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0-30V Stabilized Power Supply


redwire
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Guest VittoYi

Hi everyone!
I'm trying to build this power-suppy as well, however,  I'm doing it as a "low-cost" power supply, spending as less as I can.
Given that, I already have a 24V + 24V 300VA transformer (from an old project) which provides at top 6A for each output line.
Can I use this one to supply the circuit? Would the circuit current consumption get up to 6A or it can be limited to 3A ? ??? ???

Thank you, in advance.  :)

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Hi everyone!
I'm trying to build this power-suppy as well, however,  I'm doing it as a "low-cost" power supply, spending as less as I can.
Given that, I already have a 24V + 24V 300VA transformer (from an old project) which provides at top 6A for each output line.
Can I use this one to supply the circuit? Would the circuit current consumption get up to 6A or it can be limited to 3A ?

The improved and corrected circuit uses a 28VAC or 30VAC transformer. If you use half your transformer (24V) then the maximum output voltage from the project will be about 25VDC at 3A, not 30VDC.
The improved circuit has a trimpot to set the maximum output current at 3.0A.
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Guest VittoYi

The improved and corrected circuit uses a 28VAC or 30VAC transformer.


Can you please send me the link of the new version? Because I could only find one where a 24VCC is required. Anyway, it still seems to consume 3A to me. So, the transformer I have would work fine with that.
I mean, the fact that the transformer can supply 6A doesn't mean that the circuit would consume 6A, right?

Thanks, and sorry for my questions, I'm still learning! ;D
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Can you please send me the link of the new version? Because I could only find one where a 24VCC is required. Anyway, it still seems to consume 3A to me. So, the transformer I have would work fine with that.
I mean, the fact that the transformer can supply 6A doesn't mean that the circuit would consume 6A, right?

Thanks, and sorry for my questions, I'm still learning! ;D

I guess you found the original old project that has many errors. It cannot produce 30V at 3A and it is not reliable because many parts are overloaded.
The improved project can produce 30V at 3A and it is reliable.

I guess you did not learn the basics of simple electricity and Ohm's Law.
The battery in my car can supply 800A to the starter motor in winter when the cold oil is very thick. But the clock in the car does not use the entire 800A, instead it uses only the 0.002A that it was designed to use.
My home has electricity that has a maximum current of 200A. But my clock radio does not use the entire 200A, instead its clock uses 0.002A that it was designed to use.
The 0V-30V lab power supply consumes a little more than 3A from the transformer when its output supplies 3A DC because some of its parts use extra current to do their work.

Here are the improved schematic and parts list: 

post-1706-14279144675642_thumb.gif

post-1706-14279144675835_thumb.png

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Guest VittoYi

Okay, this sounds perfect.
Is there a PCB scheme avaliable?

About Ohm's law and stuff... well, let me say I did study those things, what I meant to say is that 6A as an input can burn the circuit if the output consumes more than 6A.
I was just worried I could not limit the current to 3A. (Now, I know this is possible thanks to the trimpot on the board)

Just one last thing, in the circuit you mentioned, is it possible to add a protection for short circuits?

Thank you, audioguru. I'm learning a lot with this project! ;D ;D

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Guest VittoYi

Yes, there are a few pcb designs posted in one of these threads about it.

There are so many PCBs that I really can't find the one for the fifth version.


Yeah, I double checked the part and it has reversed legs, why I don't know.  I mirrored it and corrected the board file and gerbers to reflect the correct part I used.  I deleted the zip file from my previous post so I don't cause confusion and I'm attaching the corrected version here for anyone that wants to use the files.  Included are the schematic and board files plus the gerbers that I used at Itead to get the boards made.  The recommended weight should be 2oz copper for 3A given the trace width, however, that adds $25 to the cost of the boards with them.  I used 1oz and am going to run 22awg jumper wire along the bottom between the components and the outputs to handle the current.  Probably not the best solution but I imagine it will work alright.

Edited to include a parts list of Digikey part numbers.


Does the one from liquidbyte work fine? I don't really need a PCB, but since I want to get two of these circuits working together in the same box, a PCB will make it easier to fit in a standard eletronics box. I'd like to get the copper traces (if anyone designed them already) so that i can get the PCB through photoengraving.
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Guest liquibyte

I have two of mine in the same box running independently and they work just fine.  I have also loaded them to the full 3A @ 30V and have seen no issues to date other than the ones reported by Redwire about the voltage spikes on power on and off.  I don't have a DSO so I can't really investigate this too much but can see the spike with the Conar 255 I do have.

I've sent out four of my boards to two other members here (philtherepairman and cscott719) and they could probably give you an indication if they are working for them as expected and perhaps they'll post here as to how things are working out for them.  I have four boards left and would like to keep two more for myself but if you're interested PM me.

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Guest EmbeddedCom

A few weeks ago I changed the board by deleting U1 and associated components and replaced it with a 12V linear voltage regulator (PN  L78L12ACUTR).    I added two cap to keep the voltage regulator smooth.  Today the new PCB boards came in.    The only other board change was C7.  I switched to a film instead of electrolytic.  I ran the same tests on the scope and there was no ringing.  Based on that, I assume the ringing was U1 trying to stabilize when the power supply was removed but C1 still had a charge.


