Transistors Flashcards
What are the 2 basic categories of transistors?
Bipolar Junction Transistor and Field Effect Transistor.
What is considered a current controlled device?
BJT
What is considered a voltage controlled device?
FET field effect transistor, JFET, MOSFET
Explain the collector on a BJT
Relatively large, weakly doped region, size reduces resistance as this are generates the largest amount of heat.
Describe the emitter part of a BJT
Strongly doped, same type as the collector
How can you tell which transistor is the NPN?
Not point in, the arrow on the symbol is pointing away from the base.
The arrow on the BJT transistor symbol indicates?
It is always attached to the emitter leg.
What are the names of the 3 terminals on a FET transistor?
Drain, Source and Gate
On an FET what is the drain and source used for?
They are normally connected to the power supply through the source and drain terminals.
What is the gate used for in an FET?
An input signal to be amplified.
Devices that use reverse-biased junction isolation are called?
Junction FET’s, Jug FET JFETS.
What are the 2 basic categories of FET’s
Reverse biased PN junctions and isolation provided by an electrically insulating material.
Devices that use insulating materials are called?
Metal oxide semiconductors MOSFET, Insulated gate IGFET
What is mainly used in todays integrated circuits?
MOSFETS
What are the modes of operation and which transistor operates where?
MOSFET - Enhancement mode & Depletion
JFETS - Depletion mode only.
Describe enhancement mode of a MOSFET
Increased voltage applied to gate increases conductivity of the channel, this allows more current to flow from drain to source or vice versa.
Explain depletion mode of a MOSFET
The transistor is “ON” by default and allowing current to flow, When a voltage is applied to the gate conductivity is reduced and can even turn the transistor OFF, like opening a switch
What controls the current flow of a JFET
Voltage connected to the gate controls the depletion region.
How does the JFET work?
By applying a reverse bias voltage to a gate terminal, at this point the channel is squeezed and the electric current is impeded or switched off completely.
How many connections does a MOSFET have?
3
The gate is insulate from the channel on a MOSFET by what material?
Thin film of silicon dioxide.
On a MOSFET, what connects the drain to the source?
The channel material.
Depletion type MOSFETS can be operated in what modes?
Depletion or in enhancement.
What controls current flow through the channels on a MOSFET?
Gate voltage controls current flow.
What happens when a + voltage is applied to the gate of a MOSFET?
The channel size increases/enhances increasing current flow from source to drain.
What happens when a higher negative voltage is applied to the gate of a MOSFET?
The MOSFET acts in depletion mode reducing the source to drain current.
What functions can the BJT be used as?
Amplifier or a switch
Explain gain
A transistor can use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals.
How does a transistor perform as a amplifier.
By the use of a small signal applied between one pair of its terminals, which controls a much larger output between the other 2 terminals.
How is a BJT current controlled?
Voltage is applied to base, therefor a VOLTAGE and a CURRENT is applied. however the voltage only performs up to sufficient voltage which creates forward bias across the base emitter junction. past this point current increases making current the controlling factor of a BJT.
