Sunday, May 20, 2012

Diode Parameters

       The manufacturer of the diode provides the detail information about the diode, in the form of datasheet. The selection of diode or replacement of diode in an application circuit becomes easy by referring the diode datasheet specifications.
       The following are the most important specifications related to a diode which are available in all the datasheets.
Table 1 Diode datasheet specifications
       The specifications Vf and If are maximum limits which diode can handle safely, at a specific temperature. The IR is generally specified at two temperatures to indicate the effect pf temperature on it.
       To understand PIV specification, consider reverse biased diode as shown in the Fig. 1. It is replaced by its model i.e. open circuit in the Fig. 1(b).
Fig. 1  PIV rating of diode
       It can be seen that the voltage between the two points P and Q is the voltage across the diode in the reverse direction. This is the voltage that diode must withstand without breakdown. The maximum value of such a reverse voltage which diode can withstand safely is called PIV or PRV rating of the diode.
       The product of the current through diode and voltage across the diode, at a particular point of operation is the power dissipation across the diode.
                                             PD = VD ID
       The maximum value of PD i.e. PDmax which diode can withstand safely, without increasing the temperature of the junction above its limiting value is called power dissipation rating of the diode.
       The values of CD and CT indicate capacitance levels of the diode.
       If the diode is going to be switched from ON to OFF and OFF-ON in the circuit frequently then the reverse recovery time is important consideration. This specification is important for the switching diodes and not much important for general purpose rectifier diodes.
       The TJ indicates the safe range of junction temperature, which should not be exceeded while the circuit operation. The Tstg indicates the safe rang of storage temperature.

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