LT1508 LINER [Linear Technology], LT1508 Datasheet - Page 14

• Manufacturer Part Number: LT1508
• Description: Power Factor and PWM Controller(Voltage Mode)
• Manufacturer: LINER [Linear Technology]

14
LT1508
APPLICATIONS
An LT1431 reference/amplifier coupled to a low cost
optoisolator closes the loop from secondary side to pri-
mary side. Efficiency versus power and line voltage is
shown in Figure 10. The PFC preregulator alone has
efficiency numbers between 90% and 97% over line and
load.
A 3-turn secondary added to the 70-turn primary of T1
bootstraps V
requirement as well as about 39mA to cover the gate
current of the three FETs and high side transformer. A
0.15 sense resistor is used to sense input current and
CC
to about 15V supplying the chip’s 13mA
U
INFORMATION
U
W
90
85
80
75
70
90
U
132
Figure 10
V
RMS
180
servo to the command created by the outer voltage and
multiplier. Thus the input current follows the input line
voltage, and changes as necessary, in order to maintain
constant bank voltage. The forward converter sees a
voltage input of 382VDC unless the line voltage drops out,
in which case the 330 F main capacitor discharges to
240VDC before the PWM stage is shut down. Compared to
a typical off-line converter, the effective input voltage
range of the forward converter is much smaller, simplify-
ing the design. Additionally, the higher bus voltage pro-
vides greater hold-up times for given capacitor size.
200W/300W
100W
30W
1508 • F1O
250