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- 2. 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
- 4. 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. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 4
- 6. The base region is very thin and lightly doped.
- 7. Most of the current carriers injected into the base pass on to the collector.
- 8. The collector region is moderately doped and is the largest of all three regions.Fig. 28-1 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 5
- 9. 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. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 6
- 12. The EB junction is forward-biased by the emitter supply voltage, VEE.
- 14. Fig. 28-4 (b) illustrates currents in a transistor.Fig. 28-4 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 7
- 16. By varying IB, a transistor can be made to operate in any one of the following regions
- 20. ActiveFig. 28-6: Common-emitter connection (a) circuit. (b) Graph of IC versus VCE for different base current values. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 8
- 22. The base-emitter junction acts like a forward-biased diode with current, IB.
- 24. If the transistor is silicon, assume that VBE equals 0.7 V.Fig. 28-7 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 9
- 25. 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 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 10
- 27. This is illustrated in Fig. 28-8 where the npn transistor is replaced by its diode equivalent circuit.Fig. 28-8 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 11
- 29. 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 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 12
- 31. For a good p-n junction made of silicon, the ratio RR/RF should be equal to or greater than 1000:1.
- 32. 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 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 13
- 33. 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 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 14
- 35. VBB is the base supply voltage, which is used to forward-bias the base-emitter junction.
- 36. RB is used to provide the desired value of base current.
- 37. VCC is the collector supply voltage, which provides the reverse-bias voltage required for the collector-base junction.
- 38. The collector resistor, RC, provides the desired voltage in the collector circuit.Fig. 28-12 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 15
- 40. For every value of collector current, IC, the corresponding value of VCE can be found by examining the dc load line.
- 41. A sample dc load line is shown in Fig. 28-14.Fig. 28-14 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 16
- 42. 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 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 17
- 45. An example of voltage-divider bias is shown in Fig. 28-18.Fig. 28-18 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 18
- 51. VCEQ = 6.32 VFig. 28-19 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 19
- 53. An example of emitter bias is shown in Fig. 28-23.Fig. 28-23 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 20
- 54. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 21 TerimaKasih