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AN1523 APPLICATION NOTE

The figure 32 has been acquired testing the open

loop protection when working in stand-by: as visible,

even in this condition the circuit stops the switching

cycles when the Vcc reaches 16.5V and the value of

the output voltages never overstress the output elec-

trolytic capacitors.

In case a lower OVP threshold is required, it is possi-

ble to connect the inverting input of the E/A (VFB-pin

5) to ground via a resistor (e.g. 1K

tween the pin 5 and Vcc. A small ceramic capacitor in

parallel to the resistor could be required. In this case

Figure 32. OPEN LOOP

Vin = 220 Vrms - 50 Hz @STAND-BY

CH1:

CH2:

CH3:

CH4:

Conducted Noise Measurements (Pre-Compliance Test)

The following pictures are shown the quasi-peak conducted noise measurements at full load and standby with

both nominal input mains voltages. The limits shown on the diagrams are referred to the EN55022 CLASS B,

which is the most widely used for domestic equipment like a TV or a STB. As visible on the diagrams, there is

a good margin of the measures with respect to the limits in overall conditions.

Figure 33. QUASI-PEAK MEASURE

Figure 34. QUASI-PEAK MEASURE

Vin = 115 Vrms - 50 Hz @FULL LOAD

Limits: EN55022 CLASS B

Vin = 220 Vrms - 50 Hz @ FULL LOAD

Limits: EN55022 CLASS B