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HELP: Hooking up two voltage regulators on a board
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Barry & Nikki
electronics forum beginner


Joined: 19 May 2005
Posts: 34

PostPosted: Mon Jul 17, 2006 2:27 am    Post subject: HELP: Hooking up two voltage regulators on a board Reply with quote

Hopefully this does not turn into a fiasco:
Anyhow I have a Pyle mobile 6" color LCD monitor (I believe it is a PLVSHR6-
NO labeling on it though). I removed two TA7805S regulators quite some time
ago. Now that I am ready to put them back in after finding replacements I
can not for the life of me remember in what combination they are mounted on
the board.
They are mounted parallel to one another on the board. There are six
holes in the board. for illustration:
1 2 3
4 5 6

hole 1 & 4 are connected with copper traces as are 2 to 5 and 3 to 6.
Obviously no matter how the regulators are mounted 2 will always be
connected to 5 (grounds). So what I am asking is it 99% (or if you can tell
me 100%) that 1 & 4 are both ins on each of the regulators making 3 & 6 outs
OR should outs be hooked to ins? Holes 1 &4 lead to the positive side of a
470uf cap, 2 & 5 lead to +side of a 4001 diode, and 3 & 6 lead to the +side
of a 100uf cap.
Basically I guess I am asking should these be hooked like to like or
opposite one another? I am sure I will be bombarded with "This is not enough
information"; but I have to try something being nobody seems to be able to
come up with a schematic diagram for ANY Pyle products. Thanks in advance
for ANY positive help anyone can offer.
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Arfa Daily
electronics forum Guru


Joined: 06 May 2005
Posts: 588

PostPosted: Mon Jul 17, 2006 8:40 am    Post subject: Re: Hooking up two voltage regulators on a board Reply with quote

"Barry & Nikki" <bearmore@ANTISPAMwhidbey.com> wrote in message
news:0YadnUV7-7inaCfZnZ2dnUVZ_t2dnZ2d@whidbeytel.com...
Quote:
Hopefully this does not turn into a fiasco:
Anyhow I have a Pyle mobile 6" color LCD monitor (I believe it is a
PLVSHR6-
NO labeling on it though). I removed two TA7805S regulators quite some
time
ago. Now that I am ready to put them back in after finding replacements I
can not for the life of me remember in what combination they are mounted
on
the board.
They are mounted parallel to one another on the board. There are six
holes in the board. for illustration:
1 2 3
4 5 6

hole 1 & 4 are connected with copper traces as are 2 to 5 and 3 to 6.
Obviously no matter how the regulators are mounted 2 will always be
connected to 5 (grounds). So what I am asking is it 99% (or if you can
tell
me 100%) that 1 & 4 are both ins on each of the regulators making 3 & 6
outs
OR should outs be hooked to ins? Holes 1 &4 lead to the positive side of a
470uf cap, 2 & 5 lead to +side of a 4001 diode, and 3 & 6 lead to the
+side
of a 100uf cap.
Basically I guess I am asking should these be hooked like to like or
opposite one another? I am sure I will be bombarded with "This is not
enough
information"; but I have to try something being nobody seems to be able to
come up with a schematic diagram for ANY Pyle products. Thanks in advance
for ANY positive help anyone can offer.


You can be 99.9% sure that they are connected in plain simple old parallel.

It's not generally considered very good practice to up the current rating by
doing this, as you can't guarantee that both will have exactly the same
output voltage, and will thus share the load exactly equally without
fighting one another. However, it would not be the first time I have seen it
done. I recently had a home cinema system in for repair, which I think was a
JVC if memory serves. This, to my amazement, used exactly the scheme you are
describing. One of the paralleled-up regulators was faulty. I replaced them
both with a pair from the same batch, in an effort to get them as closely
matched as possible, but still one ran hotter than the other, and I think
that this is probably an inevitable consequence of doing this, and may be
the reason for the early demise of one or other device. I notice you say
that there is a 1N4001 in the ground legs - presumably when you say "
positive side " you are referring to the anode, so it is the cathode that
actually goes to ground ? This is a way of jacking up the ground leg(s) by
approximately 0.6v which has the effect of upping the output volts to 5.6,
without compromising the regulation.

There is no valid reason that I can think of to connect two regulators back
to back. You would always be hooking input volts to an output on one of
them, and vice versa. Perhaps you are confusing yourself with having seen a
5v reg following on from a 12v. In this scheme, the OUT of the 12v is
connected to the IN of the 5v, and both ground pins are connected together.
However, in this case, the IN of the 12v is not connected to the OUT of the
5v.

