LUO CONVERTER

I. INTRODUCTION

DC to DC converters are important in portable

electronic devices such as cellular phones and laptop

computers, which are supplied with power from batteries.

Such electronic devices often contain several sub circuits

which each require unique voltage levels different than

supplied by the battery (sometimes higher or lower than the

battery voltage, or even negative voltage). Additionally, the

battery voltage declines as its stored power is drained. DC to

DC converters offer a method of generating multiple

controlled voltages from a single variable battery voltage,

thereby saving space instead of using multiple batteries to

supply different parts of the device.

Luo converters are DC-DC Switching Mode Boost converters.

A boost converter (step-up converter) is a power converter

with an output dc voltage greater than its input dc voltage.

Luo converters are a class of converters providing a high gain

with relatively lesser number of components. Although Luo

converters provide a high gain, when cascaded, the gain

increases stage by stage only in Arithmetic

Jayanand.B

Dept of Electrical & Electronics

Govt.Engg College,Idukki

Kerala,India

jayanandb@gmail.com

Progression i.e. these converters uses the voltage lift (VL)

technique. In order to solve this discrepancy in the Classical

Luo Converters, another class of converters called Super-lift

Luo Converters were developed. While the positive aspects

of the Classical Luo Converters are retained in Super-lift

converters, Super-lift converters also have the advantage that

the gain in this converter increases in geometric progression,

stage by stage.

II. POSITIVE OUTPUT SUPERLIFT LUO CONVERTERS

The positive output elementary super lift Luo converter is a

new series of DC-DC converters possessing high-voltage

transfer gain, high power density; high efficiency, reduced

ripple voltage and current . These converters are widely used

in computer peripheral equipment, industrial applications and

switch mode power supply, especially for high voltagevoltage

projects. The positive output elementary super lift

Luo converter performs the voltage conversion from positive

source voltage to positive load voltage. The gain in this

converter increases in geometric progression, stage by stage.

It effectively enhances the voltage transfer gain in power

series. Each circuit has one switch, n inductors, 2n capacitors,

and (3n-1) diodes. The conduction duty ratio is d, switching

frequency is f (period T = 1/ f), the load is resistive load R.

The input voltage and current are Vin and Iin, output voltage

and current are VO and IO. Assume no power losses during the

conversion process, Vin ~ Iin = VO ~ IO. The voltage transfer

gain is G. G = VO/ Vin. The first three stages of positive

output super-lift converters are shown. For convenience to

explain, we call them as

a) Elementary circuit (n = 1)

b) Relift circuit (n = 2)

c) Triple-lift circuit (n = 3) respectively.

The positive output elementary super lift Luo converter is

shown. in Fig. 1. It includes dc supply voltage Vin, capacitors

C1 and C2, inductor L1, power switch (n-channel MOSFET) S,

freewheeling diodes D1 and D2 and load resistance R.

978-1-4799-2075-4/13/$31.00 c2013 IEEE 129

Fig.1. Positive Output Elementary Superlift Luo converter

In the description of the converter operation, it is assumed

that all the components are ideal and also the positive output

elementary super lift Luo converter operates in a continuous

conduction mode. Figs. 2 and 3 shows the modes of operation

of the converter.

Fig.2. Mode I operation

In Fig. 2 when the switch S is closed, voltage across

capacitor C1 is charged to Vin. The current iL1 flowing through

inductor L1 increases with voltage Vin.

Fig.3. Mode II operation

In Fig. 3 when the switch S is opened, the inductor

current iL1 decreases with voltage (Vo - 2 Vin). Therefore, the

ripple of the inductor current iL1

dT

L

dT V 2V

L

i V

1

o in

1

in

L1

Ģ = = . (1)

o in V

1

V 2

d

d

.

= .

(2)

The voltage transfer gain is

d

G d

.

= = .

1

2

V

V

in

o

(3)

The input current iin is equal to (iL1 + iC1) during switching on

and only equal to iL1 during switching-off. Capacitor current

iC1 is equal to iL1 during switching-off. In steady state, the

average charges across capacitor C1 should not change. We

have the following relations:

in-off L off C off i i i . . = = 1 1 (4)

in on L on Ci on i i i . . . = + 1 (5)

C on C off dTi d Ti . . = . 1 1 (1 ) (6)

If inductance L1 is large enough, iL1 is nearly equal to its

average current iL1. Therefore

in off C1 off L1 i = i = I . . (7)

d

I

I

d

i I d L

in on L L

1

1 1

= +1. = .

(8)

1 1

1

C on L I

d

i = . d .

(9)

and average input current

1 1 1 (1 ) (1 ) (2 ) in in on in off L L L I =di + .d i = I + .d I = .d I . . (10)

Considering T = 1/ f and

978-1-4799-2075-4/13/$31.00 c2013 IEEE 130

R

d

d

d

d 2

o

o

2

in

in

2

1

I

V

2

1

I

V

..

.

..

.

.

= . ..

.

..

.

.

= .

(11)

The variation ratio of inductor current iL1 is

1

2

1 1

1

1 2(2 ) L

(1 )

2

/ 2 (2 )

f

R

d

d d

L I

d d TV

I

i

in

in

L

L

.

ƒÌ = ƒ¢ = . = .

(12)

The ripple voltage of output voltage Vo is

R

V

C

1

C

I (1 )

C

V o

2 2

o

2

o f

Ģ = ĢQ = . d T = .

...