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Posts posted by xristost

  1. One solution which come in my mind is to put a transformer with ratio 1 : 0.46 then at the secondary the voltage will vary from 55VAC to 276VAC. If your AC/DC converter can work with that low voltage - 55VAC, then no switching will be required. But if it can't, then the transformer should be made with two secondary windings and a schematic will switch the desired secondary winding.

  2. Hi,

    I have tried folowing for voltage reference
    1) opamp+5v6 zener
    2) tl431 (set to 10v reference with 2 resistors)
    3) 3k resistor + zener6v2 + zener3v3
    4) bf256 + zener6v2 + zener3v3

    The test was that I set output to 5.000v and I measured voltage with and without load (load was about 2.5A)
    1), 2) and 4) where OK, i didn't noticed any change (my instrument has 3 decimal places)
    3) like I said it have voltage drop of about 20mV, but that depends on positive rail (probably with stronger transformer there would be much less drop)

    Than I have done temperature stability.
    I have heated board from 20 deg. Celsius to about 60-70 deg. Celsius (I used electric fan heater)
    4) was most stable, +-10mV change below 50 deg., and +20mV from 50-70 deg. (first was -5mV, than it started to rise to 5mV, and after 50 deg. it strated to rise  to +25mV)
    2)  20-30mV change (I think it was +30mV)
    1) 40mV
    3) I haven't tried because of load voltage drop problem.

    Hi, in my variant I use resistor+ 2 zeners, because voltage is already regulated with LM317, so there will be no voltage drop (if supply voltage is high enough).
    It's interesting to compare yet another solution for voltage reference - LM317L with resistors 270/1.8k. This will produce 9.58V. According to datasheet line regulation is 0.02%/V. If input voltage change with 1V, output will change with only 0.2mV.
    Temperature stability is 0.65% which is 8mV in entire temperature range.
    I think it's worth to try.

  3. Another solution of this problem is to wire a couple of power diodes in series after the rectifier and smoothing capacitors. Each diode will reduce voltage with ≈0.7VDC.

    I started asking about hooking up the TO-3's over at EEVBlog because it's a much more active site and I was looking for an immediate answer to my question.  I am getting a bit of negative feedback regarding the fact that someone thinks that this design isn't sustainable due to the fact that with a 28V transformer after rectification and smoothing that the voltage into the opamps is going to be around 50V.  Has anyone that's built the 3 amp version run into issues with this?  If so, what sort of solution did you use to fix the issue to get the voltage to less than 44V so as to not overload the max limits on the TLE2141's?.

    Edit:  Nevermind.  I hooked up the filter cap and measured 45.1 VDC.  It's a little over the 44V max of the op amps which worries me a bit.  So I guess a new question would be, is there a recommended way to drop that to the 44V?  Voltage divider to ground?

  4. Those with LM317 don't have current regulator..and they dont go from 0V..At least not those what I found. Do you have any maybe with current regulation? I would be very thankful to you!

    If you dont, I'll try to manage somehow in this bunch of schemes here :D (saw your post, couple pages earlier)...

    Sorry for offtopic!

    It's there, in the datasheet: http://www.ti.com/lit/ds/symlink/lm117.pdf (page 21). But it is from 1.2V to 30V
    In the datasheet have also schematic which goes from 0V (page 20) but without constant current mode. Maybe its possible the first schematic to be modified to go from 0V.

  5. 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

  6. 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.

  7. Hi,

    I have 2 power supplies but I need to obtain 3 voltage levels (+5V, +12V, -12V) to bench test a circuit board… is there a simple solution or do I have to use 3 power supplies?!

    Many thanks,


    If your power supplies are variable, then you can adjust both of them at 12V and connect them in this way:


  8. I'm sorry to interrupt the conversation. I know it isn't said here often enough. But our programmers are what makes are world all the possible. Even you can take a lesson. Remember.

    Your latest posts are very cryptic, weird and not connected with the subject. Are you OK?

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

    i understand that's IC1A, IC1B, and 2N3055 mainly are regulating the voltage and current, can i swap them in the future with switching mode components/assemblies to increase efficiency??

