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Re: 100mV DC supply
On Thursday, July 13, 2017 at 12:13:23 PM UTC-4, John Larkin wrote:
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ote:
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able of sourcing up to ~50mA but will typically see high impedance. Easily  
available I have a clean 24V source and 208VAC. My intent is to drop from 2
4V to ~1.8V using a buck converter then follow it up with a 1.0V precision  
shunt (ADR510 or other) followed by a 9:1 precision resistor divider. Buffe
r the 100mV output by a low noise single supply op-amp such as ltc1014. Alt
hough it looks like ltc1014 won't be able to source enough current so possi
bly followed with a BJT?
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ion and +/- 3mV should be good enough. The environment the board will resid
e in is ~25C +/- 5deg. The output voltage must not drift above ~130mV to pr
event causing issues in the test chamber.  
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le active = 1kHz) and multiplied by 10x before being sampled. The low pas
s filter frequency is chosen to preserve rise times in the ~500uS range.  
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hunt (70ppm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but fr
om the 5 foot run of cable to the test chamber and back and am interested i
n best practice shielding techniques to mitigate induced noise.  
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hing similar to this before so I'm interested in hearing about other possib
le topologies that can meet the requirements or how others would approach t
he problem. The solution will be put onto a pcb as part of a larger circuit
 so i cannot use a benchtop supply.  
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IC and 3 resistors. The resistors are 120ohm, 82ohm and 1ohm - all 1% types
.
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eries across 5V.
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mpedance and  a SCC of 100mA.  
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bility.  
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mA  
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.

Huh, OK, I didn't know that.  Too late now.  
(I think I had a dual opamp, so I inverted twice and  
rolled of the inverters with big C's.)

George h.  
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Re: 100mV DC supply
Not to completely derail the topic but it sure seems like using google groups to view these threads is a horrible way to go about it. I assume most people use a usenet client of some kind?  

Re: 100mV DC supply
On Thursday, July 13, 2017 at 4:13:13 PM UTC+2, George Herold wrote:
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of sourcing up to ~50mA but will typically see high impedance. Easily avail
able I have a clean 24V source and 208VAC. My intent is to drop from 24V to
 ~1.8V using a buck converter then follow it up with a 1.0V precision shunt
 (ADR510 or other) followed by a 9:1 precision resistor divider. Buffer the
 100mV output by a low noise single supply op-amp such as ltc1014. Although
 it looks like ltc1014 won't be able to source enough current so possibly f
ollowed with a BJT?
Quoted text here. Click to load it
nd +/- 3mV should be good enough. The environment the board will reside in  
is ~25C +/- 5deg. The output voltage must not drift above ~130mV to prevent
 causing issues in the test chamber.  
Quoted text here. Click to load it
tive = 1kHz) and multiplied by 10x before being sampled. The low pass fil
ter frequency is chosen to preserve rise times in the ~500uS range.  
Quoted text here. Click to load it
(70ppm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from th
e 5 foot run of cable to the test chamber and back and am interested in bes
t practice shielding techniques to mitigate induced noise.  
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similar to this before so I'm interested in hearing about other possible to
pologies that can meet the requirements or how others would approach the pr
oblem. The solution will be put onto a pcb as part of a larger circuit so i
 cannot use a benchtop supply.  
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<snip>

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http://www.onsemi.com/pub/Collateral/MC33201-D.PDF

comes close.

The OP talks about a load that can source 50mA at +100mV, which seems to im
ply that he wants an op amp that can sink 50mA from +100mV into the negativ
e rail (ground here) which is asking a bit much, even from the MC33201.

You might be able to do it with an N-channel MOSFet - most op amps could dr
ive a big-enough MOSFET gate hard enough to let the MOSFet sink 50mA to gro
und from +100mV. The capacitative load would make the circuit a pain to fre
quency compensate, and you'd probably have to dump in a few extra mA from t
he positve rail to keep everything tidy when the load was high impedance.

The rest of thread makes it sounds as if he wants to deliver 50mA into the  
load at +100mV, which is much less difficult.

