Purpose of precision high-current series regulator's resisto

[Don Kuenz]

This question was originally posted to piclist.

The TL431 datasheet contains "Figure 29. Precision High-Current Series
Regulator." What's the purpose of the 30 Ω resistor, the 4.7 kΩ
resistor, and the 0.01 ÎźF capacitor?

Thank you,

--
Don Kuenz 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.

 

[speff]

On Tuesday, 11 February 2020 21:43:48 UTC-5, Don Kuenz wrote:

This question was originally posted to piclist.

The TL431 datasheet contains "Figure 29. Precision High-Current Series
Regulator." What's the purpose of the 30 Ω resistor, the 4.7 kΩ
resistor, and the 0.01 ÎźF capacitor?

Hi, Don:-

There is no "the" TL431 datasheet, as there are multiple versions from TI and at least 8 manufacturers (and probably a few more in China).

But presumably this is the schematic: https://i.imgur.com/AyaTqke.png

The 4.7K is to keep the output 2N222 from amplifying the leakage in the
other 2N222.

The other parts are for stability.The 30 ohm for keeping the Darlington
from going all Colpitts on us and the cap to keep the TL431 happy.

I'm sure someone will point out if this explanation is lacking or
incorrect in some way. ;-)

I'm not sure the 4.7K and 30 ohm are actually necessary.

Best regards,
Spehro Pefhany

 

[Don Kuenz]

speff <spehro@gmail.com> wrote:

On Tuesday, 11 February 2020 21:43:48 UTC-5, Don Kuenz wrote:
This question was originally posted to piclist.

The TL431 datasheet contains "Figure 29. Precision High-Current Series
Regulator." What's the purpose of the 30 Ω resistor, the 4.7 kΩ
resistor, and the 0.01 ÎźF capacitor?

Hi, Don:-

There is no "the" TL431 datasheet, as there are multiple versions from TI and
at least 8 manufacturers (and probably a few more in China).

But presumably this is the schematic: https://i.imgur.com/AyaTqke.png

The 4.7K is to keep the output 2N222 from amplifying the leakage in the
other 2N222.

The other parts are for stability.The 30 ohm for keeping the Darlington
from going all Colpitts on us and the cap to keep the TL431 happy.

I'm sure someone will point out if this explanation is lacking or
incorrect in some way. ;-)

I'm not sure the 4.7K and 30 ohm are actually necessary.

It may be worthy of a simulation while we wait for the critics.

Thank you,

--
Don Kuenz 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.

 

[Steve Wilson]

speff <spehro@gmail.com> wrote:

On Tuesday, 11 February 2020 21:43:48 UTC-5, Don Kuenz wrote:
This question was originally posted to piclist.

The TL431 datasheet contains "Figure 29. Precision High-Current Series
Regulator." What's the purpose of the 30 Ω resistor, the 4.7 kÎ Š
resistor, and the 0.01 ÎźF capacitor?

Hi, Don:-

There is no "the" TL431 datasheet, as there are multiple versions from
TI and at least 8 manufacturers (and probably a few more in China).

But presumably this is the schematic: https://i.imgur.com/AyaTqke.png

The 4.7K is to keep the output 2N222 from amplifying the leakage in the
other 2N222.

The other parts are for stability.The 30 ohm for keeping the Darlington
from going all Colpitts on us and the cap to keep the TL431 happy.

I'm sure someone will point out if this explanation is lacking or
incorrect in some way. ;-)

I'm not sure the 4.7K and 30 ohm are actually necessary.

Best regards,
Spehro Pefhany

The url is http://www.ti.com/lit/ds/symlink/tl431.pdf

No, they are not. In fact, the first 2N2222 (emitter follower) is not
necessary. The pass transistor can supply only a limited current, perhaps
50 mA at 80C, so a darlington is not needed.

The TL431 uses a bandgap reference and is extremely noisy, around
450nV/root Hz at 10 Hz, with a pronounced peak just above 10 KHz.

