Finding voltage change for current change for diode

[bl965]

Homework Statement

Find the change in diode voltage if the current changes from 0.1 mA to 10 mA. Ans. 120 mV

Homework Equations

V₂-V₁=V_Tln(I₁/I₂)

The Attempt at a Solution

That is all the information given. The only equation I can think to use is the diode voltage/current relationship, but a value for initial voltage is not given. The calculation assuming V₁=0.7 V V₂=0.025ln(10/0.1)+0.7 = 0.8151.

Thanks for the help.

 

[berkeman]

Homework Statement

Find the change in diode voltage if the current changes from 0.1 mA to 10 mA. Ans. 120 mV

Homework Equations

V₂-V₁=V_Tln(I₁/I₂)

The Attempt at a Solution

That is all the information given. The only equation I can think to use is the diode voltage/current relationship, but a value for initial voltage is not given. The calculation assuming V₁=0.7 V V₂=0.025ln(10/0.1)+0.7 = 0.8151.

Thanks for the help.

But the problem statement only asks for the change in voltage, not the final voltage...

 

[bl965]

But the problem statement only asks for the change in voltage, not the final voltage...

The only other equation in the section is i = I_se^V/V_T. How would I find change in voltage?

 

[berkeman]

What is the diode equation?

 

[bl965]

What is the diode equation?

i = I_se^V/V_T is the only equation and I_s is not given.

 

[berkeman]

i = I_se^V/V_T is the only equation and I_s is not given.

I_s is a constant...

 

[bl965]

I_s is a constant...

From what i researched it depends on the diodes physical characteristics. The information above is all that is provided. I could not find a constant value for I_s.

 

[berkeman]

From what i researched it depends on the diodes physical characteristics. The information above is all that is provided. I could not find a constant value for I_s.

Just assume it is the same for the test diode for the two test currents. Can you write the two equations and solve them to get the delta-V?

 

[bl965]

V2-V1=VTln(I1/I2) = 0.025 ln (10/0.1) = 115.1 mV ?

 

[berkeman]

V2-V1=VTln(I1/I2) = 0.025 ln (10/0.1) = 115.1 mV ?

Looks good. The only thing I would change would be to use 25.85mV for Vt (at room temperature).