NCP1215A ON Semiconductor, NCP1215A Datasheet - Page 13

• Manufacturer Part Number: NCP1215A
• Description: Low Cost Variable OFF Time Switched Mode Power Supply Controller
• Manufacturer: ON Semiconductor

switch’s drain voltage at light load conditions.
conditions can be observed from Channel 3 in Figure 25.
Figure 24 shows CT voltage and also by Channel 2 the
The waveform on the current sense pin at full load
Figure 25. CS Pin at Full Load Condition
Figure 24. CT and Drain at Light Load
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NCP1215A
13
current at light load conditions.
Gate−Source Resistor Design Guidelines
between the MOSFET gate and source connections. This
can preclude an eventual MOSFET destruction if, in the
production stage, the converter is powered whilst the gate is
left unconnected. However, dealing with an extremely low
startup current implies a careful selection of the gate−source
resistance. With the NCP1215A, the gate−source resistor
must be calculated to allow the growth of the V
to 4.0 V in order to not interfere with the power−on
sequence. The following equation helps deriving
R
voltage
R
Vin
R
gate−source
gate−source
gate−source
Figure 26 demonstrates the reduction of the peak primary
In some applications, there is a need to wire a resistor
min
Figure 26. CS Pin at Light Load Condition
of 100 VDC, a startup resistor of 4.0 MW, then
and
, accounting for the minimum rectified input
/(R
equals 180 kW as a minimum normalized value.
gate−source
the
startup
+ R
startup
) u 4.0 V. If we take a
resistor:
CC
Vin
capacitor
min
x