IC that generates +5 V, 0 and -5 V from 16 V single supply input?

[Bill]

Hi,

Does anyone know of an IC that generates linearly regulated +5 V (+50
mA), 0 V and -5 V (-50 mA) from an unregulated 12...18 V single supply
input?

That is, 2 input nodes (between which I apply 16 V) and 3 output
nodes, and none of the input nodes is at the same potential as an
output node.

Noise must be minimum, so I don't want to use switched-mode
regulators.

Thank you,
Bill

 

[Tim Williams]

Noise must be minimum, so I don't want to use switched-mode
regulators.

Well, I was going to suggest you use a dual 5V output DC-DC converter, but
now you've just converted that from "easy" to "impossible".

Otherwise, grab six AA's.

Tim

 

[Polyp]

Hi,

Does anyone know of an IC that generates linearly regulated +5 V (+50
mA), 0 V and -5 V (-50 mA) from an unregulated 12...18 V single supply
input?

That is, 2 input nodes (between which I apply 16 V) and 3 output
nodes, and none of the input nodes is at the same potential as an
output node.

Noise must be minimum, so I don't want to use switched-mode
regulators.

Thank you,
Bill

Perhaps stack a couple of 5V regs on top of each other. The bottom reg
supplies -5, the top one +5 and where they meet is 0V.

 

[Adrian C]

That is, 2 input nodes (between which I apply 16 V) and 3 output
nodes, and none of the input nodes is at the same potential as an
output node.

Establish a virtual ground between the two input nodes with a couple of
identical resistors and soothing caps, and then reference that for a
pair of linear regulator 78L05 & 79L05 on each input node.

 

[Bill]

That is, 2 input nodes (between which I apply 16 V) and 3 output
nodes, and none of the input nodes is at the same potential as an
output node.

Well, I don't know what I was thinking of (if that was the case), but
I meant "the input supply does not provide the 0 V node." There may be
coincidence in voltage between the input low node and the output low
node, or between the input high and the output high.

I know how to do it with two regulators. I'm just surprised there is
no IC with the two in it, being +5V/0/-5V so common.

Thanks,

 

[Bill]

Well, I was going to suggest you use a dual 5V output DC-DC converter, but
now you've just converted that from "easy" to "impossible".

Why do you say impossible? It is easy with two ICs.
I was asking about a single IC solution.

Best,

 

[Tim Williams]

Why do you say impossible? It is easy with two ICs.
I was asking about a single IC solution.

No, you can't do it with two ICs either. Your vague requirement suggests
some level of isolation is required, which is only going to happen with a
switching supply (transformer or flying-capacitor). (I suppose you could
make a photovoltaic converter, too, but that would be rather expensive,
bulky and inefficient.)

If isolation isn't actually required, and one of those
float-a-regulator-from-the-middle setups will suffice, then perhaps a
four-terminal dual tracking regulator will work. If you can find one.

Tim

 

[Spehro Pefhany]

Establish a virtual ground between the two input nodes with a couple of
identical resistors and soothing caps, and then reference that for a
pair of linear regulator 78L05 & 79L05 on each input node.

Soothing capacitors?

 

[bw]

Soothing capacitors?

Those are used in premium tube amp audio devices. Much more expensive than
regular caps.

 

[Fred Bartoli]

Spehro Pefhany a écrit :

Soothing capacitors?

Yup.
In anxious audiofools' amps it's bypass caps : the bigger the caps, the
bigger the soothing factor.

 

[Bill]

No, you can't do it with two ICs either.

Just in case someone reads you and believes you...
http://img43.imagevenue.com/img.php?image=09576_20090804A01_ngred_122_590lo.jpg
It strictly fulfills the requirements I wrote.

Your vague requirement

My (first) requirement may be strange, but not vague. I did specify
something unambiguously.

suggests
some level of isolation is required, which is only going to happen with a
switching supply (transformer or flying-capacitor). (I suppose you could
make a photovoltaic converter, too, but that would be rather expensive,
bulky and inefficient.)

I didn't mention isolation.

If isolation isn't actually required, and one of those
float-a-regulator-from-the-middle setups will suffice, then perhaps a
four-terminal dual tracking regulator will work.

I don't know exactly which configuration you are referring to, but not
any one will work. The middle output node must be able to sink and
source current.

Best,

 

[Paul Keinanen]

Just in case someone reads you and believes you...
http://img43.imagevenue.com/img.php?image=09576_20090804A01_ngred_122_590lo.jpg
It strictly fulfills the requirements I wrote.

Since you only needed 50 mA, why not just use two 5 V 1 W zeners in
series and two series resistors to 0 V and +16 V.

Paul

 

[Nemo]

Bill pondered

Does anyone know of an IC that generates linearly regulated +5 V (+50
mA), 0 V and -5 V (-50 mA) from an unregulated 12...18 V single supply
input?

That is, 2 input nodes (between which I apply 16 V) and 3 output
nodes, and none of the input nodes is at the same potential as an
output node.

Noise must be minimum, so I don't want to use switched-mode
regulators.

Texas make a "precision rail splitter" called the TLE2426 which sounds
kind of like what you want, but it only sources / sinks 20mA, and it
doesn't regulate - though you could something like it to split a 10V
rail from a linear regulator, or follow it with a dual regulator (if you
find one which does both + and -5V in the same package I'd be interested
to know what it is).

I've always thought it looked like one of those IC's which *ought* to be
useful but would never quite have all the specs you needed for any
real-life task!

I realise this doesn't answer the question you asked(!) but I throw it
into the debate in the hope that it will spark new lines of thought.

 

[Spehro Pefhany]

Just in case someone reads you and believes you...
http://img43.imagevenue.com/img.php?image=09576_20090804A01_ngred_122_590lo.jpg
It strictly fulfills the requirements I wrote.


My (first) requirement may be strange, but not vague. I did specify
something unambiguously.


I didn't mention isolation.


I don't know exactly which configuration you are referring to, but not
any one will work. The middle output node must be able to sink and
source current.

Best,

I've done this with a 78XXX regulator and an op-amp, but that's two
chips. Most regulators will not sink and source current, so you either
have to add a dummy load to avoid that requirement, or use one of the
regulator chips (for example, some of those called series voltage
references) that *can* sink and source current.

 

[Paul Keinanen]

You only need one series resistor

The original requirement also included

So you need two resistors.

If the 0 V input and -5 V output can be connected together or the +16
V input and +5 V output are the same pin, one resistor is enough.

Paul

 

[Spehro Pefhany]

I didn't post before because that wasn't clear, but now that it is, and you
want sink and source, try an op-amp as voltage follower. Tie the input to the
common point of two 1% tolerance resistors that make a series chain across a
10V zener diode, and a third resistor supplying the zener with enough current
to supply it and the small load made by those two resistors. The op-amp can
be powered direct from the main supply but the two rails will tap to each end
of the zener. You could use two zeners and one resistor as someone already
mentioned, if it's not critical that the rails be within 1% of each other's
absolute value.

If source and sink is vital, then it must be an op-amp, so you either do the
rest with discrete parts (few enough of them), or do something even more
elaborate. The op-amp trick does useful things when you want asymmetric rails
too.

Be sure to use nice big decoupling caps on the op-amp output (LOL).