JML
ONLINE INSTITUTE:	
AUTOMOTIVE ELECTRONICS:
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TRANSISTORS & DIODES:
consists of 4 main operations
1. Diodes & Transistors
2. Op-Amps
3. Regulators
4. Rectifiers

Diodes are made of  two semiconductor materials treated with impurities.  Current is applied to one end and drained from the other end.  The power applied to the diode curcuit is called the bias.  The plus side of the power source is applied to the emmitter which supplies electron holes or positive ions?  

The collector supplies electron flow to match up with the holes coming from the emitter, so current flows and it is foward biased.  The current in the opposite direction is reverse bias and nonexistent unless it is so great that it overcomes the reverse bias barrier and overflows into the emmitter.

For these reasons diodes make great one-way current passing devices to block flow in an unwanted direction.