5 Replies Latest reply on Jul 14, 2011 5:59 AM by Moriniman

    DIY OS PSU Build

    PianoKid1994

      Hello Everyone!
      I am going to build a DIY bench power supply.  I have decided to build a dual supply based on the schematic below.
      I have a couple of questions regarding this design. According to the description(translated), by selecting some resistor values, I can either build a 0-15V 4A supply, or a 0-30V 2A supply. Why is the 30V version limited to 2A? If it is not possible to build a 0-30V 4A design, which version would be more useful? I am beginning to learn electronics, but know that I will want to deal with motors, robotics, audio circuits, etc...
      To build a dual supply, will I also have to have two transformers? I will want to be able to connect them in series, and in parallel, so I know they have to be isolated from each other. What kind of transformer do I need? When searching for transformer on digikey, I do not know what I need enough to filter the results.
      On the bottom left, there is some form of temperature measurement using a 'SAA965' which is actually a KTY81-151. -  Datasheet: [url]http://www.datasheetcatalog.org/datasheet/philips/KTY81-151.pdf[/url]
      What do I use this to measure the temperature of? The heat sink of the transistor? How do I attach it to what ever I am measuring? Also in the area of the temperature measurement, there is a 5V supply. Where is the 5V supply coming from, the 7805 at the top? And what are the the two lines coming out to the left, labeled 'ST6' & 'ST7' going to?
      I will want to have panel meters displaying voltage and current output. I think I want to incorporate possibly a uC into the project, for some 'fanciness' I have in mind, once I have the foundation, so maybe just a LCD is all I need. For the Panel meter, and micro ideas, can I use the 5V supply, that is also the 5V supply for the LM324, or will I need another small transformer, to power these items?
      Some people suggested in another thread, that I use a ten turn pot on my supply. I also agree that that is a good idea. In the LM317 datasheet, there is an example(below) about digitally selected outputs. Would this also work on this supply? I think I want a button for 5 and 3.3 volts, and the micro will select the correct resistance. What are the downsides of this?
      Some people have mentioned a 'load switch.' Is that just a normal toggle switch(that can handle the current), to just quickly disconnect the output? Would a beefy switch, or a small switch with a relay be better?
      What are the funny looking pots in the top right of the schematic? Why do they have a flat end, instead of an arrow-does this represent something significant?
      One last question: What are the transistors with two lines coming out of them? What do the two lines represent?
      My goal is to have a nice dual supply, that I can use for years as I continue to learn about electronics. I will greatly appreciate any advice, answers to questions, or just ideas I haven't thought about. Also, some of the above information is not 'set in stone'. I.E. if it is better to use a different design for the supply, than I am willing to use that one instead.
      Thanks in advance,
      Joshua

      Hello Everyone!

       

      I am going to build a DIY bench power supply.  I have decided to build a dual supply based on the schematic below.

       

      http://i1210.photobucket.com/albums/cc411/pianokid1994/ELVSchematic.png

      Here is the full pdf...http://www.elv-downloads.de/Assets/Produkte/2/225/22532/Downloads/22532_Universelle_Netzteilplatine_um.pdf

       

      I have a couple of questions regarding this design. According to the description(translated), by selecting some resistor values, I can either build a 0-15V 4A supply, or a 0-30V 2A supply. Why is the 30V version limited to 2A? If it is not possible to build a 0-30V 4A design, which version would be more useful? I am beginning to learn electronics, but know that I will want to deal with motors, robotics, audio circuits, etc...

       

      To build a dual supply, will I also have to have two transformers? I will want to be able to connect them in series, and in parallel, so I know they have to be isolated from each other. What kind of transformer do I need? When searching for transformer on digikey, I do not know what I need enough to filter the results.

       

      On the bottom left, there is some form of temperature measurement using a 'SAA965' which is actually a KTY81-151. -  Datasheet: [url]http://www.datasheetcatalog.org/datasheet/philips/KTY81-151.pdf[/url]

      What do I use this to measure the temperature of? The heat sink of the transistor? How do I attach it to what ever I am measuring? Also in the area of the temperature measurement, there is a 5V supply. Where is the 5V supply coming from, the 7805 at the top? And what are the the two lines coming out to the left, labeled 'ST6' & 'ST7' going to?

       

      I will want to have panel meters displaying voltage and current output. I think I want to incorporate possibly a uC into the project, for some 'fanciness' I have in mind, once I have the foundation, so maybe just a LCD is all I need. For the Panel meter, and micro ideas, can I use the 5V supply, that is also the 5V supply for the LM324, or will I need another small transformer, to power these items?

       

      Some people suggested in another thread, that I use a ten turn pot on my supply. I also agree that that is a good idea. In the LM317 datasheet, there is an example(below) about digitally selected outputs. Would this also work on this supply? I think I want a button for 5 and 3.3 volts, and the micro will select the correct resistance. What are the downsides of this?

       

      http://i1210.photobucket.com/albums/cc411/pianokid1994/DigitallyselectableouptutsLM317.png

       

      Some people have mentioned a 'load switch.' Is that just a normal toggle switch(that can handle the current), to just quickly disconnect the output? Would a beefy switch, or a small switch with a relay be better?

       

      What are the funny looking pots in the top right of the schematic? Why do they have a flat end, instead of an arrow-does this represent something significant?

