Design circuit

AN2623

8/25

The peak current through the inductor is:

Equation 6

According to the max high frequency voltage ripple (

admitted ESR (Equivalent Series Resistance) are calculated as follows:

Equation 7

Equation 8

The RMS current through the output capacitor must not exceed the current rate of the

selected capacitor and is calculated as:

Equation 9

ZL series Rubycon electrolytic capacitor was selected with an ESR of 42 m

Ω and max

current capability of 1495 mA.

3.3

Output diodes

The maximum reverse voltages across the rectifier diode and the free wheeling diode (D1-

D2 in the Figure 2) can be calculated as:

Equation 10

Equation 11

rectifier diode, when they are forward biased, and n=1.25 is the turn ratio between the

primary and the secondary winding of the transformer. Considering that the voltage drops in

The maximum RMS and the average currents through the rectifier diode are calculated as:

I

Peak

Lout

–

I

out

∆I

Lout

I

Peak

Lout

–

5.4 A

=

=

+

=

C

outmin

V

out

∆V

outHF

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

1

8f

2

sw

⋅

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

1D

max

–

L

out

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

C

outmin

4.5

µF

=

⇒

⋅⋅

=

ESR

max

∆V

outHF

∆I

out

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

ESR

max

388 m

Ω

=

⇒

=

I

RMS

Cout

–

I

2

RMS

Lout

–

I

2

out

–

I

RMS

Cout

–

860 mA

=

⇒

=

V

diodeR

V

1max

n

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

V

dropF

V

diodeR

328V

=

⇒

–

=

V

diodeF

V

1max

n

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

V

dropR

V

diodeR

⇒

–

=