LT8310/LT1431 81W Isolated Forward Converter with Opto Feedback; VIN = 12V/24V, VOUT = 54V @ 1.5A

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 programmed 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.

Figure 1. LT8310/LT1431 Schematic Diagram

The LT8310 and LT1431 nonsynchronous forward converter design features a simple schematic, and low components count. The circuit uses the 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. The efficiency vs. load current graph and the associated thermal images (12V and 24V) are shown below. 

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


George Qian

Zhijun (George) Qian

Zhijun Qian is a senior design manager for power modules with Analog Devices. He is responsible for all LTM80xx products and some LTM46xx/LTM47xx products. He obtained B.S. and M.S. from Zhejiang University, and Ph.D. from University of Central Florida, all in power electronics. He joined ADI in early 2010.


Gabino Alonso

Gabino Alonso is currently the director of strategic marketing for the Power by Linear™ Group. Prior to joining ADI, Gabino held various positions in marketing, engineering, operations, and education at Linear Technology, Texas Instruments, and California Polytechnic State University. He holds a Master of Science degree in electrical and computer engineering from University of California, Santa Barbara.