APEC 2007 Session T8: Semiconductor Devices

Slide# 7

Defining State-Machine State-Change Limits

•

Frequency boundary between CCM and DCM operation

current limited, ON/OFF controlled, flyback converter is determined by

the steady-state minimum inductor current (I

)

||

(

))

(

(

)

1

(

min

min

IN

L

O

s

LIMIT

s

in

L

s

o

LIMIT

S

in

LIMIT

L

o

S

LIMIT

V

n

V

L

T

I

L

T

V

n

T

V

I

I

L

T

V

I

L

n

V

T

D

I

I

−

=

−

−

−

=

−

−

=

(1)

switching period (1/frequency), L is the primary winding inductance value,

V

Solving for the inductance at which I

boundary, and yields the critical switching frequency value of

)

||

(

1

IN

L

O

LIMIT

crit

V

n

V

L

I

f

=

(2)