DC1694B: 12V @ 2.5A, 22 ~ 75V in

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.