How can you enhance Sijosae splitter precision without a trimmer?...

[Don]

My proto-board needs a rail-splitter, built from parts on-hand, post
haste. A modded Sijosae splitter will work. How can you enhance its
precision without a trimmer?

Danke,

--
Don, 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.

 

[John Larkin]

On Mon, 14 Dec 2020 19:50:37 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

My proto-board needs a rail-splitter, built from parts on-hand, post
haste. A modded Sijosae splitter will work. How can you enhance its
precision without a trimmer?

Danke,

Use an opamp.

 

[Dave Platt]

My proto-board needs a rail-splitter, built from parts on-hand, post
haste. A modded Sijosae splitter will work. How can you enhance its
precision without a trimmer?

If your circuit has a completely constant current load, then you could
probably optimize it by hand selection of the various resistors.

If the current load is variable, though, I suspect you\'re going to
have difficulty making it \"precise under load variation\". It looks as
if this circuit has a relatively high output impedance, due to the use
of those 10-ohm emitter degeneration resistors. The virtual ground is
going to bounce around considerably as the load changes.

 

[John Larkin]

On Mon, 14 Dec 2020 12:57:23 -0800, dplatt@coop.radagast.org (Dave
Platt) wrote:

My proto-board needs a rail-splitter, built from parts on-hand, post
haste. A modded Sijosae splitter will work. How can you enhance its
precision without a trimmer?

If your circuit has a completely constant current load, then you could
probably optimize it by hand selection of the various resistors.

If the current load is variable, though, I suspect you\'re going to
have difficulty making it \"precise under load variation\". It looks as
if this circuit has a relatively high output impedance, due to the use
of those 10-ohm emitter degeneration resistors. The virtual ground is
going to bounce around considerably as the load changes.

We don\'t know his actual \"modded\" circuit, but the Sijosae splitters
that show up in google searches look awfully soft and sloppy.

Unless the supplies are super accurate, I can\'t see much virtue in a
precise splitter. Downstream circuits shouldn\'t care much.

 

[Don]

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

On Mon, 14 Dec 2020 12:57:23 -0800, dplatt@coop.radagast.org (Dave
Platt) wrote:

My proto-board needs a rail-splitter, built from parts on-hand, post
haste. A modded Sijosae splitter will work. How can you enhance its
precision without a trimmer?

If your circuit has a completely constant current load, then you could
probably optimize it by hand selection of the various resistors.

If the current load is variable, though, I suspect you\'re going to
have difficulty making it \"precise under load variation\". It looks as
if this circuit has a relatively high output impedance, due to the use
of those 10-ohm emitter degeneration resistors. The virtual ground is
going to bounce around considerably as the load changes.

We don\'t know his actual \"modded\" circuit, but the Sijosae splitters
that show up in google searches look awfully soft and sloppy.

Unless the supplies are super accurate, I can\'t see much virtue in a
precise splitter. Downstream circuits shouldn\'t care much.

The mod\'s whatever you guys say it is. Beings a Sijosae splitter seems
unpopular, give me an alternative, which works with parts typically
found in most parts drawers. The Sijosae splitter show below at the link
uses such parts:

https://tangentsoft.net/elec/bitmaps/vgrounds/sijosae.png

A virtual ground circuit to split a wall wart between positive and
negative rails is what\'s needed. This is for a proto-board, so it\'s
reasonable to expect a highly variable load.

Danke,

--
Don, 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.

 

[Dave Platt]

In article <ihuftfh1slneffn78vtj5lpljd5b6bmvsi@4ax.com>,
John Larkin <xx@yy.com> wrote:

We don\'t know his actual \"modded\" circuit, but the Sijosae splitters
that show up in google searches look awfully soft and sloppy.

One site I read described them as significantly better than a simple
resistive divider, but significantly worse than any other buffered
circuit they described (typically op-amp-based). Price-wise that\'s
about how they fall, too. I guess you get what you pay for.

Unless the supplies are super accurate, I can\'t see much virtue in a
precise splitter. Downstream circuits shouldn\'t care much.

