THEVENIN’S THEOREM

• Thevenins Theorem states that "Any linear circuit containing several voltages and resistances can be replaced by just a Single Voltage in series with a Single Resistor".

THEVENIN’S THEOREM

20 V

6 4

5 2

For example, refer to the circuit Find IL

IL

I1 I2

Step 1 : Open circuit of 2Ω resistor

20 V 5

6 4

A

B

2

A

B

Open circuit

Step 2 : Find the Thevenin voltage, VTH at A - B

• Thevenin voltage is the voltage across the terminals A and B is equal to the amount of algebra, which fell on the resistor voltage at 4Ω and 5Ω.

• To find the voltage dropped on both the resistor, is in looking to further advance the Ohm's law using the current multiplied by resistance (IR).

• In addition the voltage drop on both the resistor can also be found by using the following voltage divider.

Calculation of VTH

• VTH

Voltage drop across• 4 dan 5 = (4 + 5 ) x 20 V

(4 + 5 ) + 6 = 12V

20 V 5

6 4

A

B

Step 3 : Find the Thevenin Resistance, RTH – short circuit the power supply.

RTH

Short circuit the power supplies and find the Thevenin resistance is read at the terminal A and B

RTH = 6x9 (6+9)

= 54 / 15 = 3.6Ω

5

6 4

A

B

Step 4 : Draw the Thevenin Equivalent circuit

ITH is the current through resistor 2Ω = IL is required in the original question.

VTH = 12V

RTH =3.6Ω

RL = 2Ω

ITH

ITH = IL = VTH / (RTH+RL) = 12 / (3.6+2) = 2.143 Amp

Exercises ;

10

15 20

20 V

Refer to the circuit below, find I3 that flowing through 15Ω

1I

I1 I3

I2

Calculation ;

10

20 20V

15

Step 1: Open circuit the 15

THV

From the circuit ;Step 2 A VTH

BFind VTH = Voltage drop at 20Ω (using voltage

divider) VTH = 20Ω x 20 V = 13.33 V (10Ω + 20Ω)

10

20 20V

• Step 3

• RTH

• Short circuit supplies and find RTH ( perintang 10 selari dengan perintang 20 )

• RTH = 10 // 20• = 10x20/(10+20)• = 6.67

10

20

Step 4 Draw the Thevenin equvalent circuit

6.67

15 13.33 V

ITH

ITH = I3 = VTH /(RTH+RL) = 13.33 / (6.67+15)) = 0.615 A

Exercise ;