Capricious Posted June 26, 2004 Report Share Posted June 26, 2004 See my reply in your other post for a discussion about heatsinks. Maybe you need to add an additional output transistor or two.Yet another question to you gurus ::)Have a look at the attached image ... is this circuit for the 2nd transistor correct?Which values should R23 and R24 have? Should I use one variable resistor?Thanks. Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 26, 2004 Report Share Posted June 26, 2004 Capricious,You can use the 12V secondary for a 12VDC fan if you use 4 rectifiers. Put a filter cap and a series resistor to the fan if it buzzes.Thermal grease is about 0.7 Kelvin/W. I don't know which insulator that you are using, it should be rated.For the project to operate with 12VAC, the negative supply must be changed. I calculated values that will work on 12VAC and 24VAC:1) R2= 39 ohms/2W2) R3= 100 ohms/1W3) C2 and C3= 100uF/50V4) D7= 5.6V/1W zener diode.Add a 10K-1/4W resistor in series (the high side) with the 10K voltage-adjust pot P1 for low output voltages and add it in series (the low side) with the pot for high output voltages. The voltage switch will need 2 poles to do this, plus another 1 or 2 poles to change the transformer secondary. Your 2nd 2N3055 and the emitter resistors are drawn correctly. Use 0.1 ohms, 1W for each. Quote Link to comment Share on other sites More sharing options...
kobus Posted June 29, 2004 Report Share Posted June 29, 2004 I have also posted this reply on the modification thread.would just like a reply if this could be a working model.otherwise i'm starting building tommorow and see what i end up with.so far it seems that it will work.---------------------------------------------------------------------------------after 2 hours of posts reading this is what i have for modsTransformer : 30VAC @ 5A = 30*5*1.5 = 225VA stepdown transformerResistors : R2 & R3 --> 1/2 W R7 --> 10 W R1 --> 3 WCaps : C1 --> 4700 uF (prefer 10000 uF) @ 50VDiodes : Diodebridge : D1 - 4 --> Single chip diode bridge @ 8-10 APOTS : P1 --> many turns (10) P2 --> Cermet single turnOPAMP : OPA445 @ 100V Transistors : Q1 --> stays same BC548/547 Q2 --> TIP29/TIP30 (R15 becomes 100ohm) --> somebody also mentioned BD139/137?? Q3 --> Stays same BC557/BC327 Q4 --> stays same?? 2N3055 Heatsinks : Q2 & Q4 gets TO-220 package heatsinkcould someone please verify??could this possibly be a workable mod or am i still missing somethingsorry if i left something out,had to decipher my own handwriting at 03:00. please correct mekobus. Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 29, 2004 Report Share Posted June 29, 2004 Kobus,Let's keep this thread for modifications to the original 3A power supply to make it reliably meet its specs.I am replying to your other post to modify it for 5A output. ::) Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 30, 2004 Report Share Posted June 30, 2004 Hi Guys,I just realised that there is an error in the schematic and PCB for this project:The emitter of Q1 should be connected to 0V, not to the negative output of the rectifiers as it is now. While the circuit is operating, Q1 should be turned-off, since it is used only to quickly reduce the circuit's output to 0V when you turn-off the circuit's power. The way it is now, Q1 can be turned-on by the voltage-drop across R7 when the project is supplying current to a load. This will reduce the output voltage and may overheat both Q1 and U2.Q1 should be changed to a TIP31A transistor, because the little BC547 specified cannot handle the current and power imposed on it.The TIP31A has a different pin-out and will need the PCB layout to be changed. It will not need a heatsink.If a transformer of 28 or 30VAC is used, then R14 should be changed to 1.2K, so that Q1 is not turned-on by the higher voltage during normal operation. ;D ;D Quote Link to comment Share on other sites More sharing options...
MP Posted June 30, 2004 Report Share Posted June 30, 2004 audioguru, are you building this supply or just using others on this forum to test your theories?MP Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 30, 2004 Report Share Posted June 30, 2004 MP,Kobus, not I, is building this project and has asked for advice to modify it for 5A output current. I gave him advice. ;DDidn't you see Capricious's recent serious problems with very high temperatures with this project, even when using less output current? :'(Ask Mixos how poorly his project worked. :'(Do you, or anyone else, want to discuss my theories and make this project work properly? ??? Quote Link to comment Share on other sites More sharing options...
