**For Direct Current Circuits**

Currents (I) and voltages (V) are constant with time.

**For Alternating Current (AC) Circuits**

Current (i) and voltage (v) are time varying.

**What Are AC Circuits?**

• Any combination of Active and passive elements (resistors, capacitors and coils).

• The sources are AC voltage or current sources

**Basic Concepts**

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**The Electric Current (I) **

• Electric current results from the movement of electric charge.

• The SI unit of current is Ampere (A).

• For most electronic circuits the ampere is a rather large unit, the mA unit is more common.

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**The Electric Voltage (V)**

• Potential energy per unit charge.

• The measure of "push" available to motivate electrons.

• Work (W) in Joules= Volt (V) in Volts * Charge (Q) in Coulombs

• A positive charge will move from a higher to a lower potential.

• The SI unit of voltage is Volt (V).

• Current flows in a conductor if there is a potential difference between its ends.

**Resistance and Ohm’s low**

• The Resistance of an object is a function of its material and shape.

•Old Resistor values is indicated by a 3-color code.

• Resistor tolerances is in the order of 5%.

**DC Circuit**

• Any combination of Active and passive elements (usually resistors).

• Active elements are either voltage or current source.

• Power dissipated by loads and power supplied by sources.

• Active elements are either voltage or current, dependent or independent elements.

**Active Elements**

Active elements are either voltage or current, dependent or independent.

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**DC ideal independent sources**

DC Voltage Source DC Current Source

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**AC ideal independent sources**

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AC Voltage Source AC Current Source

**Ideal dependent voltage source**

· Voltage controlled voltage source (**VCVS**)

**v= μ v****x** Where, **μ is dimensionless**

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• Current controlled voltage source (**CCVS**)

** v= μ i****x**** **Where, **μ is in KΩ**

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**Ideal dependent current source**

· Current controlled current source (**CCCS**)

**i= μ ix **Where, **μ is dimensionless**

· Voltage controlled current source (**VCCS**)

**i= μ v****x **Where, **μ is in (KΩ) ˉ****¹**

**Actual sources**

• **Actual voltage source**

· **Actual current source**

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**Power & Energy Calculations**

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Power is the time rate of delivering or absorbing energy, measured in watts (W).

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For a resistor, power is always dissipated.

For a linear resistor, **V **= **I *****R**

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For a source, power is either delivered or absorbed.

**Voltage Source**

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** **P (delivered) =E*I ** **P (delivered) =-E*I

P (absorbed) = E*I

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**Power balance:**

** **Σ Power delivered by sources =Σ Power dissipated by resistors.

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**Current source**

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P (delivered) =V*I0 P (delivered) =-V*I0

P (absorbed) =V*I0

**Power balance:**

** **Σ Power delivered by sources =Σ Power dissipated by resistors.