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AN628 APPLICATION NOTE

An auxiliary winding can be used just to get a low cost supply for the I.C. It will be a low cost thin wire coil will

be used and the number of turns is the only parameter to define.

Input Bridge

The input diodes bridge can be standard off-line, slow-recovery and low cost devices. The device selection con-

siders just the input current (Irms) and the thermal data.

Input Capacitor

The maximum high frequency voltage ripple (r =

r = 0.02 to 0.08.

Output Bulk Capacitor

performances and also on the subsequent application.

The D.C. output voltage and overvoltage, the output power and voltage ripple are the first parameters to con-

and so, the output voltage ripple

(

With a low ESR capacitor can be simplify:

.

Although the ESR, normally does not affect the output ripple parameter, it has to be considered in power losses

account both for the rectified mains frequency and the switching frequency.

ing criteria will change:

where:

C

IN

K

r

I

rms

2

π f

sw

rV

lrms

⋅⋅

⋅ ⋅

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

≥

2

V

O

∆

I

O

1

2

π 2f C

O

⋅⋅

()

2

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

ESR

()

2

+

=

C

O

I

O

2

π 2f

V

O

∆

⋅⋅

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

+

P

O

2

π 2f

V

O

∆

V

O

⋅⋅

⋅

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

=

C

O

2P

⋅

V

O_min

2

V

op_min

2

–

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

=