Can you please post your modified schematics ?
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Guest VittoYi

Hi guys,
I was just wondering if a transformer with 4.17A would make a big difference instead of the one which is suggested in the scheme (4.3A).
The transformer I've got can supply 30V while the scheme says 28V are enough. The power supplied is pretty much the same. So is a 4.17A - 30V transformer suitable?
Thanks to everyone.

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Your 30V transformer supplies a voltage of 30V and its rated current is 4.17A. Then its maximum allowed power output is 30V x 4.17A= 125.1VA. 
The power supply constantly charges its main filter capacitor to the peak voltage 30V x 1.414= 42.4V. The rated output of the power supply is 3.0A plus maybe 0.1A for its circuitry so it uses a maximum power of 42.4V x 3.1A= 131.4VA.

Then your transformer will be a little overloaded but probably not enough to smoke or to catch on fire.

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Hai...

        I would like to design the same for a 0-30V / 5A power supply with the changes below.

        30V/5A transformer.
        2N3055 transistor 2nos parallel with Q4 and Q5 with same design.
        RV3 with 500K trimpot.

        Is it enough to make a 5A 30V power supply or please suggest a necessary changes.

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A 30A/5A transformer is overloaded when the output of this power supply is 5A because the rectifiers charge the main filter capacitor to almost the peak voltage of 42.4V. The circuit draws about 0.1A. Then the power from the transformer is 42.4V x 5.1A= 216VA. A 30VAC/7.2A transformer is needed to provide 216VA.

We use two 2N3055 power transistors for a 3A output and they get pretty hot when the output voltage is low. THREE of them are needed for an output of 5A.
Here is a fairly old parts list for a 5A power supply:

post-1706-14279144677659_thumb.png

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I have one small very cheap Chinese AC/DC adapter that has no safety certification markings and is rated at 9VDC/100mA. It produces a little more than 18VDC with no load and gets hot. With a load of 100mA its output is 8V with a lot of AC ripple and it is dangerously hot so I do not use it.

An overloaded transformer gets hot. A transformer with safe ratings gets pretty warm but not hot. Simply find a safe name-brand transformer with the ratings you need and compare its size with the unknown transformer. If the unknown transformer is smaller then it might be overloaded at its rating.

A 2A load on a 30VAC transformer is resistance that is 30V/2A= 15 ohms at 30V x 2A= 60W. If you find this resistor then load it on the transformer and feel if the transformer gets hot. 

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Shall I use TL081 instead of TLE2141 or MC34071

What are the changes need.

The original circuit used TL081 opamps. Its maximum supply voltage is only 36V and it needs a negative supply so it cannot produce +30V without risking damaging it with a supply voltage too high for it. It also has a problem called Opamp Phase Inversion that causes its output to go high when its negative supply voltage drops too low when the power is turned off. So transistor Q1 was added to short its output to ground when the power was turned off.

The MC34071 is not available anymore in a DIP package. It and the TLE2141 have a maximum supply of 44V and they do not need a negative supply so they work fine producing an output of +30V.

If you use TL081 opamps then they need a -5.6V negative supply as shown in the original circuit. But the positive supply in the original circuit was too high for them since it used a 24V AC transformer and without a load the positive supply was about +34V or more, then the opamps are powered with a total of 40V or more. If the transformer is 20V then without a load the positive supply will be about +28 but then the maximum output from the project will be only about +20V if you are lucky. 
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hello audioguru! i am a newbie in electronics. i want to know that why the opamps like CA3140, CA3240 etc do not work at all in this circuit though they are capable of operating with single supply. i know they have a max operating voltage of only 36 volts but still if i require a low o/p voltage from the supply, the circuit does'nt work at all with these opamps.

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hello audioguru! i am a newbie in electronics. i want to know that why the opamps like CA3140, CA3240 etc do not work at all in this circuit though they are capable of operating with single supply. i know they have a max operating voltage of only 36 volts but still if i require a low o/p voltage from the supply, the circuit does'nt work at all with these opamps.

The circuit might work with CA3140 opamps if the supply voltage is reduced by using a custom made 22V AC transformer but then the maximum output will be only about +22.5V DC at 3A if you are lucky. You might need to re-calculate a lower value many of its resistors so that the currents in the circuit are adequate. 
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I Draw this circuit with PROTEUS-ISIS but cant simulate because a error, can someone help me to find the problem pls.

Very few people use your Proteus program. For us to see if there is something wrong with your schematic then please post it as a normal PNG file type that everybody can see.

Maybe you can "copy screen" then paste the schematic into a picture viewer like Paint program then save it as a PNG file type.
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Hi again :) There is the circuit in ".png" Format.

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.
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Guest thiagoas

Would NE5532 work in this circuit? I have no LME2141 in my country.

I also simulate the circuit in proteus, and it works, just have to change SPICE options for better convergence.

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