Electrical Engineering › Section P · Semiconductor theory, diodes, and transistors › Topic P.8
The BJT as a switch, meter checks, and active-mode operation
A bipolar junction transistor lets a small current steer a much larger one. Used fully on or fully off it is a switch; held in between it is the heart of an amplifier, and both uses rest on the same three terminals and three operating regions.
In this topic
- One current controls another
- Terminals, arrows and current directions
- Two junctions, two jobs
- Three operating regions
- The transistor as a switch
- Worked example: a relay from a 3.3 V pin
- Meter checks: two back-to-back diodes
- Worked example: naming the leads
- Active mode: a current regulator
- Worked example: active or saturated?
- Common mistakes to avoid
- Key takeaways
This topic is part of Wuanberri Pro. Checking your access…