NCP1217(2004) View Datasheet(PDF) - ON Semiconductor
Part Name
Description
View to exact match
NCP1217
(Rev.:2004)
(Rev.:2004)
ON Semiconductor
NCP1217 Datasheet PDF : 18 Pages
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NCP1217, NCP1217A
Vcc 5 V/DIV
Vlatch 1 V/DIV
Time 10 ms/DIV
Figure 27. 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 28). Please note that the negative
spike is clamped to (−2*Vf) thanks to the diode bridge. Also,
the power dissipation of this resistor is extremely small since
it only heats up during the startup sequence.
Another option (Figure 29) consists in wiring a diode
from VCC to the bulk capacitor to force VCC to reach
VCCON sooner and thus stops the switching activity before
the bulk capacitor gets deeply discharged. For security
reasons, two diodes can be connected in series.
+
Cbulk
1
2
3
4
82
7
6
5
3
Rbulk
u4.7 k
1
+
CVCC
+
Cbulk
1
2
3
4
83
7
6
5
D3
1N4007
1
+
CVCC
Figure 28. A simple resistor in series avoids any
latch−up in the controller . . .
Figure 29. . . . or one diode forces VCC to reach
VCCON sooner.
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