Sallala

0-30 Vdc Stabilized Power Supply

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Hi Audioguru,

Thanks for the description of range switching.
I prefer to use just pots rather than the range switch you describe, I will get both a 10 turn and separate pots for coarse/fine & decide which I like best. This psu might be overkill for gain testing transistors, one slip and BOOM!

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Hi Thomas,
If you can't get a powerful 0.47 ohm resistor, use a 0.39 ohm one and change the other parts around the current-set pot to match.
I bought a 25W aluminum-clad resistor and was amazed at its tiny size. I thought it would smoke for sure since at what extremely high temp does nichrome melt? I bolted it to an aluminum box with some thermal grease and let it dissipate 25W. It reached the same temp as the box, just nicely warm!
The original project spec'd only a 5W resistor for R7. It, Q2 and Q4 must get incandescent!

Yeah, I'm sorry to confuse you, I made a mistake. Q1 should be wired like the original.  :-[

Hi Blacque,
That darn majic smoke smells really nasty doesn't it?  ;D

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Hi Blacque,

We are talking about these, right?



I think you are right, they shouldn't get that hot when they are bolted to the case... I think I'll try one of these. I just now discovered that they have also only 50ppm. That should work.

Annother advantage of "my" current measuring is that you can always see how much current flows to the load. You just need a switch that can stand 3 Amps.

Hi audioguru,

Okay, now I'm informed about Q1. Thank you  :)

When both values can be presetted, the usage of multi-turn pots should be no problem anymore, right? Saves space, can be well adjusted and a accidential touch of the knobs would not produce that much smoke ;)

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Hi Thomas,

Yes that's exactly what I had in mind, take note though, they are only rated for full power when bolted to another larger heatsink or chassis, eg: the 25w types are only good for 9w on their own and remember to derate if you run them hotter than 25 degrees.

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hello guys!!! :D :D :D
this is my first post here, since i registred few days ago...
i built this power supply with org.specs and it works fine...2.5 A with almost 34V....
i am going to modify it so it can hold more than 3A output current as suggested by you all...
I read all the posts about this PSU and only thing not so clear to me is the emiter of Q1...
does it go on junction of C1- and R7(negative input)  or on the junction of R7 and C7(negative output)...
Also should C7 be of a greater value???
Please help...

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Hi Costa,
Welcome to our forum.
It is wonderful to hear that your original project works fine and produces 2.5A at almost 34V. ;D

It is difficult to believe that its 24V transformer has such a high rectified DC output voltage. Without losses, 24VAC has a peak of 34V and the bridge rectifier has a 2V drop, giving an output with ripple of only 32V. The original circuit has voltage drops of at least 5V so its max output voltage at 2.5A should be only 27V. Other people's original circuits produced less. :(

The emitter of Q1 is correct on the original schematic at R7 and C1, sorry I made a mistake by changing it. :-[
With the original value of only 3300uF, C1 will have a lot of ripple voltage at full output current. At least 10,000uF is recommended for 3A, much more for 5A.

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thanks audioguru...
sorry i didnt mention that i use stronger transformer as specified... ;D
but i ask again for the cap C7 (not C1) if it could or should be of a bit larger capacity???
thanks...
btw. audioguru, i am searchin for a timer circuit that would turn off my aquarium lamp in the evening 22.00h and turn it on in the morning 07.00h,every day...have you heard of something like it???

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Hi Costa,
With a stronger transformer the ICs are operating with a supply voltage much higher than their spec'd absolute maximum. Also if you set the output voltage low or shorted, with a high current setting, then Q2 and Q4 might melt.  :o
C7 if fine with the original value of 10uF. I accidently left it off my list of changed parts.  :-[
The corrected list is attached.

