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FIXED OFF TIME CONTROL SCHEME FOR FLYBACK

IP.com Disclosure Number: IPCOM000193750D
Publication Date: 2010-Mar-08
Document File: 4 page(s) / 118K

Publishing Venue

The IP.com Prior Art Database

Related People

Shiju Wang: INVENTOR [+3]

Abstract

A power converter with a wide ranging AC input with a high power factor is implemented by a flyback converter having a fixed off time. In one particular embodiment, the input voltage ranges over 90 to 305VAC at 50 or 60 Hz, with an output voltage range of 10 to 50 VDC. A power factor of near 0.99 with total harmonic distortion of less than 10% is achieved in a single stage converter.

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Page 1 of 4

INVENTION DISCLOSURE

Inventors: Shiju Wang; Chien Nguyen; Hwangsoo Choi

FIXED OFF TIME CONTROL SCHEME FOR FLYBACK

A power converter with a wide ranging AC input with a high power factor is desired. In one particular embodiment, the input voltage ranges over 90 to 305VAC at 50 or 60 Hz, with an output voltage range of 10 - 50 VDC. A power factor of near 0.99 with total harmonic distortion of less than 10% is further preferred. To reduce cost a single stage converter is preferred.

Prior art schemes are primarily focused on current critical mode control. In particular:

Input voltage: ( )

vin V

sin

ωτ

=

Output DC voltage: Vo

Primary controlled peak current envelope:

pk

iinpk I

=

sin

(

ωτ

)

inpk

In each cycle:

During

t

:

on

v

=

di

L

in

in

dt

I

ωτ

V

sin

( ) ( )

ωτ sin

=

L

inpk

pk

t

LI

t

       inpk on

on

=

V

pk

During

t

off

nV

( )

ni

V

=

o

  d n

L

2

dt

L

sin

:

( )

ωτ

V

       inpk o

inpk

=

 I n

t

off

LI

sin

( )

ωτ

t

       inpk off

=

o

Page 2 of 4

I

sin

( )

LI

inpk

i

t

inpk

I

sin

( )

ωτ

nV

sin

ωτ

on

pk

i +

 = ⎟

        inpk
avg
V

nV

I

=( )

=

inpk

o

inpk

( ) ( )

    LI V

2 pk

o

t

+

t

=⎛ +

LI

sin

ωτV( )

ωτ

V

sin

( )

ωτ

2

( )

sin

ωτ

2

on

off

inpk

inpk

2

⎛ +

1

pk

nV

nV

pk

o

o

Therefore, avg

i is not the same phase of in

v and the power factor is less than what is

desired.

New Solution: fixed off time control scheme for a Single Stage Flyback Converter

Looking in detail at a discontinuous mode embodiment:

Input voltage: ( )

vin V

sin

ωτ

=

Output DC voltage: Vo
Primary controlled peak current envelope preferably meets a perfect power factor and

low T.H.D.: ( )

pk

sin

iinpk I

=

In each cycle:

ωτ

inpk

During

t

:

on

v

=

di

L

in

in

dt

I

sin

sin

( ) ( )

ωτ

V

ωτ

=

L

inpk

t

pk

LI

t

       inpk on

on

=

,

which

V

is

t

independen

of

sin

function

.

pk

LI

I

sin

( )

ωτ

inpk

i

t

inpk

V

2

on

i +

        inpk
avg
T

V

=( )

pk

sin

ωτ

2

t

+

t

=⎛ +

LI

2

=( ) ( )

LI

LI

on

off

2

inpk

inpk

inpk

pk

off

⎜⎝

T

V

off

pk

⎟⎠

Therefore, avg

i is the same phase of in

v and the power factor will be nearly perfect.

It is clear that a similar result can be derived for cont...