A very gentle intro

The invention that changed everything… The real thingCircuit diagram symbol

BJT’s animated

Transistors as switch 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

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

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

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

Bipolar Transistor Parameters BE: fwd bias to get e- flowing BC: rev bias to vacuum up e- making the journey through BJT

Output Characteristic Active region (light blue): I c =  I B I c ~independent of V CE Saturation (yellowish): I c depends on V CE and I B Digital switch applications 0.1 – 0.3V Saturation

Input characteristic Transistor ON  Fwd biased diode Working on the steep part of the curve (blue dotted box highlights normal operating range)   V BE small   I B relatively large * Rule of thumb: use V BE ~ 0.7V when designing BJT circuits IBIB V BE IBIB

Transistor-LED switch Example V CC = 15 V V BB = 5V R L = ?  R B = ?  V LED = 3.5 V (blue) Design: I LED  m  1. KVL CE “big loop”: 0 = V CC – V LED – I C R L – V CE 2. KVL BE “small loop” 0 = V BB – I B R B - V BE

Typical configurations

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