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basic electronics

basic components

  • resister
    • this reduces the line voltage
    • V = current in amps x resistance in ohms
  • capacitor
    • consist of two main parts: an insulating layer called the dielectric, sandwiched between two electrical conductors called “plates.”
    • this smooths out fluctuations or ripples in voltage
      • the variance in voltage (amount of ripple voltage) = Current draw in amps / ( (Ripple frequency) * (Capacitor size in Farads) )
      • when converting half-rectified AC currents to DC the ripple frequency will be that of the AC current (eg. 50Hz), whereas for full rectified AC currents to DC, the ripple frequency will be twice that
    • they can be used as frequency filters to reduce electrical noise:
    • combined with filter coils, they were an integral part of the tone generators in electronic organs of the 1960's and 1970's.
    • cars use capacitors to start the starter motor of the engine - often 6-30uF 400V ones
  • diode
    • this is a one way valve
    • commonly used to rectify the sine wave of an AC current into an almost linear DC current with only positive voltages
  • triode
    • The thermionic triode, a vacuum tube invented in 1907, enabled amplified radio technology and long-distance telephony.
  • transistor
    • a solid state version of the triode
    • 1st created in 1947
    • the metal–oxide–semiconductor field-effect transistor (MOSFET) is the most commonly used type (99.9% of all currently used) and was invented in 1959 and revolutionised the field of electronics.
    • is used as an on/off switch or amplifier
    • it is composed of semiconductor material, usually with at least three terminals - field effect transistors - FET - have four terminals named source, gate, drain, and body (substrate).
    • a voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals.
    • the controlled (output) power can be higher than the controlling (input) power, a transistor can thus amplify a signal.
    • integrated circuits consist of many transistors
  • Transistors and other solid-state devices are susceptible to damage from very brief electrical and thermal events, including electrostatic discharge in handling.
  • under-voltage may lead to increased current draw IF there is a voltage regulator module or similar in the system that maintains a given voltage or power output and this may risk burn out of wires or plugs due to the enforced higher current draw
    • in a simple circuit without such a regulator, Ohm's law states that the current would DROP if voltage drops, and thus the power usage would drop and if anything, the device would become unstable or stop working until the correct voltage is applied eg. an analogue torch gradually getting dimmer as the battery gets flat and then not turning on.
  • over-voltage or severe voltage ripple tends to damage components, especially capacitors and FETs.

AC-AC transformer

  • these change the voltage
  • they are made of two coils of wire around a piece of iron.
  • If the number of coils are the same on both sides then the AC voltage is the same on both sides.
  • If one side has 20 times the coils, it has 20 x the voltage. This is how you convert 240V AC to 12V AC output ready for conversion to 12V DC as below.
  • they do generate heat, lose some voltage due to the amount of wire, and also lose efficiency as the current increases

AC-DC transformer "power adapter"

  • these first use an AC-AC transformer as above to reduce the AC voltage then use diodes and capacitors to convert the sine wave to an almost linear voltage
  • a diode is a simple electronic 'valve' 'rectifier'- it only lets current flow one way and thus can only output the positive current but this leaves half the cycle with no current at all and the positive current is not linear but a half sine wave. This is improved by using 4 diodes in a special way to give a full wave rectifier that effectively inverts the negative cycle.
  • adding in a capacitor AFTER the diode will smooth out that half sinewave positive part and the null negative part so that there is always a reasonable level of positive voltage throughout the cycle
  • basic AC-DC power adapters will have a variable voltage output dependent upon the current draw which may be dangerous for some electronic circuitry. They are often rated at a certain voltage with a given current draw but current draw higher than this will drop the voltage below this value while current draw less than this may even double the rated voltage
  • hence there are voltage regulated AC-DC power adapters available.

Computer power supplies and internal wiring

  • Computer chips generally require a +/- 5% regulation of nominal DC voltage
  • the Serial ATA Power Connector are colour coded 1):
    • 5: orange = +3.3V DC ( removed from SATA V3.2 spec)
    • 4: black = COM
    • 3: red = +5V DC
    • 2: black = COM
    • 1: yellow = +12V1 DC
science/electronics.txt · Last modified: 2022/08/03 21:48 by gary1

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