AN1842 datasheet(8/17 Pages) STMICROELECTRONICS

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AN1842 APPLICATION NOTE

8/17

Figure 12. +5V Dynamic load 1.5 ÷ 2A, 70Hz

+12V: FULL LOAD - @115 VAC - 60Hz

In Figure 13 it is reported the response of the out-

put voltages for a load variation of the 12V output

as detailed on top of the picture. The measure-

ment has been done varying the 12V load from

50% to 100% load: the voltage variation is around

340mV and the 5V output is almost unaffected.

Therefore, the conclusion is that there is no abnor-

mal behaviour of the SMPS generated by a load

change, allowing a good confidence for the inte-

gration of the SMPS in the equipment.

Figure 13. +12V Dynamic load 2 ÷ 4A, 70Hz

+5V: FULL LOAD - @115 VAC - 60Hz

Start-Up Behaviour @full load and Wake-up time

In figure14 the wake-up time is measured at the

lower nominal input mains and the controller start-

up sequence is shown.

The Vcc capacitor is

charged by the charge pump circuit and when its

voltage reaches the start-up threshold the device

starts to operate and the output voltages begin to

rise up to the nominal value, where the control

loop provides for the regulation. The wake-up time

at 115Vac is 1.2 s, which is a quite typical time for

this kind of Power Supplies. Besides, on the pic-

ture it is clearly visible that no any overshoot, un-

dershoot, dip or lost of control happens during the

power supply start-up phase.

Figure 14. Wake-up time @115 VAC - 60Hz

Figure 15. Start-Up Behaviours @full load -

@90 VAC - 60Hz

In the above picture the rising slopes at full load of

the output voltages at minimum input mains volt-

age are captured and the rise time is measured.

As shown in the pictures, the rising time is mono-

tonic and it is almost constant overall the input

mains range. No any overshoot or abnormal be-

haviour is present overall the input main range.

CH3:

+5 Vout

CH4:

+12 Vout

CH3:

+5 Vout

CH4:

+12 Vout

CH1:

VQ4 - Drain

CH2:

VPIN8 (VCC)

CH3:

+5 Vout

CH4:

+12 Vout

CH3:

+5 Vout

CH4:

+12 Vout

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