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ta03

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Posts posted by ta03

  1. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    I tried with a 2.7ohm 200W dummy load.I set 3A output.All transistors were quite cool.I am afraid to short the output.Another discovery: From one transistor passed 1.3A,from the other 1,1A and from the third(with 0.2ohm emmiter resistor) 0.6A.My mistake is that i measured the third transistor's  resistor and found the voltage drop almost the same with the other 2,forgeting that it was not 0.1 ohm. :-\ :-\ :-\ .
    How much current can pass from one transistor without damage?

  2. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    Yes,i had a wonderfull vacation thank you!I envy you audioguru.I am still a student and i have 50 years in order to become retired.
    I finally used 3 of them with  0.1ohm emmiter resistor at 2 of them and 0.2ohm at the third one  in order to match them.What i did is ok?With a fan blowing them they dont become hot at all.Another discovery: I have 4A max output :o

  6. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    I changed the 2n3055's.Now everything is fine :I checked the voltages you mentioned and they are ok,I put the 2 transistors in the same heatsink(I forgot to buy another one  :-\ ,tomorrow i will) using thermal grease and a 12V pc case fan..Everything seems fine and i am currently testing the psu with 2A output on 2.7ohm load.One thing i noticed is that one transistor get much hotter than the other one(so as the heatsink below the hotter,meaning that it does not heat because it doesn't come to good contact with the heatsink,I believe).Can someone (audiogugu  ;D ) explain it?

  10. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    Well...end of fun for today.Q4 damaged!I used a quite large heatsink for Q4(with mika insulators) but it became really hot during tests(i could barelly touch the heatsink which was 15x10cm).Q2 was all the time cool, it did not heat up(4x2cm heatsink). I didn't use thermal grease.I will do volt measurements tomorrow when i get some new 2n3055(i will buy a stock of them  ;D )

  12. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    I found a 2.7Ohm 25W resistor.I connect it at the power supply,I put the volt pot at max and played with the current regulator.In the beginning everything is ok but after a while something happens and output jumps at about 5A,if i set high amps it jumps after a second or so(with lower amps eg.1.5A it takes about 10 seconds) and if i close the amp pot(or volt pot) it remains at 5A.If i disconnect the load and reconnect it (even fast,i disconnect it for half a second)amps drop to normal again and after a while they jump at 5A.R7 gets REALLY hot and so as Q4.Any ideas?

  15. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    Audioguru you are trully a guru!Thank you!Q2 was wrongly soldered i changed emmiter-collector and the psu works great now!Everything works!Output voltage is ok so as the current limiter!!!Q2 was indeed destroyed but fortunately i had a spare tip31c.U2 was also a bit hot before but i could touch it while hot so i did not mention it(i thought it was normal).Audioguru thanks a lot  for your help and your time!!!I will post images when i will put it in a case.Thanks again!!!  :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D

  16. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    I replaced the 2n3055.Now the its varies fron18.1 to 31 volts but now it is proportional to the volt pot.By turning the volt pot from max output to minimum,the voltage drops until halfway of the pots turning ability,and after halfway it remains steady at 18V.Now to your questions:
    1)Yes
    2)It varies from 0V to 10.7volts if i turn the volt pot from one end to the other.
    3)Emmiter of q2 is 31.8V, base 18.6,collector 18.4 with output voltage at minimum
    4)31,2V at max output ,14.4 at minimum
    5)5.85 at minimum and 9.88 at maximum

  17. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    Audioguru thanks a lot but before i do anything i just discovered that the 2 2n3055
    are probably burned and they need replacement(strange they didn't smell bad...LOL).The collector of 2n3055 is its case right?I will check what you have told me right after.Thanks again for your patience.

  19. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    with 30ohm load and pot set to 30v the output voltage is 0.81V(without  load it is 31V)  .With the volt pot set at min output voltage(with load) is 0.5V(without  load it is 19V) .By turning a bit the volt pot it jumps instantly at 0.81v and stays there independently from the pot(without load jumps from 19 to 31v the same way) .Pin 6 of u2 is at 31V  and i use a 24V 5A transformer. With the output voltage adjusted to 30V with a 30 ohm load,  it doesn't drop to 15V when the current pot is set to about 17%

  21. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    I constructed the psu but there is a problem.when i alter
    the output voltage it varies from 19v to 31v and its jumps rappidly
    from 19 to 31 not proportionally.Also the current regulator does not
    function,the led turns on only when the amps pot is on its end.Any opinions?
    which components should i check?

  23. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    I will try to find one of BZX79C5V6, BZX55C5V6 or 1N5994.Lets hope that i will find one of them!Sorry for my ignorance about zeners, i do not know much about them(I study physics, not electronics  :-\ :-\ :-\ ). When someone says the eg. 5V zener spec'd at 10mA means that with a current of 10mA or more the voltage drop across the diode is 5v ?  ???
    About tip31 the same told me the sales-person-something-whatsoever...I just wanted comfirmation(i dont want to blow anything especially the opa445ap's!).

  25. 0-30 Vdc Stabilized Power Supply

    in Projects Q/A

    Posted

    Hi all!I am planning to build this psu with the modified parts list.I managed to get 3
    opa445ap as samples from TI (they came fron the us to greece in only 2 days at my door! wow!).I will use the original pcb.Is it correct?Also in the modified partslist C5 is 220nf and in the original 200.Why c5 is changed?D7 and D8 low current diodes are common parts?If i dont find them can i use the original diodes??I am using a 24V 5A transformer.

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