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