The schottky diode got its name by its German physicist creator Walter H. Schottky. Schottky diodes are mainly used in high speed switching and in high frequency applications. Schottky diodes can also be known as hot–carrier diodes. Unlike most diodes that are created by joining two pieces of semiconductor material together, schottky diodes are constructed by joining a piece of metal with an n-type material. The resulting metal–semiconductor junction behaves like a diode. It conducts current in one direction [from the metal anode to the semiconductor cathode] and ask like an open circuit in the other direction. The current–voltage characteristic of a schottky diode is very similar to that of a pn-junction diode, with two exceptions:
1. The forward voltage drop of a schottky diode is less than that of a pn-junction diode. Schottky diodes can also be made of gallium arsenide and plays an important role in the construction of these circuits.
2. Current in a schottky diode is conducted by majority carriers [electrons]. Therefore these diodes do not show the minority–carrier charge–storage effects like a forward biased pn-junction. They are able to give up excess energy very rapidly. Schottky diodes are able to be switched from off to on, and vice versa, a lot faster than typical pn-junction diodes.
3. Reverse recovery time is probably the most important difference between a p-n junction and a schottky diode. The recovery time for a schottky is none existent when switching from conducting to non-conducting. In p-n junction switching there is also a reverse recovery current, which can create added noise in high powered semiconductors. In schottky diodes switching is practically instantaneous.
Schottky diodes are found in bipolar–transistor logic circuits, known as schottky-TTL, where TLL stands for transistor–transistor logic. Schottky diodes also have a few limitations. The biggest of which are the low reverse voltage ratings and relatively high reverse leakage current.
Applications of schottky diodes
1. Power supply - can be used as rectifiers in switched power supplies; efficiency is increased by the low forward voltage and quick recovery time.
2. Discharge and reverse card protection - can be used in photovoltaic systems to stop reverse current through the specific modules.
3. Voltage clamping - is a very popular application because of the high current density in a schottky diode. Most silicone diodes have a forward voltage drop of 0.6 volts and germanium diodes 0.3 volts. The forward voltage drop of a schottky diode can be as low as 0.15 volts.
Testing a Schottky Diode
First determine which side is the anode and which side is the cathode. The connect the positive of the ohmmeter to the anode and the negative to the cathode. If the meter beeps and reads continuity then the diode is functioning properly. Try reversing the leads if this does not happen. If continuity is still not found then the diode is not working properly.
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