ą5V from up to +12v

John Fields · Nov 5, 2013

On Mon, 04 Nov 2013 13:56:39 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Mon, 04 Nov 2013 14:48:39 -0600, John Fields
jfields@austininstruments.com> wrote:

On Mon, 04 Nov 2013 09:54:20 -0800, Daniel Pitts
newsgroup.nospam@virtualinfinity.net> wrote:

I'm trying to design a remote controlled volume controller, and the chip
I've chosen to control the volume needs ą5v for the analog side of the
circuit, and +5v for the digital.

I have several options for input voltage, mostly based on old AC
adapters I have laying around. In particular I have a "selectable"
adapter which can select up to 12v, but I may have others with higher
voltages (I haven't looked through them recently).

One idea I had was to chain 7805s together:

+12v connected to VinA & VinB

GndIn connected to GndA

VoutA connected to GndB

If I understand correctly, I could then use VoutA as my reference point,
making GndA -5v and VoutB +5v.

If I do this, am I going to let the magic smoke out? Is there an easier
way to do what I'm trying to do? It seems like most ą5v chips I've found
require a bit more complicated external components, and are far more
expensive.

WW1
+-----+
|~ +5|------>+5
| |
|~ 0V|--+
+-----+ |
+--->GND
+-----+ |
|~ +5|--+
| |
|~ 0V|------>-5
+-----+
WW2

Huh? Didn't Daniel imply he had a single +12VDC adapter as input?
Currents have to balance.

...Jim Thompson

---
He said he had a bunch of wall-warts lying around, so my suggestion
was to use two wall-warts to get plus 5 and minus 5V.

Current balance doesn't seem to be important:

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Phil Hobbs · Nov 5, 2013

On 11/05/2013 09:57 AM, George Herold wrote:

On Tuesday, November 5, 2013 9:49:28 AM UTC-5, Jim Thompson wrote:
On 5 Nov 2013 07:52:36 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

On 2013-11-04, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
big snip... includeing Jasen's circuit

Possibly. I'd probably opt for a TL431 to provide the load balance...
your approach smacks of instability.

Or make the 12 V into 10 Volts, and then a power opamp as rail splitter.
(I've got these TCA0372's in my parts box waiting for a project.)
I guess it depends on what sorts of currents are involved.

George H.

Careful with those--they work great, except that the heat sinking is
quite a bit less great. The best package runs 22 K/W junction to
"case", whatever that means in a plastic-encapsulated package with no
power tab. That's quite a bit considering that the chip can dissipate
over 40W before thermal shutdown kicks in. (Steady-state thermal
transfer calculations would put the die at about 900C with an infinite
room-temperature heat sink--a nice bright red-orange glow.)

They run warm to the touch just with their quiescent current.

As a rail splitter, you have to watch out for the chip hitting thermal
shutdown, which will probably make one rail collapse. A couple of beefy
Zeners on the output would help prevent Joergish noises.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Jim Thompson · Nov 5, 2013

On Mon, 04 Nov 2013 09:54:20 -0800, Daniel Pitts
<newsgroup.nospam@virtualinfinity.net> wrote:

I'm trying to design a remote controlled volume controller, and the chip
I've chosen to control the volume needs ą5v for the analog side of the
circuit, and +5v for the digital.

I have several options for input voltage, mostly based on old AC
adapters I have laying around. In particular I have a "selectable"
adapter which can select up to 12v, but I may have others with higher
voltages (I haven't looked through them recently).

[snip]

Tim Wescott · Nov 5, 2013

On Mon, 04 Nov 2013 09:54:20 -0800, Daniel Pitts wrote:

I'm trying to design a remote controlled volume controller, and the chip
I've chosen to control the volume needs Âą5v for the analog side of the
circuit, and +5v for the digital.

I have several options for input voltage, mostly based on old AC
adapters I have laying around. In particular I have a "selectable"
adapter which can select up to 12v, but I may have others with higher
voltages (I haven't looked through them recently).

One idea I had was to chain 7805s together:

+12v connected to VinA & VinB

GndIn connected to GndA

VoutA connected to GndB

If I understand correctly, I could then use VoutA as my reference point,
making GndA -5v and VoutB +5v.

If I do this, am I going to let the magic smoke out? Is there an easier
way to do what I'm trying to do? It seems like most Âą5v chips I've found
require a bit more complicated external components, and are far more
expensive.

