# 2 in parallel

Discussion in 'Electronic Basics' started by Jif, Dec 22, 2003.

1. ### JifGuest

Hi

Any pro could help.
I have an adjustable volt and current Power supply (0-6V and 0-8Amp)

I need 10-12Amp so would it be ok to parallel it with a smaller
transformer such (110 to 6V and current of 5Amp).

I can't read the installed diode # but what should be a good one to
use with both transformers.

Do I need to change anything else

Thanks

jif

2. ### CWattersGuest

It's not that simple.

If you had two unregulated transformers and could connect them up out of
phase so they pump into the same capacitor. That would allow you to take
more current out of that capacitor before the ripple becomes too great for
any subsequent load/regulator . BUT you said one source is a regulated
voltage source....

Think about what would happen if you try to connect two ideal voltage
sources together and one was actually 6.1V and the other 5.9V. A current
would flow from the 6.1V supply to the 5.9V supply. That current would be
given by the equation.... I= (6.1-5.9)/R where R is the resistance of the
wire you used to connect them together. If R is small I is very large. For
this reason you should never connect ideal voltage sources in parallel (or
current sources in series) or something interesting will happen.

If you use two diodes to connect two ideal voltage sources together that
would stop the current flow described above but it would also stop your
circuit working as intended. This is because the output will be 6.1-0.7=5.4V
which means the diode in the 5.9V supply will have 0.5V accross it and won't
be conducting (at least not enough). The 6.1V supply will supply all the
current and the 5.9V will supply none (or next to none).