them. 
Example

   

I just threw the PCB together from the datasheet examples.  But here's a quick circuit:

Edit:
   The LEDs are there to provide the minimum 5mA load current for the regulators. 
   You can set them for whatever current and brightness you want (5mA <= I_LED <= 20mA).

   

[xavier60]

I knocked up a simple low power multiple rail power supply using 3 pin regulators.
 I also added a variable dual tracking regulator.
It has about 1% drift over its operating temperature range because the control transistors get heated unevenly by the series pass MOSFETs. The load transient response is fast at 20us.

[Pirateguy]

i got lucky and had some extra spending cash, so i went ahead and ordered that module.

for the fixed output one i don't have a split source i think, so ill make the 5v one in your circuit
and another one like that at 12v.
for the heatsink i think i will use the big one i took out of the AT and run a fan on it the same way.

can i use 4007 diodes and 4700uf caps instead?

[MarkF]

You have a little design work and choices to make here.

The 1N400x series diodes are rated for 1A.  While the 1N539x series are 1.5A but their forward voltage drop is greater.  You might look at a full wave bridge module instead of individual diodes. Your choice.

The capacitor choice depends on voltage drop/ripple, line frequency and current.  Here is a pretty good video on choosing the values:

https://youtu.be/CAYKno16weE

[Pirateguy]

i like to use what i have, and i don't need the rectifier part if i'm using a DC source like the HP supply, do i?
but there are 2 more diodes to the right, i was thinking of those.

in any case my poly fuses are 0.9A so i guess these will do.

[Pirateguy]

i i watched the video and followed the math, and i end up with a 10uf cap.

so i am guessing that corresponds to the 10uf cap in the circuit, but i was thinking of the 6800 one.

[MarkF]

i like to use what i have, and i don't need the rectifier part if i'm using a DC source like the HP supply, do i?
but there are 2 more diodes to the right, i was thinking of those.

in any case my poly fuses are 0.9A so i guess these will do.

The two diodes on the right side are protection diodes.  They are for reverse-voltage and over-voltage being applied to the outputs.  You want those and you could use your 1N400x series diodes there.

You're right. You don't need the rectifier if you feed a DC voltage into the regulator.  And the input capacitor can be small.  I'd use something like 100uF. 

The video is not applicable if you feed the regulators with a DC voltage.

The maximum input voltage of the MC98xx regulators is 35V.  If you intend to use your 32VDC supply to feed 5V and 12V regulators, the power dissipation of the regulators will be enormous.  They will get very very very hot!  You want an input voltage to the regulators 5-10V above their output voltage to minimize the power they will need to dissipate.  Don't forget their drop out voltage is 2V.

I DO NOT think your 32VDC power supply is an appropriate choice.  If you want to build this, I highly recommend you use the bridge rectifier and obtain the appropriate sized transformer for each.

[Pirateguy]

The maximum input voltage of the MC98xx regulators is 35V.  If you intend to use your 32VDC supply to feed 5V and 12V regulators, the power dissipation of the regulators will be enormous.  They will get very very very hot!  You want an input voltage to the regulators 5-10V above their output voltage to minimize the power they will need to dissipate.  Don't forget their drop out voltage is 2V.

I DO NOT think your 32VDC power supply is an appropriate choice.  If you want to build this, I highly recommend you use the bridge rectifier and obtain the appropriate sized transformer for each.

seriously?
after 5 pages of discussion, diagrams and shopping advice, you are basically telling me to shove a 5v and a 12v wallwart into a
box and call it a project?

if i happen to have a wallwart for every voltage i want, do i still need the regulators?

[Pirateguy]

what if i use them in high current config with the power transistor?

[MarkF]

I don't know what your goal is now since your AT Power Supply died.

You could try using two regulators in series to split the load as shown in the "Tracking Preregulator Circuit" example in the datasheet.
I would configure the first regulator to always be 6.5V above the output.  This would give you a 0-20V output with your 32V supply.
   Start with R1=240,  R2=1K,  R3=330,  R4=5K and see how it works.

