Review of AC-circuit

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# Review of AC-circuit - PowerPoint PPT Presentation

Keys to deal with R, L, and C in an AC-circuit. Across R, voltage and current are in-phase Across L, the current lags behind voltage by 90 o Across C, the current leads voltage by 90 o. Review of AC-circuit. Also, . When two elements are in series  the same current passing through them

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Presentation Transcript

Keys to deal with R, L, and C in an AC-circuit

• Across R, voltage and current are in-phase
• Across L, the current lags behind voltage by 90o
• Across C, the current leads voltage by 90o

### Review of AC-circuit

Also,

• When two elements are in series  the same current passing through them
• When two elements are in parallel  the same voltage across them
Basics

I and V are in-phase

R

I lags V by 90 degree

L

I leads V by 90 degree

C

RLC in series

Key: IR, IL, and IC are all in phase

DVR ~ R

DVL ~ XL

DVC ~ XC

DVmax ~ Z

Imax

IC

How do you draw the phasor diagram?

IR = IL

DVR

What if RLC are not in series?

Which of the following is true

(a) DVc = DVL, IC = IL

(b) DVc = DVL, IR = IL

(c) DVc = DVR, IR = IL

(d) DVL = DVR, IR = IL

(e) DVc = DVL+ DVR, IC = IL

(f) DVc = DVL+ DVR, IR = IL

DVL

DVc = DVR+ DVL

Power dissipation
• Only R dissipates power

P = I *DV, always

For L and C, I and DV are 90o out of phase  PL = 0, PC = 0

For R, I and DV are in-phase  PR = IDV = Irms2R

PR = IDV = Irms2R

Where Irms = Vrms/Z

i.e.

Resonance in RLC circuit in series

For a fixed AC voltage source, maximum power dissipation occurs when XL = XC, ie. When Z = R