4 Functional Checking

AN2242

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duration increases significantly with the mains voltage. The auto-restart at short removal is

correct in all conditions.

Figure 20. and Figure 21. show the short circuit waveforms shorting the 3.3V and the 5V

output. Like the 12V output voltage the controller keeps under control the circuit preventing in

all conditions the power supply from catastrophic failures. Even the 1.8V output is well

protected against shorts, in fact figures Figure 22. and Figure 23. are relevant to a short at

minimum and maximum mains voltage. Because the coupling between the 1.8V and the

auxiliary windings is poor, to help the circuit enter in burst mode the circuitry based on Q2 and

CH1: DRAIN VOLTAGE

CH3: 12 Vout

CH1: DRAIN VOLTAGE

CH3: 3.3 Vout

CH1: DRAIN VOLTAGE

CH3: 5 Vout