1. 1 SEMICONDUCTORS Transistor Biasing

2. 2 SEMICONDUCTORS Here we have a collector junction that forms a PN junction diode configuration that is reverse biased that functions like a reverse biased diode and conducts a very small leakage current.

3. 3 SEMICONDUCTORS We should take a moment here and review a basic circuit symbol, the battery. The small cell is negative and the large cell is positive, current flows from negative to positive. We can put multiple cells together to increase voltage. We should take a moment here and review a basic circuit symbol, the battery. The small cell is negative and the large cell is positive, current flows from negative to positive. We can put multiple cells together to increase voltage.

4. 4 SEMICONDUCTORS If one cell equals 1.5 volts, then how many volts does 4 cells equal? (to increase voltage batteries are connected in series) If one cell equals 1.5 volts, then how many volts does 4 cells equal? (to increase voltage batteries are connected in series) SERIES CONNECTED BATTERIES

5. 5 SEMICONDUCTORS The collector junction in an NPN transistor is typically connected as a reverse biased arrangement with the positive lead connected to the collector lead.

6. 6 SEMICONDUCTORS Here we have an emitter junction that forms a PN junction diode configuration that is forward biased that functions like a forward biased diode and conducts a small amount of current.

7. 7 SEMICONDUCTORS Normally the emitter junction must be forward biased to function properly

8. 8 SEMICONDUCTORS You have just seen the action which takes place in an NPN transistor when the collector junction and the emitter junction are properly biased. A transistor must be simultaneously biased with the emitter junction forward biased and the collector junction reverse biased in an NPN transistor. You have just seen the action which takes place in an NPN transistor when the collector junction and the emitter junction are properly biased. A transistor must be simultaneously biased with the emitter junction forward biased and the collector junction reverse biased in an NPN transistor.

9. 9 SEMICONDUCTORS Here is the PNP transistor showing the proper biasing. The external voltages have been reversed from that of the NPN transistor. Here is the PNP transistor showing the proper biasing. The external voltages have been reversed from that of the NPN transistor. The battery (voltage) has been reversed

10. 10 SEMICONDUCTORS Compare the two transistor types and their configurations in this side by side diagram. Remember that both of these are properly biased. Compare the two transistor types and their configurations in this side by side diagram. Remember that both of these are properly biased.

11. 11 SEMICONDUCTORS In an NPN transistor the majority (95 to 99%) of the current supplied by the emitter flows through the collector. This is referred to as collector current and designated as Ic, a small percentage (1 to 5%) of the current flows through the base and is designated as I B. The current the flows into the emitter is designated as I E. In an NPN transistor the majority (95 to 99%) of the current supplied by the emitter flows through the collector. This is referred to as collector current and designated as Ic, a small percentage (1 to 5%) of the current flows through the base and is designated as I B. The current the flows into the emitter is designated as I E.

12. 12 SEMICONDUCTORS I C = Collector current I B = Base current I E = Emitter current I E = I B + I C I C = Collector current I B = Base current I E = Emitter current I E = I B + I C

13. 13 SEMICONDUCTORS In a PNP configuration the majority of the current supplied by the collector flows through the emitter and only a small percentage of the current flows through the base. This is the same action that occurs in an NPN transistor but in the opposite direction with collector current flowing through the emitter. In a PNP configuration the majority of the current supplied by the collector flows through the emitter and only a small percentage of the current flows through the base. This is the same action that occurs in an NPN transistor but in the opposite direction with collector current flowing through the emitter.

14. 14 SEMICONDUCTORS

15. 15 SEMICONDUCTORS In this diagram we see the transistor is labeled with the letter designation Q which is typical. Notice the battery on the emitter side of the transistor, what does the arrow mean? In this diagram we see the transistor is labeled with the letter designation Q which is typical. Notice the battery on the emitter side of the transistor, what does the arrow mean?