Disclaimer: I am not an EE, nor have I taken any EE classes. This is a cheatsheet, for myself, to remember some of the simple basics of transistors.

Resources

Here are some helpful resources for learning more about the basics of transistors:

What & Link	Type
Zeeshan Ali, AIKTC School of Engineering: Introduction to Transistors	Slide Deck
Zeeshan Ali, AIKTC School of Engineering: Transistor Types	Slide Deck
ElectronicsTutorials: Transistor Series - Summary (👍) - MOSFET as a Switch	Guide
Circuit Digest: Different Types of Transistors	Guide
Espruino: MOSFETs - Schematics section	Guide (Intro)

Different Types of Transistors

• BJT (Bipolar Junction Transistor)
  • Control: Current
  • Pins:
    • Base (B)
    • Collector (C)
    • Emitter (E)
  • Configurations:
    • NPN
    • PNP
• FET (Field Effect Transistor)
  • Control: Voltage
  • Pins
    • Drain (D)
    • Gate (G)
    • Source (S)
  • Configurations:
    • MOSFET
      • Depletion Mode:
        • N-Channel
        • P-Channel
      • Enhancement mode:
        • N-Channel
        • P-Channel
    • JFET
      • Depletion Mode:
        • N-Channel
        • P-Channel
    • OFET
    • NOMFET
• IGBT (Insulated Gate Bipolar Transistor)
  • This could also be considered a subset of FET

Comparing Types of Transistors

So, between some of the major types, what are the significant differences, in a broad practical sense? As in, why might you pick one over the other?

Type	Control	Pros	Cons
BJT	Current	- More robust (in comparison to MOSFET) - Often tolerant of a greater voltage range - Less expensive	- Thermal runaway - Slower switching - Typically handles less current
FET - MOSFET	Voltage	- Extremely high input resistance on Gate, means that there is very little current draw - Fast Switching speeds	- The high input resistance means they are extremely sensitive to ESD, and are more easily damaged by it
FET - JFET	Voltage	- Less vulnerable to ESD, compared to MOSFET - Often cheaper than MOSFETs	- Consumes more current than MOSFET - Only available in Depletion Mode

Other comparisons you might find helpful

• ques10: BJT vs JFET vs MOSFET
• All About Circuits
• StackExchange: When To Use What Transistor?

Sub-Type Breakdown

Type	Config	Pins	Usage Differentiator	Symbol
BJT	NPN	B,C,E	- Small current at base, allows large current from collector to emitter. - Base needs to be positive relative to Emitter.
BJT	PNP	B,C,E	- Small current at base, allows large current from emitter to collector. - Base needs to be negative relative to Emitter.
FET -> JFET	N-Channel (Depletion Mode)	D,G,S	- "On", by default. - Negative voltage at Gate (relative to Source), turns off / increases resistance / reduces current between Source and Drain (the channel).
FET -> JFET	P-Channel (Depletion Mode)	D,G,S	- "On", by default. - Positive voltage at Gate (relative to Source), turns off / increases resistance / reduces current between Source and Drain (the channel).
FET -> MOSFET	N-Channel (Depletion Mode)	D,G,S (* B)	- "On", by default. - Negative Voltage at Gate (relative to Source), turns off / increases resistance / reduces current between Source and Drain (the channel).
FET -> MOSFET	P-Channel (Depletion Mode)	D,G,S (* B)	- "On", by default. - Positive Voltage at Gate (relative to Source), turns off / increases resistance / reduces current between Source and Drain (the channel).
FET -> MOSFET	N-Channel (Enhancement Mode)	D,G,S (* B)	- "Off", by default - Positive Voltage at Gate (relative to Source), turns on / decreases resistance between Source and Drain (the channel).
FET -> MOSFET	P-Channel (Enhancement Mode)	D,G,S (* B)	- "Off", by default - Negative Voltage at Gate (relative to Source), turns on / decreases resistance between Source and Drain (the channel).

* = Sometimes MOSFETs will include a fourth terminal, B. This is often referred to as Body or Substrate, and sometimes is not broken out, but rather connected internally.