matt09

Thanks guru, the derating graph shows a temperature of 100'C at 175W per transistor so providing they are cooled below this temerature they would work? You say about cooling them in liquid nitrogen but isnt the total dissipation to the heatsink the same except with the 3055's it's spread across more lower power transistors? I have a huge heatsink able dissipate 350W with a rise in temperature below 80'C Thanks

Would this be much better than thhe 3055's, I have loads lying around? http://www.datasheetcatalog.org/datasheet/mospec/2N5683.pdf -- 2N5686 They're massive things with a 50A collector current and 300w handling, could I sub them and get away with just 2 handling 175w each for a 10A output? I don't suppose the bd139 could drive two of those together if the 3055's weren't used and it would solve the problem? If not I've also looked around for a BD139 replacement and have a TIP transistor (I'd have to go out and buy the D44 one), would this be a suitable replacement? http://pdfdata.datasheetsite.com/web/70588/TIP41C.pdf -- TIP41A http://www.fairchildsemi.com/ds/BD%2FBD135.pdf -- BD139 If guru could check over this I would be eternally grateful, pretty much all the specs match or are better, ie 6A collector current. :) Would the emitter resistor R16 value need changing from 1k or need to be a higher power value also (or both) with the new transistor ? Regarding the current control I think I'll use two pots in series of different orders in resistance for course and fine control. I assume this still doesnt solve the problem of U2 not driving this new transistor hard enough? Sorry there's a hell of alot there! Thanks so much guys :)

Thanks redwire, I'd prefer to use the 3055's as I have a few already but can the problem not simply be solved by paralleling two 139's or using a more powerful substitute such as the D44H11? I'm guessing I could change the current limiting adjustment by playing around with the value of R18? I am using this as a powerful test bench supply. EDIT: Just seen the price of those darlington transistors they're like

Thanks for the reply guru, would the circuit still work if I replace R7 with a 0.1R power resistor for minimum power dissipation or will this mean further modifications are required? Regarding the BD139 burning, could I just parallel 2 of them with another 1k resistor? I wasn't so sure about the best way to resolve the lack of drive? I have a large transformer and 100000uf cap. Thanks alot.

Hi everyone, If I used the latest circuit with 5 power transistors can I achieve a 10A constant supply with a verry large heatsink and fan, it works out to about 65W per transistor? I have a 26.3VAC 10A+ transformer with massive 2.5" wide core. Would anything else need changing other than larger supply caps - guessing about 50000uf or more? Can I draw 10A at 1V up to 30V 10A theoretically with a massive heatsink? Thanks