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DC Circuits

DC Circuits. Overview. Ohms Law and Power Series Circuits Parallel Circuits Series Parallel circuits. Ohm’s Law and Power.

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DC Circuits

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  1. DC Circuits

  2. Overview • Ohms Law and Power • Series Circuits • Parallel Circuits • Series Parallel circuits

  3. Ohm’s Law and Power Ohm’s Law is perhaps the most important law in the study of electrical circuits, since the relationship defined in the law is basic to all circuit operation. The law states the relationship between three very important electrical quantities: Voltage, Current and Resistance. The table below lists the three quantities, their units of measure, and the symbols that identify them. Voltage is the electrical pressure or force which makes current flow in a circuit. Current is the flow of electrons through a circuit. Resistance is the opposition to current flow offered by electrical devices in a circuit.

  4. Ohm’s Law and Power E Ohm’s Law The Current (I) in an electrical circuit is directly proportional to the Voltage (E) and inversely proportional to the Resistance. Ohm’s Law simply means that the Current in an electrical circuit depends on two things: the Voltage applied to the circuit and the Resistance in the circuit. R I

  5. Ohm’s Law and Power The Ohm’s Law relationships of Current, Voltage, and Resistance is expressed in three formulas: • R I E= Voltage equals current multiplied by resistance. E E • Determine the correct Formula • Substitute the known • Solve the Formula R= I= I R Current equals voltage divided by resistance. Resistance equals voltage divided by current.

  6. Ohm’s Law and Power Power Power is the amount of work performed by a circuit when voltage forces current to flow through the resistance. Thus, power is directly proportional to voltage and current. Power is measured in Watts (W). One watt of power is used when one volt causes one ampere to flow through a circuit. I • E P= Power equals current multiplied by voltage.

  7. Ohm’s Law and Power Power The Ohm's Law Wheel with Power shown below provides a graphical representation of the relationships between voltage, current, resistance and power in a direct current electrical circuit.

  8. Series Circuits Series Circuit: An electronic circuit in which the power source provides Voltage to force current to flow in a single path through all the components in the circuit. • R3 • R2 • Ea • R1

  9. Series Circuits Since allof current must go in one unbroken path through all the series resistances, the total of all the series resistors is the total resistance across the voltage source. RULE: TOTAL RESISTANCE (Rt) of the resistors in a series circuit equals the sum of the individual resistors. Rt = R1 + R2 + R3

  10. Series Circuits Current in a Series Circuit depends upon the total resistance of the circuit, and is the same at any point in the circuit. It doesn’t matter if the circuit contains one resistor, or any number of resistors. Series Circuit current follows only one path through all the components in the circuit to get from the negative terminal to the positive terminal of the power supply. RULE: TOTAL CURRENT (IT ) Total Resistance (Rt) and Applied Voltage (Ea)must be known to calculate Total Current (It). It =

  11. Series Circuits Series Circuit: Also known as a VOLTAGE DIVIDER. A Voltage Drop is the difference in potential from one side of a component to another. It is developed across each resistor depending on its resistive value. RULE: The sum of the voltage drops of the resistors should equal the APPLIED VOLTAGE (Ea) Ea = ER1 + ER2 + ER3

  12. Series Circuits The APPLIED VOLTAGEis divided across the resistors based on the value of the resistor. Rt= 3KΩ It = 2.5mA To calculate VOLTAGE DROP: It • R1= ER1 It• R2= ER2 It• R3= ER3 2.5V 2.5V 2.5V R11kΩ Ea = 7.5V R21kΩ R31kΩ

  13. Series Circuits The APPLIED VOLTAGEis divided across the resistors based on the value of the resistor. Rt= 7KΩ It = 1.07mA To calculate VOLTAGE DROP: It • R1= ER1 It• R2= ER2 It• R3= ER3 5.35V 1.61V .535V R15kΩ Ea = 7.5V R2500Ω R3 1.5kΩ

  14. Series Circuits Series CircuitsTroubleshooting • Analyze the circuitto determine whether or not the circuit is faulty. • Check the Set-up and Input to look for obvious things that could be wrong. • Calculate Values to determine what values that should be present. • Measure Values to determine what values that actually are present. • Compare the resultsto determine and verify the fault(s).