   
   

[JS]

I don't know what your goal is now since your AT Power Supply died.

You could try using two regulators in series to split the load as shown in the "Tracking Preregulator Circuit" example in the datasheet.
I would configure the first regulator to always be 6.5V above the output.  This would give you a 0-20V output with your 32V supply.
   Start with R1=240,  R2=1K,  R3=330,  R4=5K and see how it works.

   
 

I think 330Ω for R3 is too high, it's supposed to meet the minimum load specs, but for both LM317 this time, if the regulation is supposed to be maintained without any load or very low loads. Also, this circuit doesn't share the thermal load evenly between the two ICs so I don't know if it's optimal for this.

JS

[Pirateguy]

well i'm pretty sure i can pick up an ATX from a thrift store around here if need be.
in fact i saw one the last time i was there.

i ordered the dps3012 for my variable supply, along with a case for it.
so now i just want to make the fixed output one.

for that i intend to use the large heatsink from my disassembled AT,
continue using the AT housing (it's all i got atm) and for the time i do
stick to 3.3v, 5v and 12v outputs. leaving the negative unconnected for now.

so some ideas i had:

-using the bypass transistor for current to take some strain off the regulators.
-using multiple regulators in parallel.
-cascading regulators; 32v PSU to 24v regulator, from the 24v to 18v regulator, from there to 12 and so on.
-i have a fairly heavy wall wart that switches between different voltage levels, could i hack that?
maybe i can draw a line from the transformer directly and add a rectifier circuit for each?

assuming one of those ideas will work, i am again left with the challenge of finding an enclosure.
any suggestions for that?
it would have to be fairly big so i have room to add more stuff, incl power source(s)...

[Wolfgang]

... why not just add a pass transistor and keep the LM317 cool ? Its not one of the xtra stable or noise free regulators on earth anyway ?
And if you want to be really nice you can add a current limit plus an overtemp protection plus a crowbar at the output to avoid surprises ...

[MarkF]

... why not just add a pass transistor and keep the LM317 cool ? Its not one of the xtra stable or noise free regulators on earth anyway ?
And if you want to be really nice you can add a current limit plus an overtemp protection plus a crowbar at the output to avoid surprises ...

You still have to dissipate all that power if you want a variable supply (say 32VDC input and 0-20V @ 1A output).  The power will have to go to the regulator or the bypass transistor.  I proposed the preregulator to split the load (granted not evenly to get a 20V output).  I thought it the easier approach.

LET'S SEE A CIRCUIT FOR ALL YOU PROPOSE.

[MarkF]

well i'm pretty sure i can pick up an ATX from a thrift store around here if need be.
in fact i saw one the last time i was there.

i ordered the dps3012 for my variable supply, along with a case for it.
so now i just want to make the fixed output one.

for that i intend to use the large heatsink from my disassembled AT,
continue using the AT housing (it's all i got atm) and for the time i do
stick to 3.3v, 5v and 12v outputs. leaving the negative unconnected for now.

That was your original approach and from what you've said and your knowledge at this point, that is probably you best course.

Don't discount the negative voltage.  Especially since it's available.  If you end up doing any analog projects you will probably need it.

[Wolfgang]

Well, I would say that a pass transistor is about as easy as another LM317. The advantage of a pass transistor is that it could be user with a much higher dissipation than even two LM317s. A proper cooler and a fan could easily do 100W, a TO220 LM317 can only do roundabout 25W. On top of that, a regulator that does not run hot is definitely more stable.

[Pirateguy]

quick note: i just got some lm338 regulators.

negative voltage is available?
do you mean to say i should go with an ATX?

[JS]

There's no negative version of LM338, if you need dual supplies using it you need them floating and then connect them in series at the output.