Just how strict is the need for +/- 5V? With a 7905 you could make a
"strict" 5V supply, with the ground to negative voltage being whatever is
left over. The diagram shows what you'd get with your 12V supply,
assuming that it's actually 12V in practice:

V+ o------------o------------o +5V
|
.-----.
.--| |---------o GND
| '-----'
| LM7905
V- o------o------------------o -7V

As with other circuits using the LM7x05, you need to make sure that the
current is flowing the correct direction at the "out" pin -- in this case
the ground current would need to have a net flow from the +5V rail, or
the chip would fall out of regulation.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Phil Hobbs · Nov 6, 2013

On 11/05/2013 12:09 PM, George Herold wrote:

On Tuesday, November 5, 2013 10:39:31 AM UTC-5, Phil Hobbs wrote:
On 11/05/2013 09:57 AM, George Herold wrote:
On Tuesday, November 5, 2013 9:49:28 AM UTC-5, Jim Thompson wrote:
On 5 Nov 2013 07:52:36 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

On 2013-11-04, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
big snip... includeing Jasen's circuit

Possibly. I'd probably opt for a TL431 to provide the load balance...
your approach smacks of instability

Or make the 12 V into 10 Volts, and then a power opamp as rail splitter.
(I've got these TCA0372's in my parts box waiting for a project.)
I guess it depends on what sorts of currents are involved.

George H.

Careful with those--they work great, except that the heat sinking is
quite a bit less great. The best package runs 22 K/W junction to
"case", whatever that means in a plastic-encapsulated package with no
power tab. That's quite a bit considering that the chip can dissipate
over 40W before thermal shutdown kicks in. (Steady-state thermal
transfer calculations would put the die at about 900C with an infinite
room-temperature heat sink--a nice bright red-orange glow.)

They run warm to the touch just with their quiescent current.

Grin, Hey, the TCA0372's are burning a hole in my parts bin :^)
(maybe the OP only needs ~100mA)
I must admit when you (or someone else?) pointed out these 1 amp IC's in a dip8 package I was a bit 'concerned'.
(I'd really like a nice to-220 style metal tab.. or a surface mount with 'power pads' on the bottom.)

George H.

They're amazingly useful if you think of them as a 100-200 mA part with
a lot of overload capacity and a very nice low Zout.

I recently used them to make a single-ended high-Z front end amplifier
whose input could be biased +-5V from ground. I used voltage regulators
to make the +-5, referenced to the "adjustable ground" at the output of
a TCA0372. Worked great, and for half a buck, they're unbeatable. I
agree, it would be great if they came in a power pad package. Of course
there's always the LM675 for that, but it isn't half a buck!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Ian Malcolm · Nov 6, 2013

Daniel Pitts <newsgroup.nospam@virtualinfinity.net> wrote in
news:hbRdu.262470$cT3.38493@fx29.iad:

I'm trying to design a remote controlled volume controller, and the
chip I've chosen to control the volume needs ą5v for the analog side
of the circuit, and +5v for the digital.

I have several options for input voltage, mostly based on old AC
adapters I have laying around. In particular I have a "selectable"
adapter which can select up to 12v, but I may have others with higher
voltages (I haven't looked through them recently).

One idea I had was to chain 7805s together:

+12v connected to VinA & VinB

GndIn connected to GndA

VoutA connected to GndB

If I understand correctly, I could then use VoutA as my reference
point, making GndA -5v and VoutB +5v.

If I do this, am I going to let the magic smoke out? Is there an
easier way to do what I'm trying to do? It seems like most ą5v chips
I've found require a bit more complicated external components, and are
far more expensive.

Thanks,
Daniel.

The other replies have covered in some detail the disadvantages of
starting with +12V DC in.

Do you have any adapters with AC output between 8V and 12V (RMS)?

If so, a much better approach would be to half-wave rectify the AC with
a diode and electrolytic reservoir capacitor for each supply to get
positive and negative unregulated supplies with a common 0V, then using
7805 and 7905 regulators respectively to get your regulated +/-5V
output.

A 8 or 9V AC supply is ideal for +/-5V output, but higer voltages can be
used although the regulators will run hotter. Component choices depend
on input voltage, load current on each output and mains supply
frequency, so tell us what AC output supplies you have available
(nominal voltage and current + measured output voltage unloaded) and the
required output currents so we can help you pick the best one.

