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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.

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.

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.

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.

Yes, yes, whatever . . . You have only words, and I have working power supplies 8)

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

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.

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

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

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.

Maybe the regulators (LM317L and LM337L) for the opamps can be shared. And for the two channels you must double the C1 capacitor.

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.

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.

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 :)

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.

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

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 :)

I finalized my second power supply unit. Now I may combine two voltages up to 60V or use them as dual voltage PS. Pictures, details, schematic and PCB here.

I finished my version of this famous project :) Here how it looks like: http://diyfan.blogspot.com/2012/02/adjustable-lab-power-supply.html You may also download PDF files of the project on that page.

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.

I almost finished my PS. The two boards are completed, tested and they work wonderfully! I have ordered and I am expecting power transformers and digital panel meters (voltmeter and ammeter). Here some pictures of my work: http://diyfan.blogspot.com/

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.

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