Bipolar Junction Transistors A gentle intro Bipolar Junction Transistors

The invention that changed everything… The real thing Circuit diagram symbol

BJT’s animated

What transistors are good for ~731M transistors in Intel core i7

EWH kit

Transistor action: BJT BJT = Bipolar Junction Transistor Goal: control current flow from collector to emitter by input signal at base Fluid Analogy: Small signal controls a much larger signal

Another transistor analogy The gate has to swing open for horses to start running around the track. Base (B) has to ‘open’ the electrons to flow from E to C = conventional current flow from C to E

Transistor action: electron flow - Emitter - P For conventional current flow (tracking positive charge movement), flip the arrows! - Base - - - Collector N

Bipolar Junction Transistor BE: fwd bias to get e- flowing BC: rev bias to vacuum up e- making the journey through BJT 𝐼 𝐶 =𝛽 𝐼 𝐵 Current amplification:

Base-Emitter (BE) Characteristic (just a pn diode!) IB Base-Emitter (BE) Characteristic (just a pn diode!) DIB Transistor ON  Fwd biased diode Working on the steep part of the curve (blue dotted box highlights normal operating range) DVBE small DIB relatively large * Rule of thumb: use VBE ~ 0.7V when designing BJT circuits DVBE

Transistor as Switch Collector-Emitter (CE) Characteristic Curves

BJT LED switch design example 1. KVL BE “small loop” 0 = VBB – IBRB – VBE 2. KVL CE “big loop”: 0 = VCC – VLED – ICRL – VCE 𝐼 𝐶 = (𝑉 𝐶𝐶 − 𝑉 𝐿𝐸𝐷 ) 𝑅 𝐿 𝑉 𝐶𝐸 = 𝑉 𝐶𝐶 − 𝑉 𝐿𝐸𝐷 VCC = 9 V VBB = 5V RL = ? W RB = ? W VLED = 3.5 V (blue) Design: ILED ~ 20 mA

Output Characteristic Saturation Output Characteristic Active region (light blue): Ic = bIB Ic ~independent of VCE Saturation (yellowish): Ic depends on VCE and IB Digital switch applications 0.1 – 0.3V

Field Effect Transitors (FETs) Field Effect Transistor JFETs (Junction Field Effect Transistors MOSFETs (Metal Oxide Semiconductor FET) https://www.electronics-tutorials.ws/transistor/tran_6.html

What’s the difference between an Ohm and Coulomb?

FET Gallery Image credit: https://www.electronics-tutorials.ws/transistor/tran_6.html

Image credits http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/info/comp/active/BiPolar/bpcur.html http://www.electronics-tutorials.ws/transistor/tran_2.html https://sully646.wordpress.com/tag/winners-circle/ Prasad: EIS paper: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5645384/