--  
Bill Sloman, Sydney

Re: 100mV DC supply
On Thursday, July 13, 2017 at 9:32:23 AM UTC+2, Marke wrote:
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ourcing up to ~50mA but will typically see high impedance. Easily available
 I have a clean 24V source and 208VAC. My intent is to drop from 24V to ~1.
8V using a buck converter then follow it up with a 1.0V precision shunt (AD
R510 or other) followed by a 9:1 precision resistor divider. Buffer the 100
mV output by a low noise single supply op-amp such as ltc1014. Although it  
looks like ltc1014 won't be able to source enough current so possibly follo
wed with a BJT?
Quoted text here. Click to load it
/- 3mV should be good enough. The environment the board will reside in is ~
25C +/- 5deg. The output voltage must not drift above ~130mV to prevent cau
sing issues in the test chamber.  
Quoted text here. Click to load it
 = 1kHz) and multiplied by 10x before being sampled. The low pass filter  
frequency is chosen to preserve rise times in the ~500uS range.  
Quoted text here. Click to load it
pm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from the 5  
foot run of cable to the test chamber and back and am interested in best pr
actice shielding techniques to mitigate induced noise.  
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lar to this before so I'm interested in hearing about other possible topolo
gies that can meet the requirements or how others would approach the proble
m. The solution will be put onto a pcb as part of a larger circuit so i can
not use a benchtop supply.  
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The LM10 give you a 200mV reference voltage output which you could divde to
 exactly 100mV with 25-turn trim-pot. The op-amp part of the device could t
hen buffer that voltage. You might have to load the output with a resistor  
ground, but the data sheet spells it all out.

http://uk.farnell.com/w/c/semiconductors-ics/amplifiers-comparators/operati
onal-amplifiers-op-amps?brand=texas-instruments&st=LM10

http://www.ti.com/lit/ds/symlink/lm10.pdf

--  
Bill Sloman, Sydney


Re: 100mV DC supply
On Thursday, July 13, 2017 at 12:32:23 AM UTC-7, Marke wrote:

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Yep, that's good for power efficiency.   At 50 mA, that 1.8V won't take more than a tenth watt,
though; what kind of buck converter is really designed for such a low load?  There's probably
other low voltage requirements you can combine


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For 2 mV, your reference voltage requirement is a problem.
A good low-voltage LDO  <http://ww1.microchip.com/downloads/en/DeviceDoc/mic47100.pdf>
at 0.8V output, with a 7:1 divider string (14 ohm pullup,2 ohm pulldown) has
the right voltage, and only 2 ohms impedance (so your 50 mA current
draws it down, but doesn't burn anything up).   Would that work for you?

Re: 100mV DC supply
On Thursday, July 13, 2017 at 3:32:23 AM UTC-4, Marke wrote:
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ourcing up to ~50mA but will typically see high impedance. Easily available
 I have a clean 24V source and 208VAC. My intent is to drop from 24V to ~1.
8V using a buck converter then follow it up with a 1.0V precision shunt (AD
R510 or other) followed by a 9:1 precision resistor divider. Buffer the 100
mV output by a low noise single supply op-amp such as ltc1014. Although it  
looks like ltc1014 won't be able to source enough current so possibly follo
wed with a BJT?
Quoted text here. Click to load it
/- 3mV should be good enough. The environment the board will reside in is ~
25C +/- 5deg. The output voltage must not drift above ~130mV to prevent cau
sing issues in the test chamber.  
Quoted text here. Click to load it
 = 1kHz) and multiplied by 10x before being sampled. The low pass filter  
frequency is chosen to preserve rise times in the ~500uS range.  
Quoted text here. Click to load it
pm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from the 5  
foot run of cable to the test chamber and back and am interested in best pr
actice shielding techniques to mitigate induced noise.  
Quoted text here. Click to load it
lar to this before so I'm interested in hearing about other possible topolo
gies that can meet the requirements or how others would approach the proble
m. The solution will be put onto a pcb as part of a larger circuit so i can
not use a benchtop supply.  
Quoted text here. Click to load it

Once you have +1.8V, why not something like this?


    (view in Courier font)
                                   +1.8V
Vref >---.                          -+-
         |                           |
        [R1]                        [R4] 20
         |   100mV  |\               |
         +----------|+\            |/  Q1
         |          |  >---[R3]----|
        [R2]    .---|-/            |>.
         |      |   |/               |
        ===     |                    |
                '--------------------+-----> Vout = +100mV
                                     |
                                    [1k] R5
                                     |
                                    ===

Vout is a precision, low-impedance output.  R4 provides
short-circuit protection. R5 provides an optional
minimum load.

Cheers,
James Arthur

Re: 100mV DC supply
On 07/13/2017 09:10 AM, snipped-for-privacy@yahoo.com wrote:
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Looks like a TL431...

