Buck and Boost Converter Using PSPICE

Experiment Name : Buck and Boost converter using PSPICE AIM:- To simulate the Buck and Boost converter using PSPICE software and

obtain the variation of output voltage with duty cycle variation. APPARATUS REQUIRED:-

1. PC insta installed lled with with PSPIC PSPICE E Software Software 2. VDC (volta (voltage ge sou source rce)) 3. VPULSE VPULSE (vol (voltag tage e source source)) 4.

IRF150 (Switch)

5. R (Re (Resi sist stan ance ce)) 6. L (Indu (Induct ctanc ance) e) 7. C (Ca (Capa paci cita tanc nce) e) 8. DIN4 DIN400 002 2 (Dio (Diode de)) 9. GND_S GND_SIGN IGNAL/ AL/CAP CAPSYM SYM THEORY:-

A process that changes one DC voltage to a diff di ffer eren entt DC volt voltag age e is calle called d DC to DC conv conver ersio sion. n. A boost conv conver erte terr is some someti time mes s calle called d a st step ep-up -up conv convert erter er sinc since e it “steps up” the source voltage. A switch is shown, for which a device BOOST Converter:-

 belonging to transistor family like Thyristor, IGBT, MOSFET etc. are generally used. Also, a diode is used in series with the load.

A boost converter (step-up converter) is a power converter with an output DC voltage greater than its input DC voltage. It is a class of switching-mode of switching-mode power supply (SMPS) containing at least two semiconductor switches (a diode and a transistor) transistor) and at least one energy storage element. Filters made of capacitors of capacitors (sometimes in combination with inductors) inductors) are normally added to the output of the converter to reduce output voltage ripple.

The basic principle of a Boost converter consists of 2 distinct states : •

•

in the On-state, the switch S is closed, resulting in an increase in the inductor current; in the Off-state, the switch is open and the only path offered to inductor  current is through the flyback diode D, the capacitor C and the load R. This results in transferring the energy accumulated during the On-state into the capacitor.

CIRCUIT DIAGRAM:-

Waveforms of current and voltage in a boost converter operating in continuous mode.

PSPICE Simulation Diagram :

L

1

1 0

u

v

d

c

D

1

H

2 M

5

1

2 4

V

D

V V T

1 2 D

T P

R W

T P

F E

0 V 5 0

= = = = = = R

1 u s . 0 2 m

N

4

0

0

2 C

I R

1

. 0 1 u s . 0 0 4 m . 0 =

2 F

1

5

0

1 1

2

R . 8

u

1 1

0

s s

0

d u t y c y c l e

=

f s w i t c h

5 0 k h z

r i p p l e

= =

P W / P E R

0 . 0 1

i n d u c t a n c e c a p a c i t a n c e

=

{ d u t y c y c l e ) / ( r e s i s t a n c e * r i p =

{ ( d u t y c y c l e * ( 1 - d u t y c y c l e ) * ( 1 - d u t y c y c l e ) *

PLOT NO-1 DUTY CYCLE=0.3

PLOT NO-2 DUTY CYCLE=0.5

BUCK CONVERTER : THEORY:-

A buck converter is a step-down DC to DC converter . Its design is similar to the step-up boost converter , and like the boost converter it is a switched-mode  power supply that uses two switches (a transistor and a diode), an inductor and a capacitor. The simplest way to reduce the voltage of a DC supply is to use a linear  regulator (such as a 7805), but linear regulators waste energy as they operate by dissipating excess power as heat. Buck converters, on the other hand, can be remarkably efficient (95% or higher for integrated circuits), making them useful for tasks such as converting the 12–24 V typical battery voltage in a laptop down to the few volts needed by the processor . The operation of the buck converter is fairly simple, with an inductor and two switches (usually a transistor and a diode) that control the inductor. It alternates  between connecting the inductor to source voltage to store energy in the inductor and discharging the inductor into the load. A buck converter operates in continuous mode if the current through the inductor (IL) never falls to zero during the commutation cycle. In this mode, the operating principle is described by the chronogram in figure 4: •

•

When the switch pictured above is closed , the voltage across the inductor  is V  L = V i − V o. The current through the inductor rises linearly. As the diode is reverse-biased by the voltage source V, no current flows through it; When the switch is opened , the diode is forward biased. The voltage across the inductor is V  L = − V o (neglecting diode drop). Current IL decreases.

As can be seen on figure 4, and . D is a scalar called the duty cycle with a value between 0 and 1. This yields :

CIRCUIT DIAGRAM:-

Fig-4Evolution of the voltages and currents with time in an ideal buck converter operating in continuous mode.

PSPICE Simulation Diagram

:

M

1 I R

F

1

5

0

L

4

1

2 5

V 2

0

V

d

0

u

H

1

R

c

D V

2

1 D

C 1

N

4

0

0

2

1 5

0

2 1

0

u

0 V V T T T P P

1 2 D R F E W

= = = = = R

0 d u 5 0 u s f s . 0 1 u r si . 0 1 u s i n = . 0 2 m = . 0 1 cm a

t y c y c l e

=

w i t c h

5 0 k h z

p p l e

= =

P W / P E R

0 . 0 1

d u c t a n c e s

ps a c i t a n c e

=

{ ( 1 - d u t y c y c l e ) * r e s i s t a n c =

{ ( 1 - d u t y c y c l e ) / ( 8 * i n d u c t a n c e * r i p p l e * f

PLOT NO-1 VOLTAGE & CURRENT ACROSS CAPACITOR

PLOT NO-2 DUTY CYCLE=0.7

PLOT NO-3 DUTY CYCLE=0.5

PLOT NO-4 DUTY CYCLE=0.4

CONCLUSION:-

 The plot of various Duty Cycle for Buck and Boost Converter shows that output voltage can be varied by changing the duty cycle. Hence the ‘step up’ and ‘step down’ version of source voltage can be obtained at the output.