NCP1379 ON Semiconductor, NCP1379 Datasheet - Page 17

• Manufacturer Part Number: NCP1379
• Description: Quasi-Resonant Current-Mode Controller
• Manufacturer: ON Semiconductor

(FB decreasing), or lower than 1.4 V (FB increasing). This
corresponds to low output power.
variable and expands as the output power decreases. The
peak current is fixed to 17.5% of his maximum value when
V
connected to the C
constant current source and its voltage is compared to an
internal threshold (V
FB
VCO operation occurs for FB voltage lower than 0.8 V
During VCO operation, the switching frequency is
The frequency is set by the end of charge of the capacitor
< 0.56 V.
Figure 32. In VCO Mode, as the Power Output Decreases the Frequency Expands
T
pin. This capacitor is charged with a
FBth
) fixed by FB voltage (see
Figure 31. Time Out Case n52: the 3
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VCO MODE
17
Figure 23). When this capacitor voltage reaches the
threshold, the capacitor is rapidly discharged down to 0 V
and a new period start. The internal threshold is inversely
proportional to FB voltage. The relationship between V
and V
V
VCO mode at works.
rd
CT(MAX)
When V
and 4
FBth
th
is given by Equation 1.
Valley are Missing
which is typically 5.5 V. Figure 32 shows the
FB
is lower than 0.3 V, V
V
FBth
+ 6.5 * (10 3)V
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FB
CT
is clamped to
(eq. 1)
FB