LT1509ISW#TR Linear Technology, LT1509ISW#TR Datasheet - Page 14

• Manufacturer Part Number: LT1509ISW#TR
• Description: IC PFC CTRLR AVERAGE CURR 20SOIC
• Manufacturer: Linear Technology

Specifications of LT1509ISW#TR

• Mode: Average Current
• Frequency - Switching: 100kHz
• Voltage - Supply: 27V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Startup: -
• Lead Free Status / Rohs Status: Not Compliant

14
LT1509
APPLICATIONS
An LT1431 reference/amplifier coupled to a low cost
optoisolator closes the loop from secondary side to pri-
mary side. Unity loop frequency is a conservative 3kHz.
Figure 10 shows the output voltage’s response with a 2A
to almost 10A current step. Output voltage is maintained
to within 0.5V during the load step. Efficiency versus
power and line voltage is shown in Figure 11. 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
servo to the command created by the outer voltage and
multiplier. Thus the input current follows the input line
CC
to about 15V supplying the chip’s 13mA
U
INFORMATION
U
W
0.5V/DIV
5A/DIV
90
85
80
75
70
90
U
132
Figure 11
Figure 10
V
RMS
180
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 470 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.
Because the high side transformer effectively delays the
turn-on reverse recovery spike past the end of the built-in
blanking time, an external blanking transistor is needed.
Controlling the output current during an output short
circuit depends on the duty cycle reducing to a small
fraction of steady state. An additional transistor disables
blanking during turn-on and output short circuit.
200W/300W
100W
30W
LT1509 • F11
250