On 9/26/2017 9:26 AM, T i m wrote:
On Tue, 26 Sep 2017 06:46:01 -0700 (PDT), wrote:

snip

Understood. I was thinking more on the idea of when using a lower
voltage zener to be well clear of the lower voltage levels being
considered and then the potential divider to set the FSD when the
input is 15V?

And also, wouldn't the impact of the battery voltage changing from say
10.5 to 14.4V be lessened (re the series current limiting / biasing
resistor) if the voltage difference between the reference and the
supply is greater?

That seemed like the best of all worlds (for the KISS solution)?


You want a zener with a nice straight line at the low current end. One linked to from here has that.


Yeah, ok ... but what about the question re using a lower value zener
to get it away from the 'knee', especially as it's no more difficult
to do?

Cheers, T i m

Since we're just trying to be clever,
Try this:

https://i.imgur.com/irLisN7.jpg

The transistor and zener make a temperature compensated ~7V
reference (must use 6.2V zener with standard tempco).
Two pots set the min and max voltages. Rk allows you to add
current to the zener to get it past the most nonlinear portion
of it's V-I curve. This circuit has the ability to calibrate out
almost any component variation. It's relatively temperature
independent. You can use any meter that will make full scale at
less than about 7V. Downside is that the pots are vibration sensitive
and subject to moisture/corrosion.

Are we having fun yet?