If you dont have any AC output adapters, the use of a DC-DC converter
module to get a negative rail has already been mentioned. There are a
few issues with ripple on the output, and potentially with power supply
sequencing so you had better tell us which volume control chip you
intend to use.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL

Daniel Pitts · Nov 7, 2013

On 11/5/13 7:19 AM, John Fields wrote:

On Mon, 04 Nov 2013 13:56:39 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Mon, 04 Nov 2013 14:48:39 -0600, John Fields
jfields@austininstruments.com> wrote:

On Mon, 04 Nov 2013 09:54:20 -0800, Daniel Pitts
newsgroup.nospam@virtualinfinity.net> wrote:

I'm trying to design a remote controlled volume controller, and the chip
I've chosen to control the volume needs ą5v for the analog side of the
circuit, and +5v for the digital.

I have several options for input voltage, mostly based on old AC
adapters I have laying around. In particular I have a "selectable"
adapter which can select up to 12v, but I may have others with higher
voltages (I haven't looked through them recently).

One idea I had was to chain 7805s together:

+12v connected to VinA & VinB

GndIn connected to GndA

VoutA connected to GndB

If I understand correctly, I could then use VoutA as my reference point,
making GndA -5v and VoutB +5v.

If I do this, am I going to let the magic smoke out? Is there an easier
way to do what I'm trying to do? It seems like most ą5v chips I've found
require a bit more complicated external components, and are far more
expensive.

WW1
+-----+
|~ +5|------>+5
| |
|~ 0V|--+
+-----+ |
+--->GND
+-----+ |
|~ +5|--+
| |
|~ 0V|------>-5
+-----+
WW2

Huh? Didn't Daniel imply he had a single +12VDC adapter as input?
Currents have to balance.

...Jim Thompson

---
He said he had a bunch of wall-warts lying around, so my suggestion
was to use two wall-warts to get plus 5 and minus 5V.

Current balance doesn't seem to be important:

Version 4
SHEET 1 880 936
WIRE -2000 -16 -2144 -16
[snip]

Is there a program to interpret that script? Hopefully one that runs on
Mac, DOSBOX, or the web?

Thanks,
Daniel.

petrus bitbyter · Nov 7, 2013

"Daniel Pitts" <newsgroup.nospam@virtualinfinity.net> schreef in bericht
news:wTveu.152647$Us6.66703@fx12.iad...

On 11/5/13 7:19 AM, John Fields wrote:
On Mon, 04 Nov 2013 13:56:39 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Mon, 04 Nov 2013 14:48:39 -0600, John Fields
jfields@austininstruments.com> wrote:

On Mon, 04 Nov 2013 09:54:20 -0800, Daniel Pitts
newsgroup.nospam@virtualinfinity.net> wrote:

I'm trying to design a remote controlled volume controller, and the
chip
I've chosen to control the volume needs ą5v for the analog side of the
circuit, and +5v for the digital.

I have several options for input voltage, mostly based on old AC
adapters I have laying around. In particular I have a "selectable"
adapter which can select up to 12v, but I may have others with higher
voltages (I haven't looked through them recently).

One idea I had was to chain 7805s together:

+12v connected to VinA & VinB

GndIn connected to GndA

VoutA connected to GndB

If I understand correctly, I could then use VoutA as my reference
point,
making GndA -5v and VoutB +5v.

If I do this, am I going to let the magic smoke out? Is there an
easier
way to do what I'm trying to do? It seems like most ą5v chips I've
found
require a bit more complicated external components, and are far more
expensive.

WW1
+-----+
|~ +5|------>+5
| |
|~ 0V|--+
+-----+ |
+--->GND
+-----+ |
|~ +5|--+
| |
|~ 0V|------>-5
+-----+
WW2

Huh? Didn't Daniel imply he had a single +12VDC adapter as input?
Currents have to balance.

...Jim Thompson

---
He said he had a bunch of wall-warts lying around, so my suggestion
was to use two wall-warts to get plus 5 and minus 5V.

Current balance doesn't seem to be important:

Version 4
SHEET 1 880 936
WIRE -2000 -16 -2144 -16
[snip]

Is there a program to interpret that script? Hopefully one that runs on
Mac, DOSBOX, or the web?

