Strong electric system: Complete the generation, transportation, distribution and conversion of energy (high voltage, large current, strong power)

Weak current system: realizes the transmission and processing of circuit information (voltage and current are small, power consumption is not necessarily small)

An ideal circuit element is an ideal model that has certain electromagnetic properties physically and is rigorously defined mathematically, but does not exist in practice.

When the geometric size of the actual circuit is much smaller than the electromagnetic wavelength when the circuit is working, it can be considered that the parameters of the components are "all gathered" at one point.

The regular directional movement of charges forms conduction current

The strength of the current is defined by the amount of charge passing through the cross-section of the conductor per unit time.

It is specified that the direction of movement of positive charges is the true direction of current

The actual direction of voltage is defined as from high voltage to low voltage, which is the direction in which the potential actually decreases.

When the reference direction of the voltage is consistent with the actual direction, the voltage is positive (u>0); when it is opposite, the voltage is negative

When the voltage magnitude and direction are constant, it is DC voltage, U

When the reference direction of the current and the reference direction of the voltage are consistent, it is the associated reference direction, and when they are opposite, it is the non-associated reference direction.

If the component voltage and current take a non-correlated reference direction, the voltage or current can be regarded as the negative value in the correlated reference direction.

If w(t)>=0 for any time t, then the component (or circuit) is called a passive component, otherwise it is called an active component.

If the resistive element relationship does not change with time, it is called time-invariant, otherwise it is called time-varying. If its volt-ampere characteristic is a straight line passing through the origin, it is called linear, otherwise it is called nonlinear.

G is the conductance of the component, in Siemens. Under a certain voltage, the greater the conductance G, the greater the current i. Therefore, conductance is a parameter that characterizes the degree of current conduction of the resistive component. G = 1/R

Resistance and conductivity components are memoryless components, also known as real-time components.

The voltage of the capacitor is related to the current flowing through the capacitor at all previous times. The capacitor has the function of "memory" current.

At any time, the current flowing through the capacitor is proportional to the rate of change of the voltage at that time

The capacitor voltage at any time t is related to the "entire history" of the current before that time

Wrapping the wire into a coil forms the actual inductor component.

independent voltage source

independent current source

Voltage Controlled Voltage Source (VCVS)

Current Controlled Voltage Source (CCVS)

Voltage Controlled Current Source (VCCS)

Current Controlled Current Source (CCCS)

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Linear circuits must satisfy both homogeneity and superposition

When an independent power supply acts alone, the other independent power supplies are treated as zero, that is, the internal resistance is retained, the ideal voltage source is replaced by a short circuit, and the ideal current source is replaced by an open circuit, while the other structures of the circuit remain unchanged.

Equivalent to a complex linear active two-terminal network as a power supply model in which a voltage source and a resistor are connected in series

Calculate equivalent resistance

Equivalent to a complex linear active two-terminal network as a power supply model in which a current source and a resistor are connected in parallel.

The Thevenin equivalent circuit and the Norton equivalent circuit share three parameters: open circuit voltage Uoc, equivalent resistance Ro and short circuit current I(sc). The relationship is Usc = Ro*I(sc)

A circuit consisting of an independent source, a controlled source and a resistor is called a resistor circuit

In general, for a circuit with n nodes, Kirchhoff's current law can be used to list (n-1) independent equations

In general, for a circuit with b branches and n nodes, Kirchhoff's voltage law can be used to list b-(n-1) independent equations

Step 1: Determine the mesh and set the reference direction of the current of each mesh. Usually the reference direction of the current of each mesh is set to

Among the n nodes in the circuit, any one is selected as the reference point, and the voltage of the remaining (n-1) nodes to the reference point is called the node voltage of the node.

Definition: The law that describes the relationship between the currents in the branches connected to the nodes in the circuit.

For any node of a lumped parameter circuit, the sum of the currents flowing out of the node at any time is equal to the sum of the currents flowing into the node.

Kirchhoff's current law is the embodiment of charge conservation law and current continuity in lumped parameter circuits

The law describing the constraint relationship between the loop and the voltage of each branch (or each component). For any lumped parameter circuit, at any time, traveling along any closed path, the algebraic sum of the voltages of each section of the circuit is always equal to zero.

The voltage between any two points in the circuit is equal to the algebraic sum of the voltages of all components passing through any path between the two points.

KVL applies to any time. Any source of motivation. All lumped parameter circuits composed of components of any nature are also a universally applicable law in circuits.