JS

[Cliff Matthews]

Hard to understand why TO220 338's exist.. what good is the 5amps when internal thermal protection limits the whole package to dissipating ~15watts on an ideal heat sink. Seems LM317 and 337 are fine with additional pass devices..??
For the OP, maybe someone can comment on the schematic half-way down on this link:
https://electronics.stackexchange.com/questions/186760/why-do-linear-voltage-regulators-have-minimum-output-voltage-0-v

[JS]

Hard to understand why TO220 338's exist.. what good is the 5amps when internal thermal protection limits the whole package to dissipating ~15watts on an ideal heat sink.

Why do you say so?
At 0.7ºC/W it's better than the TO3 package, the thing is the TO3 package has a bigger plate with two screws so the thermal resistance case to heatsink can be made lower, plus the bigger thermal mass can make it handle higher peaks better.

Still, if what you say it's true it could work in a 3V dropout application, which it can do over the whole temp range.

JS

[Pirateguy]

well wouldn't u know it, the thrift store no longer has the ATX i saw, nor much of anything else PSU wise.
i guess ill have to take inventory of the wallwarts n stuff i have...

[Pirateguy]

scored an ATX!

[Pirateguy]

the new plan:

from the wall:

ATX:

polyfused 3.3v
polyfused 5v
polyfused -5v (7905 from -12v rail)
polyfused 12v
polyfused -12v
USB (from 5v SB)
-variable (DPS3012, from 12v rail)

on the front panel:

Thermometer with sensor broken out to binding posts. link
Thermostat controlling the fans link or link
Func gen. link
Relay timer link
usb tester link

also i think i will add a double wall socket with a dimmer on one of them, and add a halogen ballast with 2 outputs, of which one has a dimmer.

and on the wall sockets i will have this:
AC volt/amp meter link

also since i cannot find a nice box to built it into, i found some help for making a custom box out of multiplex or something like that.

also i may want to put an adjustable load in there at some point, but i need to learn more about them.
am wondering if it might be better to keep that separate cuz of temperatures? seems like that kinda thing would get hot...?

[Pirateguy]

couple of quick questions:

when a polyfuse is triggered, what exactly does it take to reset it?
could i put in a NC button to interrupt the line to reset a polyfuse?

do polyfuses work any differently on negative voltage?

can i run a 7905 on the -12 rail normally as per datasheet, or does it need something anything else?

[exe]

I think polyfuse is just a PTC -- a resistor that quickly increases resistance as it heats up. It doesn't care which way current flows imho.

I don't think it can be reset with a button. The only way to reset it is to cool it down.

I suggest read a datasheet on it, it answers all your questions. I think this is a good start: http://www.littelfuse.com/products/resettable-ptcs/surface-mount.aspx . Be sure to see different plots and numbers in the datasheet. Like, maximum guaranteed current that will not trip it (and how it depends on ambient temperature!), minimum guaranteed current that will trip it, etc.

[drussell]

couple of quick questions:when a polyfuse is triggered, what exactly does it take to reset it?

Removal of the overcurrent and time.  (On the order of a few seconds.)

could i put in a NC button to interrupt the line to reset a polyfuse?

No, that is not how they work. 

https://en.wikipedia.org/wiki/Resettable_fuse

do polyfuses work any differently on negative voltage?

No, they are not polarity sensitive.

can i run a 7905 on the -12 rail normally as per datasheet, or does it need something anything else?

You most certainly can use a 7905 on a -12 volt rail.  You're going to be limited as to the current you can draw on your negative side due to the 0.8A maximum output of the power supply compared to the huge currents available on the positive rails, but within that limit you'll be fine.  (Obviously the -5 rail will have even less than 0.8A available since the linear 7905 is going to dissipate a good chunk of your available ~10 watts.)

I think polyfuse is just a PTC -- a resistor that quickly increases resistance as it heats up. It doesn't care which way current flows imho.

