Design equations for the modified buck converter

AN2928

12/21

Figure 4.

Sawtooth signal

Equation 24

The real drain current waveform is given in Figure 5. As can be observed, the signal is quite

similar to the signal in Figure 4, except that there is no current during the off-time stage

modified to become Equation 25.

Square RMS drain current is calculated using the equation:

Equation 25

And finally it is possible to calculate the continuous conduction losses:

Equation 26

AM00369

t0

lAVG

IPP

i(t)

DT

(1- D)T

lMAX

t

tON

tOFF

-

I0

lMIN

l

RM S

2

1

T

---

i

2

t

() t

1

T

---

i

2

t

() ti

2

t

() t··

d

t

0

DT

+

t

0

T

+

∫

+

d

t

0

t

0

DT

+

∫

D

=

l

0

2

1D

–

() ⋅

+

⋅

l

MAX

l

MI N

+

2

-----------------------------

⎝⎠

⎛⎞

2

l

PP

2

12

--------

+

=

d

t

0

t

0

T

+

∫

=

l

RM S

2

D

l

MAX

l

MI N

+

2

-----------------------------

⎝⎠

⎛⎞

2

l

PP

2

12

--------

+

D

=

l

AVR ON

2

l

PP

2

12

--------

+

⋅⋅

=

P

CON

l

RM S

2

R

DS ON

()

⋅

=