Practical design example of a sepic converter

AN2435

14/25

The complete schematic of the circuit is given in Figure 13.

2.2

quantities given in the electrical specifications, the MOSFET peak current value is

using Equation 33:

Equation 33

where:

Equation 34

Under the worst case scenario, the MOSFET and the output diode have to sustain a voltage

that is the sum of the maximum peak input voltage and the maximum output voltage.

Considering the electrical specifications above and a safety margin of 10%, the minimum

Equation 35

To avoid large heat sink, the RMS value of the through current suggests using a MOSFET

2.3

Diode D1 selection

The average value of the diode D1 current is the output current . The RMS value of the

current flowing through diode D1 can be calculated using the following formula:

Equation 36

Output equivalent resistor

Table 1.

Design specification (continued)

Quantity

Value

I

O

P

O

V

O

-------

325mA

==

I

O

V

O

2

P

O

----------

615

Ω

==

I

M1RMS

I

PK

FK

vmin

()

3

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

0.678A

=

=

K

vmin

2V

ACMIN RMS

()

•

V

O

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

=

B

DVSSMin

2V

ACmax

V

O

V

OVP

∆

++

•

() 1.1

•

375V

200V

40V

++

() 1.1

•

677V

=

=

=

I

D1RMS

I

PK

1

3

---

1

π

---

K

vmin

ϑ

()

sin

3

•

1K

vmin

ϑ

()

sin

3

•

+

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

ϑ

d

•

0

π

∫

•

•

0.687A

=

=