Industrial Electronics. Fundamentals of Electric Circuits презентация

it is needed for some electrical equipment by certain
Or elements combined in a certain way up.

Current I
Voltage V
Charge Q=I*t
Resistance resistor R
Capacitance capacitor C
Inductance inductor L

nodes, loops, meshes, branches, voltage and current sources;
Apply Kirchhoff’s laws to simple electric circuits and derive the basic circuit equations.
Compute the power delivered or absorbed by circuit elements.
Apply the voltage and current divider laws to calculate unknown variables in simple series, parallel, and series-parallel circuits.

1. Circuit models（电路模型）

Two active（有源）models

Three passive(无源）models

= E – R0 I

V0 = E

Is =

　　When R0 = 0, V = E, the source is called ideal voltage source.

R0 = 0

I = IS, the source is called ideal current source.

The ideal current source:

of units; SI unit
Length [meter] (m) Mass [kilogram] (kg)
Time [second] (s)

(1) Current -- i(t), I ---- (A, mA, μA...)
The net time-rate of transference (传递) of charge is referred to as the flow of current.

(2) Energy (or work) -- w(t) (J)

The time rate of performing work is defined as power.

: Electron: negatively charged
Direction of current: is defined as the flow direction of positive charge.

... )

The relative (关联) reference directions

The reference arrow for the current variable enters the terminal, which is identified by the plus sign of the voltage reference polarity markings.

element, or it is actually generating power and delivering it to some external element.

p(t)>0 the power absorbed by the element.

types of conducting materials is directly proportional to the current flowing through the material.

The resistor is a passive element that cannot deliver power or store energy.

both vary with time in the same manner.

We define a "short circuit" as a resistance of zero ohms.

We define a "open circuit" as an infinite resistance.

more elements have common connection is called a node(节点).

Suppose that we start at one node in a network and move through a simple element to the node at the other…, if no node was encountered more than once, then the set of nodes and elements that we have passed through is defined as a path（路径）.

path in a network, composed of one simple element (or more elements ) and the nodes at each end of that element.

Kirchhoff's current law --KCL

The algebraic sum of all the currents entering any node is zero.

If the node at which we started is the same as the node on which we ended, then the path is a closed path（闭合路径）or a loop（回路）.

currents leaving a node is zero.
or: The algebraic sum of all the currents entering a node must equal the algebraic sum of all the currents leaving the node.

The three equivalent equations

The algebraic sum of all the currents entering any node is zero.

loops: loop1, loop2, loop3;
2 meshes: loop1, loop2

9 A， I2 = –2 A，I4 = 8 A.
Determine the current I3 .

9 –( – 2)+ I3 + 8 = 0

I3 = –19 A

path in a circuit is zero.

Kirchhoff's voltage law--KVL

KVL:

series resistance comprise a practical voltage source.

A practical current source is defined as an ideal current source in parallel with an internal resistance Rsi.

each produces identical current and identical voltage in any loads which is placed across its terminals.

Conditions of equivalence: