Diode ORing voltage measurement

[vinodquilon]

For the below circuit, I have placed multimeter +ve probe at 'B' wrt GND and measures 4V against the expected value of 0V.

Hence I have terminated the 'B' end with 10K to GND temporarily before taking the measurement and reads 0V.

Why this happens?

What happens to the anode of D2 while I connect a multimeter to 'B' end wrt GND ?

I have replaced the 10K temporary resistor with 1M, then again 4V measured !

 

[tellyman09]

Hi

I am not sure what you are asking as I do not understand wrt GND what do you meen by wrt?

 

[vinodquilon]

wrt---with respect to

 

[albbg]

The phenomenon should be due to the reverse leakage current of D2. In fact the reverse current in a real diode isn't 0 as in an ideal component.

But there is something not clear to me: the 1N4148 diode should exhibit a reverse current of about 30 nA at 25 degC of temperature and 30V (it increases very much with temperature and voltage). This means that across a multimeter (we can estimate an input impedance of rouhgly 10 Mohm) we will have 30nA*10Mohm=0.3V and across a 1Mohm resistor (neglecting the 10Mohm parallel) a voltage of 0.03V.