Thanks,
Daniel.

LTspice IV download from www.linear.com/designtools.

petrus bitbyter

Daniel Pitts · Nov 7, 2013

On 11/5/13 1:45 PM, Jim Thompson wrote:

On Mon, 04 Nov 2013 09:54:20 -0800, Daniel Pitts
newsgroup.nospam@virtualinfinity.net> wrote:

I'm trying to design a remote controlled volume controller, and the chip
I've chosen to control the volume needs ą5v for the analog side of the
circuit, and +5v for the digital.

I have several options for input voltage, mostly based on old AC
adapters I have laying around. In particular I have a "selectable"
adapter which can select up to 12v, but I may have others with higher
voltages (I haven't looked through them recently).

One idea I had was to chain 7805s together:

+12v connected to VinA & VinB

GndIn connected to GndA

VoutA connected to GndB

If I understand correctly, I could then use VoutA as my reference point,
making GndA -5v and VoutB +5v.

If I do this, am I going to let the magic smoke out? Is there an easier
way to do what I'm trying to do? It seems like most ą5v chips I've found
require a bit more complicated external components, and are far more
expensive.

Thanks,
Daniel.

Here you go....

http://www.analog-innovations.com/SED/Split_5V_Supplies_12V_Input.pdf

Thanks! I'll see if this is in my capability to understand and build,
but it looks nice at first glance.

Daniel Pitts · Nov 7, 2013

On 11/4/13 9:54 AM, Daniel Pitts wrote:

I'm trying to design a remote controlled volume controller, and the chip
I've chosen to control the volume needs ą5v for the analog side of the
circuit, and +5v for the digital.

I have several options for input voltage, mostly based on old AC
adapters I have laying around. In particular I have a "selectable"
adapter which can select up to 12v, but I may have others with higher
voltages (I haven't looked through them recently).

One idea I had was to chain 7805s together:

+12v connected to VinA & VinB

GndIn connected to GndA

VoutA connected to GndB

If I understand correctly, I could then use VoutA as my reference point,
making GndA -5v and VoutB +5v.

If I do this, am I going to let the magic smoke out? Is there an easier
way to do what I'm trying to do? It seems like most ą5v chips I've found
require a bit more complicated external components, and are far more
expensive.

Thanks,
Daniel.

Thanks for all the suggestions everyone. I see how my original thoughts
were flawed.

I also realized I should probably get a better idea of what my amperage
will be. I'm guessing <100ma, but I'm not entirely sure.

I'm also considering using just a pair of digital POTs instead of this
fancy schmancy volume control IC. That way I only need +5v, which is a
much easier problem for me to solve ;-)

Thanks again,
Daniel.

Jim Thompson · Nov 7, 2013

On Wed, 06 Nov 2013 10:41:19 -0800, Daniel Pitts
<newsgroup.nospam@virtualinfinity.net> wrote:

On 11/5/13 1:45 PM, Jim Thompson wrote:
On Mon, 04 Nov 2013 09:54:20 -0800, Daniel Pitts
newsgroup.nospam@virtualinfinity.net> wrote:

I'm trying to design a remote controlled volume controller, and the chip
I've chosen to control the volume needs ą5v for the analog side of the
circuit, and +5v for the digital.

I have several options for input voltage, mostly based on old AC
adapters I have laying around. In particular I have a "selectable"
adapter which can select up to 12v, but I may have others with higher
voltages (I haven't looked through them recently).

One idea I had was to chain 7805s together:

+12v connected to VinA & VinB

GndIn connected to GndA

VoutA connected to GndB

If I understand correctly, I could then use VoutA as my reference point,
making GndA -5v and VoutB +5v.

If I do this, am I going to let the magic smoke out? Is there an easier
way to do what I'm trying to do? It seems like most ą5v chips I've found
require a bit more complicated external components, and are far more
expensive.

Thanks,
Daniel.

Here you go....

http://www.analog-innovations.com/SED/Split_5V_Supplies_12V_Input.pdf
Thanks! I'll see if this is in my capability to understand and build,
but it looks nice at first glance.

