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Full-wave Rectifier. 5. Complete the sentences using while. Follow the model on page 13. 6. Pair work. Put these questions to your groupmate and let him/her answer them.
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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 high-voltage winding is positive, current flows through die upper tube.
During the opposite half cycle the lower end of die 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.
4. 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 high-voltage 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. |
5. Complete the sentences using while. Follow the model on page 13.
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 ….
6. 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?
Unit Twenty [20]
1. a) Cover the right column and read the English words. Translate them into Russian and check your translation.
b) Cover the left column and translate the Russian words back into English.
| to feed (fed) | питать | |
| to include | [ɪ nˈ kluː d] | содержать, заключать (в себе) |
| to remain | [rɪ ˈ meɪ n] | оставаться |
| to push | [puʃ ] | толкать |
| to pull | [pul] | тянуть |
| push-pull | пушпул, пушпульный | |
| push-pull amplifier | двухтактный усилитель | |
| push-pull circuit | двухтактная схема | |
| push-pull transformer | пушпульный трансформатор | |
| feedback | обратная связь | |
| feedback amplifier | регенеративный усилитель | |
| feedback coil | катушка обратной связи | |
| feeding transformer | силовой трансформатор |
2. Put down the Russian for:
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| plate current supply | ___________________________________ |
| alternating current components | ___________________________________ |
| maximum grid voltage | ___________________________________ |
| transformer secondary winding | ___________________________________ |
Push-pull Amplifier
An amplifier is used to produce the output voltage greater than the input voltage. A push-pull amplifier includes two tubes. Their control grids are connected to the opposite ends of the input transformer secondary winding. The centre of this winding is connected to the tube cathodes. When maximum grid voltage is produced in one tube, minimum grid voltage is produced in the other tube. Thus, the sum of the plate currents remains constant.
The plate currents are fed into the opposite ends of the output transformer or a choke coil. It has its centre connected through the plate current supply to the cathodes. Thus direct current plate components are eliminated but alternating current components add in the circuit.
3. Complete these sentences, using the correct variant:
| 1. An amplifier is used | a) to separate a. c. from d. c. b) to change the value of the input voltage. |
| 2. The input voltage is increased | a) by means of a rectifier. b) by means of an amplifier. |
| 3. A push-pull amplifier includes | a) only one tube. b) two tubes. |
| 4. When maximum grid voltage is produced in one tube | a) maximum grid voltage is produced in the other tube. b) minimum grid voltage is produced in the other tube. |
| 5. The sum of the plate currents | a) changes. b) remains constant. |
| 6. D. c. components | a) are eliminated. b) add in the circuit. |
| 7. A. c. components | a) add in the circuit. b) are eliminated. |
4. Complete the sentences using while. Follow the model on page 13:
1. An amplifier is used to increase the value of the input voltage ….
2. When maximum grid voltage is produced in one tube ….
3. Direct current plate components are eliminated ….
5. Answer the following questions:
1. What is an amplifier used for?
2. By what means is a greater output voltage produced?
3. What are the main parts of a push-pull amplifier?
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4. In what way are the tubes and the transformer connected?
5. Why does die sum of the plate currents remain constant?
6. Where are the plate currents fed?
7. What type of current is amplified by a push-pull amplifier?
8. What is the difference between a rectifier and an amplifier?
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