However, Fig 29 can be modified to bring the noise down to 3.3nV/root Hz at
1 Hz, and 0.6nV/root Hz at 10 Hz. Here is a 5V regulator in LTspice:

Version 4
SHEET 1 1608 1700
WIRE -464 48 -480 48
WIRE -352 48 -464 48
WIRE 96 48 -352 48
WIRE -480 64 -480 48
WIRE -352 64 -352 48
WIRE 96 112 96 48
WIRE -480 160 -480 144
WIRE -352 160 -352 144
WIRE -320 160 -352 160
WIRE -288 160 -320 160
WIRE -176 160 -208 160
WIRE -96 160 -176 160
WIRE -16 160 -96 160
WIRE 32 160 -16 160
WIRE -176 176 -176 160
WIRE -96 176 -96 160
WIRE -16 176 -16 160
WIRE -176 256 -176 240
WIRE -96 256 -96 240
WIRE -16 256 -16 240
WIRE -352 288 -352 160
WIRE -320 288 -352 288
WIRE -240 288 -256 288
WIRE -352 320 -352 288
WIRE -304 352 -320 352
WIRE -240 352 -240 288
WIRE -240 352 -304 352
WIRE -176 352 -240 352
WIRE -112 352 -176 352
WIRE 96 352 96 208
WIRE 96 352 -32 352
WIRE 144 352 96 352
WIRE 160 352 144 352
WIRE 96 368 96 352
WIRE -176 384 -176 352
WIRE -352 400 -352 384
WIRE 96 464 96 448
WIRE -176 480 -176 464
FLAG -352 400 0
FLAG 96 464 0
FLAG -16 160 Q1B
FLAG 144 352 Vout
FLAG -304 352 U1B
FLAG -464 48 VCC
FLAG -176 480 0
FLAG -480 160 0
FLAG -320 160 U1C
FLAG -176 256 0
FLAG -16 256 0
FLAG -96 256 0
SYMBOL npn 32 112 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL res 80 352 R0
SYMATTR InstName R1
SYMATTR Value 470
SYMBOL cap -192 176 R0
SYMATTR InstName C1
SYMATTR Value 1000uf
SYMATTR SpiceLine Rser=12m Lser=10n Rpar=3e6 Cpar=3e-9
SYMBOL voltage -480 48 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 10
SYMBOL res -336 160 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res -192 368 R0
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL res -16 336 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 10k
SYMBOL res -192 144 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL TL431AS -352 352 M0
SYMATTR InstName X1
SYMBOL cap -256 272 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 1000uf
SYMATTR SpiceLine Rser=12m Lser=10n Rpar=3e6 Cpar=3e-9
SYMBOL cap -112 176 R0
SYMATTR InstName C3
SYMATTR Value 1000uf
SYMATTR SpiceLine Rser=12m Lser=10n Rpar=3e6 Cpar=3e-9
SYMBOL cap -32 176 R0
SYMATTR InstName C4
SYMATTR Value 1000uf
SYMATTR SpiceLine Rser=12m Lser=10n Rpar=3e6 Cpar=3e-9
TEXT -488 -64 Left 2 ;'TL431 Noise Spectrum
TEXT -88 -32 Left 2 !.lib TL431AS.lib
TEXT -488 -32 Left 2 !.noise V(vout) V1 oct 1000 1 1e6