MP Posted July 1, 2004 Report Share Posted July 1, 2004 audioguru,It is just that I see your theories fail you so much. Hands on is the best way to solve hardware problems. Nothing can replace bench work. Also, it is not so clear to some that you are not building anything, but only giving theoretical advice in all your posts. I just wanted to clear the air.MP Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 1, 2004 Report Share Posted July 1, 2004 audioguru,It is just that I see your theories fail you so much. Fail so much? No, only occasionally. I'm sorry that I am not absolutely perfect like you.Where are your discussions for this project?What's your big problem with my recommendations of project improvements for members? Quote Link to comment Share on other sites More sharing options...
Guest Kasamiko Posted July 1, 2004 Report Share Posted July 1, 2004 Ok after so much discussion and arguments. Can someone post the UPDATED and CORRECTED schematics for this project..One that is "NEAR" perfect.. 8)Rhonn ;) ;) Quote Link to comment Share on other sites More sharing options...
kobus Posted July 1, 2004 Report Share Posted July 1, 2004 Hello Kasamiko.I don't know about 0-30V 0-3A power supply but see under electronic forums-->project design/ideas-->modify 0-30V supplyor something like that.On the last page is pretty much a summary of what audiophile thinks should be modified for a 5A supply.No-one knows yet if it works so no guarantees.I'm currently building the supply in my spare time and hope to have it done some time end of next week. Hope this helps. Quote Link to comment Share on other sites More sharing options...
kobus Posted July 1, 2004 Report Share Posted July 1, 2004 sorry meant audioguru!! Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 2, 2004 Report Share Posted July 2, 2004 Kasamiko, and others,My replies in this forum and the Parts List that follows will allow this project to meet its own specs and to operate reliably.Parts List for 3A Variable Power Supply*T1 = 30VAC, 4.3A, 130VA stepdown power transformer*R1 = 2,2 KOhm 2W R2 = 82 Ohm 1/4W R3 = 220 Ohm 1/4W R4 = 4,7 KOhm 1/4W R5, R6, R13, R20, R21 = 10 KOhm 1/4W *R7 = 0,47 Ohm 10W R8, R11 = 27 KOhm 1/4W R9, R19 = 2,2 KOhm 1/4W R10 = 270 KOhm 1/4W R12, R18 = 56 KOhm 1/4W *R14 = 1,2 KOhm 1/4W *R15 = 100 Ohm 1/4W R16 = 1 KOhm 1/4W R17 = 33 Ohm 1/4W *R22 = 3,9 KOhm 1W RV1 = 100K trimmer P1, P2 = 10KOhm linear potentiometer *C1 = 10,000uF/50V electrolytic C2, C3 = 47uF/50V electrolytic C4 = 100nF polyester *C5 = 220nF polyester C6 = 100pF ceramic C7 = 10uF/50V electrolytic C8 = 330pF ceramic C9 = 100pF ceramic *D1, D2, D3, D4 = 6-10A/50V diode bridge module D5, D6 = 1N4148 D7, D8 = 5,6V Zener D9, D10 = 1N4148 D11 = 1N4001 diode 1A *Q1 = TIP31A, NPN transistor, no heatsink *Q2 = TIP31A NPN transistor Q3 = BC557, PNP transistor or BC327 *Q4 = Two paralleled 2N3055 NPN power transistors with 0.1 ohm, 1W emitter resistors each *U1, U2, U3 = OPA445AP, operational amplifier D12 = LED"*" is a change from the original design. Quote Link to comment Share on other sites More sharing options...
Kain Posted July 3, 2004 Report Share Posted July 3, 2004 I this is a little bit off topic but I want to do nice front pannel for the PSU and I wonder how I can project some writting on alumunium pannel... I was thinking of doing it in the same way as some of us do the PCB - tonner transfer. However, if I do so I don't know how strong the layer would be and if i won't loose it soon. Maybe I can apply some protective layer too ???? Any ideas? Quote Link to comment Share on other sites More sharing options...
