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is the "X" point floating when there is no 12V applied ? Perhaps over a limited range, depending on whether the 12V line is left open or connected to something other than 12V. Case 1: The volt...
Answer
#1: Initial revision
by
Olin Lathrop
·
2023-07-06T14:00:26Z (over 1 year ago)
<blockquote>is the "X" point floating when there is no 12V applied ?</blockquote> Perhaps over a limited range, depending on whether the 12V line is left open or connected to something other than 12V. Case 1: <img src="https://electrical.codidact.com/uploads/z9bvopqki21dtsi8uoxmnt2iu6ql"> The voltage on X is bounded by the Zener diode. X can't be more than one diode drop below ground, or the Zener voltage above ground. Case 2: <img src="https://electrical.codidact.com/uploads/gjs56rffncj0uxia1tkjb9kl2e34"> X is directly tied to the 12V line, so it can only float at all if that line is not driven. In the case where 12V is left open, X can float to negative voltage within the reverse bias range of the diode. For positive voltages can float up to the diode drop. Above that, the two resistors provide impedance to keep X from "floating".