Can you put two lm7805's in parallel
to gain grator current. or will one
interfear with the other

generally not... there will always be tiny variances in the output voltage
and one will tend to pull current from the other.. these currents can be
considereable if there is no resistance between the outputs... ohms law will
tell you that even 20mV divided by 0ohms is infinite current... not actually
infinite but they will get hot and it will be a very inefficient way of
getting a greater current source. What you could do is to use one of the
5Amp versions (can't remember the number off the top of my head, LM309K or
sunnik like that?) which comes in a power transistor can (TO5?) or if that
is not enough, use a 78L05 with a 1N4001 in series with it's ground
connection, as the base voltage for an emitter follower regulator formed
from power transistors... the current capacity in this form of PSU design is
virtually limitless with the right tranny. The diode in series with ground
will actually make the output voltage about 5.6V which will counter the
voltage drop of the power transistor. Bags of designs for this sort of high
current PSU design exist from the days of neat bipolar TTL, before the
benefits of CMOS took over with 74L & 74C devices etc.

have fun.


"Gunner" wrote in message
4.17...
Can you put two lm7805's in parallel
to gain grator current. or will one
interfear with the other

The datasheet for the 78XX series regulators gives application hints for
raising the output current capacity:
http://www.national.com/ds/LM/LM78XX.pdf (page13).
There's an LM323 (3A) if you want to keep it simple. They produce an LM338
(adjustable) rated at 5A. The LM309 is rated at 1A.
Bryan

"UncleWobbly" wrote in message
.. .
generally not... there will always be tiny variances in the output voltage
and one will tend to pull current from the other.. these currents can be
considereable if there is no resistance between the outputs... ohms law
will
tell you that even 20mV divided by 0ohms is infinite current... not
actually
infinite but they will get hot and it will be a very inefficient way of
getting a greater current source. What you could do is to use one of the
5Amp versions (can't remember the number off the top of my head, LM309K or
sunnik like that?) which comes in a power transistor can (TO5?) or if that
is not enough, use a 78L05 with a 1N4001 in series with it's ground
connection, as the base voltage for an emitter follower regulator formed
from power transistors... the current capacity in this form of PSU design
is
virtually limitless with the right tranny. The diode in series with ground
will actually make the output voltage about 5.6V which will counter the
voltage drop of the power transistor. Bags of designs for this sort of
high
current PSU design exist from the days of neat bipolar TTL, before the
benefits of CMOS took over with 74L & 74C devices etc.

have fun.


"Gunner" wrote in message
4.17...
Can you put two lm7805's in parallel
to gain grator current. or will one
interfear with the other