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[Noise Spectral Density - (V/Hz˝ or A/Hz˝)]
{
Npanes: 1
{
traces: 1 {524290,0,"V(onoise)"}
X: ('M',0,1,0,1e+006)
Y[0]: ('n',1,5e-010,5e-010,6.5e-009)
Y[1]: ('_',0,1e+308,0,-1e+308)
Units: "V/Hz˝" ('n',0,0,1,5e-010,5e-010,6.5e-009)
Log: 1 0 0
GridStyle: 1
}
}
[AC Analysis]
{
Npanes: 1
{
traces: 1 {524290,0,"V(vout)"}
X: ('M',1,0.001,0,1e+007)
Y[0]: (' ',0,1.99526231496888e-006,6,0.00398107170553497)
Y[1]: (' ',0,80,20,280)
Volts: (' ',0,0,5,2.500764,6e-006,2.500842)
Amps: ('m',0,0,4,0.01000308,2e-008,0.01000334)
Log: 1 2 0
GridStyle: 1
PltMag: 1
}
}
[Transient Analysis]
{
Npanes: 1
{
traces: 1 {589827,0,"V(vout)"}
X: (' ',1,0,0.2,2)
Y[0]: (' ',4,4.9938,0.0001,4.9952)
Y[1]: ('m',4,1e+308,3e-007,-1e+308)
Volts: (' ',0,0,4,4.9938,0.0001,4.9952)
Log: 0 0 0
GridStyle: 1
PltMag: 1
PltPhi: 1 0
}
}

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* TL431AS.lib
* Models have been edited for LTspice syntax, but are otherwise per
originals

* Model developed by analogspiceman
**************************************************
..subckt TL431AS A K R ; Anode Kathode Reference
D1 R K Dc
R1 A R 1.3e6 tc1=3m
G1 A 5 R 4 1
C1 5 A 1n Rpar=600
D2 7 R Dc
D3 7 4 Dn
R2 7 4 950k
R3 6 5 600k
D4 A 6 Di
C2 K 6 40p Rser=5k Rpar=1e6
G2 K 7 6 A 95m
D5 A 7 2V5
D6 7 A Dk
C3 7 A 50p
D7 A K Dc
..model Dc d Ron=10 Vfwd=0.65 Vrev=36 Epsilon=50m
..model Dn d Is=1p Kf=0p2 Cjo=0p3
..model Di d Ron=10m epsilon=1m
..model Dk d Ron=5k7 Vfwd=0.8 Epsilon=0.5
..model 2V5 d Ron=27m Vfwd=0.6 Epsilon=10m Vrev={Vr} revEpsilon=10m
..param Vr=2.5+dt*(95u-dt*2u6) dt=temp-10
..ends TL431AS

 

[Steve Wilson]

Steve Wilson <no@spam.com> wrote:

speff <spehro@gmail.com> wrote:

On Tuesday, 11 February 2020 21:43:48 UTC-5, Don Kuenz wrote:
This question was originally posted to piclist.

The TL431 datasheet contains "Figure 29. Precision High-Current Series
Regulator." What's the purpose of the 30 Ω resistor, the 4.7 kÎ Š
resistor, and the 0.01 ÎźF capacitor?

Hi, Don:-

There is no "the" TL431 datasheet, as there are multiple versions from
TI and at least 8 manufacturers (and probably a few more in China).

But presumably this is the schematic: https://i.imgur.com/AyaTqke.png

The 4.7K is to keep the output 2N222 from amplifying the leakage in the
other 2N222.

The other parts are for stability.The 30 ohm for keeping the Darlington
from going all Colpitts on us and the cap to keep the TL431 happy.

I'm sure someone will point out if this explanation is lacking or
incorrect in some way. ;-)

I'm not sure the 4.7K and 30 ohm are actually necessary.

Best regards,
Spehro Pefhany

The url is http://www.ti.com/lit/ds/symlink/tl431.pdf

No, they are not. In fact, the first 2N2222 (emitter follower) is not
necessary. The pass transistor can supply only a limited current,
perhaps 50 mA at 80C, so a darlington is not needed.

The TL431 uses a bandgap reference and is extremely noisy, around
450nV/root Hz at 10 Hz, with a pronounced peak just above 10 KHz.

