[EE]::Turn negative regulator “upside-down” to create bipolar supply from single source

[RussellMc]

While this idea is 'obvious in retrospect' it is also useful and 'clever'.

The circuit uses a single negative regulator to provide a regulated
POSITIVE supply plus an unregulated supply of -(Vin - Vout)

Many single supply circuits would benefit from having a negative supply.
This often does not need to be well (or at all) regulated or to have a
particular value.
For many notionally single supply opamps, having a whiff of negative supply
rail can convert "sort of pulls down to ground" into a solid ground
output.
Providing an unregulated varying and possibly noisy negative supply has
potential implications for supply noise rejection and other issues, but is
still of potential value in many cases.


https://www.edn.com/turn-negative-regulator-upside-down-to-create-bipolar-supply-from-single-source/

[image: image.png]

An even more "Heath Robinson" solution is to provide a forward biased diode
in the ground return of all circuitry and to use the !~= 0.6V drop to
provide a -0.6V negative supply. It works :-).



            Russell McMahon

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[David C Brown]

Would using a regulated 10volt input (LDO regulator from 12v battery) give
you clean +5 and -5 outputs?
__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak                           Phone: [phone]
Derbyshire                eMail: [hidden email]
SK23 7ND          web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



*Sent from my etch-a-sketch*


On Sat, 27 Feb 2021 at 12:26, RussellMc <[hidden email]> wrote:

> While this idea is 'obvious in retrospect' it is also useful and 'clever'.
>
> The circuit uses a single negative regulator to provide a regulated
> POSITIVE supply plus an unregulated supply of -(Vin - Vout)
>
> Many single supply circuits would benefit from having a negative supply.
> This often does not need to be well (or at all) regulated or to have a
> particular value.
> For many notionally single supply opamps, having a whiff of negative supply
> rail can convert "sort of pulls down to ground" into a solid ground
> output.
> Providing an unregulated varying and possibly noisy negative supply has
> potential implications for supply noise rejection and other issues, but is
> still of potential value in many cases.
>
>
>
> https://www.edn.com/turn-negative-regulator-upside-down-to-create-bipolar-supply-from-single-source/
>
> [image: image.png]
>
> An even more "Heath Robinson" solution is to provide a forward biased diode
> in the ground return of all circuitry and to use the !~= 0.6V drop to
> provide a -0.6V negative supply. It works :-).
>
>
>
>             Russell McMahon
> --
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[Spehro Pefhany]

At 07:23 AM 2/27/2021, you wrote:

>While this idea is 'obvious in retrospect' it is also useful and 'clever'.
>
>The circuit uses a single negative regulator to provide a regulated
>POSITIVE supply plus an unregulated supply of -(Vin - Vout)
>
>Many single supply circuits would benefit from having a negative supply.
>This often does not need to be well (or at all) regulated or to have a
>particular value.
>For many notionally single supply opamps, having a whiff of negative supply
>rail can convert "sort of pulls down to ground" into a solid ground
>output.
>Providing an unregulated varying and possibly noisy negative supply has
>potential implications for supply noise rejection and other issues, but is
>still of potential value in many cases.
>
>
>https://www.edn.com/turn-negative-regulator-upside-down-to-create-bipolar-supply-from-single-source/
>
>[image: image.png]
>
>An even more "Heath Robinson" solution is to provide a forward biased diode
>in the ground return of all circuitry and to use the !~= 0.6V drop to
>provide a -0.6V negative supply. It works :-).

Regulators such as the LM7805 have a fairly constant ~5mA current
flowing out of
the GND pin which can be used in such a way, with a regular diode, a Schottky,
a zener, a TL431 or an LED.

Of course usually you need ground to be common with something or other or the
wasted power is too great so you end up using a 10-cent 7660 or whatever.

