SWITCH MODE DC/DC
POWER CONVERSION
TRANSFORMERS
Premier
P
M
Magnetics Inc.
"INNOVATORS IN MAGNETICS TECHNOLOGY"
! Designed for use with Leading Controller Chips
# Provides DC/DC Conversion & Isolation
" Design Engineenring Support Available.
$ Multiple Configurations.
GENERAL APPLICATION INFORMATION
Premier Magnetics' Switch Mode Output transformers have been designed for use with the most popular current-
mode switching regulators such as Linear Technologies LT1X7X & National Semiconductors LM25XX series of High
Efficiency Switching Regulators. These output transformers have been optimized to provide maximum power
throughput in the smallest packages currently available. This combination of components finds wide use in
Distributed Power Systems where a main dc voltage bus is converted for use on or near the circuits being served.
These types of switching regulators provide a very simple solution to power conversion designs. The inductor or
transformer used are critical to the overall performance of the converter and typically define the overall efficiency,
output power and physical size.
The following tables of transformers were designed for use in the Flyback Buck-Boost circuit configuration. This
conversion topology allows the output voltage to be regulated higher or lower than the input voltage. It can also
provide isolated or non-isolated multiple outputs. Typical efficiency of this topology is 75%.
Below is a typical application circuit utilizing Linear Technologies LT1X7X switching regulator in the flyback buck-
boost configuration. The use of Premiers VTP-01XXX or VTK-01XXX optional output filter choke will drastically reduce
output ripple and noise. The component values listed are intended for reference purposes only. The Output Filter(s),
Damper Network & Foldback Current Limiting Network are optional depending on the specific application.
General Component Values:
R3 = 1.0K 1/8W
C3 = 2.2uF Film
R4 = 1.5K 1W Snubber
C4 = .47uF Film
SCHEMATIC
D1 = MBRXXX, Schottky Rectifier
D2 = MBRXXX, Schottky Rectifier
D3 = MBRXXX, Schottky Rectifier
C1 = Electrolytic
R5 = 2.0K 1W
C7 = Electrolytic
C5 = 0.1uF Ceramic
L1 = 10uHy @ Rated DC amps (VTP-XXXX)
L2 = 10uHy @ Rated DC amps (VTP-XXXX)
R6 = 1% Metal Film as needed.
C6 = 1000uF Electrolytic
C8 = 1000uF Electrolytic
OUTPUT FILTER
D3
+Vout2
Np:Ns2
L2
R1 = 1% Metal Film, For 5Vdc = 3.0K, For 9Vdc = 9.09K
R1 = [Vout-Vref/Vref] * R2, where Vref = 1.244 for LT1X7X series
R2 = 1% Metal Film, For 5Vdc = 1.0K, For 9Vdc = 1.5K
C2 = Input Bypass Capacitor 100uF Electrolytic
+
+
Isolated Output
-Vout2
C7
C8
FLYBACK Buck-Boost CONVERTER USING LT1X7X
OUTPUT FILTER
RC Snubber
Damper
D1
+Vout1
+Vin
T1
L1
R4
C4
+
+
R5
C1
C6
C5
D2
R1
R6
Vin
Vsw
FB
Linear Technology
LT-1X70 = 5A
LT-1X71 = 2.5A
LT-1X72 = 1.25A
LT-107X = 40KHz
LT-117X = 100KHz
Np:Ns1
+
C2
*
*
E1 E2 GND
Vc
R3
R2
C3
Specifications subject to change without notice.
pmsm 6/97
20381 BARENTS SEA CIRCLE, LAKE FOREST, CA 92630 • TEL: (949) 452-0511 • FAX: (949) 452-0512 • http://www.premiermag.com
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