Datasheet

10
LT1072
1072fc
Flyback Converter
Negative to Positive Buck-Boost Converter External Current Limit
R1
1k
V
IN
NOTE THAT THE LT1072 GND PIN
IS NO LONGER COMMON TO V
IN
(–)
LT1072 • TA06
C1
1000pF
C2
R
S
R2
+
–
V
IN
V
SW
FB
V
C
GND
LT1072
Q1
C3
0.47µF
V
OUT
5V
1.5A
D2
D1
OPTIONAL
FILTER
1
1
3
N*
N* =
C2
0.15µF
C4
25µF*
V
IN
20 TO 30V
R3
1.5k
REQUIRED IF INPUT LEADS ≥ 2"
OPTIONAL TO REPLACE R4 AND C3
*
**
C1
500µF
R4
1k
**
R1
3.74k
R2
1.24k
V
IN
V
SW
FB
V
C
GND
LT1072
L2
10µH
C4
200µF
V
SNUB
V
OUT
+ V
f
I
PRI
I
PRI
I
PRI
(I
PRI
) (L
L
)
V
SNUB
I
PRI
N
∆I
V
IN
0V
0V
0
0
0
0
CLAMP TURN-ON
SPIKE
PRIMARY FLYBACK VOLTAGE =
LT1072 SWITCH VOLTAGE
AREA “a” = AREA “b” TO MAINTAIN
ZERO DC VOLTS ACROSS PRIMARY
SECONDARY VOLTAGE
AREA “c” = AREA “d” TO MAINTAIN
ZERO DC VOLTS ACROSS SECONDARY
PRIMARY CURRENT
SECONDARY CURRENT
LT1070 SWITCH CURRENT
SNUBBER DIODE CURRENT
V
OUT
+ V
f
N
N • V
IN
t =
a
b
c
d
LT1072 • TA04
+
+
V
IN
V
SW
FB
V
C
GND
LT1072
C2
1000µF
C1
0.22µF
C4
25µF*
R2
1.24k
R3
2.2k
R1
11.3k
V
OUT
12V, 0.5A
V
IN
–12V
D1
L1**
220µH
Q1
*
**
REQUIRED IF INPUT LEADS ≥ 2"
PULSE ENGINEERING 52626
OPTIONAL
INPUT
FILTER
L3
OPTIONAL
OUTPUT
FILTER
L2
C3
LT1072 • TA05
+
+
TYPICAL APPLICATIO S
U