Quick question, how do I supply +-5V?

Frank (Francis.invalid@hotmail.com) wrote:

...

: I don't know what you people are talking about.
: Back to my question, how do I make a +-5V?

'Buy one' is the most sensible suggestion I've seen elsewhere on the
thread.  

*BEWARE*
Another one I've seen mentioned is to get 2 stock 5V supplies, A and B, 
and connect the +5V of A to the 0V of B, and call pair this 0V, thus
making the 0V of A -5V and the 5V of B +5V.
*BEWARE*

This may or may not work - many lab power supplies and some bricks
conenct the 0V from the DC side to the mains earth, so doing this
with two such supplies will cause funny noises, bad smells and possibly
worse as the magic smoke escapes.

If you're not sure, don't try ths aproach!

---

cds

On Mon, 05 Dec 2005 22:22:54 +0000, c d saunter wrote:

> This may or may not work - many lab power supplies and some bricks
> conenct the 0V from the DC side to the mains earth, so doing this
> with two such supplies will cause funny noises, bad smells and possibly
> worse as the magic smoke escapes.
> 
> If you're not sure, don't try ths aproach!

The bricks I've used have always isolation, but I live a
relatively sheltered life. Where have you seen them, mainly?

-- 
Regards,
  Bob Monsen

"You told me, 'God made the World.'" "No, no!" Harshaw said hastily.
"I told you that, while all these many religions said many things,
most of them said, 'God made the World.' I told you that I did not
grok the fullness, but that 'God' was the word that was used." "Yes,
Jubal," Mike agreed. "Word is 'God'" He added. "You grok." "No, I must
admit I don't grok." "You grok," Smith repeated firmly. "I am explain.
I did not have the word. You grok. Anne groks. I grok. The grass under
my feet groks in happy beauty. But I needed the word. The word is
God." Jubal shook his head to clear it. "Go ahead." Mike pointed
triumphantly at Jubal. "Thou art God!" Jubal slapped a hand to his
face. "Oh, Jesus H. What have I done? Look, Mike, take it easy! Simmer
down! You didn't understand me. I'm sorry. I'm very sorry! Just forget
what I've been saying and we'll start over again on another day. But "
"Thou art God," Mike repeated serenely. "That which groks. Anne is
God. I am God. The happy grass are God, Jill groks in beauty always.
Jill is God. All shaping and making and creating together ." He
croaked something in Martian and smiled.

Bob Monsen (rcsurname@comcast.net) wrote:
: On Mon, 05 Dec 2005 22:22:54 +0000, c d saunter wrote:

: The bricks I've used have always isolation, but I live a
: relatively sheltered life. Where have you seen them, mainly?

Some of the transformer based ones I have at work are - mind you I'm
in the UK where almost everything has an earth (mechanical interlocks
stop you plugging anything in without the third pin...) - I'm guessing
this isn't an issue in places like the USA as the various American bricks
I've accumulated don't have an earth pin...

Cheers
Chris

c d saunter wrote:
> Bob Monsen (rcsurname@comcast.net) wrote:
> : On Mon, 05 Dec 2005 22:22:54 +0000, c d saunter wrote:
> 
> : The bricks I've used have always isolation, but I live a
> : relatively sheltered life. Where have you seen them, mainly?
> 
> Some of the transformer based ones I have at work are - mind you I'm
> in the UK where almost everything has an earth (mechanical interlocks
> stop you plugging anything in without the third pin...) - I'm guessing
> this isn't an issue in places like the USA as the various American bricks
> I've accumulated don't have an earth pin...

I know that you Brits have a very positive outlook, but there surely 
must be a way to supply a negative voltage?

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

"Jerry Avins" <jya@ieee.org> wrote in message
news:Db6dnTyYHMr6TgnenZ2dnUVZ_smdnZ2d@rcn.net...
>c d saunter wrote:
>> Bob Monsen (rcsurname@comcast.net) wrote:
>> : On Mon, 05 Dec 2005 22:22:54 +0000, c d saunter wrote:
>>
>> : The bricks I've used have always isolation, but I live a
>> : relatively sheltered life. Where have you seen them, mainly?
>>
>> Some of the transformer based ones I have at work are - mind you I'm
>> in the UK where almost everything has an earth (mechanical interlocks
>> stop you plugging anything in without the third pin...) - I'm guessing
>> this isn't an issue in places like the USA as the various American bricks
>> I've accumulated don't have an earth pin...
>
> I know that you Brits have a very positive outlook, but there surely must
> be a way to supply a negative voltage?
>
> Jerry
>
So, wall warts almost never have an earth, even in the UK! Our wall warts
usually have a plastic 'earth' pin to overcome the interlock. Most power
supplies that are a separate 'brick' connect with a two wire connection to
the mains, live and neutral, as in the US. Here's a photo of a UK mains lead
for this:-
http://www.maplin.co.uk/images/Full/1168i0.jpg

In the UK, such things are called 'double insulated', see :-
http://en.wikipedia.org/wiki/Double-insulated

That said, some bricks do have an earth connection as Chris says. These
often use a IEC connector like this:-
http://en.wikipedia.org/wiki/Power_connector
Dunno if the output 0V is connected to this earth. I suspect not in most
cases.

