ncp1239f ON Semiconductor, ncp1239f Datasheet - Page 35

• Manufacturer Part Number: ncp1239f
• Description: Lowstandby High Performance Pwm Controller
• Manufacturer: ON Semiconductor

primary inductance of 250 mH. To pass 120 W, we assume
that a peak current of 4.2 A was needed. Due to these
numbers, we can easily now when the GTS signal will be
asserted:
Lp, primary inductance = 250 mH
h = 85%
fsw, switching frequency = 65 kHz
Ip skip = 30% of Ip max = 1.26 A
Suppose our Flyback controller is built with a transformer
REF5V
R1
R2
One clearly sees that the GTS signal does not react to the fugitive low FB Pin condition during startup
Ip +
Skip
Adjust
h @ Lp @ fsw
2 @ P out
7
+ 4.2 A
100k
Internal Go−To−Standby signal elaboration
+
0.43V
(*) the 100 ms delay is programmed by the Pin 6 capacitor
GTS
pin1
http://onsemi.com
25r
FB > 1.7 * V
FB
Figure 58.
Figure 59.
NCP1239
FB < V
35
15r
pin7
standby is: 1/2 * Lp * Ip
can vary depending on the line level since the propagation
delay becomes a sensitive parameter, and on the efficiency
that is difficult to precisely predict in light load conditions.
The peak current at which the SMPS will leave standby is
48% of the peak current which means that a power of 28 W
is necessary to re−trigger the PFC.
pin7
The theoretical region at which the SMPS will enter
+
+
=> Stby_detect RESET
−
−
=> Skip high
100 ms timer (*)
(SS and timer block)
COMP1
COMP2
Skip
2
S
R
* fsw * h  11 W. This number
Q
Q
Stby_detect