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One clearly sees that the GTS signal does not react to the fugitive low FB Pin condition during startup
REF5V
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R1
Adjust
R2
Suppose our Flyback controller is built with a transformer
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
2 @ P out
Ip +
h @ Lp @ fsw
Ip skip = 30% of Ip max = 1.26 A
100k
7
+
0.43V
GTS
pin1
(*) the 100 ms delay is programmed by the Pin 6 capacitor
Internal Go−To−Standby signal elaboration
+ 4.2 A
http://onsemi.com
NCP1239
Figure 58.
FB < V
=> Skip high
pin7
+
−
FB
COMP1
15r
25r
COMP2
+
−
FB > 1.7 * V
=> Stby_detect RESET
pin7
100 ms timer (*)
(SS and timer block)
Figure 59.
The theoretical region at which the SMPS will enter
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.
35
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Stby_detect
S
Q
Q
R
2
* fsw * h 11 W. This number
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