Daniel Pitts · Nov 7, 2013

On 11/6/13 10:50 AM, Jim Thompson wrote:

On Wed, 06 Nov 2013 10:41:19 -0800, Daniel Pitts
newsgroup.nospam@virtualinfinity.net> wrote:

On 11/5/13 1:45 PM, Jim Thompson wrote:
On Mon, 04 Nov 2013 09:54:20 -0800, Daniel Pitts
newsgroup.nospam@virtualinfinity.net> wrote:

I'm trying to design a remote controlled volume controller, and the chip
I've chosen to control the volume needs ą5v for the analog side of the
circuit, and +5v for the digital.

I have several options for input voltage, mostly based on old AC
adapters I have laying around. In particular I have a "selectable"
adapter which can select up to 12v, but I may have others with higher
voltages (I haven't looked through them recently).

One idea I had was to chain 7805s together:

+12v connected to VinA & VinB

GndIn connected to GndA

VoutA connected to GndB

If I understand correctly, I could then use VoutA as my reference point,
making GndA -5v and VoutB +5v.

If I do this, am I going to let the magic smoke out? Is there an easier
way to do what I'm trying to do? It seems like most ą5v chips I've found
require a bit more complicated external components, and are far more
expensive.

Thanks,
Daniel.

Here you go....

http://www.analog-innovations.com/SED/Split_5V_Supplies_12V_Input.pdf
Thanks! I'll see if this is in my capability to understand and build,
but it looks nice at first glance.

I think the TL431 is still readily available. Back when I did more
discrete designs it was my favorite reference device... AND it can act
like an OpAmp (as in your case).

Looks like I can get some.
http://www.digikey.com/product-search/en/integrated-circuits-ics/pmic-voltage-reference/2556223?k=TL431

Kaz Kylheku · Dec 28, 2013

On 2013-11-04, Daniel Pitts <newsgroup.nospam@virtualinfinity.net> wrote:

I'm trying to design a remote controlled volume controller, and the chip
I've chosen to control the volume needs Âą5v for the analog side of the
circuit, and +5v for the digital.

Idea:

* Use a 5V (unregulated) adapter. Regulate to 5V with a 7805.

* Use a charge pump IC to generate a -5V rail from the regulated +5V rail.

I have several options for input voltage, mostly based on old AC
adapters I have laying around.

You can get a center-tapped transformer for a couple of dollars, or rip it out
of something. You can build your own dual-voltage AC adapter easily with a
center tapped transformer and bridge rectifier or discrete diodes. Your device
then just has to provide the reservoir capacitors and regulators.

Why not find some discarded old device (e.g. piece of audio gear) which has
a dual supply in it already and re-use its power entry and perhaps more.
Throw out the circuit board and build your own device in its place.

You can also use two identical AC adapters to get the equivalent of a
center-tapped transformer, if you can live with the clunkiness.

Maynard A. Philbrook Jr. · Dec 28, 2013

In article <20131227215419.422@kylheku.com>, kaz@kylheku.com says...

On 2013-11-04, Daniel Pitts <newsgroup.nospam@virtualinfinity.net> wrote:
I'm trying to design a remote controlled volume controller, and the chip
I've chosen to control the volume needs ą5v for the analog side of the
circuit, and +5v for the digital.

Idea:

* Use a 5V (unregulated) adapter. Regulate to 5V with a 7805.

* Use a charge pump IC to generate a -5V rail from the regulated +5V rail.

I have several options for input voltage, mostly based on old AC
adapters I have laying around.

You can get a center-tapped transformer for a couple of dollars, or rip it out
of something. You can build your own dual-voltage AC adapter easily with a
center tapped transformer and bridge rectifier or discrete diodes. Your device
then just has to provide the reservoir capacitors and regulators.

Why not find some discarded old device (e.g. piece of audio gear) which has
a dual supply in it already and re-use its power entry and perhaps more.
Throw out the circuit board and build your own device in its place.

You can also use two identical AC adapters to get the equivalent of a
center-tapped transformer, if you can live with the clunkiness.

I just scabbed an old DC drive that had a lots of pulse transformers for
the SCR's, nice ones too. Also, I got the dual SCR's and full heat sink
which like 10x15 inches..

I save parts like this for bench concept theories and home projects,
anything else, like at work, we buy new stuff. But saving parts from
these large units gives lots of parts you can hang together with jumper
wires (fuses) as some one I know referred to them, and experiment.

Jamie

ą5V from up to +12v

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