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Published byBeatrix Matthews Modified over 9 years ago
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A very gentle intro
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The invention that changed everything… The real thingCircuit diagram symbol
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BJT’s animated
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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
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What transistors are good for ~731M transistors in Intel core i7
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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
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Transistor action: electron flow N N P Emitter Base Collector - - - - - - For conventional current flow (tracking positive charge movement), flip the arrows!
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Bipolar Transistor Parameters BE: fwd bias to get e- flowing BC: rev bias to vacuum up e- making the journey through BJT
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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
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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 IBIB
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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
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Typical configurations
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Image credits http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/info/comp/active/BiPolar/bpcur.html 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 http://www.electronics-tutorials.ws/transistor/tran_2.html https://sully646.wordpress.com/tag/winners-circle/
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