All the bench DC power supplies I've used, both in the UK and in the US,
have separate isolated 0V and earth, usually connectable with a bit of
metal.

FWIW, Syms.

My first reply would be "buy one". Cost of a PSU is a lot less than the
cost of an average board...

Otherwise, and assuming your load is less than ~40mA, you can use the
circuit in http://sound.westhost.com/project43.htm with a 10v supply.
Be careful to separate GND's (since the GND of your +/- 5V is really at
5V....)

Simon

"c d saunter" <christopher.saunter@durham.ac.uk> wrote in message
news:dn2ho4$qhn$1@heffalump.dur.ac.uk...
> Bob Monsen (rcsurname@comcast.net) wrote:
> : On Mon, 05 Dec 2005 22:22:54 +0000, c d saunter wrote:
>
> : The bricks I've used have always isolation, but I live a
> : relatively sheltered life. Where have you seen them, mainly?
>
> Some of the transformer based ones I have at work are - mind you I'm
> in the UK where almost everything has an earth (mechanical interlocks
> stop you plugging anything in without the third pin...) - I'm guessing
> this isn't an issue in places like the USA as the various American bricks
> I've accumulated don't have an earth pin...

I have quite a lot of experience with power supply modules (the "open frame
type") and I dear say that for instance NONE of the types offered in the
Farnell catalog have their - or 0 connected to the PE. From a manufacturer's
point of view this would be absolutely stupid because it means that he would
have to have two types of each model, one with the + to PE and another with
the - to PE. Also in lab supplies you will always see an extra ground
terminal, often between the + and - and possibly with a supplied bracket
between the ground and -.

Besides, many applications need a complete separation from mains, even from
ground. So that is another reason for manufacturers not to connect the - to
PE(ground).

Meindert

"c d saunter" <christopher.saunter@durham.ac.uk> wrote in message 
news:dn2eju$p0p$1@heffalump.dur.ac.uk...
> Frank (Francis.invalid@hotmail.com) wrote:
>
> ...
>
> : I don't know what you people are talking about.
> : Back to my question, how do I make a +-5V?
>
> 'Buy one' is the most sensible suggestion I've seen elsewhere on the
> thread.
>
> *BEWARE*
> Another one I've seen mentioned is to get 2 stock 5V supplies, A and B,
> and connect the +5V of A to the 0V of B, and call pair this 0V, thus
> making the 0V of A -5V and the 5V of B +5V.
> *BEWARE*
>
> This may or may not work - many lab power supplies and some bricks
> conenct the 0V from the DC side to the mains earth, so doing this
> with two such supplies will cause funny noises, bad smells and possibly
> worse as the magic smoke escapes.
>
> If you're not sure, don't try ths aproach!
>
> ---
>
> cds

You are quite right. We had to pull our power supplies apart and disconnect 
the mains earth connection or they would get very hot. They have been in 
service for 5 years now and are still running OK.

Peter 

On Tue, 6 Dec 2005 08:06:58 +0100, "Meindert Sprang"
<mhsprang@NOcustomSPAMware.nl> wrote:

>I have quite a lot of experience with power supply modules (the "open frame
>type") and I dear say that for instance NONE of the types offered in the
>Farnell catalog have their - or 0 connected to the PE. From a manufacturer's
>point of view this would be absolutely stupid because it means that he would
>have to have two types of each model, one with the + to PE and another with
>the - to PE. Also in lab supplies you will always see an extra ground
>terminal, often between the + and - and possibly with a supplied bracket
>between the ground and -.
>
>Besides, many applications need a complete separation from mains, even from
>ground. So that is another reason for manufacturers not to connect the - to
>PE(ground).

For any low level measurements, the PE is badly polluted by the noise
from switching mode power supply EMC filters etc. For this reason, a
separate technical earth (TE) network is often used with only a single
contact point between the neutral, grounding electrode and PE and TE
earths. 

A single power supply with the DC side connected to PE would pollute
the whole TE network and you would very quickly get rid of such power
supplies.

Paul