Camara Practice Problem 9B

[lowcountrygamecock]

Can anyone tell me where the 40V comes from in part b of the problem? The question asks What is the current that flows when a forward bias of 0.2 V is applied at 20 degrees C. n is give n as 1.

The solution reads

I=Is=(e^((40V/n)-1))

This is part b of the example but it doesn't mention anywhere in the problem where the 40V comes from. Am i missing something simple?

 

[Flyer_PE]

Looks like the problem is in Chapter 43. All they are doing is reducing the following:

q/kT

Where:

q = 1.602x10-19

k = 1.38x10-23

T = 293

(1.602x10-19)/((1.38x10-23)*(293)=39.6

 

[cabby]

see equation 43.17 for V(T). Then substitute back into equation 43.16. Your V(T)=.025 Now you are putting that in a denominator 1/.025 which is the 40.

Took me a few minutes also.

Hope this helps.

 

[mudpuppy]

Wow, the solution in the book is confusing. Turns out the V in the first line is in italics, indicating it is a variable (voltage over the diode), while the V in the second line is not italics, signifying the units (Volts). I couldn't distinguish the diffence until I looked at eqn (43.16).

I like Wikipedia's presentation of eqn (43.16) (which is the Shockley Diode Equation) better:

I = Is(eVD/nVT-1)

where VD is the voltage across the diode and VT is the thermal voltage.