--sp  

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[Don Kuenz]

RussellMc wrote:

> While this idea is 'obvious in retrospect' it is also useful and 'clever'.
>
> The circuit uses a single negative regulator to provide a regulated
> POSITIVE supply plus an unregulated supply of -(Vin - Vout)
>
> Many single supply circuits would benefit from having a negative supply.
> This often does not need to be well (or at all) regulated or to have a
> particular value.
> For many notionally single supply opamps, having a whiff of negative supply
> rail can convert "sort of pulls down to ground" into a solid ground
> output.
> Providing an unregulated varying and possibly noisy negative supply has
> potential implications for supply noise rejection and other issues, but is
> still of potential value in many cases.
>
>
> https://www.edn.com/turn-negative-regulator-upside-down-to-create-bipolar-supply-from-single-source/
>
> [image: image.png]
>
> An even more "Heath Robinson" solution is to provide a forward biased diode
> in the ground return of all circuitry and to use the !~= 0.6V drop to
> provide a -0.6V negative supply. It works :-).

This page "plays jazz" with voltage regulator rail splitters:

https://goldpt.com/virtual_ground_circuit.html

Conventional splitters work better for me. This page provides an
excellent primer:

https://tangentsoft.net/elec/vgrounds.html

My mixer-amp project uses a conventional splitter to create +6 VDC and
-6 VDC from a 12 VDC wall wart:

https://crcomp.net/mixeramp/index.php

Danke,

--
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.


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[RussellMc]

On Sun, 28 Feb 2021 at 01:35, David C Brown <[hidden email]> wrote:

> Would using a regulated 10volt input (LDO regulator from 12v battery) give
> you clean +5 and -5 outputs?
>
>
Yes, BUT:

The 10V LDO would need to also be a negative one.

AND the negative 5 current must ALWAYS be less that the +5 current as the
-5 current always flows in the +5 load. The +5 regulator provides
whatever +5 load current is not supplied by the -5 load.

BUT

You can achieve the same result with two positive regulators.

More on that anon, maybe.


          Russell
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[David C Brown]

Very ingenious but it is no big deal to make a wall wart with a centre
tapped transformer
__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak                           Phone: [phone]
Derbyshire                eMail: [hidden email]
SK23 7ND          web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



*Sent from my etch-a-sketch*


On Sun, 28 Feb 2021 at 07:15, Don Kuenz <[hidden email]> wrote:

> RussellMc wrote:
> > While this idea is 'obvious in retrospect' it is also useful and
> 'clever'.
> >
> > The circuit uses a single negative regulator to provide a regulated
> > POSITIVE supply plus an unregulated supply of -(Vin - Vout)
> >
> > Many single supply circuits would benefit from having a negative supply.
> > This often does not need to be well (or at all) regulated or to have a
> > particular value.
> > For many notionally single supply opamps, having a whiff of negative
> supply
> > rail can convert "sort of pulls down to ground" into a solid ground
> > output.
> > Providing an unregulated varying and possibly noisy negative supply has
> > potential implications for supply noise rejection and other issues, but
> is
> > still of potential value in many cases.
> >
> >
> >
> https://www.edn.com/turn-negative-regulator-upside-down-to-create-bipolar-supply-from-single-source/
> >
> > [image: image.png]
> >
> > An even more "Heath Robinson" solution is to provide a forward biased
> diode
> > in the ground return of all circuitry and to use the !~= 0.6V drop to
> > provide a -0.6V negative supply. It works :-).
>
> This page "plays jazz" with voltage regulator rail splitters:
>
> https://goldpt.com/virtual_ground_circuit.html
>
> Conventional splitters work better for me. This page provides an
> excellent primer:
>
> https://tangentsoft.net/elec/vgrounds.html
>
> My mixer-amp project uses a conventional splitter to create +6 VDC and
> -6 VDC from a 12 VDC wall wart:
>
> https://crcomp.net/mixeramp/index.php
>
> Danke,
>
> --
> Don, KB7RPU, https://www.qsl.net/kb7rpu
> There was a young lady named Bright Whose speed was far faster than light;
> She set out one day In a relative way And returned on the previous night.
>
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

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[Bob Blick-5]

But try to buy one :)
Then it's real hard to do.
Friendly regards, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of David C Brown
Sent: Monday, March 1, 2021 7:58 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE]::Turn negative regulator “upside-down” to create bipolar supply from single source

