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Zener clamping at microamp supply levels
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jmoschetti45:
Long story short, I have an input of 4-125VAC I need to measure with a comparator. Preliminary testing shows I'll need my threshold to be around 12V. The comparator portion is easy.

My problem is the variable voltage, or I'd just use a cap dropper to drive the opto.

My thoughts are a simple full bridge with a series resistor with a zener. To keep the dissipation down, I'd shoot for something like 220k or 330k. I don't remember the op amp's input current requirements off the top of my head (LM358 ....have a ton laying around).

Usually, I'd just use a zener to limit the voltage, but will the 1mA or less cause issues with the zener?
jmoschetti45:

--- Quote from: blueskull on September 19, 2019, 06:51:33 pm ---Use a bandgap. TLV431 (the V version) goes down to 100uA.

--- End quote ---

I'm seeing a max of 7V in the datasheet?
magic:
There is a million xx431x parts differing in reference voltage (1.24/2.495/2.5), operating current range and abs maximum voltage.

Quick parametric search brings: SC431, LMV431
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