Rectifier and Filters

8/8/2019 Rectifier and Filters

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RECTIFIER

Wednesday, November 03,2010 Dr. RS 1


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Half-Wave rectifier


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Block diagram of a rectifier and a dc power supply with a load.

Thomas L. Floyd

Electronic Devices, Electron Flow Version, 5e


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Half-wave rectifier operation. The diode is considered to be ideal.

Thomas L. Floyd



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The effect of the barrier potential on the half-wave rectified output voltage is to

reduce the peak value of the input by about 0.7 V.

Thomas L. Floyd


Copyright 2005 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.


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Vp

0

-VP

T 2T

Vi(t)

t

VD

Vp - VD

0 T 2T

Vo(t)

t


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Figure 23 Average value of the half-wave rectified signal.

Thomas L. Floyd





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Average value of HWR

? A

V

cos2

V

d0dsinV21

dtVT

1V

P

0

P

2

0p

T

0DC

!

!

- !

!

T

T


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RMS Value of HWR

4

V

sin4

V

d2cos12

1

2

Vd

2

V

d0dsinV2

1

dtVT

1V

P

0

P

P

0

P

2

0

2

p

T

0

2

rms

2

2

0

2

2

2

2

2

22

1

sin

!

-

!

!!

- !

!

T

T

T


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VDC

Vrms

t0

t1

t2

t3

Vp

VO

t


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The PIV occurs at the peak of each half-cycle of the input voltage when

the diode is reverse-biased. In this circuit, the PIV occurs at the peak of

each negative half-cycle.

Thomas L. Floyd





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Half-wave rectifier with transformer-coupled input voltage.

Thomas L. Floyd





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Thomas L. Floyd





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Center-tapped Full-wave

Rectifier


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Figure 211 Full-wave rectification.

Thomas L. Floyd





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Average Value

? A

V2

cos

V

dsinV1

dtVT

1V

P

0

P

0p

T

0DC

!

!

!

!


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RMS Value

2

V

sin2

V

d2cos12

1

V

dsinV

1

dtVT

1V

P

0

P

P

0

2

p

T

0

2

s

2

2

0

2

2

2

221

!

-

!

!

!

!

T


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Figure 213 A center-tapped full-wave rectifier.

Thomas L. FloydElectronic Devices, Electron Flow Version, 5e




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Basic operation of a center-tapped full-wave rectifier. Note that the current through the load

resistor is in the same direction during the entire input cycle, so the output voltage always has the

same polarity.





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Center-tapped full-wave rectifier with a transformer turns ratio of 1.

Vp(pri)

is the peak value of the primary voltage.





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Center-tapped full-wave rectifier with a transformer turns ratio of 2.





22/36

Diode reverse voltage (D2 shown reverse-biased and D1 shown forward-biased).





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Full-Wave Bridge Rectifier


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Figure 223



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Figure 220

peration of a bridge rectifier.



26/36

Figure 221 Bridge operation during a positive half-cycle of the primary and secondary voltages.



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Vp

0

-VP

T 2T

Vi(t)

t

Vp - VD

0 T 2T

Vo(t)

t



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Figure 222 Peak inverse voltages across diodes D3

and D4 in a bridge rectifier during the

positive half-cycle of the secondary voltage.



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Figure 224 Power supply filtering.



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Figure 230



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Figure 225 peration of a half-wave rectifier with a capacitor-input filter. The current indicates charging or discharging of the capacitor.



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Figure 226 Half-wave ripple voltage (green line).



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Figure 227 The frequency of a full-wave rectified voltage is twice that of a half-wave rectified voltage.



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Figure 228 Comparison of ripple voltages for half-wave and full-wave rectified voltages with the same filter capacitor and load and derived from the same sinusoidal

input voltage.



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Vr

and VDC determine the ripple factor.


Vp(rect) : unfiltered peak rectified voltage

Vr(pp) : peak to peak ripple voltage

VDC : average value of ripple voltage

rhwr

!Vr(pp )

VDC

!1

2 3fRLC

fwr !Vr(pp )

VDC!

1

4 3fRLC


36/36

Effects of RL and C


C=1000F C=470F

C=100F

R=1500

R=1000

R=500

(a) RL

fixed (b) C fixed

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Rectifier and Filters