Transcript Lab #1: Ohm’s Law (and not Ohm’s Law)

Lab #8: Transistor
• basics of the transistor
• a few simple circuits
Bardeen’s “transfer resistance” device
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Transistor
Two back-to-back diodes, one forward and one “reverse” biased.
Three terminal device: emitter, collector, base
Small “base” current controls “large” emitter-collector current.
Voltage drop across forward-biased diode about 0.7 V
Read lab carefully; it is short.
Transistors
Transistor, two
caps, a
resistor
E
B
C
Transistor Circuit #1
C
B
C
B
E
Basic cct
Will use to study the Ebers-Moll model of the transistor
I C = I S (eVBE /VT - 1)
I B = I C / hFE
VT , I S .h FE are properties of the transistor, with
VT » 25mV
I S is the saturation current
h FE » 20 - 1000
We will plot ln(IC ) vs VBE for 2 different types of transistors
E
Transistor Circuit #2
wiggle in base voltage DV.
VBE is roughly constant, so causes a wiggle in the
voltage at the emitter of DV
DV
R2
This means the voltage at the collector wiggles by
R1
DV
R2
This means the current must wiggle by
amplifier