Possible Solution for Dual Sproggy 12V @ 10A

mp3z24 · 07-08-2003, 03:33 PM

Alright, since im ultra-bored at work today, my mind was wandering about, and suddenly something struck me.

i was thinking about all the questions that people have posed for using multiple sproggy's bridged together in order to run 12V at higher than 5A (the max for the LM2587)

well. the whole arguement that i remember was that if you hooked up the 12V out lines from 2 sproggy's you wouldnt be able to individually use the flyback regulation and you wouldnt have your 12V @ 10A (if you were running 2 in parallel).

beyond that, the use of a diode on each 12V out was suggested. the flyback would read the V out before the diode, and you would have individual regulation, but your Vout would be only 11.3V (at best).

now, thinking through this situation one more time, i thought of this idea... why not use the diode on the 12V output, take the flyback signal from before the diode (as above), but this time, add and additional diode to the feedback line. that way, you still are tricking the 12V regulator to see that it is only outputing 11.3 V at the end of the circuit. Of course this would require some work on the sproggy board, and a bit of rewiring, but that is the to be expected when you want to run this type of modification.

let me know what you all think. Im not going to try this, as i have no use for it (at the moment) but i just wanted to throw out the idea to see what everyone thinks.

~Mike

mp3z24 · 07-09-2003, 05:31 PM

bump.... anyone have an opinion on this one way or another???

~mike

MikeHunt79 · 07-09-2003, 07:07 PM

Sounds like a good idea... I don't understand it fully I'm afraid, it's the flyback stuff that I can't do. Sounds like it might work tho?

I think the sproggy design only achives about 2A from the 12v line, so running two in parallel would give 4a. Still, that's enough for a decent setup. Maybe someone should start work on a sproggy 3 incororating this?

EDIT: This worked for me for a while. I had two sproggies running kinda in parallel... One for the motherboard, and the other for the drives. It worked fine, and no extra diodes were required. They just shared the +,- and remote inputs.

Dima · 07-10-2003, 11:11 AM

Sproggy's PSU can supply 1.3A at 12V. The 5A of LM2587 that you saw is max switching current,you can achieve it only with high voltage input (48V if I remember correct).
About using two 12V lines...the voltage dropout of 0.7V because of diode....you can use low forward voltage drop diodes,like 1N5400.

mp3z24 · 07-10-2003, 11:33 AM

Quote:

Originally posted by Dima
Sproggy's PSU can supply 1.3A at 12V. The 5A of LM2587 that you saw is max switching current,you can achieve it only with high voltage input (48V if I remember correct).
About using two 12V lines...the voltage dropout of 0.7V because of diode....you can use low forward voltage drop diodes,like 1N5400.

well... im a bit off on the amperage capability on the 12V rail. thanks for pointing that out.

about the 0.7V drop... i know that it is from the diode. that voltage drop is what i was trying to counteract by placing a diode on the feedback line. by introducing the same voltage drop in the feedback, you should be able to trick the regulator into thinking it is only putting out 11.3V. the regulator should then bump up the output to compensate for the 0.7V drop across the diode.

end result. 12V at combined amperage. add more regulator sections in parallel to increase the amperage.

~mike

eugenen · 07-10-2003, 01:33 PM

Should work. I seem to remember seeing this trick somewhere with linears, you would put a doing in the ground line to raise the output up.

See if any of the national chips can run in a master/slave setup, where one follows the other, then you could ut the feedback into the master and the other woudl follow.