Embedded Systems Semiconductors

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Embedded SystemsSemiconductors
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Transistors
active components that can increase the power of
a signal

• bipolar transistor
• Si (silicon) semiconductor - tetravalent, has
  4/8 electrons
• in its outer most (valence) shell
• P (phosphorus) - pentavalent, has 5/8 electrons
  in its
• valence shell, which implies it has an extra
  loosely
• bound electron
• B (boron) - trivalent, has 3/8 valence
  electronsits also
• conducting (has holes in the electron cloud)
• Silicon is special
• doped with phosphorus becomes N type
  semiconductor
• doped with boron becomes P type semiconductor
• only semiconductor that forms an insulating
  oxide layer

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Diodes
charge distribution
depletion region
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Diodes
arrow points in the direction of current flow

• diodes are rated by the amount of current they
  can handle
• small signal diodes 100mA
• power diodes 1000s of Amps
• and the maximum reverse voltage they can
  withstand
• 75-80V
• If you can measure a reverse current --- bad diode

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Diode Impedance
I current through diode
Kirchoffs laws dont apply
reverse biased
forward biased
V voltage drop across diode
breakdown voltage 75V
if 10mA is flowing through the diode, ?Vd0.5V
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Rectifiers - how would you do it?
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Rectifiers

AC
Vload
t
two diode drops
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Rectifiers

AC
Vload
t
ripple
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Rectifiers
5V
diode clamp when V gt 5.6V diode is
conducting

AC
Vload
t
ripple
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Zener Diode
let current go through backwards, while
maintaining a near constant voltage If I gt
20-50mA, pop
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Diodes - LEDs

--
forward bias
R
conducting

--
I
forward ?V 1.5-2.5 V current must be limited to
5-20mA stress limit 20-50mA
blue higher ?V green yellow orange red
longer wavelength
red/green polarity indicators
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Flyback Diode
transistor opens VL dI/dt creates large
(negative) polarization of the inductor,
overstressing the transistor switch flyback
diode clamps inductor voltage at (V 0.6) creates
conduction path to dissipate the high tension
charge
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IR Bumper - Modulated Transmitter