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  1. This is very good advice by the way ;D I blow around 10 or more fuses when tried to connect a good ampermeter in series with the load. When me and my friend tried the PSU it worked good except when we tried to test its current limit with a low resistence ampermeter we got one big problem - the main fuse at transformer's input was unusable anymore.We thought the PSU doesnt have working current limiter because the ampermeter showed current above 3A and then the fuse blew,but it seems that was the problem - the ampermeter in series with the load. I was going to ask about this "bug" but after some time i got the answer myself.The strange thing is that with some no-name chinese ampermeter it showed some results and the current protection/regulation was OK.But when tried to connect a better device the fuse blew.Which i guess means the first "noname" ampermeter has higher resistance and therefore the results were wrong. Anyway,the PSU is somehow working and did the job it was supposed to do ;D
  2. hi again. after some time i managed to build the supply with some little differences - i used 1W R1 and 741CN / LM1458 instead of OPA445 since i cant find those OPA's. It was quite fun ti run it for first time since i forgot to put R4 and there were no change at output :) But i noticed some "issues" - R1 is heating too much and i think if it will work for long time can eventualy overheat.All other elements seemed to be cool at first run. The negative suppy from D5,D6,D7 and so is producing around minus 5-6V and dont know if it should be that way.The voltage acros U1 U2 and U3 is around 42V,41V and 40V for each of them - not 44V as stated here before,which causes me to think there is a mistake somewhere around my circuit. I use ~28V transformer rated 3,5A for idle and get around 36V after C1.The supply can regulate voltage from 0,00 up to 35,6V i think. The strange thing is that after putting some heavy load at output (reostat) and at full load (theoreticaly) it produced 27.somethingV and 2,75A with one 2N2055 (no parallel).The transformer is rated for 3,5A at 26V and i think it should be capable of doing at least 3A at 26V but...The current voltage seemed strange for me...in idle mode when using P1 for voltage regulator it changes from 0 up to 35V,but with load it didnt changed,it did when using current regulator P2.But when turning current regulator to reach max voltage the current increases to max ratings too - which i believe could burn a little load. Those are the problems,or at least i think that there are some problems...
  3. thanks for the web link audioguru ! The strange thing in this situation is the fact that i was in the farnell's distributor in my country,but they said no such op-amp is available... Seems i need to ask them again with some more details.
  4. one quick question : if i cant find OPA445AP and cant use TL081 is there any other op-amp which i can use ? Very "funny" situation - the pcb board is done and all the other parts are here,only the op-amp cant be found to complete the PSU... thanks
  5. hi again. Thanks for fixing audioguru.I didnt get any atentioned about V-A or A-V connecting of the meters,i planed to do when eventually connect them in final PSU. Can i use this "circuit" instead of previous one ?
  6. there is the schematic of the circuit i am asking about. is it possible to do it like this ? sorry for the low quality image :)
  7. thanks for the fast reply audioguru. i'll try to find some new replacements for the TL081.I think i checked some of those posted here,but couldnt find them in local stores.Which means i have to search for another replacements. The transformer is "custom made" and should have max 3,5A at 26V with some aditional Amperage as a reserve.It has more VA than should be used and i hope it an take some "pressure". But i dont think i'll need 3A load at 30V,so even 20-24 should be fine :) About the 2sc5200 - it seems i have to connect two of them after all.I am planning to use some good heat sinks,but i cant afford to dissipate too much heat. I didnt get the part with the ampermeter...so i should connect a voltmeter in paralel with R7 and measure the voltage and them scale it into Amps ? It will be interesting to do it with digital one :) And about the digital regulating - i will check the previous posts about it,but i think i will have some questions about it too :)
  8. thanks MP. But still one question remains - can i use the ampermeter to measure the current of the power supply,which is powering the ampermeter ? sounds little confusing - but the case is : if i have a stable 5V 1A+ power supply can i power the ampermeter from it and use the ampermeter to measure the current fomr that 5V 1A+ line from the power supply ?
