[volt-nuts] LTZ1000 reference appnote question

[Andreas Jahn]

Hello together,

what about another theory:
J.W. first developped the negative reference cirquit in the datasheet.
In the negative cirquit a diode is essential that on no circumstance the 
diode between reference and heater within the LTZ is not forward biased.
Later on J.W. gave the order to his apprentice to develop a positive 
cirquit.
The apprentice did not dare to remove a "holy part" from the cirquit.

3rd theory:
The diode helps to limit inrush current on startup through the zener which 
is not specified above 5mA.
I have a modified cirquit with a J-FET after the LT1013 and had to add a 
limiting resistor to limit to below 14 mA.

4th theory:
the startup pull up resistor after the diode has been forgotten in the final 
cirquit.
(like the ground connections and the "star" point).

On the other side: the cirquit in my opinion lacks on stability. (at least 
for large signal behaviour).
The 22nF is charged by a high ohmic resistor and discharged by a low ohmic 
transistor.

The DATRON reference cirquit is using some kind of integrator for the 
current regulation.

With best regards

Andreas


----- Original Message ----- 
From: "Fabio Eboli" <fabioeb at quipo.it>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Thursday, November 08, 2012 2:41 AM
Subject: Re: [volt-nuts] LTZ1000 reference appnote question


> Mitch,are you referring to startup behaviour,
> like Bob Smither suggests?
>
> Just now I was trying to imagine the startup
> (it's too late for firing up ltspice, I have to sleep :) )
> and I was thinking that on startup both inputs
> are zero and output can take both ways: go down (remain approx zero)
> or go up, depending on input offset.
> Is this correct?
>
> If so what determines the correct startup
> of the circuit?
>
> Until the output diode is not forward biased
> the opamp has no feedback and the output should amplify
> any input noise some million times (open loop gain),
> so I imagine that is only waiting that the noise on
> inputs will steer the output the rignt way to forward-bias
> the diode and start the reference.
> Does all this makes sense?
>
> Fabio.
>
> Mitch Van Ochten <mitch at vincentelectronics.com> ha scritto:
>
>> Positive input voltage range for an LT1006 is typically 1.2V below  the 
>> positive rail.
>>
>> mitch
>>
>>
>> ----- Original Message ----- From: "Fabio Eboli" <fabioeb at quipo.it>
>> To: <volt-nuts at febo.com>
>> Sent: Wednesday, November 07, 2012 7:02 PM
>> Subject: [volt-nuts] LTZ1000 reference appnote question
>>
>>
>>> Hello, in this thread on eevblog:
>>>
>>> http://www.eevblog.com/forum/projects-designs-and-technical-stuff/does-anyone-know-what-this-diode-is-for/
>>>
>>> a guy named DiligentMinds.com asked the question
>>> about why there is a 1N4148 diode on the output of
>>> the opamp in the LTZ1000 reference circuit, the one
>>> designed by Jim William in the appnotes, that can
>>> also be seen on the first page of the datasheet:
>>>
>>> http://cds.linear.com/images/product/1203_app_1.JPG
>>>
>>> Now I'm curious,
>>> anybody knows the answer?
>>>
>>> Thanks,
>>> Fabio.
>>>
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>
>
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