+
-
5
P$
40 k
:
Rectified AC
BIAS
AC
AC
LM3450A
C22
C23
R34
R36
R12
R14
R15
Q1
R5
R7
+
-
V
SEN
I
SEN
HOLD
R45
Q11
R61
D17
R44
NTC
GND
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Design Information
Input Capacitance
The input capacitor of the flyback (C1), also called the PFC capacitor, has to be able to provide energy
during the worst-case switching period at the peak of the AC input. C1 should be a high frequency, high
stability capacitor (usually a metallized film capacitor, either polypropylene or polyester) with an AC rating
equal to the maximum input voltage. C1 should also have a DC voltage rating exceeding the maximum
peak input v half of the peak to peak input voltage ripple specification. The minimum required
input capacitance is calculated given the same ripple specification:
(19)
Output Capacitance
Since the LM3450A is a power factor controller, C1 is minimized and the output capacitor (C11) serves as
the main energy storage device. C11 should be a high quality electrolytic capacitor that can tolerate the
large current pulses associated with CRM operation. The voltage rating should be at least 25% greater
than the regulated output voltage and, given the desired voltage ripple, the minimum output capacitance is
calculated:
(20)
Definitions
Δ
v
IN-PK
– Peak Input Voltage Switching Ripple
Δ
v
OUT
– Nominal Output Voltage Ripple
Δ
v
CC
– Nominal Primary Bias Ripple
V
CC
– Primary Bias Capacitance
n
AUX
– Output to Auxiliary Turns Ratio
N
A
– Number of Auxiliary Turns
f
2L
– Twice Line Frequency
Figure 14. Dynamic Hold Circuit with Thermal Protection
15
SNVA485B – June 2011 – Revised May 2013
AN-2150 LM3450A Evaluation Board
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