20381 BARENTS SEA CIRCLE, LAKE FOREST, CA 92630

Specifications subject to change without notice.

1

pmsm 6/97

SWITCH MODE DC/DC

POWER CONVERSION

TRANSFORMERS

M

P

Premier

Magnetics Inc.

"INNOVATORS IN MAGNETICS TECHNOLOGY"

!

Designed for use with Leading Controller Chips

"

Design Engineenring Support Available.

#

Provides DC/DC Conversion & Isolation

$

Multiple Configurations.

GENERAL APPLICATION INFORMATION

SCHEMATIC

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

D1 = MBRXXX, Schottky Rectifier

C3 = 2.2uF Film

D2 = MBRXXX, Schottky Rectifier

R4 = 1.5K 1W Snubber

D3 = MBRXXX, Schottky Rectifier

C4 = .47uF Film

C1 = Electrolytic

R5 = 2.0K 1W

C7 = Electrolytic

C5 = 0.1uF Ceramic

R6 = 1% Metal Film as needed.

L1 = 10uHy @ Rated DC amps (VTP-XXXX)

C6 = 1000uF Electrolytic

L2 = 10uHy @ Rated DC amps (VTP-XXXX)

C8 = 1000uF Electrolytic

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

R1

+Vin

Np:Ns1

R4

C4

D2

R5

C5

R3

C3

R2

+

C2

RC Snubber

Damper

**

Np:Ns2

++

D1

C1

L1

OUTPUT FILTER

C6

+Vout1

++

D3

C7

-Vout2

+Vout2

Isolated Output

L2

OUTPUT FILTER

C8

T1

Vin

Vsw

FB

Vc

GND

E1 E2

Linear Technology

LT-1X70 = 5A

LT-1X71 = 2.5A

LT-1X72 = 1.25A

LT-107X = 40KHz

LT-117X = 100KHz

R6

FLYBACK Buck-Boost CONVERTER USING LT1X7X