AN1453 datasheet(2/9 Pages) STMICROELECTRONICS

2 / 9 page

APPLICATION NOTE

2/9

1.1. Example 1: FLYBACK

The first example is a 24V/48W Flyback converter

working in continuous mode (Vmains=90V) with

the following conditions:

max

min

out

0.4, I

6.66A, I

3.33A, I

Calculations per diode give:

= 1A and I

= 1.6A

F(AV)per diode

F(RMS) per diode

We can now calculate the efficiency gain (

∆η(%)=

ηref - η) for this Flyback converter which has a

reference

(ref)

efficiency

85%

with

STPR1020CT:

1.2. Example 2: FORWARD

In the following example, the conduction losses in

a 12V/96W Forward converter are simulated:

Lmax

Lmin

out

0.3, I

9A, I

7A, I

Calculations per diode give:

2.4A, I

4.39A

5.6A, I

F(AV)D1

F(RMS)D1

F(AV)D2

F(R

MS)D2

6.71A

The

difference

efficiency

between

STPR1620CT (2x8A, 200V Ultrafast) and a

STPS16150CT (2x8A, 150V Schottky) for a 12V

output, are given in table Fig. 5:

These two examples show that whatever the type

of converter, a significant efficiency gain can be

achieved only by replacing a 200V bipolar diode by

a 150V Schottky.

o u t

Fig. 2: Rectification diode in a Flyback converter

Pout=48W

Vout=24V

VT0

typ(V)

Ω

Pcond

(W)

∆P

(W)

η=85

1.5A, 3A,

125°C

∆η%

STPR102CT

2x5A / 200V

PN diode

0.58 46.5

1.4

0 (ref) 0 (ref)

STPR162CT

2x8A / 200V

PN diode

0.54 46.5

1.32

-0.08 +0.12

STPS10150CT

2x5A / 150V

Schottky diode

0.50

1.22

-0.18 +0.27

STPS16150CT

2x8A / 150V

Schottky diode

0.47

1.14

-0.26 +0.39

Fig. 3: Example of efficiency gain in Flyback

converter

o u

Fig. 4: Rectification diode in a Forward converter

Pout=96W

Vout=12V

VT0

typ(V)

Ω

Pcond

(W)

∆P

(W)

η=85

7A, 9A,

125°C

∆η%

STPR1620CT

0.8

6.48

Ref

STPS16150CT 0.68

5.60

-0.95 +0.72

Fig. 5: Example of efficiency gain in Flyback

converter

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