Staff Site Universitas Negeri Yogyakarta

RECTIFIERS

RECTIFIERS

and

and

VOLTAGE REGULATION

VOLTAGE REGULATION

(2)

(2)

Analog

Analog

Electronics

Electronics

Pujianto

Pujianto

Department of Physics

Full Wave Rectifier

While discussing half wave rectifier we have noted that it suffers from many disadvantages:

1.There is excessive ripple

2.Low efficiency

3. D.C. saturation of transformer secondary coil

During positive half of input voltage the upper terminal A is positive the diode D₁ conducts and current flows through R_L. The upper end P of load R_L is positive. Path of current is AD₁PQC.

The D₂ does not conduct since the lower terminal B is negative.

The DC or average current I_dc is given by

( )

ò

=

p

w

p

2 0

2

1

t

id

I

_dc

Each diode operates independently and under

exactly the same conditions as in half wave circuit, only the load current are combined.

( )

( )

ú

û

ù

ê

ë

é

-+

=

ò

ò

p

p

p

m L m

L dc

m

E

R

I

xR

I

E

=

=

2

=

2

)

(

_{s f L}

m m

R R

R

V I

+

+

=

By substituting for i

So the output DC voltage The current of I_m

p

p

L m

m dc

I

R

E

We can conclude that for a full rectifier the DC output voltage is

pm

dc

I I = 2

L dc

dc

I

R

V

=

(

s f

)

dc m

dc

I

R

R

V

V

=

-

+

p

2

and

so

2

m rms

I

I

=

Efficiency of Rectifier

L m L dc dc

R

I

R

I

P

2 2

2

÷

ø

ö

ç

è

æ

=

=

p

( )

(

)

(

f L

)

m

L f

rms

ac

r

R

I

R

r

I

P

÷

+

Ripple Factor

Ripple factor r is defined as the ratio of two current (or voltage) components.

( )

( )

dc r

dc r

V

rms

V

I

rms

I

48

,

0

1

8

1

/

2

2

/

2 2

=

-=

-÷÷ø

ö

ççè

æ

=

p

p

m m

I

I

r

Substituting for I_rms and I_dc we have

Voltage Regulation

The degree to which a power supply varies in output voltage under conditions of load variations is

measured by the voltage regulation which is usually expressed as percentage

%

100

%

x

V

V

V

V

fullload

fullload noload

r

ú

ú

û

ù

ê

ê

ë

é

Ratio of Rectification

It is used as measure of merit to compare rectifiers

ondary r

transforme from

power input

ac

load the

to delivered

power dc

RoF

sec _

_ _

_ _

_ _

_ _

_

=

ac dc

Transformer Utilization Factor (TUF)

2

2

2

2

_ m m

L m

rated ac

dc

I

x

V

R

I

P

P

TUF

÷

ø

ö

ç

è

æ

=

=

p

(

f

L

)

m

m

I

R

R

For a Bridge rectifier the DC output voltage is

pm

dc

I I = 2

L dc

dc

I

R

V

=

(

s f

)

dc m

dc

I

R

R

V

V

=

2

-

+

2

p

and

so

2

m rms

I

I

=

p

p

m L m

L dc

m

E

R

I

xR

I

E

=

=

2

=

2

) 2

( _{s f L}

m m

R R

R

V I

+ +

=

By substituting for i

So the output DC voltage The current of I_m

p

p

L m

m dc

I

R

E

The average value of load current I_dc is the average value of the capacitor discharge current over an

interval of T₂ from q₂ to q₁.

The amount of charge lost by the capacitor

2

arg

I

xT

This charge is replanished during short interval T₁