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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?

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

Hi all!I am back from my vacations!One more question: Can i put 3 or 4 paralleled 2n3055 transistors just to be on the safe side?

Both transistors are from toshiba.Oh well...I will buy new ones. ::)

I measured the voltage drop across the emitters 0.1ohm resistanse(2A output).I measured 0.012V and 0.188V , which means from one transistor passes 1.88A and from the other 120mA !Is it strange such a difference?

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?

So... Fan it is then! ;D

Audioguru what size do you suggest for the heatsink?

Another question if someone puts maximum V and A and shortcircuits the output what will happen?

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 )

I forgot to mention that if i set volt and current pots so as the current limiter is not on, after a while amps jump at 5A and the led turns on. :-\ :-\ :-\

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?

Ok, i will use my sound card as an oscilloscope.In a couple of days i will hit the shop to buy some resistors to construct a voltage divider first(I think my soundblaster will burn if i give it 30V input :P ).

;D Of course i will test the psu and make a post.I have a dmm [a scope is a bit expensive for me :( (can i use my sound card as an osciloscope?)].I think it is accurate(0.5% accuracy in Vdc , 2% measuring Amperes). What measurements should i execute?

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

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

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.

The voltage of pin 4 of U2 is -5.58V without load and with load, with current limiting on it is -4.35V.should i measure the voltage at the transistors?

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%

I measured the volt pot and it is ok.the other pot varies from 0v to 1.6v . When i connect a 30 ohm load the out put voltage drops (without current limitation) and varies from 0.5 to 0.8v . ??? ??? ??? :-\Current limiting also seems erratic.

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?

Anyone please? ??? :-\ ???

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!).

Thanks for your reply and i am glad that i am a member here! ;D ;D ;D Indeed i was amazed with TI and FEDEX. If i use any 5.6V 1/2W zener will it be ok?Also i contacted a local electronics shop and they have tip31c insted of tip31a. Is it ok?

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.