EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: jmoschetti45 on September 19, 2019, 06:44:29 pm
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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?
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Use a bandgap. TLV431 (the V version) goes down to 100uA.
I'm seeing a max of 7V in the datasheet?
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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