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NCP1200 Datasheet(PDF) 11 Page - ON Semiconductor |
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NCP1200 Datasheet(HTML) 11 Page - ON Semiconductor |
11 / 16 page NCP1200 www.onsemi.com 11 Figure 21. A negative spike takes place on the Bulk capacitor at the switch−off sequence Simple and inexpensive cures exist to prevent from internal parasitic SCR activation. One of them consists in inserting a resistor in series with the high−voltage pin to keep the negative current to the lowest when the bulk becomes negative (Figure 22). Please note that the negative spike is clamped to –2 x Vf due to the diode bridge. Please refer to AND8069/D for power dissipation calculations. Another option (Figure 23) consists in wiring a diode from VCC to the bulk capacitor to force VCC to reach UVLOlow sooner and thus stops the switching activity before the bulk capacitor gets deeply discharged. For security reasons, two diodes can be connected in series. Figure 22. A simple resistor in series avoids any latchup in the controller CVCC D3 1N4007 8 7 6 5 1 2 3 4 + Cbulk + 1 3 CVCC Rbulk > 4.7 k 8 7 6 5 1 2 3 4 + Cbulk + 1 2 3 Figure 23. or a diode forces VCC to reach UVLOlow sooner A Typical Application Figure 24 depicts a low−cost 3.5 W AC−DC 6.5 V wall adapter. This is a typical application where the wall−pack must deliver a raw DC level to a given internally regulated apparatus: toys, calculators, CD players etc. Due to the inherent short−circuit protection of the NCP1200, you only need a bunch of components around the IC, keeping the final cost at an extremely low level. The transformer is available from different suppliers as detailed on the following page. |
Similar Part No. - NCP1200_15 |
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Similar Description - NCP1200_15 |
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