Cirrus Logic AN372 - Manual (Page 4)

AN372
4 AN372REV1
3 Design Process
The design process for a two-stage power converter system can be partitioned into six circuit blocks (see Figure 1).
The AC line voltage is passed through an electromagnetic interference (EMI) filter to suppress conducted interfer-
ence found on the power line. The output of the EMI filter is then converted to the desired DC output by a boost-buck
converter. The power converter system includes the Gate Bias, Steady State Supply, and Active Clamp support cir-
cuitry.
3.1 Operating Parameters
To initiate the design procedure, a set of operating parameters is required. Operating parameters required for
the analytical process are outlined in the table below. Parameters critical to the overall design, but not
specifically addressed in this document, include: EMI compliance, efficiency, footprint, layout, and operating
temperature.
Parameters Symbol
Output Power P
OUT
AC Line Input Voltage V
IN
Output Voltage V
OUT
Load Current I
OUT
Maximum Switching Frequency * F
SW(max)
* Increasing F
SW
may reduce the size of the magnetics but increases switching losses in the FET.
LED +
LED -
L1
L3
R8
R11
R3
R7
R1
R2
Q3
L2
Z1
C2
D7
D6
Q1
R17 R13
Q2
D5
R18
NTC
R14
R15
R22
R23
Q4
R21
R19
R9
BR1
F1
R12 D8
R4
CS1612 /13
FBGAIN
IAC
FBAUX
BSTOUT
GND SGND IPK
CLAMP
GD
FBSENSE
eOTP VDD
SOURCE
L
N
AC Mains
D4
R10
R16
R6
R20
R5
D1
BSTAUX
R24
Boost
Gate Bias
Steady State
Supply
Active
Clamp
Second Stage
Buck
EMI
C8 C10
C9
C7
C6
C5
C4
C3 C1 C12 L4
D3
D2
C11 Z2
Figure 1. Block Diagram of CS1612/13 Design