Isolated flyback converter LT3574 application circuit without optocoupler

Photocoupler

description:

It is available in a small MSOP-16 package and operates from 3V to 40V in the voltage range. It has a 0.65A NPN power switch and can deliver up to 3W of output power. Feedback is not required for the opto-isolator, the third winding, or the signal transformer because the output voltage is sensed from the main-ended flyback signal.

The LT3574 operates in boundary mode, which uses a variable frequency current mode controlled switching method that achieves ±5% regulation over voltage, load, and temperature. The boundary mode also allows the use of smaller transformers than the same continuous conduction mode design. The output voltage is very easy to set with two external resistors and transformer turns ratio. Several data-selling transformers are mentioned in the data sheet, which can be used in many applications. High integration and the use of boundary mode work provide a simple application solution to the traditionally difficult isolated power supply problem. Other features include an integrated low dropout regulator for IC power supplies, programmable soft start, undervoltage lockout, adjustable current limit, and output voltage temperature compensation.

Performance summary:

• VIN range from 3V to 40V
• Built-in 0.65A, 60V integrated NPN power switch
• Feedback without transformer, third winding or optocoupler
• Current mode control
• Boundary mode work
• Set VOUT with two external resistors
• Available transformers
• Programmable soft start
• Programmable undervoltage lockout
• Output voltage temperature compensation
• Adjustable current limit

application

• Industrial, automotive and medical isolated power supplies
  

Application circuit:

5 V isolated converter circuit

Pin configuration diagram:

The above is part of the information, see the PDF document data sheet for details!