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E3 Diodes And Transistors

Introduction

An interesting characteristic of semiconductor diode is that it can be treated as a good approximation to an ideal one-way conductor. In forward bias, the current of diode varies exponentially with voltage across it, but the current does not change much with the applied voltage in reverse bias until meet the breakdown voltage. In this experiment, the current-voltage characteristic of diodes will be investigated. In addition, some applications of the diode for DC power supplies, such as the half-wave rectifier and full wave rectifier, will be studied.

A transistor is a device which can be used for amplification, switching, signal modulation and many other functions. Transconductance can control a current through two output points by an input voltage, and a transconductance amplifier outputs a current which is proportional to its input voltage.[3] In the second part of the experiment, we will investigate some basic working principle of the transistor.

The result of the experiment will show the current-voltage dependence of the diode. At the same time, some main parameters for Si, Zener, and light-emitting diodes, like reverse saturation current, forward voltage drop and breakdown voltage, will be indicated with comparisons.   The fact that half-wave rectifier and full-wave rectifier can transform AC voltage to DC voltage with different waveforms is observed. We also study how the value of RC can affect the output ripple. When testing the transistor, an npn transistor is used. The linear relation between output current and current source is proved, and their ratio β, which is the common-emitter current gain can also be measured. In addition, we measure the phase difference between output and input voltage as well as the voltage gain G which is the ratio of their peak to peak value.

Results

The relation between current and voltage of diode is shown in Equation(3.1.2) on p.25. In a big forward bias, current varies exponentially with voltage...