Transistors and ICs

The SCR

• SCR = SILICON CONTROLLED RECTIFIER

• In the family of semiconductors that includes transistors and diodes.

• Controls current in one direction

• Not all SCRs use the casing shown, but this is typical of most of the high-power units. From

http://www.tpub.com/neets/book7/26c.htm The electrical engineering training series

• Note: the cathode side is towards the negative side of the battery

• A SCR is very sensitive to too much electrical energy, we use a 1000 ohm resistor to protect the SCR from burning out.

• Which part of the SCR needs very little current?

• The gate• Which side is the

beveled edge?• The gateGate

Anode

Beveled Edge fronta

no

de

cath

od

e

220 Ohms

+

-9 volts

1K Ohms

gate

Similar to a basic light switch, transistors have two operating positions, on and off.

•The transistor is a solid state semiconductor device

•can be used for amplification, switching, voltage stabilization, signal modulation and many other functions.

• It acts as a variable valve which, based on its input voltage, controls the current drawn by it from a connected voltage supply.

The 555 timer is an extremely versatile integrated circuit which can be used to build lots of different circuits.

Integrated circuits are used for a variety of devices, including :

•microprocessors,

•audio and video equipment,

• automobiles and more

Integrated circuits are often classified by the number of transistors and other electronic components they contain:

SSI (small-scale integration): Up to 100 electronic components per chip MSI (medium-scale integration): From 100 to 3,000 electronic components per chip LSI (large-scale integration): From 3,000 to 100,000 electronic components per chip VLSI (very large-scale integration): From 100,000 to 1,000,000 electronic components per chip ULSI (ultra large-scale integration): More than 1 million electronic components per chip