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Elektronika (16)
 

Elektronika (16)

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    Elektronika (16) Elektronika (16) Presentation Transcript

    • Elektronika
      AgusSetyo Budi, Dr. M.Sc
      Sesion #16
      JurusanFisika
      FakultasMatematikadanIlmuPengetahuanAlam
    • Outline
      28-1: Transistor Construction
      28-2: Proper Transistor Biasing
      28-3: Operating Regions
      28-4: Transistor Ratings
      28-5: Checking a Transistor with an Ohmmeter
      28-6: Transistor Biasing
      © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
      2
      07/01/2011
    • Bipolar Junction Transistors
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      © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
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    • 28-1: Transistor Construction
      A transistor has three doped regions, as shown in Fig. 28-1 (next slide).
      Fig. 28-1 (a) shows an npn transistor, and a pnp is shown in (b).
      For both types, the base is a narrow region sandwiched between the larger collector and emitter regions.
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    • 28-1: Transistor Construction
      • The emitter region is heavily doped and its job is to emit carriers into the base.
      • The base region is very thin and lightly doped.
      • Most of the current carriers injected into the base pass on to the collector.
      • The collector region is moderately doped and is the largest of all three regions.
      Fig. 28-1
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    • 28-2: Proper Transistor Biasing
      For a transistor to function properly as an amplifier, the emitter-base junction must be forward-biased and the collector-base junction must be reverse-biased.
      The common connection for the voltage sources are at the base lead of the transistor.
      The emitter-base supply voltage is designated VEE and the collector-base supply voltage is designated VCC.
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      © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
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    • 28-2: Proper Transistor Biasing
      • Fig. 28-4 shows transistor biasing for the common-base connection.
      • Proper biasing for an npn transistor is shown in (a).
      • The EB junction is forward-biased by the emitter supply voltage, VEE.
      • VCC reverse-biases the CB junction.
      • Fig. 28-4 (b) illustrates currents in a transistor.
      Fig. 28-4
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    • 28-3: Operating Regions
      • Collector current IC is controlled solely by the base current, IB.
      • By varying IB, a transistor can be made to operate in any one of the following regions
      • Saturation
      • Breakdown
      • Cutoff
      • Active
      Fig. 28-6: Common-emitter connection (a) circuit. (b) Graph of IC versus VCE for different base current values.
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      © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
      8
    • 28-3: Operating Regions
      • Fig. 28-7 shows the dc equivalent circuit of a transistor operating in the active region.
      • The base-emitter junction acts like a forward-biased diode with current, IB.
      • Usually, the second approximation of a diode is used.
      • If the transistor is silicon, assume that VBE equals 0.7 V.
      Fig. 28-7
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    • 28-4: Transistor Ratings
      A transistor, like any other device, has limitations on its operations.
      These limitations are specified in the manufacturer’s data sheet.
      Maximum ratings are given for
      Collector-base voltage
      Collector-emitter voltage
      Emitter-base voltage
      Collector current
      Power dissipation
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    • 28-5: Checking a Transistor with an Ohmmeter
      • An analog ohmmeter can be used to check a transistor because the emitter-base and collector-base junctions are p-n junctions.
      • This is illustrated in Fig. 28-8 where the npn transistor is replaced by its diode equivalent circuit.
      Fig. 28-8
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    • 28-5: Checking a Transistor with an Ohmmeter
      • To check the base-emitter junction of an npn transistor, first connect the ohmmeter as shown in Fig. 28-9 (a) and then reverse the ohmmeter leads as shown in (b).
      • For a good p-n junction made of silicon, the ratio RR/RF should be equal to or greater than 1000:1.
      Fig. 28-9
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      12
    • 28-5: Checking a Transistor with an Ohmmeter
      • To check the collector-base junction, first connect the ohmmeter as shown in Fig. 28-10 (a) and then reverse the ohmmeter leads as shown in (b).
      • For a good p-n junction made of silicon, the ratio RR/RF should be equal to or greater than 1000:1.
      • Although not shown, the resistance measured between the collector and emitter should read high or infinite for both connections of the meter leads.
      Fig. 28-10
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      © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
      13
    • 28-6: Transistor Biasing
      For a transistor to function properly as an amplifier, an external dc supply voltage must be applied to produce the desired collector current.
      Bias is defined as a control voltage or current.
      Transistors must be biased correctly to produce the desired circuit voltages and currents.
      The most common techniques used in biasing are
      Base
      Voltage-divider
      Emitter
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      © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
      14
    • 28-6: Transistor Biasing
      • Fig. 28-12 (a) shows the simplest way to bias a transistor, called base bias.
      • VBB is the base supply voltage, which is used to forward-bias the base-emitter junction.
      • RB is used to provide the desired value of base current.
      • VCC is the collector supply voltage, which provides the reverse-bias voltage required for the collector-base junction.
      • The collector resistor, RC, provides the desired voltage in the collector circuit.
      Fig. 28-12
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      15
    • 28-6: Transistor Biasing
      • The dc load line is a graph that allows us to determine all possible combinations of IC and VCE for a given amplifier.
      • For every value of collector current, IC, the corresponding value of VCE can be found by examining the dc load line.
      • A sample dc load line is shown in Fig. 28-14.
      Fig. 28-14
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      16
    • 28-6: Transistor Biasing
      Fig. 28-15 illustrates a dc load line showing the end points IC (sat) and VCE (off), as well as the Q point values ICQ and VCEQ.
      Fig. 28-15
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      17
    • 28-6: Transistor Biasing
      • The most popular way to bias a transistor is with voltage-divider bias.
      • The advantage of voltage-divider bias lies in its stability.
      • An example of voltage-divider bias is shown in Fig. 28-18.
      Fig. 28-18
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    • 28-6: Transistor Biasing
      • Fig. 28-19 shows the dc load line for voltage-divider biased transistor circuit in Fig. 28-18.
      • End points and Q points are
      • IC (sat) = 12.09 mA
      • VCE (off) = 15 V
      • ICQ = 7 mA
      • VCEQ = 6.32 V
      Fig. 28-19
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    • 28-6: Transistor Biasing
      • If both positive and negative power supplies are available, emitter bias provides a solid Q point that fluctuates very little with temperature variation and transistor replacement.
      • An example of emitter bias is shown in Fig. 28-23.
      Fig. 28-23
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