Reading. 4.Listen to the text and use the information in Fig

Listening

4. Listen to the text and use the information in Fig. 2.2 to help your comprehension.

Fig. 2.2 Internal structure of a p-n diode.

5. Listen to the text once more and decide if the sentences are true or false.

1. Bulbs save energy and money.

2. A diode is an electronic component made from a p-n junction.

3. The cathode is the negative side of the diode.

4. The positive side of a diode is called the anode.

5. The lead attached to the p-type semiconductor is called the cathode.

6. The lead attached to the n-type semiconductor is called the anode.

7. Forward bias doesn't allow current to flow.

8. Reverse bias allows current to flow through the diode.

6. Read the text and answer the questions:

Where is the anode?

Where is the cathode?

Indicate the anode and cathode in Figure 3.

Fig. 2.3. Electronic symbol of a diode.

The schematic symbol of a diode is shown in Fig. 2.3. Here are two useful tricks for remembering which side of the symbol is the anode and which is the cathode:

· think of the anode side of the symbol as an arrow that indicates the direction of conventional current flow – from positive to negative. Thus, the diode allows current to flow in the direction of the arrow;

· think of the vertical line on the cathode side as a giant minus sign, indicating which side of the diode is negative for forward bias.

7. Read the text and fill in the gaps with the words and word combinations in the box.

backward reverse biased amount peak inverse voltage forward voltage drop diode current forward biased

Forward and reverse bias can be illustrated with two very simple circuits that connect a lamp to a battery with diodes. In the circuit on the left (Fig. 2.4), the diode is (1) ………………., so current flows through the circuit and the lamp lights up. In the circuit on the right, the diode is (2) ……………, so current doesn't flow and the lamp remains dark.

Fig. 2.4 Forward biased and reverse biased circuits.

Note that in a typical diode, a certain amount of forward voltage is required before any current will flow. This (3) …………..is usually very small. In most diodes, this voltage is around half a volt. Up to this voltage, current doesn't flow. However once the forward voltage is reached, current flows easily through the (4)….............

This minimum threshold of voltage in the forward direction is called the diode's forward voltage drop. That's because the circuit loses this voltage at the diode. For example, if you were to place a voltmeter across the leads of the diode in the forward-biased circuit, you would read the (5) …………………of the diode.

Diodes also have a maximum reverse voltage they can withstand before they break down and allow current to flow (6) ……………….through the diode. This reverse voltage (sometimes called PIV, for (7) ………………, or PRV for peak reverse voltage) is an important specification for diodes you use in your circuits, as you need to ensure that your diodes won't be exposed to more than their PIV rating.

Besides the forward-voltage drop and peak inverse voltage, diodes are also rated for a maximum current rating. Exceed this (8) ………………, and the diode will be damaged beyond repair.

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