About Transistor (AT)

Transistors are electronic components that function as rectifiers, amplifiers, electrical switches, mixers, and generate electrical vibrations.

Getting to Know Transistor Components

Just like diodes, transistors also have a working voltage:

• Silicon : 0.6volt - 0.7volt
• germanium : 0.2volt -0.3volt

So if the bias voltage is less than the above provisions, the transistor will not be able to activate.

Transistor Symbol, where (a) is NPN while (b) is PNP

How to Determine Transistor Legs? 

You can read a complete review of this question  HERE .

Transistor Operating Characteristics

Transistor Operating Characteristics

Information:

• VCBO = Maximum collector base voltage
• VEBO = Maximum base emitter voltage
• VCEO = Maximum collector emitter voltage

Transistor as a switch

Information:

• If IB = 0 then IC becomes low leakage current, therefore: VCE » VCC
• If IB is small then IC = hFE * IB and the voltage through RL: VR = IC RL And VCE = VCC - IC RL
• If IB increases/enlarges then IC increases until it reaches IC RL » VCC, which is when IC cannot increase any further, even though IB continues to increase.
• At this point the transistor is said to be in saturation and the voltage VCE » 0.2 Volts.

Transistor Function

• As a rectifier
• As a voltage stabilizer
• As an Oscillator
• As a front amplifier (pre Amplifier)
• As a buffer
• As a driver
• As a power amplifier
• etc.

Common damage to transistors:

• Leakage between the electrodes.
• Connected (connected) between the electrodes.
• Break between the electrodes.
• Material damage in the form of broken emitter, base or collector electrodes.

Testing PNP transistors

1. Make sure the collector, emitter and base legs (you must know for sure).
2. Place the selector switch in the ohm meter (range) position.
3. The red (+) plug is placed on the Base leg (B), and the black (-) plug is attached to the Emitter leg (E). If the needle moves, then move the black plug to the Collector (C). If in the first and second measurements the needle moves, it means the transistor is in good condition, while if in one or both measurements the needle does not move, it means the transistor is damaged.

Testing PNP transistors

Testing NPN transistors

1. Make sure the collector, emitter and base legs (you must know for sure).
2. Place the selector switch in the ohm meter (range) position.
3. The red (+) plug is placed on leg C, and the black (-) plug is placed on leg B. If the needle moves, it means that between C and B is good. Then move the black plug to leg E, if the needle moves, it means that between E and B is good. 
4. If from one or both of these measurements the needle does not move, it means the transistor is broken.

Testing NPN transistors