LT8310/LT1431 81 Watt Isolated Nonsynchronous Forward Converter with Opto Feedback

George Qian - Senior Applications Engineer
Gabino Alonso - Strategic Marketing Engineer Jan 30th 2015

The LT8310 is a constant-frequency resonant reset forward converter controller with a low side N-channel MOSFET gate driver. The LT8310 has a wide input voltage range from 6V to 100V. Its switching frequency can be programed from 100kHz to 500kHz to optimize efficiency, performance or external component size. The LT8310's protection mechanisms end the normal switching cycle or force system shutdown to protect the application circuit. These protections include programmable overcurrent protection, adjustable input undervoltage, overvoltage lockout and built-in thermal shutdown.

The LT1431 is an adjustable shunt voltage regulator providing feedback to the primary side via an opto-coupler, it is used on the forward converter's secondary side to handle output voltage regulation.

Schematic Diagram

The LT8310+LT1431 forward converter design features simple schematic, and low components count. The following example circuit uses LT8310 and LT1431 in a resonant reset forward topology to deliver 54V @ 1.5A output from 10.8V to 26.4V input. At 1.5A load the peak efficiency is 93% for 12Vin, and 91.2% for 24Vin.

Typical Efficiency Curve

Thermal Image at 12Vin, 54V @ 1.5A Output, with No Forced Air

Thermal Image at 24Vin, 54V @ 1.5A Output, with No Forced Air

Software

LTspice

LTspice^® software is a powerful, fast and free simulation tool, schematic capture and waveform viewer with enhancements and models for improving the simulation of switching regulators. Click here to download LTspice

To launch a ready to run LTspice demonstration circuit for this part:

Step 1: If you have not installed LTspice on this computer, download and install LTspice
Step 2: Once LTspice is installed, click on the link(s) below to launch the simulation
- LT8310/LT1431 Demo Circuit - 81 Watt Isolated Nonsynchronous Forward Converter with Opto Feedback (10.8-26.4V to 54V @ 1.5A)
Step 3: If LTspice does not automatically open after clicking the link above, you can instead run the simulation by right clicking on the link and selecting "Save Target As." After saving the file to your computer, start LTspice and open the demonstration circuit by selecting 'Open' from the 'File' menu

To explore other ready to run LTspice demonstration circuits, please visit our Demo Circuits Collection.