Re: 100mV DC supply
On Thursday, July 13, 2017 at 11:27:49 AM UTC-4, bitrex wrote:
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f sourcing up to ~50mA but will typically see high impedance. Easily availa
ble I have a clean 24V source and 208VAC. My intent is to drop from 24V to  
~1.8V using a buck converter then follow it up with a 1.0V precision shunt  
(ADR510 or other) followed by a 9:1 precision resistor divider. Buffer the  
100mV output by a low noise single supply op-amp such as ltc1014. Although  
it looks like ltc1014 won't be able to source enough current so possibly fo
llowed with a BJT?
Quoted text here. Click to load it
d +/- 3mV should be good enough. The environment the board will reside in i
s ~25C +/- 5deg. The output voltage must not drift above ~130mV to prevent  
causing issues in the test chamber.
Quoted text here. Click to load it
ive = 1kHz) and multiplied by 10x before being sampled. The low pass filt
er frequency is chosen to preserve rise times in the ~500uS range.
Quoted text here. Click to load it
70ppm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from the
 5 foot run of cable to the test chamber and back and am interested in best
 practice shielding techniques to mitigate induced noise.
Quoted text here. Click to load it
imilar to this before so I'm interested in hearing about other possible top
ologies that can meet the requirements or how others would approach the pro
blem. The solution will be put onto a pcb as part of a larger circuit so i  
cannot use a benchtop supply.
Quoted text here. Click to load it

The TL431 is shunt, though, sucking maximum current all the time, and outpu
ts
2.5V where the OP requested 100mV.

Cheers,
James Arthur

Re: 100mV DC supply
On Thu, 13 Jul 2017 06:10:12 -0700 (PDT), snipped-for-privacy@yahoo.com
wrote:

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I need a .4V supply and was going to do exactly this but the opamp is
kinda expensive.  I'm used to paying 1/3 of the cost of an opam for
the entire regulator (above 1.1V).  

Re: 100mV DC supply
On Thu, 13 Jul 2017 00:32:12 -0700 (PDT), Marke

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The best references are mostly in the 2.5 to 10 volt range, so you
could use one of them and divide down. There's an LM4040 at 2.5 volts,
0.1%, fairly cheap. The ADR refs from ADI are amazing, tempcos down to
3 PPM, for a few dollars, so the ADR510 should be OK.

You might consider a 4-wire remote sense configuration to zap the
error of 50 mA in the lead wires.

Susumu makes cheap 0.1% thin-film resistors with tempcos typically
below 10 PPM.

2% tolerance should be easy, unless you have ground-loop issues. You
could start with an isolated DC-DC converter.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: 100mV DC supply
On Thursday, July 13, 2017 at 11:06:46 AM UTC-4, John Larkin wrote:
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sourcing up to ~50mA but will typically see high impedance. Easily availabl
e I have a clean 24V source and 208VAC. My intent is to drop from 24V to ~1
.8V using a buck converter then follow it up with a 1.0V precision shunt (A
DR510 or other) followed by a 9:1 precision resistor divider. Buffer the 10
0mV output by a low noise single supply op-amp such as ltc1014. Although it
 looks like ltc1014 won't be able to source enough current so possibly foll
owed with a BJT?
Quoted text here. Click to load it
+/- 3mV should be good enough. The environment the board will reside in is  
~25C +/- 5deg. The output voltage must not drift above ~130mV to prevent ca
using issues in the test chamber.  
Quoted text here. Click to load it
e = 1kHz) and multiplied by 10x before being sampled. The low pass filter
 frequency is chosen to preserve rise times in the ~500uS range.  
Quoted text here. Click to load it
ppm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from the 5
 foot run of cable to the test chamber and back and am interested in best p
ractice shielding techniques to mitigate induced noise.  
Quoted text here. Click to load it
ilar to this before so I'm interested in hearing about other possible topol
ogies that can meet the requirements or how others would approach the probl
em. The solution will be put onto a pcb as part of a larger circuit so i ca
nnot use a benchtop supply.  
Quoted text here. Click to load it

He only needs +/- 3% over 10oC, so that part should be pretty
straight-forward.  Even the humble LMV431 comes in 0.5%, jelly-bean
from Digikey.

Cheers,
James Arthur

Re: 100mV DC supply
Marke wrote:


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I think you want a 4 wire connection into the chamber, so there is no  
current flowing through the voltage sense wires.  Put modest resistors  
outside between +sense and +supply, and -sense and -supply, so if any  
connection in the chamber is broken, it will not cause overvoltage.  
Something like 100 Ohms would be fine.  When the 4 wire circuit is hooked up  
right, the resistors will become insignificant.  This is the classic remote-
sense power supply scheme.

For noise, you can use 4 wire shielded cable.

Jon

Re: 100mV DC supply
On Thursday, July 13, 2017 at 2:52:29 PM UTC-4, Jon Elson wrote:
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Yeah and get well shielded cable, copper mesh and Aluminum foil.  
And make it well bonded to ground everywhere you can.  

What's the impedance of the load?  

George H.  
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