| Author |
Message |
Frank
Guest
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 Posted:
Fri Dec 02, 2005 7:44 am Post subject:
Quick question, how do I supply +-5V? |
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I have a large board which asks for three power supplies, +3V, +3.3V and
+-5V.
First two can be easily satisfied with two HP power supplies (each has its
own
GND pin also). Regarding +-5V, can I replace with an HP power supply set to
10V, -5V pin connect to HP's ground and +5V to power? |
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Michael R. Kesti
Guest
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| Posted:
Fri Dec 02, 2005 7:54 am Post subject:
Re: Quick question, how do I supply +-5V? |
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|
Frank wrote:
| Quote: | I have a large board which asks for three power supplies, +3V, +3.3V and
+-5V.
|
If I read you correctly, that's four supplies: +3V, +3.3V, +5V, and -5V.
| Quote: | First two can be easily satisfied with two HP power supplies (each has its own
GND pin also). Regarding +-5V, can I replace with an HP power supply set to
10V, -5V pin connect to HP's ground and +5V to power?
|
No. Doing so would provide zero volts to the board's -5V rail and +10V to
its +5 rail.
You need four supplies.
--
========================================================================
Michael Kesti | "And like, one and one don't make
| two, one and one make one."
mrkesti at comcast dot net | - The Who, Bargain |
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Ryan Weihl
Guest
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| Posted:
Fri Dec 02, 2005 8:33 am Post subject:
Re: Quick question, how do I supply +-5V? |
|
|
Michael R. Kesti wrote:
| Quote: | Frank wrote:
I have a large board which asks for three power supplies, +3V, +3.3V and
+-5V.
If I read you correctly, that's four supplies: +3V, +3.3V, +5V, and -5V.
First two can be easily satisfied with two HP power supplies (each has its own
GND pin also). Regarding +-5V, can I replace with an HP power supply set to
10V, -5V pin connect to HP's ground and +5V to power?
No. Doing so would provide zero volts to the board's -5V rail and +10V to
its +5 rail.
You need four supplies.
will an ATX supply not do? |
rw |
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Jerry Avins
Guest
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| Posted:
Fri Dec 02, 2005 8:58 am Post subject:
Re: Quick question, how do I supply +-5V? |
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|
Ryan Weihl wrote:
| Quote: | Michael R. Kesti wrote:
Frank wrote:
I have a large board which asks for three power supplies, +3V, +3.3V and
+-5V.
If I read you correctly, that's four supplies: +3V, +3.3V, +5V, and -5V.
First two can be easily satisfied with two HP power supplies (each
has its own
GND pin also). Regarding +-5V, can I replace with an HP power supply
set to
10V, -5V pin connect to HP's ground and +5V to power?
No. Doing so would provide zero volts to the board's -5V rail and
+10V to
its +5 rail.
You need four supplies.
will an ATX supply not do?
rw
|
Maybe not. Compound switchers need a load on the main supply in order to
come up, and the auxiliary supplies aren't always well regulated.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Len
Guest
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Len
Guest
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Fred Marshall
Guest
|
| Posted:
Fri Dec 02, 2005 9:15 am Post subject:
Re: Quick question, how do I supply +-5V? |
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|
"Frank" <Francis.invalid@hotmail.com> wrote in message
news:438fa5a4@news.starhub.net.sg...
| Quote: | I have a large board which asks for three power supplies, +3V, +3.3V and
+-5V.
First two can be easily satisfied with two HP power supplies (each has its
own
GND pin also). Regarding +-5V, can I replace with an HP power supply set
to
10V, -5V pin connect to HP's ground and +5V to power?
|
You might with some caveats.
First, the intended +-5v supply needs to be floating with respect to the
other supplies.
Then the 10v voltage difference can be reference wherever you want in theory
and often in practice.
The challenge is: now that you've floated the supply, how will you reference
it to the ground or 0v point on the board?
Think of the +-5v supply as a 10v battery. A battery "floats" with no
problem.