We don\'t know the requirements of the downstream circuits, either -
why precision seemed to be called for.

 

[Don]

Dave Platt <dplatt@coop.radagast.org> wrote:

In article <ihuftfh1slneffn78vtj5lpljd5b6bmvsi@4ax.com>,
John Larkin <xx@yy.com> wrote:

We don\'t know his actual \"modded\" circuit, but the Sijosae splitters
that show up in google searches look awfully soft and sloppy.

One site I read described them as significantly better than a simple
resistive divider, but significantly worse than any other buffered
circuit they described (typically op-amp-based). Price-wise that\'s
about how they fall, too. I guess you get what you pay for.

Unless the supplies are super accurate, I can\'t see much virtue in a
precise splitter. Downstream circuits shouldn\'t care much.

We don\'t know the requirements of the downstream circuits, either -
why precision seemed to be called for.

It\'s for a proto-board with a variable load, which depends upon the
circuit breadboarded. This is the first circuit:

https://crcomp.net/paia/2720-2A.png

Danke,

--
Don, 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.

 

[Phil Hobbs]

On 12/14/20 8:43 PM, Dave Platt wrote:

In article <ihuftfh1slneffn78vtj5lpljd5b6bmvsi@4ax.com>,
John Larkin <xx@yy.com> wrote:

We don\'t know his actual \"modded\" circuit, but the Sijosae splitters
that show up in google searches look awfully soft and sloppy.

One site I read described them as significantly better than a simple
resistive divider, but significantly worse than any other buffered
circuit they described (typically op-amp-based). Price-wise that\'s
about how they fall, too. I guess you get what you pay for.

Unless the supplies are super accurate, I can\'t see much virtue in a
precise splitter. Downstream circuits shouldn\'t care much.

We don\'t know the requirements of the downstream circuits, either -
why precision seemed to be called for.



A resistive divider and a TCA0372.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[legg]

On Tue, 15 Dec 2020 01:07:53 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

John Larkin <jlarkin@highland_atwork_technology.com> wrote:
On Mon, 14 Dec 2020 12:57:23 -0800, dplatt@coop.radagast.org (Dave
Platt) wrote:

My proto-board needs a rail-splitter, built from parts on-hand, post
haste. A modded Sijosae splitter will work. How can you enhance its
precision without a trimmer?

If your circuit has a completely constant current load, then you could
probably optimize it by hand selection of the various resistors.

If the current load is variable, though, I suspect you\'re going to
have difficulty making it \"precise under load variation\". It looks as
if this circuit has a relatively high output impedance, due to the use
of those 10-ohm emitter degeneration resistors. The virtual ground is
going to bounce around considerably as the load changes.

We don\'t know his actual \"modded\" circuit, but the Sijosae splitters
that show up in google searches look awfully soft and sloppy.

Unless the supplies are super accurate, I can\'t see much virtue in a
precise splitter. Downstream circuits shouldn\'t care much.

The mod\'s whatever you guys say it is. Beings a Sijosae splitter seems
unpopular, give me an alternative, which works with parts typically
found in most parts drawers. The Sijosae splitter show below at the link
uses such parts:

https://tangentsoft.net/elec/bitmaps/vgrounds/sijosae.png

A virtual ground circuit to split a wall wart between positive and
negative rails is what\'s needed. This is for a proto-board, so it\'s
reasonable to expect a highly variable load.

Danke,

Stick the electrolytics on the output. Input filtering should be
minimal.

If you used an op amp, you could dump the diodes and emitter
resistors and \'decouple\' the reference in local feedback alone.

RL

 

[legg]

On Tue, 15 Dec 2020 02:19:55 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Dave Platt <dplatt@coop.radagast.org> wrote:
In article <ihuftfh1slneffn78vtj5lpljd5b6bmvsi@4ax.com>,
John Larkin <xx@yy.com> wrote:

We don\'t know his actual \"modded\" circuit, but the Sijosae splitters
that show up in google searches look awfully soft and sloppy.

One site I read described them as significantly better than a simple
resistive divider, but significantly worse than any other buffered
circuit they described (typically op-amp-based). Price-wise that\'s
about how they fall, too. I guess you get what you pay for.

