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Prepared by: Cesar Mendoza Applied Technology Teacher Prepared by: CESAR MENDOZA-Applied Technology Teacher

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Upon successful completion of this module, students should be able to: 1. State the advantages of a transistor over vacuum tubes. 2. Define a Bipolar Junction Transistor. 3. Differentiate between an NPN and a PNP transistor in terms of their construction, two-diode analogy and symbols. 4. Identify the three different BJT terminals and state the function of each terminal. 5. Recognize the low-power and high-power BJTs. 6. Measure transistor currents, and confirm that the emitter current is the sum of the collector and base currents. 7. State the common applications of a Bipolar Junction Transistor. 8. Describe the three different BJT configurations with the help of circuit diagrams. 9. Describe the application of a BJT as a switch through a practical demonstration. 10. Build and test an automatic night lamp circuit to demonstrate the function of a BJT as a switch. 11. Build and test a simple temperature control system. Prepared by: CESAR MENDOZA-Applied Technology Teacher

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The reasons are obviously its advantages over vacuum tubes such as : 1. compact size, 2. light weight, 3. more resistive to shocks and vibrations, 4. low operating voltage, 5. long life and so on. Prepared by: CESAR MENDOZA-Applied Technology Teacher

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A Bipolar Junction Transistor (BJT) is defined as a three-terminal semiconductor device, whose operation depends upon the flow of electric charge carriers within the solid. The word transistor is derived from the combination of two words, Transfer-Resistance. It means that it is a device, which transfers a low resistance into a circuit having high resistance. Transistors in general are classified as bipolar or unipolar type. The bipolar type has two PN-Junctions, while unipolar types have only one PN-Junction. Prepared by: CESAR MENDOZA-Applied Technology Teacher

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The three regions are called 1.Emitter (E), 2.Base (B), and 3.Collector (C), and the two PN-junctions are a. C-B junction and b. E-B junction. Prepared by: CESAR MENDOZA-Applied Technology Teacher

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E E - Emitter C - Collector Base -B Emitter: To emit majority charge carriers into the base. Base: Base is the middle, extremely thin, and lightly doped region. It controls the electrons flowing to the collector. Collector: To collect the emitted charge carriers through the base. The functions of the three regions are as follows:

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Lowpower, small-signal transistors are sealed in a metal, plastic or epoxy package. Prepared by: CESAR MENDOZA-Applied Technology Teacher

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High power transistors are usually designed to be mounted onto a metal frame, which acts as a heat sink (to conduct heat away). Prepared by: CESAR MENDOZA-Applied Technology Teacher

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To use a BJT, we connect it so that: A. Its emitter is its negative terminal. B. The collector is several volts positive of its emitter. C. The base is 0.7V (or slightly more) positive of its emitter. Under these conditions, we find that: 1. A small base current flows into the base. 2. A much larger current flows into the collector. 3. The base and collector currents flow out of the emitter Prepared by: CESAR MENDOZA-Applied Technology Teacher I E = I C + I B where I E Emitter current, I C Collector current, and I B Base current

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Common applications of a transistor include the following: 1. A switch 2. An amplifier Prepared by: CESAR MENDOZA-Applied Technology Teacher

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When the switch is closed, a small current flows into the base (B) of the transistor, which is just enough to make LED B glow dimly. Prepared by: CESAR MENDOZA-Applied Technology Teacher When the switch is open, no base current flows, so the transistor switches off the collector current.

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Amplification is the process of increasing the level of a weak signal. A small change in the base current of a transistor produces a large variation in the collector current Prepared by: CESAR MENDOZA-Applied Technology Teacher

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