Mains timers are common and cheap to purchase. I wouldn't bother making one.  ;D

I wonder if Gang is trying to do this:
[move]fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        He, he ;D [/move]

0-30V_Mod_parts_list.txt

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[glow=red,2,300]Hi all[/glow]

I bought one of these bog standard kits about two years ago from Quasar Electronics here in England:
http://www.quasarelectronics.com/ and I still haven't got round to finishing it yet. I also bought two 3.5 digit panel meter kits http://www.quasarelectronics.com/3061.htm from the same place. I got round the power supply for the meters by using a second, smaller junkbox transformer and making a PCB with two voltage regulators etc. on it, one 12Volts for a case fan and one 5Volts to power the meters. If anyones still interested I can post PCB layout for the second power supply, maybe? As for the main power supply, I don't really know if it will power the national grid but it worked first time with the stanard parts although R3 got hot under slight loads (everyone seems to be power mad lol). I'm sure, if I remember rightly, Smartkit do a 5Amp power supply so why doesn't everybody just buy one of those?
Thanks to Mixos at Smartkit for the great kit, not to mention the many other kits Smartkit exports.
Cheers Mixos!

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hi...
a question...
has anyone found another complementary OP's for this project...
OPA445 is very expensive and MC34071 and TLE2141 cant be found in croatia...
please help...(mixos , audioguru , anyone)

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Hi Costa,
I am sorry you can't get parts in your country. To be safe with ordinary opamps that have an absolute maximum total of their supply voltages of 36V, use a 21V or less transformer which will restrict the project's maximum fully-loaded output voltage to about 21V or less.

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Guest ElectroFreak

Hi everybody!

As you can see, I'm a newbie here and I need some help about this project.
First, I'm sorry if my english is bad...
Now, a little story: I have a couple supplies, but they're all poor and not enough for my requirements. So, I was searching on the net for some good power supply, and I found this. I liked it on the first look. But, now when I have read all posts posted by people who allready made or still making it, I'm not so shure this is it. I'm a little bit confused... :-\
I'm still ready to build this supply, (and I WILL build it) but I want know some more things:
1. Is this supply reliable and can I count on it in every moment I need it? (I answer on this question is YES, tomorow I'm going in the shop for the parts...)
2. I want to have a double output (You know what I mean, don't you?), every output to be regulated for it selfs - I've seen on this forum somenthing likely, but, can I make it on some other way, for I dont have to actually build two supplies?
3. I want also to have a AC regulated output - if I take a double - winded trafo of two trafos, can I on some simple way get the same effect as for DC, that means, voltage and current regulation? OK, it must not be simple, I just need good circuit...

I want put this everything together to get the final product - universal bench AC/DC variable power supply.
If you have some answers, ideas, tips (and will to help), I will be very happy!
I hope I'm not too booring or somewhat, and THANKS to everyone!

Btw. this site is realy great! From now, when I looking for projects, first I will look here...  ;)

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Hi ElectroFreak,
Welcome to our forum. ;D
1) If you build it according to our latest mods, it should work well and be reliable. But I don't think anyone has built it yet.
2) For a dual supply, most things need to be duplicated so just make two completely separate circuits and two transformers.
3) A regulated AC output needs a different circuit. Maybe a sine-wave generator feeding a high-power audio amp. A volume control adjusts level, and negative feedback from the output creates voltage regulation. Negative feedback could create current regulation.
Some people just use a variac with a voltmeter on it to adjust AC voltage. 

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Guest ElectroFreak

First, thanks on your answer, Audioguru.  :)

I've made a final decision to build this supply.
For beginning, I will build only a single DC supply, following the latest recommendations and modifications I've seen in this forum.
(In fact, dual supply and AC supply can wait... That I will upgrade later... Honestly, I belived that variable AC supply can be done on some easier way...)
OK, now I'm going to make a new list of parts and I'm beginning with the project...
If something goes wrong, I hope that I can get a help here...  ;D

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Guest ElectroFreak

5 minutes later  ;D: I checked availability of all parts, and I can get everything for a little money... That means - I'm IN...  :)

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1) If you build it according to our latest mods, it should work well and be reliable. But I don't think anyone has built it yet.



I' ve just soldered it together and made a few measurements. It seems to be quite fine :)

At 30V and 3A Output I couldn't measure any ripple at all. My 10.000µF cap does its job well ;). Because C1 is off the board and connected with wires to it, I soldered a 220µF on the board in order to compensate the inductivity of the wires and of C1 itself. That should help when heavy load changes occure. 

R2 is getting quite hot. The part list should be updated for a 2W one, there's just enough space on the board for it. C2 and C3 get at least lukewarm. I don't like that, but I don't think there can be done something about it.

