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AN1523 Datasheet(PDF) 12 Page - STMicroelectronics |
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AN1523 Datasheet(HTML) 12 Page - STMicroelectronics |
12 / 24 page ![]() AN1523 APPLICATION NOTE 12/24 As clearly indicated by the waveforms, the circuit starts to work in hiccup mode, keeping the current mean value of the shorted output at levels within component rating. Because the working time and the dead time are im- posed by the charging and discharging time of the auxiliary capacitor C2, it is almost constant varying the input mains voltage thanks to the internal start-up current source already mentioned. Short-Circuit Tests @ Stand-by A short circuit when the SMPS works at light-load is always a critical fault condition for any power supply circuit. In this condition, the energy deliverable to the short is the maximum one, and then it is the most stressing situ- ation for the output rectifiers and besides, sometimes the primary hiccup mode is not triggered. This may hap- pen because the short circuit reflected impedance on the auxiliary winding it is not low enough for decreasing the Vcc voltage below the under-voltage lockout threshold or spikes are present at turn off on the auxiliary wind- ing which are capable of powering the IC. The proposed circuit, even in this load condition, provides the same results as the previous tests, both at 115Vac and at 220 Vac, making it reliable in all the working situations independently from the transformer coupling. Figure 23. SHORT ON +5V Figure 24. SHORT ON +5V Vin = 88 Vrms - 50 Hz @STAND-BY Vin = 265 Vrms - 50 Hz @STAND-BY CH1: VPIN1 – DRAIN VOLTAGE CH1: VPIN1 – DRAIN VOLTAGE CH2: VPIN3 - Vcc CH2: VPIN3 -Vcc CH4: ISHORT CIRCUIT CH4: ISHORTCIRCUIT |
Similar Part No. - AN1523 |
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Similar Description - AN1523 |
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