aqmas Posted March 21, 2007 Report Share Posted March 21, 2007 o where is new pcb? I cant find :-[ Quote Link to comment Share on other sites More sharing options...
aqmas Posted March 21, 2007 Report Share Posted March 21, 2007 hmmmm, little bit strange, I discussed in www.elektronika.lt forum. And people who made this power supply said that nothing gets hot.... everything okey Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 21, 2007 Report Share Posted March 21, 2007 This original project does not get hot in Italy?1) The transformer is rated for 24VAC/3A which is only 72VA.The peak voltage is 34V and if the project delivers 3ADC then the transformer supplies 102VA and is 142% overloaded. Sure it gets hot.2) The 2N3055 transistor can dissipate about 70W if it has a huge heatsink and does not have an insulator.If the output current is set to 3A and the output voltage is set to a low voltage or is shorted then the 2N3055 transistor dissipates 96W. It is 137% overloaded. Sure it gets hot.3) The 2N3055 transistor has a minimum current gain of 25 when it conducts 3A. Therefore its base current is a max of 120mA.If the output current is set to 3A and the output voltage is set to a low voltage or is shorted then the little 2N2219 transistor dissipates 3.72W. Its max allowed dissipation is only 2.5W when it has a "perfect" heatsink. Its clip-on heatsink is far from being perfect then the transistor has its max allowed internal temperature when it dissipates only 1.8W. It is 207% overloaded. Sure it gets hot.4) People here reported that the rectifier diodes char (blacken) the pcb. They must be pretty hot.The improved circuit can use the original pcb:1) Mount the rectifier bridge module on the metal chassis.2) Mount Q2 on the chassis or on the heatsink.3) Strap the main filter capacitor beside the pcb.4) Stand up some of the larger resistors. Quote Link to comment Share on other sites More sharing options...
aqmas Posted March 21, 2007 Report Share Posted March 21, 2007 I'm from Lithuania :)We mostly use not new details. transformer mostly been from old radios or tv.O about tranzistors........ i dont know. some people said that everything is okey Quote Link to comment Share on other sites More sharing options...
ante Posted March 21, 2007 Report Share Posted March 21, 2007 hmmmm, little bit strange, I discussed in www.elektronika.lt forum. And people who made this power supply said that nothing gets hot.... everything okey How Quote Link to comment Share on other sites More sharing options...
aqmas Posted March 21, 2007 Report Share Posted March 21, 2007 I jus told a fact Quote Link to comment Share on other sites More sharing options...
ante Posted March 21, 2007 Report Share Posted March 21, 2007 If it Quote Link to comment Share on other sites More sharing options...
aqmas Posted March 21, 2007 Report Share Posted March 21, 2007 because in this forum with this project are problems, o in www.elektronika.lt no problems Quote Link to comment Share on other sites More sharing options...
ante Posted March 21, 2007 Report Share Posted March 21, 2007 Again: do you know how to read a datasheet? Do you know how to use a calculator? I can Quote Link to comment Share on other sites More sharing options...
subodhthok Posted March 24, 2007 Report Share Posted March 24, 2007 Can somebody give me the principle and working of the circuit mentioning the function of each and every component. I'm a POOR SOUL.I'll be INDEBTED! Quote Link to comment Share on other sites More sharing options...
Fluffy Posted March 24, 2007 Report Share Posted March 24, 2007 Please show a new / up-to-date parts list!! Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 24, 2007 Report Share Posted March 24, 2007 Subodhthok,It is a simple circuit with opamps and transistors. When you learn about opamps and transistors then you will understand the function of each and every component.The Articles section of this website has tutorials on opamps and transistors.Fluffy,My recommended parts list for this project has been attached many times and has not changed for more than one year. Here it is again:0-30V_Mod_parts_list.txt Quote Link to comment Share on other sites More sharing options...
valorous Posted March 25, 2007 Report Share Posted March 25, 2007 Hi again.I've build the modified circuit. Everything seems to work. The voltage goes up to 34.5V and the current to 3.8A. The op-amps U1 and U2 get very hot with no load, especially U1. I measured the voltage at pin7=46V. Also I used two 2n3055 transistors with 0.33R emitter resistors but one of the transistors gets hotter than the other one. What can I do to fix the problem?Also when I turn the current potentiometer half way the current increases to 0.5A. So when P2 is half turned the current is not half its maximum value. I'm not sure if this is a problem. Thank you for the help. Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 25, 2007 Report Share Posted March 25, 2007 Hi again.I've build the modified circuit. Everything seems to work. The voltage goes up to 34.5V and the current to 3.8A.Good, it works.Trimpots can be added in series with the voltage and current setting pots to reduce their max outputs to 30.0V and 3.0A. Then the trimpots can be measured and fixed resistors can be installed.The op-amps U1 and U2 get very hot with no load, especially U1.The max operating current of the OPA445AP opamp is only 4.7mA x 46V=216mw. Its load is (46V - 11.2V) x 5.6mA= 195mW. The total power dissipation is a max of 411mW and its max is 1000mW. It will be pretty warm but it is fine. I measured the voltage at pin7=46V.It is a little high but it is fine.A 30VAC/4.3A transformer will be about 31.5VAC without a load. Then its peak voltage is 44.5V and the rectifier bridge drops it to 43V.Also I used two 2n3055 transistors with 0.33R emitter resistors but one of the transistors gets hotter than the other one. What can I do to fix the problem?The transistors are all different. That is why the emitter resistors are used to equalize their current gains. Yours must be very different. Use a 0.22 ohms emitter resistor for the coolest one then it will heat more. 8) Also when I turn the current potentiometer half way the current increases to 0.5A. So when P2 is half turned the current is not half its maximum value. I'm not sure if this is a problem.I think the action of the current-setting pot is supposed to be linear, so half rotation is 1.5A, but maybe not. Try replacing the pot. Quote Link to comment Share on other sites More sharing options...
