LT1509CSW#TR Linear Technology, LT1509CSW#TR Datasheet - Page 12

IC PFC CTRLR AVERAGE CURR 20SOIC

LT1509CSW#TR

Manufacturer Part Number
LT1509CSW#TR
Description
IC PFC CTRLR AVERAGE CURR 20SOIC
Manufacturer
Linear Technology
Datasheet

Specifications of LT1509CSW#TR

Mode
Average Current
Frequency - Switching
100kHz
Voltage - Supply
27V
Operating Temperature
0°C ~ 100°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

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12
LT1509
APPLICATIONS
The total equivalent 120Hz ripple in the output capacitor
can be calculated by:
I
For I
120Hz ripple current is:
Table 1 lists the ripple current components from lab
measurements for various output powers and line volt-
ages. The 120Hz ripple current rating at 105 C ambient is
1.72A for the 470 F KMH 35mm 50mm capacitor. The
expected life of the output capacitor may be calculated
from thermal stress analysis:
where
L = Expected life time
L
ambient temperature
condition. T
rent, R is capacitor ESR and KA is a volume constant.
T
condition
Table 1. PFC Capacitor RMS Ripple Current
HF
O
A
V
T
T
INRMS
100
120
230
I
I
L = (L
K
O
= Operating ambient temperature
= Hours of load life at rated ripple current and rated
RMS
= 100kHz Ripple Current.
RMS
LOAD(DC)
= Capacitor internal temperature rise at rated
= Capacitor internal temperature rise at operating
=
=
O
I
120HZ
)2
0.2
0.2
0.2
I
0.62
(105 C + T
K
= 0.88A, 1
100W
120HZ
= (I
2
0.53
0.6
0.5
2
I
HF
U
+
R)/(KA), where I is the rated cur-
2
+
1.79
1.43
120Hz
1.43
K
10
I
INFORMATION
) – (T
HF
I
U
120HZ
0.41
0.41
0.41
2
2
= 0.62A and the equivalent
200W
A
= 1.4A
+ T
1.18
0.97
0.87
I
W
HF
O
)
RMS
I
120HZ
0.62
0.62
0.62
300W
U
1.79
1.45
1.26
I
HF
In our example, L
rated 1.72A. T
Assuming the operating ambient temperature is 60 C, the
approximate lifetime is:
For longer life a capacitor with a higher ripple current rating
or parallel capacitors should be used.
PWM Comparators
The LT1509 includes two comparators in the PWM section
which implement peak current mode control. The primary
current sense voltage is fed into the RAMP pin. The V
Control Voltage pin sets the primary peak current level. An
additional current limit comparator turns GTDR2 off in the
event the RAMP pin voltage exceeds 1V. Referring to the
Block Diagram, there is a 1.2V offset between the RAMP
and V
optocoupler because the V
all the way to ground to inhibit switching. On-chip blanking
avoids reset due to leading edge noise.
Typical Application
Figure 9 shows a 24VDC, 300W power factor corrected,
universal input supply. The 2-transistor forward converter
offers many benefits including low peak currents,
nondissipative snubber, 500VDC switches and automatic
core reset guaranteed by the LT1509’s 50% maximum
duty cycle.
L = (2000)(2)
= 50,870 Hours
T
O
C
= T
pin. This feature simplifies the connection to an
K
1.72A
O
I
RMS
O
can then be calculated from:
(105 C + 5 C) – (60 + 3.3 C)
= 2000 hours assuming T
2
= 5 C
C
pin no longer has to be pulled
10
1.72A
1.4A
2
= 3.3 C
K
= 5 C at
C
or

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