315 280 Electricity and Basic Electronics

Semiconductor diodes

315 280 Electricity and Basic Electronics

To make it easier to see, we make the structure into 2 dimensions.

http://www.mtmi.vu.lt/pfk/funkc_dariniai/sol_st_phys/impurities.htm

315 280 Electricity and Basic ElectronicsDoping with Arsenic gives an extra electron

Doping with Gallium gives a missing electron

http://www.mtmi.vu.lt/pfk/funkc_dariniai/sol_st_phys/impurities.htm

315 280 Electricity and Basic Electronics

When an intrinsic semiconductor gets hot, an electron may have enough energy to leave the valence band and cross to the conduction band, leaving a hole behind.

315 280 Electricity and Basic ElectronicsN-type semiconductor

Doping with a valency 5 atom gives an extra electron in the conduction band which helps to conduct current, but there is no freely moving hole produced.

315 280 Electricity and Basic Electronics

If we form p-type and n-type together in the same piece of silicon, we produce a device which conducts by electrons in the n-type part, and by holes in the p-type part.

315 280 Electricity and Basic Electronics

Connecting a battery as in the picture causes the electrons and holes to move apart, and so a current cannot flow.

http://commons.wikimedia.org/wiki/Image:PnJunction-Diode-ForwardBias.PNG

315 280 Electricity and Basic ElectronicsBut connecting the battery the other way around causes holes and electrons to move together, and so a current can flow.

http://commons.wikimedia.org/wiki/Image:PnJunction-Diode-ForwardBias.PNG

315 280 Electricity and Basic Electronics

Reverse

Forward

www.americanmicrosemi.com

http://www.mtmi.vu.lt/pfk/funkc_dariniai/diod/p-n_devices.htm

315 280 Electricity and Basic Electronics

http://faculty.evansville.edu/ar63/courses/Tutorials/Diode_Modeling_1.html

315 280 Electricity and Basic ElectronicsVR + VB + + VD I To find the voltage across the diode, and the current flowing through it, we use Kirchoff s voltage law (KVL). With this we can form an equation:

V V I=D + B R R

315 280 Electricity and Basic ElectronicsSolving two equations is easy when you know what the equations are:

3x+7y=17

12x+y=14

Gives x=1 and y=2

315 280 Electricity and Basic ElectronicsBut how do we find a solution when we don t know one of the equations?I

I =

VD

R

+

VB

R

VDhttp://faculty.evansville.edu/ar63/courses/Tut orials/Diode_Modeling_1.html

315 280 Electricity and Basic ElectronicsVB

VB/R

We use a graphical method to find the solution for I and VD, which is called the operating point.

VBhttp://en.wikipedia.org/wiki/Load_line_(electronics)

315 280 Electricity and Basic Electronics

Using diodes

315 280 Electricity and Basic ElectronicsThe most important use of a diode is in converting from AC to DC voltage and current.

http://en.wikibooks.org/wiki/Semiconductor_Electronics/Diode_Applications/Half_wave_rectifier

315 280 Electricity and Basic ElectronicsFull wave bridge rectifier

1

1

2 2

315 280 Electricity and Basic ElectronicsFull wave rectifier with centre tap

1

1

2 2

315 280 Electricity and Basic Electronics315 280 Howework 3 1. A hair dryer has a heater with an inductance of 1mH and a resistance of 100. What is the heat power generated? 2. Use the characteristic below to find the current through the diode when it is connected in series with a battery of 1.5 volts and a resistor of 50 .

I

VD

3. If we connect two diodes in series in the circuit above, what would the current be in each? 4. If they were connected in parallel, what would the current be in each?