ml4822cs Microsemi Corporation, ml4822cs Datasheet - Page 7

• Manufacturer Part Number: ml4822cs
• Description: Average Current Controller
• Manufacturer: Microsemi Corporation

Q1 Turn-On
The turn-on event consists of the time it takes for the
current through L2 to ramp to the L1 current plus the
resonant event of L2 and the ZVS capacitor. The total
event should occur in a minimum of 350–450ns, but can
be longer at the risk of increasing the total harmonic
distortion. Setting these times equal should minimize
conducted and radiated emissions.
Where I
The value of L2 is calculated to remain in discontinuous-
mode:
The resonant event occurs in 1/4 of a full sinusoidal cycle.
For example, when a 1/4 cycle occurs in 200ns, the
frequency is 1.25MHz.
Rearranging and solving for L2:
The resonant capacitor (C
equations 2 and 4 equal to each other and solving for
C
APPLICATION
Figure 3 displays a typical application circuit for a 500W
ZVS PFC supply. Full design details are covered in
application note 33, ML4822 Power Factor Correction
With Zero Voltage Resonant Switching.
ZVS
.
L2
is equal to I
C
ZVS
f
RES
t
L
Q1(OFF)
2
2
V
2
BUS
L
L1
4
2
= t
.
L
V
2
BUS
ZVS
IL2
t
1
RES
4
V
2
2
C
RMS MIN
+ t
) value is found by setting
2
ZVS
t
P
C
V
RES
RES
(
OUT
RMS MIN
ZVS
2
2
= 400ns
(
)
4
P
OUT
t
1
IL
t
)
RES
2
t
IL
2
(1)
(2)
(3)
(4)
(5)
A. SYSTEM
CLOCK
(INTERNAL)
B. R T C T
C. ZVS GATE (Q2)
D. VDS (Q2)
E. PFC GATE (Q1)
F. VDS (Q1)
G. I
L2
t
1
t
Figure 2. Timing Diagrams
2
t
3
ML4822
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