However, Fig 29 can be modified to bring the noise down to 3.3nV/root Hz
at 1 Hz, and 0.6nV/root Hz at 10 Hz. Here is a 5V regulator in LTspice:

Forgot the ASY and some other files. That's too many to handle, so here's
the whole thing zipped:

https://drive.google.com/open?id=162h1_AQ-rCfFou8LaHrKZOpMlGP1PgJP

This uses Helmut's model, and produces 2 nV/root Hz at 1 cycle.

 

[Chris Jones]

On 12/02/2020 21:24, Steve Wilson wrote:

Steve Wilson <no@spam.com> wrote:

speff <spehro@gmail.com> wrote:

On Tuesday, 11 February 2020 21:43:48 UTC-5, Don Kuenz wrote:
This question was originally posted to piclist.

The TL431 datasheet contains "Figure 29. Precision High-Current Series
Regulator." What's the purpose of the 30 Ω resistor, the 4.7 kÎ ©
resistor, and the 0.01 μF capacitor?

Hi, Don:-

There is no "the" TL431 datasheet, as there are multiple versions from
TI and at least 8 manufacturers (and probably a few more in China).

But presumably this is the schematic: https://i.imgur.com/AyaTqke.png

The 4.7K is to keep the output 2N222 from amplifying the leakage in the
other 2N222.

The other parts are for stability.The 30 ohm for keeping the Darlington
from going all Colpitts on us and the cap to keep the TL431 happy.

I'm sure someone will point out if this explanation is lacking or
incorrect in some way. ;-)

I'm not sure the 4.7K and 30 ohm are actually necessary.

Best regards,
Spehro Pefhany

The url is http://www.ti.com/lit/ds/symlink/tl431.pdf

No, they are not. In fact, the first 2N2222 (emitter follower) is not
necessary. The pass transistor can supply only a limited current,
perhaps 50 mA at 80C, so a darlington is not needed.

The TL431 uses a bandgap reference and is extremely noisy, around
450nV/root Hz at 10 Hz, with a pronounced peak just above 10 KHz.

However, Fig 29 can be modified to bring the noise down to 3.3nV/root Hz
at 1 Hz, and 0.6nV/root Hz at 10 Hz. Here is a 5V regulator in LTspice:

Forgot the ASY and some other files. That's too many to handle, so here's
the whole thing zipped:

https://drive.google.com/open?id=162h1_AQ-rCfFou8LaHrKZOpMlGP1PgJP

This uses Helmut's model, and produces 2 nV/root Hz at 1 cycle.

Hm. I think you might not really get that performance if you build it.
Base spreading resistance might be a problem and you might need at least
some special transistors to fix that.

 

[Winfield Hill]

Chris Jones wrote...

On 12/02/2020 21:24, Steve Wilson wrote:
Steve Wilson <no@spam.com> wrote:

speff <spehro@gmail.com> wrote:

On Tuesday, 11 February 2020 21:43:48 UTC-5, Don Kuenz wrote:
This question was originally posted to piclist.

The TL431 datasheet contains "Figure 29. Precision High-Current Series
Regulator." What's the purpose of the 30 Ω resistor, the 4.7 kÎ ©
resistor, and the 0.01 μF capacitor?

Hi, Don:-

There is no "the" TL431 datasheet, as there are multiple versions from
TI and at least 8 manufacturers (and probably a few more in China).

But presumably this is the schematic: https://i.imgur.com/AyaTqke.png

The 4.7K is to keep the output 2N222 from amplifying the leakage in the
other 2N222.

The other parts are for stability.The 30 ohm for keeping the Darlington
from going all Colpitts on us and the cap to keep the TL431 happy.

I'm sure someone will point out if this explanation is lacking or
incorrect in some way. ;-)

I'm not sure the 4.7K and 30 ohm are actually necessary.

Best regards,
Spehro Pefhany

The url is http://www.ti.com/lit/ds/symlink/tl431.pdf

No, they are not. In fact, the first 2N2222 (emitter follower) is not
necessary. The pass transistor can supply only a limited current,
perhaps 50 mA at 80C, so a darlington is not needed.

