Obsolete

Product(s)

- Obsolete

Product(s)

Obsolete

Product(s)

- Obsolete

Product(s)

2/20

AN1599 - APPLICATION NOTE

on VDD is above the undervoltage shutdown threshold VDDoff during normal operation. To avoid that

during start up phase the voltage across C6 is clamped below the start up threshold VDDon by D3, the

diode D4 has been added. In the SMPS here proposed the optocoupler is used not only for regulation but

it also supplies the VIPer12A during normal operation. In this way, when the output is shorted the

optocoupler is off and the VIPer12A works only with the C6 charge. The result assures a good protection

against short circuit. The zener diode D7 limits the output voltage in case of secondary feedback failure.

For the primary feedback configuration, the secondary regulated voltage is controlled by the zener diode

D7 connected to pin FB. Due to the parasitic element of the transformer is not possible to achieve a

precise regulation of the secondary voltage to supply a microprocessor, hence a low drop out voltage

regulator LE33CZ type has been used.

For the secondary regulation circuit a transil is used to keep the drain voltage at a safe level, the PKC136

type integrates both blocking diode and transil diode in a single package. For the primary feedback

configuration a cheap R-C-D clamper has been used since the voltage drain is lower due to the low power

managed by the supply.

The output rectifiers are schottky diodes for better efficiency thanks to their lower forward voltage drop

and negligible switching losses. They have been chosen according to the maximum reverse voltage and

output current.

The output capacitors have been selected to minimize the output ripple, according to the AC output

current.

For the 750mA output, a small LC filter has been added in order to filter the high frequency ripple without

increasing the output capacitors size.

For both circuits the transformer is an E13 TIW type, manufactured by Eldor Corporation according to

EN60065.

The converters are compliant to EN50022 class B and the input filter topology has been selected in order

to fit consumer application like TVC or STB.

Table 1: Operating condition

Note 1: for converter with secondary feedback

Note 2: for converter with primary feedback

Note 3: these two applications are designed to supply microprocessors and logic circuitry always working,

so a minimum load has been assumed. The value has been fixed at 20mA, compatible with most of

common application.

4. PCB LAYOUT

The PCB has been realized in FR2 with a single side copper thickness of 35 µmm. The dimensions are 52

X 98 mm. Here below there are the components side and tracks side.

The demo board has been developed for evaluation purpose so its dimensions are not optimised. To

develop SMPS reducing the board size, the VIPer12A and the other components in SMT package can be

used.

Parameter

Value

Input voltage range

90 to 264Vac

Input frequency range

50/60Hz

Output voltage

3.3V±3% @ 0.75 A

(Note1)

Output voltage

3.3V±2% @100mA

(Note2)

Minimum load

20mA

(Note 3)

Maximum working ambient temperature

60°C

EMI

EN55022 class B