Linear Technology LTC3765 Demo Manual

DESCRIPTION
Demonstration circuit 1739A is a 150W isolated forward
converter with synchronous rectification featuring the
LTC3765/LTC3766.
This circuit demonstrates a high level of performance, ef-
ficiency, and small solution size attainable using these parts
in an active-clamp-reset forward converter power supply.
It operates at 240kHz and produces a regulated 12V, 12.5A
output from an input voltage range of 18V to 72V, making
it well suited for telecom, industrial, and other applica-
tions. It has an eighth-brick footprint size of 0.90" × 2.3".
PERFORMANCE SUMMARY
SYMBOL PARAMETER
V Input Supply Range
IN
V Output Voltage
OUT
I Output Current Range, Continuous
OUT
I Output Current , Peak
OUT
f Switching (Clock) Frequency
SW
V Output Ripple
OUT P-P
I Output Regulation
REG
P /P Efficiency (see Figure 3)
OUT IN
Isolation
Approximate Size
OPERATING PRINCIPLES
The LTC3765 active clamp forward controller and gate
driver is used on the primary and provides start-up,
gate drive, and protection functions. Once start-up is ac-
complished, the LTC3766 high efficiency, secondary-side
synchronous forward controller takes over, and provides
the LTC3765 with timing information and bias power
through a small pulse transformer.
Arrow.com.
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DEMO MANUAL DC1739A
150W High Efficiency Active Clamp
Synchronous rectification helps to attain efficiency ex-
ceeding 94%. Secondary-side control eliminates complex
opto-coupler feedback, providing fast transient response
with minimum output capacitance. The proprietary Direct
Flux Limit
For other output requirements, see the LTC3766 data sheet
or contact the LTC factory.
Design files for this circuit board are available at
http://www.linear.com/demo
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation and Direct Flux Limit is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
(T = 25°C)
A
CONDITIONS
200LFM
200LFM
V = 48V, I = 12A (20MHz BW)
IN OUT
Line and Load (18-72V , 0-12A
IN
V = 48V, I = 10A
IN OUT
Basic
Component Area × Top Component Height
When input voltage is applied, the LTC3765 commences
soft-start of the output voltage. When the secondary bias
source reaches the undervoltage threshold, the LTC3766
comes alive and takes control by sending encoded PWM
gate pulses to the LTC3765 through T3. These pulses also
provide primary bias power efficiently over a wide input
voltage range.
LTC3765/LTC3766
Forward Converter
scheme guarantees no transformer saturation.
™
MIN TYP
18
12.0
0
240
) ±0.08
OUT
93.6
1500
2.3 × 0.9 × 0.47
MAX UNITS
72 V
V
11 A
12.5 A
kHz
60 mV
P–P
%
%
VDC
Inches
dc1739afa
1