DC to DC Synchronous Converter Design

Abdus Sattar, IXYS Corporation

IXAN0068

6

We can write as:

2

1

td

td

BD

P

P

P

+

=

(12)

Where Ptd1 is the body diode loss during dead time td1 and Ptd2 is the body diode loss

during dead time td2.

S

rr

rr

in

S

L

O

f

rr

cd

td

f

t

I

V

f

td

I

I

V

P

P

P

•

•

•

•

+

•

•

⎟

⎠

⎞

⎜

⎝

⎛

Δ

−

•

=

+

=

2

1

1

2

1

1

1

(13)

()

S

L

O

f

rr

cd

td

f

td

I

I

V

P

P

P

•

•

⎟

⎠

⎞

⎜

⎝

⎛

Δ

+

•

=

=

=

2

2

0

2

2

2

(14)

PWM Gate Driver Power loss: [1]

The power dissipation in the driver is defined by,

S

DD

onl

G

DRIVER

f

V

Q

P

•

•

=

)

(

(15)

The gate “point of voltage” is,

fs

O

TH

SP

g

I

V

V

+

=

(16)

The driver current is,

Gate

UP

PULL

DRIVER

SP

DD

H

L

DRIVER

R

R

V

V

I

+

−

=

−

−

)

(

)

(

(17)

Gate

DOWN

PULL

DRIVER

SP

DD

L

H

DRIVER

R

R

V

V

I

+

−

=

−

−

)

(

)

(

(18)

The rise time is,

)

(

)

(

)

(

H

L

DRIVER

on

G

on

t

I

Q

t

−

=

(19)

The fall time is,

)

(

)

(

)

(

L

H

DRIVER

on

G

off

t

I

Q

t

−

=

(20)

If an external Schottky diode (D1) is used across Q2, the Schottky’s capacitance needs to

be charged during Q1 turn-on. The power loss to charge the Schottky’s capacitance is,

2

2

)

(

S

IN

SCHOTTKY

SCHOTTKY

C

f

V

C

P

•

•

=

(21)