Transistors

By

Virus

Safety

• Remove all jewelry and watches • Wear safety glasses• Unplug power plug when placing hands inside live

equipment.• Wear static wrist strap when troubleshooting

sensitive equipment such as computers. Honestly, I never do but for static electricity if you don’t then you could damage parts.

General configuration

• A transistor is a semiconductor device, commonly used as an amplifier or an electrically controlled switch.

• The transistor is the main building block “element” of electronics • There are two types of standard transistors, NPN and PNP, with

different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon. This page is mostly about NPN transistors and if you are new to electronics it is best to start by learning how to use these first.

• It is a semiconductor device and it comes in two general types: the Bipolar Junction Transistor (BJT) and the Field Effect Transistor (FET).

• The leads are labeled base (B), collector (C) and emitter (E).Common uses are logic gates, music amplifies, and computers (memory uses this VSLI process)

Equipment needed

Qty--Name

• 5--VDC Power supply

• 2--1K OHM resistors

• 1--2N3904 NPN transistor

• 1--Digital Multi meter (DMM)

What type of transistor configuration is this?

1. PNP

2. NPN

3. BJT

4. OPAMP

5. Diode

Design: Measure/analyze test points 1 & 2 and submit results.

Failure: What would the output be at collector-emitter if Q2 was open? Reengineer a new design.

TP1

TP2

“TP” means Test points

Question: Measure/analyze test points 1 & 2 and submit results

Questions• What is the voltage drop across a single

silicon transistor?• What would you expect to see across your

multimeter (DMM)?• Why is your leads placed between the B-E or

base–emitter junction?• If you have .3Volts across a Germanium style

transistor will that saturate it?• What similar characteristic does a transistor

function as?

A .6 or .7 Voltage drop across silicon style transistor will saturate or turn the transistor on so current can flow like a simple switch

Saturated current flows in this direction from collector to emitter junction

Why does this say 775.596mV instead of .775596V?

Explain how you would fix this?

oscope

Tektronix is the preferred o-scope I use. I have always like this brand and find the digital scopes better than the old analog.

Get used to using the Tektronix because you will see them often.

What is my reading?

What is each block represent?

Each mark represent 1 volt if CH1 was set to 5V increments?

1V

1V

However, in our example each mark represents .2V. Now looking that our line is on the 3rd mark to calculate volts you multiply .2 x 3 = .6volts. (.6volts is our answer)

1V

1V

1V

Total = 5VDC

Questions• What is the voltage drop across a

Darlington silicon transistor? Hint we know have two transistors?

• What would you expect to see across your multimeter (DMM)?

• Why is your leads placed between the B-E or base–emitter junction?

Answer next time…

More to come