Lec02 transistor Circuit

Lec02 transistor Circuit - Last Lecture: Diode Circuit...

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Last Lecture: Diode Circuit… Constant Voltage Drop Model (Linear Circuit) V DD I D R L V D + - L D DD D R V V I = () 1 / 0 = kT qV D D e I I I V Exponential Diode Model (Non-Linear Circuit) ( ) 1 / 0 = kT qV e I I Solved by graphical method or by iteration
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Today’s Lecture Transistor Circuit
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Transistor tran•sis•tor (trán-zìs’ter) A solid-state electronic device that is used to control the flow of electricity in electronic equipment and consists of a small block of a semiconductor with at least three electrodes T Input Output Source Trans(fer) + (res)istor Idea: control large output with small input This device should exhibit gain
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Transistor Types In general, there are two types of transistors Bipolar Junction Transistor (BJT) Field Effect Transistor (FET) A three terminal device in which emitter to collector current is controlled by base current A transistor in which the output current is controlled by a variable electric field (gate voltage) I B I E I C B C E Collector Base Emitter Gate Drain Source Integrated circuit Single device
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Bipolar Transistor Operation “Forward Active” “Saturation” I B I E I C B C E B C I I = β I base = 0 “Cutoff” Amplifiers : typically operate in forward active mode (I C = β I B ) Digital logic : typically operate in saturation (low) or off (high)
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Bipolar Transistor Equivalent Circuit For forward active operation I C I B I E I C B C E Collector Base I B L C B β Ι B v BE + B C I I = β - I E v BE ~ 0.7V in forward active (you will learn why later!) E Looks like a current amplifier with gain β
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Bipolar Transistor Circuit Example When switch is closed, current can flow from the power supply to ground Current flows through 10k resistor and LED – this is the base current of the transistor Bipolar transistor turns on Current flows from power supply through 470 resistor and LED, through collector Collector current is the base current amplified by current gain b LED brightness is an indication of increased current flow for collector (gain)
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Lec02 transistor Circuit - Last Lecture: Diode Circuit...

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