Diode Equation needs a Knee Transplant

[jalbers@bsu.edu]

I would like to know how to modify the diode equation: I = Io (Exp(eV/
NkT)-1) to work for a germanium diode. Using Io=10E-12, e=1.602E-19,
T=295, N=1, and k=1.380E-23 has the correct knee 0.6 for a silicon
diode. What needs to be changed (or is there a new equation) to move
the knee back to around 0.3 to model a germanium diode?

Any help would be greatly appreciated. Thanks

 

[George Herold]

On Sep 10, 3:31 pm, "jalb...@bsu.edu" <jalb...@bsu.edu> wrote:

I would like to know how to modify the diode equation: I = Io (Exp(eV/
NkT)-1) to work for a germanium diode.  Using Io=10E-12, e=1.602E-19,
T=295, N=1, and k=1.380E-23 has the correct knee 0.6 for a silicon
diode.  What needs to be changed (or is there a new equation) to move
the knee back to around 0.3 to model a germanium diode?

Any help would be greatly appreciated.  Thanks

There is no band gap voltage in the "low voltage" diode equation. As
the applied voltage exceeds the band gap voltage about 0.6 for Si and
0.3 for Ge a different aproximate equation is used.
Sorry but I don't know off hand what that "high voltage" equation is.
George

 

[extremesoundandlight@yaho]

On Sep 10, 6:12 pm, George Herold <gher...@teachspin.com> wrote:

On Sep 10, 3:31 pm, "jalb...@bsu.edu" <jalb...@bsu.edu> wrote:

I would like to know how to modify the diode equation: I = Io (Exp(eV/
NkT)-1) to work for a germanium diode.  Using Io=10E-12, e=1.602E-19,
T=295, N=1, and k=1.380E-23 has the correct knee 0.6 for a silicon
diode.  What needs to be changed (or is there a new equation) to move
the knee back to around 0.3 to model a germanium diode?

Any help would be greatly appreciated.  Thanks

There is no band gap voltage in the "low voltage" diode equation.  As
the applied voltage exceeds the band gap voltage about 0.6 for Si and
0.3 for Ge a different aproximate equation is used.
Sorry but I don't know off hand what that "high voltage" equation is.
George

if the equation is not at equilibrium, a potential barrier wont
develope across the P-N junction so its not that important.

 

[Tim Wescott]

jalbers@bsu.edu wrote:

I would like to know how to modify the diode equation: I = Io (Exp(eV/
NkT)-1) to work for a germanium diode. Using Io=10E-12, e=1.602E-19,
T=295, N=1, and k=1.380E-23 has the correct knee 0.6 for a silicon
diode. What needs to be changed (or is there a new equation) to move
the knee back to around 0.3 to model a germanium diode?

Any help would be greatly appreciated. Thanks

Here's one more for all the contradictory advise:

Increase Io. Dramatically.

Perhaps take some measurements of the diode voltage at several different
current values (i.e. 1uA if you can get that low, 10uA, 100uA, 1mA --
don't exceed the diode ratings). Then do a curve fit on semilog paper
-- figure that you are going to see Io e^(eV/NkT) only, the "- 1" part
will drop right out.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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"Applied Control Theory for Embedded Systems" gives you just what it says.
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