Unless the supplies are super accurate, I can\'t see much virtue in a
precise splitter. Downstream circuits shouldn\'t care much.

We don\'t know the requirements of the downstream circuits, either -
why precision seemed to be called for.

It\'s for a proto-board with a variable load, which depends upon the
circuit breadboarded. This is the first circuit:

https://crcomp.net/paia/2720-2A.png

Danke,

In any event, the transistors will need to be capable of dissipating
full worst-case Iload x Vin/2.

RL

 

[Don]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

On 12/14/20 8:43 PM, Dave Platt wrote:
In article <ihuftfh1slneffn78vtj5lpljd5b6bmvsi@4ax.com>,
John Larkin <xx@yy.com> wrote:

We don\'t know his actual \"modded\" circuit, but the Sijosae splitters
that show up in google searches look awfully soft and sloppy.

One site I read described them as significantly better than a simple
resistive divider, but significantly worse than any other buffered
circuit they described (typically op-amp-based). Price-wise that\'s
about how they fall, too. I guess you get what you pay for.

Unless the supplies are super accurate, I can\'t see much virtue in a
precise splitter. Downstream circuits shouldn\'t care much.

We don\'t know the requirements of the downstream circuits, either -
why precision seemed to be called for.



A resistive divider and a TCA0372.

Unfortunately, there\'s nary a TCA0372 available in my parts bin. But,
there\'s a LM317, LM337, and a 3.3 V zener diode available, along with a
19 VDC wall wart from the bone pile. Beings so many think the Sijosae
splitter stinks, it may behoove me to move on to an adaptation of this
circuit:

https://i.stack.imgur.com/kPjJF.jpg

Danke,

--
Don, 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.

 

[server]

On Tue, 15 Dec 2020 03:32:46 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
On 12/14/20 8:43 PM, Dave Platt wrote:
In article <ihuftfh1slneffn78vtj5lpljd5b6bmvsi@4ax.com>,
John Larkin <xx@yy.com> wrote:

We don\'t know his actual \"modded\" circuit, but the Sijosae splitters
that show up in google searches look awfully soft and sloppy.

One site I read described them as significantly better than a simple
resistive divider, but significantly worse than any other buffered
circuit they described (typically op-amp-based). Price-wise that\'s
about how they fall, too. I guess you get what you pay for.

Unless the supplies are super accurate, I can\'t see much virtue in a
precise splitter. Downstream circuits shouldn\'t care much.

We don\'t know the requirements of the downstream circuits, either -
why precision seemed to be called for.



A resistive divider and a TCA0372.

Unfortunately, there\'s nary a TCA0372 available in my parts bin. But,
there\'s a LM317, LM337, and a 3.3 V zener diode available, along with a
19 VDC wall wart from the bone pile. Beings so many think the Sijosae
splitter stinks, it may behoove me to move on to an adaptation of this
circuit:

https://i.stack.imgur.com/kPjJF.jpg

Danke,

Use two warts, or two 9 volt batteries.



--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.

 

[Don]

legg <legg@nospam.magma.ca> wrote:
> On Tue, 15 Dec 2020 01:07:53 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

<snip>

A virtual ground circuit to split a wall wart between positive and
negative rails is what\'s needed. This is for a proto-board, so it\'s
reasonable to expect a highly variable load.

Stick the electrolytics on the output. Input filtering should be
minimal.

If you used an op amp, you could dump the diodes and emitter
resistors and \'decouple\' the reference in local feedback alone.

There\'s nary a LM337 available to me, so this is it. Back to the
original Sijosae splitter. How does this circuit look?

https://crcomp.net/sijosae/schematic.png

Danke,

--
Don, 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.

 

[Phil Hobbs]

On 12/14/20 10:32 PM, Don wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
On 12/14/20 8:43 PM, Dave Platt wrote:
In article <ihuftfh1slneffn78vtj5lpljd5b6bmvsi@4ax.com>,
John Larkin <xx@yy.com> wrote:

We don\'t know his actual \"modded\" circuit, but the Sijosae splitters
that show up in google searches look awfully soft and sloppy.