Q1 and Q2 are mounted on a heatsink (3mm of aluminium sheet) and connected to the board with short wires. That solves two problems at one time, the cooling of Q2 and the leg twisting, which looks awful. R7 is mounted on the same sheet and the sheet itself will get bolted to the heatsink later.

I did a few changes to the layout with a CAD program in order to make space for  spring-type terminals. I like them better than soldering the wires directly to the board. If anyone is interested, say something ;)

Three secondary coils had been added to the transformer. One for the additional 8,5V, and two for digital LED-Panelmeters. Equals 30m of wire to the toroidal core!  ::) Maybe i can decrease the 8,5V coil a little, because C1 has 46V across it when unloaded. That's a little heavy for a 50V one ;) The voltage of the transformer doesn't go down when loaded as much as I expected and my rectifier bridge doesn't have that much voltage drop, so I think additional ~7 V would do the job.

I thank you, audioguru, for answering my questions that well  :D

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Hi Thomas,
It's great that your modified power supply project works so well! ;D
Did you add the 8.5V winding so it is in series with your original 26V winding? It makes the voltage much higher than the 30V required. No wonder your voltage across C1 is so high.

Thanks for the tips about R2 getting hot and C2 and C3 getting warm. It's good that a 2W resistor will fit for R2 but if the values of C2 and C3 are increased for less ripple current, then R2, R3 and D7 will dissipate more.

Did you use spring terminals like on (cheap!) speakers? I don't like them. They don't hold stranded wire very well and nick tinned or solid wire. 

I am glad to help you. ;D

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Hi audioguru,

The original winding has only 20.5V rated voltage, but gives 23.5V when unloaded.

Right now I've finished some further tests with the additional voltage being smaller. 8VAC unloaded works nearly fine, with little ripple at 30V/3A. If the voltage gets smaller, the ripple increases. There's not much room left for saving C1 :(


The spring terminals (WAGO 236, rated at 16 A) do really look good. They are often used in serious industrial devices, too. You can visit the homepage of wago and look for the CAGE-CLAMP system for further informations. There are different types of spring terminals, so you really can't say they are all rubbish :D
I use them to connect the rectifier, the cap, the 2N3055s, R7 and the output to the board.

Screw terminals can get loose after a while (especially when the wire is tinned), and after ~ 25 times of openings and tightening again the soldering to the board will break. Plus, they cost about the same as the spring ones.
Soldering the wire to the board is fine and cheap until you don't move it much. But I don't like the look of it ;)

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The original winding has only 20.5V rated voltage, but gives 23.5V when unloaded.

Hi Thomas,
It seems to have poor regulation. Is it rated for the required 106VA? Does it get hot with the project at full load?
Your additional windings will load its primary even more.

It is a good thing not to use opamps with their supply rated at only 36V or 44V.

The spring terminals (WAGO 236, rated at 16 A) do really look good.

Thanks for the tip. I haven't seen them before.

I was updating the parts list with your suggestions about C1 and R2 but forgot to ask you: do R3 and D7 also get hot? ;D

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Hi audioguru,

The trafo is rated for 140W and seems to stay quite cool @30V/3A output. But I could test that high load only half a minute before my load resistors (12 paralleled 120Ohm/approx.5W) are getting bloody hot. The secondary winding will have its 20.5VAC when loaded with the rated 5,83A.
The whole output voltage from the trafo is at the moment 32VAC, and 30VAC when the output (DC) is fully loaded. That doesn't look that bad, imo?
Maybe my C1 isn't as good as I hoped... it is a used one and I don't know how old it is. By adding a second (used) 10,000µF cap, the ripple is gone. But the trafo certainly wouldn't like that :(

R3 and D7 do get warm, but are still touchable. R2 can't be touched anymore, but has still room before burning down. A 2W one should be a better solution, anyway.

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Hi Thomas,
It is good that your transformer has enough extra power capability to stay cool.
I used to test power with heater wire strung between bolts on a board. It made a strong burning smell and heated up the joint. It looked cool too when glowing red-hot! ;D

I suppose the transformer's voltage drop of 2V from no load to full load isn't bad.
How did you make it 33% better than before?

I will up the value for C1 to 12,000uF/63V (I can't find anything bigger for a reasonable price) and 1/2W for R3 on the parts list. D7 is rated for 1/2W so will be OK. 
Thanks again for your tips. ;D ;D

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