LT1950 Linear Technology, LT1950 Datasheet - Page 17

• Manufacturer Part Number: LT1950
• Description: Single Switch PWM Controller
• Manufacturer: Linear Technology

w w w . D a t a S h e e t . i n
APPLICATIO S I FOR ATIO
High Efficiency, Isolated 26V 5A Output,
Nonsynchronous Forward Converter
Figure 13 illustrates a nonsynchronous forward converter
based on the LT1950 to provide a highly efficient, 26V 5A
isolated output from 48V input. The LT1950-based con-
verter using a single switch topology and utilizing the
LT1950s adaptive maximum duty cycle clamp is a simple
and highly optimized solution. Peak efficiencies of 92.8%
(Figure 12) are achievable. Transformer and inductor are
standard components. The quarter brick sized DC/DC
converter (2.3" by 1.45") delivers over 125W and is only
0.4" high. The 26V converter can be used as a “front line”
(isolating) converter in telecom systems with multiple
outputs.
U
210k
6.8k
0.1 F
27k
U
Figure 13. 36V to 72V Input to 26V at 5A Nonsynchronous Forward Converter
5
6
3
9
4
2
1
SLOPE
V
R
BLANK
SYNC
FB
COMP
REF
OSC
TO 72V
INPUT
LT1950
36V
W
I
SHDN
SENSE
PGND
GATE
V
GND
V
+V
–V
SEC
V
IN2
IN
IN
IN
15
11
16
7
12
10
8
13
BIAS
10V
2.2 F
100V
X5R
C
+V
IN
IN
470k
18k
U
PA0581
Si7450
0.015
T1
OC1
330R
47 H
47 F
470pF
1
Figure 12. LT1950-Based Nonsynchronous
Forward Converter Efficiency vs Load
Current (Figure 13 Circuit)
5
2
18k
1 F
94
93
92
91
90
89
88
87
86
85
84
–
+
1
4
3
232k
24.9k
U3
LT1797
LT1009
U2
1 F
47k
2
LOAD CURRENT (A)
FMMT625
3
8.2V
22k
1950 F13
+V
OUT
V
V
f
OSC
IN
OUT
4
= 48V
= 235kHz
= 26V
1950 F12
LT1950
5
sn1950 1950fs
17