(09) rectifiers

7/28/2019 (09) Rectifiers

1/52

Diode Rectifiers


2/52

Rectifiers 2 , 2 2013

Block Diagram of DC Power Supply


3/52


Diodes in Rectifier Circuits


4/52


Half-wave Rectifier


5/52



6/52

Rectifiers 6 , 2

2013


7/52

Rectifiers 7 , 2

2013

Full-wave Rectifier(Centre-tap)


8/52

Rectifiers 8 , 2

2013

Full-wave Rectifier(Bridge)


9/52

Rectifiers 9 , 2

2013


10/52

Rectifiers 10 , 2

2013

Diode Ratings

1. Current Handling Capacity.2. Peak Inverse Voltage ( PIV ): It is the

largest reverse voltage that is expected

to appear across the diode. Usually,diodes are selected which have V Z atleast 50 % greater than PIV .


11/52

Rectifiers 11 , 2

2013

PIV Ratings

For half-wave rectifier : V m


12/52

Rectifiers 12 , 2

2013


13/52

Rectifiers13

, 2

2013

Figures of Merit of a Rectifier1. Ripple Factor ( r ) :

2. Rectification Efficiency ( ) :


14/52

14

Voltage Regulation :-The variation of d.c. o/p voltage as a function of

d.c. load current is called voltage regulation.

In other words, the degree to which a powersupplies varies in o/p voltage under condition of loadvariation is measured by a term known as voltageregulation.

%100V

V-VRegulationVoltage%

loadfull

loadfullloadno

An ideal power supply has full load voltage equalto the its no-load Voltage and hence zero %regulation.


15/52

Rectifiers 15

, 2

2013

Performance of Half-wave Rectifier


16/52

Rectifiers 16

, 2

2013

Total RMS Value :


17/52

Rectifiers 17

, 2

2013

RMS Value of AC Components :


18/52

Rectifiers 18 , 2

2013

Note that this is a general result. Now, forHalf-wave Rectifier :


19/52

Rectifiers 19 , 2

2013

Performance of Full-wave Rectifier

Its period is , and not 2 .How much is its period in terms of t ?


20/52

Rectifiers 20 , 2

2013


21/52

Rectifiers 21 , 2

2013

Total RMS Value :


22/52

Rectifiers 22 , 2

2013

Ripple Factor :


23/52

Rectifiers 23 , 2

2013

Rectification Efficiency :


24/52



25/52



26/52



27/52



28/52



29/52

, 2 2013 Zener Diode 29

Zener Diode


30/52

Zener Diode 30 , 2 2013

Zener Diode

This is a diode designed with adequatepower dissipation capabilities to operate inthe breakdown region.

When both sides are heavily doped, thedepletion layer is very thin (100 ). Even 4 V may give a field of 10 7 V/m,

causing breakdown.Whatever may be the breakdownphenomenon, it is called zener diode.


31/52



32/52


V-I Characteristics

Ideally the breakdown curve should be aperfect vertical line and dynamic diodeimpedance should be zero.

In practice, however, Dynamic ZenerImpedance has small values ranging fromfew ohms to several hundred ohms.


33/52


Equivalent Circuits


34/52


By controlling the thickness of thedepletion layer, Zener Diode can be made

to have breakdown at a specified Zener Voltage.Generally Zener Voltage ranges from 0

volts to 200 volts. As long as the current through the diodeis limited by the external resistance in the

circuit within permissible values, it doesnot burn out.


35/52


Zener Diode Applications

1. Voltage Stabilizer or Regulator.2. Peak Clipper.

3. Switching Operation.4. Reference Element.5. Meter Protection.


36/52


Voltage Regulator

It has the ability to maintain a constantoutput even when either the input voltageor load current varies.


37/52


A voltage regulator provides a constantvoltage from a source whose voltagemay vary appreciably.


38/52


Analysis Procedure of Circuit


39/52


Step 1 : Find the state of zener diode.(Remove diode and find voltageacross open-circuit.)

Step 2 : Substitute the appropriateequivalent model and solve.


40/52



41/52



42/52


Specifications of Zener Diode

1. Zener Voltage (V

Z )2. Maximum Power Dissipation ( P Z max )3. Maximum Current ( I Z max )

4. Minimum Current ( I Z min )I Z min = 10 % of I Z max


43/52



44/52



45/52


This voltage (82.5 V) is more thanV Z (= 60 V).

Hence, diode is ON. Replace the diode by its equivalent.


46/52



47/52



48/52



49/52


This is more than V Z . Hence diode is ONWe now calculate the minimum value of zener current.


50/52



51/52


When V 1 becomes 120 V :


52/52

Rectifiers 52, 2 2013

ReviewBlock Diagram of DC Power Supply.Half-wave Rectifier.Full-wave Rectifier

(Centre-tap).Full-wave Rectifier(Bridge).Diode Ratings.

1. Current HandlingCapacity.

2. PIV Ratings.

Figures of Merit of aRectifier :

1. Ripple Factor.2. Rectification Efficiency.Performance of Half-wave Rectifier.I dc , I rms , I rms , r , Performance of Full-

wave Rectifier.I dc , I rms , I rms , r ,

(09) rectifiers

Documents