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close this bookAmplifier Teaching Aid (GTZ, DED; 86 pages)
View the documentPreface
View the documentIntroduction
close this folderLesson 1 - Semiconductor Review
close this folderLesson Plan
View the documentIntroduction
View the documentDoping a semiconductor
View the documentDiode
View the documentWorksheet No. 1
View the documentExperiment No. 1
Open this folder and view contentsLesson 2 - Bipolar Transistor
Open this folder and view contentsBipolar Transistor II
View the documentFirst Evaluation
Open this folder and view contentsLesson 4 - Transistor Fundamentals
Open this folder and view contentsLesson 5 - Transistor Biasing
Open this folder and view contentsLesson 6 - Transistor Biasing II
View the documentSecond Evaluation
Open this folder and view contentsLesson 7 - Small Signal Amplifier
Open this folder and view contentsLesson 8 - Small Signal Amplifier II
Open this folder and view contentsLesson 9 - Small Signal Amplifier III
Open this folder and view contentsLesson 10 - Large Signal Amplifier
View the documentThird Evaluation
 

Diode

Unbiased Diode

An unbiased diode has a depletion layer at the PN-junction. The ions in this deplation layer produce a barrier potential. At room temperature, this barrier potential is approximately 0.7V for a silicon diode.


Fig. 1-2: Unbiased diode

Biased Diode

When an external voltage opposes the barrier potential, the diode is forward-biased. If the applied voltage is greater than the barrier potential, the current is large. In other words, current flows easily in a forward-biased diode.

When an external voltage aids the barrier potential, the diode is reverse biased. The width of the depletion layer increases when the reverse voltage increases. The current is approximately zero. The reverse biased diode acts like an open switch.

Breakdown

Too much reverse voltage will produce either avalanche or zener effect. Then, the large breakdown current destroys the diode.

Recap


Fig. 1-3: Forward biased diode

What happens to an electron in this circuit?

1. After leaving the source terminal, it enters the right end of the crystal.

2. It travels through the N-region as a free electron.

3. At the junction it recombines with a hole and becomes a valence electron.

4. It travels through the P-region as a valence electron.

5. After leaving the left end of the crystal, it flows into the positive source terminal.

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