AN1376 datasheet(19/35 Pages) STMICROELECTRONICS

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AN1376 APPLICATION NOTE

Figure 20. 35V OUTPUT: SHORT C18

The above pictures are relevant to a hard short by switch of the output capacitor C11. The

short by active load has not been tested because the load is not connected on this point, but

after the zener limiting resistors.

The short circuit on the +30V has not been tested because the power rating of the limiting re-

sistors in series to the zener diode is not enough to insure a reliable protection against long-

term short circuits. A solution could be to PUT a PTC resistor or similar component, or

changethe present resistor with a fusible resistor.

Figure 21. 5V OUTPUT: SHORT BY ACTIVE LOAD

@85 VAC

@265 VAC

CH1:

DRAIN VOLTAGE

CH1:

DRAIN VOLTAGE

CH2:

VC11 (Vaux)

CH2:

VC11 (Vaux)

CH4:

ISHORT CIRCUIT

CH4:

ISHORT CIRCUIT

@115 VAC

A short circuit made on the flat cable solder-

ing points with a power switch provides for

the current limiting intervention of the regu-

lator at 2A (LD1086V50) Then, due to the

internal over temperature protection the

regulator starts to switch on and off itself, al-

ways keeping the output current under con-

trol. Hence, with this transformer and this

regulator, an overcurrent on the 5V is not

able to provide for the hic-cup working

mode the previous tests but anyway all the

most important circuit parameters are be-

low any dangerous overstress point.

CH1:

DRAIN VOLTAGE

CH2:

VC11 (Vaux)

CH4:

ISHORT CIRCUIT

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