FSQ0465RS

Manufacturer Part NumberFSQ0465RS
DescriptionA Quasi-Resonant Converter (QRC) generally shows lower EMI and higher power conversion efficiency than a conventional hard-switched converter with a fixed switching frequency
ManufacturerFairchild Semiconductor
FSQ0465RS datasheet
 


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max
μ
t
=21
s
s
I
DS
V
μ
t
=15
s
DS
B
t
s
I
DS
μ
V
t
=15
s
DS
B
t
s
I
DS
V
DS
μ
t
=15
s
B
t
s
I
DS
V
DS
μ
t
=15
s
B
max
μ
t
=21
s
s
Figure 33. QRC Operation with Limited Frequency
V
gate
GateX2
fixed
One-shot
triggering
AVS
1st or 2nd is depend on GateX2
V
t
DS
B
GateX2: Counting V
every 2 pulses independent on other signals .
gate
FSQ0465 Rev. 00
© 2008 Fairchild Semiconductor Corporation
FSQ0465RS/RB Rev. 1.0.1
8. AVS (Alternating Valley Switching): Due to the
quasi-resonant operation with limited frequency, the
switching frequency varies depending on input voltage,
I
load transition, and so on. At high input voltage, the
DS
switching on time is relatively small compared to low
input voltage. The input voltage variance is small and the
A
switching frequency modulation width becomes small. To
improve the EMI performance, AVS is enabled when
input voltage is high and the switching on time is small.
Internally, quasi-resonant operation is divided into two
I
DS
categories; one is first-valley switching and the other is
second-valley switching after blanking time. In AVS, two
B
successive occurrences of first-valley switching and the
other two successive occurrences of second-valley
switching is alternatively selected to maximize frequency
modulation. As depicted in Figure 34, the switching
frequency hops when the input voltage is high. The
internal timing diagram of AVS is described in Figure 35.
I
DS
f
s
C
67kHz
59kHz
53kHz
48kHz
Constant
frequency
I
DS
D
μ
t
=6
s
W
FSQ0465 Rev.00
FSQ0465 Rev. 00
Figure 34. Switching Frequency Range
V
continued 2 pulses
V
continued another 2 pulses
gate
gate
1st valley switching
2nd valley switching
fixed
fixed
fixed
de-triggering
triggering
t
t
B
B
Figure 35. Alternating Valley Switching (AVS)
16
μ
Assume the resonant period is 2 s
AVS trigger point
Variable frequency within limited range
CCM
DCM
AVS region
D
C
B
A
V
continued 2 pulses
gate
1st valley switching
fixed
fixed
1st or 2nd is dependent on GateX2
t
t
t
B
B
B
1st valley- 2nd valley frequency modulation.
Modulation frequency is approximately 17kHz.
www.fairchildsemi.com
1
μ
15
s
1
μ
17
s
1
μ
19
s
1
μ
21
s
V
I N