       

      One last question: What are the transistors with two lines coming out of them? What do the two lines represent?

       

      My goal is to have a nice dual supply, that I can use for years as I continue to learn about electronics. I will greatly appreciate any advice, answers to questions, or just ideas I haven't thought about. Also, some of the above information is not 'set in stone'. I.E. if it is better to use a different design for the supply, than I am willing to use that one instead.

       

       

      Thanks in advance,

      Joshua

        • Re: DIY OS PSU Build
          zmrbill

          Joshua,

           

          There is a lot to learn from building a power supply and I comend your efforts.  I don't know if I would pick this circuit though.  You ask about the 15V/4A 30V/2A difference.  Do the thermal calculations and I think you will have your answer.  Also look at the junction to case thermal resistance of the TIP142.  That is really going to limit you and that is why there are two in parallel.  If you use some thing in a TO-3 you can get down to 0.6 C/W.  For a linear power supply like this you should start with the power disapation of the pass element and how will remove the heat generated by it.  The symbol for the xstrs is for a darlington.  To have a split supply you only need one xfrm with a center tap.

           

          Get yourself a copy of Art of Electronics!  Chapter 5 "Voltage Regulators and Power Circuits" is just what you need.

           

          Bill

          • Re: DIY OS PSU Build
            dmaruska

            Joshua,  I will answer some questions.

             

            1.  I have a couple of questions regarding this design. According to the description(translated), by selecting some resistor values, I can either build a 0-15V 4A supply, or a 0-30V 2A supply. Why is the 30V version limited to 2A? If it is not possible to build a 0-30V 4A design, which version would be more useful? I am beginning to learn electronics, but know that I will want to deal with motors, robotics, audio circuits, etc...

             

            This limitation is most likely due to the transformer.  When you work ohms law, you have an inverse in the Voltage to Current,  You hve halved the voltage, so your current will go up.  If I'm correct, you could change the transformer,  to a higher current rating, you will have to look at the circuit design to make sure there are no problem with 30v at 4a.  Since you are increasing the power that will be passing through the components Heat sinks will be needed, another ohms law thing.

             

            2.  One last question: What are the transistors with two lines coming out of them? What do the two lines represent?  The lines will go to a digital device,  You will set the bias resistors to what voltages you require on the output,  You will select only one at a time.  This takes the place of the trimmer resistor that you would use in the leg above the transistor.

             

            3.  Some people have mentioned a 'load switch.' Is that just a normal toggle switch(that can handle the current), to just quickly disconnect the output? Would a beefy switch, or a small switch with a relay be better?

            The switch needs to be able to handle the current and voltage.  Since you are working with a fairly low voltage, the current is the item in question.  Remember everytime you open and close a switch, the contacts will arc slightly, The metal that the contact are made from will handle arcing better then others.  You will most likely not be running the PS under full load and opening and closing the switch so you will be probly OK with one that will handle the rated load for a long period of time.  Either way, Relay or switch you should not have any problems.  Single switch is one less part to buy or fail...

             

            4. What are the funny looking pots in the top right of the schematic? Why do they have a flat end, instead of an arrow-does this represent something significant?

            Trimmer Resistor and Varible Resistor.  Trimmer resistors are the small set and forget types and Variable are ones you will use on a front panel.  They could be 15 turn or single turn.   But when buying Variable resistors, be aware of the two types, Linear and Audio Taper, Audio Taper operate in a log curve, since you do not hear in a linear method.

             

            5.  You could use a micro to control and send information back to the control PC, and you can run off the internal PS, but keep in mind that you will reduce the current of that supply by the circuit amount.  If you OK with that, insure your current measurement is taken after the internal circuit, this will keep you from getting a measurement that is high, and your not sure why.

             

            Hope this helps some...

             

            Regards,

             

            Dave M.

              • Re: DIY OS PSU Build
                der_fisherman

                I personally would not build that supply as it appears to be a linear type and will probably give off a large amount of energy as heat.

                I always buy Switched Mode power supplies, or better said I build them using a schematic from Elektor in 2003 I believe, far less components (as all the complicated stuff is done in two identical chips), only one adjustment that only needs a good meter, probably it will actually cost less in component6s, gives out upto 10 amps at 85% efficiency.....can be set between 40 and 5 volts output.

                For 5 amps or less, only one chip is needed.(and a few other components).

                Look here for the LT1074 data sheet:-

                http://www.datasheetcatalog.org/datasheet/lineartechnology/1074fd.pdf

                Only 7 other components needed for a fixed output power supply. I use mine for CNC work (the 10 amp version) and as it was designed for HiFi by Elektor, it can handle anything I throw at it.....

                If you need more details, just ask.

                Regards

                Andy

                  • Re: DIY OS PSU Build
                    Moriniman

                    There's a lot to be said for using a linear design for a bench supply. It should give you a very clean supply.

                     

                    With a switched mode supply you need to be VERY sure that the switching frequency and its harmonics are absent from the output. I had a 12bit Burr Brown serial ADC that would go logarithmic on it's four LSBs when powered from a DC/DC converter. A compatible, Linear Technology ADC worked just fine, but didn't have the input offset feature desired. A change to a higher voltage output DC/DC followed by a linear regulator solved the problem.