The performance of a diode can be described by its volt-ampere characteristics. Voltage U is applied at both ends of the diode, and the current I flowing through the diode is measured. The relationship between voltage and current I =f(U) is the volt-ampere characteristic curve of the diode, as shown in Figure 1.
Figure 1 Diode volt-ampere characteristic curve
The volt - ampere characteristic expression of the diode can be expressed as Formula 1-2-1
(1)
Where iD is the current flowing through both ends of the diode, uD is the pressure flowing through both ends of the diode, UT is taken at room temperature at 26mV. IS IS the reverse saturation current.
1. Positive characteristics
The right half of the characteristic curve 1 is called the forward characteristic, as can be seen from the figure, when the forward voltage on the diode is small, the forward current is small, almost equal to zero. The positive current increases significantly only when the voltage at both ends of the diode exceeds a certain value Uon. Call Uon the dead - zone voltage. The dead - zone voltage is related to the material of the diode. The dead zone voltage of general silicon diode is about 0.5V, and that of germanium diode is about 0.1V.
When the forward voltage exceeds the dead zone voltage, the forward current will increase rapidly with the increase of the voltage, and the relationship between the current and the voltage is basically an exponential curve. As can be seen from the forward characteristic curve, the current flowing through the diode has a great change, but the voltage at both ends of the diode remains basically unchanged. In the approximate analysis calculation, this voltage is called the open voltage. The opening voltage is related to the material of the diode. The dead zone voltage of general silicon diode is about 0.7V, and that of germanium diode is about 0.2V.
2. Reverse characteristics
The left half of the characteristic curve 1 IS called the reverse characteristic, as can be seen from the figure, when the diode IS applied with the reverse voltage, the reverse current IS very small, and the reverse current no longer increases with the reverse voltage, that IS, saturation IS reached. This current IS called the reverse saturation current and IS represented by the symbol IS.
If the reverse voltage continues to rise, when UBR is exceeded, the reverse current increases sharply. This phenomenon is called breakdown, and UBR is called reverse breakdown voltage. diode
Figure 2 Temperature characteristics of the diode
No longer has unidirectional conductivity after breakdown. It should be noted that a reverse breakdown does not imply diode damage. In fact, when the reverse breakdown, as long as pay attention to control the value of the reverse current, do not make it too large, you can avoid overheating and burn out the diode. When the reverse voltage is reduced, the diode performance may return to normal.
3. Influence of temperature on diode volt-ampere characteristics
When the temperature rises, the forward characteristic moves to the left and the reverse characteristic moves down. Near room temperature, every 1¡æ increase in temperature; Reduction of forward pressure drop by 2-2.5mV; Near room temperature, the reverse current doubles for every 10¡æ increase in temperature. The temperature characteristics of the diode are shown in Figure 2.
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