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0-30V Stabilized Power Supply


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Guest liquibyte

I've been playing around with the output of U3 and have been noticing an oscillation.  After trying various values for C8 from 100n to 10p and caps across the 10V zener and R20 I was able to minimize this to a small spike.  On a whim, I removed C8 altogether and the oscillation went away altogether.  I guess my question would be is C8 entirely necessary if the output of U3 doesn't oscillate without it?

Edit: Nevermind, I think I answered my own question.  The output of the supply drops when C8 isn't there.

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Guest liquibyte

I've been doing some serious tweaking on this circuit over the last few days and I'd like opinions about anything that won't work or what could be wrong.  I've managed to pull out the negative rail completely and I think it might work like this.  I've kept the mosfet that was part of the soft start but it's now a transient protection circuit.  I've also kept the 12V relay because it helps to shut everything down rather fast.  The only issue I've encountered with it in simulation is that when the current is low, the bleed off of the main cap and the other relevant parts of the circuit takes longer than at full current.  I'm still working on how to get these two consistent but haven't been successful to date.  I've tried to pay attention to the limits of the components but may have missed something so if you notice anything odd or off, let me know.

Edit: quick correction to the schematic.

2nd edit: I found a problem with the bleeder resistor and the base/gate of the transistor/mosfet.  I'll update when I get it figured out.

3rd edit: I thought I was right but I was wrong on the shutdown stuff.  I'm still working on it but I can't get low amperage to behave at shutdown.  Having said that, I think I'm on the right track for removing the negative supply and having things work.  Almost but not quite right.

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0-30V-0-3A-w-2141-falloff.zip

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Guest liquibyte

I used the parts from here (self extracting executable that can be opened with 7zip and the like) which I found on the LTWiki.  It's a good resource for figuring out how the program works.  I've had to go and find several other resources to elaborate at times but for the most part, it's all there.

As far as the 7905 goes, I think that part library has one if it's not in the standard parts that come with LTSpice.  Look in F2 > Vreg.  If it comes with LTSpice, it'll be there.  If not, grab that library I linked and it should come with it.  I think you can take the generic xreg and use that but you'll have to define the part with your own spice stuff.

Edit to add that if you get a "time step too small" error, go to Tools > Control Panel > Spice and choose "Alternate" under Engine > Solver.  I had to search that one out after getting the error quite a bit.  Sometimes it won't work and you can then uncheck "Skip Gmin Stepping" but that's not advised unless you really need it because it gives non-standard results that won't match reality for the most part.  You can also raise the number under "MinDeltaGmin" from the default 0.0001 to 0.001, 0.01, or even 0.1.  Neither of these last two are recommended from what I've read unless it's absolutely necessary to solve a particular issue.

Here's a nice regulator PS simulation I found somewhere.  This showed me quite a few tricks with the program itself.

90_Watt_Regulated_Dual_Power_Supply.ZIP

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The negative supply is needed for the current regulating opamp to cause the output voltage to drop to zero when the current into a short circuited output exceeds the setting of the current-setting pot. Without the negative supply then the output of the current regulator opamp cannot cause the output voltage to go down to zero volts because it feeds the voltage regulator amplifier though a diode. Short circuit current will be unlimited.

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Guest liquibyte

The negative supply is needed for the current regulating opamp to cause the output voltage to drop to zero when the current into a short circuited output exceeds the setting of the current-setting pot. Without the negative supply then the output of the current regulator opamp cannot cause the output voltage to go down to zero volts because it feeds the voltage regulator amplifier though a diode. Short circuit current will be unlimited.

That's what I thought too but the simulations I've been doing say otherwise.  I've modelled in a direct short using a voltage controlled switch and when it kicks in, the current limiting seems to kick in as well.  I obviously screwed up the bleeder part before and I'm still having a bit of trouble getting things to be stable at high voltage and low current but I'm making progress.  Here's a screenshot of 4 seconds worth shorting at 30V and 3A with the current limiting kicking in.  Obviously I've not build this and blown parts up to test it but according to the simulations it should work without the negative rail.  I'll try this out in the real world eventually just to satisfy my curiosity.

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Good point.
The current regulating opamp has its negative supply pin at the input of the 0.47 ohms sense resistor and the voltage regulating amplifier has its negative supply pin at the output of the current sense resistor which is 1.41V higher than the current regulator negative pin when the output is shorted and the current is set to 3A. Then the diode between them causes the output voltage to drop until the current is 3A. But when the output is shorted and the current is set lower than 3A then the current regulator will not work properly below a certain setting.
So the negative supply is needed after all.

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Guest liquibyte

Here's the issue I'm running into currently.  I've got the circuit behaving at high current and high voltage but as I raise the load resistance the input gets unstable and the shutdown doesn't behave as I would expect and I can't figure out why.  For one thing, you'll notice in the 3A pic that shutdown occurs at around 1 3/4 seconds.  This is because I've got the input voltage set at 100 cycles.  In the 1mA pic, nothing has changed other than the load going from 10 ohms to 30k but the shutdown occurs at just over 7 seconds.  You'll also notice that the input voltage sags drastically where shutdown should happen but things don't bleed off as I would expect.  Both output conditions have a 200ms short for testing purposes.  If I could get the low current output to shut down like the higher currents do I'd probably breadboard this to see how it went.