Very ingenious but it is no big deal to make a wall wart with a centre
tapped transformer
__________________________________________
David C Brown

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[David C Brown]

|I prefer to build quality rather than buy rubbish  :-)
__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak                           Phone: [phone]
Derbyshire                eMail: [hidden email]
SK23 7ND          web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



*Sent from my etch-a-sketch*


On Mon, 1 Mar 2021 at 16:28, Bob Blick <[hidden email]> wrote:

> But try to buy one :)
> Then it's real hard to do.
> Friendly regards, Bob
>
> ________________________________________
> From: [hidden email] <[hidden email]> on behalf of
> David C Brown
> Sent: Monday, March 1, 2021 7:58 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE]::Turn negative regulator “upside-down” to create bipolar
> supply from single source
>
> Very ingenious but it is no big deal to make a wall wart with a centre
> tapped transformer
> __________________________________________
> David C Brown
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

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[David C Brown]

Dual output USB chargers are common as muck and cheap as chips.

__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak                           Phone: [phone]
Derbyshire                eMail: [hidden email]
SK23 7ND          web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



*Sent from my etch-a-sketch*


On Mon, 1 Mar 2021 at 16:28, Bob Blick <[hidden email]> wrote:

> But try to buy one :)
> Then it's real hard to do.
> Friendly regards, Bob
>
> ________________________________________
> From: [hidden email] <[hidden email]> on behalf of
> David C Brown
> Sent: Monday, March 1, 2021 7:58 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE]::Turn negative regulator “upside-down” to create bipolar
> supply from single source
>
> Very ingenious but it is no big deal to make a wall wart with a centre
> tapped transformer
> __________________________________________
> David C Brown
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

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[Spehro Pefhany]

At 11:27 AM 3/1/2021, you wrote:
>But try to buy one :)
>Then it's real hard to do.
>Friendly regards, Bob

I just made a little audio doodad with an AC wall wart. Half-wave
rectification is no big deal, you just need to double the capacitor values,
and you use the iron efficiently if the + and - currents are similar.

$8 US for a Triad 16V/500mA wall wart in 50 quantity to make +/-15V. About $10
one-off.

--sp

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[Bob Blick-5]

That's fine for a one-off, but for a commercial product, today's efficiency requirements pretty much consign line frequency wallwarts to the history books.

Even for one-offs, when I need + and - 15V now, I use a $7 Tri-Mag 30V wallwart switching supply and rail-split inside the device using a spare opamp section or two. Another bonus to doing it this way is that it saves you from needing any voltage regulators.

Friendly regards, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of Spehro Pefhany
Sent: Monday, March 1, 2021 10:37 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE]::Turn negative regulator      “upside-down” to c reate bipolar supply from    single source

At 11:27 AM 3/1/2021, you wrote:
>But try to buy one :)
>Then it's real hard to do.
>Friendly regards, Bob

I just made a little audio doodad with an AC wall wart. Half-wave
rectification is no big deal, you just need to double the capacitor values,
and you use the iron efficiently if the + and - currents are similar.

$8 US for a Triad 16V/500mA wall wart in 50 quantity to make +/-15V. About $10
one-off.

--sp


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[Bob Blick-5]

Hi David,
How does that get you a bipolar supply? I would assume the outputs share a common negative.
Friendly regards, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of David C Brown
Sent: Monday, March 1, 2021 10:04 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE]::Turn negative regulator “upside-down” to create bipolar supply from single source

Dual output USB chargers are common as muck and cheap as chips.

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[Spehro Pefhany]

At 01:59 PM 3/1/2021, you wrote:

>That's fine for a one-off, but for a commercial product, today's
>efficiency requirements pretty much consign line frequency wallwarts
>to the history books.
>
>Even for one-offs, when I need + and - 15V now, I use a $7 Tri-Mag
>30V wallwart switching supply and rail-split inside the device using
>a spare opamp section or two. Another bonus to doing it this way is
>that it saves you from needing any voltage regulators.
>
>Friendly regards, Bob

The medical standard switchers are pretty acceptable for precision
work these days.

Thank goodness, there's probably not enough market in precision
instrumentation.

--Spehro





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