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close this bookRadio and Electronics (DED Philippinen, 66 p.)
View the document(introduction...)
close this folder1. INTRODUCTION
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View the document1.1. A TRIAL TO STATE A DEFINITION OF ELECTRONICS
View the document1.2. A SHORT HISTORY OF ELECTRONICS
View the document1.3. CLASSIFICATION OF ELECTRONIC DEVICES
close this folder2. PRINCIPLES OF RADIO COMMUNICATION UNICATION
View the document2.1. BASICAL IDEAS ABOUT COMMUNICATION
View the document2.2. DEVELOPMENT OF LONG DISTANCE COMMUNICATION
View the document2.3. FIDELITY AND DISTORTION
close this folder3. TRANSDUCERS
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View the document3.1. MICROPHONES
View the document3.2. LOUDSPEAKERS
View the document3.3. THE TELEPHON SYSTEM
View the document3.4. PROBLEM OF FREQUENCY RANGES
View the document3.5. BANDWIDTH
close this folder4. RADIOWAVES
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View the document4.1. ORIGIN OF RADIOWAVES
View the document4.2. PARAMETERS OF ELECTROMAGNETIC WAVES
View the document4.3. PROPAGATION OF RADIOWAVES
View the document4.4. SPECTRUM OF RADIOWAVES AND BANDS OF RADIOWAVES
close this folder5. MODULATION OF RADIOWAVES
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View the document5.1. THE AMPLITUDE MODULATION (AM)
View the document5.2. FREQUENCY MODULATION (FM)
View the document5.3. SIDEBANDS
View the document5.4. TRANSMISSION OF RADIOSIGNALS
close this folder6. RECEPTION OF RADIOSIGNALS (AM - TYPE)
View the document6.1. AERIAL
View the document6.2. THE TUNED CIRCUIT
View the document6.3. INCIDENTAL REMARK ON BLOCK DIAGRAMS
View the document6.4. DETECTOR OR DEMODULATOR
View the document6.5. POWER SUPPLY
View the document6.6. AMPLIFIER
View the document6.7. SUPERHET RECEIVER (the SUPER)
View the document6.8 INCIDENTAL REMARK ON MIXING FREQUENCIES
View the document6.9. CONSTRUCTION OF A SUPERHETRADIO
close this folder7. COMPONENTS OF MODERN RADIO RECEIVERS
View the document7.1.1. HANDLING OF ELECTRONIC COMPONENTS
View the document7.1.2. HANDLING OF PRINTED CIRCUITS
View the document7.1.3. DIFFERENTIATION OF COMPONENTS
close this folder8. PASSIVE COMPONENTS
View the document8.1. RESISTORS ELECTRICAL CHARACTERISTICS
View the document8.2. CAPACITORS
View the document8.3. INDUCTORS
close this folder8.4. COMBINATION OF PASSIVE COMPONENTS
View the document8.4.1. SERIES CONNECTION OF R AND C, OR R AND L
View the document8.4.2. COMBINATION OF L AND C, RESONANT (TUNED) CIRCUITS
close this folder8.4.3. TUNED CIRCUIT CONNECTED TO AN AC-VOLTAGE
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View the document8.4.4.1. QUALITY OF TUNED CIRCUITS
View the document8.4.4.2. BANDWIDTH
close this folder9. ACTIVE COMPONENTS -1- DIODES
View the document9.1. CHARACTERISTICS OF SEMICONDUCTORS
close this folder9.2. THE PN-JUNCTION OR DIODE
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View the document9.2.1. PN-JUNCTION CONNECTED TO VOLTAGE
View the document9.2.2. CHARACTERISTICS OF A PN-JUNCTION OR DIODE
View the document9.2.3. ZENERDIODE
close this folder10. BLOCKS OF RADIOS / -1- / POWER SUPPLIES
View the document10.1. GENERAL CONSIDERATIONS
View the document10.2. TRANSFORMER
View the document10.3. THE RECTIFIERS.
close this folder10.4. SMOOTHING AND FILTER CIRCUITS
View the document10.4.1. THE RESERVOIR CAPACITOR
View the document10.4.2. FILTER CIRCUITS
close this folder10.5. STABILIZATION
close this folder10.5.1. GENERAL REMARKS
View the document10.5.1.1. LOAD VARIATIONS
View the document10.5.1.2. INTERNAL RESISTANCE OF VOLTAGESOURCES
View the document10.5.1.3. PROBLEMS CAUSED BY THE SMOOTHING CIRCUIT
close this folder10.5.5. METHODS OF STABILIZATION
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View the document10.5.5.1. PARALLEL-STABILIZATION
View the document10.5.2.2. SERIES STABILIZATION
close this folder11. ACTIVE COMPONENTS -2- / TRANSISTORS
View the document11.1. CONSTRUCTION OF A TRANSISTOR
close this folder11.2. CHARACTERISTICS OF TRANSISTORS
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close this folder11.2.1 HANDLING OF CHARACTERISTICS OF TRANSISTORS
View the document11.2.1.1. CONSTRUCTION OF THE STATIC-MUTUAL-CHARACTERISTICS
View the document11.2.1.2. CONSTRUCTION OF THE DYNAMIC MUTUAL CHARACTERISTICS
View the document11.2.1.3. CONSTRUCTION OF THE MAXIMUM-POWER-LINE
close this folder12. AMPLIFIERS
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View the document12.1. STRUCTURE OF A CLASS A AMPLIFIER
View the document12.2. FUNCTION OF A SIMPLE CLASS A AMPLIFIER
View the document12.3. ADVANCED CLASS A AMPLIFIER
View the document12.4. STABILIZATION OF THE QUIESCENT VOLTAGE
close this folder13. CLASS B AMPLIFIERS
View the document13.1. LIMITS OF CLASS A AMPLIFIERS
View the document13.2. CLASS B AMPLIFIERS WITH TRANSFORMERS
View the document13.3. CLASS B AMPLIFIERS WITHOUT TRANSFORMERS
View the document13.4. POWER AMPLIFIER WITH COMPLIMENTARY TRANSISTORS.
View the document14. DETECTOR OR DEMODULATOR
View the document15. AGC-AUTOMATIC GAIN CONTROL
View the document16. IF-AMPLIFIERS
View the document17. FEEDBACK
View the document18. OSCILLATORS
View the document19. FREQUENCY CHANGERS MIXERSTAGE
View the document20. DECOUPLING CIRCUITS
View the document21. MATCHING OF AMPLIFIERSTAGES
View the document22. COUPLING OF AMPLIFIERSTAGES
close this folder23. RADIO SERVICING
View the document23.1. IMPORTANCE AND SUBJECT OF FAULT FINDING
View the document23.2. FAULTS AND FAULT FINDING
View the document23.3. FAULT FINDING METHODS
View the document24. THE USE OF THE OSCILLOSCOPE

