Diodes and Transistors

Diodes

Above we have a picture of a circuit containing a diode, which has the symbol of a triangle with a bar at the point. Diodes contain two layers of semiconducting materials N-type containing electrons, and P-type containing holes. In between the layers there is an area of neutral charge called the depletion zone. In order for electrons to flow the negative side of a DC source must be connected to the negative side of the diode. This makes the depletion zone vanish and allows current to flow. In AC, the current goes from positive to negative in a sine wave (shown above). When AC goes through a diode, the negative parts of the wave make the depletion zone in the diode larger and do not allow current to flow. Therefore, only the positive current flows.

Building an Amplifier

The schematic in the picture above was given and we wired the circuit accordingly. However, we did not use a switch and we used a voltage supply instead of a 9V battery. The circuit consisted of various resistors, capacitors, and a transistor. The was a signal from a function generator was monitored on the oscilloscope and after a second, amplified, signal was also shown on the oscilloscope. This provided a direct comparison between the original and amplified voltages.

The pictures above show the completed circuit (minus the power source) from the schematic.

We changed the voltage (and frequency) on the function generator and took pictures of the various results. The smaller wave in each case represents the voltage from the function generator and the larger wave represents the output, after the wave has been amplified. We can see that the voltage increased dramatically in each case.

Building an Amplifier Using an Integrated Circuit

Once again we created an amplifier however this time we used an integrated circuit (IC) for ease. An integrated circuit is a tiny circuit in which diodes, resistors, and transistors are connected in a tiny space (the black rectangular component above).
This time, the amplifier was more rewarding because we got to play our favorite music instead of hearing a variety of "waves" (sounds created from the function generator). We used a given schematic with a series of resistors, capacitors, and an IC. A 3.5 mm male jack connected allowed a phone with music to be hooked up and outputted through a small computer speaker. A grey voltage supply provided power. When everything was connected correctly, we played music through a phone and it was amplified significantly through the computer speaker.