What are the two most commonly-used specifications for a junction diode?

Maximum forward current and PIV (peak inverse voltage).

For more info, please see Electronics Notes site for the article on Understanding Diode Specifications, Ratings & Parameters, especially the section called
"Peak inverse voltage specification, PIV:," and
"Maximum forward current."

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What limits the maximum forward current in a junction diode?

The junction temperature.

The old problem of overheating. The diodes have a defined minimum/maximum operating temperature. The temperature rating refers to the diode junction itself.

For more info, please see Electronics Notes site for the article on Understanding Diode Specifications, Ratings & Parameters, especially the section called
Junction operating temperature and
Junction to ambient thermal resistance, ΘJA.

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MOSFETs are manufactured with THIS protective device built into their gate to protect the device from static charges and excessive voltages:

Zener diode.

MOSFET, stands for Metal-Oxide Semiconductor Field-Effect Transistor, is a FET (Field-Effect Transistor) type, used for directing, switching, or amplifying current. See Wikipedia's article on MOSFET.

The Zener diode, unlike regular diodes, does permit backward flow of the current.

Since they are used in circuits to stabilize voltage, they also prevent too much voltage, such as during an electrostatic spark or discharge.

See Wikipedia's article on Zener diode.

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What are the two basic types of junction field-effect transistors?

N-channel and P-channel.

The question asks for the TYPES. But the right answer is for the question about the components of the transistor.

The two types are FET and JFET. Also, there are the MOSFET and IGFET which belong as the subgroup of the two main types.

The N and P channels can be arranged in NPN or PNP configurations.

For more info, please see Electronics Tutorials site, for the article on Junction Field Effect Transistor

Also, see ECStudio site, for the article on Junction Field-Effect Transistors

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A common emitter amplifier has:

More voltage gain than a common collector.

This amplifier uses three basic single-stage bipolar transistor. It is used to amplify very weak radio signals by amplifying voltage. It provides high gain.

For more info, see Wikipedia's article on Common emitter.

Also, see Electronics Tutorials site for the article on Common Emitter Amplifier

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How does the input impedance of a field-effect transistor compare with that of a bipolar transistor?

An FET has high input impedance; a bipolar transistor has low input impedance.

Impedance, called Z, is the square root of resistance squared plus the difference between the inductive reactance and capacitive reactance. It is the opposition in an electronic circuit. For more info, please see Wikipedia's article Electrical impedance.

The bipolar transistor is charged by electrons and electron holes. That is electrons negatively charged and also positively charged (the holes which have no electrons). For more info, please see Electronics Tutorials site, for the article Bipolar Transistor

They are called bipolar junction transistors. Due to its low impedance at the base, a small amount of current on one of its terminals can change the flow direction of the other two terminals, it is used as a switch. For more info, please see Wikipedia's article on Bipolar junction transistor.

The field effect happens when current is applied, creating an electric field due to the electrical conductivity. Since semiconductors have a low density of electrons, using even a small amount of current can affect the semiconductor material.

For more info, please see the Field effect (semiconductor) article in Wikipedia.

The FET, field effect transistor, controls the flow of current using three terminals, the gate, source, and drain. It uses the field effect, which is the attraction of charges in a semiconductor material. Unlike bipolar which uses both the electrons and holes (positively charged), FET's are "unipolar" devices, using only either electrons or holes.

For more info, please see Electronics Notes site, for the article on What is a FET: Field Effect Transistor: Types, Technology, . .

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