LT8310/LT1431 92W Isolated Forward Converter with Opto Feedback; VIN = 48V, VOUT = 54V@1.7A

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 that provides output voltage feedback information to the primary side via an opto-coupler; it is used on the forward converter’s secondary side to handle output voltage regulation.

8310_1431 92W 48V to 54V@1.7A

Figure 1. LT8310/LT1431 92W Schematic Diagram

The LT8310/LT1431 forward converter design features a simple schematic and low components count. The circuit above uses the LT8310/LT1431 in a resonant reset forward topology to deliver 54V at 1.7A from a 43V to 53V input.The forward transformer resets through a single capacitor added across MOSFET drain and source, eliminating additional reset winding or active clamp circuits.With a nominal 48V input voltage, the circuit achieves 92.3% efficiency at 1.7A.

8310_1431 92W Efficiency vs Load

Figure 2. LT8310/LT1431 Efficiciency vs. Load Current

The LT8310 circuit's high efficiency allows the circuit to provide 92W of output power without a heat sink or forced air flow. In the thermal image below, the highest temperatures occur are 85.5C (at the diode, D1) and 80.8C (at the transformer, T1). 

8310_1431 92W Thermal Image

Figure 3. LT8310/LT1431 Thermal Image

Author

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George (Zhijun) Qian