Практическое занятие 15. Использование электронных ламп

Lesson 1 5. Use of Electron Tubes

 

1. Read and learn the words:

 

half - половина

to rectify - выпрямлять

to amplify - усиливать

to convert - преобразовывать, обращать

by means of - посредством, с помощью

that is why - вот почему

to put into operation - приводить в действие, запускать

 

Read and translate the text.

Use of Electron Tubes

Let us consider some cases of electron tube application. Tubes are common elements of radio and electronic devices. Tubes are used as rectifiers - to convert a.c. into d.c., as oscillators - to produce oscillating waves and as amplifiers - to amplify the input voltage and current.

Half-Wave Rectifier

Alternating current is converted into direct current by means of a rectifier.

A half-wave rectifier consists of a diode in series with a resistance. In order to put a rectifier into operation, a source of a.c. should be applied to it. When an a.c. source is applied the diode begins to conduct.

The rectifier passes currents during positive half-cycles of the applied voltage. That is why it is called a half-wave rectifier. When the device operates d.c. flows in the same direction. It is a pulsating current. Since pulsations should be  eliminated, a filter is applied. Pulsations are eliminated by means of this filter.

 

3. Complete the sentences using the correct variant:

1. Electron tubes are used

a) as amplifiers only.

b) as oscillators only.

c) as rectifiers, amplifiers and oscillators.

 

2. A.c. is converted into d.c.

 a) by means of a rectifier.

b) by means of an amplifier.

 

3. A half-wave rectifier consists of

a) a diode in series with a transformer.

b) a diode in series with a resistor.

 

4. In order to put a rectifier into operation

a) d. c. is applied.

b) a.c. is applied.

 

5. A half-wave rectifier passes currents

a) during positive and negative half-cycles.

b) during positive half-cycles of the applied voltage.

 

6. Rectified current is

a) direct oscillating current.

b) direct pulsating current.

 

7. Pulsations are eliminated

a) by means of a choke coil.

b) by means of a filter.

 

4. Answer the following questions:

1. How are electron tubes used?

2. What type of device is called a rectifier?

3. By what means is alternating current rectified into direct current?

4. What elements does a half-wave rectifier consist of?

5. What current should be applied to put a half-wave rectifier into operation?

6. When does a half-wave rectifier pass current?

7. By what means are pulsations eliminated?

 

Draw a scheme of a half-wave rectifier and describe its operation.

Практическое занятие 16. Двухполупериодный выпрямитель

Lesson 1 6. Full - wave Rectifier

Read and learn the words:

End - конец, конечный

Tap - отвод, ответвление

Filament - нить накала

Lower - нижний

Upper - верхний

Secondary - вторичный

end capacity - конечная емкость

end coils - концевые витки

filament battery - батарея накала

filament current - ток накала

secondary circuit - вторичный контур

secondary resistance - дополнительное сопротивление

secondary battery - аккумуляторная батарея

frequency waves - длинные волны

Read and translate the text.

Full-wave Rectifier

In a full-wave rectifier two diodes are used. They are connected to a common load resistance. The secondary of the transformers has a centre tap to which the load is connected. Current flows through the tubes from their plates to their cathodes. When the upper end of the highvoltage winding is positive, current flows through the upper tube.

During the opposite half cycle the lower end of the high voltage winding becomes positive. The plate of the lower tube becomes positive and the plate of the upper tube - negative. Thus now the lower tube conducts current. Current flows through the filament winding to its centre tap, then through the load to the centre tap of the high-voltage winding and to the tube plate which is positive.

3. Complete the sentences using the correct variant:

 

1. A full-wave rectifier contains

a) one diode.

b) two diodes.

 

2. The load is connected to

a) the centre tap of the primary.

b) the centre tap of the secondary.

 

3. Current flows through the tubes

a) from the plates to the cathodes.

b) from the cathodes to the plates.

 

4. When the upper end of the highvoltage winding is positive

a) current flows through the upper tube.

b) current flows through the lower tube.

 

5. During the negative half-cycle

a) the plate of the lower tube becomes positive.

b) the plate of the lower tube becomes negative.

 

6. During the positive half-cycle

a) the lower tube conducts current.

b) the upper tube conducts current.

 

4. Complete the sentences using while.

 

1. A half-wave rectifier contains one diode..........

2. When the upper end of the high-voltage winding is positive, current

flows through the upper tube..........

3. During the negative half-cycle the lower tube conducts current..........

 

5. Pair work. Put these questions to your groupmate and let him/her answer them.

 

1. How many diodes does a full-wave rectifier contain?

2. What element is the load connected to?

3. What is the direction of current in the tubes?

4. During which cycle does the plate become negative?

5. When does the lower tube conduct current?

6. When does the upper tube conduct current?

7. What is the difference between a half-wave and a full-wave rectifier?

8. What is the difference in their construction?

9. In what way does a full-wave rectifier operate?

10. In what way does a half-wave rectifier operate?

11. What are the main parts of a half-wave rectifier?

12. What are the main parts of a full-wave rectifier?