  15. Series Circuits Series CircuitsTroubleshooting There are three types of common faults: • Open • Short • Changed Value When one resistor in a series circuit opens, the other resistors continue to operate correctly and retain their original value. The Open resistor measures Infinite Resistance and zero Current. The Voltage drop across the open component is Applied Voltage. When one resistor in a series circuit shorts, the other resistors continue to operate correctly and retain their original value. The shorted resistor measures zero resistance and zero voltage drop. The circuit current increases and the voltage across the good resistors increase. When one resistor in a series circuit changes value, the change value component must be determined. This is accomplished by comparing the calculated and measured values

  16. Series Circuits Series CircuitsTroubleshooting • Open • Infinite R • No I • Measured Ea 7.5V

  17. Series Circuits Series CircuitsTroubleshooting • Short • Zero R • Increase total I • Voltage Drop zero 0V

  18. Series Circuits Series CircuitsTroubleshooting • Changed Value • R increases or decreases • Measured V does not equal Calculated V 5V

  19. Parallel Circuits Parallel Circuits are circuits with two or more paths (branches) of current flow. - - - - - -

  20. Parallel Circuits Total Current (It) in a parallel circuit is the sum of the currents in the individual branches. b32mA b22mA It = 6mA b12mA R22kΩ R32kΩ R12kΩ • It = Ib1 + Ib2 + Ib3

  21. Parallel Circuits The Resistance of each Parallel branch will affect the amount of current that will flow in that branch. b32mA b21mA It = 6mA b13mA R23kΩ R32kΩ R11kΩ • It = Ib1 + Ib2 + Ib3

  22. Parallel Circuits Parallel Circuits Are Current Dividers (Voltage is equal all over)

  23. Parallel Circuits Each branch is connected across the same Voltage source, So: Voltage is the same Potential Difference across each branch! 3.3V TP4 TP2 TP3 TP1 Ea3.3V TP8 TP6 TP5 TP7

  24. Parallel Circuits 2 formulas to find TOTAL RESISTANCE (Rt): Reciprocal: 1 1 1 + + Rb1 Rb2 Rb3 Ohms Law: Va 1 Rt = Rt = It

  25. Parallel Circuits Total Resistance (Rt) is alwaysless than the value of any of the resistors in the branches of the parallel circuit. Smallest Resistor Value Rt = 545Ω R1 1kΩ R3 2kΩ R2 3kΩ

  26. Parallel Circuits Parallel CircuitsTroubleshooting • Analyze the circuitto determine whether or not the circuit is faulty. • Check the Set-up and Input to look for obvious things that could be wrong. • Calculate Values to determine what values that should be present. • Measure Values to determine what values are actually present. • Compare the resultsto determine and verify the fault(s).

  27. Parallel Circuits Parallel CircuitsTroubleshooting There are three types of common faults: • Open • Short • Changed Value There is only one way to determine if there is an open resistor in a parallel circuit. The current path of the resistor must be opened and a meter inserted. Measuring the resistor value or current through the resistor will determine if the component is open. Resistance will read Infinite and current will read zero. An open component in parallel effectively removes the branch from the circuit. A shorted resistor in a parallel circuit shorts out the voltage source. To determine which resistor is shorted, you must open all the current paths in the circuit. While watching the power supply voltage, close each path or branch, one at a time. The shorted resistor shorts the power supply. The voltage reading will read zero volts, and Current will read maximum. A shorted component in a parallel circuit effectively removes other branches from the circuit. When one resistor in a Parallel circuit changes value, the change value component must be determined. This is accomplished by comparing the calculated and measured values.

  28. Parallel Circuits Parallel CircuitsTroubleshooting • Open • Infinite R • No Iin that branch

  29. Parallel Circuits Parallel CircuitsTroubleshooting • Short • Zero R • Increase total I • ALL current on shorted branch 000Ω

  30. Parallel Circuits Parallel CircuitsTroubleshooting • Changed Value • R increases or decreases • Measured I does not equal Calculated I 0.05A R2

  31. Series-Parallel Circuits An electronic circuit consisting of a group of Series and Parallel components in which at least one circuit element lies in the path of Total Current (It). Series Component (It) pass through this component Parallel Components