The TL431 uses a bandgap reference and is extremely noisy, around
450nV/root Hz at 10 Hz, with a pronounced peak just above 10 KHz.

However, Fig 29 can be modified to bring the noise down to 3.3nV/root Hz
at 1 Hz, and 0.6nV/root Hz at 10 Hz. Here is a 5V regulator in LTspice:

Forgot the ASY and some other files. That's too many to handle, so here's
the whole thing zipped:

https://drive.google.com/open?id=162h1_AQ-rCfFou8LaHrKZOpMlGP1PgJP

This uses Helmut's model, and produces 2 nV/root Hz at 1 cycle.

Hm. I think you might not really get that performance if you build it.
Base spreading resistance might be a problem and you might need at
least some special transistors to fix that.

Yep, much better parts in Table 8.1 in AoE3.

Also, the circuit model needs to be stable with an output capacitor.

--
Thanks,
- Win

 

[Steve Wilson]

Winfield Hill <winfieldhill@yahoo.com> wrote:

Chris Jones wrote...

On 12/02/2020 21:24, Steve Wilson wrote:
Steve Wilson <no@spam.com> wrote:

The url is http://www.ti.com/lit/ds/symlink/tl431.pdf

No, they are not. In fact, the first 2N2222 (emitter follower) is not
necessary. The pass transistor can supply only a limited current,
perhaps 50 mA at 80C, so a darlington is not needed.

The TL431 uses a bandgap reference and is extremely noisy, around
450nV/root Hz at 10 Hz, with a pronounced peak just above 10 KHz.

However, Fig 29 can be modified to bring the noise down to 3.3nV/root
Hz at 1 Hz, and 0.6nV/root Hz at 10 Hz. Here is a 5V regulator in
LTspice:

Forgot the ASY and some other files. That's too many to handle, so
here's the whole thing zipped:

https://drive.google.com/open?id=162h1_AQ-rCfFou8LaHrKZOpMlGP1PgJP

This uses Helmut's model, and produces 2 nV/root Hz at 1 cycle.

Hm. I think you might not really get that performance if you build it.
Base spreading resistance might be a problem and you might need at
least some special transistors to fix that.

Adding 50 ohms in series with the Q1 base increases the noise to 2.2 nV/Hz^
1/2. Base spreading resistance is not a problem.

The 2N3904 is a surprisingly good transistor. It also has an entry in both
LTspice IV and XVII

> Yep, much better parts in Table 8.1 in AoE3.

With Spice Models? What's wrong with 0.6 nV/Hz^1/2 at 10 Hz?

> Also, the circuit model needs to be stable with an output capacitor.

Adding a 1000uF from Vout to gnd drops the noise from 0.6 nV/Hz^1/2 to 0.02
nV/Hz^1/2 past 10 KHz.

The capacitors have 12 milliohms series resistance and 10 nH series
inductance.

The transient response shows 209uV overshoot with a 0.1V step at the input.
It damps out in 2 cycles. The output voltage settles 80uV higher.

 

[Michael Terrell]

On Tuesday, February 11, 2020 at 10:20:36 PM UTC-5, speff wrote:

There is no "the" TL431 datasheet, as there are multiple versions from TI and at least 8 manufacturers (and probably a few more in China).

But presumably this is the schematic: https://i.imgur.com/AyaTqke.png

The 4.7K is to keep the output 2N222 from amplifying the leakage in the
other 2N222.

Wasn't the 2N222 obsolete in 1970?

 

[Don Kuenz]

Michael Terrell <terrell.michael.a@gmail.com> wrote:

On Tuesday, February 11, 2020 at 10:20:36 PM UTC-5, speff wrote:

There is no "the" TL431 datasheet, as there are multiple versions from
TI and at least 8 manufacturers (and probably a few more in China).

But presumably this is the schematic: https://i.imgur.com/AyaTqke.png

The 4.7K is to keep the output 2N222 from amplifying the leakage in the
other 2N222.


