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Isolated flyback DC/DC controller eliminates optocoupler

August 06, 2010 // Phil Ling

Isolated flyback DC/DC controller eliminates optocoupler

Requires no opto-isolator, third winding or signal transformer


Linear Technology has introduded the LT3748, a high input voltage isolated flyback DC/DC controller that significantly simplifies the design of an isolated DC/DC converter. No opto-isolator, third winding or signal transformer is required for feedback since the output voltage is sensed from the primary-side flyback signal. The LT3748 operates over a 5V to 100V input voltage range and drives an external N-channel power MOSFET, making it suitable for a variety of industrial, medical, telecom, datacom and automotive applications.

The LT3748 operates in boundary mode, which is a variable frequency current mode control switching scheme, resulting in +/-5% typical regulation over the full line, load and temperature range. Boundary mode also permits the use of a smaller transformer compared to equivalent continuous conduction mode designs. The output voltage is easily set by two external resistors and the transformer turns ratio. Several off-the-shelf transformers identified in the data sheet can be used for numerous applications. The high level of integration and the use of boundary mode operation results in a simple, clean application solution to the traditionally tough problem of isolated power delivery.

Additional features include an onboard low dropout regulator for IC power, programmable soft start, undervoltage lockout, adjustable current limit and output voltage temperature compensation. The LT3748 is available in a small MSOP-16 package with 4 pins removed for additional high voltage pin spacing. This device is available in extended and industrial operating junction temperature range at -40°C to 125°C.

For more information, visit www.linear.com/3748.

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