One site I read described them as significantly better than a simple
resistive divider, but significantly worse than any other buffered
circuit they described (typically op-amp-based). Price-wise that\'s
about how they fall, too. I guess you get what you pay for.

Unless the supplies are super accurate, I can\'t see much virtue in a
precise splitter. Downstream circuits shouldn\'t care much.

We don\'t know the requirements of the downstream circuits, either -
why precision seemed to be called for.



A resistive divider and a TCA0372.

Unfortunately, there\'s nary a TCA0372 available in my parts bin. But,
there\'s a LM317, LM337, and a 3.3 V zener diode available, along with a
19 VDC wall wart from the bone pile. Beings so many think the Sijosae
splitter stinks, it may behoove me to move on to an adaptation of this
circuit:

https://i.stack.imgur.com/kPjJF.jpg

Danke,

You can get a TCA0372 or L270 in a day, or wrap a class-B amp made from
an NPN + PNP complementary follower inside the feedback loop of a 741.
Either would be a lot better than a crude class-AB splitter made from
two vregs.

Put a resistor from the bases to the emitters of the follower to take
the current at low load.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[piglet]

On 15/12/2020 6:55 am, Don wrote:

legg <legg@nospam.magma.ca> wrote:
On Tue, 15 Dec 2020 01:07:53 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

snip

A virtual ground circuit to split a wall wart between positive and
negative rails is what\'s needed. This is for a proto-board, so it\'s
reasonable to expect a highly variable load.

Stick the electrolytics on the output. Input filtering should be
minimal.

If you used an op amp, you could dump the diodes and emitter
resistors and \'decouple\' the reference in local feedback alone.

There\'s nary a LM337 available to me, so this is it. Back to the
original Sijosae splitter. How does this circuit look?

https://crcomp.net/sijosae/schematic.png

Danke,

That is close. You want 100% negative feedback not positive so check the
op-amp inputs. The 10k R3 R4 are unnecessary. As Phil Hobbs wrote in a
side thread have a resistor from bases to emitters so the op-amp can
supply light load currents - somewhere from a few hundred ohms to a
kilo-ohm should be about right. Happy splitting!

piglet

 

[Steve Wilson]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

On 12/14/20 10:32 PM, Don wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
On 12/14/20 8:43 PM, Dave Platt wrote:
In article <ihuftfh1slneffn78vtj5lpljd5b6bmvsi@4ax.com>,
John Larkin <xx@yy.com> wrote:

We don\'t know his actual \"modded\" circuit, but the Sijosae
splitters that show up in google searches look awfully soft and
sloppy.

One site I read described them as significantly better than a
simple resistive divider, but significantly worse than any other
buffered circuit they described (typically op-amp-based).
Price-wise that\'s about how they fall, too. I guess you get what
you pay for.

Unless the supplies are super accurate, I can\'t see much virtue in
a precise splitter. Downstream circuits shouldn\'t care much.

We don\'t know the requirements of the downstream circuits, either -
why precision seemed to be called for.



A resistive divider and a TCA0372.

Unfortunately, there\'s nary a TCA0372 available in my parts bin. But,
there\'s a LM317, LM337, and a 3.3 V zener diode available, along with
a 19 VDC wall wart from the bone pile. Beings so many think the
Sijosae splitter stinks, it may behoove me to move on to an
adaptation of this circuit:

https://i.stack.imgur.com/kPjJF.jpg

Danke,


You can get a TCA0372 or L270 in a day, or wrap a class-B amp made
from an NPN + PNP complementary follower inside the feedback loop of a
741. Either would be a lot better than a crude class-AB splitter made
from two vregs.

Put a resistor from the bases to the emitters of the follower to take
the current at low load.

Cheers

Phil Hobbs

Nobody uses 741\'s any more.

Adding a resistor is not so simple. The basic circuit has a lot of
distortion. This would create havoc in a feedback circuit at high
frequency or at DC with transients in the load.

