Electrical and electronic--second chapter--analysis method of circuit

Focus:

Branch Current method

Superposition theorem

Thévenin theorem.

Electronic technology: Digital electricity, mold power.

Equivalent transformation of 2.1 resistor series-Parallel connection

The voltage of the current source is determined by the external circuit.

The equivalent relationship between the ① voltage source model and the current source model is only the external circuit, which is not equivalent to the internal power supply.

When the voltage source open, i=0, power supply internal resistance ro on the non-loss of power.

When the current source open, the internal power supply is still current, the internal resistance of the RO power loss.

② equivalent transformation, pay attention to the corresponding relationship between the reference direction of the two power supplies, namely the polarity of the ideal voltage source and the direction of ideal current source current.

Open circuit is the most load of air, the insulation of the air is very large

G: conductivity (inverse of resistance) unit for West (men's) S

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2.4 Branch Current method: With the branch current as the unknown amount, the KCL KVL respectively to the node and the loop to list the required independent equations, and then solve.

Branch: b=3

Node Count: n=2

return: l=3

Number of mesh holes: m=2

It is assumed that the circuit is n nodes, b branches, m mesh holes.

The independent KCl equation has (N-1) a

The independent KVL equation (b-n+1) is generally the number of mesh holes

The current of each branch is solved.

No column containing constant current source of KVL, just for KVL.

2.5 Junction Voltage Method

Junction Voltage method: A node in any selected circuit is the reference node, and the voltage between the other nodes and the junction.

The branch is more, requires 4 branches of the current, to be listed 4 equations.

There are more branches, but only two circuits . The nodal voltage method can be used.

The current source inflow node is positive, and vice versa, is negative.

The resistor in series with the current source does not affect the branch current and does not count toward the denominator.

2.6 Superposition theorem

Superposition theorem: For linear circuits, the current of any one branch can be regarded as the algebraic sum of the current generated in this branch when each power supply (voltage source or current source) in the circuit is acting separately.

For the voltage source to function separately, the current source is a circuit breaker .

For the current source, the voltage source is shorted .

The superposition principle only applies to the calculation of the voltage and current in the linear circuit, and does not calculate the power .

2.7 Thévenin theorem and Norton theorem

Power supply equivalence theorem:

Two-terminal network: A partial circuit with two outlet ends.

Passive two-terminal network: The two-terminal network does not contain a separate power supply.

Active two-terminal network: The two-terminal network contains a separate power supply.

2.7.1 Thévenin theorem--Voltage source

Any active two-terminal linear network can be substituted by an ideal voltage source with an electromotive force of E and an internal resistance R0 series power supply.

(1) Disconnect the required slip road, the remaining is the active two-terminal network.  Using the end point voltage method. Ask for E

(2) The Independent power supply is set 0, the current source is disconnected, the voltage source short-circuit . Seeking R

2.7.2 Norton theorem

Any active two-terminal linear network can be substituted by an ideal current source of current and internal resistance R0 parallel power supply.

(1) External short circuit, get is, beg I

(2) Ideal voltage source short circuit, ideal current source open, seek R

An open circuit and short circuit method are used to find the equivalent resistance.

Analysis of *2.8 controlled power supply circuit.

Independent power supply: voltage source voltage or current source of the current is not controlled by the external circuit and independent existence.

Controlled power supply: The power supply in the circuit, but the voltage or current is controlled by the current or voltage in the other part of the circuit. when the control voltage or current disappears or equals zero, the voltage or current of the controlled supply will also be zero .

The so-called ideal controlled power supply is ideal for its control end (input) and the controlled end (output side).

The linear circuit containing the controlled power supply can be analyzed and calculated using the circuit analysis method described in the previous sections, but the characteristics of the controlled power supply should be considered.

Analysis of 2.9 nonlinear resistance circuit

Linear resistor: The voltage at each end of the resistor is proportional to the current passed, and the resistor is a constant that does not change with voltage or current.

Nonlinear resistor: The resistor is not a constant, but changes with voltage or current.

　　

There are two ways to represent the resistance of a nonlinear resistor element

Static resistor (DC resistance): equal to the voltage U of the operating point Q and the current I ratio.

Dynamic resistor (AC resistor): equal to the limit of the voltage micro-variable u near the operating point Q and the ratio to the current micro-variable i.

Electrical and electronic--second chapter--analysis method of circuit