Wasn't the 2N222 obsolete in 1970?

My 1974 Archer _Transistor Substitution Guide_ classifies the 2N222
as a PNP low power alloy-junction germanium transistor, which doesn't
jibe with the NPN transistors shown in the schematic.

Piclist's inimical Bob Blick says:

RB pinches off the base of the final transistor and makes
the Darlington configuration faster and more linear. RA
is called a base stopper and destroys the Q of what could
otherwise be a resonant circuit due to combination of the
output load on the regulator, interelectrode capacitances
in the transistors, and the output gain. Emitter followers
are quite susceptible to oscillation. C1 adds local
feedback to the TL431 to reduce its gain long before the
phase shift of the output transistors can cause a positive
feedback situation.

Basically, those three components all are there to give
stability. Depending on the type of load, they may not
be needed. The TL431 by itself is a pretty slow device,
but the writers of the app note probably wanted to
protect against a worst-case scenario.

BTW, there are lots of TL431 variations from different
manufacturers. Just because it's marked TL431 doesn't
mean it is anything like one from TI. Including the pinout

Thank you,

--
Don Kuenz 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.

 

[Michael Terrell]

On Wednesday, February 12, 2020 at 5:02:11 PM UTC-5, Don Kuenz wrote:

Michael Terrell wrote:
On Tuesday, February 11, 2020 at 10:20:36 PM UTC-5, speff wrote:

There is no "the" TL431 datasheet, as there are multiple versions from
TI and at least 8 manufacturers (and probably a few more in China).

But presumably this is the schematic: https://i.imgur.com/AyaTqke.png

The 4.7K is to keep the output 2N222 from amplifying the leakage in the
other 2N222.


Wasn't the 2N222 obsolete in 1970?

My 1974 Archer _Transistor Substitution Guide_ classifies the 2N222
as a PNP low power alloy-junction germanium transistor, which doesn't
jibe with the NPN transistors shown in the schematic.

Try adding the missing '2', 2N2222.

 

[Winfield Hill]

Steve Wilson wrote...

Winfield Hill <winfieldhill@yahoo.com> wrote:

Chris Jones wrote...

On 12/02/2020 21:24, Steve Wilson wrote:
Steve Wilson <no@spam.com> wrote:

Hm. I think you might not really get that performance if you
build it. Base spreading resistance might be a problem and
you might need at least some special transistors to fix that.

Adding 50 ohms in series with the Q1 base increases the noise
to 2.2 nV/Hz^1/2. Base spreading resistance is not a problem.

Yep, much better parts in Table 8.1 in AoE3.

With Spice Models? What's wrong with 0.6 nV/Hz^1/2 at 10 Hz?

SPICE models cannot nay-say bench measurements. As our table
shows, we measured 1.35 nV/rt-Hz for 2N3904 at 10mA; worse at
lower currents.** That's with Rs=0, r_bb'=110 ohms. With many
manufacturers of jelly-bean transistors, you will get noisier
ones (we used Fairchild and On Semi). Our table has 30 better
choices, and the manufacturer and process are more dependable.
Paul and I spent many many months buying transistors, making
laborious measurements, analyzing and presenting the data. So
make good use of it. Don't use SPICE models to deny reality.

** Much worse at 10Hz.


--
Thanks,
- Win

 

[Steve Wilson]

Winfield Hill <winfieldhill@yahoo.com> wrote:

Steve Wilson wrote...

Winfield Hill <winfieldhill@yahoo.com> wrote:

Chris Jones wrote...

On 12/02/2020 21:24, Steve Wilson wrote:
Steve Wilson <no@spam.com> wrote:

Hm. I think you might not really get that performance if you
build it. Base spreading resistance might be a problem and you
might need at least some special transistors to fix that.

Adding 50 ohms in series with the Q1 base increases the noise
to 2.2 nV/Hz^1/2. Base spreading resistance is not a problem.

Yep, much better parts in Table 8.1 in AoE3.

