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