[sdiy] SSM2164 last time buys

[Stewart Pye]

If the problem only occurs when the negative rail is missing then why 
not have a PNP transistor (or P channel Mosfet) to switch the V+ off 
when V- disappears. Have emitter to V+, collector to 2164 VCC pin, and a 
voltage divider between V+ and V- with the centre going to the base of 
the PNP transistor. Choose the resistor values (and perhaps put a zener 
in there) so that when V- disappears the PNP transistor is no longer 
biased on and shuts off the V+ supply.

Regards,
Stewart.



David G. Dixon wrote:
>> Yes the current source solution suggested by Steve works.
>>
>> I used the LM334 (10mA) because it is what I had at hand but it would be
>> better something like 15mA or 20mA.
>> Yes I connected the (+) to the positive rail, and (-) to the pin 16 of the
>> 2164. And a 7Ω resistor from (-) to the centre leg(r)
>>     
>
> Here's what H&H has to say about the LM334 (2nd ed., Section 16.18, p. 355):
>
> "National makes a special 3-terminal device, the LM334, optimized for use as
> a low-power current source.  It comes in the small plastic transistor
> package (TO-92), as well as the standard DIP IC package.  You can use it all
> the way down to 1uA, because the "adj" current is a small fraction of the
> total current.  It has one peculiarity, however: The output current is
> temperature-dependent, in fact, precisely proportional to absolute
> temperature.  So although it is not the world's most stable current source,
> you can use it (Section 15.01) as a temperature sensor!"
>
> Hmm.  Based on that, I'm wondering whether a simple resistor might not be
> the better choice for temperature stability.
>
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