BJT Transistors

Testing if a BJT transistor is an NPN type or PNP type

To test if a transistor is NPN or PNP you need a multimeter and put it on the diode test function.

to test for an NPN you place the red lead on the base (B) and the black lead on the collector (C) and you should get O/L when you swap the leads around you should get a reading because in a transistor the collector and emmiter are back to back diodes therefore you should not get a reading in the reverse direction (base to collector or emmiter). In a PNP transistor it is the exact opposite, you should get a reading from base to collector because noe the diodes are going the opposite way to an NPN.                                                                                                                

this table above represents the readings i got when i measured the different legs to see if the transistor was PNP or NPN and also to see if the transistor was functional.

Experiment 1: Transistor as a switch 

components 1 small NPN transistor, 2 resistors

exercise is to build this circuit on a breadboard

<>

<>

Transistor number	Vbe	Veb	Vbc	Vcb	Vce	Vec
NPN	0.719	Ol	0.722	Ol	Ol	Ol
PNP	Ol	0..722	Ol	0.718	Ol	ol

when i connected the multimeter between the base and emmiter i got a reading of 0.7v which indicates that the diode within the transistor from the base to the emitter is operating and using 0.7v.

when i connected the multimeter between collecter and emmiter i got a reading of 1.4v which means the transistor is on.

there are 3 main regions that a transistor will operate in these are the active region, cut off region and the saturated region. During the active ragion the transistor is in between aturated and cut off which means it is on. when the transistor is in the cut off region it is off because it does not have enough mA to pass through the diodes. when the transistor is in its saturated region it is fully on and fully saturated.

 to work out the power dissipation for a transistor you use this formula Pd=Vce x IB

E.g. 3 x 0.005 =0.015 therfoe the answer is 15mW.