Version 4
SHEET 1 1608 1700
WIRE 704 80 592 80
WIRE 592 96 592 80
WIRE 704 96 704 80
WIRE 384 144 320 144
WIRE 448 144 384 144
WIRE 528 144 448 144
WIRE 320 160 320 144
WIRE 704 192 704 176
WIRE 448 224 448 144
WIRE 480 224 448 224
WIRE 592 224 592 192
WIRE 592 224 560 224
WIRE 672 224 592 224
WIRE 784 224 672 224
WIRE 784 240 784 224
WIRE 320 256 320 240
WIRE 592 256 592 224
WIRE 448 304 448 224
WIRE 528 304 448 304
WIRE 784 336 784 320
WIRE 592 368 592 352
WIRE 592 464 592 448
FLAG 320 256 0
FLAG 592 464 0
FLAG 704 192 0
FLAG 784 336 0
FLAG 384 144 Vin
FLAG 672 224 Vout
SYMBOL voltage 320 144 R0
WINDOW 3 -53 150 Left 2
WINDOW 123 24 38 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 10 1e7)
SYMATTR Value2 AC 1
SYMATTR InstName V1
SYMBOL npn 528 96 R0
SYMATTR InstName Q1
SYMATTR Value 2N2222
SYMBOL pnp 528 352 M180
SYMATTR InstName Q2
SYMATTR Value 2N2907
SYMBOL voltage 592 464 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value {VCC}
SYMBOL voltage 704 80 R0
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value {VCC}
SYMBOL res 768 224 R0
SYMATTR InstName R1
SYMATTR Value 50
SYMBOL res 464 208 M90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 50
TEXT 376 -24 Left 2 ;\'Complimentary Follower
TEXT 376 0 Left 2 !.tran 0 250n 0
TEXT 552 0 Left 2 !.param VCC = 12

For low distortion at high frequency, or fast load transients at DC, a
full complimentary driver looks much better.

Version 4
SHEET 1 1608 1700
WIRE 384 80 368 80
WIRE 512 80 464 80
WIRE 592 80 512 80
WIRE 704 80 592 80
WIRE 592 96 592 80
WIRE 704 96 704 80
WIRE 368 144 368 80
WIRE 528 144 368 144
WIRE 224 192 160 192
WIRE 256 192 224 192
WIRE 304 192 256 192
WIRE 704 192 704 176
WIRE 160 208 160 192
WIRE 480 240 368 240
WIRE 592 256 592 192
WIRE 672 256 592 256
WIRE 784 256 672 256
WIRE 512 272 512 80
WIRE 512 272 368 272
WIRE 784 272 784 256
WIRE 160 304 160 288
WIRE 256 320 256 192
WIRE 304 320 256 320
WIRE 592 320 592 256
WIRE 528 368 368 368
WIRE 784 368 784 352
WIRE 368 448 368 368
WIRE 384 448 368 448
WIRE 480 448 480 240
WIRE 480 448 464 448
WIRE 592 448 592 416
WIRE 592 448 480 448
WIRE 592 464 592 448
WIRE 592 560 592 544
FLAG 160 304 0
FLAG 592 560 0
FLAG 704 192 0
FLAG 784 368 0
FLAG 224 192 Vin
FLAG 672 256 Vout
SYMBOL voltage 160 192 R0
WINDOW 3 -53 150 Left 2
WINDOW 123 24 38 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 2 1e6)
SYMATTR Value2 AC 1
SYMATTR InstName V1
SYMBOL npn 528 96 R0
SYMATTR InstName Q1
SYMATTR Value 2N2222
SYMBOL pnp 528 416 M180
SYMATTR InstName Q2
SYMATTR Value 2N2907
SYMBOL voltage 592 560 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value {VCC}
SYMBOL voltage 704 80 R0
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value {VCC}
SYMBOL res 768 256 R0
SYMATTR InstName R1
SYMATTR Value 50
SYMBOL pnp 304 240 M180
SYMATTR InstName Q3
SYMATTR Value 2N2907
SYMBOL npn 304 272 R0
SYMATTR InstName Q4
SYMATTR Value 2N2222
SYMBOL res 480 432 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 330
SYMBOL res 480 64 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 330
TEXT 376 -24 Left 2 ;\'Complimentary Driver / Follower
TEXT 376 0 Left 2 !.tran 0 2u 0
TEXT 552 0 Left 2 !.param VCC = 12





