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Operation

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When a junction is formed between N-type and P-type semiconductor materials, the resulting device is called a diode. This component offers an extremely low resistance to current flow in one direction and an extremely high resistance to current flow in the other. This characteristic allows the diode to be used in applications that require a circuit to behave differently according to the direction of current flowing in it.

An ideal diode would pass an infinite current in one direction and no current at all in the other direction. In addition, the diode would start to conduct current when the smallest of voltages was present. In practice, a small voltage must be applied before conduction takes place. Furthermore a small leakage current will flow in the reverse direction. This leakage current is usually a very small fraction of the current that flows in the forward direction.

If the P-type semiconductor material is made positive relative to the N-type material by an amount greater than its forward threshold voltage (about 0.6V if the material is silicon and 0.2V if the material is germanium), the diode will freely pass current.If, on the other hand, the P-type material is made negative relative to the N-type material, virtually no current will flow unless the applied voltage exceeds the maximum (breakdown) voltage that the device can withstand. Note that a normal diode can be destroyed if its reverse breakdown voltage is exceeded.

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