Unless you do more, the result looks like this:
+------------------------------>+5v
|
|
+----+ +--------------->+3.3v
| 10v| +----+
+----+ |3.3v| +----------+3v
| +-+--++----+
| | |3.3v|
| | +-+--+
| | |
| | |
| +-----+---------> 0v: the reference for +3.3v, +3v
|
|
|
+------------------------------>-5v
With the 10v battery floating, there is no reference to the
other batteries. Current flowing through the circuit board will cause
the +/-5v terminals to go almost anywhere relative to 0v. Depending on
what's on the board,
the +5v terminal could end up at -6v and the =5v terminal at -15v (both
relative to 0v of course).
+------+----------------------->+5v
| |
| | +--------------->+3.3v
+----+ | +----+
| 10v| | |3.3v| +----------+3v
+----+ ++-+ +-+--++----+
| |R1| | |3.3v|
| ++-+ | +-+--+
| | | |
| | | |
| +-------+-----+---------> 0v: the reference for +3.3v, +3v
| +--+
| |R1|
| ++-+
| |
+------+----------------------->-5v
A resistor divider with current much higher than the +/-5v
loads and connected to the 0v reference will refer the +/-5v
to the rest of the batteries.
It's not a very elegant or even practical solution but it makes the
point to address your question.
Fred |
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Frank
Guest
|
| Posted:
Fri Dec 02, 2005 9:15 am Post subject:
Re: Quick question, how do I supply +-5V? |
|
|
"Jerry Avins" <jya@ieee.org> wrote in message
news:gpKdnbflleKAIhLeRVn-vg@rcn.net...
| Quote: | Steve Underwood wrote:
Jerry Avins wrote:
Ryan Weihl wrote:
Michael R. Kesti wrote:
Frank wrote:
I have a large board which asks for three power supplies, +3V,
+3.3V and
+-5V.
If I read you correctly, that's four supplies: +3V, +3.3V, +5V, and
-5V.
First two can be easily satisfied with two HP power supplies (each
has its own
GND pin also). Regarding +-5V, can I replace with an HP power
supply set to
10V, -5V pin connect to HP's ground and +5V to power?
No. Doing so would provide zero volts to the board's -5V rail and
+10V to
its +5 rail.
You need four supplies.
will an ATX supply not do?
rw
Maybe not. Compound switchers need a load on the main supply in order
to come up, and the auxiliary supplies aren't always well regulated.
Jerry
They also make more noise than a neo-natal nursery. :-)
If he knows what he's doing, ha can load the 10V supply with a beefy
op-amp connected as a follower to a divider across the rails and ground
its output. If something goes wrong, it can blow the board unless he
uses Zener-cum-fuse protection. There are DC-DC power-supply bricks and
chips that can probably supply all the -5 needed from a +5 supply.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
|
I don't know what you people are talking about.
Back to my question, how do I make a +-5V? |
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Jerry Avins
Guest
|
| Posted:
Fri Dec 02, 2005 9:15 am Post subject:
Re: Quick question, how do I supply +-5V? |
|
|
Steve Underwood wrote:
| Quote: | Jerry Avins wrote:
Ryan Weihl wrote:
Michael R. Kesti wrote:
Frank wrote:
I have a large board which asks for three power supplies, +3V,
+3.3V and
+-5V.
If I read you correctly, that's four supplies: +3V, +3.3V, +5V, and
-5V.
First two can be easily satisfied with two HP power supplies (each
has its own
GND pin also). Regarding +-5V, can I replace with an HP power
supply set to
10V, -5V pin connect to HP's ground and +5V to power?
No. Doing so would provide zero volts to the board's -5V rail and
+10V to
its +5 rail.
You need four supplies.
will an ATX supply not do?
rw
Maybe not. Compound switchers need a load on the main supply in order
to come up, and the auxiliary supplies aren't always well regulated.
Jerry
They also make more noise than a neo-natal nursery. :-)
|
If he knows what he's doing, ha can load the 10V supply with a beefy
op-amp connected as a follower to a divider across the rails and ground
its output. If something goes wrong, it can blow the board unless he
uses Zener-cum-fuse protection. There are DC-DC power-supply bricks and
chips that can probably supply all the -5 needed from a +5 supply.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Steve Underwood
Guest
|
| Posted:
Fri Dec 02, 2005 9:15 am Post subject:
Re: Quick question, how do I supply +-5V? |
|
|
Jerry Avins wrote:
| Quote: | Ryan Weihl wrote:
Michael R. Kesti wrote:
Frank wrote:
I have a large board which asks for three power supplies, +3V,
+3.3V and
+-5V.
