Electrical Element - One-port Elements

One-port Elements

Only nine types of element (memristor not included), five passive and four active, are required to model any electrical component or circuit. Each element is defined by a relation between the state variables of the network: current, ; voltage, charge, ; and magnetic flux, .

• Two sources:
  • Current source, measured in amperes – produces a current in a conductor. Affects charge according to the relation .
  • Voltage source, measured in volts – produces a potential difference between two points. Affects magnetic flux according to the relation .

in this relationship does not necessarily represent anything physically meaningful. In the case of the current generator, the time integral of current, represents the quantity of electric charge physically delivered by the generator. Here is the time integral of voltage but whether or not that represents a physical quantity depends on the nature of the voltage source. For a voltage generated by magnetic induction it is meaningful, but for an electrochemical source, or a voltage that is the output of another circuit, no physical meaning is attached to it.

• Three passive elements:
  • Resistance, measured in ohms – produces a voltage proportional to the current flowing through the element. Relates voltage and current according to the relation .
  • Capacitance, measured in farads – produces a current proportional to the rate of change of voltage across the element. Relates charge and voltage according to the relation .
  • Inductance, measured in henries – produces the magnetic flux proportional to the rate of change of current through the element. Relates flux and current according to the relation .

• Four abstract active elements:
  • Voltage-controlled voltage source (VCVS) Generates a voltage based on another voltage with respect to a specified gain. (has infinite input impedance and zero output impedance).
  • Voltage-controlled current source (VCCS) Generates a current based on a voltage with respect to a specified gain, used to model field-effect transistors and vacuum tubes (has infinite input impedance and infinite output impedance).
  • Current-controlled voltage source (CCVS) Generates a voltage based on an input current with respect to a specified gain. (has zero input impedance and zero output impedance).
  • Current-controlled current source (CCCS) Generates a current based on an input current and a specified gain. Used to model bipolar junction transistors. (Has zero input impedance and infinite output impedance).