MP Posted July 4, 2004 Report Share Posted July 4, 2004 There was some conversation about this topic here: http://www.electronics-lab.com/forum/index.php?board=15;action=display;threadid=951gsmaster has a method that he has attached a photo.MP Quote Link to comment Share on other sites More sharing options...
Kain Posted July 4, 2004 Report Share Posted July 4, 2004 Hum, so he pretty much did what was thinking to do. I think after I transfer it to the aluminium I will use some transparent self-adhesive film to protect the image. Thanks tho :) Quote Link to comment Share on other sites More sharing options...
Mash_Rishi Posted July 10, 2004 Report Share Posted July 10, 2004 Hi to all electronic Guys!!!! Am new to this project. Hi AudoGuru it seems you are an expert in power supply designs. I would like to clear my elementry level doubt with all experts down there. Can I use a 15-0-15 V 5A transformer as a bridge circuit avoiding the centre tap? Could u plz attach a complete modofied circuit of this voltage regulator? Quote Link to comment Share on other sites More sharing options...
ante Posted July 10, 2004 Report Share Posted July 10, 2004 Mash,A 15-0-15V transformer can be used the same way as a 30V transformer just don Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 10, 2004 Report Share Posted July 10, 2004 Hi Mash,Welcome to our forum.Yeah, your transformer is fine for this 3A-DC power supply.I am sorry that I can't revise the schematic, since I cannot manipulate GIF images. There isn't much difference, just an added 2N3055 and emitter resistors for each one, as shown earlier. Also, the emitter of Q1 should connect to ground, instead of the negative supply. Maybe someone will make these simple changes to the schematic for us.The PCB also needs simple changes for the different pin-out for Q1 and Q2, and moving Q1's emitter as above.The revised parts list has been given recently here. ;D Quote Link to comment Share on other sites More sharing options...
Mash_Rishi Posted July 11, 2004 Report Share Posted July 11, 2004 Thanks to Ante & Audioguru for your lightining fast replays.Am assembling the whole thing on a veroboard. Let u all guys know once am done. Quote Link to comment Share on other sites More sharing options...
Kain Posted July 20, 2004 Report Share Posted July 20, 2004 Ok, now I got really weird problem. As I posted earlier in this forum:http://www.electronics-lab.com/forum/index.php?board=2;action=display;threadid=128;start=120I'm trying to use digital panel meters for this PSU project. Everything seemed to be alright untill I tried to measure voltage from any power supply. What I mean is that these digital panels work fine when I measure potential from a battery, for example. However, once I hook it up to transformer based PSU it freaks out - it shows bogus numbers that fluctuate all over the scale. The weird thing is that even if I don't hook it up the voltmeter starts fluctuating a little bit. I powered up the panel as shown on the diagram by 9V battery. Any idea what could possibly cause this? ??? Quote Link to comment Share on other sites More sharing options...
ante Posted July 20, 2004 Report Share Posted July 20, 2004 Kain,Try a capacitor connected in parallel with the input to see if the value stabilizes. Use an electrolytic 10 Quote Link to comment Share on other sites More sharing options...
Kain Posted July 20, 2004 Report Share Posted July 20, 2004 Ante, I already tried this, and just to make sure I did it once again with no improvement. I tried cap in the iput before the voltage devider as well as after the devider - no change at all. I wonder how the unit would work if I hook it up in the other way - I mean powered by +-5V. I see it has a common ground with the inputs which might turn out to be the solution. What do you think about it? ??? Quote Link to comment Share on other sites More sharing options...
ante Posted July 20, 2004 Report Share Posted July 20, 2004 Kain,Yes, try it and let us know.Ante ::) Quote Link to comment Share on other sites More sharing options...
Kain Posted July 21, 2004 Report Share Posted July 21, 2004 Ok, I managed to fix it finally. The solution was as I suspected - common ground. I used the same transformer as for the PSU and made zener stabilized +-5V with mid point output, and I filtered the output potential with 1000mF/25V cap. Now it works absolutely stable - the measured value does't fluctuate even for one digit. ;D Quote Link to comment Share on other sites More sharing options...
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