[volt-nuts] Making a Reference IC

[John Phillips]

they would not be as well matched as if they were on the same chip

On Sat, Sep 12, 2015 at 3:12 PM, Dave M <dgminala at mediacombb.net> wrote:

> I realize that better references are available.
>
> I was thinking of resurrecting a long-defunct Fluke 731 that I have in the
> garage.  The reference IC is bad in it, and (1) I don't want to throw it
> away without a meager attempt at repair, and (2) I don't want to spend a
> lot of money on it because it's in pretty bad physical condition.
>
> I was hoping that someone could lend a touch of advice on those old
> references.  I have a few 1N827A reference zeners, and a washtubful of
> transistors.  Maybe something could be cobbled together that would get the
> 731 back in operation.  Maybe not to original specs, but close, which is
> better than nothing.
>
> Thanks for your reply,
> Dave M
>
>
>
>
> Jack Mcmullen via volt-nuts wrote:
>
>> Just thinking why would you reinvent a transistor/zener reference
>> when the industry's voltage reference chips are in the $2.00 or less
>> single quanities with performance far exceeding anything previously
>> available in discrete components??
>>
>>
>>
>>
>> -----Original Message-----
>> From: Dave M <dgminala at mediacombb.net>
>> To: FEBO Volt-Nuts <volt-nuts at febo.com>
>> Sent: Sat, Sep 12, 2015 1:58 pm
>> Subject: [volt-nuts] Making a Reference IC
>>
>>
>>
>>
>> I was looking at the schematics for the Fluke 731 and 732 voltage
>> references.  these, and several other brands and models of voltage
>> references, use the same or similar reference ICs as their basis.  The
>> reference ICs are a Zener/NPN transistor pair on a single substrate.
>>
>> Please view in a fixed-width font such
>> as Courier.
>>
>>        |
>>        |
>>      C |
>>        |
>>          |
>>          |
>>           |----
>>           |  B
>>          /|
>>         / |
>>      E |
>>        |
>>        +---------------
>>        |
>>     /------/
>>       /
>>      ------
>>        |
>>        |
>>
>> Just thinking... would it be possible to make a reference with similar
>> characteristics with discrete components (a low tempco Zener and a
>> transistor)?  They would likely have to be closely coupled thermally
>> and
>> maintained at a constant temperature within an oven or by a peltier
>> device.
>>
>> What criteria would apply to the selection of the parts?
>>
>> Dave M
>>
>
>
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-- 

*John Phillips*