Correct.  They are actually known as PPTCs.  The extra P stands for Polymeric.  They are made from a special crystalline organic polymer that gives them the same kind of sharp current characteristic as a zener has on the knee voltage.  Instead of a slowly changing, smooth curve like a regular PTC has, a polyfuse stays basically the same resistance until it heats enough for the polymer to change from a crystalline state to an amorphous state, which raises the resistance very rapidly, limiting the current.  Once the current is reduced sufficiently, the polymer recrystallizes as it cools and the "fuse" is "closed" again (resistance returns to close to the original value, though it can take several hours to return fully to its original value.)

[Pirateguy]

right, so the only action i need to undertake is to disconnect the load and wait.

thanks

is 2,7 ohm enough for the load resistor?

[Pirateguy]

one day i'm looking for an ATX, the next a friend brings by 2 of them + another device that contains one
i got a small 150watt one, a large 500watt one and what looks like a 10watt one that has -24v on it for some reason
from a 'media center extender'.

anyhoo i was looking at this guide to converting atx psu and came across something odd.

Again the voltages that can be output by this unit are the same as before 24v (+12, -12), 17v (+5, -12), 12v (+12, 0), 10v (+5, -5), 7v (+12, +5), 5v (+5, 0). Note that some ATX12V power supplies with a 24-pin motherboard connector may not have the -5V (pin 20) white lead. In this case use the older ATX power supplies with a 20-pin connector above if you need the additional -5V supply.

this suggests a +5v and +12v rails can somehow be used to create 7v??

[MarkF]

this suggests a +5v and +12v rails can somehow be used to create 7v??

   +12V - +5V = +7V

You would be using the 5V rail as the reference (ground).  The ground output in this case would be -5V.  This also prevents you from using the remaining outputs in their normal way.  NOT something I would recommend on a routine bases.  I would stay away from the odd voltage combinations and just use it as designed.  i don't know why it was even brought up.  It just confuses the novice!

ONCE AGAIN.  DON'T GET CREATIVE.   

Just use the -12V, +12V, +5V and +3.3V outputs as designed.  In practice, you will seldom use or want anything else.

I would use the smaller 150 watt power supply.  There is NO way you would need the current capabilities of the larger one.

If the smallest 10W supply has a +24V output, I would use it for the adjustable supply instead of the +32V supply.  That is if you're still building the LM317/LM338 design we discussed earlier.  It would ease the power dissipation concerns.

[Pirateguy]

actually no i ordered one of those dps3012 modules.

and no worries, i already got creative


so i have a selector switch between .9A 6A and no poly fuse, and a bit with a
switch and momentary button and a 3.5mm jack on the ground in case i need
to cut power quick, or just want to give a quick jolt to see if something works or not.
the 3.5mm jack connects to another button or a foot pedal to do the same remotely.
also they are all connected to RGB LEDs to indicate power and which fuse setting they are on.

is there ever a reason to limit 3.3v or should i just skip the switch on that one and put a 6A fuse?

[ricktendo]

Don't forget to check out OpenDPS, you can remote control it over WiFi and upgrade over Serial!!!

https://github.com/kanflo/opendps

I wish I had the money to send one of each RD-DPS units to the developer, maybe somebody can contact him and/or setup a gofundme to collect money for the hardware for development!!!

[Pirateguy]

thanks

but i don't think the model i have has the wifi capability.

[ricktendo]

thanks

but i don't think the model i have has the wifi capability.

They are all WiFi capable, its a matter of adding a ESP8266 board.

[Pirateguy]

thanks

but i don't think the model i have has the wifi capability.

They are all WiFi capable, its a matter of adding a ESP8266 board.

i see a lot of different esp2866 modules on ebay.
could you link me to the correct one?

[ricktendo]

i see a lot of different esp2866 modules on ebay.
could you link me to the correct one?

Sorry I don't know, you will have to ask in his blog or the issues area of github on details of how to add WiFi capability.

https://github.com/kanflo/opendps/issues

https://johan.kanflo.com/upgrading-your-dps5005/

Note: metal enclosures block RF, so if you are adding a esp2866 you will want to mount this externally.