Principal Ratings for Diodes

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Peak Inverse Voltage (PIV)

The peak inverse voltage rating of a diode is the maximum reverse voltage that can be connected across a diode without breakdown. If the PIV rating is exceeded, the diode begins to conduct in the reverse direction and can be immediately destroyed. PIV rating extend for tens of volts to several thousand volts, depending on the construction. The PIV rating is also called the peak reverse voltage (PRV) or breakdown voltage V(BR).

Maximum Average Forward Current (IF(avg)max)

The maximum average forward current is the maximum current a diode can safely handle when forward-biased. Power diodes are presently available in ratings from a few amperes to several hundred amperes. If a diode is to be used economically, it must be operated near its maximum forward current rating.

Reverse Recovery Time (trr)

The reverse recovery time of a diode is of great significance in high speed switching applications. A real diode not instantaneously switch from a conduction to a nonconduction state. Instead, reverse current flows for a short time, and the diode does not turn off until the reverse current decays to zero, as shown in Figure 1 below. The diode initially conducts a current IF, when the diode is reverse-biased, this current decreases and reverse current IRflows. The time interval during which reverse current flows is called the reverse recovery time. During this time, charge carriers that were stored in the junction when forward conduction terminated are removed.

Principal Ratings of Diode

Figure 1

Diodes are classified as “fast recovery” or “slow recovery” types based on their reverse recovery times. Recovery times range from a few microseconds in a PN junction diode to several hundred nanoseconds in a fast recovery diode like a Schottky diode. The PN junction diode is normally sufficient for rectification of a 60 Hz AC signal. Fast recovery diodes with low trr are used in high frequency applications such as inverters, choppers, and uninterruptible power supplies (UPS).

Maximum Junction Temperature

This parameter defines the maximum junction temperature that a diode can withstand without failure. The rated temperatures of silicon diodes typically range from -40O C to +200O C. Operation at lower temperatures generally results in better performance. Diodes are usually mounted on heat sinks to improve their temperature rating.

Maximum Surge Current (IFSM)

The IFSM (forward surge maximum) rating is the maximum current that the diode can handle as an occasional transient or from a circuit fault.

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