[volt-nuts] Motorola buried zener

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Sep 13 02:06:04 UTC 2009

Bruce Griffiths wrote:
> Mike S wrote:
>> At 09:03 PM 9/12/2009, Bruce Griffiths wrote...
>>> I thought that they were 1N821 series or similar TC compensated discrete
>>> zeners ( series stack of a zener chip plus one or more forward biased
>>> diodes all in same hermetically sealed package)?
>>> IIRC thats what the manual states.
>>> I have datasheets for most of the Motorola TC zeners if thats what
>>> you need.
>> No, not the 1N82x series zeners.
>> These had a zener with the emitter of an NPN transistor against its
>> cathode (for the tempco offsetting PN junction) in the device, and
>> were used in the Fluke 731B, 732A, 332B/D, 335, and no doubt more.
>> They are 4 terminal devices. Fluke "ovenized" them.
>> Fluke service manuals only refer to them with an internal designation.
>> My understanding is that these were "state of the art" prior to the
>> National LMx99 (which was in turn followed by the LTZ1000).
> You mean the ancient Motorola reference amplifiers?
> I should also have some data on these.
> These were discrete devices in hemetic packages welded together within
> an overall 4 lead metal hermetic package.
> Depending on the voltage the zener may have had one or more forward
> biased diodes connected in series.
> Bruce
The reference amplifier(U2) on A4 reference board circuit in the 732A
appears to be compatible with one of the Motorola 6.8V reference
amplifiers such as the MCA1914N, MCA1924N or MCA1934N.
The only difference between these is the specified operating temperature
If the oven temperature is around 50C then a selected MCA19124N is likely.
They had a maximum voltage change (Iz = 5mA) of 5mV over the 0-75C
operating temperature range.
Reference voltage was 6.8V with a 10% tolerance.


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