--
The best designs occur in the theta state. - sw

 

[Steve Wilson]

piglet <erichpwagner@hotmail.com> wrote:

On 15/12/2020 6:55 am, Don wrote:
legg <legg@nospam.magma.ca> wrote:
On Tue, 15 Dec 2020 01:07:53 -0000 (UTC), \"Don\" <g@crcomp.net
wrote:

snip

A virtual ground circuit to split a wall wart between positive and
negative rails is what\'s needed. This is for a proto-board, so it\'s
reasonable to expect a highly variable load.

Stick the electrolytics on the output. Input filtering should be
minimal.

If you used an op amp, you could dump the diodes and emitter
resistors and \'decouple\' the reference in local feedback alone.

There\'s nary a LM337 available to me, so this is it. Back to the
original Sijosae splitter. How does this circuit look?

https://crcomp.net/sijosae/schematic.png

Danke,


That is close. You want 100% negative feedback not positive so check
the op-amp inputs. The 10k R3 R4 are unnecessary. As Phil Hobbs wrote
in a side thread have a resistor from bases to emitters so the op-amp
can supply light load currents - somewhere from a few hundred ohms to
a kilo-ohm should be about right. Happy splitting!

piglet

The base resistor has to be a lot lower. The circuit has high distortion
and severe voltage loss from input to output. I repeat the LTspice
version I posted to Phil. Compare the input and output voltages.

Version 4
SHEET 1 1608 1700
WIRE 704 80 592 80
WIRE 592 96 592 80
WIRE 704 96 704 80
WIRE 384 144 320 144
WIRE 448 144 384 144
WIRE 528 144 448 144
WIRE 320 160 320 144
WIRE 704 192 704 176
WIRE 448 224 448 144
WIRE 480 224 448 224
WIRE 592 224 592 192
WIRE 592 224 560 224
WIRE 672 224 592 224
WIRE 784 224 672 224
WIRE 784 240 784 224
WIRE 320 256 320 240
WIRE 592 256 592 224
WIRE 448 304 448 224
WIRE 528 304 448 304
WIRE 784 336 784 320
WIRE 592 368 592 352
WIRE 592 464 592 448
FLAG 320 256 0
FLAG 592 464 0
FLAG 704 192 0
FLAG 784 336 0
FLAG 384 144 Vin
FLAG 672 224 Vout
SYMBOL voltage 320 144 R0
WINDOW 3 -53 150 Left 2
WINDOW 123 24 38 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 10 1e7)
SYMATTR Value2 AC 1
SYMATTR InstName V1
SYMBOL npn 528 96 R0
SYMATTR InstName Q1
SYMATTR Value 2N2222
SYMBOL pnp 528 352 M180
SYMATTR InstName Q2
SYMATTR Value 2N2907
SYMBOL voltage 592 464 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value {VCC}
SYMBOL voltage 704 80 R0
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value {VCC}
SYMBOL res 768 224 R0
SYMATTR InstName R1
SYMATTR Value 50
SYMBOL res 464 208 M90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 50
TEXT 376 -24 Left 2 ;\'Complimentary Follower
TEXT 376 0 Left 2 !.tran 0 250n 0
TEXT 552 0 Left 2 !.param VCC = 12

For low distortion at high frequency, or fast load transients at DC, a
full complimentary driver looks much better.