With Spice Models? What's wrong with 0.6 nV/Hz^1/2 at 10 Hz?

SPICE models cannot nay-say bench measurements. As our table
shows, we measured 1.35 nV/rt-Hz for 2N3904 at 10mA; worse at
lower currents.** That's with Rs=0, r_bb'=110 ohms. With many
manufacturers of jelly-bean transistors, you will get noisier
ones (we used Fairchild and On Semi). Our table has 30 better
choices, and the manufacturer and process are more dependable.
Paul and I spent many many months buying transistors, making
laborious measurements, analyzing and presenting the data. So
make good use of it. Don't use SPICE models to deny reality.

** Much worse at 10Hz.

Of course. This is perfectly obvious.

However, you are measuring the transistors alone. The LTspice simulation
uses the transistor in a feedback network with heavy filtering.

The TL431 model developed by Helmut specifically includes flicker and
broadband noise. This is low-pass filtered before it reaches the
transistor. The transistor output is fed back to the TL431. The transistor
model is supplied by NXP, which you do not use. There is no way to compare
the simulation results with your measurements.

Adding a 1000uF cap from Vout to gnd significantly reduces the noise. You
do not add capacitors to filter the output of your measurements.

The simulation is essential to tell you if a circuit is worth spending time
on the bench. It is invaluable to help troubleshooting when something goes
wrong on the bench. It allows you to evaluate different component
parameters and see which ones are critical to obtaining the desired
results. It allows you to optimize the circuit and components for best
performance. You can examine the open-loop response in a feedback circuit
and optimize the loop gain, and gain and phase margin. This can be
difficult or impossible to do on the bench.

Bench work only tells you the results of one particular set of components.
It can be difficult and time-consuming to change components. You may have
to fight noise, poor connections, unwanted oscillations, test equipment
limitations, bad components, and a host of other problems that interfere
with your evaluation. You may lack the equipment needed to make critical
measurements that you can easily do in simulation.

Don't deny the value of simulation.

 

[Steve Wilson]

Winfield Hill <winfieldhill@yahoo.com> wrote:

Steve Wilson wrote...

[ snip ]

I think you'd better build one.

Of course. The LTspice results definitely show it is worthwhile.

It would be extremely useful for ultra low noise applications, such as GPSDO
OCXO'S.

Much better than a LM317, or even a barefoot TL431.

Maybe you should try it.

 

[Winfield Hill]

Steve Wilson wrote...

[ snip ]

I think you'd better build one.


--
Thanks,
- Win

 

[Steve Wilson]

Steve Wilson <no@spam.com> wrote:

Winfield Hill <winfieldhill@yahoo.com> wrote:

Steve Wilson wrote...

[ snip ]

I think you'd better build one.

Of course. The LTspice results definitely show it is worthwhile.

It would be extremely useful for ultra low noise applications, such as
GPSDO OCXO'S.

Much better than a LM317, or even a barefoot TL431.

Maybe you should try it.

Good News! A trivial change to the circuit eliminates the 2-cycle ringing,
and brings the noise down to 920 pV/root Hz at 1 Hz, 450 pV/root Hz at 10 Hz,
and 15 pV/root Hz at 10 KHz and beyond.

I will definitely have to use Gerhard's parallel LT1028 preamplifier to
measure the noise. Even then, I don't think I will be able to measure much
beyond 100 Hz.

 

[Winfield Hill]

Steve Wilson wrote...

Good News! A trivial change to the circuit ...

What is the change?

I will definitely have to use Gerhard's parallel
LT1028 preamplifier to measure the noise.

Or you could use the 80 pV/rt-Hz circuit in AoE 3.

Have you made any measurements yet? It's possible
that your SPICE model may be completely wrong, and
there will be no need for any special low-noise
preamp to take the measurement.


--
Thanks,
- Win

 

[Steve Wilson]

Winfield Hill <winfieldhill@yahoo.com> wrote:

Steve Wilson wrote...