If I read you correctly, that's four supplies: +3V, +3.3V, +5V, and
-5V.
First two can be easily satisfied with two HP power supplies (each
has its own
GND pin also). Regarding +-5V, can I replace with an HP power
supply set to
10V, -5V pin connect to HP's ground and +5V to power?
No. Doing so would provide zero volts to the board's -5V rail and
+10V to
its +5 rail.
You need four supplies.
will an ATX supply not do?
rw
Maybe not. Compound switchers need a load on the main supply in order
to come up, and the auxiliary supplies aren't always well regulated.
Jerry
|
They also make more noise than a neo-natal nursery. :-)
Regards,
Steve |
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Jerry Avins
Guest
|
| Posted:
Fri Dec 02, 2005 5:15 pm Post subject:
Re: Quick question, how do I supply +-5V? |
|
|
Frank wrote:
...
| Quote: | I don't know what you people are talking about.
Back to my question, how do I make a +-5V?
|
If you don't know what we're referring to, you're better off buying what
you need. Power supplies are cheap compares to your board. If you post
your current requirements, we can suggest specific hardware.
Using supplies with adjustable voltage but without knob locks is a
fairly common way to smoke parts. Be careful.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Jerry Avins
Guest
|
| Posted:
Fri Dec 02, 2005 5:15 pm Post subject:
Re: Quick question, how do I supply +-5V? |
|
|
Fred Marshall wrote:
| Quote: | "Frank" <Francis.invalid@hotmail.com> wrote in message
news:438fa5a4@news.starhub.net.sg...
I have a large board which asks for three power supplies, +3V, +3.3V and
+-5V.
First two can be easily satisfied with two HP power supplies (each has its
own
GND pin also). Regarding +-5V, can I replace with an HP power supply set
to
10V, -5V pin connect to HP's ground and +5V to power?
You might with some caveats.
First, the intended +-5v supply needs to be floating with respect to the
other supplies.
Then the 10v voltage difference can be reference wherever you want in theory
and often in practice.
The challenge is: now that you've floated the supply, how will you reference
it to the ground or 0v point on the board?
Think of the +-5v supply as a 10v battery. A battery "floats" with no
problem.
Unless you do more, the result looks like this:
+------------------------------>+5v
|
|
+----+ +--------------->+3.3v
| 10v| +----+
+----+ |3.3v| +----------+3v
| +-+--++----+
| | |3.3v|
| | +-+--+
| | |
| | |
| +-----+---------> 0v: the reference for +3.3v, +3v
|
|
|
+------------------------------>-5v
With the 10v battery floating, there is no reference to the
other batteries. Current flowing through the circuit board will cause
the +/-5v terminals to go almost anywhere relative to 0v. Depending on
what's on the board,
the +5v terminal could end up at -6v and the =5v terminal at -15v (both
relative to 0v of course).
+------+----------------------->+5v
| |
| | +--------------->+3.3v
+----+ | +----+
| 10v| | |3.3v| +----------+3v
+----+ ++-+ +-+--++----+
| |R1| | |3.3v|
| ++-+ | +-+--+
| | | |
| | | |
| +-------+-----+---------> 0v: the reference for +3.3v, +3v
| +--+
| |R1|
| ++-+
| |
+------+----------------------->-5v
A resistor divider with current much higher than the +/-5v
loads and connected to the 0v reference will refer the +/-5v
to the rest of the batteries.
It's not a very elegant or even practical solution but it makes the
point to address your question.
|
You can make Fred's solution more practical by adding an operational
amplifier that can deliver the difference between +5 and -5 currents.
+------+-------------------------------------------->+5v
| |
| | +--------------->+3.3v
+----+ | +----+
| 10v| | |3.3v| +---------+3v
+----+ ++-+ +-+--+ +----+
| |R1| +----------+ | |3.0v|
| ++-+ | |\ | | +-+--+
| | +---|-\ | | |
| | | +---+----------+------+---------> 0v
| +--------|+/
| +--+ |/
| |R1|
| ++-+
| |
+------+----------------------->-5v
Is it worth it?