Version 4
SHEET 1 1608 1700
WIRE 384 80 368 80
WIRE 512 80 464 80
WIRE 592 80 512 80
WIRE 704 80 592 80
WIRE 592 96 592 80
WIRE 704 96 704 80
WIRE 368 144 368 80
WIRE 528 144 368 144
WIRE 224 192 160 192
WIRE 256 192 224 192
WIRE 304 192 256 192
WIRE 704 192 704 176
WIRE 160 208 160 192
WIRE 480 240 368 240
WIRE 592 256 592 192
WIRE 672 256 592 256
WIRE 784 256 672 256
WIRE 512 272 512 80
WIRE 512 272 368 272
WIRE 784 272 784 256
WIRE 160 304 160 288
WIRE 256 320 256 192
WIRE 304 320 256 320
WIRE 592 320 592 256
WIRE 528 368 368 368
WIRE 784 368 784 352
WIRE 368 448 368 368
WIRE 384 448 368 448
WIRE 480 448 480 240
WIRE 480 448 464 448
WIRE 592 448 592 416
WIRE 592 448 480 448
WIRE 592 464 592 448
WIRE 592 560 592 544
FLAG 160 304 0
FLAG 592 560 0
FLAG 704 192 0
FLAG 784 368 0
FLAG 224 192 Vin
FLAG 672 256 Vout
SYMBOL voltage 160 192 R0
WINDOW 3 -53 150 Left 2
WINDOW 123 24 38 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 2 1e6)
SYMATTR Value2 AC 1
SYMATTR InstName V1
SYMBOL npn 528 96 R0
SYMATTR InstName Q1
SYMATTR Value 2N2222
SYMBOL pnp 528 416 M180
SYMATTR InstName Q2
SYMATTR Value 2N2907
SYMBOL voltage 592 560 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value {VCC}
SYMBOL voltage 704 80 R0
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value {VCC}
SYMBOL res 768 256 R0
SYMATTR InstName R1
SYMATTR Value 50
SYMBOL pnp 304 240 M180
SYMATTR InstName Q3
SYMATTR Value 2N2907
SYMBOL npn 304 272 R0
SYMATTR InstName Q4
SYMATTR Value 2N2222
SYMBOL res 480 432 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 330
SYMBOL res 480 64 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 330
TEXT 376 -24 Left 2 ;\'Complimentary Driver / Follower
TEXT 376 0 Left 2 !.tran 0 2u 0
TEXT 552 0 Left 2 !.param VCC = 12

The basic circuit creates havoc in a feedback circuit. It requires an op
amp with a GBW 25 times the operating frequency. Compare the input
voltage, the output voltage, and the output of the op amp. Then lower
the GBW of the op amp to 1MHz and view the distortion. The basic circuit
demands high performance from the op amp. For comparison, look at the
full complimentary driver just above for input and output voltages and
distortion.

Version 4
SHEET 1 1608 1700
WIRE 784 32 256 32
WIRE 592 80 320 80
WIRE 704 80 592 80
WIRE 592 96 592 80
WIRE 704 96 704 80
WIRE 320 112 320 80
WIRE 256 128 256 32
WIRE 288 128 256 128
WIRE 400 144 352 144
WIRE 448 144 400 144
WIRE 528 144 448 144
WIRE 192 160 128 160
WIRE 288 160 192 160
WIRE 128 176 128 160
WIRE 704 192 704 176
WIRE 448 224 448 144
WIRE 480 224 448 224
WIRE 592 224 592 192
WIRE 592 224 560 224
WIRE 672 224 592 224
WIRE 784 224 784 32
WIRE 784 224 672 224
WIRE 784 240 784 224
WIRE 592 256 592 224
WIRE 128 272 128 256
WIRE 448 304 448 224
WIRE 528 304 448 304
WIRE 784 336 784 320
WIRE 320 368 320 176
WIRE 592 368 592 352
WIRE 592 368 320 368
WIRE 592 384 592 368
WIRE 592 480 592 464
FLAG 128 272 0
FLAG 592 480 0
FLAG 704 192 0
FLAG 784 336 0
FLAG 192 160 Vin
FLAG 672 224 Vout
FLAG 400 144 U1O
SYMBOL voltage 128 160 R0
WINDOW 3 -53 150 Left 2
WINDOW 123 24 38 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 2 1e6)
SYMATTR Value2 AC 1
SYMATTR InstName V1
SYMBOL npn 528 96 R0
SYMATTR InstName Q1
SYMATTR Value 2N2222
SYMBOL pnp 528 352 M180
SYMATTR InstName Q2
SYMATTR Value 2N2907
SYMBOL voltage 592 480 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value {VCC}
SYMBOL voltage 704 80 R0
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value {VCC}
SYMBOL res 768 224 R0
SYMATTR InstName R1
SYMATTR Value 50
SYMBOL res 464 208 M90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 50
SYMBOL opamps\\\\universalopamp2 320 144 R0
SYMATTR InstName U1
SYMATTR Value2 Avol=1Meg GBW=25Meg Slew=25Meg
TEXT 376 -24 Left 2 ;\'Complimentary Follower With Feedback
TEXT 376 0 Left 2 !.tran 0 2u 0
TEXT 552 0 Left 2 !.param VCC = 12





