Multisim and Ultiboard

cancel
Showing results for 
Search instead for 
Did you mean: 

Why is diode voltage drop not consistent at 0.7V?

Solved!
Go to solution

Multisim11 student evaluation version. In a simple dc series circuit with a 10ohm resistor and (3) in4148 diodes forward biased, voltmeters across each diode show equal voltage across each diode, but as the dc supply voltage is increased, the voltage across each diode increases. A technician quiz (and diode theory) states that the voltage will not change across the diodes and should remain at 0.7V across 1 diode, 1.4v across 2, 2.1V across all three, even as the supply voltage is increased, but why does Multisim not reflect basic diode theory? I use the default settings for meters and components. This has also been a problem for reverse bias tests and measured current levels. I am almost never able to get the same results as expected in the labs at school.

 

At 10vdc I get 1.593V across each diode

At 30vdc I get 3.777V across each diode

 

What's the dealio?

 

0 Kudos
Message 1 of 2
(6,949 Views)
Solution
Accepted by topic author Chipvirtual

I may have answered my own question in experimenting with the circuit. The resister value at 10 ohm is not high enough to prevent overloading the diodes. A more realistic value of 1Kohm and voltages of 5-10V using 3 BAS16 diodes shows diode drop voltages in the range of .691mV to .750mV. Even 30V still shows a diode drop of .836mV.

 

So what kind of diodes would work properly in this circuit with a 10 ohm resistor in series and a dc voltage range of 10-30V? The technician quiz indicated this circuit had a 10ohm resistor. Maybe it was a typo?

 

 

0 Kudos
Message 2 of 2
(6,948 Views)