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Dave
Guest
|
| Posted:
Fri Dec 02, 2005 11:49 pm Post subject:
Re: Quick question, how do I supply +-5V? |
|
|
Here's a cheap and quick, potentially noisy solution:
1. Buy two 5VDC "wall wort" power supplies.
2. connect the (-) from one to the (+) from the other. This is your common
ground lead..
3. The + lead will give you +5VDC
4. The - lead will give you -5VDC.
Make sure the wall worts are rated to deliver enough current otherwise
you'll get too much voltage drop for your app. Note that this supply is
UNREGULATED, that is, increasing load will decrease your voltage.
If you need a regulated supply, use 7-12VDC wall worts (to compensate for
the voltage drop across the regulators), buy a 7805 positive and a 7905
negative 5V regulator, two 3300uF electrolytics and two 1uF ceramic caps to
filter the output and a small PCB. There are tons of diagrams how to
arrange things to get what you want. Google is your friend. Total cost of
parts should be about $5 to build the regulator, plus some sort of enclosure
if you require.
If you happen to have two matching wall worts of >6VDC you can probably use
them if you regulate, the regulator chips can accept up to ~35VDC. note
that with larger input voltages you'll need to use heatsinks on the
regulators to dissipate the extra power/heat.
Dave
"Frank" <Francis.invalid@hotmail.com> wrote in message
news:438fcbcb@news.starhub.net.sg...
| Quote: |
"Jerry Avins" <jya@ieee.org> wrote in message
news:gpKdnbflleKAIhLeRVn-vg@rcn.net...
Steve Underwood wrote:
Jerry Avins wrote:
Ryan Weihl wrote:
Michael R. Kesti wrote:
Frank wrote:
I have a large board which asks for three power supplies, +3V,
+3.3V and
+-5V.
If I read you correctly, that's four supplies: +3V, +3.3V, +5V, and
-5V.
First two can be easily satisfied with two HP power supplies (each
has its own
GND pin also). Regarding +-5V, can I replace with an HP power
supply set to
10V, -5V pin connect to HP's ground and +5V to power?
No. Doing so would provide zero volts to the board's -5V rail and
+10V to
its +5 rail.
You need four supplies.
will an ATX supply not do?
rw
Maybe not. Compound switchers need a load on the main supply in order
to come up, and the auxiliary supplies aren't always well regulated.
Jerry
They also make more noise than a neo-natal nursery. :-)
If he knows what he's doing, ha can load the 10V supply with a beefy
op-amp connected as a follower to a divider across the rails and ground
its output. If something goes wrong, it can blow the board unless he
uses Zener-cum-fuse protection. There are DC-DC power-supply bricks and
chips that can probably supply all the -5 needed from a +5 supply.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
I don't know what you people are talking about.
Back to my question, how do I make a +-5V?
|
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Dave Pollum
Guest
|
| Posted:
Sat Dec 03, 2005 1:15 am Post subject:
Re: Quick question, how do I supply +-5V? |
|
|
<previous replies were snipped>
Frank wrote:
| Quote: | I don't know what you people are talking about.
Back to my question, how do I make a +-5V?
|
We need answers to these basic questions:
1)You need -5 volts, +5 volts, +3.3 volts, and +3.0 volts - correct?
(can you use just +3.3 volts instead of both +3.0volts _and_
+3.3volts?)
2)How much current do you need for each voltage?
3)What voltages and currents do your 2 HP power supplies produce?
Assuming that the HP's can produce negative voltage (with respect to
the HP's GND), then set one HP for -5 volts and set the other one for
+5 volts. Then use Low-DropOut (LDO) voltage regulators to produce the
+3.0 volts and +3.3 volts.
Dave Pollum |
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Mark Haase
Guest
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| Posted:
Sat Dec 03, 2005 1:15 am Post subject:
Re: Quick question, how do I supply +-5V? |
|
|
In article <438fcbcb@news.starhub.net.sg>,
"Frank" <Francis.invalid@hotmail.com> wrote:
| Quote: | I don't know what you people are talking about.
Back to my question, how do I make a +-5V?
|
Swing and a miss
--
|\/| /| |2 |<
mehaase(at)gmail(dot)com |
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