The STSW-DPSLLCK1 firmware package for the STEVAL-DPSLLCK1 3 kW full bridge LLC converter kit includes the application code to regulate the output voltage, as well as all the protection and control features. The firmware comes loaded on the STEVAL-DPS334C1 digital control board and runs on the embedded STM32F334R8 microcontroller. It can be modified with the IAR Embedded Workbench toolchain.
The primary side MOSFETs are driven by 50% duty cycle PWM signals, with an appropriate dead time for each leg to ensure ZVS operation and avoid input voltage shoot-through. The PI voltage regulator runs at 50 kHz and provides the PWM switching period for primary side devices to adjust the voltage gain of the resonant tank and regulate the output voltage to the desired 48 V.
When the board is powered on, the start-up procedure decreases the frequency linearly from 380 kHz down to the value given by control loop, to avoid current spikes.
An adaptive SR algorithm based on VDS sensing drives the secondary side MOSFETs and reduces conduction losses, while Burst mode operation for light loads reduces switching losses and improves converter efficiency.
The control FW also provides fast overcurrent protection, undervoltage and overvoltage protection on the input and output, and an over-temperature protection.
An additional PWM signal is used to drive the fan on the power board at a speed that is determined from the output load and heatsink temperature.
The serial user interface allows you to change the main parameters of the converter and enable or disable control features like open loop operation.