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SEMICONDUCTOR. Diodes PN junction and diode biasing. SEMICONDUCTORS. CRYSTAL DIODE. SEMICONDUCTORS. DIODES: NOTE STRIPE AND SYMBOL FOR ANODE AND CATHODE. SEMICONDUCTORS.

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SEMICONDUCTOR

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Semiconductor

SEMICONDUCTOR

Diodes

PN junction and diode biasing


Semiconductors

SEMICONDUCTORS

  • CRYSTAL DIODE


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SEMICONDUCTORS

  • DIODES: NOTE STRIPE AND SYMBOL FOR ANODE AND CATHODE


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SEMICONDUCTORS

  • A type of semi-conductor, simple in construction used for rectification, wave-shaping, circuit protection, and logic operations.

  • A two terminal device that allows current to flow in one direction, but not the other.


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SEMICONDUCTORS

  • Formed by combining a P-type and N-type semi-conductor materials together.

  • At this junction the mobile charges in the vicinity of the junction are strongly attracted to their opposites and drift toward each other.


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SEMICONDUCTORS

  • Some of the electrons move across the junction and fill the holes near the junction in the p-type material.

  • In the N-type material, the electrons become depleted near the junction.

  • This region is called the depletionregion, and extends only a short distance on either side of the junction.


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SEMICONDUCTORS


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SEMICONDUCTORS

  • The opposite charges that build up on each side of the junction create a difference in potential or voltage, referred to as the barrier voltage.

  • The barrier voltage created at the junction is very small, 0.7 volts for silicon and 0.3 volts for germanium.


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SEMICONDUCTORS


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SEMICONDUCTORS

  • When a voltage is applied to a diode, it is referred to as a bias voltage.

  • Current does not normally flow across the P-N junction, but when just the right voltage is applied using the proper polarity, current will begin to flow.

  • This is called forward biasing.


Semiconductor

SEMICONDUCTORS

What is the purpose of the resistor in this diagram?


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SEMICONDUCTORS

  • The negative terminal of the voltage source is connected to the N-type material.

  • This forces the electrons away from the terminal, toward the PN junction.

  • The free electrons accumulate on the P side of the junction by the positive terminal.


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SEMICONDUCTORS

  • This action cancels the negative charge on the P side and the barrier voltage is eliminated and current is able to flow.

  • Current flow occurs only if the external voltage is greater than the barrier voltage.


Semiconductor

SEMICONDUCTORS

Forward bias: Negative terminal of the battery connected to N side (negative)


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SEMICONDUCTORS

  • Once a current is applied to the diode, a voltage drop occurs.

  • This voltage drop is equal to the barrier voltage of the diode.


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SEMICONDUCTORS

  • In a forward bias diode the negative terminal is connected to the N-type material and the positive terminal is connected to the P-material.

  • If the terminals are reversed, the diode does not conduct and is referred to as reverse bias.


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SEMICONDUCTORS

NOTE THAT NO CURRENT AT JUNCTION

REVERSE BIAS


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SEMICONDUCTORS

  • Reverse bias increases the depletion zone, hence increasing the barrier voltage.

  • No current will flow unless the applied voltage is greater than the break over voltage.

  • This in turn will cause excessive heat and burn up the diode.


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SEMICONDUCTORS

  • When forward-biased, there is a small amount of voltage necessary to get the diode going. In silicon, this voltage is about 0.7 volts. This voltage is needed to start the hole-electron combination process at the junction.


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SEMICONDUCTORS

  • The operation of the PN junction in a diode is unidirectional since it conducts current in one direction.

  • When the diode is forward biased, current flows through it freely.

  • When the diode is reverse biased, current doesn’t flow through it.


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