Skip to main content
4: Bipolar Junction Transistors
- Last updated
Save as PDF
- 4.01: Introduction to Bipolar Junction Transistors (BJT)
- The invention of the bipolar transistor in 1948 ushered in a revolution in electronics. Technical feats previously requiring relatively large, mechanically fragile, power-hungry vacuum tubes were suddenly achievable with tiny, mechanically rugged, power-thrifty specks of crystalline silicon.
- 4.02: The Bipolar Junction Transistor (BJT) as a Switch
- Bipolar junction transistors (Also known as BJTs) can be used as an amplifier, filter, rectifier, oscillator, or even a switch, which we cover an example in the first section. The transistor will operate as an amplifier or other linear circuit if the transistor is biased into the linear region. The transistor can be used as a switch if biased in the saturation and cut-off regions. This allows current to flow (or not) in other parts of a circuit.
- 4.03: Meter Check of a Transistor (BJT)
- 4.04: Active-mode Operation (BJT)
- When a transistor is in the fully-off state (like an open switch), it is said to be cutoff. Conversely, when it is fully conductive between emitter and collector (passing as much current through the collector as the collector power supply and load will allow), it is said to be saturated. These are the two modes of operation explored thus far in using the transistor as a switch.
- 4.05: The Common-emitter Amplifier
- At the beginning of this chapter, we saw how transistors could be used as switches, operating in either their “saturation” or “cutoff” modes. In the last section we saw how transistors behave within their “active” modes, between the far limits of saturation and cutoff. Because transistors are able to control current in an analog (infinitely divisible) fashion, they find use as amplifiers for analog signals.
- 4.06: The Common-collector Amplifier
- 4.07: The Common-base Amplifier
- 4.08: The Cascode Amplifier
- 4.09: Biasing Techniques (BJT)
- 4.10: Transistor Biasing Calculations
- 4.11: Input and Output Coupling
- 4.12: Feedback
- 4.13: Amplifier Impedances
- 4.14: Current Mirror BJTs
- 4.15: Transistor Ratings and Packages (BJT)
- Like all electrical and electronic components, transistors are limited in the amounts of voltage and current each one can handle without sustaining damage. Since transistors are more complex than some of the other components you’re used to seeing at this point, these tend to have more kinds of ratings. What follows is an itemized description of some typical transistor ratings.
- 4.16: BJT Quirks