Positive and negative voltage regulators

[Horace]

Hello ...

I have a few questions regarding the V regulators :

(1) how come some +ve regulators does not have a complementary -ve
regulator?
reason for asking : I am using 2 transformers to power an audio amp and I am
using one to supply +ve and the other one -ve. I was trying to see if I can
use the LM317/338 to regulate the +ve side and its counterpart (if any?!?!)
to regulate the -ve side.

.... which leads to my second question ...

(2) can I, in general, configure a positive voltage regulator and use it
for -ve? (I am thinking that since voltage is relative, it doesn't matter
whether I am regulating a Vin = 9V to Vout = 5V OR from Vin = -4V to Vout
= -8V ... etc).

Thanks!

 

[Olaf]

(1) [...] I am using 2 transformers to power an audio amp and I am using
one to supply +ve and the other one -ve. I was trying to see if I can
use the LM317/338 to regulate the +ve side and its counterpart (if
any?!?!) to regulate the -ve side.

that's a LM337

(2) can I, in general, configure a positive voltage regulator and use it
for -ve?

I was wondering about that also...

bye, Olaf

 

[Horace]

Thanks ...

However ... the LM337 has a much lower current rating than the LM338
(something like 1.5A vs 5.0A) .... it would be nice if I can use a negative
regulator with higher current ...

Horace

(1) [...] I am using 2 transformers to power an audio amp and I am using
one to supply +ve and the other one -ve. I was trying to see if I can
use the LM317/338 to regulate the +ve side and its counterpart (if
any?!?!) to regulate the -ve side.

that's a LM337

(2) can I, in general, configure a positive voltage regulator and use it
for -ve?

I was wondering about that also...

bye, Olaf

 

[Olaf]

However ... the LM337 has a much lower current rating than the LM338
(something like 1.5A vs 5.0A) .... it would be nice if I can use a
negative regulator with higher current ...

is a LM337 in combination with a bypass transistor an idea?

bye, Olaf

 

[Horace]

Yes ... I saw that kind of configuration suggested for the LM7805/7812, etc
.... but I didn't see in the LM 338 app notes any mention of that
configuration. However, I think it's possible =O

My coworker suggested using two of those chips in parallel ... that should
work too ...

Horace

 

[Olaf]

Yes ... I saw that kind of configuration suggested for the LM7805/7812, etc
... but I didn't see in the LM 338 app notes any mention of that
configuration. However, I think it's possible =O

My coworker suggested using two of those chips in parallel ... that should
work too ...

the LM317 datasheet gives an example for a currentboost using a bypass
transistor, so the variable voltage shouldn't be a problem in itself.
Maybe the 338 sheet doesn't mention this because the chip can already
deliver 5 amps, and if you need more it's cheaper to bypass a 317? Just a
guess.

about the parallel chips: if you parallel these, do you know for sure they
split the load equally? I'm not sure whether this can be a problem, but
better check ;-)

bye, Olaf

 

[Jamie]

i remember some where seeing a Positive regulator being connected
to the + side and the output being run to ground and thus the -
out of the supply was the high side of that transformer.
its been a while and i am only do this from memory but seems that have
seen a LM7805 being used as a - reg but from a separate transformer
supply.