2. Reverse characteristics

In the electronic circuit, the positive pole of the diode is connected to the low potential end, and the negative pole is connected to the high potential end. At this time, there is almost no current flowing through the diode. At this time, the diode is in the cut-off state, which is called reverse bias. When the diode is in reverse bias, there will still be a weak reverse current flowing through the diode, called leakage current. When the reverse voltage at both ends of the diode increases to a certain value, the reverse current will increase sharply, and the diode will lose its unilateral conductivity. This state is called the breakdown of the diode.

Main parameters of diodes

The technical specifications used to indicate the performance and scope of application of the diode are called the parameters of the diode. Different types of diodes have different characteristic parameters. For beginners, the following main parameters must be understood:

1. rated forward working current

The maximum forward current allowed for a diode to pass in long-term continuous operation. Because when the current passes through the tube, the core will be heated and the temperature will rise. When the temperature exceeds the allowable limit (about 140 silicon tube and 90 germanium tube), the core will be overheated and damaged. Therefore, the rated forward working current of the diode should not be exceeded in the use of the diode. For example, the rated forward operating current of the commonly used IN4001-4007 Germanium Diode is 1A.

2. Maximum reverse operating voltage

When the reverse voltage at both ends of the diode reaches a certain value, it will break down the tube and lose the single-guide electric power. In order to ensure safe operation, the maximum reverse operating voltage is specified. For example, the reverse voltage withstand of IN4001 diode is 50V, and that of IN4007 diode is 1000V.

3. Reverse Current

Reverse current refers to the reverse current flowing through the diode under the specified temperature and maximum reverse voltage. The smaller the reverse current is, the better the unidirectional conductivity of the tube is. It is noteworthy that the reverse current has a close relationship with temperature, and the reverse current doubles every 10% rise in temperature. For example, if the reverse current of 2AP1 Germanium Diode is 250uA at 25 o'clock and the temperature rises to 35, the reverse current will rise to 500uA, and so on. At 75 o'clock, the reverse current of 2AP1 Germanium Diode reaches 8mA, which not only loses the unilateral conductivity, but also causes the tube to be overheated and damaged. For example, the reverse current of 2CP10 silicon diode is only 5uA at 25 and 160uA at 75. Therefore, silicon diode has better stability than germanium diode at high temperature.

Testing diodes

Beginners can use multimeter to test the performance of diodes in amateur conditions. Before testing, switch the multimeter to RX1K gear of Ohm gear (pay attention not to use RX1 gear, in order to avoid excessive current burning diodes), and then short circuit the red and black pens to zero ohm.