Sallala

0-30 Vdc Stabilized Power Supply

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He must be using liquid nitrogen and a huge fan to cool his single 2N3055 transistor.


There is not need for nitrogen neither for huge fan. It's a laboratory power supply which in my book is used for testing some projects, usually for short period of time. Dissipating power will be problem if power supply is used for extended period with low output voltage and high current . When I started the project I had already the enclosures so I had to take their sizes into consideration. There is a small fan which is switched on when temperature rises.

To mjvision : there is no need for emitter resistor if there is only one transistor.

P.S. Soon there will be improved version of the schematic in my blog. Stay tuned :)

P.P.S. The improved schematic: http://diyfan.blogspot.com/2013/03/adjustable-lab-power-supply-take-two.html

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Your V3 design is very nice.

I noticed that on your V2 design the output of opamp IC1A cannot go low (because it is missing a negative supply) to regulate the current and things might burn up.

The old TL082 opamp has the "Opamp Phase Inversion" problem: If an input voltage is too close to the negative supply voltage (ground in your circuit) then the output goes high.
An input voltage is too close to the negative supply (ground) when it is lower than the common mode voltage limit of +3V to +4V in your circuit. But both inputs of opamp IC1A are always from 0V to +1V.

That is why transistor Q1 shorts the output of IC1B in your circuit when the negative supply reduces when the power is turned off. It prevents the output voltage from suddenly going up to maximum.   

post-1706-14279144533936_thumb.png

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Your V3 design is very nice.

I noticed that on your V2 design the output of opamp IC1A cannot go low (because it is missing a negative supply) to regulate the current and things might burn up.

The old TL082 opamp has the "Opamp Phase Inversion" problem: If an input voltage is too close to the negative supply voltage (ground in your circuit) then the output goes high.
An input voltage is too close to the negative supply (ground) when it is lower than the common mode voltage limit of +3V to +4V in your circuit. But both inputs of opamp IC1A are always from 0V to +1V.

That is why transistor Q1 shorts the output of IC1B in your circuit when the negative supply reduces when the power is turned off. It prevents the output voltage from suddenly going up to maximum.    


You are not quite right about IC1A - with IC1B they share common power supply pins and so there is negative voltage -3V.
And as I said in my blog both versions are tested and they work very well - I can regulate current limit almost to 5 - 10mA, below that is not possible because of input offset of the opamp.

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You are not quite right about IC1A - with IC1B they share common power supply pins and so there is negative voltage -3V.

Sorry, I got mixed up about which opamp belongs to which opamp of the duals since all the other circuits used single opamps so they stay cooler.

And as I said in my blog both versions are tested and they work very well - I can regulate current limit almost to 5 - 10mA, below that is not possible because of input offset of the opamp.

Your circuit has a -3V negative supply and your opamps worked. But the datasheet for the old TL082 shows an input common-mode limit of 4V max, not 3V. So some opamps WILL FAIL!

That is why I selected common inexpensive ordinary opamps from two manufacturers that do not have the Phase Inversion problem, that work perfectly when their input voltages are at the negative supply voltage and have a max allowed supply of 44V.

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Your circuit has a -3V negative supply and your opamps worked. But the datasheet for the old TL082 shows an input common-mode limit of 4V max, not 3V. So some opamps WILL FAIL!

That is why I selected common inexpensive ordinary opamps from two manufacturers that do not have the Phase Inversion problem, that work perfectly when their input voltages are at the negative supply voltage and have a max allowed supply of 44V.


I didn't find anything like that in the datasheet.
There is negative input voltage limit but in this schematic input voltages of IC1A NEVER go below zero, so I don't think there is such danger.
And if these opamps (TLE2141 and MC34071) are so common why there is so many question about replacing them with alternative opamps :)

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I didn't find anything like that in the datasheet.

The datasheet for the OLD TL08x opamps lists the specs with a plus and minus 15V supply. The minimum Common-Mode Input Voltage Range (where its inputs work properly) is -11V. Its typical is -12V. So some opamps fail when an input is 4V above the negative supply voltage and MOST fail when it is 3V above the negative supply.
When the input voltage is 3V or more ABOVE the negative supply voltage then the output of the opamp will suddenly go as high as it can!

