Transistors Flashcards
What is a transistor?
A semiconductor device that can amplify and switch electronic signals. Voltage/current is applied to one pair of terminals, controlling current through another terminal.
What are the three terminals of a Bipolar Junction Transistor (BJT)?
Emitter.
Base.
Collector.
What are the two types of BJTs?
PNP (Emitter emits holes, Collector collects holes).
NPN (Emitter emits electrons, Collector collects electrons).
What are the operating modes of a BJT?
Active Mode:
Emitter forward-biased, Collector reverse-biased.
Small base current controls large output current.
Saturation Mode:
Both junctions forward-biased.
Large current flows.
Cut-off Mode:
Both junctions reverse-biased.
No current flows.
What does the current-voltage characteristic of a BJT show?
Small changes in base current (I_b) cause large changes in collector current (I_c).
I_c = β ⋅ I_b, where β is the common-emitter current gain.
How does a Junction Field Effect Transistor (JFET) work?
A gate creates reverse biases, constricting flow between source and drain.
By controlling the depletion region size, the flow of carriers (current) through the n-type region is regulated.
Results in voltage-controlled current.
How does a Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) work?
Uses an electric field to control charge carriers.
Voltage at the gate terminal controls the current between source and drain.
What are the key differences between BJTs and FETs?
BJT:
Relies on both electrons and holes.
Current-controlled device (I_b controls I_c).
FET:
Relies on majority charge carriers only.
Voltage-controlled device (Gate voltage controls current flow).
What are the applications of transistors?
Signal Amplification:
Amplifies electrical signals while maintaining shape and frequency.
Small changes in I_b lead to large changes in I_c.
Switching electronic signals.
