Datasheet

23
LT1737
1737fa
TYPICAL APPLICATIO S
U
APPLICATION WITH 2-WINDING TRANSFORMER
The previous application example utilized a 3-winding
transformer, the third winding providing only feedback
information. Additional circuitry may be employed to
provide feedback information, thus allowing the trans-
former to be reduced to a 2-winding topology. (The cost
and size savings associated with the transformer often
make this a preferable alternative. Furthermore, a variety
of manufacturers offer off-the-shelf dual wound magnet-
ics which often can be applied as 1:1 transformers.)
Figure 12 shows an LT1737 configured for operation with
a dual wound toroid, the Coiltronics #CTX150-4
OCTA-PAC
TM
. A ground referred version of the flyback
voltage waveform is now provided by components Q1, R2,
R1
0.27Ω
0.5W
IRC TYPE LR 2010
M1
IRFL014
R10
5.1Ω
5%
13
4
T1
COILTRONICS
CTX150-4
V
IN
2
1737 F12
R6
100k
5%
R5
150k
5%
C5
47pF
50V
NPO
6
8
7
3
910 15
R9
33k
5%
R8
240k
5%
16
2
14 13 12 4 5 11 1
C3
1nF
25V
X7R
R7
4.7k
5%
R11
100Ω
5%
D4
1N5252
D3
MBRS1100
R4
75k
5%
C1: AVX TPS TANTALUM (TPSE226M035R0300)
C2: AVX TPS TANTALUM (TPSE336M025R0200)
D1, D3: MOTOROLA 100V, 1A SCHOTTKY DIODE
D2: SIGNAL DIODE
D4: 24V, 500mW ZENER DIODE
R3
3.01k
1%
C8
0.1µF
25V
Z5U
C4
0.1µF
25V
Z5U
C6
470pF
50V
X7R
C7
470pF
50V
X7R
•
•
D1
MBRS1100
C2
33µF
25V
+
R13
7.5k
5%
V
OUT
15V
250mA
R12
100Ω
5%
M1: INT’L RECTIFIER 60V, 0.2Ω N-CH MOSFET
D2
BAS16
Q1
2N3906
R2
35.7k
1%
C1
22µF
35V
+
PGND
I
SENSE
GATE
V
C
FB
V
CC
UVLO3V
OUT
SGNDR
CMPC
R
OCMP
MINENAB
LT1737
ENDLYSFSTOSCAP t
ON
Figure 12. 12V-18V to Isolated 15V Converter
I
LOAD
(mA)
1
60
EFFICIENCY (%)
70
80
90
10 100 1000
1737 F13
50
40
30
20
V
IN
= 12V
V
IN
= 15V
V
IN
= 18V
Figure 13. Efficiency vs I
LOAD
I
LOAD
(mA)
0
OUTPUT VOLTAGE (V)
15.0
V
IN
= 12V
1737 F14
14.5
100
200
300
15.5
V
IN
= 15V
V
IN
= 18V
Figure 14. Load Regulation
OCTA-PAC is a trademark of Coiltronics, Inc.