In this chapter we will explore semiconductor diodes and some circuits using them. We've seen that resistors have a simple linear relationship between the voltage across them and the current through them (Ohm's law). On the other hand,

• diodes have an exponential relationship between current and voltage. Mathematically this may seem much more complicated than Ohm's law, but we think you'll agree that the idea as just stated is simple enough – it just takes some getting used to! As we'll see, an important consequence of the exponential characteristic is that diodes conduct much more readily in one direction than in the other. This makes them ideally suited for rectification: the conversion of AC into DC.

Apparatus required

Breadboard, oscilloscope, one or two multimeters, one 1N914 (or similar) silicon signal diode, one 1N4001 (or similar) 1Asilicon rectifier diode, one 100Ω and one 10 k W resistor, one 1 k 2 W resistor, power transformer with 12.6 V r.m.s. output on each side of the center tap, one diode bridge element, one 100 μF electrolytic capacitor, and one 1000 μF electrolytic capacitor.

Semiconductor basics

Current will flow through a material provided that there are charge carriers free to move and an electric field to move them. Conductors (such as copper) have lots of charge carriers (electrons) ready to move in response to the slightest electric field.