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9
Design Equations
With reference to the typical application diagram in Figure 2, some useful design equations are tabulated as
below (refer to symbols to datasheet):
Transformer Calculation (Quasi Resonant flyback)
Input data
Turn ratio
Primary Inductance
Primary peak current
Primary turns
Secondary turns
Auxiliary turns
ICE2QRxx65/80x external component design
Current sense resistor
VCC capacitor
ZC resistors
ZC Capacitor
Enter burst mode
power
Leave burst mode
power
Please refer to the below references for some more useful calculation formulas.
Design Guide
Vin_min=85V
, Vin_max=400V
dc
Vdc_max=515V for 650V MOSFET, 550V for 800V MOSFET
V
V
ds
_
max
in
_
max
n
V
V
out
diode
L
p
1
1
V
n
V
in
_
min
f
= switching frequency at low line full load; suggested : 40~65kHz
sw_LF
C
= capacitance across Drain_Source of MOSFET (including C
DS
P
out
I
pk
_
P
0
5 .
L
p
L
I
p
p
_
max
N
p
B
A
max
min
N
p
N
s
n
V
V
cc
diode
N
aux
V
V
out
diode
V
CSth
R
CS
I
pk
_
P
t
I
startup
VCCch
arg
C
VCC
V
VCCon
t
= startup time of system; suggested C
startup
V
N
BUS
_
S
aux
R
;
ZC
1
0
5 .
mA
N
p
V
= output OVP voltage; V
out_OVP
1
C
tan
2
t
ZC
delay
4
t
can be taken as 100ns; f
delay
current drops to 0A (refer to Figure 3)
P
0
5 .
L
Burst
_
enter
P
f
= switching frequency before entering burst mode
sw_bb
P
0
5 .
L
Burst
_
leave
P
f
= switching frequency at burst mode
sB
23
Quasi-resonant CoolSET design guide
,
dc
1
f
P
sw
_
LF
out
0
5 .
out
f
sw
_
LF
N
s
e
2
is ≥ 22μF
VCC
R
ZC
R
ZC
2
V
N
out
_
OVP
aux
N
V
s
ZCOVP
=bulk capacitor voltage to maintain max. output power
BUS_S
R
R
ZC
1
ZC
f
osc
2
R
R
ZC
1
ZC
= measured Drain oscillation frequency after secondary side
osc2
2
V
V
FBEB
PWM
f
sw
R
G
CS
PWM
2
V
CSB
f
sB
R
CS
ICE2QRxx65/80x
f
C
sw
_
LF
DS
of MOSFET)
o(er)
1
V
diode
1
1
2
2
f
2
osc
2
_
bb
8 August 2011
2
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