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SEMICONDUCTORS

SEMICONDUCTORS. Transistor Biasing. 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. SEMICONDUCTORS.

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SEMICONDUCTORS

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  1. SEMICONDUCTORS Transistor Biasing

  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. 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.

  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) SERIES CONNECTED BATTERIES

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

  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.

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

  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 IB. • The current the flows into the emitter is designated as IE.

  12. SEMICONDUCTORS • IC = Collector current • IB = Base current • IE= Emitter current IE = IB + IC

  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.

  14. SEMICONDUCTORS

  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?

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