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A PiN diode is a type of diode that contains a semiconductor with a very large intrinsic region (the ‘i’) between a smaller-than-normal positive and negative region (the ‘P’ and ‘N’). This large neutral region in the center of the semiconductor will lower the speed at which voltage moves through the system. A PiN diode is used for three basic reasons: as a radio frequency (RF) switch, as part of a photovoltaic cell and as an emergency shunt for power overloads.
A typical diode has a very small intrinsic area. Usually, diodes are composed of two connection terminals connected by a semiconductor. Diodes take in power through an anode and release it into a positively-charged area of a semiconductor. A small intrinsic layer separates the positive area from a negative region. The power moves through the intrinsic into the negative and then out through a cathode back into the device.
A PiN diode works a little differently. The power enters the diode and transfers to the positive region normally, but then it hits an extremely large intrinsic area. This area acts like a dam to the power moving through the system. It fills with more and more power as the positive area keeps sending it over. When it finally fills to the point where it simply can’t take anymore, it begins to push power into the negative zone.
These varying areas in the PiN diode semiconductor are created through a process called doping. Most semiconductors are made of silicon. When the actual semiconductor is built, the silicon is infused with a variety of metals, some of which enhance the positive system, while others enhance the negative. The intrinsic area on the PiN diode is doped very lightly if at all. This makes power rush into it and then sit while current builds up—it then rushes out.
When used as part of an RF switch, a PiN diode isolates signals. The construction on the diode allows some signal types to move through the intrinsic area more easily than others. This allows specific signals to pass through while keeping the others permanently blocked.
Photovoltaic cells require bursts of power to operate. In this case, the PiN diode blocks power from entering the system until there is a large buildup. That power is released all at once, triggering the cell.
The last common use for a PiN diode is as an emergency power shunt. When power moves through a system, a secondary offshoot may contain a PiN diode connected directly to the device’s grounding system. If the device operates normally, the intrinsic area of the PiN never fills up and, therefore, never moves power. If a surge hits the device, the intrinsic area fills, and the current moves out of the device to the ground, hopefully before the device is damaged.