Program to Calculate Saturation Current (Is) and Ideality Factor (n) of
Small Signal Diodes. Voltages are in Volts, currents in Amps.

This program is written for use with calculators using Reverse Polish Notation and having an 'Equation Solver', such as the Hewlett Packard model 32S or 35s.  It uses only two diode forward voltage/current pairs. For simplicity, the voltage drop in the bulk series resistance of the diode is assumed to be zero. This is a good assumption for most detector diodes when the current is below a few uA.
 

  Program Line Number 

D01
D02
D03
D04
D05
D06
D07
D08
D09
D10
D11
D12
D13
D14
D15
D16
D17
D18
D19
D20
D21
D22
D23
D24
I01
I02
I03
I04

   Line Content 

LBL  D
INPUT  I
INPUT  J
/
STO  A
INPUT  U
INPUT  N
/
.0257
/ 
e^x
X
INPUT  V
RCL  /  N
.0257
/
  e^x
1
-
STO  S
+/-
+
RCL  -  A
RTN
LBL  I
RCL  1
RCL  /  S
RTN

Two diode forward current pairs are used:  Vd1 (the higher voltage)=V,  Id1 (the higher current)=I,  Vd2 (the lower voltage)=U  and Id2 (the lower current)=J.  (Is) and (n) are calculated at an equivalent actual diode forward current of 4-5 times (Is) if the voltages of the two voltage/current pairs are: V=0.055 and U=0.039 volts.  The orange colored shift key is represented by '#'

To run the program:
 

 Press Key 

#
SOLVE/S
FN
D
1
STO
N
#
SOLVE/S
SOLVE
N

R/S

R/S

R/S

R/S

#
SOLVE/S 
FN
I
R/S
Enter
 
 
 
 
 
 
 
 
 
 
 

Id1

Id2

Vd2

Vd1
*Read and record 
the value of n*
 
 
 

*Read and record 
the value of Is*

Written:  04/03/01  Clarified:  02/04/2007