V
OUT
V
OP1
V
OP2
Rectified AC
BIAS
LM3450A
V
CCUV
6V
14V
V
CC
V
CC
UVLO
C42
C44
Q1
R5
R7
Q3
V
POP2
D16
D9
D8
Q8
R18
D18
Q2
D12
R1
Q6
D11
R58
C4
C5
C11
C13
D10
D23
D4
T1
R10
R11
R6
C1
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Design Information
The rest of the transformer design should be done with the aid of the manufacturer. There are calculated
trade-offs between the different loss mechanisms and safety constraints that determine how well a
transformer performs. This is an iterative process and can ultimately result in the choice of a new core or
switching frequency range. The previous steps should reduce the number of iterations significantly but a
good transformer manufacturer is invaluable for completion of the process.
Definitions
η
– Expected converter efficiency
P
OUT-MAX
– Maximum Output Power
V
IN-MIN
– Minimum RMS AC Line Voltage
V
IN-PK-MIN
– Minimum Peak Input Voltage
I
IN-PK-MAX
– Maximum Peak Input Current
I
P-PK-MAX
– Maximum Peak Primary Current
D
@IIN-PK-MAX
– Duty Cycle at Maximum Peak Input Current
L
P-MIN
– Minimum Necessary Primary Inductance
L
P
– Chosen Primary Inductance
f
SW-MIN-DES
– Desired Minimum Switching Frequency
f
SW-MIN
– Minimum Switching Frequency
f
SW-MAX
– Maximum Switching Frequency
N
P
– Number of Primary Turns
N
S
– Number of Secondary Turns
A
E-MAX
– Core Cross-Sectional Area
B
MAX
– Maximum Operating Flux Density
A
L
– Transformer Core Figure of Merit
Figure 13. Bias Circuitry
9.5
Bias Supplies and Capacitances
Bias Supplies
13
SNVA485B – June 2011 – Revised May 2013
AN-2150 LM3450A Evaluation Board
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