DESCRIPTION
Demonstration circuit 1694B is an isolated flyback converter
featuring the LT®3748. The demo circuit is designed
for a 12V output from a 22V to 75V DC input. The output
current is up to 2.5A. The part senses the isolated output
voltage directly from the primary side flyback waveform
during the off time of the power switch. No third winding,
opto-coupler, or signal transformer is required for regulation.
A minimum load of approximately 2% of maximum
load is required on the output to maintain regulation.
The demo circuit can be easily modified for applications
of different input, and output voltage/current, with some
pre-designed transformers from vendors such as Würth
Electronics, Sumida, Pulse Engineering and Coilcraft. Both
EP13 and EFD20 core transformers can be assembled on
the board. A two-stage filter is optional for applications
requiring very small output ripple.
The LT3748 is a high input voltage isolated flyback controller
operating with input supply voltages from 5V to
100V, and 1.9A average gate drive source and sink current.
The LT3748 utilizes boundary mode operation to provide
a high efficiency, small size solution with improved load
regulation of ±5% over the full line, load and temperature
ranges. The LT3748 can be used in a wide variety of industrial,
automotive, medical, telecom, data-com applications,
where regulated isolated output is required.
The LT3748 data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this quick start
guide for Demo Circuit 1694B.