Consider the circuit arrangement shown in the attachment.
If I connect a MM in voltmeter mode at floating terminal A, What would be the reading on the voltmeter?
If I terminate the floating A terminal with a 10K resistor to GND, What would be the change in reading shown?
Diode with floating terminal
Re: Diode with floating terminal
with point A open, no current is flowing and you get the same voltage on both sides of the diode; 5V
With point A loaded with a 10K load to ground, the short circuit current is ~500uA, with the diode forward resistance it will be a little lower but you will get a voltage corresponding to ~500uA on the forward biased diode curve which in the case of this diode will be around 5V-400mV or ~4.6V. Use a smaller resistor and that voltage will shrink a bit as the operating point moves up the diode curve to a larger voltage drop.
With point A loaded with a 10K load to ground, the short circuit current is ~500uA, with the diode forward resistance it will be a little lower but you will get a voltage corresponding to ~500uA on the forward biased diode curve which in the case of this diode will be around 5V-400mV or ~4.6V. Use a smaller resistor and that voltage will shrink a bit as the operating point moves up the diode curve to a larger voltage drop.
Re: Diode with floating terminal
Here is my interpretation considering the case of non-ideal diode,haklesup wrote:with point A open, no current is flowing and you get the same voltage on both sides of the diode; 5V
With point A loaded with a 10K load to ground, the short circuit current is ~500uA, with the diode forward resistance it will be a little lower but you will get a voltage corresponding to ~500uA on the forward biased diode curve which in the case of this diode will be around 5V-400mV or ~4.6V. Use a smaller resistor and that voltage will shrink a bit as the operating point moves up the diode curve to a larger voltage drop.
CASE 1(without 10K)-- Depending on the output impedance of DC voltage source and the input impedance of the MM, the drop across the diode is not enough to turn it ON. And the MM will reads electric filed at floating terminal. And it will be high depending on the neutral to earth voltage of ac supply distribution to the voltage source (if above 1V).
CASE 2(with 10K)--The effect of high input impedance of MM get reduced due to parallel 10K. In this case diode conducts and the output at non-floating terminal will be [5V-(forward diode drop)].
@VinodQuilon
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