Good News! A trivial change to the circuit ...

What is the change?

See the zip file

I will definitely have to use Gerhard's parallel
LT1028 preamplifier to measure the noise.

Or you could use the 80 pV/rt-Hz circuit in AoE 3.

That is rediculous. It is intended for ribbon microphones, with a source
resistance of 0.2 Ohms. It is also too noisy.

> Have you made any measurements yet?

The noise is too low to measure. All the other measurements are
satisfactory.

It's possible
that your SPICE model may be completely wrong, and
there will be no need for any special low-noise
preamp to take the measurement.

After 40 years running SPICE, it is more likely the results are highly
accurate, and offer performance you could never dream of.

Hundreds of thousands of engineers have been taught SPICE in colleges and
universities. How did you miss out?

https://drive.google.com/open?id=162h1_AQ-rCfFou8LaHrKZOpMlGP1PgJP

 

[Phil Hobbs]

On 2020-02-21 07:00, Steve Wilson wrote:

Winfield Hill <winfieldhill@yahoo.com> wrote:

Steve Wilson wrote...

Good News! A trivial change to the circuit ...

What is the change?

See the zip file

I will definitely have to use Gerhard's parallel
LT1028 preamplifier to measure the noise.

Or you could use the 80 pV/rt-Hz circuit in AoE 3.

That is rediculous. It is intended for ribbon microphones, with a source
resistance of 0.2 Ohms. It is also too noisy.

Have you made any measurements yet?

The noise is too low to measure. All the other measurements are
satisfactory.

It's possible
that your SPICE model may be completely wrong, and
there will be no need for any special low-noise
preamp to take the measurement.

After 40 years running SPICE, it is more likely the results are highly
accurate, and offer performance you could never dream of.

Hundreds of thousands of engineers have been taught SPICE in colleges and
universities. How did you miss out?

https://drive.google.com/open?id=162h1_AQ-rCfFou8LaHrKZOpMlGP1PgJP

Steve, did you realize whom you were replying to? Some major fraction
of those hundreds of thousands have been taught out of AoE. I mean, a
healthy ego is one thing....

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

 

[Phil Hobbs]

On 2020-02-21 15:03, Steve Wilson wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-02-21 07:00, Steve Wilson wrote:
Winfield Hill <winfieldhill@yahoo.com> wrote:

Steve Wilson wrote...

Good News! A trivial change to the circuit ...

What is the change?

See the zip file

I will definitely have to use Gerhard's parallel
LT1028 preamplifier to measure the noise.

Or you could use the 80 pV/rt-Hz circuit in AoE 3.

That is rediculous. It is intended for ribbon microphones, with a
source resistance of 0.2 Ohms. It is also too noisy.

Have you made any measurements yet?

The noise is too low to measure. All the other measurements are
satisfactory.

It's possible
that your SPICE model may be completely wrong, and
there will be no need for any special low-noise preamp to take the
measurement.

After 40 years running SPICE, it is more likely the results are highly
accurate, and offer performance you could never dream of.

Hundreds of thousands of engineers have been taught SPICE in colleges
and universities. How did you miss out?

https://drive.google.com/open?id=162h1_AQ-rCfFou8LaHrKZOpMlGP1PgJP

Steve, did you realize whom you were replying to? Some major fraction
of those hundreds of thousands have been taught out of AoE. I mean, a
healthy ego is one thing....

Many others were taught ot of Terman, Radiation Labs, Radiotron Designer's
Handbook, various engineering magazines, etc.

AOE discusses Intusoft ICAP, but never seems to use it anywhere in the
thousands of opportunities throughout the text. This could have vastly
increased the value of AOE, especially if LTspice were used instead of
ICAP.

In this day and age, lack of skills in LTspice is a career-limiting move.

Those who learned from AOE are at a severe disadvantage.

I was looking to give you a way to climb down honourably, but if you
want to double down instead, well, you do that.

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