Edit:  I wanted to add that adding in the negative supply doesn't change the behavior of the plots.  I started out with the negative supply and the above configuration and on a whim decided to see what would happen without it.  Since nothing changed whether or not it was there, I decided to try and see if I could get it to work without it.

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Guest liquibyte

I have to test out the various components for being within their specs but I think I may have it.  There's about a 200ms difference in shutdown times at the mosfet but taking a page from the original Q1, I'm shunting the residual power to ground from the output cap instead of from the voltage op amp.  It seems to work so only a prototype will tell I guess.  The slope on the lower current is not as tight but I think I'm getting closer.

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Guest liquibyte

I've tried to get this to do better but I'm stumped on how to get it to shut down quickly at lower current loads without actually using a separate voltage source for the relay.  In the grand scheme of things I guess I'm being a little anal about it but it still bothers me.

Edit: instead of taking out the current 2.2K 2W bleeder, I've made it 1K to match the output and it seems to help in getting the low current fall off time to be shorter by a couple of seconds or so.

Sorry about the part numbering.  LTSpice seems to be kind of inconsistent in that regard.

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0-30V-0-3A-test-falloff.zip

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Guest liquibyte

I think I finally got the component limits within reasonable specs, especially the shutdown parts.  This is just a minor revision with rearranging a few parts, adding another resistor and kind of spreading things out so it's easier to read.

I've been thinking about the reasoning behind the negative supply and I'm starting to believe that it wasn't really necessary in the first place and may have just been a hack to make things behave.  Obviously these aren't real parts and actual results may differ from a prototype build but I think this may be a workable design for the most part.  Without a redesign on the current and voltage circuits I don't think we'll ever get a true zero on either but I've done my best to simulate the results accurately and to be honest if you really need that zero, you'll probably know you do and want to purchase something instead of building it based on this design.  The purpose of the mosfet and the relay, however, remain valid design choices due to the lack of control at startup and shutdown and I think they solve the problems that have been encountered.  You can use a different mosfet if you like as long as it falls within tolerance.  I have limited choices in the parts that I've obtained for simulation and haven't bothered to seek out a TO-220 part that would be a more accurate representation of reality and cost.  This is going to be my last post of this unless someone sees something glaringly wrong with it.  I've left out the transient and short circuit simulation parts and if you want to mess around with that part, let me know and I'll add them back and upload it.  Play with it, build it, let us know if it works reasonably well.

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0-30V-0-3A-test-falloff.zip

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  • 2 months later...
Guest Hans7530

Hi,
today I began to build the power supply, with the part list and the schedule on the main project page. I used the pcb from the project page too.
As I would test the circuit, I note that the output of the supply only range from 0-7V and U2 was very hot. It looks like U2 is in the shortcut mode and can`t rise its output voltage above 7V.

I build the complete power supply with the same things like the part list. I also use a 24V AC trafo.

Maybe someone can help me. Thanks for all answers.
Sorry for my bad english.

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The original project has errors that can destroy the TL081 opamps and overload many other parts. That is why we fixed it and talk about the fixes in a few long threads in the forum.

If the pins of Q1 are wired wrong and are mixed up then the reverse-biased emitter-base becomes a 8V zener diode that overloads the output of U2 and prevents the output from rising above about 7V. The pins on the European BC548 are CBE, but the pins on any American or Japanese little transistor are EBC.

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  • 6 months later...

it seems many of the links to attachments (links to post numbers,zips and pdfs) have broken in even the more recent posts in this thread and ancillaries. Any idea how to recover? In particular i am looking for thn3 trouble shooter pdf liquidbyte compiled from advanced members like audio guru. I had a version of this PSU running for several months, blew a tl2041 replaced it and ran for a few more weeks, but now I have trouble. low volts -- cannot adjust higher than a few volts, but very high current. So there must be a short some where... I havent progressed past thinking about it yet. And I did not solve (or at least understand exactly) why the first opamp blew (the amperage control circuit if I remember right). I just seated another and it worked again. I suspect the present failure is related to whatever caused the first one. Hence reading the latest posts to see if anyone else had similar and having been tempted by mention of it, I am now looking for the trouble shooter pdf. Perhaps someone could email it to me?

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  • 2 weeks later...

 

hi James Bond O ,

 

you may have to indicate the  error image and  to members.

 

Otherwise, getting some error message doesn't appear a good way of reporting.

 

you can capture the screen and  upload as  .png.

 

it helps  proteous gurus to study and comment.

Hi everyone

Sorry my bad.

There go the schematic and the error. 

I joined the Proteus file too, so you can test it if you have Proteus. 

Best regards 

 

P.S::

Can i change TLE2141 by MC34071 without any problem?