valorous Posted March 25, 2007 Report Share Posted March 25, 2007 Thanks audioguru for your quick response. I will try the tips you suggested. Quote Link to comment Share on other sites More sharing options...
Steve_hi Posted March 27, 2007 Report Share Posted March 27, 2007 Hi I think I would like to try to make this 0-30Vdc power supply does anyone have a rough idea about how much it might cost Quote Link to comment Share on other sites More sharing options...
Steve_hi Posted March 28, 2007 Report Share Posted March 28, 2007 I've been reading this thread and I see that there has been a significant amount of problems with this project heating up, with the schematic that is posted in the projects. I also see that audioguru has provided an updated parts list can some tell me why the person who maintains the projects doesnt update the parts list with the scematic :D Just curious as to how things work ??? also If i use the new parts list is the schematic still the sameThank you Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 28, 2007 Report Share Posted March 28, 2007 Hi Steve,The project is a kit. It overheats and does not have 30V/3A output. I don't know what the kit maker does about complaints to them about the kit.We leave the original project in case somebody has built it and for us to talk about it. If somebody builds the improved version and updates the schematic then it might be made into a new project.The improved circuit has the same pcb as the original except a few parts values are changed. A few parts are bigger but can be stood up, and Q2 needs to be mounted away from the pcb on a heatsink or its pins will need to be twisted around. A second 2N3055 output transistor was added to share the heat and emitter resistors are used for the output transistors to equalize their different current gains. Quote Link to comment Share on other sites More sharing options...
akhtar-ece Posted March 28, 2007 Report Share Posted March 28, 2007 how can i modify this circuit to 0 to 50 v dc supply and also for 0 to 30 v 10A Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 28, 2007 Report Share Posted March 28, 2007 how can i modify this circuit to 0 to 50 v dc supplyRe-calculate and replace every part in it.and also for 0 to 30 v 10A If it is set to 10A and the output voltage is set low or it is shorted then the output transistors must dissipate 420W. Use 6 output transistors on huge heatsinks with fans, use 3 driver transistors, add a pre-driver transistor and make many resistors larger.A larger transformer, larger main filter capacitor and larger rectifier bridge will be needed.It will cost a small fortune. Quote Link to comment Share on other sites More sharing options...
eggy Posted March 28, 2007 Report Share Posted March 28, 2007 Hi.I have just built the PSU but surprise-surprise it does not work. Output voltage of the PSU is constantly 33V. Voltage between pin4 and pin6 of u1 is chancing from 0 to 9.9V when turning voltage pot. I am using UA741 opamps. [+-22V]Voltage over pins 4 and 7 is 38V on U3 and U2. On U1 it's 33V.Chanced RV1 to 10k, short circuited R10[Like in the 741's datasheet]What purpose has D10? Doesn't it just feeds all the output voltage directly to the base of Q2? R15 is heating....voltage on it is ~33V. When I remove all opamps the output voltage stays up. When I remove Q1 or both(!) of it's base resistors then output voltage drops to zero. -Eggy Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 28, 2007 Report Share Posted March 28, 2007 Hi Eggy,Welcome to our forum. ;DQ1 is not supposed to make the output voltage high. It is supposed to make the output voltage zero when the project is turned off. Q1 does not have a positive supply.Maybe the base of Q1 or one of its base resistors is shorted to the positive supply. Then Q1 will turn on Q2 and Q4 through its forward-biased base-collector diode.D10 is normally reverse-biased. It quickly discharges the output capacitor C7 when the project is turned off to avoid exceeding the max reverse voltage rating (about 6V) of the emitter-base of Q2. Quote Link to comment Share on other sites More sharing options...
eggy Posted March 28, 2007 Report Share Posted March 28, 2007 I know that Q1 is for bringing output voltage lo. Base of Q1 is not short circuited to positive supply, only through r13 which is not connected at the moment. Let's assume that I remove Q1 temporarely, I loose thats protective idea in the circuit, BUT i should be able to chance output voltage, right? What voltage should be on pin6 of U2? Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 28, 2007 Report Share Posted March 28, 2007 Hi Eggy,If you remove Q1 then the circuit should work properly. Q1 quickly reduces the output voltage to zero when the project is tirned off, so that the output voltage doesn't rise.Pin 6 of U2 should be about 1.4V higher than the output voltage without a load.U2 and the output transistors have a voltage gain of 3.07 and amplify the voltage from pot P1. Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 28, 2007 Report Share Posted March 28, 2007 You said pin 6 of U1 changes from 0V to 9.9V when turning the voltage pot. That is wrong.Pin 6 of U1 should remain at 11.2V and the slider of the pot should change from 0V to 11.2V. Quote Link to comment Share on other sites More sharing options...
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