There is negative input voltage limit but in this schematic input voltages of IC1A NEVER go below zero, so I don't think there is such danger.

The maximum allowed maximum input voltage is not what I am talking about.

You have this OLD opamp with an input voltage THE SAME as the negative supply voltage or at 0.99V max above the negative supply voltage which is bad fort these OLD opamps.
 
And if these opamps (TLE2141 and MC34071) are so common why there is so many question about replacing them with alternative opamps :)

Are you in Russia? I am in Canada where ALL American and European ICs are available everywhere.
TLE2141 is made by Texas Instruments and MC34071 is made by Motorola/Freescale. They are HUGE companies.

Some students want to use the CHEAPEST and OLDEST opamps they can find at their school (741 opamps).

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I'm looking at R4 in the circuit and it looks like the zener diode D8 at just over 1ma. Is that the feedback ratio of U1? RV1 seems to determine the output voltage. Adusting the offset to produce the desired voltage isn't familiar. Can anyone help explain this?

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I'm looking at R4 in the circuit and it looks like the zener diode D8 at just over 1ma. Is that the feedback ratio of U1? RV1 seems to determine the output voltage. Adusting the offset to produce the desired voltage isn't familiar. Can anyone help explain this?

The BZX79C5V6 zener diode that I recommend for D8 is 5.6V when its current is near 5mA.
R4 also has 5.6V across it so its current and the zener's current are 5.6mA.

RV1 is the trimpot to adjust the output offset voltage. It varies the output voltage plus and minus a small amount. When the voltage setting pot is set to zero then RV1 is adjusted so that the output is exactly 0V.

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i know this is a stupid question, but i'll go right ahead...

i understand that's U2, U3 and Q4 mainly are regulating the voltage and current, can i swap them in the future with switching mode components/assemblies to increase efficiency??

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i know this is a stupid question, but i'll go right ahead...

i understand that's U2, U3 and Q4 mainly are regulating the voltage and current, can i swap them in the future with switching mode components/assemblies to increase efficiency??

This is a linear power supply. The circuit for a switching power supply is completely different.

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need some theory/Calculation on it....give me idea about it.

Opamp U1 has a voltage gain of 2.0 and uses a 5.6V zener diode so its output is always +11.2V.
Voltage pot P1 feeds from zero to +11.2V to opamp U2.

Opamp U2 and the driver and output transistors are a power amplifier with a voltage gain of 30.0/11.20V= 2.68 times.

Opamp U3 compares the output current in R7 with the setting of the current pot P2 and if the output current is higher then diode D9 reduces the output voltage until the output current is the same as the setting of the current pot.

Transistor Q3 turns on the LED to warn you that the current regulation is reducing the output voltage.

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Xristost, I like the stabilized 30v power supply you work on. So many people want a constant voltage...


The design in this posting in my blog is the same as the discussed one in this  topic.
There are number of small improvements that are mentioned in the posting.

The design in this posting is little different and is based on an old schematic published in a Czech electronic magazine.
The latest version I made is simpler, has only one dual opamp and is better suited for ordinary opamps like TL082.
As I said in my blog, I tested it with number of different opamps and it worked flawlessly. Couple of other people also reported that they made the schematic and it's OK.


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The design in this posting in my blog is the same as the discussed one in this  topic.
There are number of small improvements that are mentioned in the posting.

The design in this posting is little different and is based on an old schematic published in a Czech electronic magazine.
The latest version I made is simpler, has only one dual opamp and is better suited for ordinary opamps like TL082.
As I said in my blog, I tested it with number of different opamps and it worked flawlessly. Couple of other people also reported that they made the schematic and it's OK.

Your circuit has problems:
1) Its supply to IC1B is only 33V so the maximum output voltage at 3A is about 25V with lots of ripple, not regulated properly at 30V.
The opamp has loss, R14 has loss, the driver transistor has loss and the output transistor has loss. The losses add to almost 10V.

2) If the output is set to a low voltage and is set to 3A then the output transistor will burn up.
It will try to dissipate 40V x 3A= 120W!! That is why the modified circuit here uses TWO output transistors to share the heat.

