Semiconductors, Diodes, and Transistors 5/5/2014

Today we were introduced to Semiconductors.  We learned that:

Diode is a P-type of silicon butted up to an N-type of silicon charge.  When electron charge migration happen by going to the Holes, we get a depletion in the middle.  Since charge cannot pass through this depletion zone, it acts as a one way valve and current can only flow one direction.

Transistors are 3 legged circuit elements that acts like a current-controlled current amplifier.  There are two types of transistors: PNP & NPN.  To turn NPN type on, apply a positive voltage and to turn PNP type on, apply a negative voltage.

 A circuit containing a diode with two layers of semiconducting materials N-type containing electrons, and P-type containing holes. In between the layers there is a neutral charged depletion zone. When a power source is reversed to the negative side of the diode, the depletion zone disappears allowing electrons to flow to the negative.

In AC, the current flows from positive to negative in a sine wave. Going through a diode (the a triangle with a line), the negative parts of the wave falls inside the depletion zone and is filtered out.

Next, we started our lab to construct the circuit using a transistor, various capacitors and resistances in order to amplify sound using a speaker.  

We constructed the circuit on a breadboard, instead of using a 9V battery, we used a voltage supply.  Also, we did it without a switch.

Breadboard first amplifier construction

We were able to amplify the signal from a function generator and actually hear the tones it produced.  However, it was not the best.

Signal from the function generator was monitored on the oscilloscope and after a second, amplified (right), providing a direct comparison between the original and amplified voltages.


Next, we upgraded our amplifier with an Integrated Circuit........

National Semiconductor/TI Schematic of the LM386 Amplifier

Prof Mason made a slight modification to the already "minimum" parts schematic even more simplified and better quality.

As shown above, an integrated circuit (the black rectangular component left) is a tiny circuit consists of diodes, resistors, and transistors, all integrated together in one piece.

Finally, we created an amplifier again but this time we used an integrated circuit chip for the build.  This audio amplifier could be used with our MP3 players. Following the given schematic with a series of resistors, capacitors, and an IC, we connected a 9V grey power supply to provide power to the breadboard. The circuit was build around the different 8 legs of the integrated circuit chip.  As suggested by the diagram above, only a few of the legs were used, while some were to be grounded.

We successfully used this audio amplifier to play our favorite music instead of just hearing a variety of "waves" created from the function generator.  Although there was static, it was better than nothing.

Finally, a 3.5 mm male jack connected to Rudy's phone with Latino music to be hooked up and outputted through a small computer speaker.  Eddie working it duuuuude!!!