--
The best designs occur in the theta state. - sw

 

[Steve Wilson]

Was:

Then lower
the GBW of the op amp to 1MHz and view the distortion.

S.B.

Then lower the GBW and slew rate of the op amp to 1MHz and view the
distortion.

 

[Phil Hobbs]

On 12/15/20 6:58 AM, Steve Wilson wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

On 12/14/20 10:32 PM, Don wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
On 12/14/20 8:43 PM, Dave Platt wrote:
In article <ihuftfh1slneffn78vtj5lpljd5b6bmvsi@4ax.com>,
John Larkin <xx@yy.com> wrote:

We don\'t know his actual \"modded\" circuit, but the Sijosae
splitters that show up in google searches look awfully soft and
sloppy.

One site I read described them as significantly better than a
simple resistive divider, but significantly worse than any other
buffered circuit they described (typically op-amp-based).
Price-wise that\'s about how they fall, too. I guess you get what
you pay for.

Unless the supplies are super accurate, I can\'t see much virtue in
a precise splitter. Downstream circuits shouldn\'t care much.

We don\'t know the requirements of the downstream circuits, either -
why precision seemed to be called for.



A resistive divider and a TCA0372.

Unfortunately, there\'s nary a TCA0372 available in my parts bin. But,
there\'s a LM317, LM337, and a 3.3 V zener diode available, along with
a 19 VDC wall wart from the bone pile. Beings so many think the
Sijosae splitter stinks, it may behoove me to move on to an
adaptation of this circuit:

https://i.stack.imgur.com/kPjJF.jpg

Danke,


You can get a TCA0372 or L270 in a day, or wrap a class-B amp made
from an NPN + PNP complementary follower inside the feedback loop of a
741. Either would be a lot better than a crude class-AB splitter made
from two vregs.

Put a resistor from the bases to the emitters of the follower to take
the current at low load.

Cheers

Phil Hobbs

Nobody uses 741\'s any more.

Of course they don\'t--I was teasing Don about his fixation with his junkbox.

Adding a resistor is not so simple. The basic circuit has a lot of
distortion. This would create havoc in a feedback circuit at high
frequency or at DC with transients in the load

Which is why you put a BFC on it, the way you would any regulator,
including the TCA0372.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[legg]

On Tue, 15 Dec 2020 06:55:38 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

legg <legg@nospam.magma.ca> wrote:
On Tue, 15 Dec 2020 01:07:53 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

snip

A virtual ground circuit to split a wall wart between positive and
negative rails is what\'s needed. This is for a proto-board, so it\'s
reasonable to expect a highly variable load.

Stick the electrolytics on the output. Input filtering should be
minimal.

If you used an op amp, you could dump the diodes and emitter
resistors and \'decouple\' the reference in local feedback alone.

There\'s nary a LM337 available to me, so this is it. Back to the
original Sijosae splitter. How does this circuit look?

https://crcomp.net/sijosae/schematic.png

Danke,

Check the op amp input polarity.

You don\'t need R3 and R4, but with the feedback correctly inverting
you can slow the op amp down some with an input resistor and local
feedback cap around the op amp. you can degenerate the DC gain a
couple of tens of mV.

The electrolytics do the transient response, the op amp only has to
do low frequency DC. No point having the circuit oscillate
unnecessarily an light or no load - this would just consume power..

A resistor in the collectors of the transistors will improve their
ability to dissipate power and avoid a potential silicon short.

RL