basic circuit or cad

Basic Circuit Simulation using OrCAD

Prof. Anish Goel

Capacitors in Series

Series Capacitors add like Parallel Resistors: 1/CT = 1/C1 + 1/Cn

CT = .909uF

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Capacitors in Parallel

Parallel Capacitors add like Series Resistors: CT = C1 + Cn

CT = 11uF

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Inductors in Series

• Series Inductors add like Series Resistors:• LT = L1 + Ln

• LT = 11uH

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Inductors in Parallel

Parallel Inductors add like Parallel Resistors: 1/LT = 1/L1 + 1/Ln

LT = .909uH

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Capacitor Review Starts as short circuit, ends as open circuit iC = C*dVC/dt Open circuit at low frequencies Short circuit at high frequencies

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Inductor Review Starts as open circuit, ends as short circuit VL = L*dI/dt Short circuit at low frequencies Open circuit at high frequencies

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Filters Use frequency response characteristics of C and L to

filter frequency components out of a time domain signal. Low Pass High Pass Band Pass Band Stop

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Low Pass Filters RC Low Pass: fcut off frequency = 1/(2πRC)

RL Low Pass: fc = R/(2πL)

• Component selection• RC vs. RL filters

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AC Analysis (freq) Logarithmic plot (count by decades) fc defined as –3dB of input, “Half power point” Copy paste data points to excel!

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Decibels Measure of gain. Instead of saying gain is 100,000x, some

engineers prefer to say it as 100dB. Power gain: dB = 10 log(Po/Pi) Voltage gain: dB = 20 log(Vo/Vi) Always a relationship

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Decibels (cont’d) Useful values: 0dB = 1x 3dB = 2x 6dB = 4x 10dB = 10x 20dB = 100x 30dB = 1000x 3dBm is 3dB above 1mW

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Cursor Control Cursor 1: left click left/right arrows

Cursor 2: right click Shift left/right arrows

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Cursor, Mark Label

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.707? Because we are comparing gains in voltage, not power, we

must use 20log(Vo/Vi). 10^(-3dB/20) = .707V So, Vo = .707Vi at the cut off frequency

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Bode Plot (dB, logarithmic)

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Common Problems Q: Simulation not making sense A: Make sure you how things are connected.

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• RC High Pass: • fc = 1/(2πRC)

• RL High Pass: • fL = R/(2πL)

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Band Pass

HP LP

BW = (fc + 3dB) – (fc – 3dB)BW = 200.171kHz – 494.694Hz = 199.676kHz

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Response

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Band Stop

HP LP

BW = 16.216kHz –6.0833kHz = 10.133kHz

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Response

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Transformer

Easy to “Step down” or “Step up” an AC voltage (This is why AC is used for home power delivery instead of

DC.) VP/VS = NP/NS => VS = VPNS/NP

Excellent DC filter because VS = NS*dΦ/dt

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In PSPICE… Coupling = 1 Lx_Value = Nx

2

should be between 1mH and 1H

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Diode

Allow current to flow only in 1 direction Flow from left (annode+) to right (cathode-) is forward

biased. Diode causes a voltage drop due to its activation voltage. Silicon - .7V Germanium - .3V

Cathode connected to a battery is reversed biased. (blocked) Perform DC Sweep and Transient Response (use D1N4002)

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Activation Voltage

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Transient ResponseHalf Wave Rectifier

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Half Wave Rectifier

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Full Wave Rectification

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Bridge Rectifier

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In PSPICE…

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Full Wave Rectifier

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Smoothing Use capacitor to smooth the ripples of the rectified

wave form.

(Negative voltage)

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Regulators

Not in student addition Outputs a clean regulated voltage LM317 and 337 are +/- 2-18V variable regulators LM7805 is 5V regulator Input must be relatively steady or else regulator will fail.

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