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American Microsemiconductor, Inc. - Diodes, All Types of diodes, We Have Your Diode
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In this discussion the term diode and rectifier will be used interchangeably, a low current rectifier implies a diode,and a high current or power device, conducting from 1 to 1000 amps or even higher, a rectifier. Many diodes or rectifiers are identified as 1NXXXX . A semiconductor diode consists of a PN junction and has two (2) terminals, an anode (+) and a cathode (-). Current flows from anode to cathode within the diode.
Properties of a diode
An ideal diode is like a light switch in your home. When the switch is closed, the circuit is completed; and the light turns on. When the switch is open, there is no current and the light is off.However, the diode has an additional property; it is unidirectional, i.e. current flows in only one direction (anode to cathode internally). When a forward voltage is applied, the diode conducts; and when a reverse voltage is applied, there is ideally no conduction. A mechanical analogy is a ratchet, which allows motion in one direction only.
Characteristics of a diode
Diode Forward Voltage Drop , Vf : Notice that the diode conducts a small current in the forward direction up to a threshold voltage, 0.3V for germanium diode and 0.7V for silicon diode; after that the diode conducts as expected. The forward voltage drop, Vf, is specified at a forward current If, within the diode.
Leakage current in the diode : In the reverse direction there is a small leakage current in the diode until the reverse breakdown voltage is reached. This leakage in the diode is undesirable, obviously the lower the better, and is specified at a voltage less than the breakdown; diodes are intended to operate below their breakdown voltage.
Current Rating of the diode : The current rating of a diode is determined primarily by the size of the diode chip, and both the material and configuration of the package, Average Current is usually specified, not RMS current. A larger chip and package of high thermal conductivity are both conducive to a higher current rating of the diode.
Diode Switching : The switching speed of a diode depends upon its construction and fabrication. In general the smaller the chip the faster it switches, other things being equal. The chip geometry, doping levels, and the temperature at nativity determine switching speeds of the diode. The reverse recovery time, trr, is the time it takes a diode to switch from ON to OFF.
Specifications of a diode:
The very minimal diode specifications are:
- Maximum reverse voltage of the diode
- Rated forward current of the diode
- Maximum forward voltage drop of the diode
- Maximum leakage current in the diode
- Diode package style
- Maximum reverse recovery time of the diode
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