My goal is controll the PSU using arduino, but need put its to work first :)

Final.pdsprj

erro1.jpg

Schematic.jpg

Edited by James Bond
nothing special, added Proteus file
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Hi, thanks by you reply but this ins't the problem, the circuit works with 10pF.

I found how fixate this, this is a setting problem.

 

Original configuration was:

System -> Set simulations options -> Tolerances (left down corner) -> Default Settings.

I changed to:

System -> Set simulations options -> Tolerances (left down corner) -> "Settings for better convergence" (and load it).

 

Now work fine.

 

Best regards.

Edited by James Bond
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  • 1 month later...

Many, many questions keep getting asked about this thing and people keep attempting to build it without even knowing the basics, why I don't know.  The power supply suffers from a couple of issues that have never really been adequately addressed so this is going to be my attempt at bringing this thing into the modern age.  What follows is just preliminary work to right several wrongs I've noticed with the design.  It's not complete but I'm posting it to get opinions and suggestions.

This paragraph is for the newbies:  DO NOT ATTEMPT TO BUILD THIS YET.  If you don't know what you're doing, do not even try and breadboard this.  Once I have a final design, I promise that I'll post it.

Now, onward.  I'm posting my spice simulation for anyone that wants to try and give this a go.  One of the things that concerns me is the power dissipation in the op amps but I'm not sure how to get this down to a more acceptable level because I don't think 150mW at load is very good so suggestions are most welcome.

First, the voltage reference in the old version was an extremely odd thing to me so what I wanted to do was get a precision reference in there to work with.  10V seemed like a nice round number so that's what I went with and I actually have one on hand to use.

Second, the sense resistor.  0.47 ohms?  Once again, odd.  Plus, it suffers from extreme power dissipation as well.  My idea is to have a nice 0.1 ohm 3W 4 wire resistor in there to hook a meter to so I adjusted things around the reference to get me to where I wanted to be and I also have some of these.

What I'd like to eventually do is design the meters along with the supply so that what we end up with is a relatively complete project with all the nice bits people seem to be after.  No one, I repeat, no one ever offers a suggestion as to what to build to replace this, not one single engineer.  They will, however, be the first people to tell you how bad the design is but never offer any sort of advice as to why.  I know, I've asked and so have many other people.

0-30V-0-3A-redesign.zip

0-30V-0-3A-redesign.png

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The opamps will be cooler if they are TLE2141 singles.

Yeah, I know.  I did the math from the datasheet and given what the simulation is giving me, I'd say the device can probably handle it.  I don't have the equipment to lay this out and test in the real world but PD from both amps only total around 300mW and if I'm reading things right, the 2142 can probably handle it.

 

It turns out that I was under a wrong assumption about the power handling capabilities of op amps in general.

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  • 1 month later...

Hi. I think I read somewhere that I could use a voltmeter as a makeshift ammeter for this project. 

Can I use this type of voltmeter?

http://www.ebay.com/itm/2pcs-Mini-DC-0-100V-Red-LED-3-Digital-Display-Voltage-Voltmeter-Panel-Motor-/381374425176?hash=item58cbafe858:g:dtcAAOSwo8hTmvxX

How will I hook it up to the unit? 

 

I haven't built the power supply yet. I am still waiting for the parts. 

Also, I saw the original circuit in a kit form that is sold on banggood.com (link) Most of the reviews are good. The transistors were modified, and the two zeners, if I remember correctly.

Q2 = 2SD882 (2N2219 in the original)

Q4 = 2SD1047 (2N3055 in the original)

D7, D8 = 5V1 Zener (5V6 in the original)

Any insights about this? 

 

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ebay cannot even spell the word "meter" correctly, they say it is a motor. Their very cheap meter might not be able to measure its own supply, instead it might need a separate power supply or battery like most meters.

 

The Greek kit and the Chinese one cannot produce 30VDC at 3A and its main filter capacitor is much too small. Its TL081 opamps will have a total supply higher than they are allowed to have when the load current is low. Many parts are overloaded.

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Thanks for the reply audioguru! 

Yes, I will supply them with a separate supply. I added a 7812 regulator after the capacitor. I reversed engineered the PCB from banggood because I'm too lazy to make my own. 

I will change the parts according to your parts list, mr audioguru. I cannot find the MC34071 in my place, can I use the LM741 instead?

And I think they don't have 24-0/28-0 single transformers here, so how would I go about editing the rectifier circuit into accommodating a center tap trafo? (14-0-14 or 12-0-12)

The 30V  doesn't really matter much to me, though. 

Thank you so much.

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Your meter might need a completely separate supply with its own power transformer and filtering.

A 741 opamp has a design that is 47 years old and it will not work in the improved circuit. It might work in the original Greek circuit or the Chinese copy of the circuit if the transformer voltage is lower than about 20V-0-20V. If the transformer voltage is as low as 12v-0-12v then many resistor values might need to be changed.

MC34071 or TL2141 opamps can be used in the improved circuit or in the original circuit. The MC34071 is no longer made in the through holes DIP case, it is in a surface-mount case now.

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