Guest tempray Posted November 19, 2014 Report Share Posted November 19, 2014 Hello to everybody, I have encoughtered some instability problems with this schematics :I build them two, current limit works, @ 30V 2.5A load works also (100mV drop:()Then i have come up here and reed lots of audioguru posts. I decided to do some modifications:1) Added emitter 0.22ohm resistors to each toshiba, 1 unit has now two 2SC5200 output npn-s---!!--- With emitter resistors, i got little more V drop then without emitter resistors---!!---2) Replaced R7 to 0.22ohm 5W(its just for testing, later i will add 10W or more).3) I added tantalums near LM regulators, cuz they are ~10CM away from filter capacitors.4) Finally i rised output voltage on LM317 from 32.64 to 33.73V, Total voltage across the TL082 is now 38V(under current sinking its 36.8V)5) The only big differents from the posted schematics is that i have 1.3W BZV85C3v3 zener and 1.3W BZX85C6V2-TAP zener. The schematics states that both zeners must be 0.5W BZV55 type-s :(6) Transformer has exactly 30VAC 150VA when there is no load. After the rectification and filtering, there is 40,50 VDC at no load.After the four first modification i was able to suck 3.4A @ 30V with still 100mV drop :(REAL problems: A) As in schematics, i measure with multimeter 8.5V after the zener diodes... but it must be 9.5V :( And only If i apply some 3A load at 30V, then i get 9.5V at diodes as in the schematics... but thats wrong right ?B) Why i cant see -3V on the LM337 output ? I see there -1.8V.. but how than i see across TLo82 pin 4 and 8 38V when there is no current sinking(load ath the output) ? :(C)I have 14mF filter bank, and adding more 2200uF panasonic and nichicon capacitors does really help resolving that (100mV drop)I tried with 22mF and so far i got the best results: 80mV drop at 30V 3.4A output.That means if i can get there to about 100mF filter capacity, it will be around ~40mV drop... lol @3A @ 30V :D Expensive and pointless.D) According to other ppl modifications i tought i was able to sink 5A but no, i get 2V drop @ 5A of current from 30V to 28V :(Is there someone who can help me with these problems and explain why :S And the most important part of reference voltage... why do i have to buy the Exactly the same Diodes used in Schematics ? I tought bigger diode is easier to install and more releable? :(Thank you very much for reading this thread.I have attached 22mF filterbank that archieved best results but is absurdly big and not ergonomic... i use this to power AB class amplifiers.Dear ppl, my goal is to archive 5A at low ripple 30V, make it symmetrical power supply after and use current limiter for safety reasons.With regards,Rene Quote Link to comment Share on other sites More sharing options...
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