AN1523 APPLICATION NOTE

14/24

Even at turn off in short circuit the SMPS functioning is good, protecting properly the circuit. No any abnormal

transition or level has been observed during the tests, confirming the design robustness proven so far.

Over Voltage Protection

A dangerous fault that could happen is the failure of the feedback circuitry. If this occurs, the SMPS output volt-

ages can get to very high values, depending on the load on each output and on the transformer coupling be-

tween the windings. Consequently, the rectifiers and the output capacitors are overstressed or damaged. A

possible solution could be to oversize the components but this should be expensive and uneconomic. Hence,

to avoid this SMPS failure a suitable protection circuit has been added inside the L6590 and it doesn’t require

any external component for the threshold setting.

Hence, this fail has been simulated opening the feedback

loop and the circuit has been tested, giving the results shown in figures 30 and 31:

Figure 28. TURN-OFF WITH +5V SHORTED

Figure 29. TURN-OFF WITH +5V SHORTED

Vin = 88 Vrms - 50 Hz @FULL LOAD

Vin = 265 Vrms - 50 Hz @STAND-BY

CH1:

CH1:

CH2:

CH2:

CH3:

+5Vout

CH3:

+5Vout

Figure 30. OPEN LOOP

Figure 31. OPEN LOOP

Vin = 88 Vrms - 50 Hz @FULL LOAD

Vin = 265 Vrms - 50 Hz @FULL LOAD

CH1:

CH1:

CH2:

CH2:

CH3:

+5Vout

CH3:

+5Vout