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Embedded Systems Semiconductors

Embedded Systems Semiconductors. active components that can increase the power of a signal. Transistors. 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

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Embedded Systems Semiconductors

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  1. Embedded SystemsSemiconductors

  2. active components that can increase the power of a signal Transistors • 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 electrons…it’s 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

  3. anode + cathode -- P N Si + -- forward bias + + + + + -- conducting -- -- -- -- -- + -- + -- + reverse bias non-conducting charge distribution Diodes depletion region

  4. + -- forward bias R conducting I + -- reverse bias non-conducting -- + I=0 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 ~ 1000’s of Amps • and the maximum reverse voltage they can withstand • ~ 75-80V • If you can measure a reverse current --- bad diode

  5. I current through diode Diode Impedance Kirchoff’s laws don’t apply reverse biased forward biased V voltage drop across diode breakdown voltage ~75V if 10mA is flowing through the diode, Vd~0.5V

  6. ~ Rload AC Vload t Rectifiers - how would you do it?

  7. Rload Rectifiers ~ AC Vload t two diode drops

  8. Rload Rectifiers ~ AC Vload t ripple

  9. Rload +5V Rectifiers diode clamp: when V >= 5.6V diode is conducting ~ AC Vload t ripple

  10. R Vout ~zener voltage(5-6V) -- Vin I + voltage regulator Zener Diode let current go through backwards, while maintaining a near constant voltage If I > 20-50mA, “pop”

  11. 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

  12. Flyback Diode • transistor opens: • V=L 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

  13. +5VDC on 270  S1 off 5K pot 0.001 F 100K 6.9K IR Bumper - Modulated Transmitter

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