Experiment collection of University Course "Fundamentals of circuit analysis". Experiment 5 - Research on equivalent circuit of linear active two terminal network

  

experiment 5、 ... and    Research on equivalent circuit of linear active two terminal network

Catalog

Experiment five    Research on equivalent circuit of linear active two terminal network

1 The experiment purpose

2  Experimental instruments and equipment

3 Preview the experiment

4  Experimental principle

5 Experiment content and steps

6 Experimental requirements and precautions

7 Experimental report

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1 The experiment purpose

1. Learn the method of measuring the equivalent power parameters of linear active two terminal network .

2. Deepen the understanding of the equivalent power theorem .

3. Consolidate the usage of multimeter , Deepen the understanding of the internal resistance of the multimeter .

2  Experimental instruments and equipment

A multimeter                                               a

Integrated circuit test box                                       a

3 Preview the experiment

1. According to the figure 1-2 Experimental circuit , Calculate the theoretical value of its equivalent power parameters .

2. Draw up the experimental steps according to the selected measurement method .

4  Experimental principle

1． Any linear network , If we only study the voltage or current of one branch , Then the rest of the circuit can be regarded as a

An active two terminal network , Or called one port network with source , Pictured 5-1（a） Shown .

  chart 1-1   Equivalent circuit of linear active two terminal network

2.  The equivalent source theorem includes two theorems: voltage source equivalence and current source equivalence , Also known as Thevenin theorem and Norton theorem ：

Davinan's theorem ： Any linear active two terminal network , In terms of its role in the external circuit , It can always be equivalent to a voltage source and

A series circuit composed of resistors , Pictured 1-1（b） Shown . The voltage of this voltage source UOC Equal to the open circuit voltage of the two terminal network at the port

Pressure ; resistance r0 Equal to the condition that all independent sources in the two terminal network are set to zero , Equivalent resistance seen from the port .

Norton's theorem ： Any linear active two terminal network , In terms of its role in the external circuit , It can always be equivalent to a current source and electricity

A parallel circuit composed of conductors , Pictured 1-1（c） Shown . The current of this current source ISC Equal to the short-circuit current of the two terminal network at the port ;

Conductivity g0 Equal to the condition that all independent sources in the two terminal network are set to zero , Equivalent conductivity seen from the port ,g0 = 1/ r0.

Usually we call it open circuit voltage UOC、 Short circuit current ISC And equivalent internal resistance r0 Is the equivalent power parameter of active two terminal network .

3． The external characteristics of linear active two terminal network and equivalent circuit should be consistent , The volt ampere curve drawn in plane coordinates should

coincidence .

4. The maximum power transmission theorem

A linear active two terminal network , Regardless of its internal specific circuit , Can be equivalent to a string of ideal voltage source and resistance

Link circuit , Pictured 1-1（b） Shown . When the load is RL when , Get power ：

 

Take the derivative of the above formula and make it zero , Get the load RL Conditions for obtaining maximum power on RL = r0, At this time, the maximum power is ：

5 Experiment content and steps

1. Measurement of equivalent power parameters of linear active two terminal network

chart 1-2   Determination AB Terminal equivalent power parameter circuit

Pictured 1-2 The experimental circuit shown , measurement A、B Equivalent power parameters of the port UOC、ISC, Fill in the measurement data in the table 1-1 in ,r0 Optional

There are three methods to measure , Fill in the measurement data in the table 1-2 in .

（1） Measure the open circuit voltage UOC

According to the figure 1-3 Shown , stay “ Linear circuit research module ” The experimental circuit is built on the experimental board .  take +12V The power output terminal of is connected to

2P20,2P22 And 2P05 Connected to a , resistance 2R4 And 2R5 Connected in series into a 300Ω The resistance of ,2P08 And 2P05 Connected to a , 2P09 Pick up

To GND ,2P06 And 2P09 A DC voltmeter is connected in series , Used to measure the open circuit voltage of the circuit .

In the case of low accuracy requirements , The open circuit voltage of the active two terminal network circuit can be directly measured with the DC voltage block of the multimeter

UOC, Pictured 1-3 Shown . The internal resistance of the multimeter used in the experiment is large enough （ Greater than the resistance of the network under test 100 More than times ）, be

The measurement error can be ignored , It can be considered that the voltage reading of the multimeter is the open circuit voltage UOC Value . Otherwise, there will be some measurement errors

Bad .

chart 1-3   Measure the open circuit voltage UOC circuit

  chart 1-4   Measure the short-circuit current ISC circuit

             

（2） Measure the short-circuit current ISC

Replace the DC voltmeter in the above experimental circuit with a DC ammeter , Other connections remain unchanged , See the picture 1-4. Allow

In case of short circuit , The short-circuit current at the network port can be measured with the DC current gear of the multimeter . If the internal resistance of the multimeter used in the experiment

Small enough （ Less than the resistance value of the measured Branch 100 More than times ）, It has little impact on the measurement data , It can be considered that the current reading of the multimeter is

Is the short-circuit current ISC Value . Otherwise, there will be a certain measurement error .

surface 1-1   Measure the equivalent power parameters UOC,ISC

measuring The amount term Objective	UOC（V）	ISC（mA）
		10mA Block measurement	100mA Block measurement
Theoretical value
Measured value

（3） Measure the equivalent internal resistance r0

There are many methods to measure the equivalent internal resistance , in fact , Based on the measured open circuit voltage UOC And short circuit current ISC, You can get

Equivalent internal resistance r0 =UOC /ISC ; besides , Then introduce several measurements r0 Methods .

a. Direct measurement

chart 1-5   Multimeter ohm block measurement r0 circuit

Set independent sources in the network to zero , Pictured 1-5（a） Shown , Turn a linear active two terminal network into a two terminal network without independent sources , Use the ohm block of the multimeter to measure the input resistance at the network port , That is, the equivalent internal resistance r0.

b. External known power supply method

chart 1-6   Measure with external known power supply r0 circuit

According to the above figure 1-5（a） Methods , Turn a linear active two terminal network into a two terminal network without independent sources , External power supply , Measure the current I or

voltage U’, Pictured 1-6（a） and （b） Shown , According to the ratio of voltage to current , To calculate the r0.

c. External known load method

Also known as secondary voltage measurement , The circuit is shown in the figure 1-8（a） Shown , In the circuit under test A、B Either end is connected with a resistance with known resistance

RL, The first measurement is the open circuit voltage UOC（ surface 1-1 Completed ）, The second measurement is the known resistance RL Terminal voltage on

UL, From the picture 1-8（b） We know ：

The formula is obtained :                  

chart 1-8   External known load method measurement r0 circuit

surface 1-2   measurement r0

r0	Experimental method	Intermediate measurement data	result r0（Ω）
r01	Direct measurement
r02	External known power supply method
r03	External known load method
r04	Open circuit short circuit method
Theoretical value r0 =		After comprehensive analysis r0=

6 Experimental requirements and precautions

1． Measure the equivalent internal resistance r0  At least three methods are used , For comparison 3 And analyze the measurement error , Choose the one with more accurate measurement, etc

Efficient circuit .

2. In the experiment, the multimeter measures the voltage 、 There are many times of current transformation , Must be used correctly , In case of burning out the multimeter .

3. In the experiments , It is strictly forbidden to short circuit the two output terminals of the DC regulated power supply .

7 Experimental report

1. Fill in the experimental table data , List the measurement methods and circuits used .