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- Electronics: field studying the controlled flow of electrons using passive and
- active components.
- component types:
- - active: Can supply power, e.g. voltage/current sources, generators (pulse,
- DC, ...), transistors, diodes, ...
- - passive: Only receive power which they somehow transform, e.g. resistors,
- inductors, capacitors, transformers, ...
- current flow:
- By convention electricity "flows" from + to -, but in reality electrons move
- from - to +. Current can be:
- - direct (DC): Constant current in the same direction. DC is what we get e.g.
- from a battery.
- - alternating (AC): Current that changes with time and switches direction,
- normally as a sine function, due to constantly changing voltage. AC is what
- we get e.g. from electricity generators (rotating magnets that induce
- current, this current changes due to the rotation of the generator).
- circuit types:
- - short circuit: Circuit without significant load, i.e. one end of source
- connected directly to the other. This creates extreme current and great
- heat, burns the circuit in practice.
- - open circuit: Circuit with a "hole" (infinite resistance), current cannot
- flow.
- units:
- C (coulomb): charge which about 6.21 * 10^18 protons have (same amount of
- electrons have the same charge but negative)
- V (volt): J/C, unit of electric potential (or its difference), 1 V between
- two points in electric field means that moving 1 C between these points
- dissipates 1 J (joule) of energy
- A (ampere): current, charge per time, A = C/s
- Omega (ohm): V/A, resistance (attribute of resistor), 1 Omega is the
- resistance that makes 1 V produce 1 A or current
- F (farad): Q/V (charge to voltage), capacitance
- H (henry): inductance
- quantities:
- voltage (V): difference of electric potentials, measured in V
- current (I): measured in A
- resistance (R): measured in ohms, property of resistors
- capacitance (C): mesured in farads, property of capacitors
- inductance (L): measured in henrys, property of inductors, depends on geometry
- and material of the core
- laws:
- Ohm's law: I = V / R
- 1st Kirchhoff's law: Sum of current to/from a node is zero (currents flowing
- in are positive, currents flowing out are negative).
- 2nd Kirchhoff's law: The sum of voltage drops in a circuit is zero (voltage
- sources have positive voltage drops, resistors have negative).
- Thévenin's theorem: Any linear electrical network with two terminals that
- internally consists of only voltage/current sources and resistors can always
- be replaced by a Thévenin equivalent network consisting of one voltage
- source plus a resistor in series (i.e. any "abomination" of resistors and
- voltage sources can always be replaced just by one voltage source and
- resistor).
- components:
- voltage source: Active, ideally provides constant voltage (no matter
- the load resistance or current). In practice battery is used as voltage
- source, but battery is not ideal (may not provide constant voltage) and
- behaves like a voltage source with small resistor in series.
- current source: Active, ideally provides constant current (no matter the
- voltage accross it).
- resistor: Passive, provides resistance. There is a voltage drop on a resistor
- (can be computed from Ohm's law, knowing current I in the circuit and the
- resistor's resistance). Many components such as lightbulbs behave like a
- resistor. Used for: adjusting currents/voltages, terminating transmission
- lines etc.
- capacitor: Passive, stores electric energy in an electric field when voltage
- if applied to it, provides capacitance. It consists of two metallic plates
- in close proximity separated by dielectric medium: when a voltage is
- applied, charge accumulates on both plates (negative on one, positive on the
- other), when the voltage is taken away the accumulated voltage stays in the
- capacitator and will dissipate when the capacitator is connected in a
- circuit, until it discharges (it is for a short while like a mini-voltage
- source). No current will pass through capacitor but in the whole circuit a
- current will flow for a short while when chargin/discharging (thanks to the
- electric field). Capacitor can be used to block DC while letting AC pass
- through (from the point of view of DC capacitor is an open circuit) and also
- for other things like waveform generation, singal filtering,
- integration/differentiation etc. Amount of current in capacitor is
- proportional to the voltage change on it.
- inductor (coil, reactor, ...): Passive, stores electric energy in an electric
- field when current flows through it, provides inductance. It consists of a
- long wire wind around a dielectric core. When current flows through it,
- magnetic field is created, and changes to that field create voltage. It
- resists current changes and can be used to block AC while letting DC
- through, they're also used for filters etc. Amount of voltage on inductor is
- proportional to the current change on it.
- formulas:
- resistance:
- resistors in series: R = R1 + R2 + ...
- reistors in parallel: 1/R = 1/R1 + 1/R2 + ...
- capacitance:
- capacitors in series: 1/C = 1/C1 + 1/C2 + ...
- capacitors in parallel: C = C1 + C2 + ...
- inductance:
- hydraulic analogy:
- Model likening electronics to hydraulics, e.g.:
- - wire = pipe
- - C (coulomb) = amount of water
- - V = pressure
- - A = water flow, amount of water per second
- - resistor = thin pipe
- - capacitator = flexible membrane sealed in pipe
- - inductor = paddle wheel/turbine
- - battery = pump
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