Chapter 8 DC Circuits

2 Objectives –After completing this chapter, the student should be able to: Solve for all unknown values, (current, voltage, resistance, and power) in a series, parallel, or series- parallel circuit. Understand the importance of voltage dividers. Design and solve for all unknown values in a voltage divider circuit.

3 Series Circuits –Provide only one path for current flow. –Factors governing operation are: The same current flows through each component. I T = I R1 = I R2 = I R3 … = I Rn The total resistance in a series circuit is equal to the sum of the individual resistances. R T = R 1 + R 2 + R 3 … + R n

4 The total voltage across a series circuit is equal to the sum of the individual voltage drops. E T = E R1 + E R2 + E R3 … + E Rn The voltage drop across a resistor in a series circuit is proportional to the size of the resistor. I = E/R The total power dissipated in a series circuit is equal to the sum of the individual power dissipations. P T = P R1 + P R2 + P R3 … + P Rn

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6 To solve for values in a circuit (in order): –Find the total resistance. –Determine the total circuit current. –Determine the voltage drops and dissipation.

7 Parallel Circuits –Circuits having more than one current path. –Factors governing operation are: The same voltage exists across each branch of the parallel circuit and is equal to that of the voltage source. E T = E R1 = E R2 = E R3 … = E Rn

8 The current through each branch of a parallel circuit is inversely proportional to the amount of resistance of the branch. I = E/R The total current in a parallel circuit is the sum of the individual branch currents. I T = I R1 + I R2 + I R3 … + I Rn

9 The reciprocal of the total resistance in a parallel circuit is equal to the sum of the reciprocals of the individual resistances. 1/R T = 1/R 1 + 1/R 2 + 1/R /R n The total power consumed in a parallel circuit is equal to the sum of the power consumed by the individual resistors. P T = P R1 + P R2 + P R3 … + P Rn

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11 Series-Parallel Circuits –Circuits that consist of both series and parallel circuits. –To solve most series-parallel circuits, simply apply laws and rules to each type. Series formulas are applied to series parts of the circuit. Parallel formulas are applied to parallel parts of the circuit.

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13 Voltage Dividers –Used to set a bias or operating point of various active electronic components. Transistors Integrated circuits –Used to divide a higher voltage to a lower voltage. –Often referred to as scaling.

14 Ohm’s Law –The current through a circuit is directly proportional to the voltage across the circuit and inversely proportional to the resistance. Current = voltage/resistance I = E/R

15 Current Division –Current is directly proportional to voltage across the circuit. If voltage increases, current increases. If voltage decreases, current decreases. –The voltage drop is equal to the percentage of the dropping resistor to the sum of the dropping network. E Drop = E Source x R Drop / R Total

16 In Summary –A series circuit provides only one path for current flow. –Series circuit formulas include: I T = I R1 = I R2 = I R3 … = I Rn R T = R 1 + R 2 + R 3 … + R n E T = E R1 + E R2 + E R3 … + E Rn I = E/R P T = P R1 + P R2 + P R3 … + P Rn

17 –A parallel circuit provides more than one path for current flow. –Parallel circuit formulas include: I T = I R1 + I R2 + I R3 … + I Rn 1/R T = 1/R 1 + 1/R 2 + 1/R /R n E T = E R1 = E R2 = E R3 … = E Rn I = E/R P T = P R1 + P R2 + P R3 … + P Rn

18 –Series-parallel circuits are solved by using series formulas for the series parts of the circuit and parallel formulas for the parallel parts of the circuit. –Voltage dividers –Current division