audioguru Posted May 13, 2012 Report Posted May 13, 2012 If three 2N3055 output transistors share the 5A of current then each has 1.7A and its minimum current gain is 40. Then the current in the BD139 is a max of 125mA. Its max voltage is 36.2V so its max power dissipation is 125mA x 36.2V= 4.5W.The max allowed chip temperature of a BD139 is 150 degrees C but 130 degrees is safer. Your ambient might be 30 degrees. The thermal resistance from chip to case is 10 degrees/W and for thermal grease is about 0.3 degrees/W. Then with a perfect heatsink the case will be at 30 degrees C and the chip will be (4.5W x 10.3) + 30= 76.4 degrees C.Your heatsink must have a thermal resistance of (100 degrees - 76.4 degrees)/4.5W= 5.2 degrees C/W or less. Quote
denci Posted May 13, 2012 Report Posted May 13, 2012 I usually use this way to calculate the heatsink, it is wrong that way:(130°C-30°C)/4.5W - (10C/W+0.3C/W) = 11,9°C/W Quote
denci Posted May 13, 2012 Report Posted May 13, 2012 http://www.changpuak.ch/electronics/calc_23.phpWith this online claculator i have got the same results ??? ??? Quote
madafakamw Posted May 14, 2012 Report Posted May 14, 2012 Hi everyone,I've made an online order for TLE2141 and i forgot to ask what package is build in. So i'm stuck with these.Will my psu work? Quote
audioguru Posted May 14, 2012 Report Posted May 14, 2012 I've made an online order for TLE2141 and i forgot to ask what package is build in. So i'm stuck with these.Will my psu work?When the output current is 3A check that opamp U2 is not too hot. Quote
madafakamw Posted May 14, 2012 Report Posted May 14, 2012 Thank you for your quick reply. I will keep in touch. Quote
denci Posted May 14, 2012 Report Posted May 14, 2012 What is wrong with my heatsink calculation in 5 post ago?? Quote
LEECH666 Posted May 15, 2012 Report Posted May 15, 2012 I usually use this way to calculate the heatsink, it is wrong that way:(130°C-30°C)/4.5W - (10C/W+0.3C/W) = 11,9°C/WWhat is wrong with my heatsink calculation in 5 post ago??Nothing wrong really.Audioguru either made a small typo and actually wanted to type(130°C - 76.4°C)/4.5W = 11.91K/Wor he substracted another 30°C of safety margin from the maximum junction temperature value of 130°C.(130°C - 30°C - 76.4°C)/4.5W = 5.24K/WFlorian Quote
LEECH666 Posted May 16, 2012 Report Posted May 16, 2012 In any case a smaller Kelvin per Watt value is always safer.A heat sink with 5.24 K/W is most likely more expensive than one with 11.9 K/W.Florian Quote
denci Posted May 20, 2012 Report Posted May 20, 2012 Where should i place the 1kohm pot3 for fine voltage regulation? Quote
xristost Posted May 20, 2012 Report Posted May 20, 2012 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. Quote
LEECH666 Posted May 20, 2012 Report Posted May 20, 2012 Very nice. Is this the latest REV2 version of the PSU or the original version? The shematic seems to be different, and you're only using one output power transistor. Quote
audioguru Posted May 21, 2012 Report Posted May 21, 2012 Very nice. Is this the latest REV2 version of the PSU or the original version? The shematic seems to be different, and you're only using one output power transistor.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. Quote
xristost Posted May 21, 2012 Report Posted May 21, 2012 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 :) Quote
LEECH666 Posted May 21, 2012 Report Posted May 21, 2012 I've got four TIP3055 (TO-218 / SOT 93) here, and two 2N3055 (TO-3). I've decided to use silent CPU coolers. I am uncertain if a single BD139 will be enough to drive four TIP3055s. I am only aiming for 30V / 3A output, so the additional TIP3055s would just be there to compensate for the lower power rating and to dissipate the heat more easily. I have two options now ... (see attached pics): Quote
LEECH666 Posted May 21, 2012 Report Posted May 21, 2012 More pictures.Not quite sure which variant I want to use.2N3055 on a L-profle mounted on the heat sinks or TIP3055 mounted flat on the heat sinks. Quote
audioguru Posted May 22, 2012 Report Posted May 22, 2012 R15 wastes supply voltage. 1k is too high but 100 ohms is fine.When output transistors are connected in parallel so they share the heat then each one needs a 0.33 ohm emitter resistor so that their base-emitter voltage differences do not cause the one with the lowest Vbe to hog all the current.The minimum current gain of one 2N3055 with a current of 3A is about 27. Then the max current in the BD139 is 3A/27= 111mA.Two 2N3055 transistors each have a max current of 1.5A then their minimum current gain is about 42. Then the max current in the BD139 is 3A/42= 71mA.You can calculate the current in the BD139 if there are 3 and 4 output transistors. Quote
denci Posted June 1, 2012 Report Posted June 1, 2012 As we know power dissipation of one of three 2N3055 output transistor is aprox. 65W and recommended thermal resistance for heatsink for one transistor is (200-35)/65 - (1.5 + 0.2) = 0,84 °C/W, but how can i calculate the required thermal resistance of heatsnik for three same transistor with the same power dissipation?Is ther any equation for this or is eought that i get the heatsnik with thermal resistance three times smaller than thermal resistance for one of each used transistor??...sorry for my english!!TNX Quote
donr Posted June 1, 2012 Report Posted June 1, 2012 Hope I am posting right here. What I would like is the revised schematic of this power supply and also info on where to purchase pcb. I have the revised parts list posted by audioguru. Thanks Quote
LEECH666 Posted June 2, 2012 Report Posted June 2, 2012 The latest circuit diagram can be found here: http://www.electronics-lab.com/forum/index.php?topic=19066.msg1002666#msg1002666According to this application note from Fischer Elekronik (heat sink manufacturerer)http://www.fischerelektronik.de/pim/upload/fischerData/datasheet/base/technischeerlaeuterungen_d.pdf (sorry it's in German, there used to be an english version of this but it's gone) you calculate it like this.Florian Quote
donr Posted June 5, 2012 Report Posted June 5, 2012 One more question. Is there a way I can get +/- outputs on this supply. I am going to build it anyway but would be even more handy for me if I had both. Thanks. Quote
audioguru Posted June 5, 2012 Report Posted June 5, 2012 One more question. Is there a way I can get +/- outputs on this supply. I am going to build it anyway but would be even more handy for me if I had both.Make two completely separate projects (with separate transformers or separate transformer windings).One can be a positive supply when its negative output is common and the other can be a negative supply when its positive output is common. Connect the commons together and to earth if you want.Then you will have positive 0V to +30VDC at up to 3A and have negative 0V to -30VDC at up to 3A. Quote
donr Posted June 5, 2012 Report Posted June 5, 2012 Thank you audioguru for the info and please don't think I question your answer because I know next to nothing about electronics. Here's the rub, I just put a small voltage bench supply together, two 14v outlets, one plus, one neg, using center tapped trans. I was curious as to whether this one could be modified so as to have more output v and amps than the first one and have +/-. I have the parts for this 30v supply on order and thought maybe with some changes I could do what I asked about. Probably to late for that now? Quote
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