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dc1994afa

DEMO MANUAL DC1994A

Description

LT3752/LT8311

Active Clamp Forward Converter

with Synchronous Rectification

Demonstration circuit 1994A is an active clamp forward

converter with synchronous rectification featuring the

LT®3752/LT8311 chipset.

This circuit was designed to demonstrate the high levels of

performance, efficiency, and small solution size attainable

using these parts. It operates at 240kHz and produces a

regulated 12V, 12A output from an input voltage range

of 18 to 72V: suitable for telecom, industrial, and other

applications.Ithasaneighth-brickfootprintarea.Synchro-

nousrectificationhelpstoattainefficiencyexceeding94%.

The DC1994 circuit features soft-start which prevents

output voltage overshoot on startup or when recovering

from overload condition.

TheDC1994alsohaspreciseovercurrentprotectioncircuit

that allows for continuous operation under short circuit

conditions.Thelowpowerdissipationunderashortcircuit

L

, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

performance summary

condition ensures high reliability even during a prolonged

output voltage short circuit.

TheLT3752includesaninternalconstantfrequencyflyback

controller for creating a housekeeping voltage supply. The

housekeeping supply is able to efficiently provide bias

for both primary and secondary ICs, and eliminates the

need to generate bias supplies from auxiliary windings in

the main forward transformer. The housekeeping supply

also allows bias to any secondary side IC before the main

forward converter starts switching.

Please refer to LT3752 data sheet for design details and

applications information.

Design files for this circuit board are available at

http://www.linear.com/demo/DC1994A

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Input Supply Range

18

72

V

Output Voltage

11.76

12.0

12.24

V

Maximum Output Current, Continuous

200LFM

12

A

FSW

Switching (Clock) Frequency

240

kHz

Output Ripple

100

Output Regulation

±0.08

%

Efficiency (see Figure 2)

94

%