  32. Series-Parallel Circuits To calculate forTotal Resistance(Rt) in a Series-Parallel Circuit the series and parallel resistances must be simplified. Step 1. Find Total Parallel Resistance using the Reciprocal Method. This is called Equivalent Resistance (Req) Step 2. Add Req to the Total Series Resistance to find Rt. REDRAWCircuit to simplify R1 + Req = Rt Req Total Series Resistance R1 R1 Req

  33. Series-Parallel Circuits To calculate Voltage Drops in a Series-Parallel Circuit, the voltage drops in the series circuit and current in parallel circuit must be determined. ER2 • The sum of the voltage drops across resistors in a series circuit equal the voltage applied across the resistors. Ea = ER1 + ER2 + EReq • The Total Current in a parallel circuit equals the sum of all the Branch Currents It = Ib1 + Ib2 b1 b1 ER1 EReq

  34. Series-Parallel Circuits To calculate Voltage Drops in a Series-Parallel Circuit, the voltage drops in the series circuit and current in parallel circuit must be determined. ER2 • Step 1. Find Rt, then use that to find It • Step 2.Find Voltage Drops across components connected in Series • Step 3.Subtract Series Voltages from Eato find Ereq b1 b1 ER1 EReq

  35. Series-Parallel Circuits Series-Parallel circuitsTroubleshooting • Determine a defective Series-Parallel circuit by: • Calculating the expected circuit values. • Measuring the voltage drops with a voltmeter. • Comparing the measured values with the calculated values. Use the same technique used to troubleshoot parallel circuits to troubleshoot the parallel portion of the series-parallel circuit ? Use the same technique used to troubleshoot series circuits to troubleshoot the series portion of the series-parallel circuit

  36. Summary • Ohm’s Law is one of the most significant laws in electronics, since the relationship defined in the law is basic to all circuit operation. Ohm’s Law states electric Current is directly proportional to Voltage and inversely proportional to Resistance. • Power is the term which describes the amount of work done by an electrical circuit. Power is directly proportional to Current and Voltage. Power is measured in Watts (W). • One watt of Power is used when one Volt causes one Ampere to flow through a circuit.

  37. Summary • A Series Circuit is one in which the current leaves the negative terminal of the power source, flows in a single path through all components in the circuit, and enters the positive terminal of the power source. Another name for a Series Circuit is a Voltage Divider! • The Circuit Current is the same at any point in a series circuit. Total Current(It) can be calculated by dividing the Applied Voltage(Ea) by the Total Resistance(Rt). • A Voltage Drop is the difference in potential from one side of a component to another. It is developed across each resistor depending on its resistive value. The sum of the voltage drops across all resistors in series is equal to the applied voltage. • There three common faults; Opens, Shorts and Change Value Series Circuit Troubleshootingsteps: • Analyze the circuit to determine whether or not the circuit is faulty. • Check the Set-up and Input to look for obvious things that could be wrong. • Calculate Values to determine what values that should be present. • Measure Values to determine what values that actually are present. • Compare the resultsto determine and verify the fault(s).

  38. Summary • A Parallel Circuit is an electronic circuit that has two or more branches through which current flows. The Applied Voltage is the same across each resistor in the circuit. Another name for a Parallel circuit is a Current Divider! • All resistors in the circuit are across each other as well as across the power source. Total Current is the sum of all the branch currents in the circuit. • The reciprocal of the total Resistance is equal to the sum of the reciprocals of all of the resistors in that circuit. Total Resistance is ALWAYS smaller than the smallest branch resistance. • There three common faults; Opens, Shorts and Change Value. Parallel Circuit Troubleshooting steps: • Analyze the circuit to determine whether or not the circuit is faulty. • Check the Set-up and Input to look for obvious things that could be wrong. • Calculate Values to determine what values that should be present. • Measure Values to determine what values that actually are present. • Compare the resultsto determine and verify the fault(s).

  39. Summary • Most Circuit seen in electronics are Series-Parallel. An electronic circuit consisting of a group of Series and Parallel components in which at least one circuit element lies in the path of Total Current (It). • Currents and Voltage drops can be determined given the Applied Voltage and Resistor values in Series-Parallel circuits. Total Current can be determined by simplifying and finding the total Resistance. Voltage drops can be determined by using the Total Current. • When Troubleshooting a Series-Parallel Circuit you must determine a defective Series-Parallel circuit by: • Calculating the expected circuit values. • Measuring the voltage drops with a voltmeter. • Comparing the measured values with the calculated values.

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