11.1. CONSTRUCTION OF A TRANSISTOR

Transistors consist of three sections of a semiconducting base material. The two outer sections being doped in opposite sense, the centre section - called the BASE. The outer two sections are called:

COLLECTOR and EMITTER.


fig. 119

Between these three sections and obviously between the three terminals too, there are two junctions of PN-type, these two junctions can be looked at as two diodes connected in opposite direction.

Connection basically:

If the transistor is used in an electronic circuit generally the collector-base junction is connected in reverse direction and the base-emitter junction is connected in forward direction.

Function (simplified):

If there flows a considerable small current through the base-emitter junction, this allows a considerable strong current to flow from collector to emitter. The sketch in fig. 122 shows this behaviour very simplified.


fig. 122a


fig. 122b

Notation of transistors:

To find out which type of transistors we deal with we have to know the notation of transistors.

In most cases you find a combination of letters and figures on the case of the transistor. To find out exactly the specifications of this very transistor. You have actually to use a databook.

But very often the notation gives us hints about what the transistor is normally used for.

How does the transistor do its job?

Incidental remark:

Here will be derived the function of an NPN-transistor and an PNP-transistor in a similar manner.

It must be kept in mind, that the base layer in any transistor is very tiny in comparison with the two other layers. To explain the function of a transistor it must be dealt with as being connected to voltage sources. There are different possibilities to connect it two voltage sources. The possibility used here is the so called COMMON EMITTER CONNECTION.

This connection is the most often used one in practice. Therefore the other connections will not be dealt with here.

By the way: the transistor technology is still developing and this development led to new transistors, which can be used in common-emitter connection even in cases where in former times another connection was necessary.

Derivation of the function:

1. If a transistor is connected to a voltage-source as shown in fig. 123 it will not conduct any current, because one of the PN-junctions is always biased in reverse direction.


fig. 123

2. As long as the voltage between base and emitter is connected in reverse direction there will not flow any current as well - as we know already from our explanations about a diode.


fig. 124

3. As soon as a voltage source is connected to the base-emitter junction in forward direction, and the voltage reaches a level higher than the so-called threshold voltage, of this junction, there will start to flow a current through this junction.

This current causes within the transistor a very special effect:

The chargecarriers (electrons or “holes”) enter the base-region. But as the base region is very narrow, these chargecarriers comming in big numbers from the wide emitter-region cannot be channelled totally through the base terminal.

So they invade the depletion-layer of the collector-base junction. But at the collector terminal with a strong polarity of the voltage-source connected to the collector and the emitter-terminals waiting for those charge-carriers, and attracts them through the depletion layer causing a current to flow through a PN-juncion (collector-base junction) in reverse direction.


fig. 126

The current channeled from collector to emitter (or vice versa) by the base current is called the COLLECTOR CURRENT.

This collector current is depending on the amount of BASE-CURRENT which was the origin of the effect.

As soon as the base current will be changed or interrupted, the collector current will change proportionally or will be interrupted as well.

The big advantage of the transistor is: the collector current is between 20 to 200 times bigger than the base - current.

SUMMING UP:

The transistor is a device which makes it possible to control.

A big current (COLLECTOR CURRENT) by a very small current (BASE CURRENT).