Transistors

Current flows top to bottom (i.e. C to E for NPN, E to C for PNP, D to S for N-channel, S to D for P-channel).

Abbreviation:

• BJT: Bipolar Junction Transistor
• FET: Field Effect Transistor
• MOSFET: Metal Oxide Semiconductor Field Effect Transistor
• JFET: Junction Field Effect Transistor
• C: Collector
• B: Base
• E: Emitter
• D: Drain
• G: Gate
• S: Source

BJT vs MOSFET

BJT and enhancement mode MOSFET are more common in mechatronic applications so they are discussed specifically. These are deciding factors between the two:

BJT

• Works with small control voltages (< 3V).
• Cheaper than MOSFET.

MOSFET

• Works with little control current.
• Does not require base resistor like BJT.
• Low voltage drop (< 0.1V) across switch.
• Lower power dissipation (more efficient) than BJT.

MOSFET Logic

N-channel (NMOS)

		VG − VS < thresholdGS
		VG − VS > 4.5V

P-channel (PMOS)

		VS − VG > 4.5V
		VS − VG < thresholdSG

BJT Logic

NPN

		VB − VE < 0.6V
		VB − VE = 0.6V

PNP

		VE − VB = 0.6V
		VE − VB < 0.6V