  9. Hi. i decided to try making this power supply.I almost got all of the parts as described in the scheme. But have several questions ( i read most of the posts in this topic,but the 44 pages can drive reader sometimes to confusion :P ). I got the standart TL081 and i hope this wont be a problem.The 2N2219 are replaced by TIP41A,as mentioned before.I'll try to find resistors with higher power (5W+) and the C1 is 10000,0/63V. The transformer is ~26V 3,5A and i hope it'll handle the (eventual) 3A/30V load. But the questions are : 1.Can i use for Q4 "high powered" transistor? Something like 15A 200V+ and around 150W ? I got one of that from a friend building 1kW+ power amplifier and i hope one of those transistors can handle the load itself.The transistor itself is 2sc5200 from "fairchald" or something like this (sorry,cant remember correct).I saw the post about linking two 2N2055 in parallel,but decided to use single "high powered" transistor. 2.I read in past reply that using a (digital) ampermeter connected to this power supply is not recommended because will cause malfunction of the scheme.Where should i connect the ampermeter ? And what about the voltmeter - will it cause problems too if connected to the output of the scheme ? I am planning to use the digital voltmeter/ampermeter listed in project's section of the site 3. and the most important question for me - does anyone have an idea how to controll the output voltage digitaly ? Not with the standart linear potentiometers,but digital ? I saw that Analog devices and Microchip have digital potentiometers,but either i cant find them in local stores (like the good looking AD5228),or they require some kind of "SPI" controllers,which are quite infamilliar to me. I am trying to build one good power supply with some extras - like the digital controlled output voltage.Unfortunately i cant find any good schematic about digital controlling of some values,neither i can find the AD5228 digital potentiometer. Any help will be welcome.
  10. thanks MP ! I saw this schematic : it is different than the 2 ones on projects section. But i have some other questions popuped since i saw the fixed circuit. pins 32 and 35 are connected to the analog(common) ground,but in the other two schematics they are not,can this be considered as a mistake (for eventual problems)? Also pin30,the "low" in is connected to the common ground too - another difference with the other two projects.This is the biggest "confusion" for the scheme - seems strange to connect the monitored voltage to the scheme. I will remake the scheme,i hope those changes can help to run the voltmeter :)
  11. Hi. i have several questions about the voltmeter. I built it,but it has some problems. 1.When the input is empty,i.e. no voltage is monitored the circuit has random segment flashing + random flashing of the minus sign.This occurs in (average) same periods like 10sec pause then flashes,10sec pause and again. Any idea what can the problem be ? Parts that form the "logical" unit for measuring should be OK,except the R1 which is 180k as written in project page.No C6 and C7 are added. The power voltages are not perfectly equal - like +5,03V and -5,04V with common ground.The power supply is not a synchronized dual supply,it has two separate different voltages -the negative and the possitive. 2.When no voltage is monitored what should be written on display ? 3.If this voltmeter is build as an ampermeter can it be used to monitor the current usage of the same curcuit ? The output voltage is stable 5V. ( if i find the attach function will attach an image ). 4.Can this project be done with common cathode instead of common anode ? Or i should use some kind of inverting system for the display ? I read the topic and found some usefull information about this project.Unfortunately the older links are not working and cant check the whole info aboit it. The circuit is built in a pcb with many wholes on it (dont know the english name for it )- not the specific pcb on the page. Using this project : http://www.electronics-lab.com/projects/test/014/index.html the 7107 is intersil's ICL7107CPL.The 7-segment displays are some kingbright's and the are different from the displays used in project's page,but schematics is done with modifications in display part to fit the 7seven segments. And the main question of all : 5. Can someone confirm that the project is working with the circuit posted on the page withoud having to change anything on it (i.e. C6&C7,power supply,etc). I am asking,because i could done the pcb wrong and have some problems because of that,but the problem (random display flashing) is confusing me - either i messed with the circuit or the 7107 is out of use... There is no problem to make the same PCB as shown on site (and this topic too),but i need to be some kinda sure,that this project will work as voltmeter.The curcuit i've made so far is for testing only,i hoped it can work properly and then make a "good" PCB for use,but i have problems. Thanks for reading my reply and i hope someone can help me about the problems i have.
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