Just as an afterthought, is there absolutely no marking on the board at all
to indicate which way round they go ? It can sometimes be quite subtle -
just a slight thickening of one line on a box to indicate a tab-side, for
instance.

Arfa
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Franc Zabkar
electronics forum Guru


Joined: 01 May 2005
Posts: 616

PostPosted: Mon Jul 17, 2006 8:51 am    Post subject: Re: HELP: Hooking up two voltage regulators on a board Reply with quote

On Sun, 16 Jul 2006 19:27:50 -0700, "Barry & Nikki"
<bearmore@ANTISPAMwhidbey.com> put finger to keyboard and composed:

Quote:
Hopefully this does not turn into a fiasco:
Anyhow I have a Pyle mobile 6" color LCD monitor (I believe it is a PLVSHR6-
NO labeling on it though). I removed two TA7805S regulators quite some time
ago. Now that I am ready to put them back in after finding replacements I
can not for the life of me remember in what combination they are mounted on
the board.
They are mounted parallel to one another on the board. There are six
holes in the board. for illustration:
1 2 3
4 5 6

hole 1 & 4 are connected with copper traces as are 2 to 5 and 3 to 6.
Obviously no matter how the regulators are mounted 2 will always be
connected to 5 (grounds). So what I am asking is it 99% (or if you can tell
me 100%) that 1 & 4 are both ins on each of the regulators making 3 & 6 outs
OR should outs be hooked to ins? Holes 1 &4 lead to the positive side of a
470uf cap, 2 & 5 lead to +side of a 4001 diode, and 3 & 6 lead to the +side
of a 100uf cap.
Basically I guess I am asking should these be hooked like to like or
opposite one another? I am sure I will be bombarded with "This is not enough
information"; but I have to try something being nobody seems to be able to
come up with a schematic diagram for ANY Pyle products. Thanks in advance
for ANY positive help anyone can offer.

Leave them out and switch the unit on. The pin with power is the
input. Having said that, I can't understand how two 7805 regulators
can work in parallel. At the very least, I would think that one would
carry the brunt of the load.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
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Adrian
electronics forum beginner


Joined: 14 Mar 2006
Posts: 15

PostPosted: Mon Jul 17, 2006 10:36 am    Post subject: Re: HELP: Hooking up two voltage regulators on a board Reply with quote

HI Frank

On Mon, 17 Jul 2006 18:51:21 +1000, Franc Zabkar
<fzabkar@iinternode.on.net> wrote:

Quote:
On Sun, 16 Jul 2006 19:27:50 -0700, "Barry & Nikki"
bearmore@ANTISPAMwhidbey.com> put finger to keyboard and composed:

Hopefully this does not turn into a fiasco:
Anyhow I have a Pyle mobile 6" color LCD monitor (I believe it is a PLVSHR6-
NO labeling on it though). I removed two TA7805S regulators quite some time
ago. Now that I am ready to put them back in after finding replacements I
can not for the life of me remember in what combination they are mounted on
the board.
They are mounted parallel to one another on the board. There are six
holes in the board. for illustration:
1 2 3
4 5 6

hole 1 & 4 are connected with copper traces as are 2 to 5 and 3 to 6.
Obviously no matter how the regulators are mounted 2 will always be
connected to 5 (grounds). So what I am asking is it 99% (or if you can tell
me 100%) that 1 & 4 are both ins on each of the regulators making 3 & 6 outs
OR should outs be hooked to ins? Holes 1 &4 lead to the positive side of a
470uf cap, 2 & 5 lead to +side of a 4001 diode, and 3 & 6 lead to the +side
of a 100uf cap.
Basically I guess I am asking should these be hooked like to like or
opposite one another? I am sure I will be bombarded with "This is not enough
information"; but I have to try something being nobody seems to be able to
come up with a schematic diagram for ANY Pyle products. Thanks in advance
for ANY positive help anyone can offer.

Leave them out and switch the unit on. The pin with power is the
input. Having said that, I can't understand how two 7805 regulators
can work in parallel. At the very least, I would think that one would
carry the brunt of the load.

- Franc Zabkar

I'd have thought the same as you - but a couple of years ago I built
an Elextor circuit for our local Church (sort of a CD Jukebox for when
the human organist can't make it) - and that used a pair of 5v 1A
regulators and a pair of 12v 1A regulators - each pair of regulators
connected in parallel.

I'd never seen it done before - but it's still working fine !

Regards
Adrian
Suffolk UK
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