    Go and see this video:

    I think that theoretically you can replace output circuitry with switching mode regulator.

    And if you don't care much for constant current mode, then there are tons of different switching mode regulators like LM2596 or LT1074 for example. They are very efficient, with simpler schematics, have all sorts of protections build in and may suit your needs better.

  10. i just like pushing the envelope, even if i hardly know anything about the theory (software, not hardware, really is my specialization).

    alright, i'll be building your ver 2...

    i'd like to have 2 different outputs, with that, i suppose that you can always share the rectifier. but, i was wondering what other sections can be shared if i were to do so?

    Maybe the regulators (LM317L and LM337L) for the opamps can be shared.
    And for the two channels you must double the C1 capacitor.
  11. It's always amaze me how people want more and more amperage and voltage from a variable PS and most of the time they haven't any idea for what purpose they want that.

    Any way, I would suggest you to get finished module like this: http://www.ebay.com/itm/ZXY6010-DC-Constant-Voltage-Current-Power-Supply-Module-60V-10A-600W-/120963323698?pt=LH_DefaultDomain_0&hash=item1c29f9d732

    I hardly believe you would find simple circuit with your requirements.  

  12. AG
    can you check the attached and the link
    I need your feedback
    because the thing is I got the TLE2141 not the other one .

    You must rename all parts to be with same designation in two schematics. It will be much easier to check for mistakes.

    And about the transistor Q2 in the output - I think it had another purpose - to shut down output voltage quicker when schematic is powered off.

  13. 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 :)

  14. 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.

  15. 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

  16. It is a combination of the original schematic and the latest schematic:
    1) It uses Q2 to solve the "Opamp Phase Inversion" problem with the TL081 opamps used in the original project but the MC34071 opamps do not have that probem.
    2) The value of R15 is much too high.
    3) Its single 2N3055 output transistor will get extremely hot (maybe hot enough to fail) when the output is set for 3A and it is shorted or has a low voltage. Its max dissipation is about 90W.
    It has a huge heatsink and a fan so maybe it will survive.

    1) I deliberately kept Q2 because with it output voltage drop more quickly after power off.
    2) R15 is 1k in original schematic and I don't know what will change if I replace it with lower value resistor since everything is working OK.
    3) I decided to use only one output transistor, because the PS would rarely be used at low voltage and high amperage. With this heatsink and the fan running it manage to dissipate 60-70 W for a long periods without problem. For a couple of minutes it survived shorting at 3A.

    BTW, for the second unit I put 2SC5589 instead of 2N3055, because it was ease to mount :)

  17. I know. I do not really need more than 20 volts, so I think a 24 volt charger fits my needs, could use this design with the charger I mentioned earlier?

    Part of the circuit will not work, because it use AC voltage to make negative supply voltage for U3. But charger will provide only DC voltage.

  18. TL081 opamps have a problem called Opamp Phase Inversion where the output suddenly goes high if an input voltage becomes too close (within a few volts) to their negative supply voltage. The negative supply in this project was small so it collapsed first when the power was turned off which caused the output voltage of U2 to rise which caused the output voltage of the project to rise. Q1 was used to short the output of U2 to 0V when the negative supply begins to drop so the output voltage could not rise.
    The new opamps do not have this problem so Q1 is not needed.
    U3 needs to have a small -1.3V negative supply so that its output in series with D9 can go low enough to cause an output voltage of close to 0V when the output of the project is shorted. 

    There was a video posted on some page of this tread, where output voltage raise briefly. And that was with these new opamps. That's why I was thinking to put back Q1.
  19. Hello,

    I also have а couple of questions. First, the original article states:

    In order to make it possible for U2 to control the output voltage down to 0 V, it is necessary to provide a negative supply rail and this is done by means of the circuit around C2 & C3. The same negative supply is also used for U3. As U1 is working under fixed conditions it can be run from the unregulated positive supply rail and the earth.

    But in the improved schematic (latest version) pin 4 of U2 is connected to ground ("-" pin of C1). Is this done on purpose or by oversight?

    Second, what is the behaviour of the output voltage when the power is switched off with Q1 removed from the schematic? Is any harm to put Q1 back?

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