Make your own free website on Tripod.com
the drunken engineer

A system was set up and analyzed for the purpose of determining the junction capacitance (C) and the time constant (t) for a silicon and a germanium diode. In the case of the diodes used in this experiment, the recovery time is approximately three times the value of t. By using a function generator and an oscilloscope to observe the diodes in question, a series of measurements were made; recording the storage time and respective forward and reverse currents for each trial on each diode. The ratio of the reverse current over the forward current was then compared to a given graph of (storage time / t) vs (Ir / If). For each trial, a value for t was then calculated and averaged. For the silicon diode, the time constant was found to be 29.2 uS, and 2.92 uS for the germanium diode. Next, using the relationship that the recovery time is about three times the time constant (which is the resistance of the diode times the junction capacitance), the junction capacitance was calculated. For the silicon diode, the capacitance was found to be 0.23 pF, and the value for the germanium diode was 0.95 pF. Many factors may have contributed to inaccuracies in the recorded data. Loads on the wiring were not taken into account, and the oscilloscope and function generator may not have been calibrated to an accurate enough level. Experimenter's errors, however, will be much more prolific, as many of the reading taken from the oscilloscope cannot be as accurate as required to achieve acceptable results to the calculations.