3) The current regulation will not work and many parts will burn up or catch on fire when the output is shorted because IC1A is missing a negative supply voltage and D7 cannot reduce the output voltage to 0V.

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Your circuit has problems:
1) Its supply to IC1B is only 33V so the maximum output voltage at 3A is about 25V with lots of ripple, not regulated properly at 30V.
The opamp has loss, R14 has loss, the driver transistor has loss and the output transistor has loss. The losses add to almost 10V.

2) If the output is set to a low voltage and is set to 3A then the output transistor will burn up.
It will try to dissipate 40V x 3A= 120W!! That is why the modified circuit here uses TWO output transistors to share the heat.

3) The current regulation will not work and many parts will burn up or catch on fire when the output is shorted because IC1A is missing a negative supply voltage and D7 cannot reduce the output voltage to 0V.


It's obvious that you just repeat yourself endlessly. . .

3) I already said that two opamps are one dual opamp, so they have common supply, so IC1A have negative supply voltage.
Also read again that part marked in red ind the quote.

2) About the power dissipation you are right, but the number of output transistors is a matter of choice - if someone decide to use the PS at 1V/3A, he is free to put TWO or THREE output transistors.

1) And for the first "problem" - you heavily exaggerate here :)
But this "problem" have a very simple solution - we will call my schematic "Variable PS 0-25V" and everything will be OK, right?  ;D

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It's obvious that you just repeat yourself endlessly. . .

I simply stated the problems with your re-design.

3) I already said that two opamps are one dual opamp, so they have common supply, so IC1A have negative supply voltage.

But then the opamps will probably over-heat. Single opamps should be used.
Also, the negative supply of only 3.0V is too low for a TL082 that has an input common-mode range of 4V from the negative supply voltage. When the output is shorted or is at a low voltage then some TL082 opamps for IC1A WILL NOT WORK!!
That is why I used opamps that have an input common-mode range that includes the negative supply voltage.  

2) About the power dissipation you are right, but the number of output transistors is a matter of choice - if someone decide to use the PS at 1V/3A, he is free to put TWO or THREE output transistors.

How many of your project will burn up?
You mentioned a fan.  A HUGE fast fan?

1) And for the first "problem" - you heavily exaggerate here :)
But this "problem" have a very simple solution - we will call my schematic "Variable PS 0-25V" and everything will be OK, right?  ;D

I do not exaggerate since some ICs and some transistors are not as good as others. You cannot buy "good" ones, you get whatever they have that still meet their specs.

EDIT: I forgot to say that R7 also causes an output voltage loss of 0.99V. So your circuit might not produce 25V at 3A, maybe only 24V.

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Yes, yes, whatever . . .

You have only words, and I have working power supplies  8)

You did not look at the specs for your opamps and transistors like I did so only SOME of your circuits will work properly.

I designed my circuit so that ALL circuits will work properly. I always use WORST CASE SPECS in my designs so that all my circuits work properly.

I have designed and had made and sold tens of thousands of fairly complicated circuits and tested every one of them before they were sold. Not one failed except for one that had its IC installed backwards and another had a shorted electrolytic capacitor. Not a single circuit that was sold had a problem. Most of the ICs were the TL074 designed by Texas Instruments but made by Motorola-ON Semi which is the TL084 selected for low noise. Maybe the TL07x is more reliable than the same or higher price TL08x. Millions or billions of TL07x opamps were used in audio equipment.

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Hi everyone!

Im sorry but I didnt read through all 120+ pages of this topic so Im probably going to repeat a question that has already been answered..
Im going to build this power supply but I would like to have two same supplys in one case so I could use them like two seperate or like one in series so I could get + and - voltage.
Now the question is if that is possible and how should I wire the two together. I guess that ground should be isolated?

thx,
Greg

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Each of the two power supply circuits must be COMPLETELY separate from each other. Separate transformer, separate bridge rectifier and separate everything.

Do not connect any terminal to earth unless you want it like that.
Then you can connect the supplies in series and get up to 60V out, or up to plus 30V and up to minus 30V.
You cannot connect the supplies in parallel because if you do then they will fight each other.

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